| 1. |
- Alipanah, Helen, et al.
(författare)
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A new species of Sitochroa Hübner, 1825 (Lepidoptera, Crambidae, Pyraustinae) from Iran, with taxonomic notes on the genus
- 2020
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Ingår i: Nota lepidopterologica. - : Pensoft Publishers. - 0342-7536 .- 2367-5365. ; 43, s. 61-76
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Tidskriftsartikel (refereegranskat)abstract
- Sitochroa urmiensis sp. nov. is described based on a single male collected in West Azarbaijan Province, Iran. Sitochroa palealis (Denis & Schiffermüller, 1775) is considered as a senior synonym of Loxostege farsalis Amsel, 1950 syn. nov. Loxostege malekalis Amsel, 1950 is transferred to the genus Sitochroa Hübner, as S. malekalis (Amsel, 1950) comb. nov. And the hitherto unknown female of S. malekalis is described and illustrated.
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| 2. |
- ALIPANAH, HELEN, et al.
(författare)
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Taxonomic study of the subfamily Pyraustinae (Lepidoptera: Crambidae)in Iran
- 2023
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Ingår i: Zootaxa. - 1175-5326 .- 1175-5334. ; 5289:1, s. 1-82
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Tidskriftsartikel (refereegranskat)abstract
- Sixty-seven species of the subfamily Pyraustinae from 17 genera and two tribes are listed. Anania verbascalis verbascalis ([Denis & Schiffermüller], 1949) is considered as a senior synonym of A. verbascalis parvalis (Osthelder, 1935) syn. n.; Pyrausta virginalis Duponchel, 1832 as a senior synonym of P. perkeo Amsel, 1970 syn. n.; and P. ferrealis (Hampson, 1900) as a senior synonym of P. euergestalis Amsel, 1954 syn. n. Thirteen species, namely Anania coronata (Hufnagel, 1767), A. murcialis (Ragonot, 1895), A. terrealis (Treitschke, 1829), Pyrausta ferrealis (Hampson, 1900), P. armeniaca Slamka, 2013, P. zeitunalis Caradja, 1916, P. cingulata (Linnaeus, 1758), P. delicatalis Caradja, 1916, P. tatarica Kemal et al., 2020, Loxostege sedakowialis (Eversmann, 1852), L. wagneri Zerny in Wagner, 1929, L. mucosalis (Herrich-Schäffer, 1848) and L. peltaloides (Rebel in Wagner, 1932), are newly reported from Iran. Additionally, a redescription of the male of P. delicatalis and the female of L. sedakowialis, as well as description of the hitherto unknown female of P. delicatalis are presented. The intraspecific variations of the species if present are discussed and additional new diagnostic characters to separate the closely related species are presented. Data on the geographical distribution of the Iranian species of this subfamily are provided.
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| 3. |
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| 4. |
- Bernstone, Christian, et al.
(författare)
-
Verifiering av struktur och fuktmekaniska beräkningsverktyg : Tillämpning på reaktorinneslutningars betongkonstruktioner, Vercors Fas 1
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Électricité de France har utanför Paris byggt en 1/3 skalmodell av en reaktorinneslutning motsvarande en fransk fullskalereaktor modell P4. Anläggningen möjliggör studier av hur åldringsprocesser påverkar förspända reaktorinneslutningar. Syftet är att efter de 7 år som ett övergripande forskningsprojektet vid på anläggningen pågår, uppnå påverkan motsvarande den åldring som en fullskalereaktor har utsatts för efter 6o års drift.Konstruktionen har försetts med ett omfattande instrumenteringsprogram som gör det möjligt att följa konstruktionens beteende i tidigt skede och över tid. Ett av anläggningens forskningsprojekt omfattar en benchmark av olika beräkningsverktygs möjlighet att kunna förutse konstruktionens beteende i tidigt skede och under själva åldrandet, dess täthet till följd av åldrandet och beteende under svåra haveriförhållanden. Denna benchmark har genomförts via en öppen inbjudning till intresserade experter att delta. I projektet, benämnt VeRCoRs , bidrar deltagande organisationer med egna modelleringsarbeten utifrån de tre olika teman. Arbetet med det första temat startade 2015 (tidigt skede), därefter följer den åldrade konstruktionen (2017) och svåra haverisituationer (2021). Denna rapport redovisar det arbete som har gjorts för det första temat (Tema 1) inom ramen för ett Energiforskuppdrag.Modelleringsarbetet har till största delen genomförts av LTH i nära samarbete med KTH och Vattenfall. Simuleringar har gjorts för den unga betongens beteende under den ett år långa byggfasen, med hänsyn tagen till betongens hydratation (temperaturberäkningar/värmeutveckling), uttorkning (självuttorkning och fukttransport) och deformationer (temperatur-, fukt-, kryp-, och spänningsrelaterade deformationer). Resultatet har jämförts mot data från anläggningens instrumentering. Dessutom så har en genomgång gjorts av resultaten från övriga deltagares arbeten i Tema 1.Sammanfattningsvis så visar resultaten på de fördelar som finns med att genom avancerade beräkningar verifiera designparametrar och prognostisering av reaktorinneslutningars funktion, men också på utmaningar. Med hjälp av FEmodellering så kan det tidiga skedet efter färdigställd konstruktion beskrivas både vad gäller temperatur- och deformationer med rimlig tillförlitlighet. Det finns dock potential till förbättringar. Även om betongens temperatur kan predikteras noggrant så kan det skilja kraftigt i uppskattningen av inducerade påkänningar. En viktig orsak till dessa skillnader beror på osäkerheter i bestämning av krypning och krympning i betongen tidiga skede.
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| 5. |
- Ekström, Mattias, 1990-
(författare)
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SiC CMOS and memory devices for high-temperature integrated circuits
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High-temperature electronics find use in extreme environments, like data logging in downhole drilling for geothermal energy production, inside of high-temperature turbines, industrial gas sensors and space electronics. The simplest systems use a sensor and a transmitter, but more advance electronic systems would additionally require a microcontroller with memory. Silicon carbide (4H-SiC) integrated circuits target high-temperature electronics, although the current integration level is low due to immature process technology and non-volatile memory has not been demonstrated. SiC CMOS would allow highly dense integrated circuits for microcontrollers and random access memory (RAM). Ferroelectric capacitors could serve as high-temperature non-volatile memory devices.In this work, significant efforts have been taken to develop a SiC CMOS process and ferroelectric capacitors. SiC CMOS is challenging and mostly unexplored technology. A recessed channel transistor design was investigated. Several key challenges in the SiC CMOS process was identified, leading to a polyoxide-based field oxide, a deposited gate-dielectric process, reproducible Ni-Al semi-salicide contacts to p-type SiC, and a high-temperature CMP enabled two-level TiW-based metallisation. Self-aligned cobalt silicide contacts were investigated, and was found to produce low-resistance ohmic contactsto n-type SiC. Inverters and ring oscillators that operate at 200 °C were achieved in this recessed channel SiC CMOS process. It was found that steam-treating the gate oxide interface produced both NMOS and PMOS transistors that could be used for circuits. However, the reliability suffered due to poor PMOS performance. Wafer-level statistical measurements of interface trap density was performed on NMOS transistors treated by steam, dry oxygen and nitrided by nitrous oxide. A deposition and etch process for ferroelectric capacitors, using vanadium-doped bismuth titanate as ferroelectric material, was developed. High-temperature operation was demonstrated, and several scalability challenges for the etched process was identified.The implication of this thesis is that while operational recessed channel SiC CMOS was demonstrated at high temperature, more promising technologies like ion implanted bulk transistors should be investigated instead, due to the numerous difficulties in optimising both NMOS and PMOS with this recessed channel design. The presented recessed channel process technology can be used to fabricate short channel length NMOS-logic. Ferroelectric capacitors is a good candidate for high-temperature non-volatile memory applications, although more work is needed in the CMOS integration.
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| 6. |
- Eriksson, Daniel, 1987-, et al.
(författare)
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Freezing of partially saturated air-entrained concrete: A multiphase description of the hygro-thermo-mechanical behaviour
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Even though air-entrained concrete is usually used for concrete structures located in cold climates that are exposed to wet environments, frost damages are frequently detected during inspections. However, it is often hard to assess the extent and severity of these damages and, thus, there is a need for better tools and aids that can complement already established assessment methods. Several studies have successfully shown that models based on poromechanics and a multiphase approach can be used to describe the freezing behaviour of air-entrained concrete. However, these models are often limited to the scale of the air pore system and, hence, hard to use in applications involving real structures. This study proposes a hygro-thermo-mechanical multiphase model which describes the freezing behaviour of partially saturated air-entrained concrete on the structural scale. The model is implemented in a general FE-code and two numerical examples are presented to validate and show the capabilities of the model. The first concerns a series of experimental tests of air-entrained cement pastes, whereas the second aims to show the capability of the model to account for an initial non-uniform distribution of moisture. The results show that the model can reproduce the freezing behaviour observed in the experimental tests on a structural scale as well as being capable of describing freezing induced deformations caused by non-uniform moisture distributions.
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| 7. |
- Eriksson, Daniel, 1987-, et al.
