Introduction

StressCheck permits users to define practically any model input (e.g. hole diameters, node offsets, elastic moduli, load magnitudes) in terms of alphanumeric, case-insensitive variable names (i.e. parameters). Parameters are ideal for quickly assessing the sensitivity of results to model design changes, and provide flexibility to automation and standardization of solutions.

Additionally, relational rules may be defined for one or more parameters to prevent undesired combinations of parameter values.

Parameters

To access the Parameters pane, click the Edit Parameters icon , click the Parameters tab, or open the Edit drop-down and click “Parameters”. The Parameters pane provides for the definition and modification of parameters used in the construction of a StressCheck model. The parameter is assigned a Name, a Description, a default Value, a Limit test, a Class (General, Property or B. Cond.), and a Label. Optionally, instead of a default value, the parameter may be assigned an Expression which references other parameters and/or intrinsic functions in order to obtain a value (for example, parameter “Dh” is defined by the expression “Do+2*th” in Figure 1):

Defining a New Parameter

To define a new parameter, simply enter the following information:

• Name: The name to be assigned to the parameter. Avoid using an underscore (“_”) as the first character of the parameter name. An underscore indicates a reserved parameter name used to enable specific functionality.
• Description: Details on the parameter purpose and usage.
• Expression: A parameter may be assigned a value directly or defined in terms of StressCheck’s intrinsic functions or other parameters. If a parameter is to be defined in terms of other parameters, the value will be computed automatically. Care should be taken not to create a circular definition, i.e. making the parameter depend indirectly on itself.
• Value: The value assigned to the parameter.
• Limit: If the value of a parameter should be limited to a specific range in order to properly maintain the integrity of the model, it is possible to supply limits for the parameter value. Simply enter the limits using relational operators, e.g. >0, <=7, etc. If two limits are required they may be separated by a comma.
• Class: Three options are available: Boundary Condition (B. Cond.), Property and General. These options are filters to organize parameters. Note: parameters used in the Nonlinear Events dialog must be class B. Cond.
• Label: an optional alphanumeric identifier.

Once all parameter information has been entered, click the Accept button.

The below animation demonstrates the creation of a constant parameter (“a”), a trigonometric expression-based parameter (“b”), and a relational parameter dependent on “a” and “b” (“c”):

Parameter Name Limitations

The parameter name may be a string of up to 15 characters, must begin with an alphabetic character, and must not contain any arithmetic or special symbols. Parameters which begin with an underscore (_) are considered special parameters to be used in StressCheck to activate certain advanced features. The following rules apply to parameter names:

• Parameter name should not be a coordinate name (X, Y, Z, R, T, P).
• Parameter name should not be E followed by a number, e.g.: E0, E1, E2, …
• Parameter name should not be C followed by a number, e.g.: C0, C1, C2, …C10.
• Parameter name must not begin with a digit, or contain a special symbol (! # $ % & ; : , . ? + – * / ‘ @ { } ( ) [ ] = ~ ^ | \ ”).
• Parameter name must be distinct from intrinsic functions (SIN, COS, TAN, ATAN, DEG, RAD, SQRT, SINH, COSH, TANH, ASIN, ACOS, ATAN, LOG10, LOG, EXP, ABS, ATAN2, MOD, MIN, MAX, IF, PFIT).

NOTE: When a parametric expression is used in an input field, the length of the expression is limited. If your expression exceeds the length limitation of a given input field, you may use a formula definition to represent the expression and reference the formula from the parametric input field. Define a formula with the desired expression, then enter the name of the formula in the input field preceded by a pipe symbol (|) as shown in Figure 2:

It should also be noted that formulas that are preceded by a the pipe symbol may not reference spatial variables within the expression (i.e. x , y, z).

Reserved Parameters

StressCheck provides special parameters for user control of some advanced program features. All internal parameters begin with an underscore (“_”), so that they will not be confused with your own parameters used, for example, as design variables.

Sorting Parameters

To sort the parameters alphanumerically or by value, left click on the desired column header (e.g. Name, Value) and arrows will appear to indicate if the column data will be sorted in ascending or descending order. Clicking on the column header again will reverse the sorting direction. In Figure 3, parameter names were sorted alphanumerically in descending order:

Modifying Parameters

To modify a parameter value, simply enter the new value in the corresponding input field and press the TAB key to advance to the next field or the ENTER key to advance to the next parameter. When a parameter is changed StressCheck will not update the model until you click the Accept button.

