Assignment 5-RADIOSS Interfaces & Study of Effect of Notches Challenge

Aim: To run the crash tube model by using different types of contact interfaces.

         Mesh the given crash tube model with 6mm size.

Objective: Run the crash tube model with and without changing the parameters.

                 Remove the notches from the crash tube model,remove the boundary condition from rigid body node and then run the simulation.

                 Create notches in the middle and in the opposing faces of the crash tube model and then run the simulation.

                 Perform geometry clean up on the bumper assembly and mesh the bumper assembly with 6mm size.

Theoretical Framework-

What is hypermesh and Hypercrash?

Hypermesh:

• Hypermesh is a generalized preprocessor for many slovers like Abaqus,LS DYNA etc.
• In hypermesh,we can setup loadcases for optistruct,abaqus,ANSYS including radioss and LS DYNA.

Hypercrash:

• Hypercrash is a specialized preprocessor for radioss.It always exist as a part of hyperworks,hypercrash is mainly used for crash applications.
• Hypercrash supports solvers like radioss and LS DYNA. the units used in industries are KN,mm,ms,Kg.
• In hypercrash we have only 0000.rad files cause hypercrash doesnt have its own file extension.
• Hypercrash only detects the starter file cause these are the files only imported into hypercrash.
• We can export bill of material of all the models or you can also export as radioss file.We can export the model from hypercrash,but it will save the file as FIRST_RUN_0000.rad.It will create a backup file like FIRST_RUN_0000.rad.bak and store the previous file in this .bak file.
• It will also create MOOO file,whenever we export a file from hypercrash,MOOO file will be created.The MOOO file will only our filestructure details  and weld data,whenever we create weld,we will be having weld data.
• If we delete MOOO file and import only FIRST_RUN_0000.rad file,we wont able to see the connection folder in the tree browser.
• But all these connections will be listed as type 2 contact interface.It will be listed in the contact interfaces folder in tree browser.
• In hypercrash engine cards will be represented as control cards.ANIM DT files will be stored in A01 files. Data history files will go in T01 files.
• Rigid wall forces,contact forces,all energies,all those things will go in T01 files.

Interfaces:

Out of the many interface type,the most used ones for impact simulation are:

Interfaces are defined to model how parts intercat when they come into contact with each other,there are common types of interfaces called

1. Interface penality method
2. TYPE7,variable stiffness,node to surface contact.
3. TYPE11,Variable stiffness,edge to edge contact.
4. TYPE24,Linear stiffness,node to surface and surface to surface contact.
5. TYPE19,Combination of TYPE7 and TYPE11.

1)Interface penality method

• The penality mehtod treats the behaviour between slave nodes and master segments as springs that generate resistive forces as a function of penetration.

Here the interfaces are governed by the penality method.
When the parts come into contact,the slave node tries to penetrate the mid surface.
The soIlver introduces the 1D spring element once the slave node penetrate the gap.
The spring stiffness is automatically computed according to the material and property of both master segment and slave node.
If penetration is zero,the time step will be maximum,As the penetration goes on increasing the time step goes on decreasing.
Time step alpha stiffness.

Time step for contact interfaces:

Nodel time step:

Kinematic time step: 

Where dp/dt- speed of the sound wave through the material.
g-gap
p-penetration
delta t- time step
M- mass
K- stiffness

Interface Type 7: Nodes to surface contact-

It is general purpose interface and can simulate all types of impact between a set of nodes and master surface.
Non oriented and slave nodes can belong to the master surface,hence auto impact possible.
Automatic node to surface contact interface using penality method with varibale stiffness.
A gap is defined around the master segment and the slave nodes.
The contact gap can be contact or variable.
Resistive forces are applied to keep slave nodes out of the contact gap.
Interface time step is computed to insure stability.

Important Interface Parameters:

I_gap= Dtermines how the size of gap is calculated.
Gap min= Minimum gap for activation of interface.
Inacti= Action to take if initial penetration exist.
I_stf= Affects how the stiffness of the interface is calculated.
I_Form=Friction formulation.
Stmin= Minimum stiffness to use in the interface.To avoid timestep error.
Idel= What to do with slave nodes and master segments,if elements fails(deleted) that they are attached to or update for deleted elements due to failure.

