ANSYS Explicit Dynamics Solutions

• ANSYS Explicit STR is an analysis system within the ANSYS Workbench platform. It offers the Lagrange (Structural) solver capability.
• ANSYS LS-DYNA is a separate program. Complete input for ANSYS LS-DYNA can be prepared with the powerful preprocessing features of the ANSYS Workbench platform.
• ANSYS AUTODYN is a component system within the ANSYS Workbench platform. It offers a comprehensive, multiple solution capability (Advanced Numerical Methods for Nonlinear Dynamics.)

Crushing of a Metal Can

ANSYS provides a wide range of highly robust automated meshing tools – from tetrahedral meshes to pure hexahedral meshes and high quality meshes for surface and line bodies. Using the Explicit Preference in meshing will automatically generate meshes well suited for Explicit Dynamics. Additional productivity tools include the ability to control element size, defeature unnecessary details, generate swept hex dominant meshes, smoothing controls for gradual element size transitions and multizone meshing for parts made up of multiple bodies that need to be meshed uniformly.

Geometries created with CAD tools are not always well suited for explicit dynamic simulations. For example, surfaces that do not meet or overlap may need to be corrected. Very small features may need to be removed to so that meshes can be created that can be used to generate accurate results efficiently.

Automatic body-by-body meshing of a large cell phone assembly for an explicit drop test analysis

bq. ProE CAD model of perforating gun and cross section of one shaped charge mesh. Courtesy of Schlumberger

Circuit board CAD model and mesh in preparation of a drop test simulation

Once the geometry has been imported, ANSYS automatically detects and does setup for contacts, bonded contacts and interface definition for coupling between Euler and Lagrange regions for problems involving Fluid Structure Interaction (FSI). Contact settings can be modified to improve computation speed by excluding parts or surfaces that are known not to come in contact.

Automated detection of contacts is performed upon geometry import

Automated interface definition for coupling between Euler and Lagrange parts in FSI problems

The current generation of ANSYS element technologies used in explicit dynamics provides rich functionality with a consistent theoretical foundation coupled with the most advanced algorithms. The ANSYS explicit dynamics software provides a variety of elements for use with line bodies, surfaces and solid elements. Element types include: 8 node hex, 6 node penta or 4 node tet elements in 3-D, 4 node hex and 3 node tet in 2-D. The speed of calculations can be further improved with the use of 2-D axis-symmetry, 2-D planer symmetry as well as 3-D quarter or half symmetry. These options can be easily set-up on the ANSYS Workbench platform.

It is vital to understand and accurately characterize material behavior while designing or analyzing an engineering application. ANSYS explicit dynamics solutions provide a vast library of mathematical material models which aids the user to simulate virtually all kind of material behavior including:

• Metals
• Concrete
• Rock
• Soil/Sand
• Rubbers
• Polymers

ANSYS Workbench Explicit Dynamics Material Models

In addition, in order to aid in finding parameters for these materials models, ANSYS also provides a set of curve fitting tools. The engineering data library included with the ANSYS Workbench platform, not only contains an extensive list of material models, but displays the material response properties in a tabular and graphical form.

The engineering data library included with the ANSYS Workbench platform, not only contains an extensive list of material models, but displays the material response properties in a tabular and graphical form.

With a solid foundation of element and material technology, ANSYS explicit dynamics solutions offer various advanced solver technologies to best simulate a comprehensive list of dynamic applications, depending on the product. Part interactions can be through contact, bonded contact and coupling between Euler and Lagrange regions for problems involving Fluid Structure Interaction (FSI). For parts that interact via contact, the contact surfaces are automatically redefined as that elements on the surface are removed through erosion.

• The Lagrange solver utilizes a mesh that moves and distorts with the material it models as a result of forces from neighboring elements. This is the most efficient solution methodology with accurate pressure history definition. If however, there is too much deformation of any element it results in a very slowly advancing solution and is usually terminated as the smallest dimension of an element results in a time step that is below the threshold level. For problems with too much deformation involving gases and liquids, the Euler solver is better suited.
• The Euler (multi-material) solver utilizes a fixed mesh, allowing materials to flow (advect) from one element to the next. The Euler solver is very well suited for problems involving extreme material movement, such as one’s involving fluids and gases. Euler is generally more computationally intensive than Lagrange and requires higher resolution (smaller elements) to accurately capture sharp pressure peaks that often occur with shocks.
• The ALE (Arbitrary Lagrange, Euler) solver utilizes the advantages of both the Lagrange and Euler solvers. It works as a Lagrangian solver but periodically repairs the mesh as it gets distorted. It is well suited for problems in between the Lagrange and Euler sweet spots.
• The Euler – FCT used for ideal gases is a special purpose Euler solver that is very fast and highly accurate. It is best suited for use in problems simulating blast loadings.
• The SPH (Smooth Particle Hydrodynamic) utilizes a mesh free method, ideally suited for certain types of problems with extensive material damage and separation such as cracking. This type of response often occurs with brittle materials and with hypervelocity impacts.
• The Shell solver is assigned to two dimensional parts (surface bodies) such as membranes. It enables efficient computation in spite of the very small dimension of the “membrane.”
• The Beam solver is used for the one dimensional parts (line bodies) such as reinforcements. When used in conjunction with solid elements, beams can be located inside a solid element and need not be aligned wit the nodes of the Lagrangian elements, making their use unlimited, while requiring very little effort to set-up.

