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Home > Commands > 4. Finite Element Modeling > 4.3 Creating Loads And Constraints > 4.3.3 Finite Element Loads

4.3.3 Finite Element Loads

FEMAP allows you to create loads directly on finite element entities. These types of loads will be exported directly to the solver on translation, assuming that the translator supports the type of loading input. Loads can be applied to the entire finite element model (Model, Load, Body command), to individual or groups of nodes (the Model, Load, Nodal, the Model, Load, Nodal, and the Model, Node, Nonlinear Force commands), and to individual or groups of elements (the Model, Load, Element command). Each type of load and its command is discussed in more detail below.

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Home > Commands > 4. Finite Element Modeling > 4.3 Creating Loads And Constraints > 4.3.3 Finite Element Loads > 4.3.3.1 Model, Load, Body

4.3.3.1 Model, Load, Body

Body loads act on all elements of your model and represent global motions, accelerations or temperatures. You must activate the body loads that you want prior to defining load values, by checking the various Active boxes. Body loads can be separated into acceleration, velocity, and thermal.

A Coordinate System other than Global may be specified for all body loads in a particular load set. This coordinate system will be written out to the CID field of the GRAV and/or REFORCE entires for Nastran.

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Time and Frequency Dependence can be specified for Translational and Rotational Accelerations, as well as, Rotational Velocity by selecting an existing FEMAP function from the drop-down list. You can also create a new function by clicking any of the Function icon buttons next to the Time/Freq Dependence drop-down list boxes.

Translational Accel/Gravity and Rotational Acceleration

These body loads represent translational and/or rotational acceleration. Input must always be in the axis directions of the coordinate system selected in Coord Sys. Translational accelerations are often used to represent gravity loads. Watch the units however, these are not always specified in gs.

Rotational Velocity

This type of body load represents a rotational velocity and the resulting loads which are caused by centripetal acceleration.

Center of Rotations

This specifies the location of the center of rotation for the rotational body loads (rotational velocity and rotational acceleration). You can graphically select the Center of Rotations graphically by highlighting one of the fields in this portion of the dialog and then clicking in the graphics window. To select a precise position, you may want to use Snap to Grid, Snap to Point, or Snap to Nodemode.

Varying Translational Acceleration

This type of body load represents a translational acceleration which varies along a selected coordinate system axis. The coordinate system itself is specified in the Coord Sys drop-down, while the Axis to Vary Along drop-down is used to specify the axis of variation. The Ax, Ay, and Az fields



are used to specify the values of the acceleration load with regards to the selected coordinate system. In addition, an Acceleration vs. Location function (Type = 36) MUST be created to represent the different acceleration values at each location along the chosen coordinate system axis. Remember, the Ax, Ay, and Az values will be used as scalars if the actual values are in the function.

Thermal

The Default Temperature is the temperature of all nodes/elements which are not given a specific temperature in this load set by nodal or elemental temperature loads. This option can be used to quickly assign a temperature for the entire model.

Rotating Around Vector... button

This utility allows you to specify a Rotation Vector (using any vector method in FEMAP) for all rotational body loads in a particular load set. Once you select the vector, FEMAP allows you to enter a value for Velocity and Acceleration around this specified vector. Clicking OK will return you to the main Body Loads dialog box and the transformed values for the entered Velocity and Acceleration will now appear in the appropriate X, Y, and Z components.



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Home > Commands > 4. Finite Element Modeling > 4.3 Creating Loads And Constraints > 4.3.3 Finite Element Loads > 4.3.3.2 Model, Load, Nodal

4.3.3.2 Model, Load, Nodal

Creating nodal loads is a two step process. First, you must select the nodes where the load will be applied. As always, this is done using the standard entity selection dialog box. After you select the nodes, you will see another dialog box which defines the load.

The first selection you should make is the type of load you wish to create. FEMAP supports eleven (11) types of nodal loads for various types of thermal and structural analysis - forces, moments,

Note:The Varying Translational Acceleration body load type is only supported for NX Nastran and MSC Nastran. The load creates the ACCEL bulk data entry for both solvers.



displacements, enforced rotations, velocities, rotational velocities, accelerations, rotational accelerations, nodal temperatures, nodal heat generation and nodal heat fluxes.

The last 10 load types available are Fluid specific and are only accessible through the FEMAP neutral file.

