BOSfluids Engineering Workshop
Solving Water Hammer Risks in Critical Piping Systems
Consolidated Questions & Answers · Sessions of 13 and 18 June 2026
This article merges the questions and answers collected across both workshop sessions into a single reference.
Table of Contents
Fluids and materials BOSfluids can model
Which fluids can BOSfluids analyse, and is it used only for water systems?
Any fluid can be analysed, not only liquids but also gases, and compressible fluids can be modelled as well. It is used for all types of liquids and gases in piping and pipelines.
Can BOSfluids perform surge analysis for any fluid, or only a selected range?
It can be used for any fluid; the fluid is defined through the fluid database.
Do these tools include pre-installed libraries for FRP materials?
Yes. FRP materials are in the built-in database, and it can also easily be extended with user-defined materials.
Do we have materials such as DI, HDPE and GRP in the database?
Yes, we have HDPE, GRE, GRP and others.
Does BOSfluids include pipe material properties for the surge calculation?
Yes. A pipe-material database is included and can be extended with user-defined materials.
Is pipe material elasticity taken into account?
Material elasticity is defined by the selected material. In the example shown, the default “Steel” material was used, which carries its own properties.
Can material data from the PRG / MatPRO (Paulin) database be used?
The MatPRO program is not used directly, but the corresponding material properties can be set easily in BOSfluids.
How are fluid and material density defined? Can I enter a custom density?
Materials and fluids are selected from the BOSfluids database, which includes all relevant properties such as density. You can also create your own material or fluid and set its density. Specifying a fluid with a custom density is easily done in the fluid database.
What data is required to add a custom fluid?
Density, viscosity and bulk modulus, plus a vapour pressure if cavitation is a concern.
What fluid properties are needed to define a gas in the database?
Density and viscosity.
In the fluid section, can we create a mixture of components to calculate the fluid properties?
Yes. Natural gases can be defined by component, gas/liquid mixtures can be specified, and custom fluid properties can also be entered.
Can multiple fluids be used in a single model, for example to represent fluid blending?
Yes.
Is BOSfluids able to calculate the bulk modulus of a crude oil fluid?
The fluid properties need to be specified by the user. However, if the speed of sound of the crude oil is known, BOSfluids can calculate the bulk modulus from that. BOSfluids also has several built-in crude oil fluid definitions, such as crude oils at specific API gravities.
Can the software be used for dense-phase CO₂ analysis, and for hydrogen compressor transient response analysis?
Yes, the user can define their own custom fluid properties.
Can we analyse a foam-water deluge sprinkler or foam-water monitor system?
Foam-water is a non-Newtonian fluid, which will be supported in the next release of the software.
Surge, force and transient analysis
Can BOSfluids be used for steady-state and transient analysis of long pipelines?
Yes. Both steady-state and transient flow analyses can be performed on long pipelines.
How can the software help with steady-state and transient studies of pipelines?
BOSfluids supports both steady-state and transient studies for pipeline systems.
Can a steady-state analysis using only the maximum pressure from a transient (water-hammer) simulation replace a true water-hammer analysis?
No, it cannot. That is why BOSfluids performs fully transient analyses.
How do I know whether a surge analysis is needed, for example at the FEED stage?
Most systems with any degree of complexity may require a surge analysis. Pumps can trip and emergency valves can open or close, all of which generate surge loads.
Do gas pipelines generate surge, given that gas is highly compressible?
Yes, pressure surge also occurs in gas pipelines. Although the density is typically lower than for liquids, high pressure peaks may still occur depending on the operating conditions.
Which transient scenario creates a vacuum, and which creates positive pressure?
Many transient events cause both. For example, a closing valve produces a positive pressure peak upstream of the valve and a negative pressure peak downstream of it.
Can the surge force be estimated from pipe length alone, without modelling the full system?
For very simple systems a manual estimate is possible, but it is very conservative and is therefore not advised. The force calculated by BOSfluids does account for pipe length; the largest forces are typically found on the longest pipe sections.
What is the advantage of performing a full BOSpulse analysis instead of a simple empirical “design by rules” approach to determining the loads?
For complex systems, hand calculations are not really feasible or accurate, so an analysis tool is required for reliable results.
Can the natural frequency of the system be obtained?
Yes.
