Pagnotta Engineering

Modal, random response, and sine sweep analyses


MODAL ANALYSIS:
Modal Analysis is performed to determine the natural resonant frequencies and mode shapes of a structure. Resonant frequencies are an important design consideration since response to oscillating forces at or near resonant frequencies can result in high deflections and stress levels. The fundamental natural
frequency is also a measure of stiffness versus mass. A design that exhibits a higher fundamental natural frequency generally has a more efficient structure.

SAMPLE PROJECTS:
Aeronomy of Ice in the Mesosphere (AIM) spacecraft and SRG110 power source

CUSTOMER:
Orbital Sciences Corporation (AIM)
and Lockheed Martin (SRG110)

SERVICES PERFORMED:
• PEI was the analysis lead on the AIM spacecraft through PDF. Among the analyses performed was a modal
   trade study to optimize optimize stiffness and minimize mass of portions of the spacecraft bus structure.
• PEI was the analysis lead on the SRG110 power source. Among the analyses performed, modal analysis
   was used to tune resonances of internal structures to minimize modal coupling (amplification due to
   multiple close in frequency.

AIM Spacecraft SRG110

RANDOM RESPONSE ANALYSIS:
Random Response Analysis is used to determine the response of a structure to input forces defined in terms of a Power Spectral Density (PSD) function.
Generally, in the analysis of spacecraft, input PSD curves are based on vibration acceleration levels in the launch vehicle at the spacecraft
mounting location. These launch environment PSD functions are used as input in the spacecraft FE model, and in turn, the response levels of
components within the spacecraft can be obtained. RMS accelerations, velocities, displacements, stresses and strains can be calculated at
any point in the FE Model.

PEI is experienced in Force Limiting Random Response Analysis, which is a method of shaping the input PSD curve to prevent overstressing
critical components during experimental random response testing.

 

EXAMPLE PROJECT:
SAR Battery Assembly

CUSTOMER:
Eagle-Pitcher Technologies, LLC

SERVICES PERFORMED:
• PEI performed Random Response analysis on several spacecraft battery packs for EPI including the SAR pack
   shown to the right.
• Random Response analysis was used to determine equivalent quasi-static accelerations and forces to envelope
   maximum stress levels.
• Analysis results were used to validate that the mechanical packaging meet the structural performance
   requirements.

Pro/E Model of Battery Pack FE Model of Battery Pack Test Set-up

SINE SWEEP ANALYSIS:
Frequency response analysis, or since sweep analysis, is often used to show compliance with a transportaion and handling environment specification.
Sine sweep analysis entails calculating structural response due to a harmonic force, where the frequency of the oscillating force is swept through a
range of frequencies.

PROJECT:
Shipping Container for BSAT Payload Panel

 

CUSTOMER:
Orbital Sciences Corp.

 

ANALYSIS SERVICES PERFORMED:
• PEI has performed stress analysis on the BSAT payload panel shipping container, which
   included a sine sweep analysis
• Base input levels and frequency range were due to shipment in a Boeing transport jet
• Anaylsis determined the maximum amplitude of the response of the panel to verify adequate
   clearance with the shipping enclosure

• Analysis showed deficiencies in the original mounting brackets holding the panel fixture to
   the isolation mounts
• PEI redesigned the brackets to meet the strength requirements and created manufacturing
   drawings for the brackets so that the parts could be built, shipped, and installed in the time
   to comply with the customers shipping schedule

 

FE Model of shipping container
with payload attached

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