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Использование в Pro/ENGINEER

Использование Structure в Pro/ENGINEER

Определение анализа

This section discusses three major types of analyses-static, modal, and thermal-and how to define them. Following is a summary of the three main analysis types:

Pro/MECHANICA also enables you to define buckling analyses, prestress analyses, contact analyses, and vibration analyses.

When you run design studies, you have the option of running an analysis type called regeneration analysis. This type of analysis simply regenerates your model and is a means of running a design study without first having to run another type of analysis.

 

 

Using the Analyses Data Form

You use the Analysis Definition data form to define conditions for your analysis. If you have already defined at least one analysis for your model, the Analyses data form appears first:

 

 

This data form includes the following:

Defining a Static Analysis

A static analysis calculates deformations, stresses, and strains on your model in response to specified constraints. A static analysis gives you certain information about your model. For example, a static analysis tells you if the material in your model will stand stress and if the part will break (stress analysis), where the part will break (strain analysis), and how much the shape of the model changes (deformation analysis).

Pro/MECHANICA automatically calculates all measures valid for a static analysis.

Review the following guidelines before defining your static analysis:

Keep the following points in mind when specifying loads and constraint sets for static analyses:

Even if you create a new set with the same name as the set you deleted, you must edit the analysis and reselect the set. Otherwise, you may invalidate the analysis and any design studies in which you included the analysis.

How to Use the Analysis Definition Data Form

To define a static analysis, complete these steps:

1. From the MECHANICA menu, select Structure > Analyses.

 

 

If this is the first analysis you are defining for the model, Pro/MECHANICA displays the following data form:

 

 

Note:

If this is not the first analysis you are defining, the software displays the Analyses data form instead. Select Create from the Analyses data form, and Pro/MECHANICA displays the data form shown above.

 

For models that have temperature-dependent material properties, a Page Down button appears on the Analysis Definition data form. When you select the Page Down button, Pro/MECHANICA displays a second page.

2. Use the Analysis Name and Type fields to identify the analysis and select the analysis type.

3. Select a constraint set from the Constraint Set list and one or more load sets from the Load Sets list.

 

Note:

If your constraint set includes an enforced displacement constraint, you do not need to select a load set.

 

4. Use the Convergence Method option menu to select the convergence method you want Pro/MECHANICA to use when running your analysis. Depending on the convergence method, you may need to select or specify additional items on the data form.

5. Customize your results by selecting Stresses, Rotations, Reactions, and Ply Stresses as desired. Also, use the Plotting Grid entry box to specify the level of detail you want Pro/MECHANICA to use when reporting your results.

6. Select Accept to accept the data form. Pro/MECHANICA displays the Analyses data form. Use this data form to create more analyses as well as to review, copy, or delete analyses.

7. Select Done to dismiss the Analyses data form.

 

Identifying the Analysis

You tell Pro/MECHANICA what type of analysis you want to define and give that analysis a name.

Enter a name in the Analysis Name field.

Click on the option menu in the Type field and select Static as the analysis type. When you select Static, the description field appears. You have the option of entering a description for the analysis.

 

Selecting Constraint and Load Sets

You must specify one constraint set and one or more load sets to include in the analysis. To do so, use your mouse to select the appropriate constraint set and load set.

You should specify all constraints created for your model that you want included in your analysis. During an analysis, Pro/MECHANICA calculates your model based on these constraints. There is no limit to the number of constraints you can include in a constraint set. However, you can include only one constraint set in a static analysis.

 

Setting Convergence

Convergence gives you an idea of how accurate your results are. If your analysis did not reach convergence during a design study, the results may not have the desired accuracy. In this case, you need to change something about your model.

Select the convergence method you want Pro/MECHANICA to use when it runs your analysis. You can choose from three methods:

If you use the iterative solver, Pro/MECHANICA runs a first pass using the block solver at p=2, followed by a second pass (p=3) using the iterative solver. Using the stress error estimate from pass 2, Pro/MECHANICA performs a third and final pass.

