Demeass Iv D Alessandro

Progresses on the vibro-acoustic design of a

class of aluminium sandwich plates

Vincenzo D’Alessandro, Francesco Franco,

Sergio De Rosa, Tiziano Polito

DEMEASS IV, March 26-30 2011

Urspelt (Luxemburg)

ælab ‐Vibrations and Acoustics Laboratory

Department of Aerospace Engineering

Università degli Studi di Napoli “Federico II”

Via Claudio 21, 80125, Napoli, Italy

www.dias.unina.it

Outline

Synopsis

References

DEMEASS III: A Review

ECOCELL Core

Investigated Configurations

Numerical Results

Experimental Tests

Conclusions and Future Work

Progresses on the vibro-acoustic design of a class of aluminium sandwich plates 2

Synopsis


Sandwich panels are widely used in engineering

application because of the extremely high stiffness-to-

mass ratio. The design flexibility associated with such

composite structures provides significant opportunities for

tailoring the structure to the load and dynamic response

requirements.

A new concept of sandwich plate (all aluminum based)

was tested in order to get the typical results available with

more complicated configurations.

This work is the straight continuation of the work

presented in the last DEMEASS.

Activities herein presented will be continued and

extended under the project SUPERPANELS

(www.superpanels.unina.it).

http://www.superpanels.unina.it/

References


Kurtze and Watters (1959) studied the application of sandwich panels to increase the sound

insulation between adjoining spaces. They investigated the relation between bending and shear

waves and TL characteristics.

Lang and Dym (1975) optimized the design of a sandwich panel with the goal to exceed the TL

values predicted by the mass law by at least 20 dB in a selected frequency range.

Barton and Grosveld (1981) considered an aeronautical application of honeycomb panels to

improve sidewall attenuation in a light twin-engine.

Thamburaj and Sun (2002) demonstrated that an anisotropic core can lead to higher TL and that

the proper design of face sheet thickness can further improve the performance.

NASA tests (2002) about the performance of sandwich structures with a core made of a lattice of

truss elements are available.

Cunefare et al. (2003) gave additional indication that structural acoustic optimization has the

potential to achieve significant gains to reduce interior noise levels in aerospace structures.

Franco et al. (2007) analyzed the optimization of the structural-acoustic characteristics of various

and innovative sandwich configurations. They considered different core configurations, and those

having a truss geometry have been very promising configurations, since it is possible control the

stiffness along the two direction in-plane of the panel.

Franco, De Rosa and Polito (2010) demonstrated that the vibro-acoustic responses can improve

if a random stiffness is imposed over an optimized configuration, highlighting that randomization

represents a very cheap simulation step.

2 m

ete

rsd

ista

nce

DEMEASS III: A Review


Sandwich panel with truss-core

18128 and 23664 rods along the

X and Z axes, respectively

Effect of a randomization of the stiffness properties on the

optimized configuration has been analyzed.

ECOCELL Core: Concept


• Stereolithography is a costly and complicated

procedure.

• Need for both simplified plates and related models

able to take into account the peculiarities of the

configurations and results of the sandwich plate with

resin core.

• Thinking to

– the LEGO© elementary brick concept and

– classical carton filler for packaging . . . .

ECOCELL Core: Concept – Basic Unit


Equivalent COre CELL:

an aluminium (plate-like)

basic element able to

reproduce the complexity

of the resin core cells.

Core modular element (dimensions in mm)

ECOCELL Core: Global view


Truss-like core

16 stiffeners along x-axis

11 stiffeners along z-axis

ECOCELL Core: Global view of the sandwich


Basic Sandwich Panel Configuration

Lx=0.640 m, Lz=0.420 m

FE mesh: 10965 grid points

10752 four-point plate element.

2 m

Vibro-acoustic Indicators

QPdSdSPvQv

QPdSdSPvQPk

QPkQv

cdSPvPp

dSPvPvv

S S

S S

S

rad

S

MS

if ,),(),(

if ,),(||

|)|sin(),(

4);();(Real

2

1)(

);();(Real2

1)(

*

*

0

0

2*

*2

Continuos

)()()(4

)(

)()(Real2

1)(

2

2

AvARv

vv

H

a

arad

H

MS

c

v

Discrete

Thus, it is possible, on the base of the results achieved from a frequency

response analysis of the finite element model of a generic plane structure,

to calculate the radiated acoustic power.

v(ω) is the velocity vector

R(ω) is the radiation resistance matrix

A is the nodal equivalent areas matrix


ECOCELL core configurations (Mcore=0.52 Kg)

