ansys 14 structural mechanics rigid body dynamics

2011 ANSYS, Inc. November 22, 2011

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Rigid Body Dynamics 14.0 Deep Dive

Jean-Daniel Beley

September 2011


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Agenda

System level analysis using Simplorer-RBD co-simulation

Advanced user control using command snippets


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Advanced User Control Using Command Snippets

Example: Torque Limiter


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Motivation

RBD Command snippets based on the Python language allow representation of complex relationships between joints, help create new load conditions and provide results export.


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A torque limiter is an automatic device that protects mechanical equipment, or its work, from damage by mechanical overload

It couples motion as long as motion is less than the threshold

It uncouples as soon as the threshold has been reached

Example: Torque Limiter


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Grounded on one side

Simulation Model

Revolute joint for the Torque Limiter

Increasing torque applied by varying the weight location


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Coupling can be included using a zero velocity joint condition on the revolute joint

BUT joint conditions can only be activated / deactivated by (time-triggered) load steps

Time of uncoupling is not known a priori under complex loading conditions

Command snippets can help you defining more general conditions!

Overcoming Limitations with Snippets


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First we need to instrument the model, to measure the torque in the limiter.

This is done in a command snippet on the joint node in the tree

Example: Torque Limiter model


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Measures are created. These measures can be seen as Sensors capable of capturing

some values on the model over time

These sensors need to be added to the model

Here, we extract the Euclidean norm (norm 2) of the torsional torque on the ground side

Example: Torque Limiter model Model instrumentation


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We create a zero-velocity condition (driver) on the revolute joint, active only if the torque sensor delivers a value smaller than the limit

Note that the command snippet is not unit dependent.

Example: Torque Limiter model Coupling condition


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Similarly, a constant torque is applied in the revolute joint, when the torque limiter is uncoupled.

Example: Torque Limiter model Uncoupled state


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Example: Torque Limiter model Result

Python commands could also be used here to extract / export these results to other applications (Excel post processing, fatigue analysis,)


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System Level Analysis Using Simplorer-RBD Co-simulation

Examples: Landing Gear & Robotic Arm


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Include realistic control / command with a rigid dynamic system Using Simplorers large library of hydraulic, electric,

electronic components

Include realistic mechanical models as part of a system level simulation Rigid dynamics is highly non-linear. No reduced order

models can be created

Leads to higher fidelity models and lets you optimize the overall system

Motivation


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Example 1: Hydraulic command of a landing gear

Rigid Dynamics Model Simplorer Model

System level analysis using RBD Simplorer co-simulation


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RBD Model and Simplorer Model are link via PINS

These PINS are defined directly from the Mechanical Window

They are attached to joint degrees of freedom

Pins are input (Simplorer will feed the value to RBD) or output (RBD will feed the value to Simplorer

Typically, the same joint will have one input pin and one output pin

Here, the hydraulic cylinder translational joint hold an input displacement pin, and an output force pin.

Hydraulic command of a landing gear Mechanical Side


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RBD model appears as a sub-circuit

PINS are the connecting points between the RBD model and the rest of the circuit

Here the model is made of

Hydraulic pump and by-pass

Three way valve

ON/OFF Command

Cylinder, with end stop sensor

Acting on the ON/OFF and the Valve, a full simulation can be carried

Hydraulic command of a landing gear Simplorer Side


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Results are available both on the Simplorer side and in the Mechanical window

Hydraulic command of a landing gear Results

Force in the cylinder


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Example 2: Sequencing of a 5 axis robot from the Simplorer Window

Rigid Dynamics Model Simplorer Model

System level analysis using RBD Simplorer co-simulation


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RBD Model and Simplorer Model are link via PINS

These PINS are defined directly from the Mechanical Window

They are attached to joint degrees of freedom

Pins are input (Simplorer will feed the value to RBD) or output (RBD will feed the value to Simplorer

Typically, the same joint will have one input pin and one output pin

Here, each axis has an input rotation pin and an output rotation pin (for the feedback loop)

Sequencing of a 5 axis robot from the Simplorer Window - Mechanical Side


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Results are available both on the Simplorer side and in the Mechanical window

Sequencing of a 5 axis robot from the Simplorer Window - Results

Rotation of Axis 3

Pick and Drop cycled defined in Simplorer


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Contact speed and robustness greatly improved

Support of Constraint Equations objects

Extension of stops to spherical joints

Other New 14.0 Features in RBD

ansys 14 structural mechanics rigid body dynamics

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