(författare)
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Freezing of partially saturated air-entrained concrete: A multiphase description of the hygro-thermo-mechanical behaviour
- 2018
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 152-153, s. 294-304
-
Tidskriftsartikel (refereegranskat)abstract
- Even though air-entrained concrete is usually used for concrete structures located in cold climates that are exposed to wet environments, frost damage is frequently detected during inspections. However, it is often hard to assess the extent and severity of the damage and, thus, there is a need for better tools and aids that can complement already established assessment methods. Several studies have successfully shown that models based on poromechanics and a multiphase approach can be used to describe the freezing behaviour of air-entrained concrete. However, these models are often limited to the scale of the air pore system and, hence, hard to use in applications involving real structures. This study proposes a hygro-thermo-mechanical multiphase model which describes the freezing behaviour of partially saturated air-entrained concrete on the structural scale. The model is implemented in a general FE-code and two numerical examples are presented to validate and show the capabilities of the model. The first concerns a series of experimental tests of air-entrained cement pastes, whereas the second aims to show the capability of the model to account for an initial non-uniform distribution of moisture. While the model predictions underestimate the magnitude of the measured strains, the results still show that the model can capture the general freezing behaviour observed in the experimental tests on the structural scale. Furthermore, the results demonstrate that the model is capable of describing freezing induced deformations caused by non-uniform moisture distributions.
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| 8. |
- Gasch, Tobias, et al.
(författare)
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A coupled hygro-thermo-mechanical model for concrete subjected to variable environmental conditions
- 2016
-
Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 91, s. 143-156
-
Tidskriftsartikel (refereegranskat)abstract
- It is necessary to consider coupled analysis methods for a simulation to accurately predict the long-term deformations of concrete structures. Among other physical fields that can be considered, both temperature and moisture have a significant influence on the deformations. Variations of these fields must therefore be included implicitly in an analysis. This paper presents a coupled hygro-thermo-mechanical model for hardened concrete based on the framework of the Microprestress-Solidification theory. The model accounts for important features of concrete such as ageing, creep, shrinkage, thermal dilation and cracking; all of these under variable temperatures and moisture conditions. It is discussed how to implement the proposed model in a flexible numerical framework that is especially suitable for multi-physics analyses. The capabilities of the model are shown through the analysis of three experimental data sets from the literature, with focus on creep and shrinkage. Overall, the agreement between the analysis and experimental results is good. Finally, a numerical example of a concrete gravity dam with dimensions and loads typical to northern Sweden is analysed to show the capabilities of the model on a structural scale.
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| 9. |
- Gasch, Tobias, et al.
(författare)
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A coupled multi-physics model for creep, shrinkage and fracture of early-age concrete
- 2016
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Ingår i: 9th International Conference on Fracture Mechanics of Concrete and Concrete Structures.
-
Konferensbidrag (refereegranskat)abstract
- The behaviour of concrete at early-age is complex and involves several physical fieldssuch as temperature, moisture and deformations. In this paper a hygro-thermo-chemo-mechanicalmodel for the analysis of early-age concrete based on a combination of models from the literature ispresented. The chemical model is based on the reaction degree concept, also used to define internal actions such as self-desiccation and ageing of mechanical properties. A mechanical model based on the Microprestress-Solidification theory for concrete creep is used, that in a simplified manner alsoconsiders concrete fracture. The model has been implemented in a numerical framework suitable for coupled multi-physics problems. It is here applied to a case study of an un-reinforced concrete tunnel plug made of a low-pH self-compacting concrete. Good agreement is generally obtained with measurements and hypotheses previously made on the behaviour of the plug are verified.
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| 10. |
- Gasch, Tobias
(författare)
-
Concrete as a multi-physical material with applications to hydro power facilities
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During its lifetime, a concrete structure is subjected to many different actions, ranging from mechanical loads to environmental actions. To accurately predict its integrity from casting and throughout its service life, a modelling strategy is required that considers mechanical loading but also implicitly accounts for physical effects such as temperature and moisture variations. This is especially true for large concrete structures found in many infrastructure applications such as bridges, nuclear power plants and dams. Modelling concrete as a multi-physical material is becoming an increasingly used approach for which large research efforts are being made, including the development of more refined mathematical and numerical methods as well as considering more physical and chemical variables in the coupled model.The research project, of which this licentiate thesis is the first phase, aims at investigating aging concrete structures at hydro power facilities, with focus on the internal structures of the power plants. This thesis presents a review of advanced mathematical methods and concepts for modelling aging concrete found in the literature which can later be applied to study such structures. The focus is on models that describe the deformational behaviour of concrete where aspects such as aging, cracking, creep and shrinkage are investigated. However, in order to accurately describe such phenomena, a multi-physical approach is adopted where moisture and temperature variations in the concrete are studied. Also, models that describe the chemical behaviour related to hydration and thus in extension aging, are also reviewed and introduced in the multi-physical framework. The use of such models are discussed in the context of the finite element method (FEM), in which coupled models are implemented, verified and applied in the appended papers using two different FE codes.Several verification examples are presented covering different aspects of the implemented models, both in isolation and coupled in a multi-physical setting. By comparing the numerical results with experimental data from the literature it can be shown that it is possible to predict most aspects of aging concrete that have been of interest here. While these examples are all on a laboratory scale, numerical examples and case studies are also provided that exemplify how the models can be applied on a structural scale. By using the developed analysis tools, valuable information and insights can be gained on aging concrete structures and these tools will in the next phase of the research project be applied to large concrete structures at hydro power facilities.
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| 11. |
- Gasch, Tobias, et al.
(författare)
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Concrete Support Structure for Hydroelectric Generators Subjected to Rotor Dynamic Loads
- 2014
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Ingår i: International Symposium on Dams in a Global Enviromental Challange. - Bali.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In earlier times, the generators of the hydropower plants ran more or less continuously, while nowadays there are many planned starts and stops. The hydropower stations are thereby, due to the new pattern of operation, subjected to loads that they were not originally designed for. The aim of this study is to understand the complex interaction between the power generating system and the supporting concrete structure, during this new operational pattern.During inspections, cracks were discovered in the concrete structure of the power house, near the stator and rotor spider supports, at several hydropower stations in Sweden. In a previous phase of this project it was shown that these cracks initiated due to the combined effect of drying shrinkage, mechanical loads and variations in temperature due to starts and stops. Cracking of the concrete structure reduces its stiffness, which may result in larger loads acting on the structure and vibrations exceeding the unit’s strict tolerance limits.In this part of the study, the behaviour of a concrete support structure subjected to rotor dynamic loads during normal operation has been studied. A detailed 3D numerical model has been developed which include hydropower unit. The results of this study show that a reduced structural stiffness of the concrete support structure, due to cracking, influences the behaviour of the rotating system.
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| 12. |
- Gasch, Tobias, et al.
(författare)
-
Cracking in the concrete foundation for hydropower generators : Part II
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- An extensive program for improvement of the hydropower plants in Sweden is currently on-going. The aims are to secure future production and to maintain and further develop an already high dam safety.During inspection, cracks were discovered in the concrete foundation, near the stator and rotor spider supports, at some hydropower stations in Sweden. The cracks were believed to be related to new patterns for generator operation, thereby changing the dynamic loading of the stator and rotor spider supports. Previously the generators ran continuously, while nowadays there are an increased number of stops and starts, sometimes even several times during one day. Increased dynamic forces due to runaways, and also other dynamic events such as emergency stops, may also contribute to increased stress levels and cracking of the foundation. Furthermore, although extreme loads such as short circuits of the generator seldom occurs, the influence on the dynamic forces acting on the supporting structure and concrete foundation may be strongly influenced during such events.The objective of this study is to understand the complex interaction between the power generating system (stator, rotor, turbine, etc.) and its supporting concrete structure. It is important from a dam safety perspective to determine the causes of existing structural cracks in the foundation. Furthermore, to be able to predict further crack propagation of the concrete foundation will help to determine future maintenance requirements.A three dimensional non-linear finite element model developed earlier was used to evaluate a methodology for analyses of the interaction between the generator and the concrete foundation. The influence of cracks in the concrete foundation was investigated by including the fracture pattern obtained in earlier FE analyses of time-dependent thermal and moisture gradients. These analyses showed that the drying shrinkage induced cracking inside the concrete foundation and especially close to the supports of the stator and the rotor spider. The obtained fracture pattern for the previous analysis was used as input for this study, with the concrete foundation’s changed structural properties and their influence on the interaction with the generator considered in the analyses. Furthermore, deadweight and operational load were also included in the analyses.The study show that FE models with a cracked concrete foundation can be used to analyse structural interaction betwee foundation and generator components during operation of a hydro power generator. The crack pattern can be determined by FE analyses, or by in-situ measurements of existing concrete cracks for a specific concrete foundation. The analyses show that further studies are needed regarding the combined effects from thermo-mechanical loads, drying shrinkage, creep and dynamical loads caused by the generator. The combined effects may further increase the stress levels for the concrete foundation, especially locally near perforations, and stator and rotor spider supports. These analyses should be performed with an increased numerical resolution for both the concrete foundation and the supporting structure for the generator, with an increased accuracy for the local stress variations near perforations of the foundation and also at the supports for the generator. This research area will be further investigated within a recently started research project at KTH, financed by the Swedish Hydropower Centre.
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| 13. |
- Gasch, Tobias, et al.
(författare)
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Effects of aging concrete in support structures for hydroelectric machinery
- 2014
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Ingår i: XXII Nordic Concrete Research Symposium. - Reykjavik. ; , s. 237-240
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- At many of the Swedish hydropower plants, cracks have been observed in the concrete power station. Although the presence of cracks in these massive concrete structures does not pose an immediate threat to the structural safety, it of course affects its durability. Besides this, and perhaps as important in this application, the presence of cracks reduces the structural stiffness which affects the operation of the machinery.A case study is presented, where cracks have been found in the concrete support. Furthermore, analysis methods to evaluate the status of the concrete support; mainly through the use of finite element analysis are proposed.
