This article provides background information on transient force in Bentley HAMMER
Note: for background information on Transient Force calculations, see the section further below.
By default, HAMMER does not calculate force results, but you can set up the model to run these calculations. To do this, go to Analysis > Calculation Options and double-click the active Transient Calculation Option to view the properties. In the properties, find the attribute "Calculation Transient Force?" and set this to True.
Once this is done, compute the model.
There a couple of different ways to view the results. First, under the Time Histories tab of the Transient Results Viewer, you can choose "Force X", "Force Y", "Force Z" "Force Magnitude", or "Force X, Y, Z and Magnitude" as the "Graph type". Select the end point where you would like to see the force results, then click "Plot".
*For more information on how the forces are calculated please see this wiki technote.
In addition, you can see the magnitude of the force, as well as the force in the x, y, and z directions at each node in the model by viewing the Transient Output Log (Report > Transient Analysis Reports > Transient Analysis Output Log). Search for the section "Maximum Forces at Every Node" for the data. This will list the maximum force for each node and the time that the maximum force occurred.
To understand the meaning of the X/Y/Z force values (fx, fy, fz), think of the model plan view, or the top-down view. Think of the node in question as the 0,0 origin of a standard graph, with the X axis extending to the right and the Y axis extending up. The "X" force would be the force exerted from left to right. So, a negative value would mean a force exerted towards the left of the node. The "Y" force would be the force from down to up. So, a negative value for Y would mean a force exerted down. The Z force would be the force in the Z direction - perpendicular to the plane of the graph. So, a negative Z force would mean a force exerted toward the ground.
These X/Y/Z values are useful when determining required bracings (thrust blocks, restraints, etc) since it gives you the force for the important 3 directions, when the total (resultant) was at it's maximum.
Note: HAMMER models can be exported to an i-model (File > Export > Publish i-model). This file can then be opened in MicroStation to see a 3-D representation of the system, along with results that are available in the Properties dialog. Starting with HAMMER V8i SELECTseries 5, the user can also export to a Map Mobile i-model to view the system on handheld devices or tablets.
Note: A scaled model is the best way to ensure least errors in calculation of transient forces. This is because the calculation relies on the angle between connecting pipes in plan view. A scaled model can be prepared either by manually tracing a network with the help of a background file or a Bing Map or building it from external data using ModelBuilder. However, in case this is not possible or you have a schematic network in place with actual lengths between nodes input as user defined lengths; the angles between the connecting pipes should be the same as they are on field. This can be done by comparing the schematic model with your actual layout and manually adjusting the pipes to ensure the angle between them is the same. Another option is to work in an CAD integrated environment such as AutoCAD or MicroStation where you can measure and set the angle between pipes as per your field layout.
In determining the pipe direction, only pipe start and stop node coordinates (X, Y and elevation Z) are used. The bending points (vertices) in the drawing of a pipe are ignored. You will need to place junctions (or another node element) at the vertex.
You may wonder if the transient force calculations in HAMMER account for balancing effects of opposing pipe bends.
HAMMER doesn't show net forces on a pipeline; it just shows the forces at individual nodes. If you add the net forces on individual nodes, you might find they balance out at certain times during a simulation, but HAMMER doesn't attempt to show that. In order to do that properly, HAMMER would need to be augmented with numerous other components (like pipe supports, hangers, anchor blocks, etc.) and it would end up looking more like AutoPIPE (see link below).
Note: An Enhancement (#958426) has been filed to export transient force results to AutoPIPE acceptable format (.TIH and .THL) files
Additional explanation of force calculations in HAMMER is found in the Help documentation under Contents > Modeling Capabilities > Hydraulic Transient Pressure Analysis > Analysis of Transient Forces and also under Contents > Bentley HAMMER V8i Theory and Practice > Transient Forces.
The z force for my model appears unusually large. Why?
"Fluid Transient" - AutoPIPE Load Case
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