How many load scenarios can be compared, and is there a limit?
As many scenarios as you wish can be specified; there is no limit.
Can a transient simulation and the steady-state hydraulic calculation be run at the same time?
Yes. Different kinds of analyses can be run simultaneously, as BOSfluids supports running simulations in parallel on multiple processing cores.
Can the thermal expansion of trapped hot oil be analysed in transient cases?
No, thermal transient analysis is currently not supported.
Pumps and rotating equipment
If we add a pump in the middle of the system and run a transient case, will it run without problems?
Yes.
How are positive-displacement (PD) pumps modelled in BOSfluids while capturing their closed-boundary behaviour in a surge analysis?
Pumps and rotating equipment
PD pumps can be modelled as the flow boundary condition. Reciprocating pumps can also be inserted, including their flow pulsations.
How can a variable frequency drive (VFD) on pumps be modelled in BOSfluids?
These can be modelled via a dedicated pump element.
Can turbo pumps be modelled?
Yes, this is a type of centrifugal pump. Users can manually specify the characteristics.
For the high forces arising from a cooling-water pump trip with auto-restart, can these be assessed, and does a recirculation loop help?
Yes, these systems can be simulated in BOSfluids. A recirculation loop is one of the solutions that could help.
Can the software model a pigging operation?
Depending on the pigging process, BOSfluids can be used to analyse pigging processes.
Valves and surge mitigation
Is an air relief valve used to control transient surge?
Yes. Relief valves are used in these situations and are part of the program.
Does BOSfluids have surge mitigation equipment, such as air valve or breather valve models, available?
Yes, we can model those.
What is the ideal check valve and air release valve to use to minimise the surge impact?
That depends on the specific system.
Can non-slam check valves be modelled, and are dynamic check-valve characteristics an input?
Check valves can be modelled in detail, including the repeated open/close “chattering.” Non-slam check valves can be represented using parameters such as spring stiffness and disk mass taken from the check-valve specification sheet.
What must be done to control surges when filling an empty line with firewater?
As demonstrated in the case study, the system should be analysed to determine the cause so that appropriate mitigations can be applied.
In some cases a client may insist on installing surge vessels regardless of the surge pressures identified in the transient analysis. Where the analysis shows that the surge can be effectively mitigated through operational measures, such as appropriately sized slow-closing valves, the need for a surge vessel should be reassessed on technical, operational and life-cycle cost grounds. Do you agree?
Yes, we agree, since a surge vessel is often an expensive solution.
Is there an option to automatically size or optimise the surge vessel sizing?
The software provides a flexible scenario-based approach to surge vessel sizing. You can rapidly create and compare multiple surge vessel configurations within the same model, making it straightforward to evaluate performance and determine the optimal vessel size for your application.
Is the methodology applicable to liquid relief lines where the header downstream of the relief valve is empty?
Yes, relief valves that discharge to empty lines are supported.
How are controllers modelled?
BOSfluids comes with a flexible way to set up controller systems, where the user can define sensors and fully customisable programmable controllers.
Cavitation and two-phase flow
What does HVCM stand for?
Homogeneous Vapour Cavity Model, a modern cavitation model.
What is the difference between “cavity size” and “cavity volume”?
Cavity size is the cavity expressed as a percentage of the pipe cross-section (a value of 1 equals 100%). Cavity volume is the actual volume, expressed for example in m³ in metric units.
In BOSfluids, can we model a two-phase fluid other than air and liquid?
Two-phase flow is currently only supported for cavitation and for the flood-and-drain features.
If we already have two phases in our system, such as steam and condensate in a boiler blowdown system, can we use the software for a transient study?
Yes, but it depends on the nature of the two-phase flow and the transient phenomenon you are trying to evaluate.
Even if cavitation is present at steady state, can the models still carry out a transient analysis? Does the same apply to air valves that are open during steady state, for example on cooling water systems?
The transient analysis can start with sections that have cavitation; however, this should be used with care. BOSfluids assumes that air valves are closed during the steady state.
Can BOSfluids distinguish between slow filling over high points (becoming channel flow) and fast filling where siphon effects apply?
BOSfluids assumes that the flow remains rapid enough and therefore will not consider channel flow.
Solver, meshing, wave speed and performance
Are lines simulated as 1D lines? If so, would a water surge in a gas-filled pipe behave as a “moving wall” through the pipe system, or would it respect annular/slug flow?
