Users:General FEM Analysis/Elements Reference/Membrane NURBS
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Contents |
General Description
Element Type
- This membrane element is an isotropic plane stress element accounting for prestress
- The membrane element neglects bending stiffness
- The ratio of the thickness and the lengths in the other two directions is much smaller than one ( t/Lx << 1 and t/Ly << 1), the membrane is reduced to its mid-surface
- The thickness is constant over the element
An extensive description of the element can be found in [1]
Input Parameters
Parameter Description
| Compulsory Parameters | ||
| Parameter | Values, Default(*) | Description |
|---|---|---|
| MAT | EL-MAT int | Number for the used Material
e.g. MAT=EL-MAT 1 |
| THICKNESS | real | Thickness of the membrane |
| INT_TYPE_MEMBRANE_NURBS | FULL or USER | Type of numerical integration. With FULL the integration rule is automatically chosen, with USER it can manually be defined. For USER also the parameters GAUSS_U and GAUSS_V have to be defined. |
| GAUSS_U, GAUSS_V | int | Number of integration points in u and v-direction, respectively. In case of INT_TYPE_MEMBRANE_NURBS = FULL this specification is not required. |
| A_X, A_Y, A_Z
B_X, B_Y, B_Z |
Definition of the principal directions of the surface to define the prestress directions, only applied with anisotropic prestress conditions. (see description of Membrane1-element) | |
| SIG11
SIG22 SIG12 |
reals | Prestress state of the membrane. (see description of Membrane1-element) |
Example of a Complete Input Block
EL-PROP 1 : MEMBRANE_NURBS MAT= EL-MAT 1 THICKNESS= 1.0 INT_TYPE_MEMBRANE_NURBS = FULL !or USER PROJECTED_PRESTRESS=1 SIG11=400.0 SIG22=400.0 SIG12=0.0 A_X=1.0 A_Y=0.0 A_Z=0.0 !AREA FOR THE DEFINITION OF THE PRESTRESS B_X=0.0 B_Y=1.0 B_Z=0.0 !VECTOR A AND VECTOR B DEFINE THE AREA
The possibility for oriented anisotropic prestress fields is foreseen, yet no distortion control as for the classical FEM Membrane1-element is implemented.
Tests and Benchmarks
The element Membrane_NURBS has successfully been applied in 3D in various geometrically non-linear static applications, as well as in form-finding.
Benchmark examples
- form-finding of a four-point sail with with B-Rep edge cables and elastic columns as supports: ..\examples\benchmark_examples\isogeometric\iga_formfinding_4point_with_trusses\cbm_4PointSailwTrusses.txt
- static geometrically non-linear analysis of a prestressed single-patch membrane with fixed boundaries: ..\examples\benchmark_examples\isogeometric\iga_membrane_nln_1\cbm_iga_membrane_nln_1.txt
References
- ↑ B. Philipp, M. Breitenberger, I. D’Auria, R.Wüchner, and K.-U. Bletzinger. "Integrated design and analysis of structural membranes using the Isogeometric B-Rep Analysis." In: Computer Methods in AppliedMechanics and Engineering 303 (May 2016), pp. 312–340. DOI: 10.1016/j.cma.2016.02.003.
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