31-10-2012, 02:19 PM
Learning Module 3 Fluid Analysis
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Learning Objectives
The objective of this module is to introduce the user to the process of fluid flow analysis using FEM. Upon completion of the module, the user should have a good understanding of the necessary logical steps of an FEM analysis, and be able to perform the following tasks:
Creating the solid geometry
Assigning material properties
Applying boundary conditions
Meshing
Running the analysis
Verifying model correctness
Processing needed results
Prerequisites
In order to complete the learning module successfully, the following prerequisites are required:
By subject area:
oFluid mechanics
Flow analysis
By topic:
knowledge of
fluid boundary layer
laminar flow
turbulent flow
Reynolds number
volumetric flow rate
pressure drop
Pre-test
The pre-test should be taken before taking other sections of the module. The purpose of the pre-test is to assess the user's prior knowledge in subject areas relevant to fluid flow analysis. Questions are focused towards fundamental concepts including types of flow, fluid definitions, and various boundary conditions.
Tutorial Problem Statements
A good tutorial problem should focus on the logical steps in FEM modeling and demonstrate as many aspects of the FEM software as possible. It should also be simple in mechanics with an analytical solution available for validation. Three tutorial problems are covered in this learning module.
Conceptual Analysis
Conceptual analysis is the abstraction of the logical steps in performing a task or solving a problem. Conceptual analysis for FEM simulation is problem type dependent but software-independent, and is fundamental in understanding and solving the problem.
Abstract Modeling
Abstract modeling is a process pioneered by CometSolutions Inc. Abstract modeling enables all attributes of an FEM model (such as material properties, constraints, loads, mesh, etc.) to be defined independently in an abstract fashion, thus reducing model complexity without affecting model accuracy with respect to the simulation objective. It detaches attributes from one another, and emphasizes conceptual understanding rather than focusing on software specifics. Evidently, abstract modeling is independent of the specific software being used. This is a fundamental departure from the way most FEM packages operate.
Conceptual analysis focuses on the abstraction of steps necessary for an FEM simulation, while abstract modeling focuses on the abstraction and modularization of attributes that constitute an FEM model. They are powerful enabling instruments in FEM teaching and learning.
Pre-processing
The pre-processing in FEM simulation is analogous to building the structure or making the specimen in physical testing. Several sub-steps involved in pre-processing are geometry creation, material property assignment, boundary condition specification, and mesh generation.
The geometry of the model is defined in the geometry creation step. After the solid geometry is created, the material properties of the solid are specified in the material property assignment step. The material properties required for the FEM analysis depends on the type of analysis. Most of the flow analysis problems discussed in this learning module will produce the same results regardless of the material. Material properties become relevant when dealing with flow analysis when a roughness factor is introduced or the thermal fluid properties are being examined.
For most novice users of FEM, the boundary condition specification step is probably the most challenging of all pre-processing steps. Within a flow analysis problem, there are various boundary conditions that must be applied according to the problem statement. Two types of flow analysis will be discussed in this learning module: internal and external fluid flow. Different boundary conditions exist depending of the type of flow. Determining whether the flow is laminar, transitioning, or turbulent depends on a dimensionless parameter known as the Reynolds number.