• Solid186


    Grama Bhashyam Guest. Posted: Fri Aug 07, am. Joe I am not sure if I can refer you to a benchmark or whitepaper on the topic. But I can explain our understanding on this. However, hourglass mode might propagate in the model if there are not at least two layers of elements in each direction. This method is used primarily for purely linear analyses, or when the model has only one layer of elements in each direction.

    Thus, the issue of propagating a zero energy mode, is strictly in models with one element in cross section. The 2 x 2 x2 Gauss Points of integration are known to have a higher accuracy for stresses see "superconvergence" topics in literature c.

    The 14 point rule is primarily applicable to linear elasticity, and is useful for a mesh pattern that does not provide natural constraint against hourglass propagation.

    This is our way of addressing the issue: one default does not fit all! With this option, you are in fact using a 14 point rule, for SOLID using a linear elastic material. Hope that helps. One of our users here had a question I couldn't answer. Workbench meshes always use the new 18x elements. Does anyone know of any studies or white papers available that quantify the effect on accuracy for the reduced integration? I have always assumed that these element types were equivalent for linear statics.


    If the reader of this message is not the intended recipient, you are hereby notified that any dissemination, distribution, or copying of this communication is strictly prohibited.

    If you received this communication in error, please delete the message and immediately notify me via the contact numbers listed above. Back to top. All times are GMT - 7 Hours.One of the problems we can encounter in a nonlinear structural analysis in ANSYS Mechanical is that elements become so distorted that the solver cannot continue.

    We get messages saying the solver was unable to complete, and the solver output will contain a message like this one:.

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    The Solution branch will have the telltale red lightning bolts, indicating the solution was not able to complete due to nonconvergence. If you are not aware, one technique we can use to get past this problem of excessive element distortion is to have ANSYS automatically remesh the model or a portion of the model while the solution is progressing.

    The current state of the model is then mapped onto the new mesh, in the currently deflected state. In this manner we can automatically continue with the solution after a slight pause for this remeshing to occur.

    Minimally all we need to do as users is insert a Nonlinear Adaptive Region under the Static Structural branch, and review and specify a few settings more on this later.

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    This is a wedge portion of a circular hyperelastic part, subject to a pressure load on the top surface. Other boundary conditions include a fixed support on the bottom and frictionless supports on the two cut faces of the wedge. The initial mesh was setup as a default mesh, although note that for 3D models the nonlinear adaptive capability requires a tetrahedral mesh up through the current version, R2.

    With the addition of the nonlinear adaptive region, the model is automatically remeshed at the point of excessive element distortion, and the solution is able to proceed until the full load is applied. The force convergence graph has a solid vertical orange line at the point where remeshing occurred.

    The method can result in multiple remeshing steps although in the sample model shown here, only one remeshing was needed. The image on the left, below, shows the original mesh at the last converged substep before remeshing occurred.

    The image on the right is the first result set after remeshing was completed. The tabular view of a result item will show in the last column if remeshing has occurred during the solution. First, multiple substeps must be used for the solution.

    If we are performing a nonlinear analysis, this will be the case anyway. Second, Large Deflection needs to be turned on in the Analysis Settings branch. Also, as mentioned above, for 3D models, the mesh must be tetrahedral.

    In the Details view for the Nonlinear Adaptive Region, the main option to be defined is the Criterion by which remeshing will be initiated. The Energy criterion checks the strain energy of each element within the Nonlinear Adaptive Region. If the strain energy is above a criterion, remeshing is triggered. The input is an energy coefficient between zero and one, and is a multiplier on the ratio of total strain energy of the component divided by the number of elements of the component.

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    Recommended values are 0. A lower coefficient will tend to cause remeshing to be more likely.

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    The Box criterion defines a geometry region based on a coordinate system and bounds relative to that coordinate system. Elements in the Nonlinear Adaptive Region whose nodes have all moved within the box will be remeshed. The Mesh criterion allows us to specify that remeshing will occur if mesh quality measures drop below certain levels as the mesh distorts.

    For 3D models, the available measures are Jacobian Ratio and Skewness. There are some things to be aware of when you are trying to implement a Nonlinear Adaptive Region to help overcome convergence difficulties. The Nonlinear Adaptive Region capability is more suited to problems like hyperelastic seals being compressed or objects that are undergoing a high degree of bending but not snapping through.

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    Also, a coarse mesh that distorts may not produce a usable remesh. The remeshing step may occur, but the simulation may not be able to proceed beyond that and stops with an error in element formulation error.Learn more about SimuTrain or get started today by purchasing your subscription.

    This article illustrates how to detect and act on the two element types found in a hybrid-meshed body such as can result with a Hex-Dominant meshing method, a Multizone meshing method or Inflation. Workbench has meshing methods that create a hybrid mesh in selected bodies. A hybrid mesh could contain solid elements with a mix of hexahedral brick shape with 6 quadrilateral facespyramid four-sided base with four three-sided facesand tetrahedral four three-sided faces elements.

