Valve Modeling Methods for Modal Analysis

Abstract

This paper presents several modeling methods for performing a valve assembly modal analysis. It discusses the background of the methods, their strengths and limitations, and then introduces a new approach that can be used in performing valve modal analysis. An early paper presents a classical approach based on a lumped mass model and the Rayleigh energy principal to determine primary mode natural frequencies. A follow up paper reaffirms the classical method and introduces enhancements. A recent paper provides a comparative study of the classical approach, laboratory testing, and solid modeling results using the finite element analysis program ANSYS Mechanical. In this paper, a third approach is presented, which is an extension of the classical method, where 3-D beam-based geometry is defined using the ANSYS SpaceClaim program that is then ported to ANSYS Mechanical. The classical and solid modeling approaches from the previously cited papers are reviewed to highlight the modeling evolution and then the newly developed approach is presented. An example is presented that compares natural frequency results of the new method and the previous methods. The motivation for the new method is to provide better compatibility with 3-D piping system models, which are typically used to study the effect of valve mass and stiffness on system response without the complexity of a solid model or the difficulty of communicating the details of a classical model to the system modeler. Much of the process of creating a 3-D beam model is automated. It uses input from an existing classical model and employs the following ANSYS software packages: SpaceClaim, Workbench, Mechanical, and ACT. A great feature of the resulting 3-D model is that beam geometry is more realistic to scale, and therefore provides valuable user feedback for checking model validity. This approach is an improvement over the classical model where only manual data input validation is possible. Other benefits of the new method are covered in greater detail in the paper.