A340-600 FAN COWLS FINITE ELEMENT MODEL: USING …web.mscsoftware.com/events/aero2002/partner/pdf/p04301.pdf · CQUAD4 and CTRIA3 plate elements. ... parts have been simulated by

3rd Worldwide Aerospace Conference

September, 24-26, 2001

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MILITARY TRANSPORT AIRCRAFT DIVISION

A340-600 FAN COWLS FINITE ELEMENT MODEL:

USING MSC.Nastran TO MODEL CFC SECONDARY STRUCTURES

WITH CONTACT BOUNDARY CONDITIONS. 2001-43

Sofía Ponce Borrero, Juan Pablo Juste Mencía

Stress Department

Engineering Division

EADS CASA.

Military Transport Aircraft Division

Avda. John Lennon s/n, Getafe, Madrid (Spain)

Tf. +34 91 6242373

e-mail [email protected], [email protected]

ABSTRACT

EADS CASA has large experience in Finite Element Model techniques, making full aircraft

or component models. But since a few years, the modelisation of secondary structures has

taken more importance, up to become an essential part in their analysis, and also because they

are finally integrated into the full component FEM.

The optimisation of the codes and the inclusion of new capabilities in the FEM solvers, in

combination with the increasing in the computer performances have allowed the analysis of

structures under very complex load and boundary conditions using detailed FEMs.

EADS CASA Military Transport Aircraft Division is responsible under AIRCELLE contract

of the design and manufacturing of A340-600 Fan Cowl.

This article describes the process to analyse the A340-600 Fan Cowls using a non-linear

MSC.Nastran solution with contacts and large displacements.

The structure is a monolithic CFC composed by two curved stiffeners panels (barrels), loaded

by internal and aerodynamic pressures, temperature and enforced displacements.



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The structure is very high affected by the particular supporting and boundaries conditions:

four hinge fittings per side, pretension latches in between and enforced by the displacement of

the rest of the engine devices in the contour.

This method has been successfully used in EADS CASA to obtain stress and strains in CFC

panels and also to predict the correct shape of the tools, due to deformations under

temperature cycles during the manufacturing process.



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1. Introduction.

EADS CASA is an aircraft manufacturer company that has developed a technological and

productive capacity, which allows it to compete in the international market. It has large

experience in the Finite Element Model techniques in component ones and in

Multidisciplinary Global Aircraft Finite Element Model to be applied to the full aircraft

FEMs.

This article describes the A340-500 TRENT Fan Cowl model and the complexity of its study

due to the special characteristics and requirements involved (non-linear analysis, enforced

displacements, temperature effect, contact elements…). The use of pre-tension loads in order

to fulfil the aerodynamic tolerances and controlling the scooping effect within acceptable

margins is one of the most remarkable features of the Fan Cowl analysis.

The Fan Cowl model herein outlined was built up to allow its integration in the Nacelle

integrated FEM. Improved structural behaviour and more reliability on interface loads are

then achieved.



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2. Fan Cowl Finite Element Model.

The Fan Cowl Finite Element Model has been generated based on CATIA surfaces in a

directed communication between CATIA and MSC.Patran (CATIA Direct Access). The

monolithic CFC structure composed by two curved stiffeners panels has been modelled using

CQUAD4 and CTRIA3 plate elements. The rest of the model corresponds to the metallic

parts have been simulated by CROD and CBEAM elements. Figure 9.1 represents a general

view.

The model, quite complex due to the high curvature of the surface, includes in addition to the

monolithic CFC structure:

q Four hinges (per side) which represent the interface with the pylon, the landings to

support in the fan case,

q Four latches to assure the perfect closure,

q Two axial locators and a retainer (per side) to restrict the axial and radial displacement

respectively,

q Two Hold Open Rod (per side) when the fan cowl is open for,

q One actuator (per side) to open it.

All of these elements can be seen in figures in point 9.

In order to analyse and show compliance with the Fan Cowls structural requirements, three

different models were necessary to be used:

q The Ground Model used for the study of opening and closing design cases allows the

analysis of each one of the discrete opening angles by rotating of coordinate axis. Linear

Static Solution (SOL 101) has been used for this model. The Hold Open Rods and

Actuator together with the Hinge fittings are the support conditions on this model (Figure

9.5).

q The Flight Model contains non-linear elements like gaps that represent the Inlet and the

Thrust Reverse support and the contact between the two sides of the Fan Cowl. There are

other parts simulated in the flight model as latches, axial locators, retainers that mustn’t



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work when the Fan Cowl is open. MSC.Nastran’s Non-linear Static Solution (SOL 106)

has been used for the flight model. (Figure 9.1). Large displacements have been

considered to take into account the membrane effect.

q The “Damage Tolerance” model has been created to be able to demonstrate the structure

can withstand large debonding of the stiffener up to limit load. The model consists of a

refined mesh in the critical area for this condition, and the simulation of anti-peeling bolts

by means of CELAS elements between coincident nodes at the stiffener-skin interface.