The exception to this is if you enable Auto Step and increment or decrement the parameter value by clicking the up/down arrows that will appear next to the current parameter value in the Value column; this will automatically update the model.

Note: if the change in parameter value produces an invalid model configuration, an error message will be displayed and the model will automatically be reverted to the previous configuration.

Parameter Settings

The current parameter values may be saved as a “configuration” record by enabling the Settings button, entering a name for the parameter record setting, and clicking the Save button shown in Figure 4:

To recall a parameter record setting, select the name of the parameter record setting from the “Name:” combo-box. To delete the selected parameter record setting, click the Delete button. To purge all parameter record settings, click the Purge button.

This mechanism is also available in the Design Study solver and is useful for preserving various configurations of a model that have been evaluated and may need to be recalled later for further study. StressCheck automatically saves the last valid set of parameters in a configuration called “_Input_Save” in the Settings subtab, so that you can go back to them anytime.

Using Parameters

To use a parameter as a model input (e.g. system location, cylinder radius, node offset, formula definition, load assignment, etc.) or when extracting results (e.g. integration radius, independent variable), simply enter the parameter name in the input field (or begin typing the parameter name and select it from the autofill options, as shown in Figure 5):

Tip: to display a list of currently defined parameter names, hold ALT+P while the input field is in focus (Figure 5). The below animation demonstrates the usage of a parameter to define a blend radius:

TLAP Scaling

Users have the option to apply parametric scaling to TLAP loads. This functionality is implemented such that all TLAPs under a single Case ID will be uniformly scaled (i.e multiplied) by the current value of a scaling parameter. The scaling parameter may be any parameter defined within the model. It is selected using the Scaling Parameter dropdown on the Point Load Case Definitions dialog (Figure 6):

For more information, refer to Total Load at a Point (TLAP) Implementation.

Nonlinear Events

When performing material nonlinear solutions via incremental plasticity theory (IPT), the user has the option to define parameter-driven nonlinear events/steps in the Nonlinear Events pane. Note that parameters must defined in the Parameters pane as Class “B. Cond.” to be accessed in the Nonlinear Events pane’s Parameter column (Figure 7):

For more information, refer to Nonlinear Events Overview.

Design Study Solver

When performing design study solutions via the Design Study solver, the user has the option to activate one or more parameters to be increased/decreased from an initial value to a final value over a series of steps (Figure 8):

Once the design study solution is complete, all solution steps for each parameter increment will be available for results processing.

For more information, refer to Design Study Overview.

Parameter Dependencies

If a parameter name has been used in the definition of one or more model inputs (e.g., bodies, points, nodes, formulae, material definitions, loads, constraints, etc.), clicking on the parameter name in the Name column and then enabling the Dependencies button will return a comma-delimited list of parameter dependencies (Figure 9):

Selecting a new parameter name will automatically refresh the parameter dependency list.

Exporting/Importing Parameters

Parameters may be exported/imported (as .par files) using the File > Export and File > Import options, respectively. If StressCheck detects that an imported parameter name already exists, the user will have the option to ignore or overwrite the parameter row.

For more details, refer to Importing Model Inputs.

Deleting Parameters

After clicking on a parameter name, the entire row will be selected and the Delete button may be used to remove the selected parameter. Note: an error will occur if that parameter has any dependencies.

Rules

The Rules pane allows the user to define relationships between parameters which will be enforced each time new values are assigned to parameters. To access the Rules pane, click on the Rules tab or open the Edit drop-down and click “Rules” (Figure 10):

A rule is composed of a relational expression (parameter names, arithmetic operations and logical operators) and a message that will be issued if the expression is false. For example, the first rule in the above image shows the relational expression “Lo > 5*Li”:

• If Lo is greater than 5*Li, the error message will not appear and the parameter(s) will be updated.
• If Lo is less than or equal to 5*Li, the error message “Lo must be > 5*Li” will appear and the parameter(s) will be returned to their previous values.

To update the list of rules, click the Update button.