| 71. |
- Garvare, Rickard
(författare)
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Process management and sustainable development in a quality perspective : implementation and measurement related to small and medium sized enterprises
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis aims at contributing to increased knowledge regarding sustainable competitive performance of small and medium sized enterprises in harmony with nature and society. The overall purpose has been specified in the following three parts: to explore implementation of statistically designed experiments, to describe experiences of introducing process management, and to contribute to the development of a conceptual framework for integration of business excellence and sustainable development, all with a focus on small and medium sized enterprises. During the last few decades the interest and industrial use of systems, tools and methodologies related to quality has grown considerably. Some of these were originally developed with the large company in mind, but today many small and medium sized organisations also try to implement them. However, management strategies developed for large organisations do not generally translate well into small and medium sized organisations. The research presented in this thesis has been divided into three research projects. An initial longitudinal study of two case companies within the industry of high performance ceramics resulted in a three step model for implementing statistical techniques, especially design of experiments. The approach adopted for the second project was a quantitative-qualitative research design divided into three parts: a mail survey of 1,500 enterprises, followed by telephone interviews with representatives of 62 of these enterprises, and finally case studies of seven selected firms. The results indicate that the proportion of small and medium sized enterprises in Sweden that has introduced process management is in the region of 10 percent of the total population. The findings were that, in general, the studied companies had not changed directly from a functional orientated organisation to a process orientated organisation. Instead many were still in, or had recently passed through, an intermediate state characterised by a team and project based organisation where focus was shifted towards internal efficiency and shorter lead times. The transitions described have been summarized schematically in a model with three different stages: starting with functions, continuing via teams and projects, and ending with processes. As a result of the third research project, suggestions are presented regarding how the requirements of critical global processes could be translated to areas of organisational concern. A conceptual business excellence model, including measurements of sustainable development, has been developed. The triple bottom line of economy, environment and ethics (3E) are proposed as main dimensions for measuring sustainable organisational performance.
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| 72. |
- Gedda, Hans
(författare)
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Laser cladding : an experimental and theoretical investigation
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Avhandlingen omfattar studier vid laserpåsvetsning och lasergjutning med CO2-laser och Nd:YAG-laser. Avhandlingen är indelad i sex kapitel. Kapitel 1 är en presentation/introduktion av laserpåsvetsning och några applikationsområden tillsammans med alla abstract, sammanfattningar och de viktigaste figurerna som ingår i de övriga kapitlen. Kapitel 2 är sammansättning av två publikationer där energifördelningen vid påsvetsning med CO2 och Nd:YAG-laser har undersökts och kvantifierats med hjälp av kalorimetriska försök. Studierna visar att vid laserpåsvetsning minskar energiförlusterna i form av reflektionsförluster från påsvetszonen med 50% för CO2-laser till 40% för Nd:YAG-laser. Kapitel 3 är en studie av hur processparametrarna påverkar det slutliga resultatet (fyllnadsgraden) vid påsvetsning i urfrästa spår innefattande; spårgeometri, pulverapplikation och lasertyp. Studien visar att det bl.a. är möjligt att producera mer eller mindre släta påsvetsar i urfrästa spår med CO2 och Nd:YAG-laser med pulverblåsmetoden. Kapitel 4 visar att det är möjligt att påverka påsvetsarnas slutliga geometri vid laserpåsvetsning. Man använder sig av koppar som gjutformsmaterial, som fixeras på var sida om materialet som skall påsvetsas. På så sätt ”fångar” man pulvermaterialet i gjutformen. Därmed kan man skapa en trapetsformad påsvets vilket är önskvärt för skäreggar och dylikt. Det är kopparns låga absorption av laserljusets våglängd, 10.6 μm och dess snabba värmetransport som gör detta möjligt. Kapitel 5 är en utveckling av kapitel 4 som visar att man även kan producera tråd och stänger via lasersmältning av pulvermaterial. Stänger producerad med denna metod har ett cirkulärt tvärsnitt, kan bli flera mm i diameter, är raka och porfria. Tekniken kan bl.a. användas för produktion av svetstänger, dragprovstavar och andra solida stänger från ett brett urval och sammansättningar av pulverblandningar. Det är det snabba termiska förloppet som gör det möjligt att producera små serier av en unik pulverblandning/legering i små serier till en låg kostnad. Kaptitel 6 omfattar experimentella data tillsammans med matematiska modeller för att förklara vad som händer i interaktionszonen mellan pulver och substrat vid lasergjutning och laserpåsvetsning av förbelagt pulver. Kapitlet inkluderar även en förklaring varför processfönstret för att uppnå en påsvets med liten uppblandning med substratmaterialet är stort. Även växelverkan mellan smältan och pulverbädden vid lasergjutning har analyserats för att identifiera varför lasergjutna kroppar uppvisar mikroskopiskt ojämna ytor.