The required stiffener debonded area is simulated by disconnecting the corresponding

CELAS elements (Figure 9.8).

q Fail safe conditions corresponding to Ground and Flight models have been also

considered.

General data about both models are shown in the following table where there are differences

in the number of nodes, elements and coordinates frames between both models.

Number of Flight Model Ground model D/T model

Nodes 3303 3189 8257

Elements 3655 3512 11736

MPC’s & RBE’s 5 5 --

Material cards 69 69 69

Property cards 53 53 53

Coordinate frames 4 8 (*) 2

Degrees of freedom 19026 8947 49824

(*): per opening. There are different co-ordinate systems for

each opening.

3. Boundary and Contact Conditions.

Another complexity is the boundary conditions used to simulate the effect of the rest of the

Nacelle into the fan-cowl. Enforced displacements have been added in the interface to fix the

corresponding movement: Inlet, Thrust Reverse, hinge fittings and axial locators. The hinge



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fittings have all their degrees of freedom restricted except for the axial displacement that is

only restricted in Inlet and Thrust Reverse.

The Inlet and Thrust Reverse support is modelled with two points coincident with a gap in

between with a closed stiffness of 104 N/mm2, as it can be seen in the figure 3.1.

Figure 3.1: Landings.

The other existing gaps are placed in the contact between the two sides of the Fan Cowl

where the beams which carry the shear load are also placed. In the figures below it also can be

seen the latch simulated by a CBEAM element with thermoelastic properties in order to

include preload in latches. Latch is supported by means a rigid element at one end and by four

rods in the other one.

Figure 3.2: Latch and Keeper housings.

Radial direction

• • Inlet (Fix

point)

Fan Cowl point Gap

Latch

Right

Left

Gaps

Shear PIN(Beam Element)

Contact Door Points(Gap Element)Initial gap opening 1 mm

X

Y

Z

RIGHT SIDE

LEFT SIDE1 mm



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Figure 3.3: Gaps in latches.

The axial locator modelisation is also simulated by two coincident nodes attached in

longitudinal direction with stiffness in open and closed condition.

Figure 3.3: Axial locator

The retainer is also performed giving stiffness to correspond CGAP element when is open and

closed but in radial direction.

Figure 3.4:Radial retainer.

4. Loads.

Several flight cases as well as ground ones have been covered with the complete Fan Cowl

analysis.

Flight Load cases:

This type of cases is composed by several loads:

q External Cp (aerodynamic coefficient of pressure) values are provided and taken as

basis to simulate the pressure with PLOAD4 cards.

q Internal pressure is also taken into account by means of PLOAD4 cards.

q The fan cowl weight is included through a GRAV card.

q The temperature effect has been considered in the material properties and some higher

temperatures have been used in the analysis of the duct burst event.

Axial direction

• • Inlet (Fix

point)

Fan Cowl point Gap

Radial direction

• • Inlet (Fix

point)

Fan Cowl point Gap



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q Pretension load in the latches. This pretension load is simulated by nodal temperature

cards applied in the extremes of the latch, represented by a beam. Therefore TEMPD cards

have been added

q Enforced displacements coming from the Nacelle integrated FEM. They simulate the

interface with the fan case and the joint to the pylon, which have a very high influence in

the interface loads.

A significant effect studied is the scooping. It must be considered an additional internal

pressure in those cases in which displacements in the Inlet area are higher than the

thickness, due to the air stream is allowed to come into the fan cowl. This effect is included

in the loads analysed.

Ground Load cases:

The ground cases analysed are taking into account the different fan cowl openings up to 55

grades. The values for Actuator and Hold Open Rod loads, obtained for 45 Knots cases

supported on actuator and 60 Knots cases supported on Hold Open Rod, depend so much

on the fan cowl opening.

Different boundary conditions combinations are studied for the different openings due to a

few conditions of HOR and Actuator support. In one of the intermediate apertures, 38º the

HOR are blocked and they are assumed not to go down from this opening. This effect has

been considered supposing the HOR only withstand tension loads and not compression.

With 55 º the Fan Cowl is only supported in HOR and not in Actuator.

When the Fan Cowl is open it is not supported in the Inlet and Thrust Reverse, therefore

there aren’t enforced displacements in the analysis. However the Hold Open Rod and the

actuator are supported on the engine.

