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コンポーネントの方程式

カスタム コンポーネントの動作を表す式の作成

言語構文

assertProgram customized run-time errors and warnings
delayReturn past value of operand
derReturn time derivative of operand
equationsDefine component equations
functionReuse expressions in component equations and in member declarations of domains and components
integPerform time integration of expression
intermediatesDefine intermediate terms for use in equations
tablelookupReturn value based on interpolating set of data points
timeAccess global simulation time
valueConvert variable or parameter to unitless value with specified unit conversion

トピック

Defining Component Equations

The equation section of a Simscape™ file is executed throughout the simulation. The purpose of the equation section is to establish the mathematical relationships among a component’s variables, parameters, inputs, outputs, time and the time derivatives of each of these entities.

Simple Algebraic System

This example shows implementation for a simple algebraic system:

Use Simulation Time in Equations

You can access global simulation time from the equation section using the time function. time returns the simulation time in seconds.

Using Conditional Expressions in Equations

You can specify conditional equations by using if statements.

Using Intermediate Terms in Equations

Textbooks often define certain equation terms in separate equations, and then substitute these intermediate equations into the main one. For example, for fully developed flow in ducts, the Darcy friction factor can be used to compute pressure loss:

Using Lookup Tables in Equations

You can use the tablelookup function in the equations section of the Simscape file to interpolate input values based on a set of data points in a one-dimensional, two-dimensional, or three-dimensional table. This functionality is similar to that of the Simulink® and Simscape Lookup Table blocks. It allows you to incorporate table-driven modeling directly in your custom block, without the need of connecting an external Lookup Table block to your model.

Programming Run-Time Errors and Warnings

Use the assert construct to implement run-time error and warning messages for a custom block. In the component file, you specify the condition to be evaluated, as well as the error message to be output if this condition is violated. When the custom block based on this component file is used in a model, it will output this message if the condition is violated during simulation. The optional Action attribute of the assert construct specifies whether simulation stops when the predicate condition is violated, continues with a warning, or ignores the violation.

Simscape Functions

Use Simscape functions to reuse expressions in equations and member declarations of multiple components.

Import Symbolic Math Toolbox Equations

Example of using Symbolic Math Toolbox™ software to solve the physical equations, generate code in the format appropriate for the Simscape language equation section, and incorporate the generated code into the equation section of a component file.