acoustic optimization of an engine oil pan concerning the equivalent radiated sound power function

Author: Eduardo Porto 1 EATC 2013 Turin, Italy 24.04.2013

“Acoustic optimization of an engine oil pan concerning the equivalent radiated sound power function”

Author: Eduardo Porto Phone: +49 5362 17 226 Email: [email protected]

Company: Semcon Wolfsburg GmbH

Wolfsburg, Germany

Author: Eduardo Porto

• Founded in 1968 in Germany

• Operations on 45 locations and 3 000 employees

• Turnover € 295 M (2012)

• A global partner in engineering services and product information

• Competencies in several industries

2

Semcon Group in short

Automotive Manufacturing industries Energy Telecom Life Science


Introduction So far, the optimization calculations have been mostly applied to problems involving

compliance, frequency and/or stress responses;

Now with HyperWorks 12 a new class of optimization problems can be solved, concerning the task of minimizing the sound radiated power.

A new type of response, the so called ERP (abbreviation for Equivalent Radiated Power), is now officially available in OptiStruct 12 as objective function.


Problem Definition • Aim: To reduce the structure-borne sound radiation related to the oil pan bottom part.

Figure 2. Engine model exploded view.

Engine head cover

Engine head

Cylinder block

Gear unit housing

Engine front cover

Main bearing cap

Oil pan top part Oil pan bottom part

(t = 3 mm)

Figure 1. Simplified engine model.

• Oil pan bottom part modeled with CTRIA3/CQUAD4 elements; the other parts with PENTA6/HEXA10.

• Oil pan bottom part material is steel; the other parts are of aluminum.

• Average element size: 6 mm

• Total number of nodes: 75 749

• Total number of elements: 53 840

• Part connections modeled with RBE2 elements.


Problem Definition

Plot 1. Excitation force in the frequency domain.

f (Hz)

Fz (kN)

3000 400

1

Harmonic Excitation Load:

• Engine model is not constrained.

• The Fz forces are simultaneously applied.

• Overall structural damping: 4%

Fz

Fz

Fz

Section A-A

A

A

Figure 3. Excitation loads of amplitude Fz.

• 1st. eigenfrequency of the model: 653 Hz


Figure 6. Air model in the vicinity of the oil pan: 350 x 330 x 150 mm.

6 EATC 2013 Turin, Italy 24.04.2013

Analyses and Optimization Methods ERP Analysis [1]:

Optimization Techniques [1]:

𝐸𝑅𝑃 = 𝐸𝑅𝑃𝐿𝐹 ∗1

2𝐸𝑅𝑃𝐶 ∗ 𝐸𝑅𝑃𝑅𝐻𝑂 ∗ 𝐴𝑖 ∗ 𝑣𝑖

2

𝑛𝑔𝑟𝑖𝑑

𝑖

where: ERPLF = radiation loss factor; ERPC = speed of sound; ERPRHO = fluid density; A = radiating surface area; v = sound particle velocity; ngrid = number of nodes; i = node ID.

Exterior Acoustic Analysis [2]:

Radiating surface

Figure 4. Radiating surface.

Design space Non-Design space

Figure 5. Design and non-design space.

o Bead (Topography)

o Free-Size

o Topology

No air modeling required!

• For validation of the ERP

• For analyses and re-analyses


Structural Optimization

Subjected to:

h = 3 mm w = 10 mm = 60°

w

h

Design elements

Figure 7. Bead parameters.

w = bead min. width h = bead height = draw angle

Bead Optimization Free-Size Optimization Topology Optimization

MinMax ERP MinMax ERP MinMax ERP

Subjected to:

No volume restriction!

T

Shell cross-section

T0

Figure 8. Free-size element parameters

T = max. shell thickness T 0 = min. shell thickness

T = 3 mm T0 = 6 mm

Subjected to:

No volume restriction!

T

Shell cross-section

T0

Core

Designable regions

Figure 9. Topology element parameters

T = max. shell thickness T 0 = min. shell thickness

T = 3 mm T0 = 6 mm


Plot 2. Oil pan bottom part radiated sound power.

