engineers to better simulate and evaluate how a multiphase
pump design performs in context, when given a gas volume
fraction (GVF) load, requirements for total pumping head
versus volumetric flow rate for best efficiency point, and
even on specific reservoir locations with their unique inlet
In thermo-fluid applications it is known that 3-D CFD
simulations can provide detailed insights about fluid and
flow properties in complex 3-D domains. However, from
a systems level perspective, 1-D CFD simulations can give
important information with respect to performance of an
entire system of internal flows. The drawbacks of the two
simulation methods are that the former requires high computational costs while the latter cannot capture complex
local 3-D features of the flow. Therefore, the two simulation
methods must become complementary; indeed a coupling
of the two methods can incorporate the strongest attributes
of the two methods while minimizing their drawbacks. Here
lies the challenge for subsea applications.
The coupling possibility is not limited to the CFD field
but can extend to multiphysics. An example of multiphysics
one-way coupling is the simulation of vibrations in piping
systems, fluid-structure interactions, (e.g. compressed gas
systems, blow-down systems); this simulation is performed
by modeling the pressure wave propagation inside the
piping system with 1-D modeling and passing the forces
exerted by the internal flow to a structural analysis tool for
mechanical analysis. The interest in multiphysics modeling
with one-way and two-way coupling is of the utmost importance in subsea applications.
For subsea offshore applications, this involves the simula-
tion of all potential subsea equipment that may encompass
what some people have coined, “the subsea factory.” The
dynamic response modeling of an entire subsea produc-
tion factory would allow the placement of various installa-
tions such as trees, manifolds, separation systems, single
phase and multiphase boosting pumps and compressors in
strategic locations where parasitic losses due to pressure
drops, in piping systems such as jumpers, can be mini-
mized while maximizing the safe and reliable production
of valuable hydrocarbons.
Figure 8 shows a schematic of a two-point coupling
model. In the two-point coupling model the outlet of the upstream is modeled using 1-D physics, which then is coupled
with the inlet to the 3-D modeled bend, using a CFD tool,
and the outlet of the bend is coupled with the inlet of the
downstream section of pipe, again modeled using 1d physics.
Thus, a coupling of the 1-D horizontal and vertical pipe sections with the 3-D modeled elbow is achieved and analyzed.
As shown in Figure 9, the combination of coupling 3-D
to 1-D modeling gave reasonable prediction of the flow field
and thus, the forces acting on the bend induced by the fluid.
This coupling technique allows for decreased computational
needs while increasing the speed for the analysis.
In summary, while technical challenges still exist with re- spect to developing more accurate models, whether fluid,
structural, acoustic, magnetic or multiphase flow models for
boosting pumps, for subsea applications, the concept of using analysis led design methods in the up-front engineering
phase has been well proven in many industries. The challenge still lies in gaining its acceptance as a routine practice
for offshore and onshore applications to increase engineering efficiency. n
Ed Marotta achieved his B.S. degree in
chemistry from the State University of New
York at Albany, 1980, post-graduate studies
in chemical engineering at SUNY at Buffalo,
1982, and his MS and PhD degree in
mechanical engineering from Texas A&M University in
1994 and 1997, respectively.
Ed’s present responsibilities involve the management
of the Multi-Physics Simulations Group for GE Oil & Gas -
ATO. In this capacity, Ed is responsible for leading a group
of engineering specialists responsible for performing
thermal, diffusion, and multiphysics analyses on all major
systems and sub-system components, development of
thermal best practices for multiphysics analyses specific
to GE products. In addition, Ed is responsible for the
development of low-dimensional, lower-order tools for
integration and integrity management of subsea systems.
ABOUT THE AUTHOR
FIGURE 9 (Left)
Velocity profile on
the horizontal cross
section of the bend.