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The various forces and torques supported by RecurDyn are described here.

Please choose the topic you are interested in from the below list.

Spring and Damper Model

The spring is a mechanical element that can be compressed or extended when an external force is applied and return to its original shape due to its elasticity when the force is removed. Depending on the shape and material, there are various springs such as coil springs, plate springs, spiral torsion springs, rubber springs, air springs, hydraulic springs, etc. Dampers are devices that can absorb vibrational energy. They are also known as vibration isolators or absorbers. As shown below, springs and dampers are used together in suspension systems located between the wheels and vehicle body of an automobile or train to absorb the vibration that comes from the road’s surface and dampen the shock applied to the vehicle body or passengers.

Spring and Damper

(1) Translational Spring and Damper

Figure shows the connection between body i and body j that consists of the forces exerted by a translational spring damper. When two bodies connected by a spring move due to an external force, the length of the spring damper changes. At this time, the restoring force that tries to return the spring to its original length and the damping force that dampens the external force are generated due to the elasticity of the spring damper. The restoring force and damping force are in turn applied to the two bodies, causing them to move.

The force of a translational spring damper is calculated as follows using the displacement of the spring as well as the stiffness coefficient and damping coefficient.

The calculated spring force f_s is applied to bodies i and j as shown in the following figure according to Newton’s law of action-reaction. This spring force is generalized as the forces, Q_i and Q_j, which are used in the equation of motion.

Calculation of translational spring and damper force

(2) Creating a Translational Spring

To create a spring, click the spring icon, select a spring creation option, click two bodies, and click two points where the spring will be created, as shown in the figure below. Two markers are created automatically at the two points you clicked. Each marker belongs to one of the two bodies. The distance between the two markers is measured during simulation to calculate the displacement of the spring. The spring force is in turn calculated from this displacement. You can also open the Property dialog box of the created spring, edit the parameters including the stiffness coefficient and damping coefficient, and close the box to run simulations of the spring dynamic model with these parameters. At this time, the free length of the created spring is defined as the distance between the two markers by default. If you want to simulate a model where the spring is compressed, you can define the free length of the spring to be longer than the distance between the two markers. If you want to simulate a model where the spring is extended, you can define the free length of the spring to be shorter than the distance between the two markers.

Creating a Translational Spring

A. General Force

(1) Translational Spring Damper

A translational spring is the most widely used force and a mechanical element that is created by winding a spring steel into a coil. Accordingly, when a spring is distorted by applying an external force, it can absorb or store energy using its elasticity and use this energy to return to its original shape. Generally, springs are widely used in the suspension systems of automobiles or bed mattresses.

Translational Spring Damper Force

(2) Rotational Spring Damper

A rotational spring is a mechanical element created by winding a spring steel into a spiral shape. It is also called a spiral spring. It stores elastic energy by winding itself into a spiral form and uses the stored energy when it reverts to its original shape.

Rotational Spring Damper Force

(3) Axial Force

An axial force allows you to draw a straight line between two objects and define the action and reaction forces on each object as a function of time.

Axial Force

(4) Rotational Axial Force

A rotational axial force allows you to define the action and reaction torques at a rotational axis defined between two objects as a function of time.

Rotational Axial Force

(5) Translational Force

A translational force allows you to define three forces in the three translational directions, which are the x, y, and z axes of an object, as a function of time. Since you can change the reference frame for the direction of a force, you can consider the motion of a body when applying a translational force to the body.

Translational Force

(6) Rotational Force

A rotational force allows you to define the torque for each of the three rotational axes of a body as a function of time.

(7) Screw Force

A screw force allows you to define the translational forces and torques in the three translational directions and the three rotational axes of a body as a function of time.

Screw Force

(8) Bushing Force

A bushing force allows you to create translational and rotational springs in all six degrees of freedom of a specific point. With a bushing force, you can get the effect of combining two objects at one point.

Bushing Force

B. Special Force

(1) Matrix Force

A matrix force allows you to define the stiffness matrix with the forces between two bodies. Due to these properties, you can use the matrix force as any type of force that you want. For example, you can create a bearing model with a stiffness matrix for six axes and input it into the stiffness matrix of a matrix force to simulate a stiffness force that has the properties of a bearing.

(2) Beam Force

A beam force allows you to use an equation on the force of a beam between two bodies and make the two bodies to behave as if there is a beam between them. To do so, you need to enter Young’s modulus, shear modulus, the geometry of a beam’s cross-section, and area moment to run simulations on the beam.

(3) Plate Force

A plate force allows you to apply a force equation that makes four bodies behave as if they are four shells. To do so, you need to enter Young’s modulus, Poisson’s ratio, and the thickness.

(4) Tire Force

A tire force is embedded with a formula for tires to simulate the dynamic behavior of an automobile tire. It supports the Fiala and UA-Tire models, which are currently widely used, as well as the user’s tire, for which you can define your own formula.