As mentioned in Part 1 of this blog, you reduce complex 3D flows down to cross-sectional averaged values for plotting against the distance along the flow path in either of Ansys’s dedicated post-processing tools: CFD-Post and EnSight.  Part 2 of this blog will focus on the method available in EnSight.

Method 3: Query

Application: Ansys EnSight

Pro: Utilizes EnSight, which can be used for much larger models than is practical with CFD-Post

Con: Defining cross-section location can be very difficult for complex geometry

EnSight’s Query tool has a built-in feature for cycling a location over a range of values, performing a calculation as it progresses, and making a plot of that data.

The first step to use this feature is to create a location that defines the cross-section of your flow path.  For simple geometry this will just be a Clip along a particular direction, but for more complicated flow paths this could involve defining a spline path for a clip to follow.

Next, you will need to create a Variable that calculates the cross-sectional average of the quantity of interest on the clip.  For transported quantities, this should be a mass-flow-weighted average.  Unfortunately, EnSight does not have a direction-independent mass-flow-weighted average function, but one can be built in a few steps.  First, a new variable for mass flux needs to be created.

Then, the weighted average can be calculated on the clip using the SpaMeanWeighted predefined function and the MassFlux variable that was created in the previous step.

To create the plot of the averaged value as the clip progresses along the flow path, create a new Query using Query > Over time/distance, set the Sample to By constant on part sweep, select the variable that was just created, Start, set the range and number of samples, and then Create query.

Note that the plot data can be exported to a file by right-clicking on the query and choosing Data > Save CSV file.

When analyzing complex 3D flow, it’s often helpful to visualize data using simple 1D plots.  One of the most commonly requested plots is to be able to show how the flow is changing on average as you progress from inlet to outlet.  While there is a native feature in Ansys Fluent to calculate circumferential averages on boundaries and plot them with respect to the axial direction (for reference, the TUI command /plot circum-avg-axial), for volumetric data this process needs to be done in one of the dedicated post-processing tools: CFD-Post or EnSight.  This blog will show various methods to create cross-sectional average plots within each tool as well as discuss some of the pros and cons of each method.

Part 1 focuses on the two methods available in CFD-Post.

Method 1: Turbo Mode

Application: Ansys CFD-Post

Pro: Easiest method to enable and customize

Con: Limited to axially-aligned geometry

CFD-Post has a suite of turbomachinery focused post-processing tools called Turbo Mode.  However, it is not limited to just turbomachinery models.  To utilize Turbo Mode, you simply have to identify a hub, shroud, inlet, and outlet.  If those items exist as part of your geometry, you can just specify them directly, but if not you can identify them using a series of Lines.  For example, you can create a hub line along the axis of your model, a shroud line around the outer diameter, and then inlet and outlet lines to connect the two.

Note that for the purposes of calculating average data the lines do not have to follow the exact contour of the geometry.

Once this is done, within Turbo Mode you can identify the global rotation axis (the axis perpendicular to your cross-section), specify the Lines that were just created, and Initialize.  This will create a 2D grid defining the revolved region for the calculations.

Now that the region has been identified, you can use the Inlet to Outlet chart to plot area-weight or mass-flow-weighted values versus progress from inlet to outlet.

Method 2: Scripting a Session File

Application: Ansys CFD-Post

Pro: Direct control over process, allowing for complex flow paths

Con: Requires knowledge of CFX Command Language and Perl

The most direct way of getting cross-sectional averaged values along a flow path is to create a location that defines the cross-section, calculate the averaged value at that location, and then script the progression of the location from inlet to outlet.  In CFD-Post, this scripting is done using Sessions.

First, a location needs to be created: typically a simple plane, but if the flow path is complex then a bounded plane defined by point and normal.

Then, an Expression needs to be created that calculates the appropriate type of average on the plane, such as area-weighted or mass-flow-weighted.

To start the scripting process, you will need the code to modify the plane location.  This can be generated by starting a new Session, starting Recording, editing the plane location, and then stopping the Recording.  This creates a CSE file in your working directory.

The CSE file can then be modified with Perl commands to loop over the flow path from inlet to outlet and save the calculated Expression value to a file.  Once that is done, the modified Session file can then be played back in CFD-Post to perform the calculations.

