Enumerate different phases of FEA

 FEA - Finite element Analysis in General has the following four phases .

1. Problem Understanding.
2. Pre processing
3. Processing
4. Post processing

In Problem Understanding phase one should define the problem statement and requirement clealry that inturn helps to select the components that are needed to be meshed.

Pre processing involves Geometry prepartion, geometry cleanup and meshing of required components, applying load cases and other restraints.

Processing is nothing but feeding the mesh model into a FEA solver and requests the solver to run the Model and solve the calculation. Nastran,  Hyperworks optistruct are some of the familiar FEA solvers in the market.

Post processing involves interpretation of the results using a post processing application and generating reports to check whether the component meets the required target criteria like stress, amplitude, modal frequency etc.

How to perform free free run operation in ANSYS for 3d component?

 Free Free Run in FEM analysis is a common method to check in Ansys and other FEM solvers whether the FEM is mesh modelled correctly without any free edges or missing connections.

Free free Run solves the model without fixing constraints, so that the whole model will be floated in space .

If the model is meshed correctly, then if you run the free free run, then the complete mesh model will move in X, Y, Z respectively for first three mode.

Incase if the mesh is not done properly, some connections are missed, then some parts will be hanging seperately when you animate the free free run mode shapes. Based on this observation , you can fix the model.

Finite Element Simulation : Overview of Existing Packages - Hyperworks , NX Siemens Advanced Simulation

Present day CAE tools like Hyperworks, NX Advanced simulation tool  give you access to powerful geometry construction and editing capabilities, extensive capabilities for building models, and a wide selection of solutions to simulate real world conditions. Information on design performance is fed back to you in graphical form so that it's easier to understand and communicate through the design process. The Simulation tools are tightly coupled into a team engineering environment. These powerful capabilities are easy to use and provide intelligent guidance through the simulation process.

Important features of the Simulation package will include:

• Geometry tools
• Modeling tools
• Integrated solvers
• Post processing tools
• Intelligent tools

The Geometry tool will assist you to prepare the CAD model of the components and Pre-processing tasks like meshing, defining boundary conditions can be carried out using Advanced simulation tools.
The mesh model can be solved using integrated solvers like NX Nastran, Optistruct etc.

Intelligent tools will help the user to improve the design. The intelligent tools usually consists modules like design optimization, Mesh modification etc

FEA: Dragging Nodes in FEA mesh (thin shell 2D elements) | Ansys | Hypermesh | Solidworks

To meet the quality criteria like threshold angles, Jacobian ratio, aspect ratio, warp, distortion etc, we can manually drag the nodes of the elements.

Therefore, Dragging a Node can interactively re-position nodes associated with 2D type elements, such as thin shell, plane strain, plane stress, axis symmetric solid, plate, and membrane.

When you drag a node, it maintains associativity with the surrounding elements and the underlying geometry. As you drag the node, the software previews how the elements associated with the node will be affected.

In general, we can only drag one node at a time. However, any mid-nodes adjacent to the selected node will also move. If you drag a node in a mesh that contains higher order elements, such as parabolic or cubic elements, the pre processor software (Hypermesh, Ansys, Solidworks) translates the mid-nodes to preserve their initial characteristics.

Requirements for Dragging a Node on Geometry

If a node is constrained to:

• an edge or a wireframe curve, you can reposition the node along that edge or curve.
• a surface, you can reposition the node on that surface.
• a section, you can reposition the node on any surface within that section.

Note: You can't drag a node past the edge of a hole or fillet.

You can't use Drag (Node) to re-position:

• nodes on anchor nodes
• nodes associated with vertices, connectors, or centerpoints
• nodes associated with geometry-based other elements (such as a spring, rigid bar, or lumped mass)
• nodes associated with point-based geometric boundary conditions

Dragging a Node on Geometry

1. Pick the node you want to reposition.
2. Move the cursor to drag the node. As you move the mouse, the software updates all adjacent element edges in real time.
3. Use mosue buttons to drop the node in its new location,

Requirements for Dragging a Node Not Associated with Geometry

Drag (Node) also lets you drag nodes in FE models that don't contain any geometry, such as those FE models created with the bottom up meshing technique. Before you can reposition a node that isn't associated with geometry, you must first pick the plane in which you want to drag the node. The default drag plane is the average of the local normals of the adjacent elements.
Dragging a Node Not Associated with Geometry

• Pick the node to reposition.
• Pick the plane in which you want to drag the node.
• Move the mouse to drag the node or use the mouse button options 
• Use mouse buttons to place the node.

