TOPOLOGICAL, SIZE AND SHAPE OPTIMIZATION OF AN UNDERWING PYLON SPIGOT

TOPOLOGICAL, SIZE AND SHAPE

OPTIMIZATION OF AN UNDERWING

PYLON SPIGOT

Prepared by: M. Basaglia (Alenia Aermacchi), S. Boni

Cerri (Alenia Aermacchi), G. Turinetti (Altair)

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Topological, Size and Shape Optimization of an Underwing Pylon Spigot

•Aircraft pylons have the function of supporting external payloads and are

installed under the wing and / or the fuselage. Pylons that are being developed

in Alenia Aermacchi will be installed on M-346 new advanced training aircraft.

•Inside the pylon, the structure called spigot or, in some cases, pivot is a highly

stressed structure made of high resistant steel and is the component that

transfers the concentrated loads coming from the carried mass to the wing or

fuselage structure.

•The design activity started from the available space envelope, from the

interfaces that were defined as non-design zones and the sizing loads (a set of

26 load cases). The application has been performed using OptiStruct.

•Two subsequent optimizations have been conducted: the first one followed a

topological approach, the second one was set as a shape optimization.

SPIGOT OPTIMIZATION

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SPIGOT OPTIMIZATION

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RBE3 area for the

WING/SPIGOT interface

force application.

SPIGOT OPTIMIZATION

CELAS - X, Y, Z direction

Applied force - lower node

RBE3 area for the

WING/SPIGOT interface

force application.

Applied force - upper node

Spigot constrained to the ground (conservative approach) through celas elements

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SPIGOT OPTIMIZATION

Stress - max principal

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SPIGOT OPTIMIZATION

Present spigot configuration

Weight = 4.352 kg

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SPIGOT OPTIMIZATION

Non design area

Non design area

Starting volume

26 load cases

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SPIGOT OPTIMIZATION

Main advantage of topological optimization is to easily check how the

structure is designed by the optimization tool in relation to some

different design and manufacturing strategies (objective, responses and

constraints).

First optimization iterations are developed with the objective of

minimum weight compliance referred to all load conditions (with the

same weight equal to 1).

Constraints: mass fraction, minimum dimension, stress level, planes of

symmetry, direction of machining.

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SPIGOT OPTIMIZATION

Responses: Weight compliance, mass fraction

Constraint: mass fraction ≤ 0.25

Objective: MIN weight compliance

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Manufacturing constraints: XZ plane of symmetry, mindim in the whole design space


SPIGOT OPTIMIZATION

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Manufacturing constraints: YZ and XZ planes of symmetry, mindim in the whole design

space


SPIGOT OPTIMIZATION

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SPIGOT OPTIMIZATION

Responses: Weight compliance, mass fraction, stress

Constraint: mass fraction ≤ 0.25, maximum principal stress<1000MPa in the ‘non design’

area

Manufacturing constraints: XZ plane of symmetry, mindim in the whole design space

1 draw direction (Z)


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SPIGOT OPTIMIZATION

Responses: Weight compliance, mass fraction, stress

Constraint: mass fraction ≤ 0.25, maximum principal stress<1000MPa in the ‘non design’

area

Manufacturing constraints: XZ plane of symmetry, mindim in the whole design space, 2

design spaces in order to define draw directions (X, Z)

Objective: Min weight compliance

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SPIGOT OPTIMIZATION

Responses: Weight compliance, mass fraction, maximum stress


Constraint: stress in the critical area (highlighted in the above figure) ≤ 1000 MPa


draw direction (Z)


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SPIGOT OPTIMIZATION

Response: Mass, displacement

Constraint: Displacement constraint on the top of the Spigot extracted from the starting

configuration.


draw direction (Z)

Objective: MIN mass

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SPIGOT OPTIMIZATION

Side flange thickness Side cutout size Spigot base radius (dense Mesh)

Spigot conicity Lower transverse stiffener thickness

Lower hole diameter

Shape optimization phase

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SPIGOT OPTIMIZATION

Optimization problem definition:

Objective = Minimize Mass

Constraints =

• Stress ≤ Sigma max

• Bolt forces ≤ F max

In the above figure, the highlighted areas

represent a dense mesh zone, where the

stress response is checked.

The mass growth is due to the

approximation coming from the topological

optimization and the redesigning of new

CAD with some violation of stress

constraint.

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SPIGOT OPTIMIZATION

The above figure shows the

contours of shape changes,

where the red area represents

the biggest parameter

reduction.

Spigot final configuration

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SPIGOT OPTIMIZATION

The weight reduction between the starting configuration and the configuration at the last optimization is of 5%

Configuration and mass evolution

Weight at the beginning of

the shape optimization

FEM weight = 4.028 kg

CAD weight = 4.015 Kg

Weight at the end of the shape

optimization


CAD extimated weight = 4.125 Kg

Present weight


CAD weight = 4.352 Kg

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SPIGOT OPTIMIZATION

Conclusions

•The topological optimization phase gave the evidence of the

possibility of saving weight removing material in some areas,

compared to the traditional design, in a way that with a standard

sizing approach is difficult to imagine.

•The shape optimization permitted to refine the previously

identified design.

•An interesting weight reduction (for this kind of structure) of 5%

has been obtained.

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Q & A

Thank you for your attention

SPIGOT OPTIMIZATION

Technology

TOPOLOGICAL, SIZE AND SHAPE OPTIMIZATION OF AN UNDERWING PYLON SPIGOT