<p>Breast cancer affects 12.5\% of women over their life time and tissue expansion (TE) is the most common technique for breast reconstruction after mastectomy. However, the rate of complications with TE can be as high as 15\%. Even though the first documented case of TE happened in 1957, there has yet to be a standardized procedure established due to the variations among patients and the TE protocols are currently designed based on surgeon's experience. There are several studies of computational and theoretical framework modeling skin growth in TE but these tools are not used in the clinical setting. This dissertation focuses on bridging the gap between the already existing skin growth modeling efforts and it's potential application in the clinical setting.</p> <p><br></p> <p>We started with calibrating a skin growth model based on porcine skin expansions data. We built a predictive finite element model of tissue expansion. Two types of model were tested, isotropic and anisotropic models. Calibration was done in a probabilistic framework, allowing us to capture the inherent biological uncertainty of living tissue. We hypothesized that the skin growth rate was proportional to stretch. Indeed, the Bayesian calibration process confirmed that this conceptual model best explained the data. </p> <p><br></p> <p>Although the initial model described the macroscale response, it did not consider any activity on the cellular level. To account for the underlying cellular mechanisms at the microscopic scale, we have established a new system of differential equations that describe the dynamics of key mechanosensing pathways that we observed to be activated in the porcine model. We calibrated the parameters of the new model based on porcine skin data. The refined model is still able to reproduce the observed macroscale changes in tissue growth, but now based on mechanistic knowledge of the cell mechanobiology.  </p> <p><br></p> <p>Lastly, we demonstrated how our skin growth model can be used in a clinical setting. We created TE simulations matching the protocol used in human patients and compared the results with clinical data with good agreement. Then we established a personalized model built from 3D scans of a patient unique geometry. We verified our model by comparing the skin growth area with the area of the skin harvested in the procedure, again with good agreement.</p> <p><br></p> <p>Our work shows that skin growth modeling can be a powerful tool to aid surgeons design TE procedures before they are actually performed. The simulations can help with optimizing the protocol to guarantee the correct amount of skin is growth in the shortest time possible without subjecting the skin to deformations that can compromise the procedure.</p>

Concrete structures are in general expected to be subjected to cracking during its service life. This is the reason why concrete is reinforced, where the reinforcement is only activated after cracks occur. However, cracks may be a concern in large concrete structures, such as dams, since it may result in reduced service life. The underlying mechanisms behind crack formations are well known at present day. On the other hand, information concerning the crack condition over time and its influence on the structure is limited, such as the influence of water pressure within the cracks. The aim of this project is to study crack propagation influenced by water pressure and to define an experimental test setup that allows for crack propagation due to this load. Numerical analyses have been performed on an initial cracked specimen to study the pressure along the crack propagation. The finite element method has been used as the numerical analysis tool, through the use of the software ABAQUS. The finite element models included in these studies are based on linear or nonlinear material behavior to analyze the behavior during a successively increasing load. The numerical results show that a crack propagates faster if the water is keeping up with the crack extension, i.e. lower water pressure is required to open up a new crack. When the water does not have time to develop within the crack propagation, more pressure is required to open up a new crack. The experimental results show that the connection between the water inlet and the specimen is heavily affected by the bonding material. In addition, concrete quality and crack geometry affects the propagation behavior.

