Dynamic Response in NX Nastran IN THIS WEBINAR: PRESENTED BY: - - PowerPoint PPT Presentation

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Dynamic Response in NX Nastran IN THIS WEBINAR: PRESENTED BY: - - PowerPoint PPT Presentation

Apr 05, 2023 166 likes •389 views

Dynamic Response in NX Nastran IN THIS WEBINAR: PRESENTED BY: FEMAP Dynamics Add-on Overview Andrew Jabola Frequency Response Demo Senior Aerospace Stress Engineer Random Response Demo Structural Design and Analysis

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IN THIS WEBINAR:

  • FEMAP Dynamics Add-on Overview
  • Frequency Response Demo
  • Random Response Demo

Dynamic Response in NX Nastran

Andrew Jabola

Senior Aerospace Stress Engineer Structural Design and Analysis andrew@structures.aero

PRESENTED BY:

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Agenda

  • Introduction
  • Dynamic Analysis Solutions

– Solutions – Typical Applications

  • Demo

– Frequency Response/Sine Vibration Model Setup – Random Vibration Setup

  • Conclusion
  • Q/A
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Dynamic Analysis Solutions

  • What is a Dynamic Analysis?

– Any case where the load is time varying and inertia forces may be present

  • NASTRAN Dynamics adds the following solutions to FEMAP

– Transient Response – Frequency Response – Shock Spectrum Analysis – Random Vibration – DDAM Analysis

  • Most Solutions offer both direct and modal solution capabilities

– Direct – Applies the direct equations of motion to every grid point, providing a more accurate but more costly answer – Modal – Uses mode shapes to determine response and reduces overall model size

Equations of Motion – Direct Analysis Equations of Motion – Modal Analysis Full Mass Matrix of System Transforms Matrix into Modal Coordinates

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Dynamic Analysis Solutions

  • Solution Types

Type Input Output

Modal

  • Prescribed BC’s / No Force Input
  • Natural frequencies and

corresponding mode shapes

  • Stress/strain profile

Frequency Response

  • Sinusoidal excitations across a

range of frequencies (Deterministic)

  • Sinusoidal response at each

frequency

  • Min/max response over frequency

range Spectrum/Shock

  • Spectrum representing the response

to a specific time history (Deterministic)

  • Maximum response if the model were

subjected to the time history Random

  • Spectrum representing probability

distribution of excitation (Non- Deterministic)

  • Response within specified range of

probabilities Transient

  • Time-varying loads (Deterministic)
  • Time-varying response
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Typical Applications

  • Typical Applications Dynamic Response

– Aerospace Industry

  • Heavy usage of Frequency and Random Response

– Marine

  • DDAM

– Vehicle Dynamics – Civil/Structural Applications – Heavy Equipment – …anything where load is time varying and inertia and damping also play a factor into overall response

  • Focus of webinar will be on the following use cases

– Frequency Response – Sine Vibe Analysis – Random Response – Article Verification

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Frequency Response

  • Frequency Response computes the structural response to a steady-state
  • scillatory excitation

– Heavily used in aerospace industry for sine vibration tests – Provides a structural response vs. frequency for a specified range – Used as a basis for random vibration analysis

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Frequency Response Setup

  • Demonstration

– Model Overview – Checking Modes – Setting up Loads – Setting up Analysis Deck – Postprocessing Data

Model courtesy of NASA Goddard Space Flight Center – WFIRST Program

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Modal Content

  • Modal Mass Participation

– Ensure you’re capturing at least 80% of the mass participation or covering the frequency range of interest – Modal Mass Participation for first 20 modes

Mode # Frequency T1 T2 T3 R1 R2 R3 1 6.49E+01 1.00% 0.05% 2.87% 0.00% 4.10% 0.14% 2 7.99E+01 1.41% 0.24% 0.51% 0.15% 3.94% 0.01% 3 1.07E+02 0.83% 0.09% 0.04% 0.06% 0.03% 5.76% 4 1.09E+02 0.20% 4.57% 1.46% 1.99% 0.51% 0.11% 5 1.29E+02 1.41% 1.22% 0.00% 0.02% 0.18% 6.62% 6 1.94E+02 0.38% 1.32% 9.82% 0.06% 0.00% 0.00% 7 2.37E+02 0.55% 0.01% 0.22% 0.00% 0.47% 0.28% 8 2.63E+02 0.36% 0.01% 0.00% 0.00% 0.06% 0.03% 9 2.88E+02 10.29% 0.47% 0.02% 0.09% 2.06% 1.37% 10 3.24E+02 0.10% 7.98% 0.12% 2.20% 0.02% 1.28% 11 3.65E+02 0.89% 0.01% 0.33% 0.00% 0.19% 0.05% 12 3.72E+02 0.04% 0.83% 0.00% 0.18% 0.01% 0.13% 13 4.30E+02 0.47% 0.01% 0.00% 0.00% 0.04% 0.03% 14 4.59E+02 0.00% 0.00% 0.49% 0.00% 0.01% 0.00% 15 4.70E+02 0.00% 0.00% 0.01% 0.00% 0.00% 0.00% 16 4.92E+02 0.00% 0.03% 1.86% 0.01% 0.01% 0.00% 17 4.99E+02 0.00% 0.14% 0.02% 0.03% 0.00% 0.01% 18 5.05E+02 0.36% 0.06% 0.02% 0.01% 0.00% 0.00% 19 5.09E+02 0.04% 0.30% 0.00% 0.10% 0.01% 0.07% 20 5.36E+02 0.02% 0.53% 5.13% 0.06% 0.01% 0.02% Modal Mass Participation Percentage

