Analysis Wizard : MASIL
Modal dynamic analysis using MASIL is a feature that will be available in a future release of GSA. Please reach out to Oasys if you are interested in trying it out in the meantime.
For both a 'MASIL' and 'MASIL P-delta' analysis the user is brought to this page.
Definition
Target Mass Participation
Specify the target effective mass participation in each of the global x, y and z direction. The solver will attempt to capture the significant modes which when aggregated give the target participation.
Limit Maximum Number of Modes
When the analysis commences GSA needs to allocate space for result sets. This sets a maximum number of analysis cases that can be populated by the MASIL solver. If analysis cases are not required they will remain empty.
Limit Maximum Frequency
Capturing the target effective mass may require the solution of modes at very high frequencies. These are unlikely to be significant for dynamic response calculations so it can be convenient to set a frequency limit. The solution will stop once this limit is reached.
Mass Option
This specifies how the mass of the elements is to be included in a dynamic analysis, the following three options are available:
- Lumped mass at nodes - in this option, the total element mass is assigned to the nodes of the element and form the element mass matrix, the proportion of the total mass at each node depends on the length (1D element), area (2D element) or volume (3D element) covered by the nodes for 1D, 2D and 3D elements respectively, e.g. the two nodes of a beam element will each have half of the total mass of the element, the 4 nodes of a rectangular Quad4 element will each have 1/4 of the total mass of the element. The element mass matrix from this option is a diagonal matrix, this option should be used in most cases unless local vibration modes of the elements are interested.
- Calculate mass from the element shape function - in this option, the element mass matrix, called consistent mass matrix, will be calculated using the same shape function for element stiffness matrix calculation. The principle of this method is that the work done by the inertia forces of the distributed mass within the element is the same as the work done by the inertia forces of the calculated nodal masses are equal. The element mass matrix from this option is not diagonal. This option is normally used if element local vibration modes are interested
- Ignore element mass except for nodal mass - if this option is selected, the mass of all elements except explicitly defined nodal masses will be ignored in the dynamic analysis. The nodal masses will be always considered in modal dynamic analysis
A scale factor can be applied to modify the element masses. This is typically used to increase the mass to allow for connections.
Mass Derived from Loads
In addition to the mass of the elements, extra mass can be inferred from loads (Case definition) applied in a particular Direction, with a Scale factor if required. This is used where “dead loads” have been applied to the structure which represent mass in the real structure. Only externally applied forces are included; the effect of gravity (i.e. self weight) is taken into account by the mass option.
P-delta Case
This option is only present if a “modal dynamic p-delta” analysis has been requested.
This is the basis on which the geometric stiffness is calculated. This can either be a load description (e.g. 1.2L1 + 1.2L2) or an analysis or combination case (e.g. A3 or C4). When a load description is specified, GSA first analyses the structure under this load and generates a geometric stiffness from the resulting forces/moments. When an analysis or combination case is specified the geometric stiffness is constructed from the results in this analysis or combination case. Combination cases can only be simple combination cases (i.e. of the form )
Calculate modal (material) damping
If a damping value has been specified in materials used by elements in the analysis, this will calculate the resulting damping effect due to the various materials. Note that if only a single material is used in the model then the modal damping will be equal to the material damping.
MASIL is a feature that will available in a future release of GSA. Please reach out to Oasys if you are interested in trying it out in the meantime.
Advanced options
For advanced options on dynamic analysis see