skywalker
2008-01-21, 18:26
Dear all,
Please find below a research topic in tensile menbrane analysis using Ansys.
I would appreciate any replies with regards to how such an analysis could be performed.
Regards.
A similar analysis system has been analysed... please see the PDF file on the via the following link.
http://www.lmc.ep.usp.br/people/pauletti/Publicacoes_arquivos/STRUCTURAL%20ANALYSIS%20OF%20THE%20MEMBRANE%20ROOF %20OF%20THE%20MPBP.pdf
Contents:
1.
Research Area
2.
Project Title
3.
Aim and Objectives of Project
4.
ReferencesResearch Area
Tensile Fabric Structures
A special form of lightweight surface structures are fabric tensile structures (FTS) formed by continuous spatially curved surfaces elements. To resist environmental loads, uplift and down-forces, these surface elements are designed with sufficient curvature to ensure that the fabric remains in tension under all load conditions. Hence, the surface elements must be double-curved (hyperbolic) and prestressed [1] with boundary conditions, cables & anchor points, defining the shape of structure.
Behaviour of coated fabrics
Coated woven fabrics, typically used in FTS, are known to be composed of an open weave mesh of orthogonal yarns (Glass fibre or polyester fabric) sandwiched on both sides with a PTFE or PVC coating respectively. The fabric behaviour under biaxial tensile loading is highly non-linear and hysteretic due to the complex interaction of orthogonal warp and weft fibre structure compounded by the effect of the coating [2]
Form-finding process
The surface geometry of FTS starts with a process known as the form-finding process, an iterative minimal surface approach [3], where an equilibrium state of the surface elements is searched given a initial unique boundary condition. As most surfaces are direct descendants of line elements, the shape of the freely hanging chain suspended between two anchoring points is a classic derived example, where each pin-joint or nodes of successive chain links is in equilibrium between the tension forces and the force of gravity acting simultaneously on the chain links.
The determination of these minimal surfaces is known to require non-linear finite element analysis [1] as the combination of applied loads and, internal stresses dependent on the curvature of the membrane, give rise to a set of nonlinear equilibrium equations [4]
Numerical analysis methods: SSDM and DR
The matrix and vector methods are the two basic approaches that have been developed for the form-finding process and load analysis [5]. Examples of the matrix and vector methods are the surface stress density method (SSDM) and dynamic relaxation (DR) method respectively.
According D., Hegyi et al [3] the DR method is a suitable and frequently used method for non-linear analysis since both the surface geometry material properties are highly non-linear.
With DR method, the fundamental aspect is that the FTS reaches static equilibrium by tracing the motion of each unbalanced nodal forces, at time increments, under a viscous damping effect [3].
After each time increment, the nodal velocity is set to zero and the iterative calculation performed until the unbalanced forces approach or converge to zero.
Material Model for FTS
The design and successful analysis of FTS is known to be highly dependent on an accurate and reliable modelling of the entire tension system and especially that of the coated fabric element. FTS are divided into two assemblages, according to conventional design methodology, the cable-membrane and supports [6].
Cable element - A Three-dimensional line element with two end nodes and six degrees of freedom could be assumed as only tensile stresses are resisted by this element.
Membrane element – A triangular facet element of constant strain with three nodes and nine degrees of freedom could be employed.
Beam element – an appropriate linear beam element with small deflections as the supports (anchor points) of FTS are a straight beam of uniform cross section capable of resisting axial forces, bending and twisting moments.
Dynamic analysis using FEA packages
According to Tabarrok, commercial finite element programs cannot be readily used for the design of tension structures. However R., Pauletti and M., Reyolando’s work [7] is seen to undertake the task of modelling a membrane structure using a commercial ‘general’ purpose finite element program, specifically Ansys Finite element program. Here the membrane element is modelled with SHELL41 elements working exclusively in tension, and the cable elements with LINK8 elements. Although, the overall results of the analysis of FTS were deemed quite satisfactory, an important aspect of the numerical process was not presented. A similar work by R., Pauletti and M., Reyolando [7], shows the results of the structural analysis of an FTS performed with the aid of Ansys finite element code, a satisfactory procedure is thought to have been omitted to allow the form finding process to be reproduced.