Gap Definitions:

Inacti:

Inacti is noting but initial penetration.
We will be giving this parameter to get rid off penetration in the model.

Initial Penetration:

Initial penetration result if a slave node is closer to the master segment than the calculated gap.
Initial repulsion forces give an error in the energy balance due to the interfaces work.
There are options in the solver to remove initial penetrations.
Inacti= 3 may create initial energy if the node belongs to a spring element.
Inacti = 6 is recommended instead of Inacti=5,in order to avoid high frequency effects into the interface.

Initial Intersections:

Intersection result if slave node are past the master segement (shell or solids)
This condition acan cause locking situation leading to computation failure.
If slave nodes lie on the master segment an ERROR will occur because of the Type 7 contact stiffness definition.

Options for removing initial penetrations:

Istf Initial contact stiffness:

We will be giving initial contact stiffness to get rid off penetration.
Like when two components are going to penetrate,to avoid this will be giving initial contact stiffness.
For example: If the soft component coming into contact with the hard component,the soft component will absorb the resistive forces.so thats why the stiffness of the soft component is considered.
Istf=4 is mostly recommended for the crash applications.

Iform (Sliding Force Computation):

The recommended parameter is Iform=2 cause the sliding forces are computed using parameters.

Idel (Update for deleted elements due to failure):

Idel indicates the update for deleted elements due to failure.

Recommended Parameters for crash applications:

Adavntages and Disadvantages of Type7 Contact:

Advantages:

Physically correct representation.
High accuracy for describing self-contact and building.
Best used with shells to shells or solids to shells.

Disadvantages:

Requires more stringent modeling practices.
Does not tolerate intersections(slave node passing master segment)
Time step may reduce due to increasing interface stiffness.

Interface TYPE11 (Edge to Edge Contact):

Type 11 is simialr to the type 7 contact.
This interface simulation impact between edge to edge or lines.A line can be a beam or truss element or shell edge or spring elements.In association with interface TYPE 7,interface TYPE11 solves the locking cases.
Defined by identifying master and slave lines(edges)
Impact occurs between a mastr and the slave line.A slave line can impact on one or more master lines.A line can belong to the master and the slave side.This allows self-impact.
WOrks similar to TYPE7 in terms of penalty formulation,gap definition and search method.
Uses complicated mathematical algorithms:therefore it is strongly adviced to use it only when necessary.A huge interface TYPE11 can slow down the computataion.

Interface Type19 (Combination of type 7+11):

Combination of two symmetric TYPE7 interface and one TYPE11 interface
Common input based on the same slave/master surface.
Useful for complex contact problems such airbag unfolding.
Computationally expensive so only problematic segments should be defined
Edges to edge contact flag edge.

Procedure:

First import the bumper assembly into the GUI which is shown in below figure.

Then view the componenet by topo mode which is shown in below fig.

Geometry cleanup on the model:

• Now do a geometric cleanup on the model,there are some surfaces which are overlapping and the surfaces which are not equivalence which is shown in below fig.

Surface which are not Equivalenced

Surfaces which are overlapping

• To fix the surface which are overlapping and the surfaces which are not equivalenced which is shown in above fig 
• To equivalence the surfaces,Go to Geometry>>Edge Edit>> Select the lines moved edge and retained Edge>> Replace.

• We can also fix this by extending the lines over the surface using Extend tool from surface Edit Panel.
• Now select the moved edge and retained edge to equvalence the surface which is shown in below fig.

• Surfaces have been connected or equivalenced which is shown in below fig.

• Now intersect the surface which are overlapping.
• To import the surface,go to geometry>>surface edit>>trim with surf/plane>>self intersecting surfaces>>select the two surfaces >>trim.
• Select the surface and trim the surface which is shown in below fig.

• Once the geometry cleanup is done (e.g surfaces are stitched together-no unwanted free surface edges inside the geometry),meshing is next.
• Now start meshing on the surfaces which is shown in below fig.
• To mesh,Go to 2D>> automesh panel>>surfaces>>element size=6mm>>mesh type:quads or mixed>>check for align and size>>mesh.

