| 1. |
- Andersson, Linus, et al.
(författare)
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Efficient nonlinear reduced order modeling for dynamic analysis of flat structures
- 2023
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Ingår i: Mechanical Systems and Signal Processing. - : Elsevier BV. - 0888-3270. ; 191
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Tidskriftsartikel (refereegranskat)abstract
- In the present paper, strategies for reduced order modeling of geometrically nonlinear finite element models are investigated. Simulation-free, non-intrusive approaches are considered, which do not require access to the source code of a finite element program (e.g., proprietary knowledge). Our study focus on but is not restricted to flat structures. Reduction bases are generated using bending modes and the associated modal derivatives, which span the additional subspace needed for an adequate approximation of the geometrically nonlinear response. Moreover, the reduced nonlinear restoring forces are expressed as third order polynomials in modal coordinates. Consequently, the reduced systems can be effectively solved using time-integration schemes involving only the reduced coordinates. A bottleneck in the non-intrusive methods is typically the computational effort for precomputing the polynomial coefficients and generating the reduction basis. In this regard, we demonstrate that modal derivatives have several useful properties. In particular, the modal derivatives essentially provide all the information needed for generating the polynomial coefficients for the in-plane coordinates. For condensed systems, which ignores the inertia of the in-plane modes, we show that the modal derivatives can be used effectively for recovering the in-plane displacements. Based on these findings, we propose a methodology for generating reduced order models of geometrically nonlinear flat structures in a computationally efficient manner. Moreover, we demonstrate that the concepts extend also to curved structures. The modeling techniques are validated by means of numerical examples of solid beam models and continuously supported shell models. The computational efficiency of the proposed methodology is evaluated based on the number of static evaluations needed for identifying the polynomial coefficients, as compared to the state-of-the-art methods. Furthermore, strategies for efficient time integration are discussed and evaluated.
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| 2. |
- Andersson, Linus, et al.
(författare)
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Model reduction for structures subjected to blast loading by use of dynamic substructuring
- 2020
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Ingår i: EURODYN 2020 - 11th International Conference on Structural Dynamics, Proceedings. - 2311-9020. - 9786188507210 ; 2, s. 2544-2564
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Konferensbidrag (refereegranskat)abstract
- In the present study, strategies are developed to enable time-efficient models for structures subjected to blast loading, appropriate for use in a structural design process. Dynamic sub structuring is employed to obtain reduced models with localized nonlinearities, such as predefined plastic hinges in a beam column structure. The parts of the substructures that remains linear elastic are modeled by Ritz-vectors whereas parts with a nonlinear response are retained as physical degrees-of-freedom. Furthermore, a time-stepping method is presented that is shown to be suitable for reduced models including local and predefined rigid-plastic behavior. The proposed methodology is applied and demonstrated in a numerical example of a concrete frame structure. Both the well-established Craig-Bampton method and reduction bases enriched by so-called correction modes are evaluated. For the load case studied, it is shown that the standard Craig-Bampton technique is suitable for reducing the substructures. Furthermore, it is shown that only a few Ritz-vectors are needed to sufficiently describe the deformation of the structure. However, additional modes are needed to ensure an accurate representation of the interface forces between the substructures.
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| 3. |
- Andersson, Linus, et al.
(författare)
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Reduced order modeling of soft-body impact on glass panels
- 2022
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Ingår i: Engineering Structures. - : Elsevier BV. - 0141-0296. ; 256
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Tidskriftsartikel (refereegranskat)abstract
- In the paper, strategies for reduced order modeling of glass panels subjected to soft-body impact are developed by means of dynamic substructuring. The aim is to obtain accurate and computationally efficient models for prediction of the pre-failure elastic response. More specifically, a reduction basis for the subsystem representing the glass panel is established using correction modes, being fixed-interface component modes that considers loading on the substructure boundary. The soft-body impactor is effectively modeled by a nonlinear single-degree-of-freedom system, calibrated by experimental data. Furthermore, a simplified and computationally efficient modeling approach is proposed for the contact interaction between the glass panel and the impact body. An experimental campaign was carried out to validate the developed models. In particular, the glass strain was measured on simply supported monolithic glass panels subjected to soft-body impact. Additional impact tests were performed to determine the dynamic characteristics of the impactor. Moreover, a detailed numerical reference model was developed to evaluate the discrepancy between the experimental tests and the results provided by the reduced order models. The developed models show good agreement with the experimental results. For the studied load cases, it is shown that an accurate prediction of the pre-failure glass strain can be obtained by systems including only a few generalized degrees-of-freedom.
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| 4. |
- Antonelli, Alexandre, 1978, et al.