See Settings for more information on using the iterative solver.

Customizing Your Results Output

You can choose from additional options on the Analysis Definition data form to customize your results. You can leave these options set at the default or change them to customize your results.

Note:

You cannot access results for any quantity you deselect. Pro/MECHANICA calculates all stress and rotation measures even if you do not select Stresses and Rotations on the data form. But you cannot access the same results for measures that you can when you select Stresses, Rotations, and Reactions.

CASE STUDY:
Defining a Static Analysis

In a prior example, you learned about adding loads and constraints to the notch plate model. Now that these modeling entities are in place you can define analyses for the model. As a refresher, here is what the model looks like:

 

 

Recall that one of the load and constraint set combinations for this model simulates pure tension. If you want to perform a static analysis of the notch plate as it would behave under these conditions, you might fill in the Analysis Definition data form as follows:

 

 

Here is an overview of some of the choices you make when you define the analysis above:

Defining a Modal Analysis

In a modal analysis, Pro/MECHANICA calculates the natural frequencies and mode shapes of your model. Pro/MECHANICA also automatically calculates all measures valid for a modal analysis.

In a modal analysis, you can see the natural frequencies of your model when subjected to time-dependent and/or oscillatory/vibration loads.

You must run a modal analysis before running any dynamic analysis, such as dynamic vibration or dynamic shock.

Keep the following points in mind when specifying constraint sets for modal analyses:

How to Use the Analysis Definition Data Form

To define a modal analysis, complete these steps:

1. From the MECHANICA menu, select Structure>Analyses.

 

 

If this is the first analysis you are defining for the model, Pro/MECHANICA displays the following data form:

 

 

Note:

If this is not the first analysis you are defining, the software displays the Analyses data form instead. Select Create from the Analyses data form, and Pro/MECHANICA displays the data form shown above.

 

For models that have temperature-dependent material properties, a Page Down button appears on the Analysis Definition data form. When you select the Page Down button, Pro/MECHANICA displays a second page.

2. Use the Analysis Name and Type fields to identify the analysis and select the analysis type.

3. Complete each of the following steps, as applicable:

4. Use the Convergence Method option menu to select the convergence method you want Pro/MECHANICA to use when running your analysis. Depending on the convergence method, you may need to select or specify additional items on the data form.

5. Customize your results by selecting Stresses, Rotations, and Reactions, as desired. Also, use the Plotting Grid entry box to specify the level of detail you want Pro/MECHANICA to use when reporting your results.

6. Select Accept to accept the data form. Pro/MECHANICA displays the Analyses data form. Use this data form to create more analyses as well as to review, copy, or delete analyses.

7. Select Done to dismiss the Analyses data form.

 

Identifying the Analysis

You tell Pro/MECHANICA what type of analysis you want to define and give that analysis a name.

Enter a name in the Analysis Name field. You cannot use the same name for both an analysis and a design study.

Click on the option menu in the Type field and select Modal as the analysis type. When you select Modal, the description field appears. You have the option of entering a description for the analysis.

 

Selecting Modes and Constraints

This portion of the data form includes two tasks-selecting the number of modes and selecting constraint options.

You specify the options you want Pro/MECHANICA to use when calculating your analysis.

 

Selecting a Mode Option

You can select a mode option from the following (Number of Modes is the default):

If you select With Rigid Mode Search, Pro/MECHANICA includes rigid modes in the number of modes it reports after a run. You should therefore add the number of rigid modes to the number of non-rigid modes you want reported, so you get the results for all the modes you want.

For example, a model with no constraints has six rigid body modes. If you want four non-rigid modes, you should enter 10 for Number of Modes.

Enter a number from 1 to 99. The default is 4.

