Dynamic solutions for a fluid world™

AFT Fathom FAQ

 

How has AFT Fathom been verified?

There are several aspects to AFT Fathom verification. First, AFT Fathom has been compared to published data where it exists. Available published data is usually for a single pipe, which is not very challenging for a network solver. Models, comparisons and explanations for such published predictions are given the Verification folder within AFT Fathom. Second, it can be verified that the AFT Fathom predictions agree with the fundamental equations for networks. Finally, AFT Fathom predictions have been compared to test data and other analytical methods on numerous occasions and good agreement has been shown.

Can AFT Fathom be used to model gas systems?

Yes, depending on the gas system (see Walters, 2000). For incompressible gas systems, AFT Fathom is perfectly appropriate. For compressible flow gas systems, a more sophisticated tool such as AFT Arrow should be considered.

Can AFT Fathom model two-phase flow?

No, AFT Fathom models single phase flow only.

How does AFT Fathom account for heat transfer in pipe systems?

Heat transfer effects show up in several places in AFT Fathom. First, in pipes users may assign a convective coefficient and/or allow AFT Fathom to calculate convective heat transfer based on standard methods. These heat transfer calculations and the associated physical properties are determined over each solution section. Thus properties and convective coefficients can and do vary along the length of the pipe. Second, heat transfer can occur in Heat Exchanger junctions. Here the user assigns a heat load or chooses a heat transfer model for the heat exchanger. AFT Fathom performs the appropriate energy balance calculation across the heat exchanger. Third, heat transfer occurs in pumps due to inefficiencies.

Finally, at each branching location in the network an energy balance is performed so that energy is balanced from one pipe to the next.

Does AFT Fathom perform an energy balance across each junction in the model?

Yes, every junction except for heat exchanger and pumps is assumed to be isothermal.

Can I model a non-Newtonian fluid in AFT Fathom?

Yes, AFT Fathom offers several non-Newtonian fluid models including Power Law and Bingham Plastic.

Can AFT Fathom model fire sprinkler systems?

Yes. The Spray Discharge junction is perfectly appropriate for fire sprinklers. The fire sprinkler K values can be entered in directly into the Spray Discharge. In addition, Spray Discharge junctions can be turned on or off with a single mouse click. Evaluating multiple fire location scenarios is easily done, and use of the Scenario Manager allows all cases to be kept in the same model file.

Can AFT Fathom model ducting system like those in HVAC, ventilation and dust collection systems?

Yes, AFT Fathom can model ducts. The rectangular geometry is modeled as a non-cylindrical pipe using a hydraulic diameter. Since ducting systems are usually incompressible, the solution methodology is appropriate.

Can I keep all of my design cases together in a single file?

Yes, the Scenario Manager lets you create dependent design cases where changes are inherited by children.

What is the difference between using a junction to input pressure loss data and the additional (minor, fitting) losses in pipes?

A junction has several advantages. First, solutions are given at all junctions, so the user can check the results at the junction. In contrast, Additional Losses are lumped into the pipe and it is not possible to give results at the loss. Second, many junctions (such as valves) have the ability to specify a Restricted Flow Area for cavitation calculations. No such ability exists for Additional Losses; thus, cavitation is always ignored for Additional Losses. Third, when using a junction the location in the pipe system of the pressure loss is specified. In other words, the upstream and downstream pipe lengths are specified. In the case of Additional Loss, it assumed to act like a friction factor and be evenly distributed along the pipe.

The Additional Loss approach has the advantage of being able to specify multiple losses quickly and easily, and not cluttering up the model Workspace with numerous junctions.

What is the difference between a Reservoir junction and an Assigned Pressure junction?

There is an overlap in capability between the Reservoir junction and an Assigned Pressure junction and frequently they are interchangeable. Here are the differences. The Reservoir junction input pressure and temperature always corresponds to stagnation properties. In the Assigned Pressure junction, they can correspond to either static or stagnation properties. If static, only one pipe can be connected. If the stagnation option is used in the Assigned Pressure junction, it will behave identically to a Reservoir junction. Finally, the Reservoir junction allows pipes to connect at different elevations (i.e., depths), and also allows pipes to discharge above the liquid surface level.

How does AFT Fathom account for pressure losses at tees and wyes?

AFT Fathom uses the most sophisticated models available to calculate losses at tees and wyes. The methods, which come from Idelchik, take into account losses that depend on the flow split, area change and angle of the branch pipe.

How do I size a pump when there are not any flow control valves?

