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Calibri 83ffff̙̙3f3fff3f3f33333f33333.ۏTU Delft Repositoryg Ouuidrepository linktitleauthorcontributorpublication yearabstract
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departmentresearch group programmeprojectcoordinates)uuid:76b5467e63ba4fb6bc4c4f2f8548ff95Dhttp://resolver.tudelft.nl/uuid:76b5467e63ba4fb6bc4c4f2f8548ff95gA Controllability Approach for Resonant Compliant Systems: Applied to a Flapping Wing Micro Air VehiclePeters, H.J.Van Keulen, F. (promotor)lThis thesis studies a controllability approach for general resonant compliant systems. These systems exploit resonance to obtain a specific dynamic response at relatively low actuation power. This type of systems is often lightweight, is scalable and minimizes frictional losses through the use of compliant hinges. Some insectinspired Flapping Wing Micro Air Vehicle (FWMAV) designs are based on such a resonant compliant system. These designs are carefully tuned such that a particular resonance response of the system corresponds to the desired wing flapping motion. The system s resonance response depends strongly on its structural properties (i.e., mass, damping, stiffness and their spatial distribution). Resonance response modifications can, thus, be controlled using carefully selected structural property changes. This thesis contributes to the controllability of resonant compliant systems in general and the compliant FWMAV design in particular. Although there is yet no physical, controllable FWMAV design with integrated active components, the current research strongly indicates the applicability of structural property changes to reach controllability of this type of systems. Effective control requires an integrated approach that considers simultaneously the structure, the wings, the kinematics, the methods to induce property changes and the desired controllability.resonant compliant systems; resonance response; controllability; smart materials; control actuator design; Flapping Wing Micro Air Vehicle (FWMAV)endoctoral thesis
20160322.Mechanical, Maritime and Materials Engineering&Precision and Microsystems Engineering52.0167, 4.3667)uuid:ee24b1865db64c57aa503b736110ff2aDhttp://resolver.tudelft.nl/uuid:ee24b1865db64c57aa503b736110ff2aTopology Optimization with Stress ConstraintsVerbart, A.This thesis contains contributions to the development of topology optimization techniques capable of handling stress constraints. The research that led to these contributions was motivated by the need for topology optimization techniques more suitable for industrial applications. Currently, topology optimization is mainly used in the initial design phase, and local failure criteria such as stress constraints are considered in additional postprocessing steps. Consequently, there is often a large gap between the topology optimized design and the final design for manufacturing. Taking into account stress constraints directly into the topology optimization process would reduce this gap. Several difficulties arise in topology optimization with local stress constraints which complicate solving the optimization problem directly. \chap{litreview} discusses these difficulties, and reviews solutions that have been applied. Two fundamental difficulties are: (i) the presence of singular optima, which are true optima inaccessible to standard nonlinear programming techniques, and (ii) the fact that the stress is a local state variable, which typically leads to a large number of constraints. Currently, the conventional strategy to circumvent these difficulties is to apply (i) constraint relaxation, which perturbs the feasible domain to make singular optima accessible, followed by (ii) constraint aggregation to transform the typically large number of relaxed constraints into a single or few global constraints thereby reducing the order of the problem. Although there is no consensus on the exact choice of aggregation and relaxation functions and their numerical implementation, in general, this approach introduces < two additional parameters to the problem: an aggregation and a relaxation parameter. Following this approach, one solves an alternative optimization problem with the aim of finding a solution to the original stressconstrained topology optimization. The feasible domain of this alternative optimization problem is related to the original feasible domain via these parameters. In Chapter 2, we investigated the parameter dependence of this alternative optimization problem on an elementary twobar truss problem. It was found that the location of the global optimum of this alternative optimization problem with respect to the true optimum depends in a nontrivial way on these problem parameters (in their range of application); i.e., for a given parameter set, it is difficult to predict the influence of changing one of the parameter values, and if this change will result in a feasible domain in which the global optimum is closer to the true optimum. This complicates determining optimal parameter values \emph{a priori} which, in addition, are problemdependent. In Chapter 3, we investigated the effect of design parameterization, and relaxation techniques in stressconstrained topology optimization. An elementary numerical example was considered, representing a situation as might occur in densitybased topology optimization. As previously observed in truss optimization, we found that a global optimum of the relaxed optimization problem may not converge to the true optimum as the relaxation parameter is decreased to zero. In this thesis, we present two novel approaches: a unified aggregation and relaxation approach in Chapter 4, and the damage approach in Chapter 5. In the unified aggregation and relaxation approach, we applied constraint aggregation such that it simultaneously perturbs the feasible domain, and makes singular optima