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| 14. |
- Gasch, Tobias, et al.
(författare)
-
Instrumentation and Modelling of a Reactor Containment Building
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Nuclear concrete containment buildings typically consist of pre-stressed concrete. The pre-stressing tendons are utilized to enforce a compressive state of stress to ensure that cracks do not occur in the containment structure. The tendons are thereby an important part of the containment building and important for its structural integrity. In many cases, these tendons are grouted with cement grout to prevent corrosion. This results however in that it is not possible to directly assess the tendons or re-tension these if significant long term losses occurs. The drawback with cement grouted tendons is, thereby, that it is not possible to directly measure the current tendon force. One conventional method to assess the status of the containment building, and thereby indirectly the tendons, is to perform pressure tests. The pressure tests are performed where the pressure in the containment building is increased. The response of the containment can after this be determined based on measurements of displacements and strains. The purpose of this project is to perform simulations of a pressure test of a Boiling Water Reactor (BWR) that is common in Sweden and Finland. Based on these simulations, the response of the containment building is determined and suggestions are made regarding suitable placement of measuring sensors. The suggested instrumentation has been divided into different types of sensors defined as detectors and support sensors. The detectors are needed to monitor the structural response of the containment while the support sensors are needed to give sufficient input to numerical analyses. It is suggested that detector sensors are placed at four vertical positions and at three points along the perimeter. At these locations, it is recommended that displacement sensors, strain gauges and temperature sensors are installed. In addition, it is also recommended that the relative radial displacement between the intermediate slab and the cylinder wall is monitored. As support sensors, it is recommended that the ambient temperature and relative humidity is measured since these constitute important boundary conditions for numerical analyses and thereby prediction of the structural behaviour.
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| 15. |
- Gasch, Tobias
(författare)
-
Multiphysical analysis methods to predict the ageing and durability of concrete
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the societal demand for sustainability and the increasing age of infrastructure, a crucial task for the civil engineering community is to improve the durability of concrete structures. This thesis aims to contribute to such development through theoretical studies using mathematical modelling and numerical simulations. During its service life, a concrete structure is subjected to many different actions, ranging from mechanical loads to chemical and physical processes. Hence, a sound modelling strategy requires multiphysics and the inclusion of coupled chemical and physical fields (e.g. temperature, moisture and cement hydration) in addition to methods that describe mechanical integrity of the material. Conditions and phenomena critical for concrete structures at hydropower facilities have been of particular interest to study.The thesis presents several mathematical models of various complexity to describe the multiphysical behaviour of concrete using a material point description. A significant focus is on models that describe the mechanical behaviour of concrete where aspects such as ageing, cracking, creep and shrinkage are investigated. For the creep behaviour, a state-of-the-art model based on the Microprestress–Solidification (MPS) theory is reviewed and further developed. The appended papers (III to IV) presents a mathematical framework for the modelling of durability aspects of concrete based on multiphase porous media theory. The governing equations are derived with the Thermodynamically Constrained Averaging Theory (TCAT) as a starting point. It is demonstrated how this framework can be applied to a broad variety of phenomena related to durability; from the casting and hardening of concrete to the long-term absorption of water into air-entrained concrete. The Finite Element Methods (FEM) is used to solve the proposed mathematical models, and their capabilities are verified using experimental data from the literature.The main research contribution is the development and evaluation of theoretical models that advance the understanding and improve knowledge of the ageing and durability of concrete and concrete structures. More precisely, it is shown how multiphysical models and the developed multiphase framework can be used to gain insights on the material behaviour of concrete at smaller scales while they are also applicable to structural-scale simulations. During all model development, the efficient solution of structural problems has been fundamental. Through case studies and several examples from the literature, it is exemplified how these models can be used to enhance the performance and thereby increase the durability of concrete structures.
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| 16. |
- Gasch, Tobias, et al.
(författare)
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Non-linear analyses of cracks in aging concrete hydro power structures
- 2016
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Ingår i: Dam Engineering. - : International Water Power & Dam Construction. - 0958-9341.
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Annan publikation (populärvet., debatt m.m.)abstract
- The concrete structures at Swedish hydro power facilities were built during the early to mid-20th century and many of them are starting to exhibit age related wear and deterioration. It isimportant to ensure the integrity of these concrete structures from a dam safety perspectiveand also to secure a safe operation of the power facility in the future. With the latter in mind,this paper aims to study the concrete structures that house the power generating machinery ofthe facility, especially the parts close to the generator where the loads from the power unit aresupported. Cracks observed in these structures will reduce its stiffness, which affects theoperation of the rotating machinery. This paper presents and discusses some generalconsiderations and loads that are of importance for this type of structures and highlights sometypical cracks that have been observed in Swedish hydro power facilities. To complement thisdiscussion, a case study is presented of a hydro power facility where cracks have been foundin the concrete support structure of the power unit, especially at the interconnections betweenthe unit and the concrete. The most likely cause of these cracks are investigated through nonlinearfinite element analysis considering mechanical loads as well as physical loads such asdrying shrinkage and temperature variations. It is concluded that the long-term physicalloading is the most probable cause of the observed cracks. However, the operation of thepower unit and changes in its operational pattern can cause further propagation of thesecracks. Finally, suggestions on possible enhancement of the analysis methods used in the casestudy are proposed and discussed for further studies of this type of concrete structures.
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| 17. |
- Gasch, Tobias, et al.
(författare)
-
Probabilistic analyses of crack propagation in concrete dams : Part II
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Several concrete buttress dams in northern Sweden have been found to be subjected to, more or less severe, cracks according to recent assessments and investigations. Theoretical analyses and field measurements have shown that most of these cracks have developed or propagated as a result of the seasonal temperature variations. Most dams in Sweden were built for more than 50 years ago and it is therefore important to also consider the influence of long-term effects and degradation to assess the dam. The ordinary sliding and overturning stability analyses may not be sufficient when the supporting structure is cracked, since the cracks may comprise the integrity and the homogeneity of the structure.The work presented in this report is a continuation of the work on advanced numerical methods for studying crack propagation in concrete dams presented in Björnström et al. (2006), Ansell et al. (2008), Ansell et al. (2010) and Malm et al. (2013). In the latter parts of the project the main focus has been on the development of probabilistic analysis methods for studying crack propagation, mainly with respect to the stochastic variation of material properties of concrete but also with regard to loading conditions. The concepts of the used probabilistic analysis methods were introduced in a previous part of the project, (Malm et al. 2013). In the previous part, stochastic spatial distribution of material properties was only studied within local areas where a crack was expected to be developed. In the work presented in this report, this concept has been expanded to cover stochastic spatial distribution of material properties within an entire buttress wall of one monolith. A sensitivity study is also presented regarding variations in the assumed temperatures of the seasonal temperature loading.To increase the accuracy of the numerical model a new FE-model was developed with a refined mesh compared to previously used meshes. The new mesh size was chosen with respect to the smallest characteristic crack length of a concrete sample in the stochastic population. All other aspects of the model were defined equally as in previous models.The results of the probabilistic analyses with respect to variation in material properties showed a significant increase in developed cracks, compared to a deterministic analysis. The main crack patterns were, however, similar, but additional cracks were developed adjacent to previous cracks and the inclination of some cracks was changed. These findings should be included when assessing different dam stability failure modes of buttress dams. The sensitivity study of the assumed temperatures showed that it was mainly the low temperatures in combination with temperature differences that initiate cracking in the monolith.
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| 18. |
- Gasch, Tobias, et al.
(författare)
-
Seismic analyses of nuclear facilities with interaction between structure and water : Comparison between methods to account for Fluid-Structure-Interaction (FSI)
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Methods to describe the interaction between fluids and solids has been one of the biggest focus points for the research within the field of computationalengineering for the recent years. This area is of interest to a variety ofengineering problems, ranging from flow in blood vessels, aerodynamics andof course the interaction between water and civil engineering structures. Thetypical civil engineering application of fluid-structure interaction (FSI)encountered in a nuclear facilities is obtained at seismic loading, where the nuclear facilities consists of water filled pools of various sizes, for example the spent fuel and condensation pools. These water filled pools contribute with added mass to the structure, which lowers the natural frequency of thestructure as well as hydrostatic and hydrodynamic pressure that acts on thewalls of the pool due to wave propagation in the fluid. In addition, as the pools also have a free water surface towards the environment of thestructure, free surface wave propagation also has to be accounted for; i.e.sloshing. This introduces extra non-linearity to the problem, since a freesurface constitutes a boundary condition with an unknown location.The main part of this report constitutes as a state-of-the-art summary whereconcepts important for FSI analyses are presented and important differencesare discussed. Due to the different interests of the numerous disciplinesengaged in this research area, a large number of methods have been developed, where each has different strengths and weaknesses suited for the problem in mind when developing the method. The focus of this report havebeen to describe the most important numerical techniques and the categories of methods that or of most interest for civil engineering problems, such as simplified analytical or mass-spring models, Acoustic Elements, ArbitraryLagrangian-Eulerian (ALE) and coupled Eulerian-Lagrangian (CEL).Thereafter two benchmark examples are presented, intended to highlightdifferences between the different methods. In the first study, sloshing of aliquid tank is studied where the numerical methods are compared toexperimental results, regarding the movement of the free water surface. In addition, the hydrodynamic (fluid) pressures on the walls of the tanks arecompared between the different numerical methods. It was shown that mostanalysis methods give accurate results for the sloshing wave height whencompared with the experimental data. It should however be mentioned that the tank was only excited by a simple harmonic motion with a frequency thatdo not give rise to any resonance waves in the water body.Also when it comes to fluid pressure good agreement between the differentanalysis methods was found, although no experimental data was available forthis parameter. It was also noticed that for the sloshing tank, most of the change in pressure occurred close to the free surface of the water, which indicates that it mainly consists of a convective pressure, i.e. from the sloshing. Thereby, finite element programs that account the impulsive mass incivil engineering FSI problems should not be used for this type of analysis. In the second study, the numerical methods are compared based on differenttypes of seismic input, such as a large earthquake with mainly low frequencycontent typically like an earthquake on the US west coast and one smallerearthquake with relatively higher degree of high frequency content typicallylike a Swedish type of earthquake. One important observation was that the relative increase in induced stresses in the structure, with and withoutconsideration of the water was significantly larger for the Swedish earthquakethan for the US earthquake. One possible reason for this may be that the Swedish earthquake is not large enough to excite the relatively stiff structurewithout any water, but it will induce significant dynamic effects in the waterwhich give rise to higher stresses in the concrete as well. However, this shows that it is very important to include water in seismic analyses.
