| 1. |
- Andersson, Håkan, et al.
(författare)
-
A co-simulation method for system-level simulation of fluid-structure couplings in hydraulic percussion units
- 2017
-
Ingår i: Engineering with Computers. - : SPRINGER. - 0177-0667 .- 1435-5663. ; 33:2, s. 317-333
-
Tidskriftsartikel (refereegranskat)abstract
- This paper addresses a co-simulation method for fluid power driven machinery equipment, i.e. oil hydraulic machinery. In these types of machinery, the fluid-structure interaction affects the end-product performance to a large extent, hence an efficient co-simulation method is of high importance. The proposed method is based on a 1D system model representing the fluid components of the hydraulic machinery, within which structural 3D Finite Element (FE) models can be incorporated for detailed simulation of specific sub-models or complete structural assemblies. This means that the fluid system simulation will get a more accurate structural response, and that the structural simulation will get more correct fluid loads at every time step, compared to decoupled analysis. Global system parameters such as fluid flow, performance and efficiency can be evaluated from the 1D system model simulation results. From the 3D FE-models, it is possible to evaluate displacements, stresses and strains to be used in stress analysis, fatigue evaluation, acoustic analysis, etc. The method has been implemented using two well-known simulation tools for fluid power system simulations and FE-simulations, respectively, where the interface between the tools is realised by use of the Functional Mock-up Interface standard. A simple but relevant model is used to validate the method.
|
|
| 2. |
- Borrvall, Thomas, 1974-
(författare)
-
Computational topology optimization in continuum mechanics
- 2002
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation concerns theoretical and computational methodologies in topology optimization in continuum mechanics.A general procedure for treating problems of this kind starts with the establishment of a well-posed continuum problem formulation, in the sense that one can prove existence of at least one solution to the problem. When straightforward mathematical modelling of a physical situation results in an ill-posed formulation, i.e., no solutions exist, the problem is regularized by means of restriction methods in order to remedy this. These are general and appealing regularization approaches that apply to a large class of problems and have increased in popularity of later years. In this dissertation, some new restriction methods are introduced, and an overview and characterization of such methods are made that indicate theoretical and numerical advantages and drawbacks.Topology optimization of elastic solids and structures is a well established discipline but little efforts have previously been made to apply the methodology in fluid mechanics. In this dissertation, topology optimization of viscous fluids in Stokes flow is successfully performed, yielding many potential applications. -while regularization often is needed for the problems encountered in topology optimization of continua, this problem is a rare exception. The underlying physics allows for a mathematical problem formulation that is well-posed without any regularization. The presented methodology can also be seen as a guideline for how to proceed with research in topology optimization in fluid mechanics.A well-posed problem formulation serves as a basis for a finite element discretization procedure performed such that finite element convergence can be proved. This asserts an a priori reliability in the sense that discrete solutions will not suffer from typical artifacts known of in the field. The discretized problem is solved numerically by mathematical programming algorithms, a general and powerful approach that is applicable to many problems of varying degree of complexity. In addition to using powerful solution algorithms, object-oriented implementation techniques and high performance computers and computing are incorporated as means to facilitate encounter of new applications and to improve computational efficiency. The advantages of these approaches are exemplified by solving problems from several disciplines of physics within the same object-oriented framework and by solving large scale "real-life" problems in an industrial environment using parallel computing.
|
|
| 3. |
- Borrvall, Thomas, 1974-
(författare)
-
Computational topology optimization of elastic continua by design restriction
- 2000
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is concerned with theoretical and computational approaches in topology optimization of elastic continua. It consists of three papers.Paper I is a review of existing approaches for formulating and solving problems in topology optimization. Advantages and drawbacks of the different methods are discussed as well as their relations to each other.Paper II presents a new way to formulate topology optimization problems which is based on an explicit penalization of intermediate design values. In order to obtain a well posed optimization problem, a penalty function is regularized with the use of a compact operator. The method, called regularized intermediate density control, is illustrated in some 2D numerical examples that show its ability to produce discrete valued optimal designs.Paper III is a continuation of paper II, where the method has been extended to be used in 3D. In order to get a proper resolution of realistic cases in 3D, parallel computing is employed. An iterative equilibrium solver is used for this purpose and the parallel implementation is described closely. The use of parallelization in topology optimization is motivated both through a theoretical analysis and through numerical examples involving several hundreds of thousand finite elements.
|
|
| 4. |
- Borrvall, Thomas, et al.