Yes. The assumption is that the wave front is perpendicular to the pipe.
How does the software handle several different materials? Are the wave speed and time step updated automatically during the calculation, and is there a risk of inaccuracy, given that standard models work with a single wave speed and time step?
When using multiple pipe materials, such as steel and GRE together, this leads to differences in the fluid wave speed. This is accounted for in BOSfluids so that systems with multiple pipe materials are simulated accurately.
How does BOSfluids select the appropriate mesh size and time step?
The mesh size and time step are determined automatically by BOSfluids to produce a good mesh, but the user can also override them.
Do these model optimisations come at a cost to accuracy? Could you give some detail on how this is done while still adhering to the governing equations? I assume BOSfluids still uses the Method of Characteristics.
Yes, BOSfluids is based on the Method of Characteristics. Please contact us so we can explain in more detail, as it is not possible to cover every aspect in the chat.
Is the quadratic growth in run time caused by a larger network, or by a reduction in section length? My understanding is that reducing the section length reduces the time step by an equal amount, causing the quadratic increase.
Yes, that is inherent in the basic flow equations. However, BOSfluids includes smart adaptations that make the solvers very fast compared with other solutions.
Is four cores the maximum the software can use?
No. The maximum number of cores is limited only by the computer running the simulation.
What are the accuracy limits of the model for small-bore (small DN) piping and for high-viscosity fluids?
Fluid flow as low as Re = 64 can be accurately handled by the flow solver.
Can BOSfluids perform CFD?
The simulations that BOSfluids performs fall under Computational Fluid Dynamics (CFD), but CFD usually refers to fully free-flowing fluid dynamics, such as in vessels, whereas BOSfluids is limited to pipe flow. General CFD packages are much more elaborate and require far more computation time even for very small systems, so actual piping networks are typically not simulated with them.
Can the software handle large transmission lines and large-network water-hammer studies, and can a 2D EPANET hydraulic model be converted into a 3D model?
Yes, both are supported.
Building the model: geometry and boundary conditions
During the FEED phase, when the 3D details are not yet available, can a process engineer enter a simpler model manually into BOSfluids?
Yes. Process engineers can start with a simple 2D approach to run models for pipe sizing and similar tasks.
How are bends defined along a long pipeline (for example, a bend at the midpoint of a 500 m section)?
Bends can be specified in a table for the pipe line. If full detail is required, the bends can also be modelled explicitly.
In the BOSfluids model, can the pipeline profile be developed from mile-post data, importing a single pipe element with its length and elevation profile, instead of using multiple pipe segments?
You can model a long pipeline via a special Pipe Line element that allows you to specify the number of bends and the length of pipe line.
How is elevation specified?
All elevations come from the 3D geometry. When working in 2D view, the elevation can be entered in a dedicated field.
Building the model: geometry and boundary conditions
How do I distinguish above-ground from underground pipe?
This is set through an input field on the pipe.
For underground piping, what soil models are available, and is NEN 3650 supported?
You can simulate buried piping; this affects how the pipe is restrained and, in that way, affects the flow. However, displacements are not part of a flow study, so no soil models are included for the flow analysis.
How are underground pipelines modelled, as a rigid pipe due to the surrounding soil, with the wave speed equal to the propagation wave speed?
The wave speed in buried piping is calculated based on coefficients from the literature.
Can a valve closure profile be entered as a custom (e.g. exponential) characteristic rather than linear?
Yes, any closure profile can be specified in a table.
For the valve-closure simulation that leads to a pressure rise (surge), is the pump still running? And what about the slow-closure scenario, where the valve takes 35 seconds to close?
Yes, in that case the pump still runs, but you can also change the pump speed.
Can flow rate be applied as a boundary condition?
Yes; a large set of boundary conditions can be used.
How does the flood-and-drain feature comply with the Method of Characteristics? Is a downstream boundary at atmospheric pressure considered to move with the fluid along the length of the piping at the bulk fluid flow rate?
It couples the gas pocket dynamics to the Method of Characteristics. The pressure and temperature of the gas are tracked during the simulation.
Does dry-line filling consider the gas flow of the air being expelled, for example the compressibility in dead-legs?