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| 19. |
- Gasch, Tobias, et al.
(författare)
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Three-dimensional simulations of ageing concrete structures using a multiphase model formulation
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The durability of concrete structures is in no small degree determined by the quality and integrity of the concrete, where structural damages such as cracks negatively affect many of the functions of the structure. Often cracks are formed due to restrained thermal and hygral deformations, where the risk is exceptionally high during the early stages after casting. This study presents a hygro-thermo-chemo-mechanical model that accounts for phenomena such as hydration, external and internal drying, self-heating, creep, shrinkage and fracture. The model is derived as a modified version of a fully-coupled multiphase model recently proposed by Gasch et al. (2019) and implemented in the Finite Element Method. Here the governing equations are simplified, and a more efficient solution method is proposed. These modifications are made with the intention to obtain a model more suitable for structural scale simulations. To validate the model, one of the end-restrained beams tested within the French research project CEOS.fr is analyzed. Laboratory data on the concrete is used to calibrate to model and recordings of ambient conditions makes it possible to define accurate boundary conditions. Results from the simulation are compared to measured temperatures and deformations from the first 60 days after casting and are found to generally be in good agreement. Compared to the fully-coupled model by Gasch et al. (2019), the modifications proposed in this study reduce the computational cost by a factor five; without any noticeable differences to the structural results.
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| 20. |
- Gasch, Tobias, et al.
(författare)
-
Three-dimensional simulations of ageing concrete structures using a multiphase model formulation
- 2019
-
Ingår i: Materials and Structures. - : Springer Netherlands. - 1359-5997 .- 1871-6873. ; 52:4
-
Tidskriftsartikel (refereegranskat)abstract
- The durability of concrete structures is in no small degree determined by the quality and integrity of the concrete, where structural damages such as cracks negatively affect many of the functions of the structure. Often cracks are formed due to restrained thermal and hygral deformations, where the risk is exceptionally high during the early stages after casting. This study presents a hygro-thermo-chemo-mechanical model that accounts for phenomena such as hydration, external and internal drying, self-heating, creep, shrinkage and fracture. The model is derived as a modified version of a fully-coupled multiphase model recently proposed by Gasch et al. (Cem Concrete Res 116:202–216, 2019. https://doi.org/10.1016/j.cemconres.2018.09.009) and implemented in the Finite Element Method. Here the governing equations are simplified, and a more efficient solution method is proposed. These modifications are made with the intention to obtain a model more suitable for structural scale simulations. To validate the model, one of the end-restrained beams tested within the French research project CEOS.fr is analyzed. Laboratory data on the concrete is used to calibrate to model and recordings of ambient conditions makes it possible to define accurate boundary conditions. Results from the simulation are compared to measured temperatures and deformations from the first 60 days after casting and are found to generally be in good agreement. Compared to the fully-coupled model by Gasch et al. (2019), the modifications proposed in this study reduce the computational cost by a factor five; without any noticeable differences to the structural results.
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| 21. |
- Johanson, Kjell Arne, 1966-, et al.
(författare)
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Description of six new species of Oecetis (Trichoptera, Leptoceridae) from Vietnam
- 2020
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Ingår i: Zootaxa. - 1175-5326 .- 1175-5334. ; 4816:3, s. 311-324
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Tidskriftsartikel (refereegranskat)abstract
- The following six new Oecetis species have been described and illustrated: O. lata, O. gretae, O. malickyi, O. porntipae, O. olahi, and O. hageni. The following three Oecetis species are recorded for the first time from Vietnam: O. maron Malicky & Chantaramongkol 2005 (in Malicky 2005), O. iakchos Malicky 2005, and O. jachin Malicky & Mey 2010 (in Malicky 2010a). We present new records of the following six Oecetis species that are previously known from Vietnam: O. raghava Schmid 1995, O. biramosa Martynov 1936, O. tripunctata (Fabricius 1793), O. meleagros Malicky & Thani 2005, O. asmada Malicky 1979, and O. empusa Malicky & Chaibu 2000. A map presents the distribution of the Oecetis species included in this report.
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| 22. |
- Johanson, Kjell Arne, 1966-, et al.
(författare)
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Description of three new species of Oecetis McLachlan, 1877 (Trichoptera: Leptoceridae) from Laos
- 2021
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Ingår i: Aquatic Insects. - : Taylor & Francis Group. - 0165-0424 .- 1744-4152. ; 42:1, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Three new species of Oecetis McLachlan, 1877 from Laos are described, O. asymmetrica sp. n., O. conjuncta sp. n. and O. triangulata sp. n. Additional faunistic records are provided for two species already known from Laos: O. empusa Malicky and Chaibu, 2000 and O. raghava Schmid, 1995.
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| 23. |
- Johanson, Kjell Arne, 1966-, et al.
(författare)
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Description of two new species of Oecetis (Trichoptera, Leptoceridae) from Borneo
- 2022
-
Ingår i: European journal of taxonomy. - : Museum National D'Histoire Naturelle. - 2118-9773. ; 819, s. 158-165
-
Tidskriftsartikel (refereegranskat)abstract
- Two new species of Oecetis from Maliau Basin, Malaysian Borneo, are described for the first time, O. mesospina sp. nov. and O. apelqvisti sp. nov. These two new species bring the total number of Oecetis found on the island of Borneo up to 16.
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| 24. |
- Johanson, Kjell Arne, 1966-, et al.
(författare)
-
Eighteen new species of Oecetis McLachlan 1877 (Trichoptera, Leptoceridae) from New Caledonia
- 2020
-
Ingår i: Zootaxa. - 1175-5326 .- 1175-5334. ; 4809:2, s. 201-240
-
Tidskriftsartikel (refereegranskat)abstract
- Eighteen new species of Oecetis are described, diagnosed, and illustrated from New Caledonia: Oecetis amphora sp. nov., Oecetis ovula sp. nov., Oecetis ramosa sp. nov., Oecetis loyolaensi sp. nov., Oecetis millei sp. nov., Oecetis christinae sp. nov., Oecetis rostrata sp. nov., Oecetis alicae sp. nov., Oecetis oxybelis sp. nov., Oecetis dorsospina sp. nov., Oecetis multidentata sp. nov., Oecetis gracilis sp. nov., Oecetis rostra sp. nov., Oecetis triramosa sp. nov., Oecetis flucta sp. nov., Oecetis nouvellecaledoniensis sp. nov., Oecetis variabilis sp. nov., and Oecetis ovata sp. nov. A diagnostic key is provided for males of Oecetis species of New Caledonia. The species display similarities in genitalic characteristics but also a high diversity of apomorphic features. The new species were collected from lotic habitats across most of Grande Terre.
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| 25. |
- Johanson, Kjell Arne, 1966-, et al.
(författare)
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Molecular phylogeny of Sericostomatoidea(Trichoptera) with the establishment of three newfamilies
- 2017
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Ingår i: Systematic Entomology. - : Wiley. - 0307-6970 .- 1365-3113. ; 42, s. 240-266
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Tidskriftsartikel (refereegranskat)abstract
- We inferred the phylogenetic relationships among 58 genera of Sericostom-atoidea, representing all previously accepted families as well as genera that were notplaced in established families. The analyses were based on ve fragments of the proteincoding genes carbamoylphosphate synthetase (CPSase of CAD), isocitrate dehydroge-nase (IDH), Elongation factor 1a (EF-1a), RNA polymerase II (POL II) and cytochromeoxidase I (COI). The data set was analysed using Bayesian methods with a mixedmodel, , and parsimony. The various methods generated slightly different resultsregarding relationships among families, but the shared results comprise support for: (i)a monophyletic Sericostomatoidea; (ii) a paraphyletic Parasericostoma due to inclusionof Myotrichia murina, leading to synonymization of Myotrichia with Parasericostoma;(iii) a polyphyletic Sericostomatidae, which is divided into two families, Sericostom-atidae sensu stricto and Parasericostomatidae fam.n.; (iv) a polyphyletic Helicophidaewhich is divided into Helicophidae sensu stricto and Heloccabucidae fam.n.; ( v) hypoth-esized phylogenetic placement of the former incerta sedis genera Ngoya, Seselpsycheand Karomana; (vi) a paraphyletic Costora (Conoesucidae) that should be divided intoseveral genera after more careful examination of morphological data; (vii) reinstatementof Gyrocarisa as a valid genus within Petrothrincidae. A third family, Ceylanopsychi-dae fam.n., is established based on morphological characters alone. A hypothesis ofthe relationship among 14 of the 15 families in the superfamily is presented. A key tothe families is presented based on adults (males). Taxonomic history, diagnosis, habitatpreference and distribution data for all sericostomatoid families are presented.
