Static body-load

Background

Represent a body/volume force that is applied on an Element object. This force is represented by a constant magnitude and direction that is applied on the element. The Load object created in this manner is transformed in the element level using its volume into node forces and then assemble directly to the global force vector. The static body load direction needs to coincide with the global coordinate system.

REFERENCE:

• Bathe K. Jurgen, "Finite Element Procedures", Chapter 4: pages 161-166, Table 4.3, Prentice-Hall, 1996.

Pre-Analysis

The python Pre-Analysis in the 01-Pre_Process/Method/Attach.py file provides with an interface to create a STATIC BODY LOAD. For example, to create a Static body-load using json format, use:

• addLoad(tag, name, attributes):

  • tag : The identifier of this load, i.e., tag > -1
  • name : The Seismo-VLAB load class name, in this case 'ElementLoad'.
  • attributes : Specific properties for the created load, for example
    • 'fun' : The function identifier
    • 'list' : The identifier of the elements where this load acts upon
    • 'type' : The type of element load, in this case 'Body'.

  Example

  A STATIC BODY LOAD can be defined using the python interface as follows:
  SVL.addLoad(tag=1, name='ElementLoad', attributes={'fun': 1, 'type': 'Body', 'list': [1,2,3,4,5]})

The information required to define the magnitude and direction of this Load is provided in the attributes['fun'] identifier. Thus, to create a CONSTANT FUNCTION using the json format, use:

• addFunction(tag, name, attributes):

  • tag : The identifier of this function, i.e., tag > -1
  • name : The Seismo-VLAB function class name, in this case 'Constant'.
  • attributes : The constant function information
    • 'dir' : The direction of the acting function
    • 'mag' : The magnitude of the load

  Example

  A CONSTANT FUNCTION can be defined using the python interface as follows:
  SVL.addFunction(tag=1, name='Constant', attributes={'mag': 10.00, 'dir': [0.0, 0.0, -1.0]})
  

Application
Please refer to the I05-ST_Lin_3DBodyLoad_Elastic_Hexa8.py file located at 03-Validations/01-Debugging/ to see an example on how a STATIC BODY LOAD and its CONSTANT FUNCTION are defined.

On the contrary, the 01-Pre_Process/Method/Remove.py file provides with an interface to depopulate the Entities dictionary. For example, to remove an already define Load, use:

• delLoad(tag):
  • tag : The identifier of the load to be removed, i.e., tag > -1

Now, to remove a already defined function, use:

• delFunction(tag):
  • tag : The identifier of the function to be removed, i.e., tag > -1

Run-Analysis

The C++ Run-Analysis in the 02-Run_Process/05-Loads/Load.cpp file provides the class implementation. A STATIC BODY LOAD is defined inside the "Loads" json field indicating its "Tag" as follows,

• {
      "Loads": {
          "Tag": {
              "name" : "ELEMENTLOAD",
              "attributes": {
                  "name": "CONSTANT",
                  "type": "BODY",
                  "mag": double,
                  "dir": [ ],
                  "list": [ ]
              }
          }
      }
  }
  

  Variable	Description
  Tag	Unique load object identifier.
  mag	Magnitude/intensity of the applied force, traction or body load.
  dir	Vector containing the direction of the force.
  list	List of Element identifiers that share this load.

  
  

  Attention

  Body forces are applied to the specified elements only if the material has density.

  Example

  A 2D gravitational STATIC BODY LOAD applied on elements 1,3,5, and 7:
  { "Loads": { "1": { "name" : "ELEMENTLOAD", "attributes": { "name": "CONSTANT", "type": "BODY", "mag": 9.80, "dir": [0.000, -1.000], "list": [1,3,5,7] } } } }