Concrete dams located in northern regions are exposed to large seasonal temperature variations. These seasonal temperature variations have resulted in cracking in thin concrete dams. Continuous monitoring and evaluation of existing dams are important to increase the knowledge about massive concrete structures and to ensure dam safety.  The aim of this degree project is to increase the knowledge about how cracking occurs in concrete dams and how it affects the dam safety. This was achieved by simulating the development of cracks in a concrete arch dam exposed to seasonal temperature variations using finite element analysis (FEA). The accuracy of the model was evaluated by comparing the results with measurements from a Swedish concrete arch dam. Finally, effect of cracks and temperature on the dam safety was investigated.  FEA was used to predict the crack pattern and displacements in the arch dam. The analyses were performed both with linear elastic and nonlinear material behavior. Two models were analyzed, in one model the dam was considered to be a homogeneous arch, the other model included contraction joints. The cracking was simulated using temperature envelopes from the location of the Swedish arch dam. To evaluate the displacements in the arch, further analyses were carried out, where the cracked arch dam was exposed to the actual temperature variations at the location. The results were compared to the crack pattern and measurements of displacements of the Swedish arch dam. To investigate the effects from the cracking on the safety of the dam, a progressive failure analyses performed.  The results show that the downstream face of the arch cracked under hydrostatic pressure. The cracks propagated further during winter when the temperature load was applied. The resulting crack pattern corresponded well with the survey of the cracks from the Swedish arch dam. The FE-models with nonlinear material developed a horizontal plastic hinge due to excessive cracking in a region halfway down from the crest. The plastic hinge affected the shape of the deflected arch. The magnitude of the displacements and the shape of the deflected arch was captured with the nonlinear models. A safety factor of 3 for internal structural failure in the arch was found in the failure analyses. The safety factor of the arch only decreased slightly due to the cracking. During a cold winter, the safety factor decreased to 2.5. / Betongdammar belägna i nordliga klimat blir utsatta för stora säsongsburna temperaturvariationer. Dessa temperaturvariationer har orsakat sprickbildning i tunna betongdammar. Kontinuerlig övervakning och utvärdering av befintliga dammar är viktigt för att öka kunskapen om massiva betongkonstruktioner och för att säkerställa dammsäkerheten.  Syftet med det här examensarbetet är att öka kunskapen om hur sprickor uppstår i valvdammar samt hur de påverkar anläggningens säkerhet. Målet är att med finit elementanalys (FEA) analysera uppsprickningen av betongen i en valvdamm som påverkas av säsongsburna temperaturvariationer. Tillförlitligheten i modellen utvärderas genom att jämföra med mätningar från en svensk valvdamm av liknande dimensioner. Slutligen utvärderas hur dammens säkerhet påverkas av sprickbildningen.  FE-analys användes för att förutsäga sprickmönstret och förskjutningarna i valvdammen. Analyserna utfördes både med linjärelastiskt och icke-linjärt materialbeteende. Två modeller användes i analysen, i ena modellen betraktades dammen som homogen och i den andra inkluderades gjutfogar. Sprickmönstret simulerades med temperaturcykler baserade på extremtemperaturer tagna intill den svenska valvdammen. För att utvärdera förskjutningarna i dammen gjordes vidare analyser där den spruckna dammen utsattes för temperaturvariationer uppmätta från samma plasts. Resultaten från analysen jämfördes med mätningar av förskjutningar och kartering av sprickor från den svenska valvdammen. För att undersöka hur säkerheten påverkades av sprickbildningen utfördes progressiv brottanalys.  Resultaten visar att dammen spricker på nedströmssidan när den utsätts för vattentryck. Sprickorna fortplantas under vintern när temperaturlasten appliceras. Sprickmönstret stämmer överens med kartering av den verkliga dammen. FE-modellerna med icke-linjärt materialbeteende utvecklade en plastisk led längs horisontella sprickor halvvägs ner från krönet. Den plastiska leden påverkade dammens utböjda form. Förskjutningarna och dammens utböjda form i de ickelinjära modellerna stämmer väl överens med de uppmätta förskjutningarna. Vid brottanalysen var säkerhetsfaktorn mot materialbrott i dammen 3. Säkerhetsfaktorn minskade något till följd av sprickorna. Under en kall vinter sjönk säkerhetsfaktorn till 2,5.

The intention of this thesis is to develop, evaluate new concepts and look over the current design for a container sized barge module. By request of Group Ocean, a cost and weight reduction is the main improvement criteria along with keeping the strength of the module.Five concepts are developed, analyzed and discussed with the supervisor at Group Ocean, where three are decided to be presented here. The other two are left out, since they are considered way too expensive without giving a satisfying result. The three concepts that are developed throughout this thesis are; changing to high strength steel, changing to sandwich panels and increasing stiffeners with smaller dimensions.A structural optimization is made in the software MATLAB to find out the best dimension to use for the sandwich panels. To determine the local stresses, the finite element method is used in Inventor Professional. It is also where the design and CAD modules are built in, so for simplifications it is used for FEA (Finite Element Analysis) as well. To reduce the amount of elements and nodes, shell elements and other structural constraints are used in the FEA. All the concepts are modelled with the same structural constraints so a practical comparison study can be made.The final designs resulted in a total weight reduction up to 40% with a material cost reduction of 12%. Based on what type of material is chosen, the material cost reduction range is between 3-12% and the weight reduction range is between 13-40%.

