Computational morphogenesis of free form shells: Filter methods to create alternative solutions

p. 536-547Actual trends in numerical shape optimal design of structures deal with handling of very large dimensions of design space. The goal is to allowing as much design freedom as possible while considerably reducing the modelling effort. As a consequence, several technical problems have to be solved to get procedures which are robust, easy to use and which can handle many design parameters efficiently. The paper briefly discusses several of the most important aspects in this context and presents many illustrative examples which show typical applications for the design of light weight shell and membrane structures.Bletzinger, K.; Firi, M.; Linhard, J.; Wüchner, R. (2009). Computational morphogenesis of free form shells: Filter methods to create alternative solutions. Editorial Universitat Politècnica de València. http://hdl.handle.net/10251/654

Calculation of static deformation of membrane structures under the load of ponding water

Ponding refers to a phenomenon of accumulation of water on top of a structure. Even though most light weight membrane structures are designed to prevent its occurrence, it can be initiated in some cases during rainfall by an event such as drifted snow settling on the surface of the structure causing a local depression of the membrane structure. The present work proposes a method to calculate the static deformation of a membrane structure due to a given volume of ponding water. The method involves coupling of a structural solver for the membrane and a volume conserving solver representing the static behavior of an incompressible fluid. The coupling is performed in a partitioned manner with the linearized behavior of the incompressible fluid incorporated in the structural equations to accelerate the coupling iterations. Using this method, the final deformation of the structure due to ponding is calculated by applying loads due to a fixed volume of water

The eXtended Updated Reference Strategy for the form finding of tensile structures

In this paper, the eXtended Updated Reference Strategy is presented. Starting from the established Updated Reference Strategy all related issues, which are involved for this methodology, are identified. It will be shown that the eXtended Updated Reference Strategy is able to solve the “correct” form finding problem in one non-linear iteration step. By applying the eXtended Updated Reference Strategy to well-known form finding problems the difference in convergence in comparison to establish methods like the force density method or the Updated Reference Strategy is discusse

Neural Network-Based Surrogate Models Applied to Fluid-Structure Interaction Problems

Traditional computational methods face significant challenges with ever-increasing complexity in the problems of engineering interest. One category of problems that suffer from this phenomenon is those where Fluid-Structure Interaction (FSI) is present. One set of problems that suffer from this phenomenon is those where Fluid-Structure Interaction (FSI) is present. FSI simulations are traditionally time-consuming and computationally extremely expensive. Potential alternatives rely on using a surrogate model to substitute one or more systems involved. A promising approach employs artificial neural networks as the basis for such a surrogate model combined with strong physics simulations based on finite element methods (FEM). This approach requires the seamless integration of AI algorithms and packages into the simulation workflow. Such an example is the NeuralNetworkApplication developed in KratosMultiphysics. The routines related to the neural networks are executed through an interface with the Keras API. Mok's benchmark is chosen as the study case to test the capacity of the previous method applied to FSI problems. Two cases in which one of the systems is substituted by a neural network-based surrogate model are analyzed. Strong and weak coupling scenarios are considered. The results present improvements in simulation time without sacrificing accuracy, especially when compared with the original benchmark. This contribution discusses the influence of the original data and network architecture on the simulation outcome and different considerations for generating surrogate models for FSI

Advanced cutting pattern generation – Consideration of structural requirements in the optimization process

This paper presents extensions to optimized cutting pattern generation through inverse engineering regarding structural requirements. The optimized cutting pattern generation through inverse engineering is a general approach for the cutting pattern generation which is based on the description of the underlying mechanical problem. The three dimensional surface, which is defined through the form finding process, represents the final structure after manufacturing. For this surface the coordinates in three dimensional space Ω3D and the finally desired prestress state σprestress are known. The aim is to find a surface in a two dimensional space Ω2D which minimizes the difference between the elastic stresses σel,2D→3D arising through the manufacturing process and the final prestress σprestress. Thus the cutting pattern generation leads to an optimization problem, were the positions of the nodes in the two dimensional space Ω2D are the design variables. In this paper various improvements to the method will be shown. The influence of the seam lines to the stress distribution in the membrane is investigated. Additionally, the control of equal edge length for associated patterns is an example for important enhancement

Coupling of structural solver and volume-conserving solver for form-finding of membrane structures subjected to ponding

The current study deals with coupling of a volume conserving solver and a structural solver to calculate the static deformation of flexible structures under the load of a given volume of water. The volume-conserving solver contains a horizontal plane representing the free surface of the fluid, which is moved in the non-linear iterations to conserve the volume. The Partitioned approach is chosen to have code modularity and reusability with many structural codes

Coupling of structural solver and volume-conserving solver for form-finding of membrane structures subjected to ponding

The current study deals with coupling of a volume conserving solver and a structural solver to calculate the static deformation of flexible structures under the load of a given volume of water. The volume-conserving solver contains a horizontal plane representing the free surface of the fluid, which is moved in the non-linear iterations to conserve the volume. The Partitioned approach is chosen to have code modularity and reusability with many structural codes

Conception and design of membrane structures considering their non-linear behavior

The lack of unified verification approaches and standards like the Eurocodes for various materials is a limiting factor to further propagation of architectural membranes. This paper will discuss the possibilities and challenges of integrating the design and verification of membrane structures into the Eurocodes’ philosophy. Therefore an overview of existing guidelines will be given, followed by a discussion of the underlying principles of the Eurocodes. Especially the non-linear behavior of architectural membranes distinguishes them from other structures. Therefore the focus of this contribution is to discuss the implications of this non-linearity on verification approaches. Theoretical considerations as well as in-depth examples help to clarify the necessary basis. Finally the consequences of non-linearity on the verification of the primary structure and hybrid structures are presented

Isogeometric analysis for staged construction within lightweight design

Hybrid, bending-active structures constitute a challenging task for structural design due to the high dependency between shape and forces. Isogeometric analysis suggests itself in this context because of several advantages. Model conversion with concomitant corruption of the simulation results can be overcome. All stages of the construction, which are necessary for the correct simulation of such structures, can be modeled and correctly linked. Moreover, the parameter space of the NURBS description provides a perfectly suited, additional design space for embedded entities, which can be defined independently of the parametrization. The contribution of this paper is a presentation of the basics for embedding within isogeometric analysis and reveals beneficial aspects of nested NURBS descriptions in the context of staged construction. A case study of a staged simulation is carried out and another one for the form-finding procedure of hybrid structures

Code verification examples of a fully geometrical nonlinear membrane element using the method of manufactured solutions

This paper presents an effective method to perform Code Verification of a software which is designed for structural analysis using membranes. The focus lies on initially curved structures with large deformations in steady and unsteady regimes. The material is assumed to be linear elastic isotropic. Code Verification is a part of efforts to guarantee the code’s correctness and to obtain finally predictive capability of the code. The Method of Manufactured Solutions turned out to be an effective tool to perform Code Verification, especially for initially curved structures. Here arbitrary invented geometries and analytical solutions are chosen. The computer code must approach this solution asymptotically. The observed error reduction with systematic mesh refinement (i.e. observed order of accuracy) must be in the range of the formal order of accuracy, e.g. derived by a Taylor series expansion. If these two orders match in the asymptotic range, the implemented numerical algorithms are working as intended. The given examples provide a complete hierarchical benchmark suite for the reader to assess other codes, too. In the present case several membrane states were tested successfully and the used code Carat++ assessed to converge - as intended - second order accurately in space and time for all kind of shapes and solution