Project Title
Form finding of tensile membrane structures: An Ansys FEA computer method
Aim and Objectives of Project
Aim:
The aim of the project is to present a FEM process for form finding of FTS using Ansys
Objectives:
•
To obtain the nodal values of velocity and displacements from initial condition to final equilibrium state
•
To apply the DR method in form finding
•
To verify that the Ansys [SHELL41 & LINK8] material elements are appropriate in representing an FTS
•
To apply a suitable Ansys material model to represent the fabric element and beam elements
•
The determination of internal stress, anchor and boundary loads due to applied environmental loads
On completion of this project the following will have been achieved:
•
A double-curved FTS, near equilibrium, through form finding will presented
•
A step-step numerical Ansys FEA method to model & analyse FTS
References:
[1] B. N., Bridgens, P. D., Gosling, M. J. S., Brichall, Tensile fabric structures: Concepts, practice & developments, The Structural Engineer,
[2] B. N., Bridgens, P. D., Gosling, Direct stress-strain representation for coated woven fabrics, Computers & Structures, 82, 2004, p1913-1927
[3] D. Hegyi, I. Sajtos, G. Geiszter, K. Hincz, Eight-node quadrilateral double curved surface element for membrane analysis, Computers & Structures, 84, 2006, p2151-2158
[4] B. Tabarrok, Z. Qin, Dynamic Analysis of tension structures, Computers & Structures, 62, 1997, p 467-474
[5] D. S., Wakefield, Engineering analysis of tension structures: Theory and practice, Engineering structures, 21, 1999, p680-690
[6] J.-J, Li, S,-l, Chan, An integrated analysis of membrane structures with flexible supporting frames, Finite elements in analysis and design, 40, 2004, p529-540
[7] R. M. de,-O, Pauletti, M. L. R. F., Reyolando, online [www.lmc.ep.usp.br/people/Pauletti] (accessed august 2007)
Please find below a research topic in tensile menbrane analysis using Ansys.
I would appreciate any replies with regards to how such an analysis could be performed.
Regards.
A similar analysis system has been analysed... please see the PDF file on the via the following link.
http://www.lmc.ep.usp.br/people/pauletti/Publicacoes_arquivos/STRUCTURAL%20ANALYSIS%20OF%20THE%20MEMBRANE%20ROOF %20OF%20THE%20MPBP.pdf
Contents:
1.
Research Area
2.
Project Title
3.
Aim and Objectives of Project
4.
ReferencesResearch Area
Tensile Fabric Structures
A special form of lightweight surface structures are fabric tensile structures (FTS) formed by continuous spatially curved surfaces elements. To resist environmental loads, uplift and down-forces, these surface elements are designed with sufficient curvature to ensure that the fabric remains in tension under all load conditions. Hence, the surface elements must be double-curved (hyperbolic) and prestressed [1] with boundary conditions, cables & anchor points, defining the shape of structure.
Behaviour of coated fabrics
Coated woven fabrics, typically used in FTS, are known to be composed of an open weave mesh of orthogonal yarns (Glass fibre or polyester fabric) sandwiched on both sides with a PTFE or PVC coating respectively. The fabric behaviour under biaxial tensile loading is highly non-linear and hysteretic due to the complex interaction of orthogonal warp and weft fibre structure compounded by the effect of the coating [2]
Form-finding process
The surface geometry of FTS starts with a process known as the form-finding process, an iterative minimal surface approach [3], where an equilibrium state of the surface elements is searched given a initial unique boundary condition. As most surfaces are direct descendants of line elements, the shape of the freely hanging chain suspended between two anchoring points is a classic derived example, where each pin-joint or nodes of successive chain links is in equilibrium between the tension forces and the force of gravity acting simultaneously on the chain links.
