SIMA Shipbuilders Use ALGOR FEA to Design Dredging Barge
for NATURAL GAS LIQUIDS Pipeline
When undersea piping was needed to complete a South American
pipeline project that traverses the Amazon jungle and the Andes Mountains to
the Pacific coast, ALGOR finite element analysis (FEA) software was chosen
to help get the job done quickly and economically. The pipeline originated
in the Camisea fields of eastern Peru, which are among the world's largest
natural gas (NG) reserves, holding approximately 11 trillion cubic feet of
NG and 600 million barrels of associated natural gas liquids (NGL).1
To access these reserves, a $500-million (USD) project was led by Pluspetrol
Peru Corporation S.A. (Pluspetrol) that included construction of two
pipelines – one for NG (714 km) and the other for NGL (540 km). As
construction of the pipelines neared completion, work focused on endpoints
such as the fractionation plant in Pisco, where NGL would be processed into
commercial products including propane, butane and condensates.
The Leyla barge was designed and manufactured at the SIMA shipyard in Callao, Peru (upper left). As shown in the map, two pipelines, one for natural gas and the other for natural gas liquids, run from the Camisea fields in eastern Peru, one of the world's largest resources of natural gas, to the Pacific coast of Loberia. There, undersea piping was installed (lower left) to transport products made from natural gas liquids at the Pisco fractionation plant to a marine platform (lower right) for export on ships. (Pipeline photographs courtesy of Pluspetrol Peru Corporation.)
Servicios Industriales de la Marina (SIMA Peru S.A.), a
state-owned corporation and shipyard serving the Peruvian Navy, was
commissioned by Pluspetrol to build a steel barge that could carry a 180-ton
excavator and related equipment for digging a sub-sea piping canal in Pisco
Bay. SIMA used ALGOR FEA software to verify the barge and meet the
challenging design and fabrication schedule. "With ALGOR, we designed a
safe barge requiring less steel than had been originally quoted and approved
by the customer," said Eddy Cordova, SIMA structural projects chief
designer. "We were able to deliver a fabrication drawing of the barge's
spud legs to our shop less than one month after obtaining ALGOR software.
All fabrication drawings were delivered in less than two months and the
manufactured barge was delivered to the customer within four months."
The canal was dug, the piping installed and the Pisco plant is now
transporting NGL products through the sub-sea piping to a loading platform
for export on ships.
Applying FEA to Ship Design
SIMA has a long history tracing back to 1845 with the
founding of the Bellavista Naval Factory, the first in South America. Today,
SIMA has three shipyards and a labor force of 1,200 for shipbuilding and
repairs, steelwork, electronic systems and safety and defense. "We had
been modeling our designs with Mechanical Desktop and AutoCAD, but without
FEA," said Cordova. "We decided to get FEA software because it
would allow us to quote and design new projects faster, optimize our
existing designs and design steel structures of less weight compared to
previous manual designs."
After comparing available FEA packages, SIMA chose ALGOR.
"We chose ALGOR over NASTRAN because of confidence in ALGOR's meshing
capabilities and over SAP2000 because ALGOR's expansive analysis
capabilities were better suited for our range of applications," said
Cordova.
The general barge structure was modeled and analyzed with ALGOR for linear static stress and critical buckling load, which verified that the design would withstand the specified loads. Load conditions included the weight of the excavator and other equipment, wind and ocean waves. SIMA engineers tested several variations and determined the optimal thickness of plates, which reduced the amount of steel required for manufacturing. Additionally, several components in high-load zones were modeled and analyzed separately including the spud helmet, bulkheads and spud leg structure.
Due to the tight schedule of the barge project, the FEA
software had to be easy to learn. Cordova quickly learned to use ALGOR
through keystroke-specific tutorials, two Spanish-language distance-learning
courses, online documentation and customer service. "I had used ALGOR
several years ago," said Cordova. "With ALGOR's latest FEMPRO user
interface, the current version is even easier to use."
Engineering Considerations
The barge, named Leyla, was designed and manufactured at the
SIMA shipyard in Callao, Peru. SIMA designed the barge as a steel platform
with three spud legs of hydraulic operation (with independent drive and
lift), similar to an off-shore oil rig. "A spud is a sharp-pointed
vertical post that can be forced by power through a socket or bearing to
anchor a barge or platform into the ocean floor," explained Cordova.
"The three spuds of the Leyla barge, which were 20 meters in length,
provided a self-elevating and stable work platform."
The barge carried a 180-ton Hitachi EX 1800-II excavator.
Cordova said, "The excavator lifted soil from the sea bottom at a
maximum depth of 16 meters and deposited it onto other barges called 'ganguiles'
for transport. All barges used for the project were designed and fabricated
by SIMA."
