COMPARING THE SIMULATION RESULTS FOR CRASH BEAM FILE OF THE BASE SETUP AND IMPROVED SHELL ELEMENT PROPERTIES

OBJECTIVE :

COMPARING THE SIMULATION RESULTS FOR CRASH BEAM FILE OF THE BASE SETUP AND IMPROVED SHEELL ELEMENT PROPERITIES

base setup means with out giving any properities (with the default values) first we run the simulation for given crash beam file

after that by changing the shell element properities we run the simulation and comapare the

obtained results.

UNDERSTANDINGS FROM THE PROJECT :

WHAT IS REDUCED INTEGRATION ?

Reduced integration can lead to non physical zero energy modes called hourglass modes.

this reduced and full integartion methods are used to compute the stiffness matrices .

Full integration schemes are used for static and dynamic problems with implicit time

integration,in full integraion method problems there is no energy errors . reduced integration

it reduces the simulation time.

THE CRITICAL LENGTH CAN VARY WITH

. SHELL FORMULATION

. HOUR GLASS CONTROL PARAMETERS

. NUMERICAL DAMPING

. MEMBRANE DAMPING

radioss provides reduced and fully integrated 4 noded shell elements and 3 noded shell

elements also available

HOURGLASSING DUE TO REDUCED INTEGRATION

hourglass modes are non physical modes of deformation that occur in under integrated

elements and produce no stress

There are 2 methods used to control formtion of hour glassing

1 . PETRURBATION (Ishell = 1,2,3 OR 4)(Q4 elements)

In case of large rotations and destortion it may have bad behaviour , and inhibits

hourglassing deformations,viscous forms are recommended for high velocity problems

in this type there is one integration point on the surface and default it takes Ishell = 1

2. PHYSICAL STABILIZATION (QEPH elements)

Hourglass deformation is detected with the velocity of the elements

When the hourglassing is detected a force is applied on the node to stabilize the deformation

and this force is defines according to the element stiffness

and this force introduces artificial energy (HOURGLASS ENERGY).

It reduces the hour glassing coefficient from 0.10 to 0.03 .

under integrated 4 node element with 1 integration point on the surface.

FOR crash anlysis QEPH elements are sufficinet .

Using the crash beam file from the previous assaignment,change the run time 55 ms

changed the number of animation steps during simulation as minimum of 25 and maximum of 60 in the ENGINE_ANIM_DT properities card as shown in the above figure .

and also changed the run time to 55 as shown in the above figure .(Tstop = 55)

1ST SIMULATION BY USING DEFAULT PARAMETERS (HOURGLASS )

1. import the geometry

FILES-------> ELEMENT FORMULATION FILE--------->CLICK IMPORT

2nd For analysis we should provide no.of threads (-nt 4)

And go to save as for saving all the files after simulation.

for default values when we give the simulation it will run the simulation and after job completed it will shows like below image

after that quickly go to the hyperview and after that open h3d files that where we saved all the run simulation files .

WE SHOULD CHECK THE ENERGY ERRORS AND MASS ERRORS FOR DEFAULT VALUES

FOR CYCLE 29150 AND TIME 54.99 THE ENERGY ERROR IS -10.3 AND MASS ERROR IS 0.1659E-03

NOW OPEN THE HYPER VIEW FOR VIEWING THE SIMULATION

AFTER THAT PLOT THE GRAPHS

1.GRAPH FOR KINETIC ENERGY AND INTERNAL ENERGY AND TOTAL ENERGY

. KINETIC ENERGY WILL START AT HUGE VALUE AND JUST SEE THE GRAPH FOR KINETIC ENERGY ,the graph is decreasing and if we give run for longtime that graph will lead to zero .

. INTERNAL ENERGY IS STARTING AT \'0\' POINT AND THIS GRAPH IS INCREASING IT WILL ALMOST REACH THE MAX VALUE BUT NOT EXACT MAX.VALUE.

2.PLOT FOR RIGID WALL FORCES :

. FROM THE ABOVE GRAPH ,WHEN THE FIRST IMPACT WAS HAPPENED IS A HUGE FORCE AFTER THAT BECAUSE THE INTERNAL DEFORMATION INSIDE THE CRUSH BEAM IT STARTED DECREASING.

. SIGNIFICANT AMOUNT OF FORCE THAT CONVERT INTO FRICTIONAL FORCE (RESULTANT- TANGENT FORCE)

. TOTAL RESULTANT FORCE MEANS IT WILL COMBINE BOTH NORMAL AND TANGENTIAL FORCE.

3. PLOT FOR TIME STEP (FOR DEFAULT VALUES)

below image shows that how PLOTTED the GRAPH BY CHANGING THE ENTITIES

---------------------------------------------------------- ------------------------------------------------------------------ -------------------------------------------------

2nd simulation by using recommended properities

changing the default properities to recommended properities as shown in the given image

after that export files and saveas in another folder as like in 1 st step.

and after the running the simulation just go to the files where we saved it .

in that files go to the out file there we can find out the error values as shown in the below

image

AFTER APPLYING THE RECOMMENDED PROPERTIES THE ERROR WAS DECREASED TO 0.1% FOR THE CYCLE AT 27500 TO 27710.

5% ERROR IS GOOD FOR QEPH ELEMENTS.

PLOTTING THE GRAPHS FOR INTERNAL ENERGY AND KINETIC ENERGY and total energy

I.E is increasing to the approx. maximum value ,and K.E. is decreasing towards zero

PLOTTING THE GRAPHS FOR rigid wall vs time

FROM THE ABOVE GRAPH ,WHEN THE FIRST IMPACT WAS HAPPENED IS A HUGE FORCE AFTER THAT BECAUSE THE INTERNAL DEFORMATION INSIDE THE CRUSH BEAM IT STARTED DECREASING,and after that at time 50 ms NF RESULTANT NORMAL FORCE started increasing.

PLOTTING THE GRAPH FOR TIME STEP

FOR KNOWING HOW THE TIME STEP IS VARYING WE CAN GO TO THE OUT FILES AND JUST BY SEEING THOSE VALUES LIKE GIVEN BELOW IMAGE

CONTOUR :

BY USING ABOVE CONTOUR OPTION WE CAN ASSAIGN DIFERENT PARAMETERS LIKE DISPLACEMENTS AND VONMISES STRESS AND etc....

AFTER GIVING THE RECOMMENDED PROPERITIES WE CAN SEE THE SIMULATION AS SHOWN IN THE GIVEN BELOW :

WE CAN SEE HOW THE DISPLACEMENT IS CHANGES FROM 0 TO 8.4 AND ALSO WE CAN SEE MINIMUM DICPLACEMENT AND MAXIMUM DISPLACEMENT ALSO.

CONCLUSION :

ENERGY ERROR RESULTS ARE DECREASED TO -10.3% to -0.1% after changing the values from default properities to recommended properities, AND BY SEEING THE GRAPHS we learnt that how the internal energy and kinetic energy varies,

from this assaignment we learnt that what is the importance of shell element properities to caluculate crashworthiness analysis.