• After meshing the entire bumper component,the bumper model will be seen as which is shown in below fig.

Import the starter file into the solver deck Radioss:

While opening hypermesh software,a user profile window will pop up,switch to the radioss user profile as shown in below fig and start importing the model into the solver deck.

• Now after switch the user profile to radioss,import the model into the radioss solver deck.

• To import the model,go to standard panel>>import>>import solver deck.
• Import solver deck option should be selected to import the radioss starter file.

• Here the import browser will appear as shown in above fig,select the appropriate starter file to import into GUI.
• Switch the file type to radioss block and import the model into GUI.

• Here the model is in wireframe mode,switch to the standard mode as shown in below fig.
• To switch to shaded mode,go Visualization tab>>shaded elements and mesh lines.

CASE-1 Run the crash tube model as it is default:

• Here we have to create TH for the all parts.
• Before running the simulation,we have to create TH for the interfaces,It should be followed for all the cases.
• To create Th,go to solver browser>>right click on TH>> create>>Inter,which is shown in below fig.

• After creating Th,the contact interfaces should be assigned to that,which is shown in below fig.

• Now run the simulation,to run simulation go to analysis panel as shown in fig.
• Go to analysis panel>>radioss>>select the input file>>save it in different folder and rename it as case-1>>run.
• Check the include connectors,if there are any connectors in the model.The connectors will also be taken into account.
• Type -NT 4 in options tab,this will make the simulation faster.
• Where NT indicates no of threads,4 indicates assigning the tasks to 4 cores in the system.

• Here save the input file in a different folder and rename it as case-1 which is shown in below fig.
• Now run the solver by hitting on radioss.

• After completing the simulation,the radioss will pop up a solver window stating radioss job completed which indicates the simulation has been completed,which is shown in below fig.

• After running the simualtion,the animation files will be generated where we specifed a location to store the files which is shown in below fig.

• Now go and open the 0000.1 out file with notepad.
• The obtained values for energy error,mass error,internal energy error,kinetic energy error,contact energy error has been shown in below fig.

Postprocessing:

1) Review the simulation using-Hyperview

2) Plot the graph using-Hypergraph 2D

1) Review the simulation using-Hyperview

• Hyperview allows for loading and viewing result files obtained from several sources.
• Based on the solver type of the files and the results you would like to visualize and analyze,there are different ways to load the input deck and their corresponding results into hyperview.
• First to begin the postprocessing in the hypermesh,split the screen as shown in below fig.
• Import the animation file .h3d into the hyperview.

• And then activate the client hyperview.

• To access the load model panel.
• Select load model button from the hyperview panel and open .h3d file as shown in below fig.

• After loading the model into hyperview,it will be represented as shown in below fig.

• After importing the .h3d file into the GUI enable the contour.
• The contour tool create contour plots of a model graphically visualize the analysis result.
• To enable contour,Go to results toolbar>>contour.

• Now switch to the von misses stress in result type and select the component,select the averaging method as simple and then click apply as shown in below fig.

• After applying,run the simulation,the simulation animation is shown in below fig.

2) Plot the graph using -Hypergraph 2D

• Now plot the graph using hypergraph 2D we are plotting the graphs to see what is happening in the rail component.
• Hypergraph 2D is a powerful data analysis and plotting tool with interfaces to many popular file formats.
• It is sophiscated math engine capabale of processing even the most complex mathematical expressions.
• Hypergraph 2D combines these features with high quality presentation output and customization capablities to create a complete data analysis system for any orgainzation.

• Here switch to the hypergraph 2D to plot the graphs.
• To switch,go to client selector>>choose the hypergraph 2D as shown in above fig.

• The first graph is plotted for the rigid wall forces.
• To plot the graph,go to hypergraph 2D>> data file>>crash_tubeT01>>Apply.

• Here the graph has been plotted for rigid wall forces as shown in below fig.
• There are various parameters in rigid wall like normal force,tangent force,FX-X Total force,FY-Y Total force,FZ-Z total force,total resultant force.
• We are selecting only tottal resultant force because we dont know the exact axis of the component placed,so that's why we are selecting total resulatant force and then plotting the graph.