There exists several different methods that can be used to implement a level of safety when performing non-linear finite element analysis of a structure. These methods are called safety formats and they estimate safety by different means and formulas which are partly discussed further in this thesis. The aim of this master thesis is to evaluate a model uncertainty factor for one safety format method called the estimation of coefficient of variation method (ECOV) since it is suggested to be included in the next version of Eurocode. The ECOV method will also be compared with the most common and widely used safety format which is the partial factor method (PF). The first part of this thesis presents the different safety formats more thoroughly followed by a theoretical part. The theory part aims to provide a deeper knowledge for the finite element method and non-linear finite element analysis together with some beam theory that explains shear mechanism in different beam types. The study was conducted on six beams in total, three deep beams and three slender beams. The deep beams were previously tested in the 1970s and the slender beams were previously tested in the 1990s, both test series were performed in a laboratory. All beams failed due to shear in the experimental tests. A detailed description of the beams are presented in the thesis. The simulations of the beams were all performed in the FEM- programme ATENA 2D to obtain high resemblance to the experimental test. In the results from the simulations it could be observed that the ECOV method generally got a higher capacity than the PF method. For the slender beams both methods received rather high design capacities with a mean of about 82% of the experimental capacity. For the deep beams both method reached low design capacities with a mean of around 46% of the experimental capacity. The results regarding the model uncertainty factor showed that the mean value for slender beams should be around 1.06 and for deep beams it should be around 1.25.

Quantifying the core mechanics of putting is imperative to developing a reliable model that predicts post-collision ball behavior. A preliminary model for the stroking motion of putting and putter-ball collision is developed alongside experiments, establishing an empirical model that supports the theory. The goal of the present study is to develop a correlation between the backstroke of a putt, or the pre-impact translation of the putter, and the post-impact displacement of the golf ball. This correlation is subsequently utilized to generate an algorithm that predicts the two-dimensional ball trajectory based on putt displacement and putting surface texture by means of finite element analysis. In generating a model that accurately describes the putting behavior, the principles of classical mechanics were utilized. As a result, the putt displacement was completely described as a function of backstroke and some environmental parameters, such as: friction, slope of the green, and the elasticity of the putter-ball collision. In support of the preliminary model, experimental data were gathered from golfers of all levels. The collected data demonstrated a linear correlation between backstroke and putt distance, with the environmental parameters factoring in as a constant value; moreover, the data showed that experienced golfers tend to have a constant acceleration through ball impact. Combining the empirical results with the trajectory prediction algorithm will deliver an accurate predictor of ball behavior that can be easily implemented by golfers under most practical applications. Putt distance to backstroke ratios were developed under a variety of conditions.

Tooth cusp radius of curvature (RoC) has been hypothesized to play an important role in food item breakdown, but has remained largely unstudied due to difficulties in measuring and modeling RoC in multicusped teeth. We tested these hypotheses using a parametric model of a four cusped, maxillary, bunodont molar in conjunction with finite element analysis. When our data failed to support existing hypotheses, we put forth and tested the Complex Cusp Hypothesis which states that, during brittle food items breakdown, an optimally shaped molar would be maximizing stresses in the food item while minimizing stresses in the enamel. After gaining support for this hypothesis, we tested the effects of relative food item size on optimal molar morphology and found that the optimal set of RoCs changed as relative food item size changed. However, all optimal morphologies were similar, having one dull cusp that produced high stresses in the food item and three cusps that acted to stabilize the food item. We then set out to measure tooth cusp RoC in several species of extant apes to determine if any of the predicted optimal morphologies existed in nature and whether tooth cusp RoC was correlated with diet. While the optimal morphologies were not found in apes, we did find that tooth cusp RoC was correlated with diet and folivores had duller cusps while frugivores had sharper cusps. We hypothesize that, because of wear patterns, tooth cusp RoC is not providing a mechanical advantage during food item breakdown but is instead causing the tooth to wear in a beneficial fashion. Next, we investigate two possible relationships between tooth cusp RoC and enamel thickness, as enamel thickness plays a significant role in the way a tooth wears, using CT scans from hundreds of unworn cusps. There was no relationship between the two variables, indicating that selection may be acting on both variables independently to create an optimally shaped tooth. Finally, we put forth a framework for testing the functional optimality in teeth that takes into account tooth strength, food item breakdown efficiency, and trapability (the ability to trap and stabilize a food item).

