Applies To Product(s): PULS Version(s): XM & V8i Environment: N/A Area: modeling Subarea: Original Author: Bentley Technical Support Group Comments, Questions, and Answers about modeling with Bentley PULS Items #1: **Attention** Please see the following AutoPIPE help section, Help Tutorial This help has been provided in order to give users ideas for modeling typical piping arrangements. The steps shown in each example should not be taken as the only method available to create models. In addition, the intent of the examples is to present ways to create adequate models for analytically purposes. Tutorial #1 : Acoustic Mode Shapes The purpose of this tutorial is to introduce the basic operations of the PULS application. The tutorial will show you how to produce acoustic mode shapes of a simple system. It will walk you through the various steps in model building. You will define the piping system by specifying system geometry, fluid properties and boundary conditions. You will learn how to view and print your results. Tutorial #2 : Modeling a Reciprocating Compressor The purpose of this tutorial is to introduce the basic operations of PULS to model a reciprocating compressor system. This tutorial assumes that you have not completed Tutorial 1, therefore, some of the information may be repeated. Item #2: The following model files are included with PULS : 2CYL.LP1 - TWO CYLINDER COMPRESSOR EXAMPLE COOLER.LP1 - GAS COOLER EX-BOT.LP1 - SUCTION BOTTLES AND COMPRESSOR EX-SUCT.LP1 - SUCTION SYSTEM METER.LP1 - METER RUN : Globe Valve Source PISTON.LP1 - Piston (Volume Velocity) source.VS = 0.01 m3/sec, Natural gas/ sound speed = 494 m/sec PRESURE.LP1 - Press source for a branch system., PS = 10 kPa, Natural gas, sound speed = 494 m/sec PUMPFIX.LP1 - PULS models involving a reciprocating triplex pump PUMPSUC.LP1 - PULS models involving a reciprocating triplex pump RECIPP. LP1 - RECIPROCATING COMPRESSOR EXAMPLE T1. LP1 - Pulsation Source: T1 - Mode 1 T1-1. LP1 - Pulsation Source: T1 - Mode 1 Items #3: We would like to know if PULS (Option 3) is suitable for modelling the shaking forces in dead-leg side branches from vortices generated by a corrugated pipe with flow. We already know the amount of energy and flow conditions which the vortices generate in the corrugated pipe, so PULS does not need to calculate them. We just need a way of putting in an energy source in the (e.g. middle of the corrugated pipe). We have considered using a suitably scaled velocity source or pressure source, but both of these would impose reflective boundary conditions (like an open or closed end) which do not exist in reality. Is there a way of modelling this in PULS? Answer: Suggest to try and insert a tee point on the tee branch very close to tee point. The length would be short and you would add a velocity source there. They can scale the source to give a known pulsation at the dead end if known. Item #4: When I try to adjacent flow directions, I mess the pulsation, and when I go to adjust the pulsation, it messes the flow direction. Have been doing that for the last hour. Is there anyway to avoid this interactions ? Answer: These should not interact usually. Send model for review. Item #5: If I have two nodes which I would to turn them into one, what do I need to do to equate them? Answer: Delete the element joining them and then you update one element and change the node number to be same as other node. Item #6: Does adding a Volume element have the same acoustic effects as adding an enlarged pipe say that is having the same volume? Answer : Not exactly. The pipe element has a length and hence it has some possible frequencies. But these may be ignored since they are usually high, but not always. It is more accurate to model using lengths since most vessels or passages have lengths. Item #7: Could you provide some instruction on how to make liquid pump model and check it? could PULS support liquid's model building and checking? Answer: PULS does not have a centrifugal pump. If you have to model it I would use a pipe or reducer or something to simulate volume or length. Noise cannot be simulated from centrifugal pump. If you have to, you may try a velocity source at a dead end near the pump. You may create a fictitious short branch and add a velocity source at the dead end. For reciprocating pump you can choose the recip boundary condition and works the same way as recip compressor. We have two pump examples pumpsuc and pumpfix and they are documented in the comparison to experiment and on chapter on liquid modeling in the PDF manual. Item #8: Adding side streams - single system with multiple gas compositions Answer : Please see the following procedure: 1. Select Tools options change fluid to "user defined". 2. Make a selection of piping 3. Press Modify++ properties over range fluid enter a new fluid property or select an existing one from the list provided. Item #9: Designing multi-chambered bottles: Answer : See attached image for modeling a muffler with a choke tube. As you already know, bottles can be modeled as a combination of pipe, two-port, and three-port elements. In addition, you can also use a half-pipe or half-vessel(e.g., for the internals of a pulsation bottle). Suggest to model the multi-chambered bottle as designed with components mentioned above, you may need to add a small amount of length to some components to be modeled correctly. See example model C:\Bentley\PULS XM\Project\ EX-BOT for additional suggestions. Item #10: When there are multiple compressors in a single acting condition. If you choose closed for the single acting side (head end or crank end) you must also have a value for the flow. When the machine is single acting, there is no flow through one side of cylinder. So, do you leave the single acting head end selected as unloaded when the corresponding crank end side is selected as closed? Answer: When a double acting compressor is in a single acting mode, one side is unloaded while the other is loaded. Unloaded for discharge is equivalent to closed. Unloading in suction is a very severe scenario and it is full sinusoidal piston motion with no flow. The flow comes from the loaded end. If compressor is a single acting compressor, then it has one end and you would set it either loaded or closed. Bentley technical support does not have any example models. However, the closest t that are the muffler models in the comparison to experiments in the online help. Item 11: Does the program model reciprocating pump / compressors? What about multi-cylinder and multi-pump/compressor scenarios? Answer: Puls can Handle Centrifugal and Reciprocating Compressors, Reciprocating Pumps, or the ability to accommodate a Pressure or Velocity source. Multi cylinders are handled nicely using phase angles between cylinders. For multi-compressor units, each unit is analyzed separately assuming the others closed or inactive. User then has to combine the responses manually for the most conservative response since phase angles are unknown. Since this approach is time consuming, many assume all compressors are in phase initially and they may evaluate phase information for just a few critical points. See the example in the online help and additional information here: https://communities.bentley.com/products/pipe_stress_analysis/m/pipe_stress_analysis_gallery/269624.aspx Item #12: In the online help, Valve Delay, but there is no way to enter this value in Puls dialog. Answer: The Valve delay option is on the Recip Pump dialog (see below). However it is only available for systems with Liquid contents and NOT gas contents. Item #13: How to distinguish single acting and double acting cylinder in Puls? Answer: See online help, search for "acting": and select the "Theory" topic: For detailed pump modeling, PULS assumes each cylinder has a head end valve for single acting and a head end valve and a crank end valve for double acting cylinders. For the simpler pump nozzle model, you can enter the pump type, such as triplex as described later in this section. In this case, the pump detail passages are not necessary and the cylinder number refers to the unit number, since every boundary condition can have up to nine single acting cylinders. See Also Bentley AutoPIPE External Links Bentley Technical Support KnowledgeBase Bentley LEARN Server Comments or Corrections? Bentley's Technical Support Group requests that you please submit any comments you have on this Wiki article to the "Comments" area below. THANK YOU!
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