About Measures
A measure lets you investigate several predefined and user-defined characteristics of your model during or after a simulation. For example, you can use a measure to find the angle between two links connected by a revolute joint, the x component of relative velocity between two parts, and more.
The following explain more about measures:
Types of Measures
There are two types of
Measures available:
■Predefined measures that automatically output information.
■User-defined measures that you define to obtain more specific information about your model.
Predefined Measures
This type of measure: | Lets you capture and investigate: |
|---|
| Characteristics of the parts, forces, and constraints in your model. |
| Characteristics of a point, such as its location relative to the global coordinate system or the sum of forces acting on it. |
| Kinematic characteristics of a point relative to another point, such as the relative velocity or acceleration. |
| The orientation of one marker with respect to another marker using a variety of known schemes, such as successive rotations, Euler parameters, direction cosines, and so on. |
| The included angle defined by three points in space. |
| Statistical characteristics of another measure, such as its maximum, average, and more. |
User-Defined Measures
This type of measure: | Lets you capture and investigate: |
|---|
| A design expression that you want Adams View to evaluate before or after a simulation. |
| A function expression that you want Adams Solver to evaluate during a simulation. |
Ways to Use Measures
You can use
measures in a variety of ways. You can use measures to:
■Plot system characteristics during a
Simulation. Because Adams View computes most measures during a simulation, you can monitor their values in strip charts to view them as the simulation progresses.
■Plot characteristics after a simulation.
■Define other elements. For example, you can use a measure as an expression in a force definition.
■Create user-defined expressions that take advantage of both the Adams View and Adams Solver environments.
Limitations of Measures
The following are limitations to using
measures:
■Many characteristics in measures are computed from the last
Simulation of the model. If you change your model after running a simulation, the characteristics will no longer be correct. You need to simulate the modified model again.
■You cannot include Adams View computed measures in an Adams Solver run-time function expression. Only Adams View can process computed measures.
■Only
Adams Solver can evaluate Adams Solver computed measures. Therefore, you must define an Adams Solver computed measure before you run a simulation. Adams View cannot evaluate the measure after a simulation.
Measure Reference Frames and Coordinate Systems
Reference Frames
When you define a velocity or acceleration measure, be sure to pay close attention to the motion reference frame you use in defining the measure. The motion reference frame specifies the observer relative to whom time-derivatives are performed.
Measure Coordinate Systems
There are two coordinate system options that you specify when you create a measure:
■Type of coordinate system in which location coordinates can be described. You can use any of the three standard coordinate systems:
Cartesian,
spherical, and
cylindrical.
■The coordinate system in which vector components are expressed. The global coordinate system is used by default.
Using Measures in Definition of Model
You can use a
measure in the definition of your model. For example, you can create two measures that define a spring force (for example, Fk) and a damping force (for example, Fc), respectively. These two measures, when combined to define the
Single-component force element, actually create the equivalent of an Adams spring-damper. The use of the measures and the single-component force, however, provides a few advantages not available with the linear spring-damper. Because you used measures in your model, you can:
■Automatically see the measures displayed in strip charts during
Simulation and subsequent animations.
■Plot the measures in Adams PostProcessor after a simulation.
■Plot the individual effects of the spring force and the damping force. A linear Adams View spring-damper element shows the combined effects of both forces, and it is very difficult to determine how much the spring and damping forces contribute individually to the total force.
To use a measure in the definition of your model:
■In a text box that accepts a function expression, create an expression that uses the measure in its definition.
For example, to use the two measures explained above in the definition of a single-component force, you would select Custom as you create the force and then modify the force by entering a function expression, such as:
.model_1.FUNCTION_MEA_Fk + .model_1.FUNCTION_MEA_Fc
You can use the Function Builder for assistance in building the expression.
Measures in Adams Solver Datasets
How Measures Are Represented in a Dataset
Adams Solver represents measures in
Adams Solver dataset files as algebraic state variables or VARIABLE statements. Adams Solver does not differentiate these variables from any other user-defined algebraic state variable. If you export your model to an Adams Solver dataset file, Adams View defines the measures as VARIABLE statements. Therefore, when you import your dataset file back into Adams View, Adams View no longer recognizes the original measures, but, instead, recognizes them as generic algebraic variables.
We recommend that you use
Adams View command files to archive your Adams View models that contain measures.
Measures Not Represented in Datasets
There are three kinds of measures that are currently not represented in an Adams Solver dataset file:
■Pressure angle associated with point-on-curve constraints.
■Power consumption associated with motions.
If you export your model to an Adams Solver dataset, and then import it back into Adams View, you lose the associated measure information. We recommend that you use command files to archive models that contain measures.