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Translation

Translation (1 DOF) is used to dictate the linear motion of boundaries and volumes, either explicitly or in terms of a dynamic force balance. The translational motion is available only in one direction. Any number of Translation (1 DOF) modules can be added, each with its own dynamics, but they need to be given a different Module Name.

The parameters under Translation (1 DOF) can be specified as follows: Model Panel > Dynamics > [Translation (1 DOF)] Properties Panel > Model Tab > (Desired Option) The following conditions and parameters are available in the Properties Panel: Setup Options Key Dynamics Simulation Method Time Definition (when Simulation Method is set as Transient (Moving Grid)) Motion Type ODE Time for Steady-state Run (when Simulation Method is set as Steady (Fixed Position)) Movement Direction Minimum Displacement Maximum Displacement

Figure 5.269 - Dynamics - Translation options

Note: The template, if used should be in Extended Mode to view all the parameters.

 

Setup Options

This applies to the display of settings/parameters and can be switched back and forth without resetting any parameter. Setup Options offers two modes for the setup of a model: Normal Mode: Limits the options visible for a selected Dynamics module with the intent of simplifying the setup. Advanced Mode: Displays all options available for a selected Dynamics module. When the Advanced Mode is selected from the Setup Options drop-down list, the following settings appear in the Properties Panel: Stability Factor (0 - 0.9): Allows control of the amount of implicit verses explicit solver schemes are used for a selected Dynamics module. A value of zero for the Stability Factor corresponds to a fully explicit solver scheme and any non-zero value weights the solver method with some percentage of the implicit solver scheme, i.e., a value of 0.3 results in 70% explicit and 30% implicit. The higher the value for the Stability Factor, the solution is more stable at the expense of numerical effort. Contact Friction Model: Used to specify an additional force due to friction in the force balance equation. This friction model can be activated by selecting Yes. The options specified under Contact Friction Model are: Static Friction Coefficient Sliding Friction Coefficient Contact Force Bounce Model: The rebound behavior of an associated volume/boundary when it reaches the limit of its motion. The kinetic energy associated with bounce is applied at the point where the motion reaches either the Minimum Displacement or the Maximum Displacement. The available options for Bounce Model are: No Bounce: Complete loss of kinetic energy. Partial Bounce: The Volume/Boundary changes direction with a loss in energy based on the Kinetic Energy Loss input by the user. Kinetic Energy Loss is a user input and the value have to be defined between 0 and 1. A value of Kinetic Energy Loss = 1 results in a total loss of kinetic energy. Perfect Bounce: The Volume/Boundary changes direction with no loss in energy. For a Perfect Bounce, the momentum and kinetic energy of the particle are perfectly conserved. ODE Integrator: Offers three options for the Ordinary Differential Equation (ODE) solver. The three integrator options for the ODE solver are: Stiff: A proprietary Simerics explicit solver for ODEs. It is the default setting for this module and accepts a Tolerance specification. Euler: A first-order numerical procedure for solving ordinary differential equations (ODEs) with a given initial value. Runge Kutta: An explicit method for numerical integration of ordinary differential equations. It accepts a Tolerance specification.

Figure 5.270 - Advanced mode options     Figure 5.271 - Bounce model options     Figure 5.272 - ODE integrator options

 

Key Dynamics

Key dynamics for a selected Dynamics module may be set to No or Yes. Yes, means that module will control the Time Definition for all modules.

Note: Only one module among Translation (1 DOF)/ Rotation (1 DOF) may be designated as Key Dynamics = Yes. Setting Key Dynamics = Yes for a second Module will reset the first module’s Key Dynamics to No.

 

Simulation Method

The two methods of simulation available under Simulation Method are: Steady (Fixed Position): The Volume/Boundary translates to a stable position based on a Prescribed position or a Force Balance. Prescribed: Volume/Boundary will move directly to prescribed position at the first iteration. Force Balance: The valve position is obtained by solving ODE following pseudo time stepping in each iteration. Upon selection of steady simulation method, the General.ODE Time for Steady-State Run (see, Figure 5.275) activates and the value provided is the pseudo time step in seconds. Transient (Moving Grid): The Volume/Boundary translates in time based on a Prescribed motion or a Force Balance. The Transient (Moving Grid) corresponds to a Transient simulation in the Simulation Panel.

