PREPROCESSING OF REAR SUSPENSION OF A CAR USING ANSA

PREPROCESSING OF REAR SUSPENSION OF A CAR USING ANSA

Aim:

Midsurfacing geometry with thickness less than 6mm and meshing.

Tetra meshing thick geometry such as tyre, rim and other surfaces with thickness greater than 6mm

Introduction:

Suspension is the system of tires, tire air, springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two.

Any four wheel vehicle needs suspension for both the front wheels and the rear wheels, but in two wheel drive vehicles there can be a very different configuration. For front-wheel drive cars, rear suspension has few constraints and a variety of beam axles and independent suspensions are used. For rear-wheel drive cars, rear suspension has many constraints and the development of the superior but more expensive independent suspension layout has been difficult. Four-wheel drive often has suspensions that are similar for both the front and rear wheels.

The suspension system contains three major parts: a structure that supports the vehicle’s weight and determines suspension geometry, a spring that converts kinematic energy to potential energy or vice versa, and a shock absorber that is a mechanical device designed to dissipate kinetic energy.

An automotive suspension connects a vehicle’s wheels to its body while supporting the vehicle’s weight. It allows for the relative motion between the wheel and vehicle body; theoretically, a suspension system should reduce a wheel’s degree of freedom (DOF) from 6 to 2 on the rear axle and to 3 on the front axle even though the suspension system must support propulsion, steering, brakes, and their associated forces. The relative motions of the wheels are its vertical movement, rotational movement about the lateral axes, and rotational movement about the vertical axes due to the steering angle.

Functions of suspension system

• Safety
• Gripping
• Handling

Types of suspension system:

1)Independent suspension system

This system means that the suspension is set-up in such a way that allows the wheel on the left and right side of the vehicle to move vertically independent up and down while driving on an uneven surface. A force acting on the single wheel does not affect the other as there is no mechanical linkage present between the two hubs of the same vehicle. In most of the vehicles, it is employed in front wheels.

2)Dependent suspension system

There is a rigid linkage between the two wheels of the same axle. A force acting on one wheel will affect the opposite wheel. For each motion of the wheel caused by road, irregularities affect the coupled wheel as well. It is mostly employed in heavy vehicles. It can bear shocks with a great capacity than independent suspension.

3)Semi-Dependent suspension system

This type of system has both the characteristics of a dependent as well as independent suspension. In semi-independent suspension, the wheel move relative to one another as in independent suspension but the position of one wheel has some effect on the other wheel. This is done with the help of twisting suspension parts.

Components of a rear suspension system

Procedure:

1.The geometry is imported and all geometry checks are done and all errors present were resolved.

2. Different PID are assigned to each of the suspension components as shown

3. The following parts are taken seperately for ease of meshing.

TYRE

The tyre geometry is selected and checks are done to resolve any unchecked faces.

Meshing is done as per below quality criteria

Ortho tria is used in curved areas and for plane areas tria elements are utilized.

In the volume tab the volume to be meshed is defined and a Tetra Rapid volume meshing is done.

The quality criteria for tetra mesh is as shown below

The cross sectional view is as shown below.

RIM

The tyre geometry is selected and checks are done to resolve any unchecked faces. Defeaturing is done as shown below so that surface meshing can be done smoothly.

Meshing is done as per below quality criteria

Any off elements present are resolved using Split and Improve tools in the Mesh Tab.

In the volume tab the volume to be meshed is defined and a Tetra Rapid volume meshing is done.

The quality criteria for tetra mesh is as shown below

Any tet collapse errors are resolved using auto fix.

SUSPENSION

Components with thickness greater than 6mm is taken into consideration for surface meshing. Best mesh is done as per below quality criteria.

Each of the component is taken seperately and checked for any off elements so that meshing can be done smoothly.

In the volume tab the volume to be meshed is defined seperately for each and a Tetra Rapid volume meshing is done.

The quality criteria for tetra mesh is as shown below

Any tet collapse errors are resolved using auto fix.

For components less than 6mm in thickness as shown below mid surfacing is done.

Mid surface mesh is done by using the best method available. A mixed tria and quad elemts are used for meshing. Below quality criteria is used for meshing.

The overall volume and surface meshing is done and a smooth mesh is obtained as shown below.

4. Connections are provided at all the seam and bolt areas of the geometry before analysis.

An RBE2 multi node is used to define bolt areas as shown below. The connections between two holes are provided using the RBE2 two nodes.

Bolt connections are provided at the rim bolt areas so that while analysis proper visualization can be done.

The seam weld areas are connected using the RBE2 Two node node set elements as the overlap and Y joint shell elements will cause a distortion of surface geometry and the distance between the two PID components is very less to realize any shell elements.

The spring element is defined as a CBAR with a radius of 5mm as shown below.

The CBAR element is connected to the main geometry using the multi node RBE2.

Final result:

Learning outcome:

1. Geometry check and cleanup.
2. Shell and solid meshing
3. Implementing connection using RBE2 and CBAR
4. Detailed study on car suspension system components.

Conclusion:

All the components of a suspension system are captured with solid elements(Tetra) and shell element (Quad+Tria) as per the quality requirements. The bolt connections are given with the RBE2 cluster and two-node RBE2. There is a total to 914040 tetra element under the volume meshing (3D) free from any Tetra collapse. The curved areas were mainly captured with the ortho Tria element during shell meshing on solid objects which helped to capture the feature correctly. The mid surfaced components are meshed with good quality with a tria percentage of 6% only. The meshed final model has a smooth surface free from any dip or kinks and can be considered further processing.

Link:

https://drive.google.com/file/d/1ovVQe-ntp8dbOYc6AE7AdSED3nuyGXWB/view?usp=sharing