accessible. Consequently, conventional relaxation techniques become unnecessary when applying constraint aggregation following this approach. The main advantage is that the problem only depends on a single parameter, which reduces the parameter dependency of the problem. The damage approach is presented as a viable alternative for conventional methodologies. Following the damage approach stress constraint violation is penalized by degrading material where the stress exceeds the allowable stress. Material degradation affects the overall performance of the structure, and therefore, the optimizer promotes a design without stress constraint violation. Similar to conventional constraint aggregation techniques a large number of local constraints can be controlled by imposing a single or a few global constraints. Both novel approaches are validated on elementary truss examples and tested on numerical examples in densitybased topology optimization. In contrast to the conventional strategy of relaxation followed by aggregation, there exists a clear relationship between the perturbed feasible domain and the original unperturbed feasible domain in terms of a single problem parameter.TTopology Optimization; Stress Constraints; Structural Optimization; Material failure
20150703)uuid:4d9aa8136d514a0183f8bb8ed6bcc274Dhttp://resolver.tudelft.nl/uuid:4d9aa8136d514a0183f8bb8ed6bcc274lPushing the Boundaries: Levelset Methods and Geometrical Nonlinearities in Structural Topology OptimizationVan Dijk, N.P.This thesis aims at understanding and improving topology optimization techniques focusing on densitybased levelset methods and geometrical nonlinearities. Central in this work are the numerical modeling of the mechanical response of a design and the consistency of the optimization process itself. Concerning the first topic, we investigate different means to improve the robustness of densitybased numerical models including geometrical nonlinearities. The conventional approach (scaling the local material properties) can result in convergence problems due to excessive deformation in lowstiffness finite elements. To avoid excessive deformation, we combine the element connectivity parameterization method (adapting the conn< ectivity between finite elements) with levelsetbased topology optimization. Furthermore, we achieve greater robustness of analysis method using a second and improved approach called element deformation scaling. This approach eliminates the need for solving internal equilibrium equations (needed for the element connectivity parameterization method) via an explicit relation between the local internal and global external displacement field. The second focus of this thesis is on the optimization process of levelsetbased topology optimization, and in particular its numerical consistency. We observe that signeddistance reinitialization of the levelset function affects the shape of a design in the optimization process. To minimize this effect, we propose a discrete levelset method that is based on an approximate Heaviside function and focusing on the implementation. Furthermore, we also propose a levelsetbased topology optimization method using an exact Heaviside function and mathematical programming that effectively eliminates the need for reinitialization. We demonstrate that our densitybased levelset method is closely related to conventional densitybased topology optimization methods, while offering the advantage of more control over the geometrical complexity. On the other hand, we confirm that the dependence of the final result on the initial design which remains one of the big challenges for levelsetbased topology optimization. The potential of the proposed levelset method is shown by applying it on problems with stress constraints and geometrical nonlinearities and performing manufacturing tolerant topology optimization. Finally, this thesis offers a review of levelset methods for structural topology optimization to identify and discuss the different approaches that are available in literature. We can distinguish between levelset methods by examination of their design parameterization, sensitivities, update procedures and regularization techniques. A levelsetbased design parameterization offers the advantage of a crisp distinction between subdomains. For this reason, XFEM approaches and conforming discretizations are an interesting option to retain the crisp nature of the levelsetbased description of the design. Many levelset methods are combined with densitybased numerical models and are, therefore, closely related to conventional densitybased topology optimization methods. In particular, recently proposed projection methods have much in common with a levelsetbased design description. The results of levelsetbased TO methods often rely heavily on regularization techniques that introduce inconsistencies in the optimization process. Numerical consistency does not necessarily lead to the best search direction, but is essential to find a KarushKuhnTucker point of the discretized optimization problem.Ctopology optimization; levelset method; geometrical nonlinearities)uuid:4bd7b1abab6c4ec581953028ba681e50Dhttp://resolver.tudelft.nl/uuid:4bd7b1abab6c4ec581953028ba681e50DMechanical Stability of Cementless Implants: The Glenoid ReplacementSuarez Venegas, D.R.2Van Keulen, F. (promotor); Rozing, P.M. (promotor) The aim of this project is to evaluate the contribution of different variables to the mechanical (in)stability of a cementless glenoid component. This is done using both numerical and experimental methods that allow the measurement or estimation of the boneimplant interface micromotions around the glenoid component in several scenarios that are clinically relevant. Minimum boneimplant interface micromotions not only imply an adequate mechanical stability of the implant within the bone, they are also an essential requirement for a successful