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| 26. |
- Johanson, Kjell Arne, et al.
(författare)
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Testing the monophyly of Calocidae (Insecta: Trichoptera) based on multiple molecular data
- 2010
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Ingår i: Molecular Phylogenetics and Evolution. - : Elsevier Inc.. - 1055-7903 .- 1095-9513. ; 54, s. 535-541
-
Tidskriftsartikel (refereegranskat)abstract
- Calocidae constitute a hypothesised monophyletic group of caddisflies (Trichoptera) being geographically restricted to New Zealand (one genus) and Australia (five genera). This analysis tests the monophyly of the family based on sequences from five different molecular genes. The complete data set includes 29 species and covers a complete genus representation of the Calocidae as well as representatives of other families in which one or more calocid genera have been classified. Sequences from two mitochondrial (cytochrome oxidase I and 16S) and three nuclear (elongation factor 1-a, RNA polymerase-II, and Cadherin) genes were used, resulting in a 3958 bp data set and 37.1% parsimony informative characters. The Cadherin (CAD) and RNA polymerase-II (POL-II) genes are used for the first time for revealing Trichoptera phylogenies. The character matrix was analyzed by using maximum parsimony (MP) and Bayesian criteria, the latter by applying three different partition strategies for comparison. Two most parsimonious trees were found, differing in the position of one clade within the sister-group to a monophyletic Calocidae. The Bayesian tree based on the maximum number of partitions differs from trees based on a reduced partition analysis with respect to taxa outside the current circumscription of Calocidae. Both the MP and Bayesian analyses left Calocidae monophyletic, with a monophyletic clade of all Australian genera being sister-group to the New Zealand genus. The results from the agreement subtree analysis demonstrates that CAD performs well both separately and in combination with other genes and adds substantial resolution to the calocid phylogeny in a combined MP analysis.
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| 27. |
- Johanson, K.A., et al.
(författare)
-
Testing the monophyly of the New Zealand and Australian endemic family Conoesucidae Ross based on combined molecular and morphological data (Insecta: Trichoptera: Sericostomatoidea)
- 2009
-
Ingår i: Zoologica Scripta. - : Wiley. - 0300-3256 .- 1463-6409. ; 38:6, s. 563-573
-
Tidskriftsartikel (refereegranskat)abstract
- Conoesucidae (Trichoptera, Insecta) are restricted to SE Australia, Tasmania and New Zealand. The family includes 42 described species in 12 genera, and each genus is endemic to either New Zealand or Australia. Although monophyly has been previously assumed, no morphological characters have been proposed to represent synapomorphies for the group. We collected molecular data from two mitochondrial genes (16S and cytochrome oxidase I), one nuclear gene (elongation factor 1-alpha) (2237-2277 bp in total), and 12 morphological characters to produce the first phylogeny of the family. We combined the molecular and morphological characters and performed both a maximum parsimony analysis and a Bayesian analysis to test the monophyly of the family, and to hypothesize the phylogeny among its genera. The parsimony analysis revealed a single most parsimonious tree with Conoesucidae being a monophyletic taxon and sistergroup to the Calocidae. The Bayesian inference produced a distribution of trees, the consensus of which is supported with posterior probabilities of 100% for 15 out of 22 possible ingroup clades including the most basal branch of the family, indicating strong support for a monophyletic Conoesucidae. The most parsimonious tree and the tree from the Bayesian analysis were identical except that the ingroup genus Pycnocentria changed position by jumping to a neighbouring clade. Based on the assumption that the ancestral conoesucid species was present on both New Zealand and Australia, a biogeographical analysis using the dispersal-vicariance criteria demonstrated that one or two (depending on which of the two phylogenetic reconstructions were applied) sympatric speciation events took place on New Zealand prior to a single, late dispersal from New Zealand to Australia.
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| 28. |
- Johanson, Kjell Arne, et al.
(författare)
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The Trichoptera of Vanuatu
- 2011
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Ingår i: Deutsche Entomologische Zeitschrift. - : Wiley. - 0012-0073 .- 1435-1951. ; 58:2, s. 279-320
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Tidskriftsartikel (refereegranskat)abstract
- The Trichoptera diversity of Vanuatu is reviewed based on earlier and recently collected material. Altogether, 20 species in 12 genera and 8 families are now recognized for the country, of which 12 species are described as new to science in the families Hydrobiosidae (1 species), Hydroptilidae (5 species), Philopotamidae (3 species) and Leptoceridae (3 species). The previously known species from Vanuatu are re-described with illustrations and photographs. A key to adults of the Trichoptera fauna of Vanuatu is provided.
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| 29. |
- Junno, Tobias, et al.
(författare)
-
Single-electron devices via controlled assembly of designed nanoparticles
- 1999
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Ingår i: Microelectronic Engineering. - 0167-9317. ; 47:1-4, s. 179-183
-
Tidskriftsartikel (refereegranskat)abstract
- Single-electron transistors (SET) rely for their functionality on extreme control of lithography and lateral positioning as well as of properties of the building blocks from which the devices are built. By an aerosol-based nanoparticle fabrication we can prepare nanocrystals down to sub-10nm dimensions with metallic or semiconducting character, as well as having a core + shell design for definition of tunnel-gaps. We present here results for a type of device that is based on the possibility to design functionality in the internal structure of the nanoparticles which are used as building blocks. We use such pre-fabricated building blocks to construct coulomb blockade devices and show that they operate at temperatures above 150K.
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| 30. |
- Leppänen, Sanna, et al.
(författare)
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A Comparative Analysis of Genetic Differentiation across Six Shared Willow Host Species in Leaf- and Bud-Galling Sawflies
- 2014
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:12, s. 1-19
-
Tidskriftsartikel (refereegranskat)abstract
- Genetic divergence and speciation in plant-feeding insects could be driven by contrasting selection pressures imposed by different plant species and taxa. While numerous examples of host-associated differentiation (HAD) have been found, the overall importance of HAD in insect diversification remains unclear, as few studies have investigated its frequency in relation to all speciation events. One promising way to infer the prevalence and repeatability of HAD is to estimate genetic differentiation in multiple insect taxa that use the same set of hosts. To this end, we measured and compared variation in mitochondrial COI and nuclear ITS2 sequences in population samples of leaf-galling Pontania and bud-galling Euura sawflies (Hymenoptera: Tenthredinidae) collected from six Salix species in two replicate locations in northern Fennoscandia. We found evidence of frequent HAD in both species complexes, as individuals from the same willow species tended to cluster together on both mitochondrial and nuclear phylogenetic trees. Although few fixed differences among the putative species were found, hierarchical AMOVAs showed that most of the genetic variation in the samples was explained by host species rather than by sampling location. Nevertheless, the levels of HAD measured across specific pairs of host species were not correlated in the two focal galler groups. Hence, our results support the hypothesis of HAD as a central force in herbivore speciation, but also indicate that evolutionary trajectories are only weakly repeatable even in temporally overlapping radiations of related insect taxa.
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| 31. |
- Mally, Richard, et al.
(författare)
-
Revision of Afrotropical Udea Guenée in Duponchel, 1845, with description of five new species of the U. ferrugalis (Hübner, 1796) group (Lepidoptera, Crambidae, Spilomelinae)
- 2022
-
Ingår i: Nota lepidopterologica. - : Pensoft Publishers. - 0342-7536 .- 2367-5365. ; 45, s. 315-353
-
Tidskriftsartikel (refereegranskat)abstract
- The Udea species (currently six) present in the Afrotropical realm are revised based on adults. Phlyctaenia epicoena Meyrick, 1937 syn. nov. is found to be identical with U. ferrugalis (Hübner, 1796). Udea delineatalis (Walker in Melliss 1875) and U. hageni Viette, 1952 are redescribed. In addition, five species of Udea are described as new to science: U. kirinyaga Mally sp. nov. from Mount Kenya in Kenya, U. nicholsae Mally sp. nov., U. meruensis Mally sp. nov. and U. momella Mally sp. nov., all three from Mount Meru in Tanzania, and U. namaquana Karisch & Mally sp. nov. from South Africa. A phylogenetic analysis based on morphological data and mitochondrial COI as well as the nuclear wingless gene, where available, places the new species in the U. ferrugalis species group, which also comprises U. ferrugalis as well as U. delineatalis from the oceanic island of St. Helena. Another island endemic, Udea hageni from Tristan da Cunha, is found to be a member of the U. numeralis group, as sister to U. numeralis. An additional synapomorphic character of the genitalia is recognised for the U. ferrugalis group. Udea infuscalis (Zeller, 1852) and U. melanostictalis (Hampson in Poulton 1916) are misplaced in Udea and transferred to Pyraustinae, as Lirabotys infuscalis comb. nov. and Achyra melanostictalis comb. nov., respectively. Adults, tympanic organs, and genitalia of both sexes, where available, are illustrated. A checklist summarises the now eight Afrotropical Udea species.