(författare)
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Settling a family feud: a high-level phylogenomic framework for the Gentianales based on 353 nuclear genes and partial plastomes
- 2021
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Ingår i: American Journal of Botany. - : Wiley. - 0002-9122 .- 1537-2197. ; 108:7, s. 1143-1165
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Tidskriftsartikel (refereegranskat)abstract
- Premise: Comprising five families that vastly differ in species richness—ranging from Gelsemiaceae with 13 species to the Rubiaceae with 13,775 species—members of the Gentianales are often among the most species-rich and abundant plants in tropical forests. Despite considerable phylogenetic work within particular families and genera, several alternative topologies for family-level relationships within Gentianales have been presented in previous studies. Methods: Here we present a phylogenomic analysis based on nuclear genes targeted by the Angiosperms353 probe set for approximately 150 species, representing all families and approximately 85% of the formally recognized tribes. We were able to retrieve partial plastomes from off-target reads for most taxa and infer phylogenetic trees for comparison with the nuclear-derived trees. Results: We recovered high support for over 80% of all nodes. The plastid and nuclear data are largely in agreement, except for some weakly to moderately supported relationships. We discuss the implications of our results for the order’s classification, highlighting points of increased support for previously uncertain relationships. Rubiaceae is sister to a clade comprising (Gentianaceae + Gelsemiaceae) + (Apocynaceae + Loganiaceae). Conclusions: The higher-level phylogenetic relationships within Gentianales are confidently resolved. In contrast to recent studies, our results support the division of Rubiaceae into two subfamilies: Cinchonoideae and Rubioideae. We do not formally recognize Coptosapelteae and Luculieae within any particular subfamily but treat them as incertae sedis. Our framework paves the way for further work on the phylogenetics, biogeography, morphological evolution, and macroecology of this important group of flowering plants.
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| 5. |
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| 6. |
- Florisson, Sara
(författare)
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Moisture-induced stress and distortion of wood : A numerical and experimental study of wood's drying and long-term behaviour
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the current advances made in three-dimensional modelling of wood, it is possible to provide an overall picture of moisture flow, and moisture-induced stress and deformations, whereas previously, experiments only provided local measurements. The main aim of the doctoral thesis is to investigate the possibilities of the developed three-dimensional numerical model to predict the behaviour of wood when simultaneously exposed to a mechanical load and a particular climate. Three applications in the fields of wood drying and long-term behaviour of wood are considered: 1) the effect of green-state moisture content on the drying behaviour of timber boards, 2) the calibration of the numerical model based on a long-term four-point bending tests using small wood beams subjected to a constant temperature and systematic relative humidity (RH) changes, and 3) the validation of the numerical model by means of a long-term four-point bending test on solid timber beams subjected to Northern European climate. As part of the second application, an experimental methodology and analytical method were designed. The numerical model was developed in finite element software Abaqus FEA® and consists of several user-subroutines to include material orientation (i.e. annual ring pattern, conical shape and spiral grain), and the selected constitutive behaviour and required boundary conditions. To simulate the moisture flow, a nonlinear single-Fickian approach was combined with a nonlinear Neumann boundary condition, which describes the flux normal to the exchange surface based on a moisture and temperature dependent surface emission coefficient. A strain relation was used that accounts for hygro-expansion, and the elastic, creep and mechano-sorptive behaviour. The analytical method describes the elastic and creep deflection in the constant moment area of the four-point bending setup, and was used to isolate and assess the mechano-sorption deflection in the cumulative moisture content domain. The results show that the three-dimensional character of the numerical model contributed to the analysis and visualisation of the different stress states and deformations that are affected by material properties that vary (i.e. from pith to bark, between heartwood and sapwood, and due to temperature and moisture content), fibre orientation and climate. The simulations made on timber boards clarified phenomena, such as stress reversal and casehardening associated with wood drying, and showed that the green-state moisture content affected the time, size and frequency with which extremes in tangential tensile stress developed inside the timber during drying. The results of the calibration and validation indicated that the numerical model is able to describe moisture change and gradients in the considered temperature and relative humidity ranges (between -2-60℃ and 40-80% RH), as well as the deflection. The experimental methodology and analytical method led to a successful identification of each deflection component and isolation of the mechano-sorptive deflection curves. The experimental methodology benefitted the calibration of the numerical model. In conclusion, the presented three-dimensional numerical model compatible with Abaqus FEA® provides a powerful tool for scientists and timber engineers to study the combined effect of load and climate on stress state and deformations of various timber products in a wide field of applications.
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| 7. |
- Haller, Stefan, 1982-, et al.