The primary engineering challenge in designing the Leyla
barge was to ensure it would withstand the high-load operating conditions
expected while in 24/7 service. "The service loads of the excavator as
well as ocean wave surge, wind and weights, including ballast and deck
equipment, were considered," said Cordova. In addition to the
excavator's 180-ton weight, its service loads were calculated at 30 to 66
tons depending on the sea height. The ballast weight was 210 tons and the
deck equipment was 60 tons. The effects of a maximum wind speed of 28 knots
and maximum wave height of 0.7 meters were also considered.
"All of the high-load zones were important," said
Cordova, "but the spud legs were of particular concern because they are
very large and tall structures and had to work 24 hours per day under high
loads." The load on the three spud legs was 340 tons.
Cordova designed the spud legs, spud houses and high-load
zones of the barge. The general structure of the barge was designed by
Domingo Mussio, SIMA engineering department chief. Mechanical and structural
CAD draftsmen Gerson Silva and Eduardo Flores used AutoCAD software to
create shop drawings of the barge and spud legs. The project was overseen by
Victor Pomar Calderon, SIMA Callao chief.
"The general structure of the barge was designed in
compliance with the American Bureau of Shipping: Rules for Building and
Classing Steel Barges," said Cordova. "High-load zones,
including below the excavator, spud legs, spud houses, structural spud
bearings and interior bulkheads of the spud zone, were designed using
allowable stresses from the AISC Manual of Steel Construction."
Simulating the Leyla Barge
SIMA created finite element models of the general barge
structure as well as several components in high-load zones including the
spud helmet, bulkheads and spud leg structure. Linear static stress and
critical buckling load analyses were performed to determine how the design
would withstand the expected loading conditions. "The goals of the
ALGOR analyses were to cut the design cost by making the barge in less time,
ensuring safety and reducing the steel quantity required by optimizing the
design," said Cordova.
The model of the general barge structure consisted of four
parts: the main platform (including the shell plate, deck plate, bottom and
bulkheads), modeled with 8-mm-thick plate elements; supports, modeled with
truss elements; spud legs, modeled with beam elements; and spud helmets,
modeled with truss elements and used to apply loads to the spud legs.
"We used beam elements to model the spud legs in order to get the
maximum normal forces and bending moments," said Cordova.
One complicating factor in modeling the spud legs concerned
the constraints. "Not all of the spuds' bearing points work
simultaneously," explained Cordova. "If all three spuds are driven
into the sea bottom, then the boundary conditions in the three bearing
points are pinned -- Tx, Ty and Tz constrained. However, there is the
possibility of one of them slipping horizontally over a rock or stone on the
ocean bottom. In this case, only two spuds would be pinned and the third
would have only vertical translation constrained."
Static stress analyses with linear material models were
performed for several different load combinations and constraints, which
varied the number of spuds pinned, the excavator position, the wave
position, the sea height and the wind direction. "In this simulation,
the most important results were the beam and truss stresses and
deflections," said Cordova. "We determined the critical load
combination and found that we could reduce the spud plate thickness from 19
to 12.5 millimeters for 9.0 meters of the spud length while maintaining
structural integrity. This significantly reduced the amount of steel
required to manufacture the spud legs."
The detailed model of the spud leg structure was then
modeled with 12.5-mm-thick plate elements and included transversal
stiffeners (or diaphragms), which were omitted from the general structure
model. A critical buckling load analysis was performed, which verified that
the spud leg would not buckle.
"The ALGOR models of the spud legs, spud boxes, spud
houses and the high-load zones below the excavator were used for fabrication
drawings," said Cordova. "This challenge could not have been met
on time without ALGOR finite element software. Using ALGOR FEA allowed us to
design the high-load zones of the barge very fast and analyze different load
combinations, which gave us a better understanding of the structure's real
behavior during operation. This helped us to improve the design by getting
structures that weighed less, such as the spud legs. Without ALGOR FEA
software, designing and fabricating the barge would have taken more time and
material."
Lessons Learned and Future Applications
Cordova revealed, "I learned many things from using FEA
on the Leyla barge project. For example, I learned how the behavior of a
structure can vary regarding loads and constraints. It's necessary to
understand the physical-mechanical phenomenon that controls the model in
order to apply the correct loads and constraints. This software is a
powerful tool, but it does not replace engineering knowledge."
The SIMA team that designed and analyzed the Leyla barge included (top) naval captain Víctor Pomar Calderon, SIMA Callao chief; Domingo Mussio, engineering department chief; and Eddy Cordova, structural projects chief designer.
Cordova concluded, "We plan to use ALGOR FEA for future
projects such as steel bridges, pressure vessels, fishing vessels, barges
and mechanical components."
Eddy Cordova is a structural projects chief designer with
SIMA Peru S.A. in Callao, Peru. He earned a bachelor degree in Mechanical
Engineering at Pontificia Universidad Catolica del Peru.
