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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
731

Residual stresses and indentation. / Restspänningar vid intryckningsprov

Blanchard, Pierre January 2011 (has links)
The correlatioin between residual stresses and the global properties from an indentation test, i.e. hardness and size of the contact area, has been studied frequently in recent years. The investigations presented have been based on experimental, theoretical and numerical methods and as a result, the basic features of the problem are fairly well understood in the case of residual equi-biaxial surface stresses. The more general case, when the principal surface stresses are not necessarily equi-biaxial, has received nuch less attention and it is therefore the aim of the present study to remedy this shortcoming. In doing so, qualitative results are of immediate interest in this initial study but possible ways of quantitative descriptions are also discussed for future purposes. The present analysis is based on numerical methods and in particular the finite element method (FEM) is relied upon. Classical Mises elastoplastic material behavior is assumed throughout the investigation.
732

Stability Analysis of Embankments Founded on Clay : a comparison between LEM & 2D/3D FEM

Habibnezhad, Zhaleh January 2014 (has links)
Rapid constructed embankments founded on soft deposits have a negative influence on the short term stability. Many engineering constructions such as road and railway embankments are often constructed on soft clay deposits. In stability analysis calculation of safety factor (SF), as the primary design criteria can be evaluated through different numerous methods such as limit equilibrium method (LEM) and finite element method (FEM). It is of particular interest to determine/estimate appropriate stability of the specified embankment which is highly dependent on the analysis method used. Therefore, it is a challenge for geotechnical engineers to judge which analysis method can simulate better the reality.  The aim of this thesis is to increase understanding applicability of the three applied programs; Plaxis2D, Plaxis3D and Slope/W in simulating and stability analysis/estimation of embankments founded on clay deposits.  The work has involved analysis and comparison of the stability through estimate of the SF and the critical failure surfaces obtained through 2D and 3D programs. Four case configurations were studied for the stability analysis. In each case variation in plastic parameters of clay (φ-c) or load geometry, was the scenario to make the comparison analysis. Moreover, application FEM3D offers an attractive alternative to traditional approaches to the problem (especially for LEM).  The main conclusions from this study are the following:  (1)   Concerning the three applied programs, FEM3D has the minimum SF sensitivity to change in plastic parameters of clay deposit. (2)   For embankments founded on clay deposit, the 3D failure surfaces are easily found via the FEM3D analysis program, which is closer to reality, while failure results of 2D analysis programs can never occur in reality. (3)   Using 2D analysis method instead of 3D, to investigate the stability of 3D embankment model tend to give higher SF results up to 14% for embankments  founded on undrained clay deposit. (4)   The failure surfaces in 3D analysis are likely to be shallower than in the corresponding 2D model. (5)   Results from the 3D analysis through hand calculation and program calculation do not correspond with each other for embankment founded on soft clay deposit. The first reason is rooted in limitation of the hand formula. The formula is suitable for embankment founded on one layer deposit (soil); however an embankment founded on 3 layers of deposit (soil) was analyzed in this study. The second reason is related to applied method of calculation. 3D hand calculation formula is based on method of slices however; analysis method in program calculation is based on FEM.
733