The determination of these minimal surfaces is known to require non-linear finite element analysis [1] as the combination of applied loads and, internal stresses dependent on the curvature of the membrane, give rise to a set of nonlinear equilibrium equations [4]
Numerical analysis methods: SSDM and DR
The matrix and vector methods are the two basic approaches that have been developed for the form-finding process and load analysis [5]. Examples of the matrix and vector methods are the surface stress density method (SSDM) and dynamic relaxation (DR) method respectively.
According D., Hegyi et al [3] the DR method is a suitable and frequently used method for non-linear analysis since both the surface geometry material properties are highly non-linear.
With DR method, the fundamental aspect is that the FTS reaches static equilibrium by tracing the motion of each unbalanced nodal forces, at time increments, under a viscous damping effect [3].
After each time increment, the nodal velocity is set to zero and the iterative calculation performed until the unbalanced forces approach or converge to zero.
Material Model for FTS
The design and successful analysis of FTS is known to be highly dependent on an accurate and reliable modelling of the entire tension system and especially that of the coated fabric element. FTS are divided into two assemblages, according to conventional design methodology, the cable-membrane and supports [6].
Cable element - A Three-dimensional line element with two end nodes and six degrees of freedom could be assumed as only tensile stresses are resisted by this element.
Membrane element – A triangular facet element of constant strain with three nodes and nine degrees of freedom could be employed.
Beam element – an appropriate linear beam element with small deflections as the supports (anchor points) of FTS are a straight beam of uniform cross section capable of resisting axial forces, bending and twisting moments.
Dynamic analysis using FEA packages
According to Tabarrok, commercial finite element programs cannot be readily used for the design of tension structures. However R., Pauletti and M., Reyolando’s work [7] is seen to undertake the task of modelling a membrane structure using a commercial ‘general’ purpose finite element program, specifically Ansys Finite element program. Here the membrane element is modelled with SHELL41 elements working exclusively in tension, and the cable elements with LINK8 elements. Although, the overall results of the analysis of FTS were deemed quite satisfactory, an important aspect of the numerical process was not presented. A similar work by R., Pauletti and M., Reyolando [7], shows the results of the structural analysis of an FTS performed with the aid of Ansys finite element code, a satisfactory procedure is thought to have been omitted to allow the form finding process to be reproduced.
Project Title
Form finding of tensile membrane structures: An Ansys FEA computer method
Aim and Objectives of Project
Aim:
The aim of the project is to present a FEM process for form finding of FTS using Ansys
Objectives:
•
To obtain the nodal values of velocity and displacements from initial condition to final equilibrium state
•
To apply the DR method in form finding
•
To verify that the Ansys [SHELL41 & LINK8] material elements are appropriate in representing an FTS
•
To apply a suitable Ansys material model to represent the fabric element and beam elements
•
The determination of internal stress, anchor and boundary loads due to applied environmental loads
On completion of this project the following will have been achieved:
•
A double-curved FTS, near equilibrium, through form finding will presented
•
A step-step numerical Ansys FEA method to model & analyse FTS
References:
[1] B. N., Bridgens, P. D., Gosling, M. J. S., Brichall, Tensile fabric structures: Concepts, practice & developments, The Structural Engineer,
[2] B. N., Bridgens, P. D., Gosling, Direct stress-strain representation for coated woven fabrics, Computers & Structures, 82, 2004, p1913-1927
[3] D. Hegyi, I. Sajtos, G. Geiszter, K. Hincz, Eight-node quadrilateral double curved surface element for membrane analysis, Computers & Structures, 84, 2006, p2151-2158
[4] B. Tabarrok, Z. Qin, Dynamic Analysis of tension structures, Computers & Structures, 62, 1997, p 467-474
[5] D. S., Wakefield, Engineering analysis of tension structures: Theory and practice, Engineering structures, 21, 1999, p680-690
[6] J.-J, Li, S,-l, Chan, An integrated analysis of membrane structures with flexible supporting frames, Finite elements in analysis and design, 40, 2004, p529-540
[7] R. M. de,-O, Pauletti, M. L. R. F., Reyolando, online [www.lmc.ep.usp.br/people/Pauletti] (accessed august 2007)