An example of this script can be obtained by e-mailing support@drd.com

Bucket conveyor models in Ansys Rocky use somewhat complex motion definitions to define the motion up the grain leg, around the head pulley, down the grain leg, and finally around the tail pulley. It is common to know the RPM of the driven pulley, so defining the motion based on this parameter is very convenient. In this post, we will demonstrate the use of expressions in Ansys Rocky to do just that. 

When setting up a bucket elevator simulation, import only a single bucket. The bucket’s mounting location should be even with the center of the tail pulley. The geometry will be replicated using the “Replicate Geometry” feature.

Next, insert a motion frame, connect the motion frame to the bucket geometry, and via the tools menu enable Expressions/Variables. The image below details the initial position of the bucket geometry and the relevant motions that must be defined. Note that based on the initial position of the bucket, there will need to be four sequential motions defined for the motion frame. These are Translation 1, Rotation 1, Translation 2, and finally Rotation 2.

These motions will be defined based on start and stop times for a given motion as well as the relevant velocity. This leads to the relevance of expressions to define the time required to perform each motion as well as the velocity based on the relevant known parameters. It is important to also note that the motion frame does not need to be in contact with the object that it is tied to. In this case it is beneficial to locate the motion frame at the center of the tail pulley. This location will make it easier to define the rotation motions.

Take the first translation as an example. The motion will start at t=0 and the bucket must traverse the distance equivalent to the center to center distance between the two pulleys, which is known to be 182.6 inches. Using the known head pulley diameter and rotational speed of 65 RPM, the linear velocity of the belt can be determined using Pi * Diam * PulleyRPM/60 as shown below.

The other required input for Translation 1 is to compute the length of time it will take the bucket to traverse the first straight section of belt. This can be computed via dividing the straight length of belt by the belt speed as shown below.

To setup Translation 1 in the motion frame, add a translation motion with a “Stop Time” equal to “StraightTime” and a velocity of “BeltSpeed” in the appropriate direction.

Note that it is important to add units to these inputs. [s] for StraightTime and [in/s] for BeltSpeed.

The next motion will require a few additional expressions. First, we will define the time to complete a semicircular rotation around the head pulley. Knowing the RPM of the pulley and that the desired motion is half of a revolution, the formula to compute the time of half a rotation simplifies to RotTime = 30/PulleyRPM. Finally, we need to determine the angular velocity. This can be computed as AngVel = -180/RotTime [dega/s]. This can be entered directly into the motions panel, or can be added as an additional Variable.

The Start and Stop Times can be defined using the StraightTime and RotTime variables already defined. The Start Time for this motion is after the end of the initial translation, therefore the start time is equal to “StraightTime.” The Stop Time is the duration of the translation and the impending rotation, so is equivalent to “StraightTime+RotTime.” The Initial Angular Velocity field is filled using the angular velocity calculation noted above.

The remaining translation and rotation motions can be defined using the same approach.

Following the remaining motion setup, the final step is to include replication of the bucket geometry. Navigating to the bucket geometry, set the Motion Frame to the frame just created and proceed to the Replication tab. Enter the number of buckets you will need and enter the replication period. The replication period is the length of time needed to complete one full loop around the conveyor. In this case it is equivalent to “2*StraightTime + 2*RotTime.”

Note that the Expressions section of the Expressions/Variables panel is a list of where expressions or variables have been used in the model.

While this article explains the setup of a bucket elevator, expressions are quite valuable for other Rocky simulations as well. When calculation is needed to convert between a key value and the inputs needed to implement that change in Rocky, expressions and aid in accuracy and speed of running multiple test cases. For this example, it is trivial to run the model at different head pulley speeds as only the PulleyRPM variable needs to be modified.

Check out our website for other tips, tricks, and Ansys content.

Introduction

In the ever-evolving world of product development for all kinds of industries including aviation, automotive, manufacturing, and healthcare, engineers face many challenges while developing a final product that meets requirements. Both physical prototyping and software simulation help engineers model and analyze different systems, processes, and products. Understanding the differences between these two methods becomes crucial for developing products on-time and on-spec. In this blog, we’ll explore the distinctions between traditional prototyping and software simulation to help you choose the right path for your project.

Physical Prototyping

The setup and integrations required for physical prototyping consists of having design software, materials, test equipment and techniques, and quality assurance. The materials will vary depending on the nature of the project but can include raw materials, electronic components, or mechanical parts. Having the proper equipment also requires the right safety equipment to ensure a safe working environment.

