Catálogo de publicaciones - libros

The influence of the development of computer programmes and automatic generation of cable nets and membrane structures will be shown in some examples. The main interest is laying on new evaluation methods of cable nets and membrane structure and the design process of membrane structures, integrating the material behaviour of coated fabric.

This paper deals with the design of lightweight structures. In particular the role of computational modelling software in this process is discussed. The state-of-the-art is first described paying close attention to the requirements for industrially effective solutions. Some of the less well understood aspects of the modelling processes are discussed. In particular the load analysis, form-finding and cutting pattern generation processes are covered. The modelling of textile is addressed in detail. Approaches to the design of software design systems for lightweight structure design are discussed in the context of system flexibility and effectiveness. Finally, interesting applications in the field of lightweight structures arising from design system developments are highlighted.

The task of determining appropriate forms for stressed membrane surface structures is considered. Following a brief introduction to the field, the primitive form-finding techniques which were traditionally used for practical surface design are described. The general concepts common to all equilibrium modelling systems are presented next, and then a more detailed exposition of the Force Density Method follows. The extension of the Force Density Method to geometrically non-linear elastic analysis is described. A brief overview of the Easy lightweight structure design system is given with particular emphasis paid to the formfinding and statical analysis suite. Finally, some examples are used to illustrate the flexibility and power of Easy’s formfinding tools.

The task of generating planar cutting patterns for stressed membrane surface structures is considered next. Following a brief introduction to the general field of cutting pattern generation, the practical constraints which influence textile surface structures are presented. Several approaches which have been used in the design of practical structures are outlined. These include the physical paper strip modelling technique, together with geodesic string relaxation and flattening approaches. The combined flattening and planar sub-surface regeneration strategy used in the Easy design system is described in detail. Finally, examples are given to illustrate the capabilities of Easys cutting pattern generation tools.

This paper summarizes the development for a large displacement formulation of a membrance composed of three-node triangular elements. A formulation in terms of the deformation gradient is first constructed in terms of nodal variables. In particular, the use of the right Cauchy-Green deformation tensor is shown to lead to a particulary simple representation in terms of nodal quantities. This may then be used to construct general models for use in static and transient analyses.

This paper shows applications of a recently developed shell element to the analysis of thin shell and membrane structures. The element is a three node triangle with only translational DOFs (rotation free) that uses the configuration of the three adjacent elements to evaluate the strains. This allows to compute (constant) bending strains and (linear) membrane strains. A total Lagrangian formulation is used. Strains are defined in terms of the principal stretches. This allows to consider rubber materials and other type of materials using the Hencky stress-strain pair. An explicit central difference scheme is used to integrate the momentum equations. Several examples, including inflation and deflation of membranes show the excellent convergence properties and robustness of the element for large strain analysis of thin shells and membranes.

Current work summarizes the experience of the writer in the modeling of membrane systems. A first subsection describes an efficient membrane model, together with a reliable solution procedure. The following section addresses the simulation of the wrinkling phenomena providing details of a new solution procedure. The last one proposes an efficient technique to obtain the solution of the fluid structural interaction problem.

This paper investigates the wrinkling of square membranes of isotropic material, subject to coplanar pairs of equal and opposite corner forces. These membranes are initially stress free and perfectly flat. Two wrinkling regimes are observed experimentally and are also reproduced by means of finite-element simulations. A general methodology for making preliminary analytical estimates of wrinkle patterns and average wrinkle amplitudes and wavelengths, while also gaining physical insight into the wrinkling of membranes, is presented.

This chapter presents a complete numerical formulation for the nonlinear structural analysis of prestressed membranes with applications in Civil Engineering. These sort of membranes can be considered to undergo large deformations but moderate strains, consequently nonlinear continuum mechanics principles for large deformation of prestressed bodies will be employed in order to proceed with the analysis. The constitutive law adopted for the material will be the one corresponding to a prestressed hyperelastic Saint Venant-Kirchhoff model. To carry out the computational resolution of the structural problem, the Finite Element Method (FEM) will be implemented according to a Total Lagrangian Formulation (TLF), by means of the Direct Core Congruential Formulation (DCCF). Eventually, some numerical examples will be introduced to verify the accuracy and robustness of the aforementioned formulation.

This paper deals with the control of mesh distortions which may appear during the form finding procedure of membrane design. The reason is the unbalance of surface stresses either due to the interaction of edge and surface or incompatibilities along the sewing lines of adjacent membrane patches. An approach is presented which is based on a rational modification of the surface tension field. The criterion is based on the control of the element distortion and derived from differential geometry. Several examples demonstrate the success of the method.

In statics, the large deformation analysis of membrane or shell structures loaded and/or supported by gas or fluid can be based on a finite element description for the structure only. Then in statics the effects in the gas or the fluid have to be considered by using the equations of state for the gas or the fluid, the information about the current volume and the current shape of the structure. The interaction of the gas/fluid with the structure, which can be also otherwise loaded, is then modelled by a pressure resulting from the gas/fluid always acting normal to the current structural part. This description can be also directly used to model slow filling processes without all the difficulties involved with standard discretization procedures. In addition the consistent derivation of the nonlinear formulation and the linearization for a Newton type scheme results in a particular formulation which can be cast into a very efficient solution procedure based on a sequential application of the Sherman-Morrison formula. The numerical examples show the efficiency and the effects of the developed algorithms which are particularly important for structures, where the volume of the gas of fluid has to be considered.