COMBINED PHYSICS AND BMP SIGNALING NETWORK DYNAMICS TO MODEL EARLY EMBRYONIC DEVELOPMENT IN ZEBRAFISH

Linlin Li (10716573) 28 April 2021 (has links)
<p>Embryonic development is a complicated phenomenon influenced by genetic regulation and biomechanical cellular behaviors. However, the relative influence of these factors on spatiotemporal morphogen distributions is not well understood. Bone Morphogenetic Proteins (BMPs) are the primary morphogen guiding the dorsal-ventral (DV) patterning of the early zebrafish embryo, and BMP signaling is regulated by a network of extracellular and intracellular factors that impact the range and signaling of BMP ligands.  Recent advances in understanding the mechanism of pattern formation support a source-sink mechanism, however, it is not clear how the source-sink mechanism shapes patterns in 3D, nor how sensitive the pattern is to biophysical rates and boundary conditions along both the anteroposterior (AP) and DV axes of the embryo.</p><p> Throughout blastulation and gastrulation, major cell movement, known as epiboly, happens along with the BMP mediated DV patterning. The layer of epithelial cells begins to thin as it spreads toward the vegetal pole of the embryo until it has completely engulfed the yolk cell. This dynamic domain may influence the distributions of BMP network members. This project aims to investigate the multiscale regulatory network of the BMP signaling dynamics along with the biophysical deformation of the embryo tissue during epiboly. </p><p> In this study, we present a three-dimensional (3D) growing domain mathematical modeling framework to simulate the BMP patterning and epiboly process during the blastula to gastrula stage zebrafish embryo, with both finite difference and finite element approaching. These models provide a starting point to elucidate how different mechanisms and components work together in 3D to create and maintain the BMP gradient in the zebrafish embryo. We are interested in how the cellular movements impact the formation of gradients by contributing an advective term whereby the morphogens are swept with the moving cells as they move vegetally. Dynamic cell imaging data are used to quantify the cell movement during the epiboly. We evaluated the accuracy of the mesh updating compared to the advection caused by cell movement and its role in embryonic patterning. Quantitative whole-mount RNA scope data of BMP2b, Chordin, Noggin, Sizzled, and phosphorylated-SMAD data are collected and analyzed precisely to test the hypotheses of the gradient formation mechanism in our model. We also present a novel approach of Neuro Network model to accelerate the computationally intensive PDE simulations. Our goal is to develop a complete advection-diffusion-reaction model that incorporates all stages of zebrafish embryonic development data. By combining the biophysics of epiboly with the regulatory dynamics of the BMP network, we can test complex models to investigate the consistent spatiotemporal DV patterning in the early zebrafish embryo.</p>
734

The impact of connection stiffness on the global structural behavior in a CLT building : A combined experimental-numerical study

Abrahamsson, Jenny, la Fleur, Filip January 2021 (has links)
Cross Laminated Timber (CLT) has in recent years become a more important building material. This means that the demand for accurate calculation methods in building standards such as Eurocode 5 has increased. There is limited knowledge about the connections in CLT buildings which is an important part of a CLT structure. This thesis was therefore focused on investigating a wall-floor-wall type connection commonly found in platform type buildings.  An experimental and numerical study on typical wall-floor-wall connections was carried out in this thesis. In the experimental part 60 tests with 8 different configurations were conducted to investigate the influence of different parameters on the connection, moment capacity and rotational stiffness. During the tests the deformation of the specimens under four load levels were investigated. Compression tests were also performed on the specimens to determine the compressive strength and stiffness of the elements. In the numerical part two different models for the connection were created. One simplified model with rotational springs and one more complex model with compression springs. With these models the influence from the number of stories, span and thickness of the wall on the global behavior of a structure was investigated.  The result from this thesis shows that there is both moment capacity and rotational stiffness in the wall-floor-wall type connection that can be utilized in the design phase of a structure. This was proven by both the experimental and the numerical study. The parameters that influence the behavior of the connection most were the load level applied on the wall and the wall thickness. The model created in the numerical study showed great potential regarding the replication of the connection behavior observed in the experimental study.
735

Prototyp för att öka kundvänligheten i varubutiker

Bjerkén, Lovisa, Nguyen, Sara January 2021 (has links)
Syftet med detta examensarbete var att förbättra kundupplevelsen med avseende på en viss typ av konsument. Dagens matbutiker har hyllplan som är högt placerade och för en del konsumenter är detta ett problem. De konsumenter som upplever höga hyllplan som ett problem är bland annat funktionsnedsatta och personer med en kortare längd än genomsnittet. I många matbutiker är avståndet mellan det högsta hyllplanet och taket stort och då är inte ytan utnyttjad maximalt. Resultatet är tänkt att ge ett förslag på hur dessa två problemen kan lösas. En strukturerad produktutvecklingsmetod har applicerats genom hela processen av examensarbetet för att ta fram en lösning på hur varubutikerna kan optimeras till att det blir mer lättillgängligt för alla typer av konsumenter. Planeringen av detta utfördes med hjälp av ett Gantt-schema. Konceptet som framtogs i rapporten optimerades genom att komplettera med en till komponent. Konceptet har som syfte att kunna förlängas för att kunnata ner produkter med en max vikt på 0,5 kg från den högsta hyllplanet.Avgränsningarna för arbetet har tagit hänsyn till de hyllor som finns igångarna i dem större matbutikerna samt att arbetet har en begränsad tidsram och hur prototypens framtagning kommer att ske.
736