Selecting a Frequency Option

You can select a frequency option from the following:

Selecting a Constraint Option

You can select a constraint option from the following:

If your model is not fully constrained, you should also select With Rigid Mode Search, located to the right of Constrained. When you select With Rigid Mode Search, Pro/MECHANICA looks for and reports rigid body modes when it runs a design study containing this analysis.

If you do not select With Rigid Mode Search and the model is not fully constrained, you will get a fatal error when you try to run a design study containing this analysis. If you are not certain that your model is fully constrained, you should select this item.

If you select With Rigid Mode Search and your model is fully constrained, it does not cause any problems in the design study run. However, Pro/MECHANICA makes extra calculations, adding time to the run.

Setting Convergence

Convergence gives you an idea of how accurate your results are. If your analysis did not reach convergence during a design study, the results may not have the desired accuracy. In this case, you need to change something about your model.

Select the convergence method you want Pro/MECHANICA to use when it runs your analysis. You can choose from three methods:

If you use the iterative solver, Pro/MECHANICA runs a first pass using the block solver at p=2, followed by a second pass (p=3) using the iterative solver. Using the stress error estimate from pass 2, Pro/MECHANICA performs a third and final pass.

See Settings for more information on using the iterative solver.

Customizing Your Results Output

You can choose from additional options on the Analysis Definition data form to customize your results. You can leave these options set at the default or change them to customize your results.

CASE STUDY:
Defining a Modal Analysis

In addition to defining a static analysis for the notch plate model as described in Defining a Static Analysis, you probably want to define a modal analysis to study the various mode shapes associated with different frequencies. Once again, here is what the model looks like:

 

 

Recall that one of the constraint sets for this model fixes the far end of the model in all degrees of freedom-in effect, turning the model into a cantilevered beam. If you want to perform a modal analysis of the notch plate as it would behave if thus constrained, you might fill in the Analysis Definition data form as follows:

 

 

Here is an overview of some of the choices you make when you define the analysis above:

Defining a Thermal Analysis

You can define two types of thermal analyses: steady-state thermal and transient thermal. Steady-state thermal is described here.

A steady-state thermal analysis calculates a thermal response to specified heat loads subject to specified prescribed temperatures and/or convection conditions. For example, you could define a steady-state thermal analysis for a model with a metal cooling fin, as on a lawn mower engine. Through analysis definition, you would subject the cooling fin to a constant head load (piston heat output) and a forced convection (moving air).

Pro/MECHANICA also automatically calculates all generic, mass property, and thermal measures.

Review the following guidelines before defining your thermal analysis:

Keep the following points in mind when specifying loads and constraint sets for thermal analyses:

How to Use the Analysis Definition Data Form

To define a thermal analysis, complete these steps:

1. From the MECHANICA menu, select Thermal > Analyses.

 

 

If this is the first analysis you are defining for the model, Pro/MECHANICA displays the following data form:

 

 

Note:

If this is not the first analysis you are defining, the software displays the Analyses data form instead. Select Create from the Analyses data form, and Pro/MECHANICA displays the data form shown above.

2. Use the Analysis Name and Type fields to identify the analysis and select the analysis type.

3. Select a constraint set from the Constraint Set list. If you defined heat loads for the model, use the Load Sets list to select one or more load sets as desired.

4. Use the Convergence Method option menu to select the convergence method you want Pro/MECHANICA to use when running your analysis. Depending on the convergence method, you may need to select or specify additional items on the data form.

5. Use the Plotting Grid entry box to specify the level of detail you want Pro/MECHANICA to use when reporting your results. Also, you can optionally select Calculate Heat Flux at this time.

6. Select Accept to accept the data form. Pro/MECHANICA displays the Analyses data form. Use this data form to create more analyses as well as to review, copy, or delete analyses.

7. Select Done to dismiss the Analyses data form.

 

Identifying the Analysis

You tell Pro/MECHANICA what type of analysis you want to define and give that analysis a name.

