Run-Time Functions Categories

The two major types of run-time functions are:

This section introduces you to the run-time functions categories as they appear in the Function Builder. For more details regarding each function, please see Run-Time Functions Examples.

Note that although some run-time functions have the same names as certain design-time functions, they only work with a model at an analysis-time step.

The following sections give you an overview of the run-time functions categories. The functions categories are presented in the order they appear in the Function Builder.

Displacement functions return scalar measures associated with a particular component of the translational displacement vector from one coordinate system marker to another or an angular displacement from one coordinate system marker to another.

You can use the displacement functions during a simulation to obtain from Adams the displacement measurements of an object. Displacement functions provide measurements that can be useful in:

The following table lists the names and definitions for the displacement functions:

Velocity functions return a requested magnitude or component of the translational or rotational velocity vector between two markers.

You can use the velocity functions during a simulation to obtain from Adams the velocity measurements of an object. Velocity functions provide measurements that can be useful in:

The following table lists the names and definitions for the velocity functions:

Acceleration functions return a requested magnitude or component of the translational or rotational acceleration vector between two markers.

You can use the acceleration functions during a simulation to obtain from Adams the acceleration measurements of an object. Acceleration functions provide measurements that can be useful in:

The WDT prefix used for angular acceleration functions implies or omega-dot, the time derivative of angular velocity.

The following table lists the names and definitions for the acceleration functions:

You can use contact functions to define collision forces. The functions are built so as to turn on and off during simulation, which makes them useful for representing bodies that come into intermittent contact with one another.

The following table lists the names and definitions for the contact functions:

Splining is a method of interpolation that allows derivation of intermediate locations on a curve or surface between known points.

You can use spline functions during a simulation to define smooth functions to approximately fit data points. Spline functions can be useful when:

The following sections provide more information about splines:

Interpolation Methods Overview

Adams View allows you to use three interpolation methods, as shown below:

The Akima interpolation is a local fit. Local methods require information only about points in the vicinity of the interval being interpolated to define the coefficients of the cubic polynomial. This means that each data point in an Akima spline only affects the nearby portion of the curve. Since it uses local methods, Akima is very fast.

Akima always produces good results for the value of the function being approximated. AKISPL returns good estimates for the first derivative of the approximated function when the data points are evenly spaced. In instances where the data points are unevenly spaced, the estimate of the first derivative may be in error. In all cases, the second derivative of the function being approximated is unreliable.

The cubic interpolation is a global fit. Global methods use all the given points to calculate all the coefficients for all the intervals in question, simultaneously. Therefore, each data point affects the entire cubic spline: if you move one point the whole curve changes accordingly, making a cubic spline wigglier and harder to force into a desired shape. This is especially noticeable on functions with linear portions or sharp changes in the curve. In these cases, a cubic spline will almost always have more wiggles than an Akima spline.

Both global and local methods work well on smoothly-curving functions.

CUBSPL, though not as fast as AKISPL, always produces good results for the value of the function being approximated, as well as its first and second derivatives. The data points don't have to be evenly spaced. The solution process often requires estimates of derivatives of the functions being defined. The smoother a derivative is, the easier it is for the solution process to converge.

Smooth (continuous) second derivatives are important if you use the spline in a motion. The second derivative is the acceleration enforced by the motion, which defines the reaction force required to drive the motion. A discontinuity in the second derivative means a discontinuity in the acceleration and therefore in the reaction force. This can cause poor solver performance or even failure to converge at the point of discontinuity.

The B-spline interpolation method is primarily designed to describe 3D geometric curves. Although the B-spline can be useful for geometric applications, you should use AKISPL or CUBSPL to construct most motions, forces, and other such entities.

The following table lists the names and definitions for the spline functions:

Force in object functions are used to return instantaneous force values generated by modeling elements.

The following sections further explain the force in object functions:

You can use the force in object functions during a simulation to obtain from Adams the force measurements due to constraints (such as joints and motions), compliant connections (such as spring-dampers and bushings), and applied forces (such as multiple-component general-equation force elements). The force in object functions provide measurements that can be useful in:

Most constraints have the following characteristics:

Most forces have the following characteristics:

In Adams, you can define force magnitudes in two ways:

When you define your own equations for force magnitudes, you have to tell Adams what the force depends on. For instance, a force could depend on the displacement between two coordinate system markers or their relative velocity or acceleration, or the force applied to a coordinate system marker by a constraint or force element.To help you define these dependencies, Adams offers you displacement functions (Displacement Functions), velocity functions (Velocity Functions), acceleration functions (Acceleration Functions), resultant force functions (Resultant Force Functions), as well as force in object functions.

Whenever you use the force in object functions, you must tell Adams how you want the force to be measured. You must specify:

In this example we'll calculate the force acting on a block located on an incline, as illustrated in body 1. Before working through this example, reference Six-component Force/Torque (GFORCE).

This example consists of a system defined as follows:

In this example, GFORCE is defined as: .

The GFORCE yields different results, as we change the arguments used:

The following table lists the names and definitions for the force in object functions:

Resultant force functions return either the net applied action and reaction force between two markers, or the net applied action-only forces at a marker.

Where to Find the Resultant Force Functions

The following table lists the names and definitions for the resultant force functions:

Math functions apply to scalar numbers or matrices. If you input a scalar, Adams returns a scalar. If you input a matrix, Adams returns a matrix.

The following table lists the names and definitions for the math functions:

Vector functions represent the class of functions that carry out vector operations. The following table lists the names and definitions for the Vector functions available through the Function Builder:

 

Data elements give you access to the values of states of generic system modeling entities.

The following table lists the names and definitions for the data elements available through the Function Builder:

The user-written subroutine invocation allows for values to be passed into subroutines that you create in order to define enhanced function expressions. Only certain modeling elements allow you to define them by way of your own customized subroutines. For more information about subroutines, see the guide, Using Adams Solver Subroutines.

The following table lists the name and definition for the user-written subroutine.

Constants and variables represent values that are frequently used to perform mechanical system simulation, such as time or conversion functions between angular units of radians and degrees.

The following table lists the names and definitions for the constants and variables:

User-supplied run-time functions are parameterized runtime functions that are defined by the user that contain an expression which is made up of a combination of design variables, system supplied functions, design time expressions and constants.

User-supplied run-time functions consist of an expression whose evaluated form will be used by the solver at the time of simulation.

You can create these functions via Adams View command language, using the "runtime_function create" command. Alternatively, you can create them using the Function Builder in runtime mode. During creation you must specify the text of the run-time function and optionally the parameter names. When you use these functions, Adams substitutes the user parameters (if any) into the function text in place of the parameter names.

For example:

 

In the example above, P1 and P2 are the formal arguments to the function runtime_func__1.

We can apply above function on sforce.

For Example:

 

One can also use an Adams ID instead of the full object name.

For Example:

Adams expands the expression by replacing the arguments for the formal parameters before exporting to an Adams Solver dataset (.adm file) or passing to Adams Solver from Adams View.

For Example:

Exporting an .adm file, the above runtime_func__1 applied to sforce_1 will be expand like so in the .adm file:

Therefore, like other forms of design-time model parameterization, the parametrized version of the expression can only be found in the Adams View representation of the model.

You can create user-written run-time functions using the function builder. The function builder launched from two ways:

After creating run-time function, you can view it Model browser:

Elements → Functions