One of the biggest trends that has emerged in the CAD industry in the past several years is the push for simulation and analysis earlier in the design process. The simulation and analysis method that has seen the greatest adoption is finite element analysis (FEA). What was once the domain of PhD-level specialists became available to mere mortals when integrated into a number of mainstream CAD applications. Still, not everyone needs CAD for learning FEA or in their work. There has been and still is a need for a standalone FEA product, especially for educational applications. One of the obvious FEA solutions today is Abaqus 6.9 Student Edition (SE) from SIMULIA, a Dassault Systemes company.
Abaqus is not just a single application, but rather a suite of simulation programs that can solve a broad range of linear and non-linear problems and includes Abaqus/CAE, Abaqus/Standard, and Abaqus/Explicit. The Student Edition contains an extensive library of solid, shell, beam and connector elements that let you model just about any geometry. It also has a lot of material models that let you simulate the behavior of engineering materials ranging from metals to composites. Also worth mentioning is the extensive documentation available for Abaqus 6.9 SE. There are many volumes available remotely, as well as verification files, both good features for learning Abaqus. Because it is a general purpose simulation tool, Abaqus can be used to simulate and analyze problems beyond structural (stress/ displacement), but we'll stick with the basics for the purposes of this review.
Designed for personal educational use, and with a maximum model size of 1,000 nodes, Abaqus 6.9 Student Edition includes the core Abaqus products: Abaqus/Standard, Abaqus/Explicit, and Abaqus/CAE. As in the professional release of Abaqus, the Abaqus 6.9 Student Edition features capabilities for modeling, meshing, contact, materials, and multiphysics. Abaqus/CAE has basic geometry building capabilities that are very similar to standalone CAD systems, so it is an efficient way for users who know feature-based modeling to become productive with Abaqus/CAE.
I'll be honest that even though I'm an engineer and have used (with some degree of success) the rudimentary FEA capabilities integrated into many of the mainstream CAD packages, I haven't had nearly the level of comfort or success with standalone FEA applications. This was one of my primary motivations for reviewing Abaqus 6.9 SE - to see if I could actually learn and use a relatively sophisticated FEA application.
I reviewed Abaqus 6.9 Student Edition on an HP 8730w mobile workstation that was well-suited because of its optimized visual computing performance and its excellent image quality (resolution and brightness).
According to SIMULIA, some of the highlights of Abaqus 6.9 SE include:
- The Extended Finite Element Method (XFEM) that has been implemented in Abaqus, providing a tool for students simulating crack growth along arbitrary paths that do not correspond to element boundaries. In the aerospace industry, XFEM can be used in combination with other Abaqus capabilities to predict durability and damage tolerance of composite aircraft structures.
- The general contact implementation offers a simplified and highly automated method for students to define contact interactions in a model. This capability provides substantial efficiency improvements in modeling complex assemblies such as gear systems, hydraulic cylinders, or other products that have parts that come into contact.
- A new co-simulation method lets students combine the Abaqus implicit and explicit solvers into a single simulation for substantially reducing computation time. For example, automotive engineering students can now combine a substructure representation of a vehicle body with a model of the tires and suspension systems to evaluate the durability of a vehicle running over a pothole.
- A new viscous shear model allows simulation of non-Newtonian fluids such as blood, paste, molten polymers, and other fluids often used in consumer product and industrial applications.
Getting Started With Abaqus 6.9 Student Edition
Before we get started, let's briefly discuss exactly what FEA is. The finite element method (FEM) is probably most recognized for its widest application known as finite element analysis (FEA). FEA is a numerical technique for finding approximate solutions of partial differential equations (PDE) as well as of integral equations. For example, FEM can solve partial differential equations for complicated mechanical designs, such as cars and oil pipelines, as the design changes due to external forces, such as a simulating car crash or an earthquake affecting a pipeline.
Generally, an Abaqus analysis is comprised of the following three basic steps:
- Pre-processing using Abaqus/CAE where you define the model of the physical problem of the physical problem and create an Abaqus input file (.inp). You can also directly create an Abaqus input file for a simple analysis using a text editor.
- Simulation using Abaqus/Standard or Abaqus/Explicit that actually solves the numerical problem previously defined in the model.
- Post-processing using Abaqus/CAE lets you evaluate the results of the completed simulation and the displacements, stresses or other variables have been calculated. This interactive evaluation is usually performed using Abaqus/CAE's Visualization module.
When an Abaqus 6.9/CAE session is started, a window opens prompting you what you want to do, such as create or open an existing model database, or run a script. For our purposes here, I'll be creating a new model database and running the simulation based on it.
An Abaqus model is comprised of the following elements that describe the physical problem that you define before running a simulation and solving the problem and is usually performed with the Abaqus/CAE preprocessor:
- Discrete geometry with finite elements and nodes that define the basic geometry of the physical structure being modeled in Abaqus. Each element in the model represents a discrete part of the physical structure. Elements are connected with shared nodes, and all of the elements and nodes comprise what is known as a mesh. It is important to keep in mind that the mesh is only an approximation of the physical structure's actual geometry.
- Element section properties that are used when geometry is not completely defined by the coordinates of its nodes.
- Material data that defines material properties for all elements.
- Loads that will distort the physical structure and create stress in it.
- Boundary conditions that constrain parts of the model to remain fixed with no displacement or to move with displacement.
- Analysis type that is either static (long-term response of a structure to applied loads) or the dynamic response of a structure to a load that changes over time.
- Output type of results that lets you limit the output data from being too excessive for interpreting simulation results.
Setting Up and Running a Simulation
I worked through several different problems with (what I thought was) increasing complexity, starting with an overhead hoist, moving on to a cargo crane under dynamic loading, then the behavior of dropping a circuit board in protective crushable foam packaging, among others. Although, obviously, these are all different types of simulations and analysis, the basic steps performed are roughly the same using modules for performing specific tasks.
First, the pre-processing phase. Unless you have previously created geometry, you start off by sketching 2D geometry and creating a part that represents the physical structure that you will be performing the simulation/analysis.
You define the material and section properties of the physical structure. If you have more than one part, each part is independent of each other, and constitute the assembly that will be simulated. Geometry of the assembly is defined by creating instances of a part and positioning the instances relative to each other in a global coordinate system. With the assembly created, it's time to configure the analysis by applying boundary conditions and loads to the model. I found this to be the most demanding part so far, because boundary conditions and loads are step-dependent, meaning that you have to specify the step or steps during the simulation when they are active.
You now have to generate the finite element mesh by actually creating the mesh and assigning the element type, such as a truss. Meshing involves choosing the edges of a part instance, then meshing the part instance. If the model can not be meshed without further intervention by you, it displays in orange, signaling a problem that must be addressed. Because an analysis can be a lengthy process, it's always a good idea to run a data check analysis before running the simulation. This check minimizes the probability of errors in the model due to incorrect or missing data.