FEA Procedure - loads, bc, solution

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Engineering | Finite Element Analysis | Stress

Value Design

Consulting

Apply Loads.

Some type of load is usually applied to the analysis model. The loading may be in the form of a point load, a pressure or a displacement in a stress (displacement) analysis, a temperature or a heat flux in a thermal analysis & a fluid pressure or velocity in a fluid analysis. The loads may be applied to a point, an edge, a surface or a even a complete body. The loads should be in the same units as the model geometry & material properties specified. In the cases of modal (vibration) & buckling analyses, a load does not have to be specified for the analysis to run.

Apply Boundary Conditions.

If you apply a load to the model, then in order to stop it accelerating infinitely through the computer's virtual ether (mathematically known as a zero pivot), at least one constraint or boundary condition must be applied. Structural boundary conditions are usually in the form of zero displacements, thermal BCs are usually specified temperatures, fluid BCs are usually specified pressures. A boundary condition may be specified to act in all directions (x,y,z), or in certain directions only. They can be placed on nodes, keypoints, areas or on lines. BC's on lines can be in the form of symmetric or anti-symmetric type boundary conditions, one allowing in plane rotations and out of plane translations, the other allowing in plane translations and out of plane rotations for a given line. The application of correct boundary conditions are a critical to the accurate solution of the design problem. At least one BC has to be applied to every model, even modal & buckling analyses with no loads applied.

Solution.

The FE solver can be logically divided into three main parts, the pre-solver, the mathematical-engine & the post-solver. The pre-solver reads in the model created by the pre-processor and formulates the mathematical representation of the model. All parameters defined in the pre-processing stage are used to do this, so if you left something out, chances are the pre-solver will complain & cancel the call to the mathematical-engine. If the model is correct the solver proceeds to form the element-stiffness matrix for the problem & calls the mathematical-engine which calculates the result (displacement, temperatures, pressures, etc.). The results are returned to the solver & the post-solver is used to calculate strains, stresses, heat fluxes, velocities, etc.) for each node within the component or continuum. All these results are sent to a results file which may be read by the post-processor.