Using ANSYS for Finite Element Analysis, Volume II

Wael A. Altabey, Mohammad Noori, Libin Wang

• Publisher: Momentum Press
• Year: 2018
• ISBN:
  9781947083233
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Over the past two decades, the use of finite element method as a design tool has grown rapidly. Easy to use commercial software, such as ANSYS, have become common tools in the hands of students as well as practicing engineers. The objective of this book is to demonstrate the use of one of the most commonly used Finite Element Analysis software, ANSYS, for linear static, dynamic, and thermal analysis through a series of tutorials and examples. Some of the topics covered in these tutorials include development of beam, frames, and Grid Equations; 2-D elasticity problems; dynamic analysis; composites, and heat transfer problems. These simple, yet, fundamental tutorials are expected to assist the users with the better understanding of finite element modeling, how to control modeling errors, and the use of the FEM in designing complex load bearing components and structures. These tutorials would supplement a course in basic finite element or can be used by practicing engineers who may not have the advanced training in finite element analysis.

CHAPTER 1

DYNAMIC ANALYSIS

Structural analysis is mainly concerned with finding out the behavior of a physical structure when subjected to force. This action can be in the form of load due to the weight of things such as people, furniture, wind, snow, and so on, or some other kind of excitation such as an earthquake, shaking of the ground due to a blast nearby, and so on. In essence all these loads are dynamic, including the self-weight of the structure because at some point in time these loads were not there. The distinction is made between the dynamic and the static analysis on the basis of whether the applied action has enough acceleration in comparison to the structure’s natural frequency. If a load is applied sufficiently slowly, the inertia forces (Newton’s first law of motion) can be ignored and the analysis can be simplified as static analysis. Structural dynamics, therefore, is a type of structural analysis that covers the behavior of structures subjected to dynamic (actions having high acceleration) loading. Dynamic loads include people, wind, waves, traffic, earthquakes, and blasts. Any structure can be subjected to dynamic loading. Dynamic analysis can be used to find dynamic displacements, time history, and modal analysis.

A dynamic analysis is also related to the inertia forces developed by a structure when it is excited by means of dynamic loads applied suddenly (e.g., wind blasts, explosion, and earthquake).

Dynamic analysis for simple structures can be carried out manually, but for complex structures finite element analysis can be used to calculate the mode shapes and frequencies.

1.1 TUTORIAL 1: HARMONIC ANALYSIS OF STRUCTURE

In this tutorial, the harmonic analysis of a cantilever beam will be addressed. Harmonic analysis is used to determine the response of a structure to harmonically time-varying loads. This tutorial was created using ANSYS 7.0. The purpose of this tutorial is to explain the steps required to perform harmonic analysis on the cantilever beam shown as follows.

We will now conduct a harmonic forced response test by applying a cyclic load (harmonic) at the endof the beam. The frequency of the load will be varied from 1–100 Hz. The following figure depicts the beam with the application of the load.

ANSYS provides three methods for conducting a harmonic analysis. These three methods are the Full, Reduced, and Modal Superposition methods. This example demonstrates the Full method because it is simple and easy to use as compared to the other two methods. However, this method makes use of the full stiffness and mass matrices and thus is the slower and costlier option.

1.1.1 STEP-BY-STEP ANSYS SOLUTION

1.1.1.1 Preprocessing: Defining the Problem

Student should be able to make simple cantilever model himself or otherwise use the following command list:

1.1.1.2 The Command Log File

/TITLE, Dynamic Analysis

/FILNAME,Dynamic,0 ! This sets the jobname to “Dynamic”

/PREP7

K,1,0,0

K,2,1,0

L,1,2

ET,1,BEAM3

R,1,0.0001,8.33e-10,0.01

MP,EX,1,2.068e11

MP,PRXY,1,0.33

MP,DENS,1,7830

LESIZE,ALL,,,10

LMESH,1

FINISH

1.1.1.3 Solution: Assigning Loads and Solving

1. Define analysis type (Harmonic)

Solution > Analysis Type > New Analysis >
Harmonic ANTYPE,3

2. Set options for analysis type

Select Solution > Analysis Type > Analysis Options.
The following window will appear....

Table of contents

• Cover
• Half-title Page
• Title
• Copyright
• Abstract
• Contents
• List of Figures
• Preface
• 1 Dynamic Analysis
• 2 Composite Materials
• 3 Probabilistic Design Analysis
• 4 Apdl Programming
• 5 Design Optimization
• Bibliography
• About the Authors
• Index
• Adpage
• Backcover