Assignment 6

Aim:

1.Compare the model weight with the full scale 300k nodes model and use added masses to reach target weight 700kg while getting CG about the required range.

2.Make sure of no penetrations and intersection.

3.Use model checker to ensure good quality.

4.Create appropriate interface ,friction 0.2 and recommended parameters.

5.Run 80 ms

Solution:

 1.Frame /Skew 

This is used to define the local coordinate systems using nodes with which velocity can be applied . There are two types of frames :

1.Moving Frame 

2.Fixed Frame .

2.Imposed Velocity 

This is a velocity which is imposed upon any element irrespective of how much reaction forces is being applied on the element.

3.Kinematic Joints : 

It used for creating various joints between two nodes which can be rigid ,rotational ,etc .In this the one node is from the slave and the other is from the slave segement of two different rigid bodies .They are usually coincident as it helps to define the axis etc .

Types of Springs :

Type 4 : It has dof of 1 ,used for tension ,compression and has its applications such as ropes pulleys etc .It requires two nodes for definition.

Type 12  : It has dof of 1 ,used for tension ,compression and has its applications such as ropes pulleys etc .It requires two or three  nodes for definition.

Type 13: It has dof of 6 ,used for spring type beam element  and has its applications such as ropes pulleys etc .It requires two or three  nodes for definition.

Type 45:It has dof of 6 ,used for simplified joint type beam element  and has its applications such as ropes pulleys etc .It requires two or 6  nodes for definition

4.Incompatible Kinematic Conditions : 

This is a condition when two kinematic conditions are applied to the same nodes which leads to error .

4.Load Definition :

Concentrated Load : Specific nodes are selected and equal amount of load is applied on all those nodes .

Pressure Load : A pressure load defines a distributed force applied to each element face of a prescribed surface group.

5.Time Step Control : 

There are two types of time step control :

Elemental Time step Control :

6.Stability Conditions :

Critical Time step : It is the time taken for the information such as pressure ,stress to pass on from one element to another element ,in order for the solution to be stable the computed time step should be lesser than the critical time step.

Now we will be doing the crash analysis of the following component as shown below  : 

 1.Contact Interface Type :

As you can see the default the contact interface type is type 7 which defines the node to node interface and leads to error as it does not consider the edge to edge contact which leads to lots of energy dissiaption .Hence the contact interface is changed to type 19 which is a mixture of type 11 (edge to edge ) and type 7 .This will lead to less energy dissiaption .

Now the recommended properties for Type 19 are as follows below :

Igap = 2 

Sets variable gap to take into account the true distance between parts .

Gapmin= 0.5 mm

Specify minimum thickness of the model in order to make sure no calculation mistakes are made .

Inacti=6 

Removes all intial penetrations possible ,otherwise reduces the gap by 30% of the intial gap and adjust the gap height.

Istf=4

Set stiffness based on the softer of the master or slave 

Stmin =1000 N/mm

Specify a minimum stiffness so that the there is not a soft contact .

Idel = 2 

Removes the slave nodes from contact because  of element deletion

Iform = 2 

 Sliding forces are calculated using stiffness parameters of the interface .Usually results in bigger time steps .

2.Penetrations and Intersections

As you can see there are 402 intial penetrations and these need to be removed as they can increase the energy error .

Using penetration checker ,all intersections and penetrations have been removed.

Creation of Rigid Wall :

A rigid wall has been created in hypermesh using a search distance of 1000 mm.

4.Intial Velocity 

An intial velocity of 35 mph(15 mm/ms) is given as shown above.

Sections : 

Following sections are created so that the amount of stress created during the crash is analysed 

The output files have been created in the following manner : 

Mass Balancing 

In order to get a good amount  of accuracy the mass needs to be placed properly as shown below : 

As you can see the COG is in the centre and needs to be shifted towards the right by adding mass .

Total Weight :

Total Weight : 188.21 Kgs

Ideal Mass Balancing : 

Added Mass :

A mass of 700 kgs is added to 135 nodes each node having 5.1 kgs on it as shown below :

Accelerometer : 

An accelerometer is created to see the acceleration curve at base of B pillar .

Now we will be doing the crash analysis with a run time of 80 ms and time step of 0.5 ms as shown below :

Results : 

Now we will look at the energy error ,mass error and time step that have occured during the simulation:

As you can see the energy error ranges from 1% to 1.2 % hence the results are mostly accurate and can be considered for analysis .

Mass error refers to the mass addition to the system so that the time step can be increased more than the critical time step so that the simulation can be completed .In this case the mass error ranges from 2%  to 3 % and hence is within the required limits.

Forces acting on the sections : 

Acceleration Curve : 

Other Energies :