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| 73. |
- Gehlin, Signhild
(författare)
-
Thermal response test : method development and evaluation
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the first introduction of thermal response tests with mobile measurement devices in Sweden and USA in 1995, the method has developed and spread in North America and Europe. Thermal response tests have so far been used primarily for in situ determination of design data for BHE (borehole heat exchanger) systems, but also for evaluation of grout material, heat exchanger types and groundwater effects. A variety of analytical and numerical data analysis models have been developed. Various applications of the line source theory is the most commonly used model for evaluation of the response test data because of its simplicity and speed, and is dominant in Europe. The use of the cylinder source model and numerical models coupled with parameter-estimation techniques are common in USA. The Swedish response test apparatus TED has been used at a number of tests since 1996. The main purpose has been to determine in situ values of effective ground thermal conductivity, including the effect of groundwater flow and natural convection in the boreholes. The tests indicate that convective heat transfer may play an important role for the thermal behaviour of groundwater-filled BHE, which is the typical BHE design in Sweden. The magnitude of the induced natural convection depends on the heat transfer rate and the temperature level. The influence is small on grouted boreholes. To shed light on the influence of groundwater flow on thermal response testing, simulation models for estimating the heat transfer effect of groundwater flowing near a borehole heat exchanger were developed. The groundwater flow was represented as 1) a flow through an equivalent porous medium (continuum), 2) a flow through an impermeable medium with a porous zone, and 3) a flow through an impermeable medium with a thin vertical fracture. The three cases result in significantly different temperature field patterns around the borehole and all three cause lower borehole temperatures. The fracture flow model results in higher effective thermal conductivity than the continuum and porous zone models within a certain flow rate interval. This illustrates the efficiency of the high flow velocity in the fracture and the large temperature gradient between the borehole and the fracture flow. The effect of the flow in the fracture or porous zone decreases with the distance from the borehole, but even at distances of half a meter or more the porous zone or fracture may result in significantly enhanced heat transfer. Even a relatively narrow fracture close to a borehole may result in greater effective thermal conductivity, although estimations made with a continuum approach may indicate otherwise. A thermal response test is likely to induce a thermosiphon flow due to the temperature difference between borehole and surroundings, resulting in an enhanced effective thermal conductivity estimation. The enhancement of the effective thermal conductivity of the BHE depends on injected power rate and flow resistance in fractures. The fracture flow resistance may be quantified in terms of hydraulic condcutivity. The findings from the groundwater flow and thermosiphon simulation are encouraging for further studies, both as simulations and in field experi- ments. The author suggests further studies of the possibility to develop models for estimating and investigating the influence of groundwater from drilling data and hydraulic testing. A future aim should be to gain enough knowledge of fracture flow and thermosiphon effects that hydraulic well test and drilling data may be used in borehole thermal energy storage design.
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| 74. |
- Geng, Qiuqing
(författare)
-
Hand cooling, protection and performance in cold environments
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation presents experimental data on hand/finger cooling responses and performance in cold environments with and without gloves. The first part concerned studies of hand/finger cooling behaviors under various cold conditions. The experimental results with human subjects indicate that a reduction in the contact temperature is a function of thermal properties and surface temperature of the materials, skin and the nature of the contact as well. Manual performance reduced after gripping the cold objects. A decrease of the hand skin temperature causes the performance loss. The safety criteria for the contact temperature are suggested to be 0°C (freezing), 7°C (numbness) and 15°C (pain sensation). An artificial heated finger model was developed and used to derive additional cooling information for extremely cold metallic surfaces. All results were utilized to establish relations between contact temperature, contact time and material used and compiled in an ergonomic database. The information can be used for risk assessment and for setting temperature limit values for products in appropriate standards for cold work. Manual performance, such as dexterity and tactile sensitivity of gloved hand in the cold operation, has been investigated. The relations among physical properties of protective gloves and hand performance were evaluated objectively and subjectively. Human subjects wearing four different work gloves and three different types of gloving (outer, inner and double) participated in the experimental studies during cold exposure. It is indicated that wearing various work gloves gives impairment in both manual dexterity and tactile sensitivity in cold operations. The performance was affected both by glove design and by hand/finger cooling. Use of double gloving is recommended to be an appropriate approach to use the protective gloves in the cold while inner glove can be used to perform some precision work. In extremely cold exposures hand cooling overrides the effect of glove on tactile performance. Development and use of an electrically heated glove should be considered for hand protection in a prolonged cold operation.
