Using the Force Reaction and Moment Reaction probes, the application enables you to generate reaction force and moment results from the forces generated at specified boundary conditions, such as fixed supports, displacements, as well as other constraints. Furthermore, you can determine how these forces are created at connections, such as contact regions, mesh connections, beams, or springs.
At the solver level, the output of reaction forces and moments is controlled via the Mechanical APDL OUTRES command. Support types marked RSOL are governed by the RSOL option, which refers to nodal constraint reactions. Those marked NLOAD and MISC are governed by the NLOAD and MISC options, which refer to the elemental nodal loads and elemental miscellaneous data, respectively. In addition, some analysis and support types require you turn them on in the Output Controls. If no setting is specified for a reaction type, the output occurs automatically.
When you request a Force Reaction or a Moment Reaction in a Cartesian coordinate system at a specific time point by setting Display to Single Time Point in the Details for Static Structural and Transient Structural Analysis, the Force Reaction or Moment Reaction is displayed by an arrow in the Geometry window. Force Reaction uses a single arrowhead and Moment Reaction uses double arrowhead. The arrows are drawn on the deformed mesh.
Similarly, when moment reaction results are requested based on Frequency or Set Number and Phase Angle for Harmonic analysis or Mode Number for Modal analysis, the base of the arrow of the moment probe is placed at the Summation Point (or "centroid": the simple calculated average: unweighted by length, area, or volume). However, a Moment Reaction probe whose Location Method is a remote point will place the base of the arrow at the location of the remote point. In this case, there is no detail for Summation Point, and Mechanical does not employ a moment arm calculation. The moments are precisely the nodal moments for the remote point in the result file (as printed by the PRRSOL command in Mechanical APDL).
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Note the following when working with Force Reaction and Moment Reaction probes:
- Display
For solved reaction probes, the arrow that displays for the probe represents a resultant vector, regardless of the axial direction that you specify in the Result Selection property of the probe. Vector displays in Mechanical always use the Global Coordinate System.
- Analysis Specific
Modal and Harmonic Response analyses do not support Mesh Connections.
For Modal analysis, reaction results in damped modal analysis provide a By field option in the result definition to compute results based on Mode Number, Phase of Maximum, and Maximum Over Phase.
For a Harmonic Response analysis, reaction results support all options of the result definition available for other harmonic results, and are reported based on the nearest frequency results available: no interpolation is done.
In order to evaluate reactions successfully for a standalone Mode Superposition Harmonic Response analysis that has the Clustering property set to , you need to also make sure that either the Stress, Strain, Nodal, or the General Miscellaneous properties in the Analysis Settings>Output Controls are also set to .
Reaction results sweep through a phase period of 0o and 360o at a specified increment. In previous releases of Mechanical (14.5 and earlier), the default value for this increment was 1o in order to determine the Phase of Maximum and the Maximum Over Phase values. For Harmonic Response analyses only, the phase increment can be controlled using the Phase Increment option. A Phase Increment entry can be between 1o and 10o. The default Phase Increment value is 10o but for legacy database results it is 1o.
Response Spectrum and Random Vibration analyses, the probes do not:
Display arrows.
Support animation.
- Geometry
When you scope this result to geometry, including contact surfaces and cut surfaces, the application calculates the probe using element-nodal data. These calculations are equivalent to those of the FSUM command. That is, the sums for each component direction for the total selected node set and the nodal force and moment contributions of the selected elements attached to the node set.
Recommendation: You should examine your results carefully for geometry scoping. If all elements are selected, the sums of the result are usually zero except where constraints or loads are applied. Element-nodal results for geometry-based scoping should be the same as the node-based results when you specify Boundary Condition as the Location Method if the geometry-based scoping is the same as the boundary condition scoping. However, because of certain limitations associated with how Mechanical calculates scoping, and perhaps based on a model's geometry, the application may produce unexpected element-nodal results.
A reported reaction may be inappropriate if its support shares a face, edge, or vertex with another support, contact pair, or load. This is because the underlying finite element model will have both loads and supports applied to the same nodes.
If a model contains two or more supports that share an edge or vertex, use caution in evaluating the listed reaction forces at those supports. Calculation of reaction forces includes the force acting along bounding edges and vertices. When supports share edges or vertices the global summation of forces may not appear to balance. Reaction forces may be incorrect if they share an edge or face with a contact region.
