Design Optimization of a Weather Radar Antenna using ... · optimization study of a positioning...

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Design Optimization of a Weather Radar Antenna using Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD)

Design Optimization of a Weather Radar Antenna using Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD)

Fernando PrevedelloRegis AtaídesNícolas Spogis

Wagner Ortega GuedesFabiano Armellini

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Summary

• Introduction

• Objectives

• Geometric model

• Computational model

• Domain and Computational Mesh

• Boundary Conditions

• Results

• Conclusions

• Next steps

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Introduction

• Weather antenna positioning is a very complex mechanism and someknowledge is required for the effective design and implementation;

• The air flow around the antenna can affect directly the positioning mechanism behavior;

• FEA and CFD models are useful for obtaining the knowledge about the plant without the need of physical construction of a model or prototype for experimentation;

• CFD analysis can be used to determine the air flow pressure field and the vortex separation frequency;

• FEA modal analysis is useful for determining the natural frequencies of the structure and for the qualification, validation and approval of the mechanisms after they are built.

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Objective

• The aim of this work is to perform a design optimization study of a positioning mechanism for a S-band Doppler weather radar antenna;

• The specific objective of this study is to analyze and validate the prototype of the positioning mechanism designed for RMD700S-1M Radar, the first Weather Radar totally developed in Brazil.

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Computational Model

• CFD Flow characteristics:– Steady State with Mesh Adaptation using velocity variable to

obtain the first mesh refinement;– Transient simulation for the final mesh;– Incompressible Flow;– Turbulent Flow: Shear Stress Transport turbulence model;– Advection scheme: High-resolution.

• FEA characteristics:– Bearing modeled by Coupled DOF’s;– Static simulation using surface effect elements to apply the

wind loads;– Harmonic simulation with given rotation.

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Computational Model

• Fluid properties:– Air

• Density: 1.185 [kg m^-3];

• Dynamic Viscosity: 1.831e-05 [kg m^-1 s^-1]

• Material properties:– Aluminum Alloy

• Density: 2800 [kg m^-3];

• Young Modulus: 70 [GPa]

• Poisson Ratio: 0.3

– Structural Steel• Density: 7850 [kg m^-3];

• Young Modulus: 200 [GPa]

• Poisson Ratio: 0.3

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Computational Model

• Numerical Data (CFD)

– Mesh: Ansys ICEM CFD 10.0

– Solver: Ansys CFX 10.0

– Post-Processor: Ansys CFX Post

• Numerical Data (FEA)

– Mesh: Ansys ICEM CFD 10.0

– Solver: Ansys 10.0

– Post-Processor: Ansys 10.0

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Geometric Model

Antenna

Positioning Mechanism

Support

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The CFD Model and Results

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CFD Computational Model - Antenna

Geometric simplifications

Wind direction

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Inlet:

Velocity = 100 km/h

Outlet – Opening

• Boundary conditions

AntennaGround - wall no slip

Far field – Opening Monitor Points

• Boundary conditions

CFD Computational Model

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• Mesh – last adaptation refinement

Ground Wall (Prism Layer)

Mesh adaptation

CFD Computational Model

Side view

300000 nodes1480000 elements

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CFD Computational Model

Top view Vortex separation region

• Mesh – last adaptation refinement

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Side View

Top View

CFD Results

• Time average pressure field

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Side View

Top View

CFD Results

• Time average velocity

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0.2s 0.4s 1.0s

1.2s 1.4s 1.6s

CFD Results

• Transient Vorticity field

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CFD Results

• Time average 3D streamlines

Main vortex caused by antenna

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Vectors Movie

Vorticity Movie

CFD Results

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Pressure distribution that will be used at Ansys Structural analysis

CFD Results

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6Re 7.57 10VDρµ

= = ⋅100 [ ^ 1] 27.7778 [ ^ 1]V k h m s= − = −

4212.3[ ] 4.2123[ ]D mm m= =

Reynolds Number

21.831 10 [ ^ 1 ^ 1]kg m sµ −= ⋅ − −

1.185 [ ^ 3]kg mρ = −

Considering the antenna as a flat plate:

nDStV

=

0.14 ( )St Flat Plate=100 [ ^ 1] 27.77778[ ^ 1]V k h m s= − = −4212.3[ ] 4.2123[ ]D mm m= =

0.9232 [ ]n Hz=

Strouhal Number

Frequency Analysis

Analytical frequency

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CFD Frequency Response (FFT)

Four points were monitored. Pressure variation was calculated as a function of time at each point. A classical Fast Fourier Transform was applied on the results in order to obtain a frequency response function.