As you choose a load type, FEMAP will disable or hide any controls in the load definition dialog box which are not required. After choosing a load type you can proceed to define the other load parameters and values.

Title:

Allows you to enter a title for the Load Definition being created. If you do not enter a title, a default title will be created based on the type of load which was created.

For example, if you create a Force on a selected node or nodes, the default title will be Force on Nodes.

Color/Palette and Layer:

These controls define parameters for the load to be created.

Coordinate System:

This option is only available if you select the Components method for direction for non-thermal load types. The components are defined relative to the selected coordinate system. If you select a cylindrical or spherical system, the true direction of the loads also depends on the location of the node where it is applied. For example, a positive radial force goes in a different direction if the node is at 0 degrees, than if it is at 180 degrees.

Direction:



All non-thermal load types are vector quantities which require a direction. FEMAP provides five methods to define the direction of a load: Components, Vector, Along Curve, Normal to Plane, and Normal to Surface. The Components method simply requires input of components in the three directions. For all methods except Components, you must check the Specify button to either define the vector (FEMAP standard vector definition dialog box will appear), select the curve, define the plane (FEMAP standard plane definition dialog box will appear), or select the surface. These methods provide great flexibility for defining the direction of the loads.

Choosing a Load Creation Method

There are three methods available to create loads on the nodes that you selected. The simplest, and default method, is to assign a constant load value to each of the nodes. As an alternative, you can define an equation which defines the value at each node. If you choose this method, you must select a variable (default is i - must select Advanced under Variable to change it) which will be updated to contain the ID of the node where loads are being defined. Then, instead of entering a numeric value for the loads, enter an equation in Value which uses the variable. You will find the XND(), YND() and ZND() functions very useful in defining loads in terms of the locations of the nodes that you are loading.

If instead of entering an equation, you enter a numeric value, that value will be assigned to every node, just as if you had specified a constant. Conversely, if you enter an equation, but also setConstant, the equation will be evaluated prior to load definition and the constant result will be assigned to all selected nodes.

For example, if you choose to enter an equation in Value such as:

10*(xnd(!i)-xnd(1))+50

each node will receive a load which is equal to fifty, plus ten times the length in the X direction between that node and node 1.

Note:

Since these loads are created on the nodes themselves, the actual method of computing the direction is not stored. FEMAP calculates the direction from the method, and then stores the result in component form. This enables you to modify or remove any geometry that was created to specify the direction without changing the load direction. If you attempt to edit or list the load, the values listed will be in component form. Only loads attached directly to geometry store any information regarding the direction method.

Hint:

When choosing the Along Curve or Normal to Surface options, be careful that the nodes fall within the length of the curve or the area bounded by the surface. If the curve is anything but a line, FEMAP will attempt to project the position of the nodes onto the curve to determine the direction of the curve at that location. A similar projection is also required for the Normal to Surface method. If the projection falls well outside the curve or surface actual bounds, unexpected values for the direction may result.

Note:The XND(), YND(), and ZND() functions will use a loads definition coordinate system. For example, in a cylindrical coordinate system, XND() would be the radial coordinate of the node, YND() would be theta coordinate of the node, and ZND() would be the coordinate in the Z-axis of the node.

Note:The equation is evaluated at each node, and the actual calculated value of the load is stored as a nodal load. The equation, itself is not stored. Equations are only stored for geometric loads.



A third method is to use a Data Surface. There are several different types of Data Surfaces which can be created and in most cases, a Data Surface allows you to vary a value based on specific parameters of an entity (i.e., XYZ coordinates; Node or Element ID; spatial locations - 1-D, 2-D, or 3-D; mapped results from different mesh; parametric locations on geometry). These Data Surfaces can be created prior to load creation using the Data Surface Editor (For more information on the Data Surface Editor, see Section 7.2.6, "Tools, Data Surface Editor"). You can also click the Data Surface Icon button in the Create Loads dialog box and choose from the list of available Data Surfaces to create a new one.

Time, Temperature or Frequency Dependent Loads

If the loads that you are creating are constant, simply set this option to 0..None. However, if your loads vary with either time, temperature or frequency, you can choose the appropriate function to define that dependence. Prior to creating your loads, you must use the Model, Function command to create the functions, so that they can be selected from the list. The Y values of the function are used to multiply the constant values that you specify in this dialog box. Do not confuse frequency dependence of the load value (specified here) with frequency dependence of the phase (specified at the bottom of the dialog box for frequency analyses).