(författare)
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Multi-phase winding with in-conductor direct cooling capability for a 48V traction drive design
- 2020
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Ingår i: Proceedings - 2020 International Conference on Electrical Machines, ICEM 2020. - : IEEE. - 9781728199450 ; , s. 2118-2124
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Konferensbidrag (refereegranskat)abstract
- Traction drive applications demand high power density motors with a good stator cooling design. We propose a novel multi-phase winding for a 48 V traction drive design having identical preformed hollow copper conductors with in-conductor direct cooling capability. This paper studies the cooling performance of an individual conductor phase using either EGW50/50 or water as coolant. Analytical calculations and experiments are conducted on a straight conductor of the same length using 20°C water as coolant. The results are then cross verified with those from the FEM simulations to validate the simulation setup. Then a final simulation is conducted at a current of 700A and a current density of 49.5 A/mm 2 on the preformed conductor using 65 CEGW50/50 as coolant at a pressure of 140kPa. The results highlight the exceptional performance of the cooling design which enables a power dissipation of 71OW at a maximum conductor temperature rise of only 56. 9 C.
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| 8. |
- Iresjö, Britt-Marie, 1963, et al.
(författare)
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Preoperative supportive nutrition at major cancer surgery in weight-losing patients. Effects on muscle transcriptome (abstract 5-03). : Abstract 5-03, sid 2422
- 2023
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Ingår i: Journal of Cachexia, Sarcopenia and Muscle. - 2190-5991 .- 2190-6009.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Preoperative supportive nutrition at major cancer surgery in weight-losing patients: effects on muscle transcriptome Britt-Marie Iresjö and Ulrika Smedh and Cecilia Engström and Jan Persson and Christian Mårtensson and Kent Lundholm Department of Surgery, University of Gothenburg and Sahlgrenska University Hospital, Göteborg, Sweden Introduction: Recommendations of strict pre-operative fasting have later on become replaced by provision of carbohydrate rich nutrition drinks prior to surgery. Carbohydrate (cho) drinks are shown to reduce postoperative insulin resistance and thus assumed to improve post-surgical muscle protein metabolism with expectations to reduce morbidity and complication rate, though meta-analyses indicate few clinical benefits. However, such studies investigating skeletal muscle metabolism are lacking. Therefore, our study evaluates skeletal muscle transcriptome alterations with relevance to carbohydrate and protein metabolism, by two different nutrition interventions. Method: Patients scheduled for major upper gastrointestinal cancer surgery were asked to participate. Mean weight loss in the patient group was 7%. Provision of either oral carbohydrate -rich nutrition drinks (804 kcal cho/96 kcal protein) or provision of peripheral total parenteral nutrition (TPN) (400 kcal cho/180 kcal protein/350 kcal fat) were administered in a 12-h over-night period prior to surgery. The control group received infusion of clear fluids only. Arterial blood samples and abdominal muscle biopsies were collected at operation start (n = 38). Blood amino acids were quantified by LC–MS/MS and muscle mRNA transcripts were analysed with Agilent SurePrint G3 Human GE v3 8x60K Microarrays. Data evaluation was done in Genespring software v.14.9.1. Results: Statistical analyses indicated ~1200 transcripts as altered among groups (Anova, P < 0.05). Post-Hoc analyses indicated ~500 transcripts as altered by each nutrition protocol with most alterations specific to each treatment. The results indicate that both carbohydrate rich nutrition drinks and total parenteral nutrition influenced muscle glucose metabolism, while transcript alterations related to protein translation were induced by parenteral nutrition only. Conclusions: Carbohydrate rich drinks were not sufficient to sustainably support muscle metabolism and should not be recommended in combination with major cancer surgery.
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| 9. |
- Karlsson, Stefan, 1984-, et al.
(författare)
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Hållfasthetsklassificering av planglas för bättre kvalitet
- 2021
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Ingår i: GLAS. - : Glasbranschföreningen. ; :4, s. 60-61
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- I dagsläget finns endast förstörande metoder för att bestämma hållfastheten för planglas. Det har medfört att på grund av den stora spridningen i hållfasthet av planglas behöver man ta till en stor säkerhetsfaktor. En ”säker” designhållfasthet som med andra ord behöver vara så låg så att risken är minimal att glaset går sönder. Resultatet blir att onödigt mycket glas används eftersom glas i princip alltid är starkare än designhållfastheten. Dessutom finns det idag heller ingen metod som kan mäta att glaset faktiskt upprätthåller designhållfastheten. Det finns med andra många skäl, både miljömässiga och kvalitetsskäl, till att utveckla en icke-förstörande metod till att bestämma hållfastheten av planglas.
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| 10. |
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