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Damping

  • Types of Damping
  • For frequency response and random response, modal

damping is typically used

  • It can be specified by the following methods:

– Critical Damping (2.5%) – Structural Damping (5.0%) – Q Damping (20)

  • Relationship shown below

Q Damping Critical Damping Structural Damping

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Frequency Cards

  • Responses are specified at certain frequencies based off a

variety of criteria using the FREQ Cards

– Frequency List Methods (explicitly define frequencies by a range)

  • FREQ, FREQ1, FREQ2

– Modal Frequency Methods (list frequencies based off modes and generating points around each mode)

  • FREQ3, FREQ4, FREQ5

– It is common to use the modal frequency to fill in data around modes and using the list methods to catch any missing data – Can be combined

  • Refer to NX NASTRAN QRG for more detail of FREQ –

FREQ5 Cards

FREQ4 Frequency Spread

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Random Response

  • Random Response is used to look at load environments that

are non-deterministic

– Uses a statistical approach to analyzing the response to a structure where the instantaneous magnitude is not known at a given time

  • Applications include acoustic environments from launch, earthquake

analysis, and wind pressure fluctuations

– Analysis uses frequency response as basis for determining overall statistical response by multiplying the transfer functions of the frequency response and the input PSD to develop a response spectral density

  • This is in turn used to determine an RMS response, which is used to

determine the statistical response of the structure

Sine Vibe Transfer Function Input PSD Response Spectral Density

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Random Response Setup

  • Demonstration

– Show Input PSD – Show Additional Analysis Setup – Postprocess Data

Model courtesy of NASA Goddard Space Flight Center – WFIRST Program

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Random Response

  • Standard Input

– Power Spectral Density (PSD) function, determines the input environment for the structure – Specs are determined by analyzing time history responses of various environments – Typical spec shown below (Source: GSFC GEVS-STD-7000)

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Random Response

  • Random Output

– Random will generate the following data

  • PSDF Data

– Used for looking at overall spectral densities to determine areas of high response

  • CRMS Data

– This is cumulative RMS value that shows how the energy adds together as you increase in frequency

  • RMS Response

– The RMS response of each data point of interest » This is equal to the square root of the area under the PSDF data curve – This RMS values is typically multiplied by a factor (typically 3) to show the highest stress within a certain probability » 3 Sigma ensures that the highest stress due to the environment will not exceed this value 99.7% of the time

  • Positive Crossings

– Determines the amount of cycles per unit of time occur » Typically used for fatigue calculations

RMS Output Value RMS Von Mises Stress Acceleration Spectral Density

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VIEW THE WEBINAR RECORDING

  • If you would like to see the

demonstrations from this presentation, you can view the recording of this webinar at:

https://structures.aero/webinar/ dynamic-response-nx-nastran/

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Tips and Tricks

  • Several Tips and Tricks

– Run Modes First!

  • Understand the natural frequency of the system to get an idea of what frequencies will play a

major role in your system. This should be performed in combination with understand modal mass participation to determine what modes will likely be significant

– Ensure that modal analysis captures full modal content

  • Ensure that you are capturing at least 80% of mass participation or full range of frequencies of

interest

– Verify input by looking at response at constraint location

  • This will verify that your load is correct for the model

– Turn on RESVEC

  • Captures the higher modal content that is not captured in lower modes frequency content
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Conclusion

  • FEMAP Dynamics Add-on adds several dynamic solutions to the FEMAP

environment:

– Transient Response – Frequency Response – Random Response – Shock – DDAM

  • Bulk of analyses focus on random and frequency response, using the modal

method for solution

  • Dynamic Analyses are very use for time varying loadings and any places

where inertia and damping play a major affect on the response of a structure

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Structural Design and Analysis (Structures.Aero)

Structural Analysis

  • Team of 14 engineers that help our clients

design lightweight and load efficient structures.

  • We service aerospace companies and other

industries that require high level analysis.

  • Specialty in composites and lightweight

structures

  • Tools used include hand analysis, HyperSizer,

Femap, NX Nastran, Fibersim, NX, Solid Edge, Simcenter 3D, LS Dyna, and LMS.

Software Sales and Support

  • Value added reseller providing software, training,

and support for products we use on a daily basis.

  • Support Femap, NX Nastran, Simcenter 3D,

Fibersim, Solid Edge, and HyperSizer.

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GET DYNAMIC RESPONSE

  • You can acquire the Dynamic

Response add-on for Femap with NX Nastran for less than $3K.

  • Contact Marty Sivic for a quote

For questions about pricing, or to see a demo, please contact Marty Sivic.

Marty Sivic

Director of Sales msivic@structures.aero 724-382-5290

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For questions on the material covered today, please contact Andrew Jabola. For questions about pricing, or to see a demo, please contact Marty Sivic.

Questions?

Marty Sivic

Director of Sales msivic@structures.aero 724-382-5290

Andrew Jabola

Senior Aerospace Stress Engineer andrew@structures.aero 703-935-2827