All these points are necessary to take into account all the requirements that must fulfil the Fan

Cowl, and they make its analysis quite complex and time consuming. 82 static cases, 30

fatigue cases, 121 fail safe cases and 2200 ground cases have been considered. It has been

necessary to create automatic procedures to be able to study all these cases, methods that read



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the MSC.Nastran output files. With these results it has been obtained the interface loads,

strains and stress values in skin and stiffeners, displacements in Inlet and Thrust Reverse, …

5. Analysis.

The different models are analysed in different ways:

q For all the flight cases, non-linear analysis has been studied because there are non-linear

elements as the gaps that simulate the supports in Inlet and Thrust Reverse and the contact

between both sides in the latch area.

As it is a non-linear analysis there are quite important parameters used in the NLPARM

card to assure the solution convergence.

NLPARM card Default Used

NINC 10 25

KMETHOD AUTO SEMI

KSTEP 5

MAXITER 25

CONV PW

INTOUT NO

EPSU 0.01

EPSP 1.0E-3 0.01

EPSW 1.0E-7

1.0E-5 1.0E-6

q In the ground cases these elements do not appear because the fan cowl is open, therefore

it can be used a linear solution (SOL 101) to analyse the results. A non-linear solution is

not necessary because the most important effect is bending and not membrane one, and

because there aren’t gaps.

q The “Damage Tolerance” model study has been performed using a buckling solution

(SOL 105).

Some results for the three models are shown in figures 9.6-9.8.

The parameters in the case control statement are the following:



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- LGDISP=1: Large displacement effects (updated element co-ordinates and follower

forces).

- AUTOSPC=NO: The singularities are not constrained.

- K6ROT=100: It’s a high value to be able to suppress the grid point singularities.

Another analyses performed with the Fan Cowl model are Engine Imbalance and

environmental dynamic analysis. These dynamic analyses have the particularity to combine a

non-linear FEM structural model with input loads that are given in terms of vibration spectra

(which in turn implies linear calculation). The first work consists of studying linearised

conditions approach and then develops the methodology and application to the Fan Cowls

considering non-linear conditions. The second one starts with the linearisation of boundary

conditions and goes on with the application of the vibration envelope spectrum to the Fan

Cowl. Figures 9.9 and 9.10 show different responses.

6. Quality Assurance.

A full static and dynamic quality assurance has been performed with the Fan Cowl model to

assure a quality level giving good static and dynamic responses following EADS CASA

procedures.

The geometrical checks, performed using the MSC.Nastran V68.2.3 with solution 101 and

with MSC.Patran V8.0, are the following: coincident nodes only in boundaries between the

Fan-Cowl and the nacelle, and in the door area; coincident elements connecting coincident

nodes in door area; free edges, element warping, interior angles, ELAS and GAP elements,

rigid elements, co-ordinate systems, connectivity and element co-ordinates, material co-

ordinate systems…

In the static validation the model is loaded with a test load case in order to check the general

model performances.

The results of the static checks show there are only reactions where the model is supported,

the MPC forces in latches are in the right direction, the applied load resultant is equal to the

reaction forces resultant, maximum ratio, epsilon and external work are under limit values,…



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In the dynamic validation the structure is free without interface with the nacelle. Seven

different runs have been performed using different values for PARAM and SPC.

7. Future Improvements.

A possible improvement that can be developed in the future is the use of Superelements to

replace the enforced displacements nowadays applied. With the use of imported stiffness

matrix to simulate the rest of the structure the results accuracy would be improved.

8. Conclusions.

The analysis performed by EADS CASA for the Fan Cowl study has demonstrated that the

modelisation of secondary structures is an essential work to reproduce the real behaviour of

the structure with a high precision, integrating it then in a full component model.

The boundary conditions complexity simulating the contact with the rest of the nacelle, the

non-linear solutions analysed, the amount of load cases studied let us reproduce the real

behaviour of the structure with more accuracy taking into account all the possible situations in

flight and in ground.



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9. Figures.

Figure 9.1.- General Fan Cowl view.

FWD

RWD



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Figure 9.2.-: Hinge fitting view.

Figure 9.3. Locator and retainer positions.

Figure 9.4. Landing positions.

Lower right locator

Lower left locator Retainers

Thrust reverse

landings

Inlet

landings



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Figure 9.5.- Fan Cowl open.

Figure 9.6.- Duct burst case displacements.

Actuators

Hold Open

Rods



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Figure 9.7. Displacements

Figure 9.8.- Stiffener disbonding.



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Figure 9.9. A340-500/600 fan cowl normal mode: Local first upper fitting mode (89.08 Hz).

Figure 9.10. A340-500/600 fan cowl normal mode: Local rear latch mode (93.40 Hz).

Documents

A340-600 FAN COWLS FINITE ELEMENT MODEL: USING …web.mscsoftware.com/events/aero2002/partner/pdf/p04301.pdf · CQUAD4 and CTRIA3 plate elements. ... parts have been simulated by