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| 32. |
- Malm, Richard, et al.
(författare)
-
Concrete arch dam at seismic loading with fluid structure interaction
- 2013
-
Konferensbidrag (refereegranskat)abstract
- A concrete arch dam have been analyzed during seismic loading with a model based on acoustic elements to describe the water and infinite elements as quiet boundaries to prevent wave reflection. The results have also been compared with a simplified model based on Westergaards added mass approach. The simplified model is only used, in this study, for comparison with the more advanced model with acoustic elements. Therefore the results from this simplified model are just used as a rough estimate of the induced stresses and displacements. Despite this, the simplified Westergaard model gives similar results compared to the more advanced model with acoustic elements for the water and infinite elements for the boundaries. The largest difference between the models often occurs at the nodes in the base of the arch dam, which may be due to poor discretization. Generally, the Westergaard added mass gives higher maximum principal stresses at the base on the upstream side than the acoustic model, while often underestimating the min principal stresses at the base on the downstream side. Both models show high tensile stresses near the base of the arch dam that would result in cracks.
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| 33. |
- Malm, Richard, et al.
(författare)
-
Cracking in the concrete foundation for hydropower generators : Analyses of non-linear drying diffusion, thermal effects and mechanical loads
- 2013
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- An extensive program for improvement of the hydropower plants in Sweden is currently on-going. The aims are to secure future production and to maintain and further develop an already high dam safety.During inspection, cracks were discovered in the concrete foundation, near the stator and rotor spider supports, at some hydropower stations in Sweden. The cracks were believed to be related to the function of the stator supports and to new patterns of generator operation. In earlier times, the generators ran continuously, while nowadays there are many stops and starts, sometimes even several times during one day. The objective of this study is to understand the complex interaction between the power generating system (stator, rotor, turbine, etc.) and the supporting concrete structure. It is important from a dam safety perspective to determine the causes of the structural cracks that have been found in-situ.A three dimensional non-linear finite element model has been developed in order to analyse formation and propagation of the cracks. Several different load effects have been studied in this project in addition to the mechanical loads during operation. The new pattern of generator operation with several starts and stops lead for instance to variations in temperature which have been studied. Besides this, the uneven drying shrinkage of concrete has also been studied in this project. Thereby, the structural behaviour of a concrete foundation for the power generating system has been analysed taking into account the transient thermal and moisture gradients in combination with dead loads and some of the operational loads imposed to the foundation.The analyses shows that reinforced concrete structure that constitute a support to the generator is subjected to cracking due to the loads considered in this study, where the cracks near the supports are caused by a combination of mechanical loads, long-term drying shrinkage and temperature variations. The analyses showed that even after 20 years, the moisture content in the centre of the thicker part in the concrete foundation still had a high relative humidity. At the same time the concrete close to the free surfaces and the slender parts of the concrete foundation had reached the same relative humidity as the environment. Thereby, a large difference in drying shrinkage is obtained between different parts of the concrete foundation and thereby large forces due to restrain. The analyses showed that the drying shrinkage induced cracking inside the concrete foundation and especially close to the supports of the stator and the rotor spider which coincides with location of the cracks found in-situ.The results show that the cracks found in-situ can be simulated and explained with advanced numerical methods. The results also indicate that the dynamic effect from the loads caused by the power generating system have to be studied further, since a reduced structural stiffness due to cracking may result in larger loads imposed on the structure from the magnetic eccentricity and turbine imperfections or alternatively lead to a fatigue failure of for instance the reinforcement.
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| 34. |
- Malm, Richard, et al.
(författare)
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Evaluating Stability Failure Modes due to Cracks in a Concrete Buttress Dam
- 2013
-
Ingår i: Changing Times. - United States of America : U.S. Society on Dams. ; , s. 415-424
-
Konferensbidrag (refereegranskat)abstract
- Several concrete buttress dams in northern Sweden have been found to be subjected to, more or less severe, cracks according to recent assessments and investigations. Theoretical analyses and field measurements have shown that most of these cracks have developed or propagated as a result of the seasonal temperature variations. Most dams in Sweden were built for more than 50 years ago and it is therefore important to also consider the influence of long-term effects and degradation to assess the condition of the dam. In this paper, simulations have been performed with detailed 3D nonlinear numerical analyses in order to study crack initiation and crack propagation due to stochastic variation in material properties, which represent concrete degradation. The structural response due to loads from gravity, hydrostatic water pressure and thermal seasonal effects have been considered in the studies. It was shown that weak material properties near the crack-tip will govern the trajectory of the crack. According to the analyses, significant amount of cracking can occur in the front-plate and buttress if the strength of the concrete is reduced, which lead to new potential failure modes. In addition, the extent of cracking in the buttress dam is largely governed by the induced cracking in the front-plate since these cracks have a tendency to propagate into the concrete buttress. Based on the calculated extent of cracking in the dam body, different failure modes can be assessed in order to determine the dam stability failure.
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| 35. |
- Malm, Richard, et al.
(författare)
-
Finite element analyses of an arch dam subjected to seismic loads and hydrodynamic forces
- 2014
-
Ingår i: XXII Nordic Concrete Research Symposium. ; , s. 465-468
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A concrete arch dam subjected to seismic ground accelerations has been analysed using the finite element method. The response of the concrete structure is calculated through dynamic implicit analyses using two different modelling approaches, the Westergaard added mass approach with hydrodynamic inertia forces from a finite water volume and a model based on acoustic elements. The models show high tensile stresses near the base of the dam which indicate a risk for cracking. The study demonstrate that the choice of damping, the type of seismic excitation and use of quiet boundaries have a significant influence on the result.
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| 36. |
- Malm, Richard, et al.
(författare)
-
Probabilistic analyses of crack propagation in concrete dams : Part 1
- 2013
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Several concrete buttress dams in northern Sweden have been found to be subjected to, more or less severe, cracks according to recent assessments and investigations. Theoretical analyses and field measurements have shown that most of these cracks have developed or propagated as a result of the seasonal temperature variations. Most dams in Sweden were built for more than 50 years ago and it is therefore important to also consider the influence of long-term effects and degradation to assess the dam. The ordinary sliding and overturning stability analyses may not be sufficient when the supporting structure is cracked, since the cracks may comprise the integrity and the homogeneity of the structure.This project is a continuation from previous projects presented by Björnström et al. (2006), Ansell et al. (2008) and Ansell et al. (2010). In these previous projects, Storfinnforsen hydropower dam located in northern part of Sweden was studied and the purpose of the projects was to explain the cause for cracking found in situ. In the present project, the previously developed numerical model was verified against measured variations in crest displacement and crack width due to temperature variations during one year. The results showed that the numerical model, which was used, could predict both variations in displacements and crack width with good accuracy compared to the measurements on the actual dam.The studies of this project which are presented in this report are focused on the crack propagation due to stochastic variations in material properties. This was performed with probabilistic analyses based on a local model of an inclined crack in the supporting buttress. Monte-Carlo simulations were performed where each element was randomly assigned a concrete strength according to an assumed material distribution. It was shown that weak material properties near the crack-tip will govern the propagation and the trajectory of the crack. The results also showed that the average crack propagation from the probabilistic analyses differed both regarding inclination and length compared to the deterministic analysis which was based on mean values. In addition to the local analyses, global analyses were also performed, where stochastic variations in material properties were assigned to the whole monolith. The analyses showed that using design values or characteristic values of the material strength may give a different failure mode compared to the case where mean values of the material properties are used. When considering nonlinear properties for verification analyses, it is important to base the material properties on as accurate material properties as possible. In addition, the extent of cracking in the buttress dam is largely governed by the induced cracking in the front-plate since these cracks have a tendency to propagate into the concrete buttress. The results also showed that if the dam have been subjected to degradation and thereby has reduced concrete strength, the thermal stresses could induce significant cracking in the monolith which could lead to new failure modes. Based on the calculated extent of cracking in the dam body, different failure modes should be assessed in order to determine the dam stability failure.
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| 37. |
- Malm, Richard, 1980-, et al.
(författare)
-
Probabilistic Analyses of Thermal Induced Cracking in a Concrete Buttress Dam
- 2011
-
Ingår i: Risk Analysis, Dam Safety, Dam Security and Critical Infrastructure Management.
-
Konferensbidrag (refereegranskat)abstract
- Recent assessments and investigations of buttress dams in northern Sweden reveal several types of cracks. The theoretical analysis and field measurements have showed that the most of the cracks are either developed or propagated as a result of the seasonal temperature variations. Cracks influence the behaviour of the dams in different ways, such as reducing the tightness of the dam and increasing the hydraulic pressure within the material/structure. Furthermore, cracks may have an impact on the stiffness and stability of the dam. The ordinary sliding and overturning stability analyses are not sufficient when the supporting structure is cracked. The cracks may comprise the integrity and the homogeneity of the structure. A cracked, and for that matter even repaired structure, can’t be regarded as a homogenous structure and should be treated accordingly. Consequently, other types of models instead of the conventional design models should be utilized for the stability analyses of the cracked and repaired dams.The mode of the failure is one of the decisive elements considering determination of the probability of the failure. The conditions for crack initiation and the trajectory of the crack propagation are the decisive factors which govern the failure mode. Ordinary design methods and advanced numerical models which are based on the elastic behaviour of the structure can’t be utilized, since these models are not able to describe the non-linear behaviour and to predict the failure mode of the structure.A finite-element model based on non-linear fracture mechanics is being utilized to study crack development in a buttress dam. The aim of the study was to reveal crack trajectories and different probable failure modes, and moreover to determine the influences of the cracks on the overall behaviour of the structure. In a real structure the loading (mechanical and environmental) and boundary conditions are decisive factors regarding initiation, propagation and trajectory of the cracks. Furthermore, the material properties and their statistical distribution may influence the formation of cracks and the mode of failure.