Figure 5.273 - Simulation method options

 

Motion Type

The motion for a selected Volume/Boundary is specified as follows: (see Figure 5.274)

1. Force Balance: The valve position is obtained by solving ODE following the transient time step. The Force Balance parameters for the Translation (1 DOF) include (see Figure 5.275):
   • Initial Displacement
   • Initial Velocity: Allows to introduce an initial velocity (t=0) for a moving Volume/Boundary. This is applied at the start of the simulation (t=0). The unit for Initial Velocity is m/s. A positive value of the Initial Velocity is in the same direction as the direction of movement vector.
   • Body Mass
   • Spring Constant
   • Spring Preload Force
   • Damping Coefficient: Generates a force opposite to the velocity and depends on the average value defined by the user. The force associated with the damping coefficient opposes the direction of motion.
   • Additional Force on Body: Allows the user to add a force to the force balance for Translation (1 DOF) motion. This option is relevant and displayed when Advanced Mode is selected. This is applied in the direction of the Movement Direction vector.
2. Prescribed: Volume/Boundary will move directly to prescribed position at the first time-step. The Displacement is specified here. Having selected the Prescribed option, the user typically provides an expression for the displacement as a function of time using the Expression Editor. This specified Displacement and associated velocity can be accessed via the Expression Variables: trans_1d.displacement and trans_1d.velocity. The unit for Displacement is m.
   • When a constant displacement is specified for a Transient (Moving Grid) simulation, the Volume/Boundary will move directly to that position at the first time-step.
   • When Steady (Fixed Position) is used with the Prescribed option, the Volume/Boundary will move directly to the displacement position corresponding to t=0.

Figure 5.274 - Motion type options

Figure 5.275 - Motion type - Force balance

 

Time Definition

This determines the number and size of time-steps for a transient simulation based on: Cycles and Total Time Steps. This option is relevant and displayed only for Transient (Moving Grid). This option is enabled for a selected module when the corresponding Key Dynamics option is set to Yes. The Time Definition options are: Cycles: Determines the number and size of the time steps in a simulation based on: Number of Cycles Number of Time Steps per Cycle Motion Frequency (Hz): The default value of Motion Frequency (Hz) is computed based on the natural frequency of the system. Total Time Steps: Determines the number and size of the time steps in a simulation based on the Number of Time Steps per Cycle and the Motion Frequency (Hz).

Figure 5.276 - Time Definition options

 

ODE Time for Steady-state Run

The default value for the General.ODE Time for Steady-State Run is 1. A smaller value implies a smaller pseudo time-step, resulting in a slower, but more stable solution. This option is enabled for a selected module when the corresponding Key Dynamics option is set to No.

 

Movement Direction

This is used to specify the direction of the positive motion for a translating Volume/Boundary. This is specified in terms of components relative to the model coordinate system.

Note: For the Valve Template Mesher available in Simerics-MP, the Movement Direction should be selected to correspond with the opening direction of the valve.

 

Minimum Displacement

This limits the minimum value of displacement specified by the Translation (1 DOF) module. The unit for Minimum Displacement is m. It can be thought of as a physical limitation or stop.

When the displacement (trans_1d[.subname].displacement) corresponding to Prescribed or Force Balance reaches the Minimum Displacement:

• The value of trans_1d[.subname].displacement will not decrease below that point.
• The volume/boundary bounces back with an energy corresponding to the selected Bounce Model.

Note: The default value of -1.#INF means there is no physical limitation to the object’s motion opposite to the Movement Direction, i.e. trans_1d.displacement can go to “negative infinity.”

 

Maximum Displacement

This limits the maximum value of displacement specified by the Translation (1 DOF) module. The unit for Maximum Displacement is m. It can be thought of as a physical limitation or stop.

When the displacement (trans_1d[.subname].displacement) corresponding to Prescribed or Force Balance reaches the Maximum Displacement:

• The value of trans_1d[.subname].displacement will not increase beyond that point.

• The volume/boundary bounces back with an energy corresponding to the selected Bounce Model.

Note: The default value of 1.#INF means there is no physical limitation to the object’s motion in the Movement Direction, i.e. trans_1d.displacement can go to “positive infinity.”