Impulse Features

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AFT- Impulse
Fluid Hammer & Transient Flow Analysis for Incompressible Network Piping Systems

Impulse evaluates transient and water hammer events, caused by pump trips, sudden valve closures and various ESD conditions

SUMMARY
FEATURES

 

FEATURES

AFT Impulse provides a practical tool for the piping systems engineer to address the complex subject of liquid piping systems waterhammer and surge transient events. AFT Impulse incorporates an integral steady-state solver to calculate the initial conditions and seamlessly transfer these to the transient solver. Based on the same, proven solver in AFT Fathom, steady-state solutions are determined using a modified Newton-Raphson matrix interation. AFT Impulse's transient flow solution engine is based on the Method of Characteristics, which utilizes time steps and pipe section lengths that are an integral fraction of the wave speed. This permits a direct solution of each time step, making AFT Impulse highly efficient.

AFT Impulse lets you specify transients both on a time and event basis. For example, initiate a pump startup based on the pressure at a selected location in the system or a valve closure upon the flow direction at selected location. This powerful capability greatly expands the type of transients that may be modeled including a variety of control logic functions.

Pump modeling can be as simple as a fixed flow or as sophisticated as pump curves and four quadrant effects modeling the various possible combinations of forward and reverse flow and rotation. Startup includes the ability to determine pump acceleration from specified pump/driver inertia and driver torque vs speed. Pump models may include integral check valves and reverse rotation brakes.

Impulse also provides the ability to generate Force-Time files for direct import into CAESAR II, Intergraph's world-leading pipe stress analysis software.

The following outline will provide you an overview of AFT Impulse's interface and capabilities. For a first hand demonstration, ask us for a free, working demo version of AFT Impulse.


The Workspace
AFT Impulse models are built in a graphical environment, displaying the model in a familiar schematic format. AFT Impulse models contain two constructs, pipes and junctions. Junction types included are:
  • Reservoir (up to 25 pipes may be connected, transient level)
  • Branch (up to 25 pipes may be connected to each)
  • Pump (assigned flow or pump curve, transient speed, four quadrant modeling, pump trip & startup)
  • Assigned flow (transient in/out flow)
  • Assigned pressure (transient pressure)
  • Stop valve (valve closure/opening)
  • One way valve (check valve function)
  • Tee/Wye (utilizes Idelchik & Miller loss modeling)
  • Area change
  • Relief valve (end of line or inline, variable Cv vs deltaP)
  • Control valve (pressure & flow, transient setpoint)
  • Gas accumulator (user specified volume, gas constant & connecting pipe)
  • Liquid accumulator (user specified volume, elasticity & connecting pipes)
  • Surge tank (constant or variable cross section vs height)
  • Spray discharge (single or multiple nozzles, transient Cd)
  • Vacuum breaker valve (models vacuum breaker, gas release or both)
  • Dead end
  • Volume Balance (model interface of two different fluids)
  • General component (user defined component)

An AFT Impulse model is 'assembled' by dragging the junctions to be included onto the Workspace and connecting them with pipes (this can be done in any order and pipes and junctions can be added and deleted at any time). The resulting system schematic clearly displays the connective relationship between system components and pipe runs in the same way traditional schematics and diagrams do.

Model Data
The Model Data window provides a tabular listing of the input data. This is a great aid for some types of input review. For example, knowing that your pipe lengths are the range of a few feet to several tens or hundreds of feet, a scan down the pipe length column will quickly reveal an input value with an extra digit or two or a length unit mistakenly specified as miles instead of feet.

Double-clicking on an item within the Model Data window opens its Specifications window for editing.

Pipe Sectioning
As the Method of Characteristics divides pipes into section lengths that are an integral fraction of wave speed, and modeled pipe length is segment length times the number of segments, there is inherently an approximation in the modeled pipe lengths. The smaller the section lengths and time steps used, the closer this Fundamental to the Method of Characteristics used for modeling is the division of pipes into an integral number of segments with a time step duration related to this segment length by the wave speed (speed of sound through the fluid). Since, in most cases, there are a number of different pipes lengths in a system and, usually, no one segment length will integrally divide into all pipes, modeled pipe lengths will approximate the actual length of some of the pipes. Smaller segment lengths result in a more accurate approximation but result in a longer analysis run time. A traditionally laborious aspect of the Method of Characteristics is analyzing the trade-off between smaller pipe segments and the required run time.