Creating Component Loads (Forces, Moments, etc.)

For component of non-thermal loads (forces, moments, displacements, enforced displacements, velocities, rotational velocities, accelerations, and rotational accelerations) you must activate the various load components, using the option boxes, prior to setting the load value. There is no load applied to any component which is not activated. For forces, moments, velocities, rotational velocities, accelerations, and rotational accelerations, this is equivalent to activating the component and then applying a zero (or blank) load. For displacements and enforced rotations, however, these two alternatives are not equivalent. With the component deactivated, that component is free to move (displace) freely. Activating the component and then specifying a zero displacement (or a blank), prevents all movement of that component. This is similar to a constraint.

As just described, FEMAP will allow you to activate load components which have a zero (or blank) load value. You may not however, have all load values equal to zero. If you want to use displacement loads as pseudo-constraints, you must specify at least one small nonzero value, like 1E-10 or smaller. You should never have to create a zero force or acceleration, since it will have no effect.

Phase:

Non-thermal loads also allow you to specify a phase. This value is only used for frequency analyses. In addition, for frequency response analyses, you can make the phase frequency dependent by selecting an additional function.



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Home > Commands > 4. Finite Element Modeling > 4.3 Creating Loads And Constraints > 4.3.3 Finite Element Loads > 4.3.3.3 Model, Load, Nodal On Face...



4.3.3.3 Model, Load, Nodal On Face...

... is the same as Model, Load, Nodal, except that instead of directly selecting the nodes where the loads will be applied, here you select the faces of elements. You will first use the standard entity selection dialog box to select the elements which reference the nodes where you want to place loads. Then, the face selection dialog box (as described later in Model, Load, Elemental) is used to limit the nodal selection to specific element faces. When you have selected the element faces, FEMAP will automatically determine the nodes where loads will be defined, and this command will continue, just like the normal Model, Load, Nodal command.



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Home > Commands > 4. Finite Element Modeling > 4.3 Creating Loads And Constraints > 4.3.3 Finite Element Loads > 4.3.3.4 Model, Load, Elemental...

4.3.3.4 Model, Load, Elemental...

...is used to create elemental loads. The process is very similar to Model, Load, Nodal. You must first select the elements where the load will be applied using the standard entity selection dialog box. Then, another dialog box allows you to define the load type and values similar to the Create Loads on Nodes dialog box. The one major difference is that you will not be able to specify a direction. All elemental loads have a certain prescribed direction (typically normal to face of application).

There are seven types of elemental loads in FEMAP: distributed loads on line elements, pressure, temperature, and four types of heat transfer loads - heat generation, heat flux, convection and radiation. Again, just like nodal loads, you should select the load type first. This choice will disable or hide all controls which are not necessary for the type of load you are defining. Finally, specify the

Note:This command can be a convenient method of specifying nodal loads on complex models, especially on solid models where you can use the adjacent faces approach (see Section 4.3.3.2, "Model, Load, Nodal"). This is an alternative to creating geometric loads and can be very useful to create loads on a portion of a surface.



other load parameters and values.

You can also make elemental loads function dependent, just like nodal loads, as well as input a constant or variable load. You will find the XEL( ), YEL( ), ZEL( ), XEF( ), YEF( ) and ZEF( ) functions very useful in defining loads in terms of the locations of the elements and element faces that you are loading. If instead of entering an equation, you enter a numeric value, that value will be assigned to every element, just as if you had specified a constant. Conversely, if you enter an equation, but also set Constant, the equation will be evaluated prior to load definition and the constant result will be assigned to all selected elements.

Creating Distributed Loads

Distributed loads are forces applied along the length of line elements (bars, beams...). Their load values are specified as a force per unit length.

You can specify a different value at each end of the element. If you want a constant load along the length, you must specify the same End A and End B values. If you leave End B blank, zero load will be applied at that end.

In this case the same function dependence will apply to the loads at both ends of the element.

Distributed Load Direction

After you specify the load magnitude and phase, press OK. You will be prompted for the load direction, which can be along any of the elemental or global axes. You can not specify an arbitrary direction or the axis of any other coordinate system. The elemental axes are determined by the element orientation. For elements that do not require an orientation (rods, axisymmetric shells...) you should always use the global directions.

Creating Pressure Loads

Elemental pressure loads always act normal to an element face or edge. For this reason, you can only apply pressure to plane or solid elements. You may not apply pressure to line, or other element types.