1st. Eigenmode at 653 Hz

Acoustic pressure in the air

Air density = 1.204E-12 ton/mm3

Sound speed = 3.43E5 mm/s

Result Discussions

Author: Eduardo Porto 9 EATC 2013 Turin, Italy 24.04.2013 Plot 3. Acoustic radiated power versus ERP.

Result Discussions

Acoustic Radiated Power (Exterior acoustic analysis)

Fluid-structure interaction considered

Equivalent Radiated Power (Frequency response analysis)

Radiation loss factor = 1.0


Figure 10. Bead optimization results.

10 EATC 2013 Turin, Italy 24.04.2013

Result Discussions

Optimal solution

Interpretation of the optimal solution

Bead Optimization

∆ = -25%


Figure 11. Free-Size optimization results.

11 EATC 2013 Turin, Italy 24.04.2013

Result Discussions

Optimal solution


Free-Size Optimization

∆ = -18%


Figure 12. Topology optimization results.

12 EATC 2013 Turin, Italy 24.04.2013

Result Discussions

Optimal solution


Topology Optimization

∆ = -21%


Figure 13. Conventional approach result.

13 EATC 2013 Turin, Italy 24.04.2013

Result Discussions

Conventional bead pattern

Conventional Approach

∆ = -3%


Result Discussions

Bead Optimization Free-Size Optimization Topology Optimization Baseline Conventional

Max. Value:

169.7 Pa Min. Value:

21.2 Pa

Max. Value:

157.1 Pa

Min. Value:

19.6 Pa

Max. Value:

168.5 Pa

Min. Value:

21.1 Pa

Max. Value:

164.7 Pa

Min. Value:

20.6 Pa

Max. Value:

176.7 Pa

Min. Value:

22.1 Pa

Figure 14. Acoustic pressure results at the critical excitation frequency.


Result Summary

Model Bead Pattern Pre-

processing Convergence

Curve Iteration Number

CPU-Time *

Post-processing

Acoustic Radiated

Power

Max. Acoustic Pressure

Baseline - - - - -

Bead

Free-Size

Topology

Conventional - - - - -

* JOB-Machine: 8 CPU Intel(R) Xeon(R) @3.30GHz, 32162 MB RAM. Table 1. Result summary.

No difficulties

No difficulties

No difficulties

Monotonic

Monotonic

Non-monotonic

12

9

16

New FE-mesh required



00:16:13

00:34:37

00:41:46

122.1 mW @810Hz (-25%)

133.1 mW @810Hz (-18%)

128.6 mW @783Hz (-21%)

157.8 mW @796Hz

(-3%)

162.0 mW @653Hz

157.1 mW @810Hz

168.5 mW @810Hz

164.7 mW @783Hz

176.7 mW @796Hz

169.7 mW @653Hz


Methodology Overview

Re-analyses

(exterior acoustic analyses)

FE-Modell

Optimal results interpretation

Structural Optimization

(Goal: MinMax ERP-Function)

ERP-Analysis

(no FSI)

Bead Optimization

Free-Size Optimization

Topology Optimierung

Konventionelles Modell

Basis

Exterior acoustic

analysis (with FSI)


Conclusions & Significance of the Work The acoustic optimization task is successfully performed without requiring the fluid-

structure interaction modeling.

The structural optimizers show exactly where the beads have to be implemented on the radiating component in order to reduce the acoustic radiated power efficiently.

The three optimal proposals are clearly more efficient than the conventional design (acoustic sound power reduction: 18-25% vs. 3%).

Three different optimization techniques can be applied to the optimal bead pattern generation on a radiating surface in the detailed project phase.

The methodology here demonstrated can also be applied to problems concerning radiating casting parts (thin shells on the radiating surface).

The presented methodology has been already applied successfully to real powertrain problems.


Acknowledgments To Altair`s support team in Germany, especially to Mr. Jürgen Kranzeder (Altair’s

technical manager in Böblingen), for the excellent technical support on the optimization topics as well as for the very good client relationship.


Q&A

Thank you!

acoustic optimization of an engine oil pan concerning the equivalent radiated sound power function

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