Enter a name in the Analysis Name field. You cannot use the same name for both an analysis and a design study.

Click on the option menu in the Type field and select Steady Thermal as the analysis type. When you select Steady Thermal, the description field appears. You have the option of entering a description for the analysis.

 

Selecting Constraint and Load Sets

Select one constraint set. You can select as many load sets as you wish, although no load sets are required for a thermal analysis.

The constraint set should include all the constraints in your model that you want included in your analysis. During an analysis, Pro/MECHANICA calculates the behavior of your model based on these constraints. There is no limit to the number of constraints you can include in a constraint set. However, you can only include one constraint set in a thermal analysis.

 

Setting Convergence

Convergence gives you an idea of how accurate your results are. If your analysis did not reach convergence during a design study, the results may not have the desired accuracy. In this case, you may need to change something about your model. Defining convergence for your analysis involves four steps-selecting the method, selecting the quantity, setting the accuracy, and setting the polynomial order:

To learn about these steps, read the following:

 

Selecting the Method

You tell Pro/MECHANICA which convergence method to use when running your analysis. You can choose from two methods:

If you use the iterative solver, Pro/MECHANICA runs a first pass using the block solver at p=2, followed by a second pass (p=3) using the iterative solver. Using the stress error estimate from pass 2, Pro/MECHANICA performs a third and final pass.

Selecting the Quantity

Pro/MECHANICA uses quantities to calculate convergence for your model. You can select one of three options for the convergence quantity:

The energy norm of an element is a scalar quantity that is proportional to the integral over the element of the flux squared. It is analogous to element strain energy in a static structural analysis.

Local Temperatures + Lcl Energy Norms is the default quantity.

The global energy norm error measure is a single scalar value proportional to the square root of the estimated error in the global energy norm.

Pro/MECHANICA checks convergence for the global energy norm by extrapolating the global norm of three successive calculations. As a result, global norm convergence considers the rate of convergence. This option provides high accuracy but can also mean greater computation time.

Use Measures for convergence if you are interested either in results for one or more specific quantities, such as maximum flux magnitude, or in results at a particular location, such as a boundary condition or local flux concentration.

Using Measures ensures that results will converge for the quantities in which you are interested. Using measures may also lower the computation time for your design study.

Setting the Accuracy

You set a convergence accuracy percentage for Pro/MECHANICA to use in calculating your analysis.

Pro/MECHANICA displays a percentage field. You can enter the percentage Pro/MECHANICA uses to determine convergence for this analysis. This option is available for multi-pass adaptive convergence only.

The Structure engine performs calculations at increasingly higher polynomial orders, converging when the difference in the results of the last two calculations is within the percentage you specify here.

The engine finishes calculating results when the analysis converges or when it has reached the maximum polynomial order that you also specify on this data form.

If an analysis does not reach convergence during a design study, you may need to change something in your model to get better results.

Lower convergence percentages yield more accurate results, but Pro/MECHANICA may take longer to reach convergence. You should balance the level of accuracy you need with the amount of time it will take to run a design study containing this analysis.

The default convergence value is 10%. For most analyses, you should enter a value between 1% and 25%. If you enter a convergence value outside this range, Pro/MECHANICA asks you to confirm the value you entered when you select Accept on this data form.

Pro/MECHANICA measures convergence for one or more quantities that you specify.

 

Setting the Polynomial Order

You can enter minimum and maximum values to determine the polynomial orders Pro/MECHANICA uses when analyzing your model. The available values are from 1 to 9. The default minimum is 1; the default maximum is 6. This option is available for multi-pass convergence only.

The Structure engine begins with all element edges at the minimum polynomial order and repeats its calculations at increasingly higher polynomial orders for each edge until it reaches one of the following values:

When entering values for the polynomial order, consider the following points:

Customizing Your Results Output

You can choose from additional options on the Analysis Definition data form to customize your results. You can leave these options set at the default or change them to customize your results.