Just like distributed loads, you first define the load magnitude and phase, then any function dependence. You have the option to input the pressure at corners. This will require input of four values and enables you to specify a varying pressure load across an element. This capability is most useful when defining a variable pressure load across a surface.

Note:Not all analysis programs support pressures at the corners of elements. If you translate to a program that does not support corner pressures, FEMAP will automatically average the corner pressures and output a centroidal value.



You also have the option to specify the direction of the pressure. When this option is selected FEMAP will prompt you for the direction of the pressure using coordinates or a vector.

Specifying a direction for pressures is only supported for Nastran. If pressures are defined in this manner for other solvers FEMAP will simply create pressures normal to the selected element face.

Specifying Face IDs

For pressures, when you press OK, you will be presented with the following dialog box to choose the face or faces where the pressure will be applied:

This provides four ways to select the faces. The most obvious is to simply choose Face ID and select the ID of a face. For details on how face numbers for plane and solid elements are defined, see Section 6, "Element Reference" in the FEMAP User Guide. Alternatively, you can simply choose the face graphically by moving the cursor near the center of the face and clicking the left mouse button. The selected face will be highlighted. If you chose an unexpected face, simply move the mouse and click again until you get the face you want. Also, you have the option to select the Front Face or the Back Face when choosing the face of a plate element. This is strictly a way to choose a particular face without having to rotate the model.

While this method is easy to understand, it has the disadvantage of applying the loads to the same face number on all selected elements. If the elements where you need to apply loads are oriented randomly, this method is not very effective. You will either need to use one of the other methods, or in some cases you can reorient the elements (see Section 4.8.3.12, "Modify, Update Elements, Reverse/Orient First Edge..."

In most cases, loads on plane elements will be applied to face 1. In this case positive pressure acts in the same direction as the face normal (as determined by the right-hand rule). Conversely, if loads are applied to face 2, their positive direction will be opposite to the face normal. Therefore a positive pressure on face 2 is equivalent to a negative pressure on face 1. If you need to apply edge loads,



they can be applied to faces 3 through 6 as shown. Their positive direction is inward, toward the element center.

Choosing Faces Near a Surface

If you have used geometry to define your elements, or if you just have surfaces in your model, you can apply loads to element faces which are close to a selected surface. When you choose Near Surface, you must also choose a sur-face and specify a tolerance. Loads will be applied to the faces of the selected elements that are closer

than your specified tolerance from the surface. This method can only be used to apply pressure to Face 1 of planar elements (not to the edges).

Choosing Faces Near a Plane

The Near Coordinates method is very similar to Near Surface. Instead of specifying a surface, however, you choose a coordinate system, direction and position. This defines a planar surface, which is used along with the tolerance to find the closest faces.

Choosing Adjacent Faces

The final and most powerful method for choosing faces, especially for complex solid and planar element models, is Adjacent Faces. You choose just one initial face (and the associated element ID). This can be done very easily by graphically selecting the face. You then specify a tolerance angle. FEMAP will search all selected elements for faces that are connected to the face that you chose and that are within the specified tolerance from being coplanar (colinear for planar elements) with an already selected face. This can be used to find all faces on an outer surface (or edge) of a solid (or planar) - regardless of the shape. By selecting the option Matching Normals Only you can further limit the faces selected by allowing only elements with matching normals to be selected.

In the picture above, loads could have been applied to all exterior faces, including those inside the hole, by choosing a tolerance greater than 90 degrees. Loads could have been applied just in the hole by selecting a face inside the hole and specifying a fairly low tolerance.

As with Face ID, you have the option to select the Front Face or the Back Face when choosing the face of a plate element. This is strictly a way to choose a particular face without having to rotate the model.



Choosing Faces Model Free Faces

The Model Free Faces method simply applies the load to every free element face in your model.

For more information about determining Free Faces see Section 7.6.3, "Free Face".

Pressures on Axisymmetric shells

Axisymmetric shell elements only have a top and bottom surface. With the top defined as the positive normal direction from node 1 to 2. You have the choice of loading either the top or bottom surface.

Creating Elemental Temperatures

For temperature loads, you can specify a single Temperature value. This value is assigned to all selected elements. You may also specify a Gradient value which will be also simply be assigned to the element and will vary the temperature by this amount between the top and bottom face of the element. No face specification is required for temperatures, they apply to the entire element.