Platta på mark av korslimmat trä : En undersökning av bärförmåga med och utan kantförstyvning

Hellman, Linnéa, Falck, Nils January 2021 (has links)
Purpose: This work investigates the load-bearing capacity of a foundation built out of cross-laminated timber. The foundation is built with the same principles as a slab on grade made out of concrete. The purpose is also to account for the different operating principles of a wooden slab on grade with, and without, an edge beam. Method: To answer the issues at hand, a literature study was used to collect relevant information. Calculations were made with data from an example house which is presented with various drawings that illustrate the building’s size and form. Data from the example house is used to determine the loads. Thereafter, calculations were made both by hand and with the computer software FEM-design which uses the finite element method. Results: The main principle of shallow foundation design is contact pressure. The calculations show a range of contact pressure applied to the underlying soil and insulation of the foundation. Load combinations according to Eurocode 1 are used to determine the sum of loads affecting the foundation. All load combinations result in a higher contact pressure when using a foundation without an edge beam. Calculations done by hand presents the maximum value of contact pressure of the two separate foundations and highlights the difference between the two. The results from hand calculations and computer software regarding contact pressure varies. Calculations performed in FEM-design use three variations of the modulus of subgrade reaction to investigate the impact of said modulus. FEM-design also calculates the deflection which is significantly larger without an edge beam. The Conclusions of this work include a reduction in contact pressure when the wooden foundation is constructed with an edge beam. Calculations done by hand may overestimate the stiffening ability of the wooden edge beam. The modulus of subgrade reaction affects the magnitude of deflection in a larger extent than the contact pressure. It is suitable to design a wooden foundation with an edge beam with the purpose of keeping deflection to a minimum.
737

Möjligheter och hinder för samverkansprocesser mellan yrkesroller i gymnasiesärskolan

Lennartsson, Cecilia, Geczi, Susanna January 2021 (has links)
Sammanfattning: Studiens syfte var att undersöka möjligheter och hinder kring lärares och elevassistenters samver- kan inom gymnasiesärskolan och hur dessa faktorer påverkar elevernas skolvardag. Studien har ett interaktionsperspektiv. Elevassistenter och lärare är två yrkesroller som påverkas av faktorer på både individ- och organisationsnivå. Det övergripande ansvaret har rektor, därför valdes även att inkludera rektorns perspektiv i undersökningen. Senges teori (2006) om samverkan för organi- sationsutveckling har utgjort utgångspunkt för uppläggning och genomförande av studien. Som metod valdes semistrukturerade, kvalitativa intervjuer. Studien riktade sig till tre yrkeskategorier: elevassistenter, lärare och rektorer. Detta för att spegla upplevelser och perspektiv från olika håll/ nivåer inom organisationerna. Resultatet avtäcker en mångfacetterad bild av sanningar utifrån respektive yrkesroll och organisation. Undersökningens slutsats gav bilden av en komplex yrkes- vardag där framgångs- och motgångsfaktorer är ständigt närvarande och hanteras kontinuerligt i yrkesrollernas dagliga strävan för samverkan med elevens bästa i fokus.
738

Grundskolelärares val av undervisningsmetod i ett matematikklassrum / Primary school teachers’ choice of teaching method in a mathematics classroom