(författare)
-
Large-scale topology optimization in 3D using parallel computing
- 2001
-
Ingår i: Computer Methods in Applied Mechanics and Engineering. - 0045-7825 .- 1879-2138. ; 190:46-47, s. 6201-6229
-
Tidskriftsartikel (refereegranskat)abstract
- We consider large-scale topology optimization of elastic continua in 3D using the regularized intermediate density control introduced in [1]. The nested approach is used, i.e., equilibrium is solved at each iteration. To get a high-quality resolution of realistic designs in 3D, problems involving several hundreds of thousand finite elements are solved. In order to deal with problems of this size, parallel computing is used in combination with domain decomposition. The equilibrium equations are solved by a preconditioned conjugate gradient algorithm and the optimization part is solved using sequential convex programming. Several numerical results obtained from computations performed on a Cray parallel computer are presented. © 2001 Elsevier Science B.V. All rights reserved.
|
|
| 5. |
- Borrvall, Thomas, et al.
(författare)
-
Topology optimization of fluids in Stokes flow
- 2003
-
Ingår i: International Journal for Numerical Methods in Fluids. - : Wiley. - 0271-2091 .- 1097-0363. ; 41:1, s. 77-107
-
Tidskriftsartikel (refereegranskat)abstract
- We consider topology optimization of fluids in Stokes flow. The design objective is to minimize a power function, which for the absence of body fluid forces is the dissipated power in the fluid, subject to a fluid volume constraint. A generalized Stokes problem is derived that is used as a base for introducing the design parameterization. Mathematical proofs of existence of optimal solutions and convergence of discretized solutions are given and it is concluded that no regularization of the optimization problem is needed. The discretized state problem is a mixed finite element problem that is solved by a preconditioned conjugate gradient method and the design optimization problem is solved using sequential separable and convex programming. Several numerical examples are presented that illustrate this new methodology and the results are compared to results obtained in the context of shape optimization of fluids. © 2003 John Wiley and Sons, Ltd.
|
|
| 6. |
- Borrvall, Thomas, et al.
(författare)
-
Topology optimization using regularized intermediate density control
- 2001
-
Ingår i: Computer Methods in Applied Mechanics and Engineering. - 0045-7825 .- 1879-2138. ; 190:37-38, s. 4911-4928
-
Tidskriftsartikel (refereegranskat)abstract
- We consider topology optimization of elastic continua. The elasticity tensor is assumed to depend linearly on the design function (density) as in the variable thickness sheet problem. In order to get "black-white" design pictures, the intermediate density values are controlled by an explicit constraint. This constraint is regularized by including a compact and linear operator S to guarantee existence of solutions. A proof of convergence of the finite element (FE) discretized optimization problem's solutions to exact ones is also given, so the method is not prone to numerical anomalies such as mesh dependence or checkerboards. The procedure is illustrated in some minimum compliance examples where S is chosen to be a classical convolution-type operator. The FE-discretized optimization problems are solved by sequential convex approximations. © 2001 Elsevier Science B.V. All rights reserved.
|
|
| 7. |
- Wiker, Niclas, 1976-, et al.
(författare)
-
Applications of Bottom Profile Optimization in Linear Viscous Shallow Water Flow
- 2007
-
Ingår i: Proceedings of the 7th World Congress on Structural and Multidisciplinary Optimization, Seoul, Korea, May 2007. - Guseong-dong, Yuseong-gu, Daejeon, Republic of Korea : ISSMO. ; , s. 2283-2292
-
Konferensbidrag (refereegranskat)abstract
- In this paper, the design method for creating optimal bottom profiles inshallow water flow problems, proposed in Wiker et al., is investigated further.The method was inspired by techniques commonly found in the area oftopology optimization of structures, and uses the linear viscous shallow water equations as state equations in the optimization problem. In Wiker et al.,an area–to–point flow problem was investigated, seeking the bottom profilewhich most efficiently transports a fluid added inside the domain, towards apoint on the boundary. Specifically, the influence on the solution of some ofthe problem parameters was tested, and it was concluded that natural–likedesigns can be created for proper choices of parameter values.In the present work, bottom profiles of two other problem types are studied— the point–to–line problem and the line–to–line problem. In the firstproblem, in order to mimic a river delta, an inflow is prescribed on a smallpart (point) of the boundary of a domain. To exit the domain on the oppositeside, the fluid is forced to pass a line of limited depth. For the secondproblem, a number of inflows are prescribed on one side (inflow line) of a rectangular domain and the fluid is then allowed to exit anywhere on theopposite side (outflow line). This can be seen as modeling the spillway frome.g. a dam.
|
|
| 8. |
- Wiker, Niclas, 1976-
(författare)
-
Optimization in Continuum Flow Problems
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work presented in this dissertation was carried out at the Division ofMechanics, Department of Management and Engineering at Link¨oping University,between 2003 and 2008. It was supervised by Prof. Anders Klarbring,head of the division, and financially supported by the National GraduateSchool of Scientific Computing (NGSSC) and the Swedish Research Council(VR).There are many people to whom I would like to express my gratitude: firstand foremost I would like to thank my supervisor Prof. Anders Klarbring forhis help, support and endless patience during our discussions, and for alwayshaving time to read and comment on the numerous drafts that eventually ledto the research manuscripts presented in this thesis. I would also like to thankmy co–supervisor Dr. Thomas Borrvall for all his help regarding numericalissues, especially with the implementation of the models. Moreover, I wouldlike to thank present and former colleagues for their inspiration and assistanceduring my time as a graduate student at the division.Last but not least, I am very grateful for having a family that has alwaysbeen there to support me, and for all my friends who enrich my life outsidethe office walls in more ways then I can say.
|
|
| 9. |
- Wiker, Niclas, et al.