Software Simulation

The setup and integrations required for software simulations depend on a few common elements and considerations. Hardware must be capable of running the simulation software with sufficient processing power and memory, and software should be selected based on specific features for your simulation. Lastly, training and support materials for users and developers are helpful for long-term success.

Both software simulation and physical prototyping have a place in the product development cycle. These two approaches serve different but complementary purposes within the product development process. Engineers must determine how much physical testing can be avoided through the use of software simulation during product development.  With the understanding of cost, time, and product requirements, they can choose the best path to ensure that the final product meets the desired specifications and quality standards.

Cost Considerations Drive Decisions

Software simulation may result in a higher initial investment in terms of software and training. These upfront costs are associated with developing or implementing a simulation software system for a specific purpose. Many simulation products come with licensing or subscription fees that can be one-time, monthly, or an annual renewal cost. However, software simulations generally have a lower long-term cost and reduce the need for physical materials, machinery, and labor that are necessary for physical testing. For applications where upfront cost is the absolute deciding factor, physical prototyping can be the right solution. For organizations looking to invest in their product development cycle, simulation provides a long-term solution that can be used repeatedly as you modify and evolve a product or create new products.

Speed

Time to market is a critical factor for many projects across all industries. It is based on the scope and complexity of the project, the team’s experience with software, and access to all resources required to complete the project. Simulation provides a digital platform that invites collaboration for sharing, analyzing, and discussions. It is more accessible to work collaboratively across distances saving time than requiring physical presence, which can create logistical challenges.

Risk assessments are paramount in product development. Simulation can help identify potential risks and issues early in the process, saving time and resources. The common risks and challenges associated with simulation varies from the quality of data input, the possibility of bugs or limitations in software tools to produce inaccurate results, and ensuring the model accurately fits the real-world representation. When time is not a critical factor for projects, physical prototyping is often used in product development. One would have the ability to physically interact with the product quickly, giving you a real-world sense of its form, function, and usability. Simulation abates the need for physical components – when supply chain constraints are an issue, engineers using simulation can begin testing based on the software-defined version of their product rather than having to wait for physical prototypes.

End Product Variables

Building physical prototypes can be expensive if numerous iterations are required.  Several types of products and industries often involve more than one iteration due to the complexity and need for optimization. In the electronics industry, products like smartphones and laptops undergo frequent iteration to incorporate the latest improvement and enhance user experience. In the Aerospace industry, complex systems like aircraft and satellites require extensive iterations to meet the strict guidelines. Car manufacturers and development of medical devices to name a few more.

Software simulation allows for rapid testing and iterations as many changes can be made virtually with a few clicks. This allows for quick changes and adjustments without the need to rebuild physical models. The flexibility to develop multiple iterations saves both time and resources. In contrast, physical prototyping may require more time and resources through each iteration. While physical prototyping for real-world testing is a crucial phase in product development, ideally it would be limited due to the time and costs involved. In addition, during real-world testing, unexpected issues or challenges can arise that are native only to the test environment.

Nelson Global harnessed the power of software simulation in this real-world example to optimize their muffler designs for refrigerated transport vehicles. By leveraging simulation, Nelson Global significantly reduced development time and costs, all while enhancing efficiency, reducing emissions, and meeting regulatory requirements. Nelson Global used the Ansys software suite to design two mufflers within three days. The typical duration for physical prototyping would be weeks involving manual hand calculations with less of an accurate outcome. 

In the end, both software simulation and physical prototyping have their places in product development. For many, a combination of both approaches can be the most effective solution. Starting with software simulation for the initial design and risk assessment, and then transitioning to physical prototyping for real-world testing. The right approach is the one that will align with your project’s requirements. 

The combination of Ansys, a globally recognized simulation tool, and DRD Technology, an integrator for Ansys tools, offer a comprehensive approach to product design and optimization. Ansys provides a suite of engineering simulation software tools that are widely used in various industries to simulate real-world scenarios. Ansys software simulation includes but is not limited to structures, fluid dynamics, electromagnetics, optical simulation, acoustic, and thermal analysis. These tools can be used in a wide range of industries including aerospace, automotive, electronics, manufacturing, and many more. Ansys Elite Channel Partner, DRD Technology, has achieved the highest level of proficiency and met rigorous performance requirements with the Ansys platform so that we can help you design, simulate, and succeed.

To learn more, read the full case study documenting how Nelson Global took their prototyping process from weeks to just three days using simulation.