The Flex Representation Method (FRM) leverages unique computational advantages of splines to address limitations in the process of building CAE simulation models from CAD geometric models. Central to the approach is the envelope CAD domain that encapsulates a CAD model. An envelope CAD domain can be of arbitrary topological and geometric complexity. Envelope domains are constructed from spline representations, like U-splines, that are analysis-suitable. The envelope CAD domain can be used to approximate none, some, or all of the features in a CAD model. This yields additional simulation modeling options that simplify the model-building process while leveraging the properties of splines to control the accuracy and robustness of computed solutions. Modern integration techniques are adapted to envelope domains to maintain accurate solutions regardless of the CAD envelope chosen. The potential of the method is illustrated through several carefully selected benchmark problems.

Continuous casting represents 96% of all steel products made worldwide. To cast new alloys, optimal process parameters must be determined that reduce quality issues. Traditionally, this is a time-consuming and expensive process due to the need to run multiple casting trials. Alternatively, numerical models can be used to help guide development of optimal process parameters. In this thesis, a 3D thermal-solute-mechanical finite element model has been created using the THERCAST software to simulate the casting process of a new advanced high strength steel grade at Stelco’s Lake Erie Works facility. The model represents the caster from mould to exit, and takes into account heat transfer from the mould, sprays, rolls, and ambient air. The model has been extensively validated using plant measurements from steel shim trials and pyrometer data. The model is used to investigate the evolution of temperature and shell thickness along the cast length, and the effect of spray cooling and casting speed on the surface temperature at unbending to predict transverse cracking during secondary cooling. It was found that the susceptibility to cracking increased with lower casting speed and increased water spray cooling. Increasing the casting speed had a negligible effect, and it was found to decrease with decreasing water spray cooling. This decreased water spray cooling is also accompanied by an increase in metallurgical length, so further work is required to determine appropriate safety factors to ensure the steel is completely solidified. However, preliminary results of solute and mechanical models are also presented. Further work is required to improve the predictions made by these simulations. / Thesis / Master of Applied Science (MASc)

By using the rotor dynamic capabilities of Simcenter Nastran Rotordynamics, an eigenvalue analysis of 3D-finite element models of the Jeffcott rotor and the overhung rotor were conducted and compared to the results with beam-based, lumped parameter models. The first two critical speeds of the Jeffcott rotor were estimated with variations of 3.9 and 6.4%. The first three critical speeds of the overhung rotor were estimated with 8.5, 6.7 and 6.5% variations, respectively. The Jeffcott rotor was also analysed with different element configurations: Solid elements, axisymmetric Fourier elements, beam/solids and all beam elements. The Fourier elements were the most appropriate option for axisymmetric rotors regarding computational time and accuracy. Tilting pad journal bearings were simulated and validated against data from Vattenfall's facilities in Älvkarleby, where a vertical rotor is connected to two four-pad tilting pad journal bearings. The bearing formulation was defined in a Fortran based subroutine, which acquires the rotor's speed and position to supply a bearing load vector in Simcenter Nastran's transient solver. The experimental rig was also modelled to include the rotor/stator interaction. The force and displacement orbits at the bearings were replicated adequately concerning experimental data, where a maximum deviation of 20.8% and 9.8% were observed for the forces in x and y-directions.  A 3D-finite element model and a beam based finite element model were compared for an actual hydropower unit, which aimed to investigate the mode extraction procedure and how high mass, elastic rotor components influence the system's dynamics. Consistent rotor modes were identified at frequencies within 15% deviation, where the maximum deviation occurred in the upper range frequency pairs. Convergence between the models was observed for the static, lower range frequencies when considering a rigid generator rotor in the 3D finite element model. The outcome is consistent with the model assumptions and underlines that the beam based model cannot capture specific contributions from elastic rotor components. 3D-finite element analysis is a viable option when considering non-axisymmetric and complex rotors. High mass, non-rigid components must be analysed  in this manner as their dynamic contributions may not be captured with other approaches. Intricate and non-rigid supporting structures are also suitable for 3D modelling to properly reflect the stator-rotor interaction. It is a delicate matter to pinpoint when these conditions occur, and modelling decisions must be therefore be substantiated by simulations and experimental validation.