Yes, this is considered in the simulation
Is dry-line filling only for water, or can it handle any hydrocarbon fluids?
It can handle all fluids.
Interfaces, file import and integration
You mentioned that structures can be modelled in your software and exported to CAESAR II. Can piping models also be exported from CAESAR II and imported into BOSfluids/BOSpulse, and vice versa?
Yes, that works both ways.
Is BOSfluids compatible with AVEVA E3D output, or must the model come through CAESAR II?
The current interface is between CAESAR II and BOSfluids.
Can we import models directly from Revit, AutoCAD or Navisworks? Does BOSfluids import Navisworks 3D models?
Not as native files. The current interface is via PCF or CAESAR II. Most 3D CAD programs can export to PCF files, which can then be imported.
Can a model be built from CAD / SHP files?
If the CAD software can generate a PCF file, the geometry can be imported.
How are GIS / SHP files imported?
GIS data is typically imported using the EPANET file interface.
Can BOSfluids import AFT files?
A direct, native AFT import is not possible, but it can be achieved through third-party file formats.
Coming from AFT Fathom, Arrow and Impulse: can BOSfluids perform steady-state analysis as AFT does, can models be exchanged between AFT and BOSfluids, and when should each tool be used?
BOSfluids can perform both steady-state and transient analysis for liquids and gases, so there is no need for three separate programs like AFT Fathom, Arrow and Impulse. AFT native model files cannot be read directly by BOSfluids. Please contact us to see how we can help transfer your AFT models to BOSfluids.
Can BOSfluids import from RD coordinate systems?
That depends on the file format it is presented in. A spreadsheet with x, y and elevation coordinates can be imported.
If I have a Civil 3D pressure network model, can it be imported directly with all network components (pipes, valves, bends, fittings)? Does BOSfluids automatically recognise the component data such as pipe diameters, bend angles and valve types, and does it take the pipeline design profiles into account in the hydraulic and surge analysis?
Yes. Depending on the file format, all relevant data is imported.
Is there integration with BIM?
This will be possible in the upcoming release of BOSfluids.
Can we transfer stream data (composition) from HYSYS to BOSfluids, or import a HYSYS file or model to use its fluid properties and work further inside BOSfluids?
Currently there is no direct interface with HYSYS; it is only possible through PCF and the various other interfaces shown during the presentation. Please contact us for the details.
What about data transfer to other programs such as ROHR2 and AutoPIPE?
Exporting to AutoPIPE is supported. ROHR2 also uses the CAESAR neutral file interface, so that can be used as an intermediate file format.
Can the calculated forces be transferred to Bentley AutoPIPE?
Yes, the forces can be transferred to Bentley AutoPIPE.
What is the required format / column structure for the pipe-profile import file, and is a template available?
This is a simple text-based Comma-Separated Values (CSV) file, which can be read and written by any spreadsheet program such as Excel. An example is included in the software.
Stress analysis, supports and structural response
Is there any difference between the water-hammer loads generated by CAESAR II and BOSfluids?
CAESAR II cannot simulate fluid flow. The loads due to water hammer are calculated by BOSfluids, and the resulting stresses in the piping are calculated by CAESAR II.
Can the transient forces calculated in BOSfluids be extracted and used directly in CAESAR II for piping stress analysis?
Yes.
Can we use BOSfluids on its own, without CAESAR II, so that all our systems are modelled and simulated for stress, supports and guides?
You can model all of those, but bear in mind that BOSfluids is not a piping stress analysis package, so it cannot perform the stress analysis itself.
Do I have to run the stress analysis in CAESAR II, or can BOSfluids do it?
You can use CAESAR II, but also other stress packages such as ANSYS or AutoPIPE.
How do I get the water-hammer force into my piping stress software, and do I need to apply a Dynamic Load Factor (DLF) when importing into CAESAR II?
BOSfluids exports the transient hydraulic loads generated by the surge event. These loads should normally be imported into CAESAR II without applying an additional Dynamic Load Factor. (As several participants noted, a DLF is generally relevant only when representing a dynamic load within a static analysis, and remains a matter of engineering judgement.)
Can the analysis be run through the CAESAR II Dynamic Module?
Yes. BOSfluids is especially well equipped to work with the CAESAR II dynamic module. An example was given during the workshop, where BOSfluids generated the CAESAR II dynamic input file.