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| 75. |
- Glavatskikh, Sergei B.
(författare)
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On the hydrodynamic lubrication in tilting pad thrust bearings
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The primarily objective of this work was to investigate the performance of environmentally adapted synthetic oils in the hydrodynamic lubrication regime. A special test facility has been designed and manufactured for this purpose. The facility contains two equalising tilting pad thrust bearings typical of design in general use. One of the bearings is instrumented with thermocouples, pressure and oil film thickness sensors. Three thermistors and two pressure sensors are installed in one of the shaft collars. Power losses are measured by monitoring bearing friction torque and by the calorimetric technique. All sensors are connected to a PC based high-speed data acquisition system. The facility allows a complete set of bearing operating parameters to be obtained. Bearing characteristics in steady state and transient operating conditions were investigated at different load-speed combinations as well as at various supplied oil temperatures and flow rates. Steady state results were compared with the outputs of THD and TEHD theoretical models. The agreement was found to be good. Tests were run to find a possible replacement of ISO VG68 mineral oil currently used in thrust bearing units of hydroelectric power stations. Oils tested included mineral base ISO VG68 and ISO VG46 oils, PAO and ester base ISO VG46 oils. Tests showed that a change from VG68 oil to the lower viscosity grade oil reduces bearing peak temperatures. It is also shown that the energy savings associated with the use of VG46 oil in place of VG68 are significant. However, such a change may only be justified for the ester base oil since it gives as thick oil films as mineral oil ISO VG68 does. Alternatively, if the ester base oil is used instead of a mineral oil of the same viscosity grade bearing reliability is increased due to the increased oil film.
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| 76. |
- Graciano, Carlos
(författare)
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Patch loading : resistance of longitudinally stiffened steel girder webs
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In most cases, longitudinal stiffeners increase the resistance of steel girder webs subjected to concentrated forces, commonly referred to as patch loading. During the last three decades, a number of experimental investigations have been undertaken in all over the world in this regard. The test results shows that the patch loading resistance increases when a longitudinal stiffener is placed rather close to the loaded flange, however very little has been done to quantify this increase which in most design codes has been disregarded. At first the effect of a longitudinal stiffener on the structural behaviour of plate girder webs subjected to patch loading is investigated by means of nonlinear finite element analysis. Two plate girders with extreme values for the flange-to-web thickness ratio were modelled taken into account material and geometrical nonlinearities. The numerical results were validated with test results from others. Thereafter, a parametric study was conducted in order to investigate the relevance of some parameters such as the relative position and flexural rigidity of the stiffener and the size of the loaded flange in increasing the ultimate resistance of the steel girder webs to patch loading. In the past, it has been customary to calculate the patch loading resistance of the girder web with a longitudinal stiffener by multiplying the corresponding resistance of the unstiffened girder web (web only with transversal stiffeners) with a correction factor, obtained by a regression analysis, depending mainly on the relative location of the stiffener. Herein, a sensitivity analysis was conducted showing also the relevance of the flange-to-web thickness ratio and the ratio of the yield strength of the flange to the yield resistance of the web. Accordingly, a new correction factor was proposed taken into account the aforementioned parameters. The failure mechanism of longitudinally stiffened girder webs subjected to patch loading observed in the experiments is similar to that of unstiffened girder webs. This is characterised by the presence of elastoplastic deformation in the patch loaded flange (plastic hinges) and in the web (yield lines). From this deformed configuration, a mechanism resembling the distortions in the web plate and loaded flange was developed in order to obtain the patch loading resistance of longitudinally stiffened girder webs. This failure mechanism model fails in that the actual material and geometrical properties of the stiffener are not taken into account and certain assumptions are accordingly made to overcome this situation. In the latest edition of the Eurocode 3 Part 1.5 the patch loading resistance of unstiffened girder webs is obtained using a resistance reduction factor applied to the yield resistance to patch loading. This factor depends on a slenderness parameter, which is the square root of the ratio of the yield resistance to the critical buckling load (according to classical theory of elasticity) for patch loading. However, the interaction with longitudinal stiffening is not considered. In some respect the use of a longitudinal stiffener is comparable with a reduction in the slenderness ratio of a girder web. An expression is found for the buckling coefficient used for calculating the critical buckling load for patch loading based on finite element analysis. The interaction between the web plate with flanges and a longitudinal stiffener (open and closed section) was considered in the numerical analysis. Consequently, the critical buckling load increases due the presence of the stiffener and then the slenderness parameter is reduced. This leads to an increase in the patch loading resistance. Finally, the results obtained using the methodologies described above and those found in the literature are compared with available tests results. The goodness and flaws of each methodology are further discussed.
