ACOSTA-Solid shell user element and ABAQUS shell elements ... · PDF fileACOSTA-Solid shell...

ACOSTA- Solid shell user element

and

ABAQUS shell elements

A comparisonA comparison

INTALES GmbH, 1st NL Workshop, Natters/TYROL, 15/06/20101

- David Chipperfield -

1st Workshop

on Nonlinear Analysis of Shell Structures

AS 9100

Outline:

• The model is formulated in the

general purpose code ABAQUS.

• EXEN nodes are connected to

the body shell with kinematic

BOUND1ORIGIN

EXEN2 EXEN1

Model Desciption

2

the body shell with kinematic

coupling

• Model is constrained about

BOUND1 at the origin using

kinematic coupling

BOUND4

EXEN2

DAAV loads

EXEN1

DAAV loads


Generation of Mesh

Shell Element:

• S4 (Abaqus)

Solid shell elements:

• HC24_9 (UEL , User element)

• SC8R (Abaqus)

Degrees of freedom:


Solid model Shell model

318 612 244 254

A numerical model for test purpose:

• Close to practical problems

• Reasonable computational costs

Generation of Mesh

Two different models

-Solid model displays frame thickness in mesh

Solid shells:

• More overall DOFs

• More elements in model due to

- Intersections

- Modelling of Frames


Solid model (HC29_9, SC8R) Shell model (S4)

- Modelling of Frames

Load Steps - Overview

• 3 Initial Loads;

• Thermal Loading - Initial thermal

loads

• Tank Loading - Pressure of the LOX

tank

• Aero Pressure – Aerodynamic

pressure on fuselage

5

• 2 Mechanical Loads;

• Flight simulation – Load to simulate

flight conditions, applied to DAAV

loads reference points and STN 31

nodes.

• Artificial load – create buckling,

applied to DAAV loads reference

points and STN 31 nodes


STN 31

DAAV

Loads

Load steps - Order

Step Describtion

1 Temperature

2 Tank pressure

3 Aero pressure

4 Flight simulation


4 Flight simulation

5 Artificial load (to create

buckling)

Load steps - Temperature

Step Describtion

1 Temperature

2 Tank pressure

3 Aero pressure

4 Flight simulation


4 Flight simulation


buckling)

Application:

All elements of the model are

subjected to initial thermal loads

Step Describtion

1 Temperature

2 Tank pressure

3 Aero pressure

4 Flight simulation

Load steps – Tank Pressure


4 Flight simulation


buckling)

Application:

LOX pressure load applied to

Lower cylinder and both

hemispheres

Load steps – Aero Pressure

Step Describtion

1 Temperature

2 Tank pressure

3 Aero pressure

4 Flight simulation


4 Flight simulation


buckling)

Application:

Artificial aerodynamic pressure

applied to external sections

Load steps – Flight Simulation

Step Describtion

1 Temperature

2 Tank pressure

3 Aero pressure

4 Flight simulation


4 Flight simulation


buckling)

STN 31

DAAV

Loads

Application:

Booster loads applied to DAAV (up),

Tension loads applied to STN31

Load steps – Artifical Load

Step Describtion

1 Temperature

2 Tank pressure

3 Aero pressure

4 Flight simulation


4 Flight simulation


buckling)

STN 31

DAAV

Loads

Application:

Artificial loads applied to DAAV

(down),

Compression loads applied to STN31

Mode of failure

Computations are aborted at

70% through step 5.

This is due to buckling that is This is due to buckling that is

induced through the articial

compression load applied

during step 5.


Problems with the SC8R, Part 1

Model using SC8R elements, did not deform about frames in step 1

as per UEL and Shell elements


Consequence:

Remodelling of frames with solid elements (C3D8)

UEL:

Problem does not occur for the user element, thus making the User

element is suitable to model massive structures

Undeformed frames (blue)

Problems with the SC8R, Part 2

SC8R model does not pass step 1 due to massive local distortion of

elements about the hemisphere end:


S4 SC8R

UEL:

The user element successfully passed the step with deformation of

the hemisphere similar to S4 model

Consequence:

Reduce the initial temperature load by 50% of original load

specification

Comparison of Convergence

100% Temp.

Step UEL S4 SC8R

1 12 12 n. c.

Number of increments and maximal step time

50% Temp.

UEL S4 SC8R

12 12 12


1 12 12 n. c.

2 12 12 -

3 12 12 -

4 12 12 -

5 20 18 -

max 4.68 4.72 0.63

12 12 12

12 12 12

12 12 12

12 12 15

22 15 20

4.69 4.72 4.71

Comparison of Local Strain Energy Density

Comparison of Total Strain Energy Density


Comparison of Total Strain Energy Density

Comparison of Displacements


Comparison of Displacements


Summery of Comparison:

• Similar total and local strain energy

density

• Diverging results for displacements

• Close coincidence of the results is

obtained for small and moderate

deformations

Summary

• Application of UEL for a practical problem has been

demonstrated

• More DOF for solid shell elements due to model differences

• UEL suitable to model massive structures

• UEL more stable than SC8R element of Abaqus for such large

structures

• Similar convergence• Similar convergence

• Similar total and local strain energy density

• Diverging results for displacements


ACOSTA-Solid shell user element and ABAQUS shell elements ... · PDF fileACOSTA-Solid shell...

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