    Mesh methods producing hybrid meshes include Hex-Dominant, Multizone with certain Details settings, and Inflation. The hexahedral elements share the same element type as the pyramid elements, while the tetrahedral elements get their own element type number, yet share the same MATID material number in a given body.

    A tetrahedral 10 node element derived from first principles use less storage than a node brick degenerated to a node tetrahedral shape, resulting in less model memory and storage use, plus faster solving, so the separate element type is appropriate. APDL coding can detect whether any given part has hybrid meshing, and act accordingly on the two element types. Two examples are presented next. In the Workbench Mechanical Outline, desired required element changes can be introduced by a Commands Object at each body in the Geometry section.

    Changes can be made according to whether the element types are discovered. Alternative commands can detect whether two more arbitrary element types have been meshed into a body. Note that while there is a pyramid form for low-order 8-node hex thermal SOLID70 elements, low-order 8-node structural SOLID elements do not have a pyramid form, and so are not used in bodies with a hybrid mesh.

    There is no low-order pyramid for structure models. Here is example APDL coding that discovers the element names for two element types found in one body after hybrid meshing. Changes can be made according to the element types. If only one element type is discovered, the second possibility is skipped. This prototype example does not make changes:. Element type name e. Number assigned to the attribute ENAM!

    Some solid bodies may have been meshed with hybrid elements containing two element types that share the same MATID material number. Statements in an APDL commands object can detect the presence of a second element type in a body. When hybrid meshing produces two element types in one body, APDL coding can be used to detect this, and programmed to change each of the two element types as appropriate.

    When general purpose APDL Commands Objects used on Bodies in Geometry are intended to modify KEYOPT settings, element attributes, or element types, they should be programmed to treat the possibility of hybrid meshing so that models behave as expected. This leaves analysts free to choose whichever meshing technique is desired without worrying about APDL Commands Object side effects.

    This article has illustrated two techniques—one acts directly on SOLID and SOLID elements, while the other discovers the element names of the two elements types, leaving it to the user to program changes according to the element name that is discovered.

    Get SimuTrain Now! Materials Semiconductors Optical Systems. Local Seminars Webinars.It is defined by eight nodes having three degrees of freedom at each node: translations in the nodal x, y, and z directions. The element has plasticity, hyperelasticity, stress stiffening, creep, large deflection, and large strain capabilities.

    It also has mixed formulation capability for simulating deformations of nearly incompressible elastoplastic materials, and fully incompressible hyperelastic materials. It allows for prism, tetrahedral, and pyramid degenerations when used in irregular regions. Various element technologies such as B-bar, uniformly reduced integration, and enhanced strains are supported. The element is defined by eight nodes and the orthotropic material properties. The default element coordinate system is along global directions.

    You may define an element coordinate system using ESYSwhich forms the basis for orthotropic material directions. Element loads are described in Nodal Loading. Positive pressures act into the element. Temperatures may be input as element body loads at the nodes. If all other temperatures are unspecified, they default to T I. For details on the use of mixed formulation, see Applications of Mixed u-P Formulations. Use RSYS to choose output that follows the material coordinate system or the global coordinate system.

    The effects of pressure load stiffness are automatically included for this element. For a general description of element input, see Element Input. Full integration with method default. SOLID Homogeneous Structural Solid uses the full-integration method also known as the selective reduced integration methodenhanced strain formulationsimplified enhanced strain formulationor uniform reduced integration.

    For more information, see Element Technologies. The Element Output Definitions table uses the following notation:. The O column indicates the availability of the items in the file Jobname.Log In.

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    Are you an Engineering professional? Join Eng-Tips Forums! Join Us! By joining you are opting in to receive e-mail. Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. Am I missing anything here?

    Any help is appreciated. Thanks, Krishna. It is impossible for proper change element type after mesh in Ansys. I just figured it out.

    Detecting Hybrid Meshing with an APDL Commands Object for a Body in ANSYS® Workbench Mechanical

    Later you can delete the solid elements. Red Flag This Post Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework. Several of the tooling and casting requirements of a part can be addressed at the design stage.

    If these requirements are not addressed at the design stage, lot of time is spent in design iteration when the design reaches the die caster. These design issues lead to increase in time and cost of production leading to delay in time to market and reduced profits for the organization. Download Now. The benefits of cost and time savings using effective collaborative mechanisms at the right time have been highlighted in this white paper.

    Assembly level constraints need to be satisfied before the design can move downstream. This white paper will go through the various assembly level issues, which need to be tackled by various organizations on a regular basis. Know more about DFMPro, a design for assembly software. Close Box. Students Click Here Join Us! Posting Guidelines Promoting, selling, recruiting, coursework and thesis posting is forbidden.To define a shell made of a single material, use a material definition Material data definition to define the material properties of the section and associate these properties with the section definition.