A limitation exists when the scoping of a probe is applied to a geometric entity (Location Method = ) that shares more than one body. The (unscoped) elements that are adjacent to the scoped body contribute to the probe's results.
- Coordinate System
Force Reaction probes support Cartesian or cylindrical coordinate systems.
Moment Reaction probes support Cartesian coordinate systems only.
For a Static Structural analysis that includes a Cyclic Region object, the application requires that you specify the same coordinate system used by the Cyclic Region for your reaction probe (Orientation property). Reaction probes calculate a preliminary sum using the base sector of the symmetric model in the cylindrical coordinate system of the cyclic analysis. It then multiplies the sum by the number of sectors to obtain the final reaction. Currently, you cannot rotate these final reactions to a different coordinate system.
For Response Spectrum and Random Vibration analyses only, when you set the Location Method to and specify a or a , the application uses the . For any other supported option, such as , the application automatically uses the .
- Connections/Contact
Will not solve if scoped to a Contact Region that includes a rigid body.
Do not support the Location Method option Contact Region when the corresponding Contact Region is scoped to element faces.
For a Moment Reaction scoped to a contact region, the location of the summation point may not be exactly on the contact region itself.
A Moment Reaction probe cannot be scoped to a Grounded Spring.
Since Beam Connections are, by definition, three dimensional in nature, the reactions object scoped to grounded beams may produce reactions in all three directions/axes for two-dimensional analysis. The Tabular Data view will reflect the reactions in all three axes, while the Results view will only reflect values in two axes. The total reactions will be calculated taking into account the reaction components in all three axes.
- Summation Property
For the Moment Reaction probe, the Summation property is available for most Location Method property selections and enables you to select or for your scoped entity. If your selected Location Method does not display this property, the application automatically uses the centroid of the scoped entity for the moment calculation.
- Surface Location Method
When you set the Location Method property to , you need to specify the following additional properties:
Surface: Select a construction Surface created using the Construction Geometry feature.
Geometry: Select the body or bodies that the construction Surface intersects (slices through).
Extraction: The options for this property depend upon the setting of the Location Method property. See the description for the Extraction property in the Probe Property Descriptions section.
The Location Method property enables you to study reactions on cutting planes. You can extract generated member forces and reactions through a model by using a reaction probe scoped to a Surface object. For this probe type, you must explicitly select the body or bodies (via the Geometry property) to be sliced. You then specify the Extraction property based upon whether you want to study the nodes in front of the plane, behind the plane, or that lie on the specified plane. The Force Reaction probe operates on the elements cut by the plane and only the nodes on those elements that are on the selected by the Extraction property. The application uses a slice algorithm for the option. Because of very slight numerical accuracy issues, such as the number of significant digits used, the algorithm may not capture all expected nodes.
option of theThe application can also fail to include a node based on how you slice an element. For example, if a slice plane produces a degenerate polygon, which can happen when a planar shell has only one node in the slice plane, the reaction calculation does not use the node from the element.
For a Moment Reaction probe, when you set the Location Method property to , you must select a body or bodies for the surface to cut. If the Summation property is set to Centroid and you select multiple bodies, the application will use the average the centroids of the bodies for the summation point. The application does not use weighting by volume or by mass for this averaging.
Note: This calculation is different from the calculation used to determine the origin of a coordinate system where geometry consists of multiple bodies.
Important: Do not apply reaction probes to cutting planes that intersect a boundary condition because the reported reactions become unreliable.
Note:Based on the Extraction property setting, the probe uses the nodes of the cut elements, either positive, negative, or that lie on the plane. This requires the application to create certain tolerances along the plane as well as calculated roundoffs of the points. Based on these calculations, the application could produce unexpected results. If the reactions differ significantly, you should modify the location of the Surface plane slightly.
Surfaces used in reaction probes do not currently intersect all geometries, such as line bodies, joints, springs, and MPC contact.
Currently, surface-based probes cannot intersect a plane strain or an axisymmetric model and consequently no results display for this scoping.
