Translational Hard Stop
Two-way progressive rigid limiter.
Description
The Translational Hard Stop unit is a bilateral mechanical progressive hard stop that restricts body movement between the upper and lower limits. It is assumed that the impact interaction between the stem and the stops is elastic. The limiter is represented as a spring that comes into contact with the stem when the gap is eliminated. The spring counteracts the movement of the stem inside the limiter with a force linearly proportional to the magnitude of this movement. To account for energy dissipation and inelastic effects, damping is introduced as a block parameter to account for energy loss. The diagram shows the idealisation of the mechanical progressive motion limiter adopted in the block.
The basic stiff stopping model Full stiffness and damping applied at bounds, damped rebound is described by the following equations:
,
Where:
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- is the interaction force between the stem and the housing.
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- is the initial clearance between the rod and the upper boundary.
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- initial clearance between stem and lower edge.
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- stem position.
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- contact stiffness at the upper boundary.
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- contact stiffness at the lower limit.
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- damping coefficient at the upper boundary.
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- damping coefficient at the lower boundary.
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- stem velocity.
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- time.
In the rigid stopping model Full stiffness and damping applied at bounds, undamped rebound the equations contain additional terms and . These terms ensure that no damping is applied at bounds, undamped rebound.
The by default Stiffness and damping applied smoothly through transition region, damped rebound' model adds two transition regions to the equations, one on each boundary. As the stem passes through the transition region, the block smoothly increases the force from zero to the full value. At the end of the transition region, full stiffness and damping are applied. At rebound, both stiffness and damping forces decrease smoothly to zero. The comparison functions `ge and le are also used in these equations.
The block is orientated from R to C. This means that the block transfers force from port R to port C when the gap is closed in the positive direction.
Ports
R - rod
` translational mechanics`
A mechanical progressive port corresponding to a stem that moves between stops mounted on the housing.
C - housing
translational mechanics.
Mechanical progressive port corresponding to the hull.
Parameters
Upper bound, m - clearance between stem and upper boundary
0.1 m (by default)
The gap between the stem and the upper boundary. The direction is set in the local coordinate system, with the stem at the origin. A positive value of the parameter defines the clearance between the stem and the upper boundary. A negative value sets the stem as penetrating the upper boundary.
Lower bound, m - clearance between the rod and the lower boundary
-0.1 m (By default).
Clearance between stem and lower boundary. The direction is set in the local coordinate system, with the stem at the origin. A negative value of the parameter defines the clearance between the stem and the lower boundary. A positive value sets the stem as penetrating the lower boundary.
Contact stiffness at upper bound, N/m - coefficient of collision stiffness at upper boundary
1e6 N/m (By default).
This parameter defines the collision stiffness property when the stem reaches the upper boundary. The larger the value of the parameter, the less the bodies penetrate each other, the stiffer the limiter becomes. A smaller value of the parameter makes the contact softer, but generally improves convergence and computational efficiency.
Contact stiffness at lower bound, N/m - coefficient of elasticity at lower boundary
1e6 N/m (by default).
This parameter defines the collision elasticity property when the stem reaches the lower bound. The larger the value of the parameter, the less the bodies penetrate each other, the stiffer the limiter becomes. A smaller value of the parameter makes the contact softer, but generally improves convergence and computational efficiency.
Contact damping at upper bound, N/(m/s) - damping coefficient at upper boundary
150.0 N/(m/s) (by default).
This parameter defines the damping at collision when the stem reaches the upper bound. The higher the value of the parameter, the more energy is dissipated by the interaction.
Contact damping at lower boundary, N/(m/s) - damping coefficient at lower boundary
150.0 N/(m/s) (by default).
This parameter defines the damping at impact when the stem reaches the lower bound. The higher the value of the parameter, the more energy is dissipated by the interaction.
Hard stop model - selection of the hard stop model
Stiffness and damping applied smoothly through transition region, damped rebound (by default) | Full stiffness and damping applied at bounds, undamped rebound | Full stiffness and damping applied at bounds, damped rebound.
Select a set of assumptions for block operation:
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`Stiffness and damping applied smoothly through transition region, damped rebound' - define a transition region in which the drag force increases from zero. At the end of the transition region, full stiffness and damping are applied. In this model, rebound damping is applied, but it is limited by the value of the stiffness moment. In this sense, damping can reduce or eliminate the torque provided by stiffness, but never exceed it. All equations are smooth.
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Full stiffness and damping applied at bounds, undamped rebound- this model has full stiffness and damping applied at impact at upper and lower bounds, with no damping at rebound. The equations do not result in a zero crossing when the velocity changes sign, but there is a zero crossing at the boundaries based on position. The lack of rebound damping helps get the rod out of this position quickly. This model has nonlinear equations. -
Full stiffness and damping applied at bounds, damped rebound- this model has full stiffness and damping applied at impact at upper and lower bounds, with damping applied at rebound too. The equations switch linearly, but result in a zero crossing based on position.
Transition region, m - the region in which the force increases
0.1 mm (by default)
The region in which the force increases from zero to the full value. At the end of the transition region, full stiffness and damping are applied.
Dependencies
To use this parameter, set Hard stop model to `Stiffness and damping applied smoothly through transition region, damped rebound'.
Initial Targets
Initial value of velocity, m/s - initial value of velocity
0.0 (by default)
Initial value of velocity.
Initial value of force, N - initial value of force
`0.0 (by default).
Initial value of force.
Initial value of position, m - initial value of position
0.0 (By default)
Initial value of position.