Faceted geometry comes in several different formats with OBJ, PLY, and STL being commonly used.  Some simulation tools require solid geometry before importing.  Fortunately, Fluent Meshing is designed to work with surface models. These faceted file formats are often the standard when working with 3D scanned geometry in the medical community and in the field of additive manufacturing. Faceted geometry approximates a geometric shape by representing it as a triangular surface mesh rather than using a solid body representation. Many commercial CAD and CAE packages do not natively represent geometry using facets but use a technique called Constructive Solid Geometry (CSG) to represent geometry which is the process of combining simple shapes using Boolean operations to create more complex shapes. One of the issues when working with faceted geometry is CSG-based CAD and CAE programs are not well equipped to convert the surface mesh associated with faceted geometry into a solid, and it can be a time-consuming process to do so.

Fluent Meshing (a feature in Ansys CFD licenses) can work directly with faceted or solid geometry. The user will need to use Ansys Discovery to convert the faceted geometry file (OBJ, PLY, STL, etc.) into a TFG (Fluent-Meshing faceted geometry) before reading into Fluent Meshing. See below:

All the named selections and geometry preparation that was done on the faceted geometry in Ansys Discovery will be preserved in Fluent Meshing when reading in the TGF. The user can then use some of the mesh diagnostic tools in the Outline View to evaluate the quality and check for connectivity issues if needed. There are automatic operations that can be used to improve the quality of the mesh as required. See below:

The user can generate the volume mesh in the Outline View or use one of the more user-friendly task-based workflows such as Fluent Watertight Workflow. The task-based workflows do not yet support TGF geometry import, so the user will need to write out a .msh.h5 in Fluent Meshing before reading into the workflow. See below:

It is business as usual with the faceted geometry loaded into the import geometry task of the workflow. The user will start from the top and work their way down in the task-based workflow until a volume mesh is generated.

Some engineering tools require that geometry be represented as a solid, and it can be challenging to convert faceted geometry into a solid in many cases. Fluent Meshing is designed to work with surface models so faceted geometry does not need to be converted into solid before import. This can be a quality-of-life improvement when working with surface representations of solid bodies in Ansys CFD products.

Computational Engineering International, Inc. (CEI) originally developed a suite of products that included EnSight and was acquired by Ansys in 2017. EnSight is a market leading post-processor for Computational Fluid Dynamics (CFD) with multiphysics visualization capabilities. It is easy to use with a modern interface that has transient capabilities and can efficiently handle very large data sets, which are common in CFD simulations, especially transient ones.

EnSight has continued to improve their Python integration over the years and continues to lead in automation capabilities for the world of CFD post processing. Any action that takes place in EnSight is recorded in what is referred to as the command language. Whether the action is a zoom, translate, or rotate of the camera, or the creation of post processing objects like a clip plane, vector arrow plot, or contour – the action is saved in the command language. See below Command Panel:

The command language is a comprehensive journaling language in EnSight that contains all the detailed information associated with the operations or actions taken place in the current session. This command language can be converted into a Python script which can be executed using the built-in interpreter. The user will copy the commands to be converted into Python and paste them into a new file.

The actions are more human-readable in Python and allow for logic operations and loops. The user can make changes to the Python script as appropriate and save for use in other EnSight sessions to automate processes, which can be a huge time saver in certain situations. For example, if you need to create several post processing objects in EnSight for a variety of result files for use in a report, you will only need to do it once because you can reuse the commands for all results files.

Check out this YouTube video on automating the creation images of post-processing objects in EnSight using Python.

Utilizing the built-in Python interpreter in EnSight is a great way to automate repetitious post-processing procedures.

Not if, but when you run into CFD convergence issues, it is often due to a poor-quality mesh, an ill-posed problem, or inappropriate solver settings. There are a variety clues that indicate lack of solution convergence such as high residuals, solution monitors that do not make sense, and mass or energy imbalance. When residuals are high or increasing (diverging) it is a good indication that there is unphysical behavior in the solution that is the cause. You will need to identify where this unphysical behavior is occurring in the model so that it can be remedied.

Often reporting minimum and maximum values of the solution variables (velocity, pressure, temperature, etc.) is a good place to start when attempting to identify unphysical behavior. For example, if the maximum flow speed is measuring much higher than you’re expecting, you will want to identify where in the domain this unexpected behavior is occurring. An iso-surface is a good tool to use for identifying the location of odd behavior in the solution field.