• While plotting the graph,units profile window will opo up.,there select solver units and plot the graph because the graphs will be plotted according to the solver units.
• Now plot the graph for the rigid wall forces which is shown in below fig.

Rigid wall forces:

• Here the rigid wall forces starts from origing,cause initially there is no contact between the crash tube and rigid wall.
• And it goes on increasing cause the elements are getting deformed and the rigid wall forces suddenly reaches peack,cause the entire crash tube collides with the rigid wall.
• And again its decreasing cause after the collision,the entire component will be at rest,so its decreasing.

Kinetic Energy:

• Here kinetic energy is increasing in the begining itself,why because the initial velocity is given for the component.
• And it goes on decreasing,cause the deformation is happening to the crash tube,so the kinetic energy is decreasing.

Internal Energy:

• The formula for internal energy is E=Q+-W.
• Here the heat is neglected cause there is no heat transfer,we will be having only workdone.
• W=FxD
• F=ma.
• Here the internal energy is in zero because there is no deformation initially,so the internal energy is in zero and starts from zero and goes on increasing.
• The internal energy increases because the deformation is happening there is a displacement,so the initial energy increases,when the displacement or deformation occurs.

Contact Energy:

• Here the contact energy starts from origin,cause the crash tube component is in initial condition.
• Initially there is no contact between the crash tube component and rigid wall.
• There is also no deformation initially but when the component goes and hits on the rigid wall,the contact energy starts increasing.
• When the deformation or displacement happens to the component,the contact energy increases cause the crash tube comes into the contact to the rigid wall,so the contact energy goes on increasing.

Total Energy:

• Total energy is um of kinetic energy+contact energy+hourglass energy+internal energy.
• Here total energy starts from higher value,in starting itself its increasing why because the total energy is sum of kinetic energy+contact energy+hourglass energy+internal energy.
• All energies are in initial condition except kinetic energy so kinetic energy is only there
• Total energy= kinetic enery+0+0+0.
• Kinetic energy is directly proportional to the total energy.
• So the toatal energy is increasing in the begining.
• And its slightly decreasing due to -3.8% of energy error,the total energyis decreasing.

Hourglass Energy:

• Here the hourglass energy is constant because the recommended parameters Ishell=24 has been assigned to the property card,so the hourglass energy is constant.

All Energies:

 

Case-2 Change the Inacti=6 and run:

• Here change the parameter value as Incti=6 keep the remaing parameters as it is default.
• When we change the Inacti parameter=6,it will remove the penetration,the penetration won't happen between the solver and master node.
• It will reduce the gap and gap like the gap will be reduced and scaled.the lancti value is charged which is shown in below fig.

• Similarly,now run the simulation using radioss,after running the simulation.the animation and TH files will be obtained in a required location,which is shown in below fig.

• Now go and open the 00001.out file with notepad.
• The obtained values for energy error,mass error,internal energy error,kinetic energy error,contact energy error has been shown in below fig.

1) Review the simulation using-Hyperview

• After completion of running the simulation,switch to the hyperview.
• Open the appropriate .h3d file to review the simulation.
• The .h3d file is loaded and it is shown in below fig.
• Here the stress generated for this case is 0.73 Mpa.The behaviour is similar to the previous case 1.

2) Plot the graph using-hypergraph 2D

• Now switch to the hyperview 2D and plot the graphs.
• The rigid wall forces graph is plotted which in below fig.

Rigid wall forces:

• The obtained graph for rigid wall forces is shown in above fig.here the rigid wall forces is similar to the previous case1.

Kinetic Energy:

• The obtained graph for the kinetic energy is shown in below fig,here also kinetic energy is similar to the previous case1.

Contact Energy:

• The obtained graph for contact energy is shown in below fig,here also contact energy is similar to the previous case 1.

Internal Energy:

• The obtained graph for internal energy is shown fig,here also internal energy is similar to the previous case 1.