We can also pick Drag (Node) from the Element Quality Checks form to improve particular aspects of element quality. For example, if a quality check reveals a high amount of skew in a particular region, we can try repositioning nodes in that area to reduce skew.

FEA : Steps for Collapsing and Removing Triangular Elements | Meshing in Ansys, Hypermesh, Solidworks

When we use Element Collapse to remove triangular elements from your model, we should be very careful in selecting the elements to collapse.
In many cases, we won't want to collapse all elements that don't meet the specified quality criteria like, included angle threshold.
For example, depending on your geometry, when you use Element Collapse, the resulting mesh may not have nodes at the vertex of two edges.



For illustration, just assume a simple model of a block with a shallow groove cut through the top. and an FE models created and defined a mesh of linear triangle elements on all surfaces.

Now, assume We used the Tri-Inc Angles option on the Element Quality Checks form to check the model for triangular elements with included angles smaller than 15°.

Now the software will

• show a group of the elements that failed the check.
• show the same group of elements displayed within the context of the model's surfaces.

As case 1, we can make Element Collapse to remove all the elements that failed the initial Tri Inc Angles check. By collapsing those elements, we significantly change the relationship between the mesh and the geometry in the region of the groove. Specifically, the software no longer generates a node at the vertex between the two edges


In case 2, we can make element Collapse to remove only the eight elements in the middle of the groove. Notice the difference in the resulting mesh at that vertex. However, also notice that there is now no longer a node at a different vertex.

FEA : Solving element interference in mesh model | Ansys, Hypermesh, Solidworks, Nastran NX

To solve Element Interference

Interference Check tools are used to check the mesh model for element interference, the Element Interference Result/Fix form allows us to view, manipulate, and try to solve the areas where interference occurs.

The tools on the Element Interference Result/Fix form should only be used to repair regions where the amount of interference is relatively small, relative to the elements' size and thickness.
Usually, the Element Interference Result/Fix form does not allow we to fix areas of self-intersection within a single component.

The Element Interference Result/Fix form divides the model into separate "problem areas" that represent the regions where interference occurs. Generally the pre-processor software designates these regions by finding each interfering element and then clustering an interconnected set of elements that interfere with each other. Because resolving interference on a large model can be a difficult and iterative process, working with one problem area at a time can help we manage the scope of the problem. Each problem area is comprised of multiple components.

To actually repair the interference between components, the pre-processor moves the nodes on the interfering elements as well as on the elements surrounding them based on a percentage of the elements' thickness. Different options on the Element Interference Result/Fix form allow we to constrain either specific nodes or entire components to control this movement. If we're repairing the interference on a model that contains associated geometry, the software maintains the geometry association.

Process of Interference Repair

The following is a general process to guide we through the basic steps of identifying and repairing element-based interference:

1. Use Interference Check to check the model for interference. Use the Interference Check Options form to specify options for performing the check.
2. If the software detects interfering elements, pick Result/Fix Form from the right hand menu to open the Element Interference Result/Fix form.
3. Use the different display and grouping icons at the top of the form to examine the different problem areas and determine in which order we're going to try to address them.
4. Use the constraint icons at the bottom of the form to view the existing nodal constraints on each component and modify them if necessary.
5. When we are satisfied with the nodal constraints,we can pick Fix Interference to repair selected components.
6. Select OK to accept the changes to mesh model, or Select Undo to undo the interference repairs between selected components.

Nodal Movement during Interference Repairs

With Fix Interference, the software moves the nodes in the direction of their constraints. In order to prevent the drastic changes in curvature that could by caused by moving just the nodes on the interfering elements, the software also moves nodes on four surrounding rings of elements.
Interference Repairs Performed in a Series of Iterations

The pre-processor would move the nodes on the rings of elements in a series of up to ten iterations. After we use Fix Interference, the software reports the number of iterations performed in the List region. If the software is unable to repair the interference in ten iterations, we can pick Re Iterate from the right hand menu to have the software perform up to ten additional iterations.

FEA : Shell Element Normals, Assign Material Side orientation in Thinshell Meshing, | Ansys , Hypermesh, Solidworks, Nastran NX

Checking Shell Element Normals in thin shell meshing

All shell elements have a normal (perpendicular) that defines the top and bottom of the mid surface meshing.
If we create,copy or move elements, shell normals may have a chance to change their different directions. During Post Processing and Optimization, it is necessary that the elements should have consistent tops and bottoms. All perpendiculars must point the same direction.

