
	Applies To

	Product(s):	AutoPIPE,
	Version(s):	2004, XM, & V8i
	Environment:	N/A
	Area:
	Subarea:
	Original Author:	Bentley Technical Support Group

The Load/Wave command enables the user to model the effect of ocean waves impacting a partially submerged piping system.

The Wave command uses static analysis to model hydrodynamic effects. A given static analysis computes the response of the structure to a static load representing the force distribution at a given instant of the wave loading cycle (defined by the phase angle, q). Thus, a series of these instantaneous static analyses can be used to trace out the system response over the entire wave cycle.

AutoPIPE does not print any calculated wave results. Internally, the wave results are converted as loads on the piping.
AutoPIPE modeling suspended piping from from vessel, platform, or buoyancy modules should be limited to vertical riserr as a snakeing catenary shape as seen below cannot be modeled in AutoPIPE.
In AutoPIPE buoyancy weight is applied in GR case. It has both longitudinal and transverse components. When the pipe is vertical, difference in pressure cap forces is the same as buoyancy load and the transverse buoyancy is zero. When the pipe is horizontal, the cap forces from external hydrostatic load adds longitudinal stress and associated movements in addition to non zero transverse (vertical) buoyancy load.
Waves forces are applied at bend nodes (near, far and if present a mid point).
Qestion: It appears that AutoPipe can only input one drag and inertia coefficient per wave. Is there a way to enter multiple drag and inertia coefficients for different size pipes?
Answer: Yes, use can Insert> Xtra data> Hydrodynamic data for each point or selected range.
Wave loading beyond water depth:
When a user defined current profile (depth - 0 to 115 ft , for example) does not cover the entire range of submerged pipe (Water elevation to Depth: 0 to 270 ft ) AutoPIPE extrapolates the current velocity as explained below.
In the above instance, for depths between 115-270 ft, index is set to 5 and the following equations are usedV=VCUR_index+DVWhere, DV=(DCUR_index-DFP) ((VCUR_(index-1)-VCUR_index )) / ((DCUR_index-DCUR_(index-1)) ) …..(i.e. difference in depth x slope)
DCUR - current depth from table (DCUR4 = 75 ft, for example)
VCUR - current velocity from table (VCUR5 = 1500 ft/s, for example)
DFP - depth of the point below 115 ft
Index - index of the table. When DFP > DCUR5, AutoPIPE sets index = 5This set of equations creates a linearly varying velocity profile for depths below 115 ft:
If decreasing velocity was defined between index 4 & 5 i.e. depth 75 & 115 ft, then this profile would've been linearly decreasing below 115 ft. Note that it may not necessarily reach 0 at depth of ocean bed. The affects wave force calculation has not yet been investigated to see any affects.
Question: How many nodes do we need to put on the pipeline in order to simulate the hydrodynamic forces same as while we are defining the CD and CM in the wave load interface (from Wave/Load)?
Answer: One approach, duplicated the same number of node points per span equal to the number of mass points per span calculated by AutoPIPE.
Question: Since the wave load interface doesn't have the space that we can input the lift coefficient, how can we define the lift coefficient if we don't want to use the function defined in "Insert> Xtra Data> Hydrodynamic data"?
Answer: The Lift coefficient for all points is assumed zero unless identified by Insert> Xtra Data>Hydrodynamic Data.
Question: Are there any sample models for incorporating wave loading imposed displacements?
Answer: In the Advanced training we have 2 models showing imposed wave displacements from the platform.RISER_SEABED_SOIL_2.dat
RISER_SEABED_VSTOPS_1.dat
Question: for wave loading, can you specify the location in the model where the wave phase angle is occurring, or is it just based on the origin?
Answer: Wave loading phase is specified to occur at the model's origin point only.
Question: In AutoPIPE modeling, marine growth thickness are specified under Wave loading, however marine growth density data filling is not indicated anywhere. How to input marine growth density?
Answer: Marine growth is attached to the submerged structure. The marine growth thickness value is used to calculate the effective diameter to be used in force calculations. Marine growth is assumed zero above still water level. Currently, there is no calculation that takes into account the weight of marine growth. However this weight can be accounted for by adding a distributed load over the area of pipe affected. Select Insert and then Distributed Load.
Question: In my model the seabed is used as the global-Y zero coordinate. The water is 185.5m deep, so the water elevation's global y-coordinate is 185500 (in mm) and this is the value entered in the buoyancy data table. In the wave data table the water elevation and depth are both listed as 185500. I am unsure on how to enter the current depths based on this set-up. Is it appropriate to list the current depths relative to the water elevation (i.e. the seabed is 185500 mm below the surface hence its height value would be -185500mm and the surface a value of 0) or relative to the global y coordinates (i.e. the seabed listed as 0, the water surface as 185500mm)?
Answer: With an open AutoPIPE model, select Load> Wave, press the help button, and select the Wave Theory link. Here you will see a picture of the wave parameters. The Water - elevation is the Still Water Level in the image. You would enter the actual vertical global coordinate location (185500 mm). The Depth is measured from the water body surface to the sea/lake bed (this is a positive value, in your case = 185500). The Water depth profile, Enter the water depth relative to the water body surface elevation specified above for the corresponding current and growth data. Again these data points are positive values from the Water elevation.
Question: If an insulation thickness is provided for a member, does AutoPIPE adjust the effective diameter for wind/wave force calculations?
Answer: Yes.
Checked the Stream Function Wave water velocities at the following net link:
http://www.coastal.udel.edu/faculty/rad/streamless.html
Suggest performing an complete review of the wave by adding multiple wave loading with same data but assigning different phase angles U1-U5 = 0,45,90,135,180.
The forces on the pipe are the sum of drag (velocity) and Inertia(acceleration). The chart below is a manually calculated with these values using Airy Wave.
Note: The maximum force due to drag occurred at 0 deg phase angle, while maximum force due to inertia occurred around 90+/- deg phase angle. For this wave, with the given parameters, total max force on the pipe, sum both curves, occurred at approximately 90+/- deg phase angle.
Hydrodynamic factors are only applied to physical points in the model. They are not interpolated for soil and mass points. Only imposed displacements are interpolated and applied to mass points.