If you do not select Calculate Heat Flux, you cannot access results for heat flux when you look at results for this analysis.

This value is the number of intervals along each edge or across a face of each element that Pro/MECHANICA uses to create plotting grids. Pro/MECHANICA calculates quantity values at the intersections of grid lines.

Pro/MECHANICA reports results for each grid intersection point and interpolates these values to show results elsewhere.

If you enter a higher number, the grid will be finer, and Pro/MECHANICA reports values from more locations on each element. At lower numbers, Pro/MECHANICA takes less time to calculate results, and the data requires significantly less space. The default is 4.

Understanding Buckling Analyses

You can use a buckling analysis to calculate the critical load at which a structure will buckle, as well as the model's stresses, strains, and deformations at the onset of buckling.

In a buckling analysis, Pro/MECHANICA calculates a buckling load factor (BLF) and mode shape for each buckling mode you request. The BLF is the magnification factor by which the loads applied in a previously specified static analysis would have to be multiplied to produce the critical buckling load. The constraint set specified in the previous static analysis is also used in the buckling analysis. Pro/MECHANICA automatically calculates all predefined measures valid for a static analysis.

 
Note:

Pro/MECHANICA buckling analysis is a linear eigenvalue bifurcation instability analysis as described in The Finite Element Method, Third Edition, by O.C. Zienkiewicz, pages 513-514. Large displacement or nonlinear buckling investigations may produce significantly different results, depending on the type of model and loads being examined.

 

Before defining your buckling analysis, you should have defined a static analysis. In the static analysis, Pro/MECHANICA calculates the stress stiffening of your model due to the applied forces. You then define your buckling analysis. Pro/MECHANICA uses the buckling analysis to calculate the model's elastic stiffness-stiffening due to geometry and material properties. Pro/MECHANICA then uses the two solutions to calculate the BLF.

 

Understanding Prestress Static Analyses

You can use a prestress analysis to simulate how a prestiffened or prestressed structure affects your model's deformations, stresses, and strains.

Before running a prestress static analysis, you must first run a static analysis. Pro/MECHANICA uses the results from your static analysis to calculate the prestress static analysis. In a prestress static analysis, Pro/MECHANICA calculates deformations, stresses, and strains on your model in response to specified loads and subject to specified constraints. Pro/MECHANICA also automatically calculates all measures valid for a static analysis.

You run a prestress static analysis in addition to a static analysis for the following situations:

Review the following guidelines before defining your prestress static analysis:

Even if you create a new set with the same name as the set you deleted, you must edit the analysis and reselect the set. Otherwise, you may invalidate the analysis and any design studies in which you include it.

Pro/MECHANICA enables you to run either a static analysis or a prestress static analysis. In a static analysis, you calculate stresses and strains on your model subject to loads and constraints you assigned. However, you may need more specified information about your model than a static analysis can provide. For example, if the specified loads in the static analysis are close in magnitude to a corresponding buckling load, the pre-stiffening effects are negligible from a static analysis. In this case, you should run a prestress static analysis.

A prestress static analysis determines the strengthening or weakening of the part due to the applied loads. For example, Pro/MECHANICA can determine the strengthening or weakening of an applied load on a ski lift-for example, a pretension cable.

 

Understanding Prestress Modal Analyses

You can use a prestress modal analysis to determine the natural frequency and mode shapes of your model.

In a prestress modal analysis, Pro/MECHANICA uses results from your previously defined static analysis to calculate the natural frequencies and mode shapes of your model. Pro/MECHANICA also automatically calculates all measures valid for a modal analysis.

Review the following guidelines before defining your prestress modal analysis:

Even if you create a new set with the same name as the set you deleted, you must edit the analysis and reselect the set. Otherwise, you may invalidate the analysis and any design studies in which you include the analysis.

