Translational
Translation (1 DOF) determines the linear motion of boundaries and volumes, explicitly or in terms of a dynamic force balance. Translational motion is available only in one direction. You can add unlimited Translation (1 DOF) modules, each with its own dynamics, and give each module a different name.
The following conditions and parameters are available in the Properties panel:
• Setup Options
• Key Dynamics
• Simulation Method
• Time Definition when you set Simulation Method to Transient (Moving Grid)
• Motion Type
• ODE Time for steady-state run when you set Simulation Method to Steady(Fixed Position)
• Movement Direction
• Minimum Displacement
• Maximum Displacement
Setup Options
This applies to the display of settings and parameters that you can alternate without resetting any parameter. There are two Setup Options for the setup of a model:
• Normal Mode—Limits the options that appear when you select a Dynamics module with the intent of simplifying the setup.
• Advanced Mode—Displays all options available when you select a Dynamics module.
When you select Advanced Mode from Setup Options, the following settings appear in the Properties panel:
• Stability Factor (0-0.9)—Controls the amount of implicit versus explicit solver schemes that are used for a selected Dynamics module. A value of zero corresponds to a fully explicit solver scheme. A non-zero value weights the solver method with some percentage of the implicit solver scheme where 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—Specifies an additional force due to friction in the force balance equation. To activate this friction model select Yes. The options specified under Contact Friction Model follow:
◦ Static Friction Coefficient
◦ Sliding Friction Coefficient
◦ Contact Force
• Bounce Model—Specifies how an associated volume or boundary rebounds when it reaches the limit of its motion. The kinetic energy associated with bounce is applied at the point where the motion reaches minimum displacement or the maximum displacement. The options for this model follow:
◦ No Bounce—Complete loss of kinetic energy.
◦ Partial Bounce—Volume or boundary changes direction with a loss in energy based on the kinetic energy loss that you specify. Value of kinetic energy loss is defined between 0 and 1. A value of Kinetic Energy Loss = 1 results in a total loss of kinetic energy.
◦ Perfect Bounce—Volume or 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—Specify one of the following options for the ordinary differential equation (ODE) solver:
◦ Stiff—A proprietary Creo Flow Analysis explicit solver for ODEs. Stiff is the default setting for this module. You can specify Tolerance.
◦ 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. You can specify Tolerance.
Key Dynamics
If you set Key Dynamics to No or Yes for a selected Dynamics module, that module will control the Time Definition for all modules.
 |
For one module Translation (1 DOF) or Rotation (1 DOF), you can set Key Dynamics to Yes. If you set Key Dynamics to Yes for the second module, it resets Key Dynamics to No for the first module.
|
Simulation Method
The two methods of simulation available under Simulation Method are:
1. Steady(Fixed Position)—Volume or boundary translates to a stable position based on the following:
◦ Prescribed—Volume or boundary moves directly to the prescribed position at the first iteration.
◦ Force Balance—You obtain valve position by solving ODE following pseudo time stepping in each iteration. After you select the steady simulation method, the ODE Time for Steady State Run option is activated and the value provided is the pseudo time step in seconds.
2. Transient (Moving Grid)—Volume or boundary translates in time based on a prescribed motion or a force balance. It corresponds to a transient simulation in the Flow Analysis tab.
Motion Type
Motion that you select for a volume or boundary is specified as follows:
• Force Balance—Valve position is obtained by solving ODE following the transient time step. The Force Balance parameters include the following:
◦ Initial Velocity (m)—Introduces an initial velocity (t=0) for a moving volume or boundary. This is applied at the start of the simulation (t=0). A positive value of the initial velocity is in the same direction as the direction of the movement vector.
◦ Body Mass
◦ Damping Coefficient—Generates a force opposite to the velocity and depends on the average value that you specify. The force associated with the damping coefficient opposes the direction of motion.
◦ Additional Force on Body—Adds a force to the force balance for Translation (1 DOF) motion. This option appears when you select Advanced Mode. This is applied in the direction of the movement direction vector.
• Prescribed—Volume or boundary moves directly to the prescribed position at the first time-step. Displacement value is specified here. After you select Prescribed, you provide an expression for the displacement as a function of time using the Expression Editor. This specified displacement and associated velocity are accessed using the expression variables trans_1d.displacement and trans_1d.velocity. The unit for displacement is m.
◦ If you specify a constant displacement for a transient (moving grid) simulation, the volume or boundary moves directly to that position at the first time-step.
◦ If you set steady (fixed position) for Prescribed, the volume or boundary moves directly to the displacement position corresponding to t=0.
Time Definition
This determines the number and size of time-steps for a transient simulation based on cycles and total time steps. This option appears for Transient (Moving Grid). If you select a module and set Key Dynamics to Yes, the Time Definition option appears:
• 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)—Default value 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 following:
◦ Number of Time Steps per Cycle
◦ Motion Frequency(Hz)
ODE Time for Steady-State Run
The default value for ODE Time for Steady State Run is 1. A smaller value implies a smaller pseudo time-step, that results in a slower and more stable solution. If you select a module and set Key Dynamics to No, the ODE Time for Steady State Run option appears.
Movement Direction
This sets the direction of the positive motion for a translating volume or boundary. This is specified in terms of 
components relative to the model coordinate system.
components relative to the model coordinate system.Minimum Displacement
This limits the minimum value of displacement specified by the Translation (1 DOF) module. The unit for minimum displacement is m, which you can consider as a physical limitation or stop. When the displacement trans_1d[.subname].displacement that corresponds to Prescribed or Force Balance reaches the minimum displacement, the following happens:
• Value of trans_1d[.subname].displacement does not decrease below that point.
• Volume or boundary bounces back with an energy corresponding to the selected bounce model.
| | Default value of 1.#INF means that there is no physical limitation to the motion of the object opposite to the movement direction and 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, which you can consider as a physical limitation or stop. When the displacement trans_1d[.subname].displacement that corresponds to Prescribed or Force Balance reaches the maximum displacement, the following happens:
• Value of trans_1d[.subname].displacement does not increase beyond that point.
• Volume or boundary bounces back with an energy corresponding to the selected bounce model.
| | Default value of 1.#INF means there is no physical limitation to the motion of the object in the movement direction and trans_1d.displacement can reach positive infinity. |