Piping Simulation Comparison – Chapter 6


The three tools are sufficient alone but to allow various simulations or to avoid human typing error, it is sometime interesting to have links between software.

We will initially present how to import data from CAD and in a second and third step, how to export data or to have co-simulation.

Importing CAD data


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The CAD2FM tool from Mentor Graphics

Cad to FloMaster (CAD2FM) is a fully automated function to convert MCAD piping geometry into an equivalent FloMaster sub-system, bypassing data re-entry errors and compressing the time required for such a conversion from hours to minutes compared to manual ‘measure and re-enter’ approaches. This entails the use of FloEFD to prepare the geometry for export, perform the conversion using a simple ‘coarse/fine’ slider bar to control the level of abstraction, then export of a .cad2fm file containing the FloMaster sub-system. The .cad2fm file is then imported into FloMaster and saved to the sub-system catalogue for subsequent reuse.


Flownex is able to import data from PDMS and also from Geographical Informatiom Systems (GIS).


Tableau CAD

Hydrosystem has interfaces with following design and analysis software.

Moreover PSRE released in March 2020 an integration system between PASS software (hydrosystem and Start-Prof) and Autodesk Revit. The Revit-PASS integration system allows you to accurately transfer the geometry of the pipeline and attributive information from the BIM design system to the system for calculating the strength and rigidity of pipelines.

Data exchange is implemented through an open format, which makes it possible to divide the roles of users in the project and optimize the organization’s budget by using only the necessary products.

Using the Revit-PASS integration system will allow design organizations to effectively organize the design of industrial facilities due to a significant reduction in the time required for re-entering data. In addition, the use of the integration system when Autodesk Revit and PASS are used together excludes the possibility of errors associated with manual data entry into the calculation model.

The video above was done with Start-Prof but the link for Hydrosystem is similar.

Exporting data


FloMASTER, long considered one of the most accurate tools for water hammer analysis has introduced the ability to automatically calculate and easily export this data as a time history plot to the industry leading pipe stress analysis tools. 

You may now export a hydrodynamic force time history plot for use in Intergraph CAESAR II.


Flownex adds value to structural simulations and can be used to transfer 1D flow results to a FEA simulation package such as ANSYS Mechanical.

The ANSYS Mechanical coupling finds application in many industries. An example of the ANSYS Mechanical coupling in the power generation industry is illustrated below.

It shows a model of a boiler where the flows are calculated using Flownex and the thermal stresses are calculated using ANSYS Mechanical. Using this analysis technique, start-up conditions can be simulated in a transient environment and boiler design can be modified to ensure the stresses are all within allowable limits before construction begins.

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Network modelled in Flownex

Flownex can also calculate pressure forces on elbows and pipes: these can be used as an input to mechanical design for the calculation of pressure stress analyses and frequency analyses based on pressure signal (using Fast Fourier Transform).

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Flownex and ANSYS Mechanical – Thermal Stresses


Hydrosystem is of course linked to the other main software from the PASS suite : start-prof.

Start-Prof provides comprehensive pipe stress, flexibility, stability, and fatigue strength analysis with related sizing calculations according to international and national codes and standards. First introduced in 1965, it combines a highly efficient solver, powerful analysis features, a user friendly GUI, an intuitive 3D graphical pre/post-processor, and a detailed help system with embedded intelligence from generations of piping design experts.

It can be used to simulate stress behaviour from hydrosystem results like in the waterhammer example below.

Co-simulation 1D-3D

One dimensional (1D) CFD allows engineers to understand how flow rates and pressures may change within a network flow system of interconnected components. In contrast, three dimensional (3D) CFD allows design engineer to understand how detailed flows interact with all manner of complex geometry. Of course, 1D calculations are much faster, only a few minutes, when 3D CFD may take hours or days.

Co-simulation of a 1D with a 3D model will potentially offer the best of both worlds. It enables the sharing of boundary data between 1D and 3D models in a single or multi-domain system to facilitate the simulation of the overall fluid system coupled with more detailed CFD simulation of 3D flows within a critical part of the network.

Today, two 1D leaders are offering 1D-3D co-simulation: FloMaster (the former Flowmaster) and Flownex.