Rabe, Frida, Wiklund, Malvina January 2021 (has links)
Detta examensarbete syftar till att med digitala kvalitativa intervjuer undersöka lärares användning av den kooperativa och traditionella undervisningsmetoden i matematikklassrummet i årskurs F-3. Studiens syfte är även att ta reda på vilken av de två metoderna lärare anser är den mest effektiva för att främja alla elevers kunskapsutveckling. Studien utgår från de fem grundprinciperna för kooperativt lärande; positivt ömsesidigt beroende, lika delaktighet och samtidig stödjande interaktion, eget ansvar, samarbetsfärdigheter och ‘feedback, feedup och feedforward’ (3F). Resultatet visar på att lärarna applicerar en blandning av de olika metoderna. Detta beror på att läraren kan behöva individanpassa beroende på vad som gynnar den enskilda eleven. Resultatet visar även på att de olika metoderna används i olika stor grad beroende på vilket arbetsområde lektionen behandlar. Den kooperativa undervisningsmetoden anses vara den mest effektiva för att främja elevernas kunskapsutveckling men eftersom den inte passar alla elever behövs en blandning av de båda för att tillgodose alla elevers olika behov.
739

Three-dimensional Modeling and Simulation of a Tuning Fork

Larisch, Lukas 16 September 2018 (has links)
The mathematical characterization of the sound of a musical instrument still follows Schumann’s laws [1]. According to this theory, the resonances of the instrument body, “the formants”, filter the oscillations of the sound generator (e.g., strings) and produce the characteristic “timbre” of an instrument. This is a strong simplification of the actual situation. It applies to a point source and does not distinguish between a loudspeaker and a three-dimensional instrument. In this work we investigate Finite-Element-based numerical simulations of eigenfrequencies and eigenmodes of a tuning fork in order to capture the oscillation behavior of its eigenfrequencies. We model the tuning fork as an elastic solid body and solve an eigenvalue equation derived from a system of coupled equations from linear elasticity theory on an unstructured three-dimensional grid. The eigenvalue problem is solved using the preconditioned inverse iteration (PINVIT) method with an efficient geometric multigrid (GMG) preconditioner. The latter allows us to resolve the tuning fork with a high resolution grid, which is required to capture fine modes of the simulated eigenfrequencies. To verify our results, we compare them with measurement data obtained from an experimental modal analyses of a real reference tuning fork. It turns out that our model is sufficient to capture the first eight eigenmodes of a reference tuning fork, whose identification and reproduction by simulation is novel to the knowledge of the author.
740

An investigation of the design of cylinderical steel tanks modelled according to EN14015 and according to the Eurocodes

Gebre, Yonas January 2022 (has links)
Abstract Storage tanks are above or below ground vessels for storing chemicals, petroleum and other liquid products. Above ground vertical cylindrical shells are typically thin walled structures prone to buckling and lose their stability especially when they are empty or have lower fluid level due to external loads.According to the Swedish National board of Housing, Building and Planning (Boverket), the Eurocodes and the Swedish national annex and building code for structural design, EKS (BFS 2011:10) should be used for verification of mechanical resistance of storage tanks. However the industry has been using a European design standard EN14015, for design of large site built steel tanks. The research question is if this design fulfils the requirements in the Swedish building code EKS and the Eurocodes. In order to investigate this, a parametric study of the buckling resistance of an empty tank has been performed, by comparing the design according to EN14015 With the requirements according to the Swedish building code and the Eurocodes. The finite element analysis was done with the finite element tool ABAQUS, The parametric study was carried out for three terrain categories0, I and II, for thesix snow load zones and for six basic wind velocities according to the Swedish snow and wind maps in EKS. The buckling resistance also further investigated for three reliability classes, reliability class 1, 2 and 3 according to the Swedish national annex and for two fabrication classes, fabrication class A and B usingEN1991-1-6The finite element analysis result of linear elastic and nonlinear buckling analysis with imperfections showed that, design according to EN14015 can meet the requirements of Eurocodes and EKS at lower basic wind velocities, terrain category (I and II) for smaller imperfections . But it does not meet the requirements at terrain category-0, for all reliability classes and all imperfection classes.The tank shell showed in some cases an increase in the load proportionality factorin nonlinear analysis for the load combinations considered in this study. It is thus necessary to study further on the finite element modelling of thin walled large tanks on relations of local buckling effect due to highly stiffened regions and the effect of magnitudes and applications of imperfections for large tanks using EN1993-1-6

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