See Size a Pump in the Help system or User's Guide.

How do I size a pump when there are flow control valves?

See Size a Pump with a Flow Control Valve in the help system or User's Guide.

How do I model a variable speed pump?

Enter the pump data as a polynomial in the Pump Specifications window and then set the pump speed directly. No entry is assumed to be 100% speed. If you enter something other than 100%, AFT Fathom uses the affinity laws to adjust the curve.

How do I find the pump speed to obtain a desired flow or discharge pressure?

Enter the pump data as a polynomial in the Pump Specifications window and set the desired flow or discharge pressure on the "Auxiliary Input" folder tab. AFT Fathom will calculate the pump speed required to produce the flow or pressure conditions specified and display the speed in the Pump Summary report.

How do I close a valve, pump or pipe?

Select the pipe or junction you want to close and choose Special Condition from the Edit menu. By default, AFT Fathom will display a red "X" next to the pipe or junction label on the Workspace. It will also redraw your Workspace and show the closed sections of the model with dashed lines for the pipes and dashed outlines for each junction. Some special condition settings do not close the junction but have different purposes. For example, the normal condition for a relief valve is to be closed, so its special conditions causes it to be open.

How do I model the pressure drop across a component when there is only one data point? See Using Manufacturer Pressure Drop Data in the Help system or User's Guide.

How do I model a relief valve in a system?

You can model a relief valve using either a Relief Valve junction or a regular Valve junction. The Relief Valve junction is always closed when you run the model (unless you set it’s Special Condition), and AFT Fathom will run the Solver to determine if sufficient pressure exists to crack it. If so, it will run the Solver again with the relief valve open. If you know the condition you are modeling will crack the relief valve, it is more efficient to just use a regular valve junction. In this case, AFT Fathom assumes the valve is open from the start, and does not have to go through the extra step of solving the network to check for sufficient system pressure to crack it.

How do I show the pipe or junction names on the Workspace?

Open the pipe or junction specifications window, click the Optional folder tab, and check or clear the check boxes for showing the number or name. This will affect the current pipe or junction. You can set the default behavior in the Workspace Preferences window available on the Options menu.

How do I change the display of pipe or junction names on the Workspace after the model has been built?

You can use the Global Edit windows to change the current model settings for all pipes or junctions or only selected ones. See the Global Pipe Edit or Global Junction Edit window for more information.

How do I set my preferred engineering units as defaults?

From the Options menu, open the Parameter and Unit Preferences window. Change to the Unit Preferences folder tab. Choose the Unit Type on the left and the preferred unit you would like to use in the list on the right. Then click the "Set as Preferred Unit" button. At this point, the preferred unit applies only to the current model. To make this the default for all models, click the Set as Default button at the bottom.

How do I change the input data for multiple pipes or junctions all at one time?

The Global Pipe Edit and Global Junction Edit windows offer tremendous power and flexibility in changing all or parts of your model input all at once. See Global Pipe Edit and Global Junction Edit topics for more information.

How do I create a liquid mixture?

You can create gas mixtures with the optional Chempak add-on. The AFT Standard database does not support mixing. To create a mixture, open the System Properties window from the Analysis menu, choose the Chempak Mixture option, and then click the “Create New Mixture and Add…” button. Here you can specify the mixture components and percentages.

How do I merge two models together?

Use the Merge feature on the File menu to merge models together.

How do I automatically run multiple models right each after?

Multiple models can be run sequentially using the Batch Run feature.

How do I enable or disable the Highlight feature in the Pipe and Junction Specifications windows?

There are three ways to enable or disable the Highlight feature. The first is toggling the option on the Options menu. The second is pressing the F2 function key while in a Pipe and Junction Specifications window. The third is double-clicking the anywhere in the Pipe and Junction Specifications window.

How do I automatically save my results after the model is run?

Open the Output Control window from the Analysis menu, change to the Format & Action folder tab, and choose to select the Transfer Results to Initial When Done, Transfer Valve States When Done, and Save Model When Results are Transferred options.

How do I quickly find a particular pipe or junction on the Workspace?

Use the Find feature to quickly find a pipe or junction.

How do I change the reference positive flow direction for one or more pipes?

Select the pipe or pipes and choose the Reverse Direction feature on the Arrange menu.

How do I access pipe and junction Specifications windows from the Model Data window?

In the Model Data tabular displays, click the far-left column where the pipe or junction number is located and the appropriate Specifications window will be opened.

How do I display only selected pipes or junctions in the output?