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0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.5 1 1.5 2 2.5 3

Frequency [Hz]

INT

[Pa]

Monitor Point 1

0.9375 [Hz]

1.1914 [Hz]

Main Frequency

CFD Frequency Response (FFT)

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0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 0.5 1 1.5 2 2.5 3

Frequency [Hz]

INT

[Pa]

Monitor Point 2

0.9375 [Hz]

1.1914 [Hz]

Main Frequency

CFD Frequency Response (FFT)

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0

1

2

3

4

5

6

7

0 0.5 1 1.5 2 2.5 3

Frequency [Hz]

INT

[Pa]

Monitor Point 3

0.9375 [Hz]

1.1914 [Hz]

Main Frequency

CFD Frequency Response (FFT)

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0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 2 2.5 3

Frequency [Hz]

INT

[Pa]

Monitor Point 4

0.9375 [Hz]

1.1914 [Hz]

Main Frequency

Frequency influenced from antenna support

vortex separation

CFD Frequency Response (FFT)

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Monitor Point 1

Monitor Point 4

Results – Frequency Analysis

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The FEA Model and Results

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Structural Steel

Aluminium Alloy

FEA Computational Model

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FEA Computational Model

FEA ModelFEA Model

45958 Nodes43779 Elements

From original geometry, a mid-surface model was taken. The Finite Element Model has been built using SHELL181 on those surface, BEAM188on bolts and bars, and SURF154 on concave surface of Antenna for input the wind loads.

Coupled DOF`s were considered to simulate the bearing of Azimuth and Elevation axles.

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• Boundary Condition

Fixed SupportUx = 0 mmUy = 0 mm Uz = 0 mm

G = 9810 mm s^-2

FEA Model – Static Analysis

Pressure distribution from CFD Results

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Displacement (mm) Von Mises Stress (MPa)

FEA Results – Static Analysis

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Fixed SupportUx = 0 mmUy = 0 mm Uz = 0 mm

• Boundary Condition

FEA Model – Modal Analysis

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Mode 1 : 5.43 Hz Mode 2 : 9.60 Hz

FEA Results – Modal Analysis

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Mode 3 : 13.95 Hz Mode 7 : 16.03 Hz

FEA Results – Modal Analysis

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Fixed SupportUx = 0 mmUy = 0 mm Uz = 0 mm

Given Displacement = One degree rotation about Azimuth Axis

Damping = 2% Critical

FEA Model – Harmonic Analysis

• Boundary Condition

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Response Points

Point 1 Point 2 Point 3

FEA Results – Harmonic Analysis

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Point 1

Point 2

Point 3

Point 1

FEA Results – Harmonic Analysis

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Conclusions

• CFD and FEA computational models were developed in order to study the flow around a weather radar antenna and its structural response;

• For the transient case, a preliminary CFD mesh adaptation study was performed in order to obtain an adequate mesh refinement;

• The CFD transient model was used to obtain the flow behavior and the vortex separation frequency;

• The comparison between the theoretical frequency and the result obtained in CFD model presented good agreement (~1.5% of difference);

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• The static analysis, using pressure distribution from CFD analysis, showed that the structure is over dimensioned in terms of mechanical failure, therefore it is possible to reduce the systems total payload, specially at the structure’s base;

• From the modal analysis, the first two modes are the most significant for the control system. The first mode is due to torsion of the axis of elevation and the second is due to torsion at the azimuth axis.

Conclusions

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• The lowest natural frequency found was 5.4Hz (at elevation axis). Thus, the dynamic response and the specifications of the system (maximum speed of 36o/s and maximum acceleration of 10o/s2) are not coincident.

• The excitation due to the wind flow along the parabolic antenna do not affect the control system. The frequencies obtained from the CFD analysis were considered.

Conclusions

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Next Steps

• Use CFD response into a dynamic structural analysis (Fluid Structural Iteration);

• Design optimization using Workbench Design Xplorer.