(författare)
-
Optimization of bottom profile in shallow water flow
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In t his paper, a design method for creating optimal bottom profiles in flow systems, described by the linear shallow water equations, is proposed. The method is based on techniques commonly found in the area of topology optimization of structures. The presentation includes a derivation of the linearand stationary shallow water equations, which are used as state equations in the optimizaton problem. The final problem definition is closely related to the Darcy-Stokes fluid flow topology optimization problem, from which many results are derived by analogy.From the numerical examples, it is concluded that natural-like designs can be created for proper choices of parameter values.
|
|
| 10. |
- Wiker, Niclas, 1976-, et al.
(författare)
-
Simplified shallow water flow equations and their potential use in bottom profile optimization
- 2007
-
Ingår i: Zeitschrift für angewandte Mathematik und Mechanik. - : Wiley. - 0044-2267 .- 1521-4001. ; 87:11-12, s. 792-808
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, an optimization method for systems described by linearizedviscous shallow water equations is proposed. It can potentially be used tooptimize bottom profiles and is based on techniques commonly found in thearea of topology optimization of structures, but with the difference that acontinuous, and not discrete, design is sought. The presentation includes aderivation and linearization of the stationary viscous shallow water equations,which are used as state equations in the optimization problem. The finalproblem definition is closely related to the Darcy–Stokes fluid flow topologyoptimization problem, from which many results are derived by analogy.From the numerical examples it is concluded that natural–like designscan be created for proper choices of parameter values. However, presentlythe model is not physically validated and its exact domain of application isnot yet known.
|
|
| 11. |
- Wiker, Niclas, 1976-, et al.
(författare)
-
The Darcy-Stokes Topology Optimization Problem
- 2006
-
Ingår i: IUTAM Symposium on Topological Design Optimization of Structures, Mashines and Materials: Status and Perspectives,2005. - Dordrecht : Springer. ; , s. 551-
-
Konferensbidrag (refereegranskat)abstract
- This paper treats the optimal layout of mixtures of regions of Stokes viscosity dominated flow and regions of Darcy porous flow. The problem of minimizing the potential of the state problem, representing essentially dissipation, is formulated, and can be shown to have a solution under appropriate filtering of the design. It can also be shown that the unfiltered design has a zero--one property. An area-to-point flow problem is solved for various filter radii.
|
|
| 12. |
- Wiker, Niclas, 1976-, et al.
(författare)
-
Topology Optimization Applied to Crack Patterns in Drying Porous Material
- 2008
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Based on topology optimization techniques, a model for crack formation indrying porous materials is developed. The state problem derived representsthe mulitphysic flow of a mixture of fluid (air) and moister. A topologyoptimization problem is defined, where the layout (topology) of cracks andporous material, as well as the length scale of the crack pattern are used asoptimization variables. The problem is solved using a two–stage continuationmethod, labelled phase I and phase II. In phase I, a relaxed version of theproblem is solved to generate“clever”initial guesses for phase II. In the secondphase, the full problem is solved using a ten–step procedure. Two examplesare provided showing the dependence on different problem parameters, and,given the limitations in the model, the results show nature–like trends.
|
|
| 13. |
- Wiker, Niclas, 1976-, et al.
(författare)
-
Topology optimization of regions of Darcy and Stokes flow
- 2006
-
Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 69:7, s. 1374-1404
-
Tidskriftsartikel (refereegranskat)abstract
- This paper treats the topology optimization problem of obtaining an optimal layout of regions of Darcy and Stokes flow, where the objective is the total potential power functional representing average fluid pressure. It extends the work of Borrvall and Petersson, which concerned optimal layout of Stokes flow only. A generalization of Stokes' equations is derived and used as state constraints in the optimization problem. A proof of existence of solutions is provided, and it is seen that although the corresponding proof in Borrvall and Petersson does not need regularization, the present one does. It is also concluded that linear interpolations of state parameters will result in black and white (unfiltered) designs. The method is tested on an area-to-point flow problem of the type discussed by Bejan, where the influence of various parameters and numerical strategies on the design are studied.
|
|