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| 77. |
- Gren, Per
(författare)
-
A pulsed TV holography system for the study of transients in experimental mechanics
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An all-electronic system for pulsed holographic interferometry called pulsed TV holography is developed. This is a whole-field non-contacting optical measurement method suitable for studies of transient events like wave propagation in solids and fluids. Chemical wet processing of holographic film and optical reconstruction of holograms are no longer needed. The technique was first developed using a double pulsed ruby laser as light source. The holograms are recorded directly on a CCD-detector. Quantitative data of changes in optical path length, caused either by a deformation of a solid object or a change in refractive index in a fluid, are calculated directly in a computer. The system for pulsed TV holography has recently been further developed by the purchase of a new pulsed laser (twin cavity, injection seeded pulsed Nd:YAG) and a CCD camera (PCO Sensicam) with higher spatial resolution and dynamic range. In the survey of this thesis the increased versatility compared to a ruby laser based system is discussed. During the development of the pulsed TV holography system a number of experiments in mechanics and acoustics have been accomplished. Bending waves in impacted plates propagating at a speed of about 2000 m/s are easily “frozen” due to the short duration laser pulses (<30 ns). These waves act as supersonic travelling acoustic sources and generate sound waves in the surrounding air. For the first time, transient sound fields from impacted plates have been visualised and measured using pulsed holographic interferometry. In another experiment, we have demonstrated that the pulsed TV holography system is feasible in combination with tomography. By recording a three-dimensional acoustic pressure field from a number of viewing directions followed by a tomographic reconstruction, the pressure in any point can be calculated. Finally, a method to restore fringes lost by large bulk motions is proposed. This technique may become very attractive in the study of vibrations (preferable transient) on moving or rotating objects. In conclusion, pulsed TV holography is proved to be a fast and reliable method to quantitatively study transients in mechanics and acoustics. The technique has a great potential in experimental mechanics in the future.
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| 78. |
- Grip, Niklas
(författare)
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Wavelet and gabor frames and bases : approximation, sampling and applications
- 2002
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to both theoretical and practical aspects of applied mathematics. It consists of three main parts: Part I consists of an application-oriented introduction to the theory of frames and bases for separable Hilbert spaces, as well as an introduction to the main tools used in the remaining Chapters: Time-frequency analysis, Gabor frames and wavelet frames. Part II contain five publications in the fields of approximation theory, sampling and perturbation stability. One paper and one research report consider different estimates of the error (measured in L^p, Besov or Triebel-Lizorkin norm) when a function is projected on certain so-called shift-invariant spaces. This is closely connected to a certain class of wavelet subspace sampling problems (containing the classical Shannon sampling theorem as a special case), prefiltering of the discrete wavelet transform and a certain perturbation stability theorem called the Kadec 1/4-theorem. These are the topics of the three remaining papers in Part II. Chapter 3 contains estimates of the L^p-norm error in certain projections of a function f onto a shift-invariant space V_j, spanned by translated copies of some given function. In Chapter 4, we propose a method which is well-suited for studying irregular sampling problems in such spaces. The main advantage of our method is that it provides an intuitive understanding and relatively simple proofs of some studied problems. The method builds on a study of an equivalent coefficient mapping, which we also use in Chapter 5. There we propose an improved low-complexity approximation of an often neglected prefilter which is needed when the discrete wavelet transform is used for analysis of real-world (i.e., non-discrete) signals. Chapter 6 consists of further results and remarks. First we prove some new results related to Chapter 3, but now the error estimates are measured in other function space norms. Then we conclude Part II with a collection of remarks on some recent proofs of some perturbation theory theorems, including the Kadec 1/4-theorem, which is equivalent to the classical Shannon sampling problem and a special case of the problems studied in Chapter 4. Part III contains one selected publication from each the two practical applications which I have been working with during my years as Ph.D. student: VDSL signal transmission and bearing condition monitoring. The first paper is one of four papers which were included and defended in my licentiate thesis. They describe the solutions to some important problems during the development of a duplex method (called Zipper) for very high speed digital communication in ordinary unshielded telephone copper wires. This was done together with Telia Research and the Division of Signal processing and the end-product (VDSL modems for up to 52 Mbit/s) is currently under development by the French-Italian company ST Microelectronics (former SGS-Thomson). The paper included here describes a patented method for reducing the interference that the unshielded copper wires experience from high-power narrowband radio transmissions, such as radio amateurs. The last paper, finally, is an overview article about bearing condition monitoring. Here the main problem is to find a method for predicting bearing failures by analysis of vibration measurements from rotating machines. The paper contains the main results of a co-operation with (among others) Nåiden Teknik and three forestry combines. We argue that time-frequency analysis based methods are well suited for this task and compare such methods with different old and new methods, using a large number of (mainly industrial environment) test signals.