- Mesh Connection Location Method
If you specify a Mesh Connection as the reaction type for a probe, make sure you review the scoping of the associated Mesh Connection object. The reaction probe’s evaluation is dependent on this scoping. The color-coding of the Mesh Connection object indicates the scoping of the object. The application displays the primary body’s scoping in red and the secondary geometry’s scoping in blue. The application only uses the color-coded nodes to define the mesh connection and therefore the calculation of the probe result value.
Using the Mesh Connection illustrated below as an example, the application only uses the nodes, and therefore only those elements, of the secondary edge-based (blue) geometry as compared to all of the nodes and elements of the primary face-based (red) geometry. The application excludes the translucent portion of the body associated with the edge scoping when evaluating the result. You must assess whether this selective inclusion of geometry aligns with your intended analysis objective.
See the Mesh Connections section in the Meshing User’s Guide for more information about creating a Mesh Connection.
- Extraction Property
If you set Extraction equal to Contact (Underlying Element) or Target (Underlying Element) in the Details of either a Force Reaction or Moment Reaction probe, the reaction calculations work by summing the internal forces on the underlying elements under a contact region. These probes can also extract reaction data from surface effect elements. The application creates surface effect elements during the solution process to simulate loads, such as pressures. However, the application does not currently display surface effect elements from the Mesh object or the Connections object.
Therefore, a reported reaction may be inappropriate on a contact face if that face shares topology with another contact face/edge or external load (such as a force or fixed support), which would contribute to the underlying elements' internal force balance. In addition, during a Transient analysis, inertial and damping forces are also included. Another possible scenario could arise for MPC contact of solid surfaces. In this case, if a gap is detected, the solver may build constraints on an additional layer into the solid mesh from the TARGET elements. This produces a more accurate response but will invalidate any reactions from the underlying solid elements of the TARGET elements. If symmetric contact is chosen, be careful to verify which side becomes active for the TARGET elements so that the correct reaction can be determined.
When scoping Force Reaction or Moment Reaction probes to geometry, it is possible that there may be elements (and as a result, element-based reactions) that are currently unavailable for summing purposes. For example, you scope a pressure to a face on your geometry. The solution process also applies surface effect elements to the same face to simulate the pressure loading. The probes, scoped to geometry, currently cannot extract reaction data from the surface effect elements and therefore, in the case of this example, only the underlying solid/shell/line elements of the original mesh contribute reaction data to the probe results.
If mesh elements overlap, reaction probes scoped using the Geometry Selection method may produce unexpected or unreliable results. Select the Mesh object to examine whether elements from one body cross an edge and overlay elements of other bodies.
When you specify a Moment Reaction probe in a large-scale deformation analysis (Large Deflection property set to ), the application uses the displaced mesh when calculating moment arms for moment probes, as defined by:
Where sx,sy,sz
is the setting of the
Summation property, x,y,z
is the nodal
location, and ux,uy,uz
is the displacement at the node
location.
Important:
This is the same as using FSUM command with the NLGEOM,ON command in the Mechanical APDL application.
Currently, the specified Summation location does not move or offset to account for any of its own displacements (or deformations), unlike the FSUM command that enables you to account for those changes.
When the Large Deflection property set to , the displacements are not used in the moment arm calculation, as defined by:
For the Rigid Dynamics solver, when force or moment reaction probes use Contact Region for the Location Method, it allows you to display the resulting contact forces on a specific contact region. The contact region can be picked using the Contact Region drop-down menu. The Contact Force menu allows you to display either the Total force, the Normal, or the Tangent force. By definition, frictionless contact always reports a normal force and the tangent force reports zero for all components.
Note: Contact regions between the same pair of parts are merged into a single contact region. Consequently, the probes will report the same values for the entire contact region.
The following topics discuss each type of reaction, the option that controls the output, and any required setting in the Output Controls. Make sure you review this content in addition to the information in Support Requirements and Limitations.