    Optionally, you can refer to an orientation Orientations to be associated with this material definition. A spatially varying local coordinate system defined with a distribution Distribution definition can be assigned to the shell section definition. Linear or nonlinear material behavior can be associated with the section definition.

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    However, if the material response is linear, the more economic approach is to use a general shell section see Using a general shell section to define the section behavior. You specify the shell thickness and the number of integration points to be used through the shell section see below.

    For continuum shell elements the specified shell thickness is used to estimate certain section properties, such as hourglass stiffness, which are later computed using the actual thickness computed from the element geometry.

    If the orientation definition assigned to a shell section definition is defined with distributions, spatially varying local coordinate systems are applied to all shell elements associated with the shell section. A default local coordinate system as defined by the distributions is applied to any shell element that is not specifically included in the associated distribution.

    You can define a laminated layered shell made of one or more materials. You specify the thickness, the number of integration points see belowthe material, and the orientation either as a reference to an orientation definition or as an angle measured relative to the overall orientation definition for each layer of the shell.

    The order of the laminated shell layers with respect to the positive direction of the shell normal is defined by the order in which the layers are specified. Optionally, you can specify an overall orientation definition for the layers of a composite shell. A spatially varying local coordinate system defined with a distribution Distribution definition can be used to specify the overall orientation definition for the layers of a composite shell. For continuum shell elements the thickness is determined from the element geometry and may vary through the model for a given section definition.

    Hence, the specified thicknesses are only relative thicknesses for each layer. The actual thickness of a layer is the element thickness times the fraction of the total thickness that is accounted for by each layer. The thickness ratios for the layers need not be given in physical units, nor do the sum of the layer relative thicknesses need to add to one. The specified shell thickness is used to estimate certain section properties, such as hourglass stiffness, which are later computed using the actual thickness computed from the element geometry.

    Spatially varying thicknesses can be specified on the layers of conventional shell elements using distributions Distribution definition. A distribution that is used to define layer thickness must have a default value.


    The default layer thickness is used by any shell element assigned to the shell section that is not specifically assigned a value in the distribution. An example of a section with three layers and three section points per layer is shown in Figure 1.

    The material name specified for each layer refers to a material definition Material data definition. The material behavior can be linear or nonlinear. The orientation for each layer is specified by either the name of the orientation Orientations associated with the layer or the orientation angle in degrees for the layer. Spatially varying orientation angles can be specified on a layer using distributions Distribution definition. Unless your model is relatively simple, you will find it increasingly difficult to define your model using composite shell sections as you increase the number of layers and as you assign different sections to different regions.

    It can also be cumbersome to redefine the sections after you add new layers or remove or reposition existing layers. For more information, see Composite layups. Simpson's rule and Gauss quadrature are provided to calculate the cross-sectional behavior of a shell. You can specify the number of section points through the thickness of each layer and the integration method as described below.


    The default integration method is Simpson's rule with five points for a homogeneous section and Simpson's rule with three points in each layer for a composite section. The three-point Simpson's rule and the two-point Gauss quadrature are exact for linear problems. The default number of section points should be sufficient for routine thermal-stress calculations and nonlinear applications such as predicting the response of an elastic-plastic shell up to limit load.

    For more severe thermal shock cases or for more complex nonlinear calculations involving strain reversals, more section points may be required; normally no more than nine section points using Simpson's rule are required.

    Gaussian integration normally requires no more than five section points.Log In. Thank you for helping keep Eng-Tips Forums free from inappropriate posts. The Eng-Tips staff will check this out and take appropriate action. Click Here to join Eng-Tips and talk with other members!

    Using a shell section integrated during the analysis to define the section behavior

    Already a Member? Join your peers on the Internet's largest technical engineering professional community. It's easy to join and it's free. Register now while it's still free! Already a member? Close this window and log in. Are you an Engineering professional? Join Eng-Tips Forums!

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    Join Us! By joining you are opting in to receive e-mail. Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. Hello, I'm modelling a composite cylinder along the x axis with solid elements.

    My problem is that I can't get the element coordinate system that I want in order to correctly model the layup of the cylinder. I want the x axis of the elements to be parallel to the axis of the cylinder which is in advance parallel to the global cartesian x axis.

    Actually both Y and Z axes can be parallel to the axial direction but not X axis. I will be glad to hear that there is a way to achieve this because I'm in the final stage of my Thesis and need to complete some runs with a solid model before finish. Thanks in advance. Store top and bottom data for all layers. Sets the element coordinate system attribute pointer. Defines property data to be associated with the temperature table. Longitudinal Lines lesize,17,A,,1! Specifies the divisions and spacing ratio on unmeshed lines.


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