Code Stiffeners Configuration

Base Stiffeners in both directions: tx = tz= 1 mm

B No stiffeners along x-axis: tz= 1.9545 mm

C No stiffeners along z-axis: tx 2.0476mm

D Half stiffness along x-axis: tx = 0.6825 mm, tz= 1.3030 mm

E Half stiffness along z-axis: tx = 1.3625 mm, tz= 0.6515 mm

Skin thickness configurations: panel mass distribution

Skin Thickness [mm] Skin Mass [Kg] Sandwich Mass [Kg]

1 0.726 1.972

2 1.452 3.424

3 2.178 4.876

Coding: CODE_THmm


Investigated Configurations

Numerical Results (cont’d)Influence of Core Configuration

Spatial Mean Square Velocity – Face Sheet Thick 1mm – Panel Weight 1.97Kg – BC = SS

Frequency [Hz]

V2M

S[m

2/s

2]

0 1000 2000 3000 4000 5000

106

105

101

103

102

104

Base_1mm

D_1mm

E_1mm

C_1mm


30

40

50

60

70

80

Radiated Acoustic Power – Face Sheet Thick 1mm – Panel Weight 1.97Kg – BC = SS

Numerical Results (cont’d)Influence of Core Configuration

Frequency [Hz]

dB

0 1000 2000 3000 4000 5000

C_1mm configuration

Base_1mm

D_1mm

E_1mm

C_1mm


30

40

50

60

70

80

Radiated Acoustic Power – Different Face-Sheet Thickness

Numerical Results (cont’d)Influence of Face-Sheet Thickness

Frequency [Hz]

dB

0 1000 2000 3000 4000 5000

Base_1mm

Base_2mm

Base_3mm


Numerical Results (cont’d)Randomness of the Core Stiffness (1/4)

It was investigated the effect of the addition of a random distribution of the

core stiffness. The random distributions were based on two (uncoupled)

Gaussian functions.

Frequency [Hz]

V2M

S[m

2/s

2]


0 1000 2000 3000 4000 5000

106

105

101

103

102

104

sr = 70%

Base_1mm

sr = 40%

sr = 60%

sr = 70%


101


105


Frequency [Hz]

V2M

S[m

2/s

2]

106

103

102

104

0 1000 2000 3000 4000 5000

C_1mm

C1_1mm

C2_1mm

C3_1mm

C4_1mm

C5_1mm

C6_1mm

C7_1mm

C7_1mm


20

Radiated Acoustic Power – Face Sheet Thick 1mm – Panel Weight 1.97Kg – BC = SS


Frequency [Hz]

dB

106

30

40

50

60

70

80

0 1000 2000 3000 4000 5000

C_1mm

C1_1mm

C2_1mm

C3_1mm

C4_1mm

C5_1mm

C6_1mm

C7_1mm


Optimization of the ECOCELL Core (1/2)

NX NASTRAN optimizer (SOL 200) - Modified Method of Feasible

Directions

Twenty-seven design variables: thickness of the stiffeners

Constraint: weight of the core, i.e. the thickness of the stiffeners are

explicitly linked because is imposed a constraint on their variations so

as to keep the core weight less or equal to the value of the initial

configuration

Objective Functions: the simplest objective function is the average of

the square structural velocity on the radiating face sheet and over the

chosen frequency range

2

,1 1

1 NG NF

i ji j

F VNG NF

• NG = number of discrete sample

points on the face of the panel

• NF = number of frequency sample

points

Numerical Results (cont’d)


Optimization of the ECOCELL Core (2/2)

NG = 30, NF = 21, Range 1800 – 2300 Hz, base_1mm starting configuration

Frequency [Hz]

V2M

S[m

2/s

2]

1800 2000 2200 2400

101

102

104

103

C7_1mm

Optimizer configuration

Numerical Results (cont’d)


Experimental Tests – The 1st prototype


Manufacturing Problems

1. ECOCELL core in steel instead

of aluminum alloy

2. Face sheet 3 mm thick and

grooved in correspondence of

the stiffeners positions to

facilitate their installation

3. Pods filled with epoxy glue

4. There is contact in the

intersection of stiffeners!

Experimental Tests – The 1st prototype


Modal analysis – Impact testing by using LMS TESTLab

Conclusions and Future Work Concept of ECOCELL core has been introduced

Vibro-acoustic response of several articles with common structure and

difference in skin and core have been analyzed in terms of mean

square velocity and radiated acoustic power, evaluating the influence

of core configurations.

Confirm that randomization approach allows an improvement of vibro-

acoustic behavior.

First experimental test has been introduced, without significant results

due manufacturing problems.

Future Work

Numerical developing: identifying an optimization method that lead an

optimal configuration (multicriteria genetic algorithm)

Find the right technology to manufacture the sandwich panel, in order

to compare numerical and experimental tests.


Thanks for your attention


Demeass Iv D Alessandro

Technology

Transcript of Demeass Iv D Alessandro