Design Optimization of a Weather Radar Antenna using ... · optimization study of a positioning mechanism for a S-band Doppler weather radar antenna; • The specific objective of
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• 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.
• 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.
• 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.
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.
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.
• 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.
• 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.