Open the Output Control window from the Analysis menu, change to the Show Selected Pipes/Jcts folder tab, and select the pipes and or junctions you want to display.

How do I quickly change the units for an output parameter?

Whereas the Output Control window allows you specify units for all parameters, when in the Output window viewing results you can quickly change the units for parameters in the tabular displays by double-clicking the column header.

How do I model elevation changes in my pipe system?

Set the elevations in the elevation fields for each junction. Pipes are assumed to be straight between junctions. If you need to model a system other than a stationary earth-based system, the gravitational acceleration can be changed in the System Properties window.

How do I show data for only selected pipes or junctions in Visual Report?

Open the Visual Report Control window, change to the Show Selected Pipes/Jcts folder tab, and use the provided features to specify which pipes and junctions should display data and which should not.

How do I make the Pipe Drawing Tool stay active so that I can continue to draw pipes without having to click it each time?

If you hold down the CTRL key when completing the pipe drawing (just before releasing the mouse button), the Pipe Drawing tool remains active, and you can draw a series of pipes without returning to the Toolbox each time. If you double-click the Pipe Drawing tool it remains active until you click it again a single time. This allows you to draw a series of pipes without returning to the Toolbox each time.

How do I add graphical segments to a pipe so it is not constrained to a single straight line? Use the Segment Pipe tool found on the Arrange Menu.

How do I set up custom databases on my local PC?

See Custom Database Overview in the help system or User's Guide.

How do I set up custom databases on our local or wide area network?

See Network Database Overview.

How do I customize the toolbars or create my own toolbars?

See Customizing the Toolbars and Menu in the help system or User's Guide.

How do I change the icon for a junction in AFT Fathom?

Open the Junction Specifications window, click the Optional folder tab, and then click the Change Icon button.

Can I customize the junction icons in AFT Fathom?

No, AFT Fathom icons are in a resource file that cannot be edited by the user. This capability is planned for a future release.

What is the limit to the size of model I can create with AFT Fathom?

There are no theoretical limits to model size, but there are a few practical limits. First, AFT Fathom accepts pipe and junction ID numbers up to 9999. This limits the model size to 10,000 pipes and 10,000 junctions. Before you reach that limit, however, you will likely encounter a limitation of your available RAM to hold all of the solver parameters. To determine how much RAM you need, add up the number of branches and tees in the model. Take the square of this number. Then multiply it by 32 to get the amount of RAM that must be available. For example, with 1,000 branches and tees, the square is 1 million, and after multiplying by 32 you need 32 million bytes of RAM (i.e., 32 MB).

Can AFT Fathom model reacting flows?

No, AFT Fathom 4.0 models only non-reacting flows.

Can I install AFT Fathom onto a local or wide area network?

Yes, AFT Fathom can run off the network or local PC. When installed on a network, the number of concurrent users is limited to the number of licenses purchased. See the Information on Software Installation topic.

What is the difference between Fathom XTS and Impulse?

While both do time transient modeling, they use entirely different methods and are intended for different applications. AFT Impulse models what are sometimes referred to as 'fast transients', transients dominated by wave speed, communication time, and momentum and pipe stiffness. Fathom XTS, for extended time simulation, models 'slow transients', slow in the sense that factors such as wave speed, momentum, etc. can be ignored. Where AFT Impulse uses the method of characteristics to calculate transients, Fathom XTS runs a series of steady-state solutions with changing parameters, e.g. liquid levels, transferred from one time step solution to the next.

Since AFT Titan's solution capability is the same as AFT Arrow, won't it take an excessive amount of time to run an optimization?

It is true that AFT Titan's solution time frame is slower than AFT Mercury. This is why the new Lumped Adiabatic and Lumped Isothermal solution methods were added. While still slower than incompressible methods, they are much faster than the default marching method.

I see cost settings for Material, Installation, Maintenance and Operation. Do I need to specify costs for each one?

No. Depending on your goal, you need only specify the costs for which you are interested. If you are looking for just a first-cost estimate then you need to only specify Material and possibly Installation. Remember, these are very broad categories and can be tailored to meet your specific application.

How does the Fathom Settling Slurry module help designing a slurry transport system for best energy efficiency?

The Fathom SSL module provides key information directly related to the energy efficiency of your slurry transport system including the Specific Energy Consumption, a direct measure of the energy required to move a unit mass of solid a unit distance (e.g. KW-hr/mton-km). Fathom SSL also calculates pump power consumption including pump efficiency and the effect on pump performance caused by the slurry.

