6.4. Gravity Analysis

modeller.do_gravity_analysis(nG=100, ansys_soe='UmfPack', constraints_handler='Transformation', numberer='RCM', test_type='NormDispIncr', init_tol=1.0e-6, init_iter=500, algorithm_type='Newton', integrator='LoadControl', analysis='Static')[source]

Perform a gravity analysis on a multi-degree-of-freedom (MDOF) system in OpenSees.

This method sets up and runs a gravity analysis using specified parameters for various analysis objects in OpenSees. The gravity analysis solves for the static equilibrium of the system under self-weight loads (e.g., gravity loads).

Parameters:

  • nG (int, optional) – Number of gravity analysis steps to perform. Default is 100.

  • ansys_soe (string, optional) – The system of equations type to be used in the analysis. This defines how the system of equations will be solved. Default is ‘UmfPack’ (sparse direct solver).

  • constraints_handler (string, optional) – The constraints handler determines how the constraint equations are enforced in the analysis. It controls the enforcement of specified values for degrees-of-freedom (DOFs) or relationships between them. Default is ‘Transformation’ (transforming the constrained DOFs into active ones).

  • numberer (string, optional) – The degree-of-freedom numberer defines how DOFs are numbered. This is important for system efficiency in solving. Default is ‘RCM’ (Reverse Cuthill-McKee, a reordering algorithm).

  • test_type (string, optional) – Defines the test type used to check the convergence of the solution. It is used in constructing the LinearSOE and LinearSolver objects. Default is ‘NormDispIncr’ (norm of displacement increment).

  • init_tol (float, optional) – The tolerance criterion for checking convergence. A smaller value means stricter convergence. Default is 1.0e-6.

  • init_iter (int, optional) – The maximum number of iterations to check for convergence. Default is 500.

  • algorithm_type (string, optional) – Defines the solution algorithm used in the analysis. Common options are ‘Newton’ (Newton-Raphson) for solving the system of equations. Default is ‘Newton’.

  • integrator (string, optional) – Defines the integrator for the analysis. The integrator dictates how the analysis steps are taken in time or load. Default is ‘LoadControl’ (control load increments).

  • analysis (string, optional) – Defines the type of analysis to be performed. ‘Static’ is typically used for gravity analysis, but other options (e.g., ‘Transient’) can be used depending on the type of analysis. Default is ‘Static’.

Return type:

None.

Notes

  • This method sets up the analysis using OpenSees by defining the system of equations, constraints handler, numberer, convergence test, solution algorithm, integrator, and analysis type.

  • The gravity analysis solves for the static equilibrium under self-weight or gravity loads and is typically used to determine the initial equilibrium state of a structure before dynamic loading.

  • The analysis can be modified by changing the parameters to adjust solver settings, tolerance, and other relevant options.

  • After the analysis is completed, the analysis objects are wiped to ensure a clean state for further analyses.