In a static analysis, Pro/MECHANICA calculates stresses and strains on your model subject to loads and constraints you assigned. However, you may need more specific information about your model than a static analysis can provide. For example, in rotating machinery, such as a turbine blade, you may want to run a prestress modal analysis after your static analysis to get more detailed information about the applied loads and the stiffening and weakening of those loads.

 

Understanding Contact Analyses

You can use contact analyses to observe how displacement, stresses, contact pressures, and/or measures affect the contact regions of your model. During a contact analysis, Pro/MECHANICA monitors any changes to the surfaces of your model that are defined as contact regions.

Review the following guidelines before defining a contact analysis:

Understanding Vibration Analyses

You can use vibration analyses to perform four types of dynamic analyses-dynamic time, dynamic frequency, dynamic shock (or seismic analysis), and dynamic random.

If the requirements of your design demand more complex analysis than a static analysis, you should run a vibration analysis. The type of vibration analysis you run is determined by the input forcing function.

Review the following to determine which type of dynamic analysis you should use for your model:

Review the following guidelines before defining a dynamic analysis. These guidelines apply to all Pro/MECHANICA dynamic analyses.

Dynamic Time

Pro/MECHANICA calculates displacements, velocities, accelerations, and stresses for your model at different intervals in response to a load that varies with time. Pro/MECHANICA also calculates all valid measures for dynamic time response analyses that you defined for your model.

By placing a gravity load on the model, you can run a dynamic time analysis to define the equivalent of a base excitation case. You can direct Pro/MECHANICA to report complete results at specified time intervals. For dynamic time analyses with full results, you can animate results of a fringed display for each time step of your analysis.

 

Dynamic Frequency

Pro/MECHANICA calculates the amplitude and phase of displacements, velocities, accelerations, and stresses for your model in response to a load oscillating at different frequencies. Pro/MECHANICA also calculates all valid measures for dynamic frequency analyses that you defined for your model.

By placing a gravity load on the model, you can run a dynamic frequency analysis to define the equivalent of a base excitation case. You can direct Pro/MECHANICA to report complete results at specified frequency steps.

 

Dynamic Random

Pro/MECHANICA calculates the power spectral densities and RMS values of displacements, velocities, accelerations, and stresses at points for your model in response to a load of specified power spectral density (PSD).

Pro/MECHANICA also calculates all valid measures for dynamic random response analyses that you defined for the model. You can obtain results for the PSD of a quantity at a point by defining measures.

You can also define measures that yield the RMS value or apparent frequency of a quantity.

In a dynamic random analysis, the PSD is equal to gravity squared over frequency.

 

Dynamic Shock

In a dynamic shock response analysis, Pro/MECHANICA calculates maximum values of displacements and stresses for your model in response to a base excitation with a specified response spectrum.

Pro/MECHANICA also automatically calculates all measures valid for a static analysis.

 

Understanding Transient Thermal Analyses

You can use transient thermal analysis to measure temperatures and fluxes in your model over a particular time range.

A transient thermal analysis differs from a steady-state thermal analysis because the analysis determines the temperature in the model over a period of time. If you are not interested in the variation of temperature over time in your model, you should use steady-state thermal analysis instead.

Review the following guidelines before defining your transient thermal analysis:

Transient thermal analyses support both single-pass adaptive and quick check convergence methods. Since transient thermal analyses take longer to run than steady-state thermal analyses, you may prefer to use the quick check convergence method to get a quick reading of your model.

Transient thermal analyses do not support:

When you run a transient thermal analysis, Pro/MECHANICA calculates temperatures and fluxes in your model over a specified time range. It also calculates measures that you defined for your model. You can direct Pro/MECHANICA to report full results or temperature loads at specified time intervals.

When you define your analysis, besides specifying the initial temperature of your model, you also specify the following values:

A transient thermal analysis is best used for situations where you want to find out the following types of information about your model:

Note:

Excluded elements as explained in the Design Study Reference online document do not appear in the integrated version of transient thermal analysis.

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