What types of fluids does the Fathom NSL module model?

Broadly stated the Fathom NSL module models the behavior of non-settling slurries and non-Newtonian fluids. The terminology for these fluids is less than precise since some non-Newtonian fluids are slurries while some fluids are liquid only.

What kinds of transients can Fathom XTS model?

A wide range, including liquid levels, valve open/close, pump speed changes, relief valve opening and more. Just as important, Fathom XTS can model time transients, event transients and inherent transients. Time transients are changes that are specified to occur based on the model time. Event transients, on the other hand, are triggered by an event that occurs in the system. Many kinds of events can be used, such as pressure, flow, velocity and liquid level. Inherent transients are changes that occur by the very nature of a system component. Two examples would the liquid level change that occurs in a finite reservoir (or tank), while another would be a check valve opening and closing as a result of flow reversals.

AFT Fathom models heat transfer, so does this mean Fathom XTS does as well?

No, when using the Fathom XTS module heat transfer is turned off because XTS does not model transient heat transfer. This is primarily because the input required by the user to model transient heat transfer would be very complicated for some components. Consider a tank, for example. What part of the tank structure participates in transient heat transfer? The immediate tank boundaries would seem to be fairly clear, but what about the supporting structure? It too would be involved to some degree, but to model this would require extensive definition by the user.

Do I have to have one Fathom XTS module license for each AFT Fathom license?

No, there does not need to be a one-to-one relationship in the number of Fathom XTS and AFT Fathom modules. This provides users the flexibility to choose the level of capability they need. For example, you may have several AFT Fathom licenses deployed on your network but only need to use Fathom XTS half the time and, therefore, have a correspondingly lower number of XTS licenses. If you open a model previously saved using Fathom XTS, AFT Fathom will first try to activate the XTS module. If all of the XTS licenses are being used, a message will be displayed telling you a XTS license is not available and provide you a choice of continuing to open the model or canceling the load. This same message will remind you that if you do open and work with the model, XTS specifications contained in the model may be lost.

What is the difference between goal seeking and control?

Fathom GSC, Goal Seek & Control, extends Fathom's capabilities in two ways. One is goal seeking, automatically finding the value of one or more inputs that will produce a specify value for one or more outputs. The second is to extend AFT Fathom's control modeling capabilities to remote sensing. AFT Fathom can model flow and pressure control valves and controlled, variable speed pumps. With basic Fathom, the variable controlled is the one at the control component. That is, a pressure reducing valve controls the outlet pressure at the valve. With GSC, control can be based on a variable located anywhere in the system. Instead of controlling the pressure at the valve outlet, it could be a pressure downstream at some other location. Additionally, control can be based on the difference between two variables, such as a differential pressure between two points, and on group sums, maximums or minimums, simulating some of the more sophisticated control logic that is sometimes implemented in real systems through computer based control systems.

Is there a limit on the number of variables and goals Fathom GSC can handle?

While there is no limit, the time required to find a solution will increase with the number of variables and goals that must be solved since the number of possible variations increases exponentially with the number of variables and goals. Fathom GSC employs a robust and efficient numerical optimization engine to be able to handle models with large numbers of variables and goals.

Do I have to have one Fathom GSC module license for each AFT Fathom license?

No, there does not need to be a one-to-one relationship in the number of Fathom GSC and AFT Fathom modules. This provides users the flexibility to choose the level of capability they need. For example, you may have several AFT Fathom licenses deployed on your network but only need to use Fathom GSC half the time and, therefore, have a correspondingly lower number of GSC licenses. If you open a model previously saved using Fathom GSC, AFT Fathom will first try to activate the GSC module. If all of the GSC licenses are being used, a message will be displayed telling you a GSC license is not available and provide you a choice of continuing to open the model or canceling the load. This same message will remind you that if you do open and work with the model, GSC specifications contained in the model may be lost.

Can I account for the time-value of money?

Yes. You can specify an Interest Rate and an Inflation Rate which are used over the System Life.

How do I enter the costs for my pipes, components and fittings?

Costs are entered in a one or more user-defined Cost Databases using the Cost Database editor. You can keep separate databases for each type of cost or put all the costs for a project into one database. These databases can also be used in multiple models and can be shared among all the users over a network.

Can I change what is shown in the Cost Report?

Yes. The Cost Report is fully customizable through the Output Control. You can set the column types and order, units used, number of significant digits and order of magnitude displayed.

end faq