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| 79. |
- Groth, Margareta Ring
(författare)
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Structural adhesive bonding of metals : surface and fracture mechanics aspects
- 2001
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Strukturell, eller lastbärande, limning ökar alltmer i volym. Strukturell limning har tidigare mest använts i flygindustrin för lätta metaller och legeringar, men används nu inom ett flertal industrier för andra material. Limning har många fördelar jämfört med andra fogningsmetoder, det skapar lätta, starka fogar med mycket goda utmattningsegenskaper, och har den stora fördelen att man kan foga olika material till varandra. All limning är beroende av goda egenskaper hos ytorna som ska limmas, ytan måste vara ren och ha en sådan struktur att den lämpar sig för limning. Ytan måste vara ren före limning. Rengöring kan ske på ett flertal sätt, vanligast är mekaniska och kemiska rengöringsmetoder. Inom traditionella limområden används nästan alltid kemiska rengöringsprocesser, men inom de nya användningsområdena så är det önskvärt med mekaniska alternativ, som har mindre inverkan på ekonomi, miljö och arbetsmiljö. Det första syftet med avhandlingen var att undersöka om mekaniska rengöringsmetoder kan ge hållbara fogar som har en acceptabel livslängd. De mekaniska metoder som använts har visat sig ge bra resultat. Det är inte helt enkelt att beskriva en yta. Det finns vanliga ytparametrar såsom Ra (ytråhetsvärde), men en ytas Ra-värde går inte att direkt koppla till fogegenskaper hos ett förband. Därför undersöktes om det kan gå att beskriva ytan på ett sådant sätt att det kan kopplas till foghållfasthet. Vi har använt fraktalteori, och karakteriserat ytornas fraktala egenskaper, och visat att det går att korrelera ytans fraktala dimension och fraktala råhetsparameter till styrka och beständighet hos limfogen, under förutsättning att ytan är ren. När man så kan skapa en fog med goda styrke- och beständighetegenskaper kan man arbeta med att prediktera fogens styrka. I dagsläget finns inga generellt accepterade dimensioneringsregler för limfogar. Foggeometri och fogbelastningar kan vara komplexa, och det gör det svårt att dimensionera limfogar. Finita elementmetoder kan användas, men kräver avancerade beräkningar, och endast specifika resultat kan fås. Brottmekaniska beräkningar verkar lovande, framför allt för att kunna göra geometrioberoende analyser. Brottmekaniska analyser kan vara ett bra sätt att karakterisera fogens hållfasthetsegenskaper.
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| 80. |
- Groth, Patrik
(författare)
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Fibre reinforced concrete : fracture mechanics methods applied on self-compacting concrete and energetically modified binders
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fibre reinforced concrete (FRC) is a type of building material that is increasing in use. As new types on concrete develops the need to update the knowledge on the use of fibre reinforcement increases. This thesis covers test methods for FRC that ranges from standard beam tests to sophisticated uniaxial tension tests. The consequence of applying fibre reinforcement in concrete made using various modified cementitious binders has also been studied. The binders used in this study are energetically modified cements (EMC). They consist of a mix of ordinary cement and different fillers, which has been processed through a vibrating mill. The influence of fibre reinforcement in self-compacting concrete (SCC) has been studied with regard to its feasibility in full-scale production. The fibre reinforced SCC has been studied with regard to its ability to retain its workability after addition of fibres and on its toughness properties. Finally, early age concrete and its fracture mechanical properties have been modelled. FRC is often used in structures where its task is to distribute cracks originating from stresses caused by volume changes in combination with restraint. In these cases, the appearance of cracks is a time-dependent phenomenon that occurs mainly in early ages. In this study a finite element model for localisation of strains in discreete cracks, the Inner Softening Band model, has been adopted and implemented with a model for the visco-elastic behaviour of early age concrete.
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