Shell normals and material orientation are independent of one another.Usually the pre-processing softwares have two tools for controlling shell element normals.

• Shell Element Normals (Meshing task) lets you change shell element normals on a model that doesn't contain underlying geometry.
• Material Side (Modeling task) lets you specify shell element normals on a model that contains underlying geometry.

Using Shell Element Normals

To use Shell Element Normals, select a "base element" with the desired orientation. Starting at that element, the command shifts the shell normals of the elements adjoining the base element until every element in the model is aligned.

For example, let us consider a sheet metal car bracket has been created in one quarter and then duplicated downward by reflecting. As a result, the shells normals of the lower half point in the opposite direction. By choosing a base element in the upper half, the command adjusts the lower elements until they're all pointing in the same direction.

Using Material Side

We can use Material Side in the Modeling task to control the direction of shell element normals when we mesh surfaces. Once you assign a material side to a surface, the mesh generator uses the material side's direction as the direction of the element normals.

We can't modify the material side for surfaces that make up a volume.

If we don't set the material side before you mesh surfaces, the mesh generator would automatically assigns a consistent direction for element normals. For example, let us consider of a mesh is generated on a non-manifold part and a manifold part where the software assigned the element normals.

If we use material Side and then mesh the part, the element normals point in the direction of the material side. Here, we should use Material Side to control the shell element normals on a non-manifold part and a manifold part .

FEA : Finite element Analyis topology, shape optimization, adaptive analysis - Basics

Intelligent Tools

Finite element modeling requires some necessary decisions like selecting

• Element type,
• Mesh density
• Applying Constrains, Restrains and loads 

Current generation Pre processing tools has several capabilities that intelligently guide us through the simulation process, and help us to get accurate / correct results.

Adaptive Analysis

One of such major intelligent tool is Adaptive analysis capability.
Adaptive analysis includes some primary decision parameters like number of elements required to accurately capture the desired performance measure.

1. To capture displacements or Eigen values (resonant frequencies), generally a relatively coarse mesh will suffice.
2. To study the stress results generally requires more elements and more attention to having elements in high stress regions.

Finite element mathematical formulations generally assume limited variation of stress across any one element. Adaptive analysis allows proper element density to be set automatically.

Simulation offers r (node position), h (element refinement and remeshing), and p-element adaptivity. A p-element tetrahedron has been implemented for linear statics analysis. The p-element implementation takes full advantage of the automatic meshing capability and geometry-based loads and boundary conditions. The combined r,h,p adaptive approach now available for solids leads to the most rapid solution convergence on problems with highest geometric complexity.

Optimization

All processors like Hyperworks - Optistruct , NX Nastran, Solidworks  etc come up with optimization strategy which help us to design an cost effective, strength sufficient design .

Generally the Optimization module will provide the ability for analysis to directly guide design. It can help us rank possible design changes and understand the required magnitude of changes to achieve a particular goal.

• Optimization allows you to effectively improve complex structures with interacting loads that cannot be handled with manual methods.
• The geometry-based optimization capabilities work directly with the Modeler geometry. Allowable geometry changes are defined by selecting dimensions and entering variations in a form.

Design goals, as well as other constraints on deflection, stress, or natural frequency, are also entered through forms. As the design is updated through optimization iterations, the FE model (mesh, loads, and restraints) is updated automatically. Geometry updates maintain original design intent through the variational geometry constraint network defined during geometry construction. Modified versions of geometry are maintained through the data management capability. 

Element Quality Check Criteria in FEA meshing - FEA applications and Tutorials

Quality of the element is very important criteria , in FEA pre-processing. Higher the qulaity of the mesh, we can get reliable results given that you have given perfect boundary conditions.

At the same time, we should also consider the memory limitation of the computers available with us. So , we should optimize the FE model equally considering the cost of the solving and accuracy that is needed.

Understanding Element Quality Checks

Quality checks measure different aspects of an element's deviation from an ideal size and shape. That ideal shape depends upon the element type.You can choose one or more checks and set threshold values, or limits for deviation, for each. You can perform these checks on shell and solid elements.
There are several ways to check your mesh. You can use:

• Auto Mesh Checking to have the software automatically evaluate aspects of element quality while it generates a mesh

• Element Quality Checks to set quality threshold values and evaluate element quality once you've generated a mesh

• The various element quality icons and menu commands, such as Coincident Nodes or Coincident Elements, to run individual quality checks

Once you've identified element quality problems, you can use tools such as Plump or Straighten Edge to fix distorted tetrahedral elements. You can also use the Node or Element menu commands to adjust other elements.
After you've checked the mesh, you can generate statistical data on element quality or create a result set and display the elements in Post Processing. You can also filter the selection of elements from the results of these mesh checks.