For fixed boundary conditions, including:
Face, Edge, and Vertex Rotations (do not include Force reactions)
Displacements for Faces, Edges, and Vertices
Cylindrical Support
Frictionless face
Simply Supported Edge and Vertex
Finite Element (FE) Connection Boundary Conditions (Nodal Displacement and Nodal Rotation)
Reaction Type |
Output Controlled By |
---|---|
Static |
The output of these options are controlled by the RSOL option of the OUTRES command. |
Transient - Full | |
Modal |
The output of these options are controlled by the RSOL option of the OUTRES command. To enable the output, set Calculate Reactions = in the Output Controls. |
Harmonic Response - Full | |
Harmonic Response - Mode-Superposition |
If results are expanded from a modal solution, then the output of these options are controlled by both the RSOL and NLOAD options of the OUTRES command. You must set the Calculate Reactions property to and the Nodal Forces property to either or in the Output Controls. Recommendation: is the preferred option, as the results file size will be smaller and the process time shorter. Otherwise, the output of these options are controlled by the RSOL option of the OUTRES command. Set Calculate Reactions = in the Output Controls. Important: Force and Moment Reaction probes cannot be evaluated when you specify damping in combination with setting the Expand Results From property to either or . Review the MXPAND command in the Mechanical APDL Command Reference for additional information about this limitation. |
Transient - Mode-Superposition | |
Response Spectrum |
In the upstream Modal analysis, under the Analysis Settings Output Controls , you must set the Nodal Forces property to either or Constrained Nodes and set the Store Modal Results property to or For Future Analysis. Note: The setting is the preferred setting because the results file size will be smaller and the processing time shorter.
|
Random Vibration |
Reaction Type | Output Controlled By |
---|---|
Static |
The output of these options are controlled by the RSOL option of the OUTRES command. |
Transient - Full | |
Modal |
The output of these options are controlled by the RSOL option of the OUTRES command. |
Harmonic Response - Full | |
Response Spectrum | |
Random Vibration PSD | |
Harmonic Response - Mode-Superposition |
If results are expanded from a modal solution, then the output of these options are controlled by both the RSOL and NLOAD options of the OUTRES command. You must set both Calculate Reactions and Nodal Forces to either or in the Output Controls. Recommendation: is the preferred option, as the results file size will be smaller and the process time shorter. Otherwise, the output of these options are controlled by the RSOL option of the OUTRES command. Set Calculate Reactions = in the Output Controls. Important: Force and Moment Reaction probes cannot be evaluated when you specify damping in combination with setting the Expand Results From property to either or . Review the MXPAND command in the Mechanical APDL Command Reference for additional information about this limitation. |
Transient - Mode-Superposition | |
Reaction Type |
Output Controlled By |
---|---|
Static |
The output of these options are controlled by the RSOL option of the OUTRES command. Reaction probes scoped to a Compression Only boundary condition cannot display results if the solver did not converge. |
Transient - Full |
Reaction Type | Output Controlled By |
---|---|
Static |
The output of these options are controlled by the NLOAD option of the OUTRES command. To enable the output, set Nodal Forces = in the Output Controls. |
Transient - Full |
Reaction Type | Output Controlled By |
---|---|
Static |
The output of these options are controlled by the RSOL option of the OUTRES command. |
Transient - Full |
Reaction Type | Output Controlled By |
---|---|
Static |
The output of these options are controlled by the RSOL option of the OUTRES command. |
Transient - Full |
Reaction Type | Output Controlled By |
---|---|
Static |
The output of these options are controlled by the RSOL option of the OUTRES command. |
Transient Full | |
Modal |
The output of these options are controlled by the RSOL option of the OUTRES command. To enable the output, set Calculate Reactions = in the Output Controls. |
Harmonic Response - Full | |
Harmonic Response - Mode-Superposition |
If results are expanded from a modal solution, then the output of these options are controlled by both the RSOL and NLOAD options of the OUTRES command. You must set both Calculate Reactions and Nodal Forces to either or in the Output Controls. Recommendation: is the preferred option, as the results file size will be smaller and the process time shorter. Otherwise, the output of these options are controlled by the RSOL option of the OUTRES command. Set Calculate Reactions = in the Output Controls. Important: Force and Moment Reaction probes cannot be evaluated when you specify damping in combination with setting the Expand Results From property to either or . Review the MXPAND command in the Mechanical APDL Command Reference for additional information about this limitation. |
Transient - Mode-Superposition |
Reaction Type | Output Controlled By |