The approach used by Simcenter FloMaster and Simcenter FloEFD is different than past approached as it does not require a middleware program to manage the passing of data between programs and sequencing time steps. On the contrary, the tools share a common solver matrix and both models are solved simultaneously. This provides simulation efficiencies throughout the process by reducing the time to set up the co-simulation, reduced data handling and simpler post processing.

For the first time in the industry, Mentor Graphics was providing a tightly coupled general-purpose 1D-3D CFD simulation software combination. With this combination, engineers can characterize the more complex elements of the system with full 3D and easily insert those models into the 1D system level model for simulation.

FloEFD Concurrent CFD can reduce simulation time by as much as 65–75% in comparison to traditional CFD tools. Concurrent CFD enables design engineers to optimize product performance and reliability while reducing physical prototyping and development costs without time or material penalties.

And because FloMaster offers a fast and reliable solution to 1D flow problems, designers can expect unrivalled savings in both time and process compression.

Mentor Graphics 1D-3D solution provides an opportunity to increase digital prototyping information earlier in the product development process. This kind of analysis performed upfront accelerates design and development cycles by orders of magnitude and optimizes product design workflows. It increases engineer and designer productivity and minimizes design risk and re-spins.

This 1D-3D combination provides the best of both worlds, thus reducing time to get essential component information to system engineers and improving system-level accuracy with highly complex geometries, thus reducing the design cycle time.

Simulation Based Characterization is a methodology that enables complex multi arm geometries to be characterized using the power of 3D Computational Fluid Dynamics. FloEFD is used to perform the 3D characterization in a mechanical cad environment using a (computational) design of experiments and response approach to extract hydrodynamic and thermal response surface models that are then imported into FloMaster and represented with an ‘N-Arm’ component.

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The Simulation Based Characterization from Mentor Graphics

OneSim is a tightly coupled co-simulation workflow that enables a 3D FloEFD model to be considered as part of a FloMaster system simulation. First, one or more FloEFD boundary conditions are linked to nodes within a FloMaster network. Then a simulation instigated from within FloMaster will solve both the FloEFD model and the FloMaster network concurrently, until steady state or transient convergence is achieved. Flow rates, pressures and fluid temperatures will be communicated through the linked boundary conditions nodes throughout the solution process. An implicit coupling technology is used to enable solutions to be achieved more readily compared to more classic co-simulation approaches that can be prone to instabilities, often requiring middleware to govern the solver communication and can be notoriously tricky to set-up.

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The Onesim tool from Mentor Graphics

It was easier to combine those technologies in the SimCenter as now Mentor Graphics (presently a Siemens Business) was owner of the 1D and 3D software.


On the other side, Flownex made the choice to collaborate with ANSYS and decided to integrate their 1D system tool to the workbench environment.

Flownex is linked to both ANSYS CFD and FEA codes for more localized results where required.

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1D and 3D flows are solved together, and information is exchanged at the boundaries. The entire simulation is controlled by Flownex interface

In particular Flownex can be coupled with ANSYS Fluent to provide an interactive communication between a CFD 1D system and CFD 3D analyses. This allows the inclusion of the effect 3D complex geometries in terms of pressure losses, multiphase flows and non-homogenous heat transfer.

Flownex can also be coupled with the FEA code ANSYS Mechanical: thermal and pressure stress analyses can be performed starting from the temperature and pressure calculated by Flownex. Co-simulations between 1D network and FEA 3D code can be used to model conjugate heat transfer with 3D geometries: this approach keep the accuracy of temperature distribution in the solid domain and reduce the computational effort on the fluid side.

One application of the coupling with ANSYS Fluent can be illustrated in the simulation of the HVAC system in a server room. In this case Flownex is used to simulate the fan, heat exchanger and ducting to the server room while ANSYS Fluent is used to simulate the heating of the air by the electronics and the air flow in the room.

The interface points are chosen at the vents that supply air to the room, where the temperature and flow results from Flownex are transferred to Fluent and the backpressure results from ANSYS Fluent are returned back to Flownex. In this simulation, control elements are added to automatically adjust the fan speed and the vent openings in order to study the transient scenario of the system.

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Flownex and ANSYS Fluent link – HVAC system in a server room

Each situation is different

The needs of your company are not necessarily the same as another society, they may also have changed with years.

Do not hesitate to contact Fluids & Co to have a personalized study of your project.


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