Total Energy:

• The obtained graph for total  energy is shown in below fig, here also total energy is similar to the previous case 1.

• Here the hourglass energy is constant,beacuse the recommended parameter Ishell=24 has been assigned to the property card,so the hourglass energy is constant.

All Energy:

 

CASE-3 Create the type 11 contact and run:

• Now for this case,we have to create new contact called type 11.some parametrs should be given which is shown in below fig.
• Here I'm giving type 7 parameters to the type11,cause the type 11 is sismilar to the type 7 contact.

• Now define the slave and master for the type11 contact which is shown in below fig,select all the elements.

• Now reuest for the TH,TH is reqested for type 11 contact,while defining TH all the interfaces should be selected which is shown in below fig.
• To create TH,go to solver browser>>right click on TH>>create>>inter, Which is shown in below fig.

• After creating TH,the contact interfaces should be assigned to that,which is shown in below fig.

1) Review the simulation using-Hyperview.

• Now run the simulation,after running the simulation,switch to the hyperview and load the .H3D file to view the results of simulation which is shown in below fig.

• Now go and open the 00001.out file with notepad.
• The obtained values for energy error,mass error,internal energy error,kinetic energy error,contact energy error has been shown in below fig.

2) Plot the graphs using-Hypergraph 2D.

• Here the kinetic,internal,contact,internal and hourglass energy is simialr to the previous case.
• The graphs plotted for kinetic,internal,contact,internal and hourglass energy is shown in below fig.

Rigid wall forces:

• The graph obtained for all the rigid wall forces is shown in below fig.

• Here the rigid wall forces are increased when compared to the previous case,it is increased between the range of (1400-1600).
• They are increased cause the type 11 contact is also defined with the type 7 contact,so they are increased.

Self contact forces:

• The graph obtained for the contact forces is shown in below fig.

• Here the contact forces starts from the origin and suddenly reaches peak,cause the all the elements come into the contact ,in that time the contact forces  reaches peak and decreases  cause the crash tube will be in rest after collision.

TYPE 11 contact forces:

• The graph obtained for the TYPE11 contact forces is shown fig.

• Here the TYPE11 contact forces are strating from origin and increasing due to the element comes into the contact,so its suddenly reaches the peak.
• And its decreasing after the collision,cause the crash tube will be at rest.

CASE-4 Remove both notches and remove boundary condition on rigid body node then run:

• Here in the case,we have to remove the notches and boundary conditions as per the question.
• To remove the notches,use align node tool and align them properly to remove the notches.
• To align,go to geometry>>node edit>>node 1,2,3>> align node.
• The notches have been removed for this case,which is shown in below fig.

• Then remove the boundary condition which is shown in below fig.

1) Review the simulation using-Hyperview

• Now run the simulation,after running the simulation,switch to the hyperview and load the .h3d file to view the results of simulation which is shown in below fig.
• Here the buckling is happening at the contact due to removal of notches.
• In previous cases buckling was happpening where the notches were.

• Now go and open the 00001.out file with notepad.
• The obtained values for energy error,mass error,internal energy error,kinetic energy error,contact energy error has been shown in below fig.

2) Plot the graph using-Hypergraph 2D

Rigid wall forces:

• The obtained graph for the rigid wall forces is shown below fig.
• Here the rigid wall forces is reduced due to removal of notches.
• The maximum rigid wall forces value obtained in this case is 1213.89.it is low when compared to the previous cases.

Internal Energy:

• The obtained graph for the internal energy is shown in below fig.
• It is similar to the previous case.

Kinetic energy:

• The obtained graph for the kinetic energy is shown in below fig.
• It is similar to the previous case.

Total energy:

• The obtained graph for the total energy is shown in below fig.
• It is similar to the previous case.

All Energy:

• The obtained graph for all energies is shown in below fig.

CASE-5 Create a new notch in the middle,select the whole section and run:

• Here for this case,create notches in the middle by using element offset.
• To create notches in the middle, go to 2D panel>>element offset>>select elements>>distance=2>>offset+

• Here you have to give a distance,to give distance,measure the distance between the notches which is shown in below fig.
• Here the distance is 4,you have to offset,so give the distance as 2 to create a notches in the middle which is shown in below fig.