Creating Loads for Heat Transfer

All of the loads for heat transfer analysis are created similarly to pressure and temperature loads, the only difference is the parameters that need to be specified.

Heat Generation

For heat generation, only a single constant is required - the generation rate.

Heat Flux

Elemental heat flux is applied normal to an element face. You must specify the rate of flux, and, just like pressure, apply the flux to a specific face.

Alternatively, you can define a directional heat flux. In this case, you must also specify a surface absorptivity and temperature for the selected face.

And, after pressing OK, you must specify a flux direction. The direction is defined either as a constant by giving the components of a vector in the direction of the flux, or as a time varying vector, by choosing three functions which contain the components defined as a function of time. In either case the components must be specified in global rectangular coordinates.

Note:Not all analysis programs support pressures at the corners of elements. If you translate to a program that does not support corner pressures, FEMAP will automatically average the corner pressures and output a centroidal value.



Finally, after defining the direction, you will choose the face(s) where the fluxes will be applied. For more information about choosing faces, see "Creating Pressure Loads".

Convection

Free convection loads require the convection coefficient and the film temperature, along with the face where the convection is acting. As always, the face is chosen after you press OK, in the standard fashion. For more information about choosing faces, see "Creating Pressure Loads".

Forced convection loading is also supported, although only for a 1-D type analogy. In this case you must specify the flow rate and diameter along with the temperature, so the proper coefficients can be calculated. For this type of analysis, you will also have to specify numerous fluid properties in the Model, Loads, Body command described earlier.

Special Case - Forced Convection Over a Plate or Surface

For Nastran, forced convection loads can also be used to model one or more flows over a plate. This is a very specialized capability and requires a thorough understanding of Nastrans thermal capability before you attempt to perform this type of analysis.

To model this condition you must follow these steps:

1. Model the plate. You can use any general mesh, however a rectangular mapped mesh will be much easier to understand, and will more accurately represent the flow.

2. Model flow tubes. Since Nastran only has forced convection along line elements, i.e. a 1-D case, you must define a series of tube elements that represent the flow location and direction. These are typically placed at some location above/below the plate.

If you are going to have more than one discreet flow, place all tube elements from each flow on a separate layer. Use the Create Layer command to create a layer, then choose that layer when creating the elements, or use the Modify, Layer command to change it later.

Unlike most general modeling techniques in FEMAP, tube elements are required for this special capability. In most cases, where these tubes are simply a modeling convenience and do not represent a physical tube with thermal properties, you will not want them to be written to your Nastran model. In that case, just define both the inner and outer diameters of the tube property as 0.0 - this indicates that you want the tube to be skipped during translation. If you do want the tube to be translated, just specify nonzero diameters.

If you need to use tube elements in your model that are not being used to represent flow tubes, you MUST place them on a layer that is not used by any of the forced convections that you will later apply to the plate elements. If you do not, FEMAP may create improper links that do not represent the situation that you are attempting to represent.

3. Model the mass flow. The mass flow is modeled by applying forced convections to each of the flow tube elements. For all of these loads you must check the Disable Convection option. This will result in a load that simply models the mass/energy transfer down the flow stream, and not the convection effects. You must specify a flow diameter on these loads. Even though it is not required for the mass transfer equations, it is necessary to properly connect the convections from the plate. Typically you will want to specify a value that is near (or at least the same order of magnitude) the flow diameter for the plate convections.

4. Model the convection on the plate. Next, apply forced convections to the plate elements where the



flow is occurring. All forced convections on plate elements are placed on Face 1, flowing from the middle of the first edge of the plate to the middle of the third edge (to the opposite node for triangular plates). If you created your elements in a manner where this does not really represent the direction of your flow you should use the Modify, Update, Reverse command, and the Align First Edge to Vector option to realign your plates so that the flow is properly represented. This is the step that can become very difficult if you have an arbitrary (non-rectangular or non-mapped) mesh. It is very important that as they are displayed, all of these convections on the plate point along the general flow direction.

On all of these plate convections you should check the Disable Advection option. This will effectively eliminate the mass transfer, and indicate that you are trying to associate this load with a flow tube. You must also specify the flow diameter (hydraulic diameter). This diameter will be used in the calculation of the Reynolds number. In addition, when you check this option you will see an additional option displayed that is titled Area Factor. If you do not specify anything here, FEMAP uses the plate areas to compute coefficients in the heat transfer equation. By specifying a value you can scale that computation to allow for fins or any other area correction that you wish to apply.

