After you enter the variables for the mesh and analysis of your design model, you can specify the type of analysis you want to run with the properties and conditions you specified.
FE Analysis/Stress offers several types of analyses to choose from: Linear Static, P-Linear Static, Linear Static H-Adaptive, Modal, P-Modal, Linear Buckling, and Steady-State Thermal Analysis.
Linear Static Analysis is used to find the stress and displacements of a structure with a given set of loads and constraints.
Linear static analysis represents the most common type of analysis. The term "linear" means that the computed response, displacement or stress, for example, is linearly related to the applied force. The term "static" means that the forces do not vary over time or that the time variation is insignificant and can be safely ignored.
An example of a static force is a building's dead weight, which is comprised of the building's weight plus the weight of the offices, equipment, furniture, etc. This dead load is often expressed in terms of lb/ft2 or N/m2. Such loads are often defined using a maximum expected load with some factor of safety applied for conservatism.
The static equation is:
[K]{u}=(f)
• K = system stiffness matrix (generated automatically by Creo Elements/Direct Finite Element Analysis)
• u = vector of displacements computed by Creo Elements/Direct Finite Element Analysis
• f = vector of applied forces (which you specify)
Once the displacements are calculated, Creo Elements/Direct Finite Element Analysis uses these to compute stresses, reaction forces, and strains.
Linear Buckling Analysis is used to find the multiplication factor for the load that will make a structure buckle, and to find the shape of the buckled structure.
In a linear static analysis, a structure is assumed to be in a state of stable equilibrium. As the applied load is removed, the structure is assumed to return to it's original undeformed position. Under certain combinations of loadings, however, the structure continues to deform without an increase in the magnitude of loading. In this case, the structure has become unstable; it has buckled. For a linear buckling analysis, it is assumed that there is no yielding of the structure and the direction of the applied forces does not change.
In a buckling analysis, we solve for the eigenvalues. These are the scale factors that multiply the applied load in order to produce the critical buckling load. In general, only the lowest buckling load is of interest, since the structure will fail before reaching any of the higher order buckling loads. Therefore, usually only the lowest eigenvalue needs to be computed.
The buckling equation is:
[ K + E1 Kd ] = 0
Where:
• K= stiffness matrix
• Kd= differential stiffness matrix
• E1= the eigenvalues to be calculated
Once the eigenvalues have been computed, the critical buckling load is then solved:
Pcr1 = E1Pa
Where:
• Pcr1 = critical buckling loads
• Pa= applied loads
• E1= the eigenvalues to be calculated
Again, only the lowest critical buckling load is of interest.
Modal Analysis is used to find the natural frequencies and mode shapes of a structure.
A modal analysis (also known as natural frequency or vibration analysis) computes the natural frequencies and mode shapes of a structure. The natural frequencies are the frequencies at which a structure will tend to vibrate if subjected to a disturbance. For example, the strings of a piano are each tuned to vibrate at a specific frequency. The deformed shape at a specific natural frequency is called the mode shape.
A vibration analysis forms the foundation of a thorough understanding of the dynamic characteristics of the structure.
Some of the reasons a vibration analysis is performed include:
• To assess the dynamic interaction between a component (such as a piece of rotating machinery) and its supporting structure.
If the natural frequency of the supporting structure is close to an operating frequency of the component, there can be significant dynamic amplification of the loads.
• To assess the effects of design changes on the dynamic characteristics.
• To assess the degree of correlation between modal test data and analytical results.
In a vibration analysis, the eigenvalues and eigenvectors of the model are computed. For each eigenvalue, which is proportional to a natural frequency, there is a corresponding eigenvector or mode shape.
Each mode shape is similar to a static displaced load in that there are displacements and rotations for each node. The major difference between the mode shape and the static displacements is the scaling. In a static analysis, the displacements are the true physical displacements due to the applied loads. Since there is no applied load in a vibration analysis, the mode shape components can be scaled to an arbitrary factor.
• P-Linear Static analysis is the same as Linear Static Analysis but uses adaptivity with p-elements (better curved geometry and mathematical representation).
• Linear Static H-Adaptive analysis is the same as Linear Static Analysis but uses adaptivity with h-elements (element size reduced and number of elements increased).
• P-Modal analysis is similar to Modal Analysis but uses adaptivity with p-elements (better curved geometry and mathematical representation).
• Steady-State Thermal Analysis analysis is used to analyze, temperature distribution, and heat flux within a part.