---|---|
Static |
The output of these options are controlled by the ESOL option of the OUTRES command. To enable the output, set both the Calculate Reactions and Nodal Forces properties of the Output Controls (Analysis Settings) to Yes. Note:
|
Transient Full/MSUP | |
Modal | |
Harmonic Response Full/MSUP |
Reaction Type |
Output Controlled By |
---|---|
Static |
The underlying element options are controlled by the NLOAD option of the OUTRES command. To enable the output, set Nodal Forces = in the Output Controls. The contact element options are governed by the MISC option of the OUTRES command. To enable the output, set either the Contact Miscellaneous or General Miscellaneous property to in the Output Controls. |
Transient - Full | |
Modal |
These analysis types do not support contact reactions using the contact element option. They only support contact reactions using the underlying element option. You control the underlying element options using the NLOAD option of the OUTRES command. To enable the output, set the Nodal Forces property to in the Output Controls category. |
Standalone Harmonic Response - Full | |
Standalone Harmonic Response - Mode-Superposition | |
Harmonic Response Analysis Linked to Modal Analysis | |
Transient - Linked to Modal Analysis |
Reaction Type |
Output Controlled By |
---|---|
Static |
The output of these options are controlled by the RSOL option of the OUTRES command. |
Transient - Full | |
Modal |
The output of these options are controlled by the RSOL option of the OUTRES command. To enable the output, set Calculate Reactions = in the Output Controls. |
Harmonic Response - Full | |
Harmonic Response - Mode-Superposition |
If results are expanded from a modal solution, then the output of these options are controlled by both the RSOL and NLOAD options of the OUTRES command. You must set both Calculate Reactions and Nodal Forces to either or in the Output Controls. Recommendation: is the preferred option, as the results file size will be smaller and the process time shorter. Otherwise, the output of these options are controlled by the RSOL option of the OUTRES command. Set Calculate Reactions = in the Output Controls. Important: Force and Moment Reaction probes cannot be evaluated when you specify damping in combination with setting the Expand Results From property to either or . Review the MXPAND command in the Mechanical APDL Command Reference for additional information about this limitation. |
Transient - Mode-Superposition |
Reaction Type | Output Controlled By |
---|---|
Static |
The output of these options are controlled by the RSOL option of the OUTRES command. |
Transient - Full | |
Modal |
The output of these options are controlled by the RSOL option of the OUTRES command. To enable the output, set Calculate Reactions = in the Output Controls. |
Harmonic Response - Full | |
Harmonic Response - Mode-Superposition |
If results are expanded from a modal solution, then the output of these options are controlled by both the RSOL and NLOAD options of the OUTRES command. You must set both Calculate Reactions and Nodal Forces to either or in the Output Controls. Recommendation: is the preferred option, as the results file size will be smaller and the process time shorter. Otherwise, the output of these options are controlled by the RSOL option of the OUTRES command. Set Calculate Reactions = in the Output Controls. Important: Force and Moment Reaction probes cannot be evaluated when you specify damping in combination with setting the Expand Results From property set to either or . Review the MXPAND command in the Mechanical APDL Command Reference for additional information about this limitation. |
Transient - Mode-Superposition | |
Random Vibration |
To enable the output, set Calculate Reactions = in the Output Controls of the upstream Modal analysis. |
Response Spectrum |
Reaction Type |
Output Controlled By |
---|---|
Static |
The output of these options are controlled by the NLOAD option of the OUTRES command. To enable the output, set Nodal Forces = in the Output Controls. |
Transient - Full | |
Modal | |
Transient - Mode-Superposition |
Reaction Type |
Output Controlled By |
---|---|
Static |
The underlying element options are controlled by the NLOAD option of the OUTRES command. To enable the output, set Nodal Forces = in the Output Controls.
Note: Mechanical supports geometry/mesh scoping for vertices, edges, faces, and element faces only.
|
Transient - Full |
Important: If you scope a Force Reaction or Moment Reaction probe to a geometric entity (Location Method = ) that shares more than one body, the adjacent elements not included in the geometric/mesh scoping contribute to the probe's results.
Reaction Type | Output Controlled By |
---|---|
Static |
The output of these options are controlled by the NLOAD option of the OUTRES command. To enable the output, set Nodal Forces = in the Output Controls. |
Transient - Full | |
Transient - Mode-Superposition |
Reaction Type | Output Controlled By |
---|---|
Static | The underlying element options are controlled by the NLOAD option of the OUTRES command. To enable the output, set Nodal Forces = in the Output Controls. |
Transient - Full |