For slug forces, are the displacements on the steelwork calculated within BOSfluids or by an external solver?
The steelwork is built in BOSfluids and the results (stresses, displacements) are presented in BOSfluids. The structural analysis itself is performed by an ANSYS engine that BOSfluids calls automatically; as a user you do not interact with ANSYS directly.
Does the use of ANSYS imply that junction coupling (fluid-structure interaction) effects can be captured?
Yes. The ANSYS interface allows you to analyse the mechanical response of the system due to the flow. In the background, BOSfluids creates and runs an ANSYS model, and the results are imported back into BOSfluids, allowing you to review both the flow results and the mechanical results in the same program.
Are slug forces incorporated in the case studies, and can slug forces be derived from this type of analysis?
Yes. For the examples shown in the case studies, the filling of empty firewater systems included the impact loads of liquid slugs on fittings.
Can the calculated slug force also be imported into CAESAR II?
Yes, these forces can be exported to CAESAR II.
Does BOSfluids provide support loads for pipe supports?
BOSfluids itself does not perform a structural analysis. The hydrodynamic forces resulting from a flow analysis are evaluated in a third-party stress analysis package, such as CAESAR II or ANSYS, and those packages calculate the pipe support loads.
Noise, vibration, AIV and FIV (BOSpulse)
Can flow-induced vibration in a short piping segment due to flow separation be examined with BOSfluids?
This is handled by our other software package, BOSpulse.
Can it also predict noise, in dB, across the valves?
This is currently possible in our other software package, BOSpulse.
Does the software use IEC 60534-8-3 to model valve noise and its propagation down the pipe?
BOSfluids implements the Energy Institute guidelines.
Noise is hard to predict because it depends on the pipe material, the type of soil and the depth. How is this handled?
BOSfluids implements the Energy Institute guidelines.
For AIV, is the software simply calculating the sound power level and its attenuation along the piping based on the EI guidelines, or are the vibration modes, frequencies and resulting stress levels in the pipe wall calculated from the actual structural response to the energy released downstream of the pressure-reducing devices?
BOSfluids implements the Energy Institute guidelines.
Is an AIV/FIV assessment file available?
This is an upcoming feature and is not yet available.
Codes, standards and validation
Has the software been formally validated against experimental test data and benchmark problems covering multiple analysis scenarios?
Yes. Each release is thoroughly tested against a large set of both analytical and experimental results.
Can simulations be code-specific, i.e. carried out in accordance with a chosen design code such as ASME or EN, or must any specifics be entered by the user?
Many codes are supported, and parameters can also be user-defined.
Is there a guideline, other than the EI AVIFF guidelines, for when a detailed analysis is required, especially for water hammer during FEED? This would help justify including it during the design phase.
Unfortunately, there are no codes that make a surge analysis mandatory. However, as the case studies show, it is very important to carry one out.
Results, outputs and reporting
Can we display the main parameters at nodes around the various points in the simulation, for review across different scenarios?
Yes. All the data sets shown in that list can be visualised.
What profiles can be extracted other than time versus pressure?
All the data sets shown in that list can be visualised.
Can a time plot or results be exported to Excel?
Yes.
Can the output time step shown on the results graph be changed?
Yes, the output time step can be set in the analysis settings.
Can the data-point density on the results graph be adjusted directly in the results tab?
The data-point density is set by the user. It can be decreased after the simulation, but not increased.
Is there a provision to extract reports?
Yes. Reports can be extracted in PDF, Word or text format.
Application scenarios and specific systems
In a power plant natural gas feed system to a gas turbine, can the software simulate transients during a gas turbine trip or load rejection, an upstream pressure regulator failure, or a compressor trip?
Yes. Gas turbines, including turbine surge and choking, are included.
Does BOSfluids also work for high-pressure steam headers and traps?
Yes.
For an FPSO firewater network, can ship movement (hog and sag) and structural deflection be simulated within a single large model?
No, external displacements are not supported.
Could you also demonstrate the flood-and-drain feature?
Yes; it was demonstrated during the session.
For entrapped air or residual liquid at pump start, can fluid properties that change with temperature be used, for example methane pumps where the methane volume changes rapidly with temperature?
The fluid properties are reported to the user in a dedicated fluid properties report.