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| 38. |
- Malm, Richard, 1980-, et al.
(författare)
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The Influence of Cracks on the Structural Behaviour of a Buttress Dam
- 2011
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Ingår i: Studies on Modern Technologies and Long-term Behavior of Dams. - : China WaterPower Press. - 9787508490182 ; , s. 677-685
-
Konferensbidrag (refereegranskat)abstract
- Buttress dams located in cold areas are often subjected to severe environmental conditions. Recent assessments and investigations of buttress dams in northern Sweden reveal several types of cracks. Theoretical analysis and field measurements have showed that the most of the cracks are either developed or propagated as a result of the seasonal temperature variations.Cracks influence the behaviour of the dams in different ways, such as reducing the tightness of the dam and increasing the hydraulic pressure within the cracks. Furthermore, cracks may have impact on the stiffness and stability of the dam. The ordinary sliding and overturning stability analyses are not sufficient when the supporting structure is cracked. The cracks may comprise the integrity and the homogeneity of the structure. A cracked, and for that matter even repaired structure, can’t be regarded as a homogenous structure and should be treated accordingly. Consequently other types of models instead of the conventional design models should be utilized for the stability analyses of the cracked and repaired dams.There are at least two major aspects which must be considered when a cracked or repaired structure is being analysed. The first aspect is the principle of superposition and the second aspect is probability of the failure. It is well known that a cracked structure does not behave linearly, consequently the principle of superposition can’t be applied to determine the overall effects of the several simultaneously acting events.The mode of failure is one of the decisive elements considering determination of the probability of the failure. The condition for crack initiation and the trajectory of the crack propagation are the decisive factors which govern the failure mode. Ordinary design methods and advanced numerical models which are based on the elastic behaviour of the structure can’t be utilized, since these models are not able to describe the non-linear behaviour and to predict the failure mode of the structure.A finite-element model based on the non-linear fracture mechanics has been utilized to study crack development in a buttress dam. The aim of the project was to study crack trajectories and to determine the influences of cracks on the overall behaviour of the structure, for instance in the global stiffness of the structure and possible failure modes. The paper will present the structure, the numerical model and the results.
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| 39. |
- Malm, Tobias, et al.
(författare)
-
A new classification of the long-horned caddisflies (Trichoptera : Leptoceridae) based on molecular data
- 2011
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Ingår i: BMC Evolutionary Biology. - : Springer Science and Business Media LLC. - 1471-2148. ; 11, s. 10-
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Tidskriftsartikel (refereegranskat)abstract
- Background: Leptoceridae are among the three largest families of Trichoptera (caddisflies). The current classification is founded on a phylogenetic work from the 1980's, based on morphological characters from adult males, i.e. wing venation, tibial spur formula and genital morphology. In order to get a new opinion about the relationships within the family, we undertook a molecular study of the family based on sequences from five genes, mitochondrial COI and the four nuclear genes CAD, EF-1 alpha, IDH and POL. Results: The resulting phylogenetic hypotheses are more or less congruent with the morphologically based classification, with most genera and tribes recovered as monophyletic, but with some major differences. For monophyly of the two subfamilies Triplectidinae and Leptocerinae, one tribe of each was removed and elevated to subfamily status; however monophyly of some genera and tribes is in question. All clades except Leptocerinae, were stable across different analysis methods. Conclusions: We elevate the tribes Grumichellini and Leptorussini to subfamily status, Grumichellinae and Leptorussinae, respectively. We also propose the synonymies of Ptochoecetis with Oecetis and Condocerus with Hudsonema.
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| 40. |
- Malm, Tobias, 1979-, et al.
(författare)
-
A new classification of the long-horned caddisflies (Trichoptera: Leptoceridae) based on molecular data
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Background The Leptoceridae is among the three largest families within the order Trichoptera (caddisflies). The current classification is founded on a phylogenetic work from the 1980’s, mainly based on morphological characters from adult males, i.e. wing venation, tibial spur formula and genital morphology. In order to get a second opinion about the relationships within the family, we have undertaken a molecular study of the family based on sequences from five genes; one mitochondrial and four nuclear. Results The resulting phylogenetical hypotheses are more or less congruent with the morphologically based classification, with most genera and tribes recovered as monophyletic, but with some major differences. For monophyly of the two subfamilies Triplectidinae and Leptoceriane, one tribe of each had to be removed and erected to subfamily status and the monophyly of some genera and tribes have to be questioned. All clades but the subfamily Leptocerinae were stable across different analysis methods, results presumably based on the taxon sampling. Conclusions With support from the results obtained here we erect the tribes Grumichellini and Leptorussini to subfamily status, Grumichellinae and Leptorussinae, respectively. We are also confident in the discovery of a few non-valid genera that are synonymised, e.g. Ptochoecetis with Oecetis and Condocerus with Hudsonema.
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| 41. |
- Malm, Tobias, et al.
(författare)
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A simple method for data partitioning based on relative evolutionary rates
- 2018
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Ingår i: PeerJ. - : PeerJ. - 2167-8359. ; , s. 1-21
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Tidskriftsartikel (refereegranskat)abstract
- Background. Multiple studies have demonstrated that partitioning of molecular datasets is important in model-based phylogenetic analyses. Commonly, partitioning is done a priori based on some known properties of sequence evolution, e.g. differences in rate of evolution among codon positions of a protein-coding gene. Here we propose a new method for data partitioning based on relative evolutionary rates of the sites in the alignment of the dataset being analysed. The rates are inferred using the previously published Tree Independent Generation of Evolutionary Rates (TIGER), and the partitioning is conducted using our novel python script RatePartitions. We conducted simulations to assess the performance of our new method, and we applied it to eight published multi-locus phylogenetic datasets, representing different taxonomic ranks within the insect order Lepidoptera (butterflies and moths) and one phylogenomic dataset, which included ultra-conserved elements as well as introns.Methods. We used TIGER-rates to generate relative evolutionary rates for all sites in the alignments. Then, using RatePartitions, we partitioned the data into partitions based on their relative evolutionary rate. RatePartitions applies a simple formula that ensures a distribution of sites into partitions following the distribution of rates of the characters from the full dataset. This ensures that the invariable sites are placed in a partition with slowly evolving sites, avoiding the pitfalls of previously used methods, such as kmeans. Different partitioning strategies were evaluated using BIC scores as calculated by PartitionFinder.Results. Simulations did not highlight any misbehaviour of our partitioning approach, even under difficult parameter conditions or missing data. In all eight phylogenetic datasets, partitioning using TIGER-rates and RatePartitions was significantly better as measured by the BIC scores than other partitioning strategies, such as the commonly used partitioning by gene and codon position. We compared the resulting topologies and node support for these eight datasets as well as for the phylogenomic dataset.Discussion. We developed a new method of partitioning phylogenetic datasets without using any prior knowledge (e.g. DNA sequence evolution). This method is entirely based on the properties of the data being analysed and can be applied to DNA sequences (protein-coding, introns, ultra-conserved elements), protein sequences, as well as morphological characters. A likely explanation for why our method performs better than other tested partitioning strategies is that it accounts for the heterogeneity in the data to a much greater extent than when data are simply subdivided based on prior knowledge.
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| 42. |
- Malm, Tobias
(författare)
-
Becoming a rock band : The challenges of group identity
- 2017
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Ingår i: Journal of Popular Music Education. - : Intellect. - 2397-6721 .- 2397-673X. ; 1:2, s. 165-182
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Tidskriftsartikel (refereegranskat)abstract
- Rock bands feature increasingly in music education. They are essential parts of popular culture and are increasingly highlighted as entrepreneurial organizations in a global music industry. However, to develop and stay together as a band is a difficult task. This study aims to develop an understanding of the challenges of becoming a rock band, shedding new light on previously underexplored complexities of band life by considering the impact of group identities. The methodology entails storytelling and identity work, inspired by a biographical approach. Six explorative interviews with band members were conducted. The results suggest that productive activities form several kinds of work group identities, whereas low-activity periods threaten group identification. The article discusses how diversity of group identities promotes development while uniformity promotes stability. To cope with this paradox, this article suggests that band members ought to learn to develop multiple group identities and flexible ways of relating to one another.