You can compute the range of a particular solution variable in the iso-surface panel. If the range is not what you expect or does not make physical sense, it is a good idea to create an iso-surface to identify where the potential unphysical behavior is occurring. You can use the iso-surface in concert with other mesh objects in a scene and take a look at where the unexpected behavior is occurring:

In this example the location of high flow speed appears to be unphysical. You will want to interrogate the mesh in that particular region to look for clues – this can be done in the solver or mesher. Everyone is in a hurry to get results and it can be tempting to move forward with a poor-quality mesh in the solver, but you run an increased risk of solution convergence issues in the solver when doing so. It is best to start with a good quality mesh to accelerate solution convergence. Meshing is somewhere between an art and a science, but there are four primary mesh metrics that are used in concert when judging overall mesh quality – orthogonal quality, skewness, aspect ratio, and size change. To avoid mesh-related convergence issues, it is best to keep the minimum orthogonal quality above 0.1, skewness below 0.95, aspect ratio below 100, and size changes below 5.

To inspect the mesh quality inside of Ansys Fluent meshing, open the Display Grid panel from the menu bar, select the specific mesh quality metric to measure, then choose the quality range before hitting the display button. The elements within the specified range will be displayed in the graphics window as shown below:

To inspect the mesh quality in the Ansys Workbench mesher you will display the mesh histogram from within the mesh tab then choose the mesh metric to measure as shown in the figure below.

You can limit the range of the histogram to only contain the poorest quality elements by clicking the control button to access the range controls. From here you can limit the range of the x-axis then hit the reset button adjust the y-axis range. You may also want to consider reducing the number of bars in the histogram as well. Click the bars of the histogram to display the elements of that quality indicated:

In many situations, we have seen customers ask for ways to output custom results from ANSYS Mechanical. The usual results like Total Deformation, Equivalent Stress or Equivalent Plastic Strain may not be enough for your needs. Depending on the requirements (say a specification you are designing a part to), you can create a User Defined Result to output the needed result. ANSYS already outputs various quantities via User Defined Results that can be viewed in the Worksheet. Here is a quick look at some of what is available:

These quantities are used to create your own results output. User Defined Results can be operated on in several ways. Here is an excerpt from the ANSYS Help documentation (Mechanical Applications > Mechanical User’s Guide > Using Results > User Defined Results > User Defined Results Expressions):

Just as a simple example, say Total Deformation is required and is not output automatically (it is, just an example). If you add an UDR to the results, then type in the expression sqrt(Ux^2+Uy^2+Uz^2), keeping in mind these expressions are case sensitive, you get to resultant deformation from all three component values. Compare this to Total Deformation.

One can also do something more complex, say safety factor calculations. If your specified safety factor is not directly related to the Yield Strength or Ultimate Strength of the material, but some factor of, an UDR can be used; constants can be created and used just like any User Defined Result in the Worksheet. An example is shown here, where a safety factor is calculated based on a value of 6,200 psi. The safety factor looks at the First Principal Stress output, computes the safety factor, then caps the display at 7. Values less than 0 psi (compression when looking at the First Principal Stress) are set to the highest safety factor allowed (7 in this case).

A small note on the equation written in the graphic, in order to display a constant value (0 or 7 in this example), it must be multiplied by the identity matrix (matrix of 1’s). If you are just using a constant for equation manipulation, the identity matrix is not required.

User Defined Results can be a powerful tool if the output from Ansys Mechanical isn’t quite tailored to your needs.

There are situations in which it may be necessary to tweak friction coefficient in a nonlinear contact analysis during the simulation. Currently, the Ansys Workbench GUI does not support this capability directly; however, it is possible to vary the friction coefficient using a command object.

The Ansys documentation has several references of doing this as listed under the Help section; Mechanical APDL > Material Reference > Nonlinear Material Properties > Contact Friction as shown below.

This section on the documentation describes defining contact friction using TB,FRIC which is a material property used with current technology contact elements. It can be used to define coefficient of friction for both isotropic or orthotropic friction models. It further discusses varying friction coefficient in a multiple load step scenario, as well as implementing user defined friction  using TB,FRIC with TBOPT = USER.

The example presented here will show how to use commands object within Workbench to vary friction coefficient. The friction coefficient is defined via the TB,FRIC command. To define the friction that is function of temperature, time, normal pressure, sliding distance, etc. you can use the TBFIELD command in conjunction with the TB,FRIC. In this example presented, the friction is varied with time (to simulate it’s change through the load step).

Below is a graphic of the nonlinear contact between the Aluminum housing and steel ring gear.

