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Document Type: FAQ Product(s): Bentley HAMMER Version(s): V8 XM Original Author: Jesse Dringoli, Bentley Technical Support Group
Document Type: FAQ
Product(s): Bentley HAMMER
Version(s): V8 XM
Original Author: Jesse Dringoli, Bentley Technical Support Group
Yes. HAMMER V8 XM uses the same file format as WaterGEMS/CAD V8 XM, so you can directly open the files. All 3 programs conveniently use a .wtg and .wtg.mdb file to store the model data.
HAMMER uses the Method Of Characteristics.
The transient results are viewed in the Transient Results Viewer, located under the Analysis menu. The amount of results included in here is determined by the report period, report points and "generate animation data" settings, under Analysis > Calculation Options > Transient calculation option
The starting conditions of the model before a transient occurs are defined in one of two ways. First, you can invoke the WaterGEMS steady state solver (Analysis > Compute initial conditions) to calculate them for you, based on the demands, boundary conditions and other element attributes. This is the same solver that Bentley WaterCAD and WaterGEMS use. The transient solver then uses the computed flows and hydraulic grades as the starting conditions.
Alternatively, you can define your own starting conditions (flow and head) by choosing "true" for the attribute called "specify initial conditions?" in the transient calculation options (Analysis > Calculation options.) When doing this, the transient solver will no longer use the head/flow computed by the "compute initial conditions", but instead will use the head and flow values that you must enter in, in the "transient (initial)" section of each element's properties. Note that if you want to slightly modify some computed initial conditions, you can copy them over to the user defined initial conditions fields first by using the "copy initial conditions" tool (under the Tools menu) and then alter them as you see fit.
First, enter a number for the "Report period" attribute of an element. This represents how often the results will be saved for. For example, a report period of '10' means that results will be shown at every 10 timesteps. Make sure text reports are enabled in the transient calculation options. Now, when you compute initial conditions, extended results will be displayed, under Report > Transient Analysis Reports > Transient Analysis Detailed Report. Scroll down to the bottom to see a table of data for the element(s) with a report period.
The pressure reducing / pressure sustaining / flow control properties of these valves are only used during the initial conditions calculation. This is because HAMMER assumes that during the transient event, these valves cannot react quickly enough to the changes in flow/pressure. If you are running a long transient simulation and need to model the effects of these valves, you'll need to use an operating rule on the valve to close them.
The deviation mentioned here is based on a percentage, which you can see by the units, under analysis > transient timestep options. Basically, based on the time step, Hammer tries to have a wave be able to travel from one end of the pipe to the other end in even multiples of the time step. Therefore, Hammer will try to adjust the length of the pipe to allow this to happen. By default, if it has to adjust the length more than + or - 50% (the default option at the bottom right of the transient timestep options window), then you get that warning. Basically the best scenario is to have all your pipe lengths the same length, however, that is usually not possible. So you just have to get them close. You can also adjust the time step to be smaller and that usually helps. Or you could possibly ignore the warning if the results make sense and look correct to you - it`s your judgment. You can certainly make some adjustments, go back to the Timesteps, click the update button and see the new max/mean adjustment. You can also change the timestep as previously mentioned and check the new max/mean using the same update button as well as choose between adjusting wave speed or length. Typically this is just a trade-off between accuracy and run time. The smaller you make the timestep, the better the accuracy (less adjustment will need to be made), but the longer the transient run will take to complete.
For more information, see Bentley Technical Support KnowledgeBase.
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