If you are working with multiple discreet flows, once again you must use the FEMAP layer capability to assign these convections to a flow number. Set the convection load layer to the same ID as that of the associated flow tubes.

Specify additional fluid/heat transfer options. Go to the Model, Load, Body command and choose the Heat Transfer button. This will display a dialog box where you can specify the fluid properties and other flow parameters. Currently only one fluid and set of parameters can be specified.

5. Translate to Nastran. When you translate these loads to Nastran, the translator creates Plot-Only elements to represent the CHBDY elements that are required, and also create the links shown above. These links represent how each of the convection only plates are linked to the advection onlyflow tubes. Also, during the translation you will be asked to specify a factor that is used to disable the convection and advection. Since Nastran really has no way to disable these portions of the problem, we simulate this effect by scaling the appropriate components downward by the scale factor that you specify. Make sure that you always specify a small number (

For enclosure radiation only an emissivity is required. The absorptivity is assumed to be equal to the emissivity, and the view factor will be automatically calculated by the analysis program (currently only supported for NX Nastran or MSC.Nastran). Optionally, you can speed up the view factor calculations by limiting calculations to surfaces which can shade or can be shaded by other surfaces.

If you are working on a single enclosure problem, make sure that you set the same layer on all of the radiation loads.



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Home > Commands > 4. Finite Element Modeling > 4.3 Creating Loads And Constraints > 4.3.3 Finite Element Loads > 4.3.3.5 Model, Load, Nonlinear Force...

4.3.3.5 Model, Load, Nonlinear Force...

... is used to define nonlinear transient loads that apply forces to a node based upon displacement and/or velocity at one or two other nodes. You must define the type of relationship, the node and degree of freedom for the applied force, and the node(s), degree of freedom, and value (displacement / velocity) that the force will be based upon.

Relationship defines the type of nonlinear transient loads to be created. As shown in the table, four types are available.

Note:

Enclosure radiation problems also require a cavity/enclosure number - even if you are using only a single cavity. Surfaces in each cavity are totally independent of other cavities. They neither shade nor radiate to any surfaces other than the ones in their own cavity. To provide maximum flexibility in viewing and verifying cavity definition, FEMAP uses the layer number that is defined with each radiation load (not the layer for the element), as the specification of the cavity number. In this way, you can turn on/off as many cavities/layers as you want to visually verify the loading that you have defined.

Relationship Definition (F=Force, X=Disp/Vel)Tabular FunctionProduct of Two Variables

Positive Variable to Power



The other options simply define the arguments to these equations. In all cases, you must specify a scale factor. The X(t) arguments represent the displacement or velocity at node/DOF j (the first node) or k (the second).

For Tabular Function loads, you must define and select a force vs. displacement/velocity function which will be used by the analysis program to calculate the force. Since FEMAP does not currently contain a vs. Force function, any function type can be used, but it should contain the appropriate force values. The nodal degrees of freedom must be specified as 1 through 6. For the Positive and Negative Power relationships, power is the exponent, A, of the equation shown.



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Home > Commands > 4. Finite Element Modeling > 4.3 Creating Loads And Constraints > 4.3.3 Finite Element Loads > 4.3.3.6 Model, Load, Enforce Motion

Negative Variable to Power



4.3.3.6 Model, Load, Enforce Motion

...enables you to define a base acceleration. This option creates a base mass, links it to a set of base nodes in your model with a rigid element, and applies an equivalent base force.

To begin you specify coordinates for the base mass using the standard coordinate definition dialog box. A node will be automatically created at this location. The next dialogue box is the standard entity selection box, which asks you to choose the nodes on the base. A rigid element is then created with the newly generated node as the independent node and the selected nodes as the dependent nodes. Next you define the base acceleration using the standard load creation dialog box. The type of load to create will be limited to either acceleration or rotational acceleration. You must choose a time or frequency dependent function to associate with the acceleration.

The final required input is the mass and the acceleration scale factor. They are utilized to generate a nodal force (force = base mass * specified acceleration) at the independent node of the newly created rigid body. The values are automatically computed based on your current model and the acceleration that you chose. The default for the mass value is several orders of magnitude larger than the mass of the current model so the large mass will drive the rest of the model. You can either simply press OK to accept them, change them here, or edit the force later with the Modify, Edit commands.



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