bone ingrowth into the porous coating of the implant and, subsequently, a long term implant fixation. This book consists of ten chapters that can be divided in four main sections. The first section covers a short theoretical background about glenoid components, their most common failures, cementless fixation (Chapter 2) and a description of a cadaverspecifi< c finite element model that is used along the entire study (Chapter 3). A second section is dedicated to the study of the influence of implant positioning, as a surgeon and techniquerelated variable, on the initial mechanical stability of the glenoid component (Chapter 4). Both computational tools and an experimental technique are used in the second section to study the effect of the implant design and primary fixation on the initial mechanical stability. Comparisons of the boneimplant interface micromotions are made when the joint conformity of the implant changes (Chapter 5) or when different types and number of screws are used for the initial fixation of the cementless glenoid component (Chapter 6). The influence of patientrelated variables on implant stability is the main topic of the third section. The computational model described in the first section is used to evaluate how the clinical status of patient s soft tissues (Chapter 7) and bone (Chapters 7 and 8) may hamper the initial mechanical stability of the implant and, thus, the subsequent bone ingrowth. The last and fourth section deals with the possible bone adaptation around a cementless glenoid component and a longterm prediction of its mechanical stability. This is done through the previously described numerical model and the implementation of a bone remodelling algorithm together with a realistic range of loading conditions after surgery (Chapter 9). After the fourth section, this work concludes with a short review of the obtained results, the conclusions and recommendations for further work (Chapter 10)..prosthesis; cementless; interface micromotions
20130401)uuid:157c231854754b71b7ffd4a1e766a4a9Dhttp://resolver.tudelft.nl/uuid:157c231854754b71b7ffd4a1e766a4a9Simulation of bone ingrowth
Andreykiv, A.van Keulen, F. (promotor)Abstract not availableMechanical Maritime and Materials Engineering)uuid:7bf2a037c8eb44be96ef411529c4be0bDhttp://resolver.tudelft.nl/uuid:7bf2a037c8eb44be96ef411529c4be0bDTopology Optimization using a Topology Description Function Approachde Ruiter, M.J.#During the last two decades, computational structural optimization methods have emerged, as computational power increased tremendously. Designers now have topological optimization routines at their disposal. These routines are able to generate the entire geometry of structures, provided only with information on loads, supports, and space to work in. The most common way to do this is to partition the available space in elements, and to determine the material content of each of the elements separately. This thesis presents a different approach, namely the \emph{Topological Description Function} (TDF) approach. The TDF is a function parametrized by design variables. The function determines a geometry using a levelset approach. A finite element representation of the geometry then is used to determine how well the geometry performs with respect to objective and constraints. This information is given to an optimization program, which has the purpose of finding an optimal combination of values for the design variables. This approach decouples the geometry description of the design from the evaluation, allowing the designer to tune the detailedness of the geometry and the computational grid separately as wished. In this thesis, the concept of a TDF is explained in detail. Using a genetic algorithm for the optimization turns out to be too computationally expensive, however, it shows the validity of the TDF as a geometry description method. A method based on an intuitive updating scheme shows that the TDF approach can be used to do topology optimization.level set method; topology; optimization; tdf; topology description function; genetic algorithm; optimality criteria method; structural optimization)uuid:e592b6f17f0f499ba9852705a7a2ecbaDhttp://resolver.tudelft.nl/uuid:e592b6f17f0f499ba9852705a7a2ecba.Gradientbased approximate design optimizationVervenne, K.The research presented in this thesis deals with gradientenhanced approximate design optimization. This r<xesearch has been carried out as part of the ADOPT project (Approximate Design OPTimization), a joint STW project with the Eindhoven University of Technology. In structural optimization, sensitivity analysis is often performed by means of the semianalytical method. In the present thesis it has been shown that the accuracy of the design sensitivities can be improved by using Laplacian smoothing instead of a boundary node approach. In many applications of structural optimization, sensitivity information is available at low computational cost. Various methods to include this information in the response surface method have been investigated. It has been shown that including gradient information in the response surface may be considered as a multiobjective optimization problem, in which a tradeoff between accuracy in function values and gradients has to be made explicitly. In addition, the use of fast reanalysis is considered in order to reduce the computational time required to carry out the function evaluations. As an application, the optimization of composite laminates has been considered. These types of problems lead to a nonsmooth response. It has been investigated whether an optimizer based on a sequential approximate method can be used to solve these types of problems. The proposed approach has been applied to the optimization of composite tubes./gradient; response surface; design optimizationDelft University PressAerospace Engineering
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