The command object used to modify friction as a function of time is shown below.

This command object uses the information in the table below to modify friction :

Time                Friction Coefficient
0                      0
0.2                  0.1
0.4                  0.3
0.6                  0
0.8                  0.15
1                      0

As an example of the friction can vary, notice the friction coefficient is zero for time = 0.6 and time = 1.0.

During the run, the output controls under Analysis Settings was set to Yes for Nodal Forces, Contact Miscellaneous and General Miscellaneous.

A quick look at the contact results confirms our findings. The contour plot for contact friction stress shows zero results for time = 0.6 and 1 which m

Another sanity check is to check for reaction force through the frictional contact with the extraction method set to contact element option; this also reveals zero (nearly zero reaction force at these time points). The very small discrepancy noted on the reaction force is due to a few overlapping nodes on a boundary condition.

‘Restarting’ the process in ANSYS Mechanical Products by which a model is solved starting from a previously solved point. The previously solved point contains data for all nodes/elements in the model; there is no results mapping and interpolation when a restart is performed. This is the most accurate method for starting an analysis from a previously solved point.

By default, restarts are not kept when a simulation finishes. The user must modify the Analysis Settings in ANSYS Mechanical to keep the restarts points that will be needed. Those options are shown below:

Restarts do have limitations. For instance, modification of loads in a step before a restart point is to be used invalidates that restart point. Several tables in the ANSYS Help documentation characterize what happens to restart points if objects in the model tree are changed. This section can be found in Mechanical Applications > Understanding Solving > Solution Restarts, as shown.

Here’s one of the tables showing where restarts can be used followed by common questions we related to restarts.

What can solution restarts be used for?
For cases where some subset of the loads does not change and only a few loads change/vary. This is commonly referred to as load case modeling. ANSYS Mechanical FEA can do load case modeling.

Can you give an example of load case modeling?
A model that solves bolt pretension in the first several steps and then locks them in place. Commonly, service loads are applied after the bolt tightening is simulated. The service loads can represent multiple load cases, say one load case is a pressure load, another is a force load.

Another example is a ROPS (Roll Over Protection System) analysis, where loads are sequentially applied on a structure until some criteria is met (usually energy dissipated by the structure). Once the criteria are met for one load case, the load is removed and another load is applied. This process can also be done via restarts.

Why would we do this?
This saves time on solving models. Using the example above, without restarts, the bolt pretension steps would need to be solved every time a load case is added/modified. With restarts, loads can just be activated/deactivated in a step following the bolt pretension and the bolt pretension final step used as the restart point.

Things to know before attempting this method:
All of the load cases that will be solved should be known beforehand. The restart analyses require that ALL loads are defined in the initial model. In ANSYS Mechanical, loads cannot be added to the model tree without invalidating the previous results (ignoring the ability to use restarts).

Newly added loads also will not be applied in a restart analysis as the restart method does not create new elements for these new loads.

If bolt pretension is to be used, any loads defined for a load case should be applied in a step after the final bolt pretension, as usual.

Also, if bolt pretension is used, a step after the final pretension occurs IS REQUIRED. If this is not included, ANSYS assumes the last bolt pretension will be Loaded and not Locked. This means that ANSYS would modify the pretension to maintain whatever preload you have assigned, rather than applying the service loads as a working load on the bolt. Physically, it would be like tightening/loosening the bolt as the service loads are applied.

Method:
The general steps to this method are as follows:

1. Set up a model with all of the loads applied to the structure. This includes bolt pretensions and any loads that need to be simulated for the load cases. Set up the Analysis Settings as required for the analysis (multiple load steps, Large Deflections, etc.).
2. Modify the Restart Controls to keep all restart points once the model is solved.
3. Modify the loads for the load case studies to be inactive.
4. Solve the model.
5. Duplicate the analysis, sharing the Engineering Data, Geometry and Model cells. This guarantees the model setup remains the same for all models.
6. In the new system, activate the load for the first load case study.
7. Use the Tools > Read Results File… and locate the file.rst from the previously run analysis. This imports the results data into the model.
8. Modify the Restart Analysis options in Analysis Settings to restart from the end of the first simulation (the final bolt pretension loading, for example).
9. Solve the model.

Example:
The example shown here uses an oil field fluid end model with bolt pretensions applied. There are two load cases: 1) a pressure load on the cylinder bore, 2) a force load applied on one side of the fluid end body.