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| 43. |
- Malm, Tobias, 1979-
(författare)
-
Climbing the Trichoptera Tree : Investigations of Branches and Leaves
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Trichoptera (caddisflies) is the largest of the primary aquatic insect orders, currently including more than 13,500 species. With more than 100 species new to science described annually, the known caddisfly diversity is rapidly increasing. In the first four papers of this Thesis, a total of 22 species new to science are described. The first three papers include revisions of the New Caledonian species for the genera Symphitoneuria, Gracilipsodes and Triplectides, with descriptions of 3, 7 and 11 new species, respectively. In these papers I strengthen our image of New Caledonia as a biodiversity hotspot. The fourth paper describes a new genus and species from Madagascar, another biodiversity hotspot. These four papers all deal with species and genera of the family Leptoceridae, which ranks among the three largest families within Trichoptera. The family comprises high species diversity together with a widespread distribution and has been of interest to many trichopterologists. However, the classification used for genera and tribes within the family follows a phylogenetic hypothesis from 1981. In paper V I apply a molecular approach for hypothesising phylogenetic relationships within the family, revealing support for the erection of two tribes to subfamily level and for the synonymisations of 2 pairs of genera. At order level, the progress of illuminating the evolutionary history of Trichoptera is advancing with recent analyses using molecular based data. Previously published phylogenetic hypotheses of the order were to a large degree dependent on ribosomal DNA, a source of molecular data not without its controversies, particularly regarding alignment procedures. Paper VI presents Trichoptera phylogenies based on sequences of protein-coding nuclear and mitochondrial genes. My results correspond well to previously published hypotheses among suborder relationships, but show additional and contrasting resolution within suborders.
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| 44. |
- Malm, Tobias, et al.
(författare)
-
Description of eleven new Triplectides species (Trichoptera: Leptoceridae) from New Caledonia
- 2008
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Ingår i: Zootaxa. - 1175-5334. ; :1816, s. 1-34
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Tidskriftsartikel (refereegranskat)abstract
- The Oceanian country of New Caledonia has been shown to have a great diversity of Trichoptera, but prior to this work only 3 species from the large Leptoceridae genus Triplectides were known from there. Extensive sampling on the main island, Grande Terre, revealed 11 new species in the genus, as well as a male of the seemingly widespread species Triplectides australis. These 11 new species are here described and illustrated, and a key to males of the New Caledonian Triplectides species is provided. The new species are: T. mouiensis, new species; T. abnormalis, new species; T. minutus,new species; T. noumeiensis, new species; T. tigrinus, new species; T. koghiensis, new species; T. wardi, new species; T. nathaliae, new species; T. mariannae, new species; T. dawnae, new species; T. aequalichelatus, new species. Fifteen species within the genus are now known from New Caledonia; relative to land mass, this is a high diversity compared to the 25 species recorded from Australia.
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| 45. |
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| 46. |
- Malm, Tobias, 1980-
(författare)
-
Från album till låtar : tio år med Spotify
- 2019
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Ingår i: Starka tillsammans. - Stockholm : Trinambai. - 9789188226099 ; , s. 199-208
-
Bokkapitel (populärvet., debatt m.m.)abstract
- I detta kapitel vill jag belysa hur tio år med Spotify har inneburit förändrade förutsättningar för att vara ett band. Jag kommer också att fundera något över hur detta kan tänkas påverka framtidens musikliv och dess folkbildande potential inom civilsamhället. Med band menar jag i första hand så kallade ”originalband”, det vill säga små musikgrupper som organiserar sig själva och i huvudsak är inriktade på egenskrivet låtmaterial. Jag talar alltså om en stor och på många sätt ”underjordisk” verksamhet som alltsedan sin populariserings-boom under 1960-talet har ägt rum i källare, garage, skolor, fritidsgårdar och musikhus, samt på scener, i studios, turnébilar- och bussar, backstageloger, musikaffärer, och inte minst i dagdrömmar och storslagna planer. Många musikanter formar sina första band i tidiga tonåren, och där var jag själv inget undantag. Av de internationellt framgångsrika musiker och producenter som har satt vårt lilla land på kartan och banat väg för uttrycket ”det svenska musikundret”, är det många som har en bakgrund inom bandlivet. Att ha ett band kan vara att umgås med kompisar kring ett särskilt musikintresse, till exempel indie pop eller death metal, och samtidigt ett fritt och frivilligt sätt lära sig musikens hantverk. Men band handlar lika mycket om att lära sig att fungera som en liten organisation tillsammans – något som jag fokuserar särskilt på i min forskning.
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| 47. |
- Malm, Tobias, 1980-, et al.
(författare)
-
Från källarband till småföretag : kreativitet och entreprenörskap i popband
- 2018
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Ingår i: Den lärande organisationen 2.0. - Lund : Studentlitteratur AB. - 9789144114798 ; , s. 99-127
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Kreativitet och entreprenörskap är något som ses som allt viktigare inom dagens arbets- och samhällsliv. I Sverige framhålls ofta musik-, datorspels- och modebranschen som särskilt framgångsrika i ett internationellt perspektiv. På musikens område tar sig detta bl.a. uttryck i att regeringen årligen tilldelar svenska artister och grupper ett musikexportpris och lyfter fram dessa som viktiga ambassadörer för vårt nationella varumärke. Det faktum att ett litet land som Sverige brukar räknas som världens tredje musikexportnation efter USA och Storbritannien, har delvis gett upphov till uttrycket det svenska musikundret. Popband kan dock sägas växa fram i gränslandet mellan marknad och civilsamhälle, professionell kontra hobbyverksamhet samt mellan arbete och fritid, vilket bakom all framgång och statistik handlar om en social verklighet som lätt hamnar under den mediala och ekonomiska ”radarn”. Den synliga musikbranschen kan beskrivas som toppen på ett isberg som till stora delar består av små självorganiserade grupper, exempelvis pop- och rockband. Mot bakgrund av att sådana grupper traditionellt inte fokuserar på företagande och kommersialism, kan de tänkas möta en rad utmaningar då de formas till ett självständigt småföretag. I detta kapitel avser vi belysa i vad mån och på vilket sätt små självorganiserade, kreativa grupper kan ses som lärande organisationer.
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| 48. |
- Malm, Tobias, 1979-, et al.
(författare)
-
Highlighting the Trichoptera tree with new molecular markers
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We here present phylogenetic hypotheses of the insect order Trichoptera, based on molecular data from four nuclear protein-coding genes, Cadherin-like gene (CAD), Elongation-factor 1 alpha (EF1a), Isocitrate dehydrogenase (IDH) and RNA polymerase II (POL), and the mitochondrial Cytochrome oxidase subunit I (COI) gene. Ribosomal RNA and morphological characters have previously been widely used for reconstructing phylogenetic hypothesis at order level among insects, but were excluded from this study in order to explore the potential of only using easily amplified and aligned protein-coding genes in resolving phylogenies of this level. Analyses were performed to investigate the signal and contribution of each gene in light of the final phylogeny derived from combined data. The study is based on 139 specimens from 46 families of the order Trichoptera, as well as 10 outgroup taxa from the sistergroup Lepidoptera. The results show great similarities to previously published phylogenies mainly based on rRNA and morphology, but differ from those in some interesting aspects. The CAD, IDH and COI genes provided strong signal to the phylogeny, whereas EF1a and POL provided less strong signal, but nevertheless did all the genes contribute well to the combined data phylogenies.
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| 49. |
- Malm, Tobias, 1980-
(författare)
-
Konsten att hålla ihop : Om lärande och organisering i rockband
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rock bands are foundational for modern day music life. These small groups provide well-being and self-fulfillment to its members, as well as fuel for the cultural life and the increasingly highlighted creative industries. Rock bands, however, are particularly difficult to organize. Bands face a range of challenges in keeping together and developing as a group.The aim of this doctoral thesis is to develop knowledge on rock band formation and development over time. Based in the discipline of education, the thesis mainly contributes to the fields of organization studies, social theories of learning, and music and cultural life research.The thesis uses the theory of situated learning to explore rock band formation and development. The methodology is qualitative and ethnographic, and the research design builds on three studies: an interview study with three rock bands and two case studies. All five bands are Swedish and have found different degrees of success and popularity.The thesis investigates band activities and courses of events, band members’ identities, and challenges faced. The findings indicate that a rock band’s activities shift between a production mode – i.e. highly productive times associated with public performances, record releases and marketing, and behind the scenes processes of creating, recording and planning – and a contrasting less active hibernation mode without bigger public projects or goals. The amount of time spent in production mode depends on the band’s degree of “membership” in the music industry. Moreover, a band member forms and actualizes identities of colleague, creator, entrepreneur, friend, hobbyist and professional, in differing combinations, situations and modes. Furthermore, the members’ most significant challenges relate to identity dilemmas.Based on these findings, the thesis formulates a model for a rock band’s learning trajectory and argues that a band may develop as it approaches, or becomes a more central member in, the music industry. This development demands increased public success and organizational ability: the band members’ ability to form business-oriented practices, to participate uniformly in an overarching community of practice, and to be flexible as they must identify with, and ascribe meaning to, a variety of activities in different and sometimes contradictory ways.The thesis concludes that the challenges of persistence as a rock band or similar group relates chiefly to group member difficulties in identifying with different activities and situations that are necessary to sustain and develop as a collective. Eventually, individual members tend to handle the experience of uncertainty and ambivalence by holding on to one singular identity, which may prevent group development, foster intra- and interpersonal tensions, and ultimately can lead to significant conflicts and/or a band’s breakup.
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| 50. |
- Malm, Tobias, 1980-
(författare)
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Learning to Become a Band, Learning Popular Music
- 2022
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Ingår i: Places and Purposes of Popular Music Education. - : Intellect Books. - 9781789386288 ; , s. 85-89
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Bokkapitel (refereegranskat)abstract
- This chapter aims to show how learning popular music involves often- overlooked processes of learning to become a band, it discusses implications for educators and calls for more research. Based in Sweden, a small country with relatively large impact on popular music, the author currently sets out to answer that call.
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