1) Review the simulation using-Hyperview

• Now run the simulation,after running the simulation,switch to the hyperview and load the .h3d file to view the results of simulation which is shown in below fig.
• Here the buckling is happening,where the notches exist.

• Now go and open the 00001.out file with notrpad.
• The obtained values for energy error,mass error,internal energy error,kinetic energy error,contact energy error has been shown in below fig.

2) Plot the graph using-Hypergraph 2D

Rigid wall forces:

• The obtained graph for the rigid wall forces is shown below fig.
• Here the rigid wall forces are simialr to the previous case but the buckling is happening where the notches exist in the crash tube.

Internal Energy:

• The obtained graph for the rigid wall forces is shown below fig.
• It is similar to the previous case.

Kinetic energy:

• The obtained graph for the rigid wall forces is shown below fig.
• It is simialr to the previous case

Total energy:

• The obtained graph for the rigid wall forces is shown below fig.
• It is similar to the previous case.

All Energy:

• The obtained graph for all energies is shown in below fig.

CASE-6 Create a new notch with nodes only from opposing 2 faces and run:

• Here for the case create a notches in the two opposite faces and run the simulation.
• The notches created in the opposite faces is shown in below fig.

1) Review the simulation using-Hyperview

• Now run the simulation,after running the simulation,switch to the hyperview and load the .h3d file to view the results of simulation which is shown in below fig.
• Here also the buckling is happening,where the notches exist.

• Now go and open the 00001.out file with notrpad.
• The obtained values for energy error,mass error,internal energy error,kinetic energy error,contact energy error has been shown in below fig.

2) Plot the graph using-Hypergraph 2D

Rigid wall forces:

• The obtained graph for the rigid wall forces is shown below fig.
• Here the rigid wall forces are simialr to the previous case but the buckling is happening where the notches have been created in the crash tube.

Internal Energy:

• The obtained graph for the rigid wall forces is shown below fig.
• It is similar to the previous case.

Kinetic energy:

• The obtained graph for the rigid wall forces is shown below fig.
• It is simialr to the previous case

Total energy:

• The obtained graph for the rigid wall forces is shown below fig.
• It is similar to the previous case.

Hourglass Energy:

 

All Energy:

• The obtained graph for all energies is shown in below fig.

Comparison of all cases:

CASES	ENERGY ERROR	INTERNAL ENERGY	KINETIC ENERGY	EXTERNAL WORK	MASS ERROR	ELAPSED TIME	TOTAL NUMBER OF CYCLES	INTERFACE TYPE	CHANGES IN MODEL
case-1	-3.8%	0.4202E+05	592.8	-105.3	0.000	135.61S	83469	TYPE 7	No change
case-2	-3.8%	0.4202E+05	592.8	-105.3	0.000	80.95	83469	TYPE 7	changed into Inacti=6
case-3	-1.4%	0.4267E+05	901.8	-185.4	0.000	125.29S	85006	TYPE 11 & TYPE 7	changed into recommended parameters
case-4	-3.0%	0.4234E+05	554.2	-163.5	0.000	75.31S	78457	TYPE 11 & TYPE 7	Removed notches and boundary conditions.
case-5	-2.6%	0.4234E+05	669.0	-249.9	0.000	86.34S	92501	TYPE 11 & TYPE 7	Created notches in the middle
case-6	-3.4%	0.4208E+05	528.1	-318.0	0.000	175.35S	92558	TYPE 11 & TYPE 7	Created notches in the opposite faces only.

Result:

• Hence the simulation for all the cases were carried out with different parameters.
• Hence the simulation for all the cases were runned successfully.
• Hence the simulation for all the cases were reviewed by hperview.
• Hence the graph were plotted for all the cases successfully.
• Hence meahsed the bumper component with 6mm size.
• Atlast,compared all the results for those cases.

Conclusion and learning outcome:

• In this challenge,i came to know about
• The types of interfaces and their applications.
• The effect of notches in the model.
• The penetration causes.
• The different parameters for the interfaces.
• The elements deformation during the interface.