AFT Impulse's Pipe Sectioning greatly simplifies this task. The user specifies a range of mininimum and maximum number of pipe segments to be considered and maximum length approximation error, and AFT Impulse will calculate and display the available pipe sectioning schemes that meet these requirements.

Scenario Manager
A powerful aspect of modeling software is the ability to change the system and study the effects - 'what if'. AFT Fathom's Scenario Manager raises this 'what if' capability to new levels by, first, allowing the user to define variations of a model and save them within one model file and two, automatically keeping common attributes between scenarios synchronized.

Scenarios may vary by almost modeling parameters; pipe sizes, fluids, pump curves, valve settings, indeed, scenarios may differ by the elements present. For example, a variante of a model may have an additional branch or loop than its 'parent'.

Changes in higher order scenarios are automatically passed downward to their 'children' for the parameters that are linked. Consider, for example, having a base scenario with several variants each with different pump curves. To change, say, the size of the pump discharge line on all variants, the Base can is selected, the change made and automatically passed to the 'children', both saving time and ensuring the variants remain synchronized in their common attributes.

Output Window
A tabular display of calculated results, the Output window is organized into General, Pipes and Junctions sections, which can be displayed all at once or individually. In addition to general information regarding the model and analysis, the General Section provides tabs with specifically formatted output for valves, pumps and other specialized system components as well as a summary of when various events occurred. The Pipes section displays initial steady-state data, transient max/min by pipe and transient output data for each pipe segment at each time step. The Junctions section provides summary output for all junctions along with tabs for each type of junction present in the model and transient junction data for each time step. Design alerts may be specified that will automatically highlight output values outside of the specified range for flow, pressure or velocity.

Output format, units and which items are displayed in the output are readily selected through Output Control, and may be changed without requiring re-running the analysis. Output Window results may be exported to a file for incorporation into post processing calculations, such as forces exerted on pipe supports.

Graph Results
Graphs of a wide variety of output data may be readily generated using Graph Results. Flows, pressures, velocities, and more, may be plotted vs. time. Both instaneous flow and integrated flow plots are supported. Graph formatting may be customized by the user.

Animated graphs dynamically display results (pressure, flow, velocity, etc.) vs time for one or multiple flow paths providing valuable insight into the dynamic response of your piping system.

Fluid Properties
Fluids may be chosen from the standard AFT Fathom database of 9 fluids, user specified or from the optional Chempak Property Database add-in. With the Chempak add-in almost 700 fluids are available as well as the ability to assemble non-reacting mixtures. Non-Newtonian fluid modeling is supported using Bingham Plastic, Power Law and paper stock viscosity models.
Customization
AFT Impulse provides extensive customization features including:
  • Workspace appearance (colors, line widths, fonts, junction sizes and appearance, location of pipe numbers and names, notation and more are all user selectable.
  • Fluid, Component, Material and Insulation Databases - AFT Impulse comes standard with a database of 9 fluids and engineering data for eight commonly used piping and tubing materials ranging from steel to cast iron, copper and PVC pipe. Additional fluids and pipe materials may be readily added to these standard databases along with and type of component modeled as a junction. Specified a pump that you will use again? Click on 'Add Component to Database' and it's readily available from a drop down list. In fact, you can easily compile catalogs of pumps, valves, heat exchangers...virtually any kind of piping component to be quickly and easily selected within AFT Fathom. Better yet, database files can be shared either by copying between stand alone computers or across a network. Selecting which databases are used in a particular model, creating new databases and modifying existing ones is easily handled through the Database Manager.
Additional Losses
In addition to modeling fittings and valves as junctions, loss values for these components may be directly included in the pipe through Additional Losses. Loss values may be directly specified or you may select from the comprehensive database including data from a variety of standard references for over 500 commonly used fittings and valves.
System Requirements
Windows 95 and higher or NT 4.0 and higher
64 MB RAM minimum
800x600 display minimum
Stand-alone or network

 

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