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How to Set Up Physics Constraints Using OnScale Solve™

By Ananth Sridhar 20 November 2020

This is part of a series of articles on “Getting Started” with OnScale Solve™ . In this article, we discuss the ways and methods to set up physics constraints using OnScale Solve for different types of analysis.

As with all numerical analysis an improper definition of a model setup will lead to erroneous results. With OnScale Solve, we tackled this problem by building in guard rails to help users complete the model setup correctly.

The model setup begins with an imported CAD file. The Modeler tab includes a Quick Guide that directs the user to import a CAD file either from a local directory or directly from Onshape. Materials are then assigned to the various parts in the model.

The next step in the model building process is assigning the required boundary conditions, i.e., loads and constraints. This is done in the Physics tab. Because constraints are required for every model, a Help window appears on the right side of the screen to notify users when no constraints have been defined.

OnScale SolveConstraints are applied consistent with the type of analysis being performed. At this time, OnScale Solve supports static mechanical analysis, steady-state thermal analysis, and static thermomechanical analysis. The physics constraints available for each type of analysis are described below.

Mechanical Analysis

Mechanical analysis is implied when the user applies either loads (forces, pressures, or tractions) or imposed displacements to a model. This kind of analysis requires one or more of the following boundary conditions to be specified:

General Restraint

Surfaces can be restrained from displacing in any of the global directions. The option to apply restraints can be found on the mechanical boundary condition toolbar, identified by the wrench icon.

Physic Constraints

 

When a new restraint is defined, blue “lock” icons are used as a toggle to restrain a surface in a particular direction. Depending on the combination of directions selected, the user may define the following conditions:

Fully fixed – The surface is restrained in all directions. No translation is allowed. This is the default option.

Restraint

 

Slider X – This option restrains the motion along the Y- and Z- directions while allowing the surface to “slide” along the X-direction.

Physic Constraints
Slider Y
– This option restrains the motion along the X- and Z-directions while allowing the surface to “slide” along the Y-direction.

Physic Constraints

Slider Z – This option restrains the motion along the X- and Y- directions while allowing the surface to “slide” along the Z-direction.

 

Contraint

Restraint X – This option restrains the motion only along the X-direction, allowing the face to move in the YZ-plane.

Physic Constraints

Restraint Y – This option restrains the motion only along the Y-direction, allowing the face to move in the XZ-plane.

Physic Constraints

Restraint Z – This option restrains the motion only along the Z-direction, allowing the face to move in the XY-plane.

Physic Constraints

Symmetry Constraint

For symmetric models, it is often convenient to model only one half of the model and apply a symmetry constraint to the plane of symmetry. As with other mechanical boundary conditions, this option is found on the mechanical boundary condition toolbar, identified by the wrench icon.

Symmetry Constraint

Note that this constraint is functionally equivalent to the Restraint X, Restraint Y, and Restraint Z options described above. The main difference, however, is that the symmetry constraint offers the option to plot the model mirrored across the symmetry plane. For example, the image below shows a model of a plate with a hole modeled in quarter-symmetry. The CAD model as imported into Solve is shown in grey. The translucent blue regions represent the equivalent or virtual full model obtained by using symmetry planes.

 

Symmetry Physic Constraints  

 

Displacement Constraint

While the Restraint option prevents surfaces from displacing, the Displacement option allows the user to impose a specified displacement on a surface. This option is also found under the mechanical/wrench icon. Both displacement constraints and fixed restraints, described above, can be used in the same model, but not on the same surfaces.

Displacement Constraint

 

The blue “lock” icon can be used as a toggle to either impose a specific displacement along a specific axis or “unrestrain” a particular axis.

Displacement

Thermal Analysis
A thermal analysis is implied when the user applies thermal loads via the Heat Flux or Power boundary conditions. This kind of analysis requires one or more of the following physics constraints to be used:

Convection Constraint

OnScale Solve allows for defining convection coefficients on the faces of the imported geometry. This option is also found under the thermometer icon.

Convection Contraint

The Convection property window requires the user to specify a reference temperature. Selecting the default option of “Ambient” specifies a temperature of 20° C. Alternatively, a custom temperature may be specified if more appropriate. A heat transfer coefficient must be defined in the Convection Coefficient field, in units of W/(m2-°C).

Convection

Temperature Constraint

Depending on the selection, temperature loads can be assigned to entire parts or faces of the geometry. This option can be found under the thermometer icon. The default unit of temperature is Celsius.

Temperature Contraint

Thermomechanical Analysis

The physics constraints for thermomechanical analysis depends on the individual constraints defined for the mechanical and thermal loads. Once the necessary conditions are met for each physics independently, OnScale Solve will allow the users to run a thermomechanical analysis.

For more information, check out our other resources:

1) Introducing OnScale Solve Webinar

2) Key Features and Enhancements

3) Guided Video Tour, from login to simulation

4) OnScale Solve Simulation Details

Ananth Sridhar
Ananth Sridhar

Ananth Sridhar is an Application Engineer at OnScale. As part of our engineering team he assists with developing applications, improving our existing software and providing technical support to our customers.