We have an exciting announcement about badges coming in May 2025. Until then, we will temporarily stop issuing new badges for course completions and certifications. However, all completions will be recorded and fulfilled after May 2025.
Structural Dynamics

Structural Dynamics

  1. All Categories
  2. Structures - Structural Dynamics
  3. Are PSD results correct if the following message is used during the solve. “One or more diagonal terms of the modal covariance matrix (i.e., when mode i = mode j) is negative. The 1 sigma results may be incorrect as a result of the input PSD curve being improperly represented.”

Are PSD results correct if the following message is used during the solve. “One or more diagonal terms of the modal covariance matrix (i.e., when mode i = mode j) is negative. The 1 sigma results may be incorrect as a result of the input PSD curve being improperly represented.”

Tagged: 6.1, Mechanical APDL (f. ANSYS), Modal/Harmonic Response, PSD results, structural-dynamics, structural-mechanics
    • January 25, 2023 at 7:34 am
      FAQFAQ
      Participant

      No. Some recommendations are: 1. Check the PSD input curve fit with PSDGRAPH. PSD input frequencies should not increase by more than one order of magnitude per point. 2. Take the square root of the integral of the response PSD [RPSD in post26] and compare this quantity to the Post1 1 sigma value. They should be equal. 3. Do not input a curve with very low frequency values, far below the natural frequencies of the structure.

Featured Articles

Introducing Ansys Electronics Desktop on Ansys Cloud

The Watch & Learn video article provides an overview of cloud computing from Electronics Desktop and details the product licenses and subscriptions to ANSYS Cloud Service that are...

How to Create a Reflector for a Center High-Mounted Stop Lamp (CHMSL)

This video article demonstrates how to create a reflector for a center high-mounted stop lamp. Optical Part design in Ansys SPEOS enables the design and validation of multiple...

Introducing the GEKO Turbulence Model in Ansys Fluent

The GEKO (GEneralized K-Omega) turbulence model offers a flexible, robust, general-purpose approach to RANS turbulence modeling. Introducing 2 videos: Part 1 provides background information on the model and a...

Postprocessing on Ansys EnSight

This video demonstrates exporting data from Fluent in EnSight Case Gold format, and it reviews the basic postprocessing capabilities of EnSight.

© 2025 Copyright ANSYS, Inc. All rights reserved.