Understanding Quality Threshold Values

This table lists the possible threshold values for each type of element and shows how they're calculated. In this table:

• X = supported by Quality Checks

• LX = calculations use linearized edges

• SX = calculations use shape functions

• LMX = calculations use linearized midside to corner edges

Quality Check	Threshold1	Threshold2	Quad Shell	Tri Shell	Solid	Linear	Parabolic	Cubic
Skew	(>) 0-360	-	X	X	-	X	SX	SX
Warp	(>) 0-180	-	X	-	-	X	LMX	LMX
Taper	(>) 0-1	-	X	-	-	X	LMX	LMX
Aspect Ratio	(>) 0-100	-	X	X	X	X	LX	LX
Distortion	(<) 0-1	-	X	X	X	SX	SX	-
Stretch	(<) 0-1	-	X	X	X	X	SX	LX
Jacobian	(<) 0-inf	-	X	X	X	SX	SX
Element Size	(<) 0-inf	(>) 0-inf	X	X	X	X	LX	LX
Quad Included Angles	(<) 0-90	(>) 90-180	X	X	X	X	SX	SX
Tri Included Angles	(<) 0-60	(>) 60-180	X	X	X	X	SX	SX

Using Automatic Mesh Checking

Nowadays, every pre-processing software comes with automatic mesh checking feature. We can use Auto Mesh Checking to have the software automatically evaluate element quality while it generates a mesh. The Automatic Mesh Checking form lets you specify values for checks such as Distortion and Stretch.

This form also lets you control whether mesh smoothing is turned on for meshes that contain linear or parabolic tetrahedrons. Mesh smoothing improves stretch and distortion. 

How to solve Free element Edges in FEA meshing - FEA applications and Tutorials

Handling Free Element Edges

When we combine elements within a mesh, it may result in the creation of free edges in the interior of the mesh. It is mandatory to cross check and ensure that there are no free edges at the interior of the mesh , before sending the model to Solver.

For example, let us assume we combined four linear elements to create a single linear element (A). And now, the mid-nodes on the new element aren't connected to this element; they're connected to surrounding elements (B). (The new element isn't a 6-noded quadrilateral hybrid element.) Therefore, free edges occur in the interior of the mesh where the new element is adjacent to existing elements (C).




You can eliminate free element edges in one of two ways:

• Use Combine Elements option to propagate the combined elements throughout the mesh. This eliminates all free element edges. Here:

A = mesh containing combined elements

B = combined groups of four elements

C = Free Element Edges verifies there aren't any free edges in the interior of the mesh.

• Stitch the new elements into the mesh by using various combinations of Split Elements, Combine Elements, Delete, (Create) Element, and Node Connectivity commands. 

C = Use Free Element Edges to verify that there aren't any free edges in the interior of the mesh. 

Defining and Generating a FEA Mesh - FEA Practical applications and tutorials

In general , the basic platform and tools for Meshing task is common in all FEA pre-processing softwares like NX Nastran, Hypermesh,Cosmol, Abaqus, Ansys etc. This article will give a brief overview of the basic of mesh generation technique in FEA.

Defining and Generating a Mesh

The Meshing task will provide tools to help us to define and generate a FE mesh. We can

• use the geometry checking tools to verify that your geometry is ready for meshing
• define parameters for the mesh
• preview the mesh before you generate nodes and elements
• generate the mesh based on the mesh parameters
• check the quality of the mesh
• update the mesh after solution
• modify individual nodes and elements as necessary

Defining a Mesh

When we define a mesh, we should specify parameters such as:

• mesh type. Mesh generation can produce either regularly-spaced finite elements (mapped mesh) or less restrictive free elements (free mesh).
• element type and length
• elements' physical and material properties
• We can always choose default or previously-defined settings when you create a mesh. Often, however, you will want to control the meshing process more by changing some of the default parameters

Meshing Limitations

• We can't mesh adjacent entities with a different element order defined. For example, we cannot define a linear element type (say four node element) for a mesh on one surface (x) and then define a parabolic element type ( say eight node element) for an adjacent surface (y). This creates a mismatched element order where the surfaces join (z).

• We can't mesh adjacent entities that have a free and a mapped mesh defined on them.