ANSYS explicit dynamics solutions offer a powerful collection of tools for increasing productivity, reducing the effort to set-up, run and analyze simulations, increasing accuracy, reducing simulation time and in general making the engineer/scientists job easier and more enjoyable. The list below contains just a few of the numerous tools available to the user.

• Interactive problem set-up (pre-processing) solution and analysis (post-processing). Working interactively with a graphical user interface, as compared to preparing a text input file makes it easy and convenient to immediately identify and correct bad input values, thus resulting in a working solution in the shortest possible time.
• Intuitive User Interface. The user interface is set up to guide the user through the set-up process such that it can be done in the most efficient sequence, so as an example selecting materials from the material library at the beginning of the set-up, enables the program to offer a choice from the preloaded materials when “filling” a part with material.
• Safe default values. The majority of input values have a safe default value, making it easy for users to quickly set-up and run a problem without a great deal of effort. If the default values are not best suited for a specific problem their vale can be overridden at any time.
• Remapping in space. High resolution fast running 1-D problems can be mapped into 2-D or 3-D, enabling highly accurate results to be created extremely fast. The remapping is accomplished with just a few clicks of the mouse. 3-D problems can also be remapped into 3-D for extending the physical size of the problem.
• Remapping solution method. The solution method for a part can be changed when the problem requires a different methodology. In the example to the right a 2-D axis-symmetric Euler solution is mapped into a 3-D Lagrange solution enabling the simulation of an oblique impact. Running this problem in 3-D with the same result resolution and accuracy would require 1,000 times as much computer time.
• Import of data from Geographic Information System (GIS) services. For modeling large city structures information from a GIS data base can be imported, making the creation of a mesh and solution space virtually automatic. Manual set-up of this type of a problem would make it totally unpractical.
• Mass scaling. Mass is artificially added to individual elements to ensure that the timestep is at least equal to a user defined value. This is a valuable technique for problems with a limited number of small elements. A contour plot of the time step for each element enables quick identification of the scope of the problem and whether this technique is practical and safe.
• Dezoning. Parts using the Euler solver can be “dezoned” increasing the size of each element thus reducing the number of elements and increasing the usable timestep. This tool provides a way to increase the computational speed during the later stages of a calculation when less resolution might be required.
• Part activation. During the solution process the problem can be viewed interactively. It is possible to stop the calculation, add or remove parts and resume. Parts can also be “deactivated” so they visually remain part of the problem but are no longer included in the calculations. During problem setup, an activation time can also be used to activate a part at a specific time. These techniques allow for faster computations with very little user intervention.
• Erosion. Erosion is a numerical method (non-physical) used to eliminate elements that have become degenerate, or have caused the time step to be reduced below a minimum value. Erosion criteria can be based on minimum time step values, values of strain or material failure. The eroded element can optionally be retained as a point mass, enabling more accurate momentum conservation and potential loading from the eroded nodes.
• Natural Fragmentation. Natural fragmentation provides a statistical way to model failure due to impurities. This technique is invaluable when modeling symmetrical parts under uniform strain, where normally all elements would fail at the same time. Natural fragmentation introduces minor variance in the failure criteria randomly in the elements that make up the part, resulting in “natural fragmentation.”

ANSYS provides a comprehensive set of post-processing tools to display results of the models as contours or vector plots, and provide summaries of the results (like min/max values and locations). Powerful and intuitive slicing techniques allow the user to get more detailed results over given parts of the geometries. All the results can also be exported as text data or to a spreadsheet for further calculations. Animations of all or any individual part can be created with ease. Variables at tracer point locations can be plotted as time histories.

ANSYS lets you explore your design in multiple ways. All the inputs and results can be efficiently documented. ANSYS will provide you instantaneous report generation to gather all input data specifications, material models used and a copy of all the pictures and graphs that were generated in the set-up and post-processing of the model in a convenient format (HTML, MS Word, MS PowerPoint).

Example Explicit Dynamics Report

ANSYS explicit dynamics solutions offer a comprehensive set of tools that facilitate the reduction of the solution time and increase in accuracy of the results generated. Parallel processing through the use of domain decomposition can reduce the solution time for large problems. Parallel solutions can be used with any computer configuration, such as multi-core, multi CPU or networked computers.

Domain decomposition of a model with performance improvements as a function on the number of processors used

ANSYS explicit dynamics solutions offer an open architecture enabling customers to extend the standard capabilities of the program easily and conveniently. Customization capabilities through user defined subroutines are available for a list of functions, such as materials equation of state material failure model, erosion model, strength model, boundary conditions, input and output functions and many more. Templates are provided for all user definable subroutines with documentation on how they can be used, the variables available for use and the variables that must be defined within the subroutine. The modified user subroutines are linked with the standard program and a new executable is created.