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Wireline view of SPM CALM Buoy modeled in OrcaFlex.

A Suezmax tanker is moored via a hawser.  View list of STA software.

Suezmax tanker seen in shaded perspective view in OrcaFlex, moored to SPM CALM buoy during squall analysis.

The portfolio item below provides a short OrcaFlex Tutorial with a Mooring Analysis example.

The post SPM Squall Analysis appeared first on Stewart Technology Associates.

Example of hydrodynamic analysis at CALM buoy SPM with VLCC tanker moored when a squall, or sudden wind shift, occurs.  The time domain analysis is performed with OrcaFlex and hydrodynamic characteristics (diffraction forces, added mas and radiation damping) are taken from analyses in the frequency domain with MDL Hydro.

Ship hydrodynamic and aerodynamic drag terms are calculated by STA using shallow water effects and OCIMF coefficients.

Published by Stewart Technology Associates on June 20, 2016

View list of STA software.

The portfolio item below provides a short OrcaFlex Tutorial example of Mooring Analysis.

Water can behave in many different ways, depending on the circumstances, and any structure or equipment that is in a marine environment or to be used near the water, must be thoroughly prepared for the forces that will operate on it. These forces are constantly changing and include tidal forces, wave action, undersea currents, high pressures, corrosion and chemical reactions. If a structure or piece of equipment is not designed properly for a marine setting, it could have a significantly reduced lifespan, require increased maintenance and pose a threat to nearby personnel.

Industry personnel can use hydrodynamic analysis to improve marine equipment and structure designs. By modeling the behavior of the water and the structure or equipment exposed to it, design problems and structural deficiencies can be discovered, and the design can be improved before the equipment or structure is put into production. This process can save large amounts of time and money, and can improve the safety of marine structures and equipment.

Here are a few examples of projects that can benefit from thorough hydrodynamic analysis:

#1 Oil Rig Design

Large, off-shore oil rigs are often limited-production designs, with only a few examples actually being built. This means it is difficult to test the designs thoroughly before production, and any mistakes in the design can be difficult and expensive to repair later. By using hydrodynamic analysis, the manufacturer can thoroughly test the design before it is put into production, and improve it to minimize any problems.

The hydrodynamic analysis will model the effects of the marine environment on every part of the oil rig, from the anchors that tie it to the seafloor, to the platform legs, risers and superstructure. It can pinpoint structural deficiencies, where forces like wave action slowly wear away at sensitive components, such as moving joints, and eventually cause dangerous structural failures or prolonged maintenance problems. This allows the designers and engineers to redesign these components to better withstand the forces at work in the marine environment, reducing maintenance costs, increasing the design life and protecting the safety of the personnel.

#2 Pump Design

Pumps are critical in a marine environment. Bilge pumps remove excess water from a ship’s hull to prevent an over-accumulation that could cause the ship to sink. Fresh water pumps circulate drinking water through the plumbing for ship personnel, and other pumps may be used for fire protection. Oil pumps are used to keep the moving parts of a ship lubricated, or to transfer oil from production wells to tankers. Fuel pumps provide ships and generators with the fuel they need to run.

Pumps used in a marine environment must be able to withstand corrosion and electrochemical reactions caused by saltwater exposure, and they must be able to transfer fluids quickly and efficiently without overheating and failing. Hydrodynamic analysis can be used to model both the behavior of water on the exterior of the pump and the behavior of liquids as they travel through the pump.

The models can be used to design pumps which are better suited to the forces at work in a marine environment, making them stronger and more resistant to the effects of pressure and corrosion that cause maintenance problems. They can also be used to increase the efficiency of the pump, by showing how the fluids travel through the body and the impellers. By using the results to eliminate unnecessary cavitation and friction, the pump design can be made much more efficient, saving energy, reducing maintenance requirements, and extending the pump’s lifespan.

#3 Accident Reconstruction

Working in a marine environment can be especially dangerous for personnel and equipment. Bad weather, rogue waves, fire, equipment failures and other common problems can quickly lead to dangerous situations in the contained environment of a ship, drilling rig or other marine platforms. Accidents can and do happen, including collisions, fires, oil spills, sunken vessels and other catastrophes. Determining the cause of an accident and the results are often the key to improving marine designs and preventing similar accidents in the future.

Hydrodynamic analysis is one of the most powerful tools for determining the cause of a marine accident. The process can be used to model the behavior of the water and any structures, vessels, or equipment that are in the water. It can help determine why two ships collided using accurate modeling, which part of a structure failed, why fire protections systems malfunctioned during an emergency, or how an oil leak was caused and where the oil will be traveling.

With accurate modeling, hydrodynamic analysis in conjunction with other tools can reconstruct every variable at play during an accident, and determine the cause and effect of each action taken. The results can be used to improve the designs of marine equipment and structures to prevent similar accidents in the future, to institute new safety procedures that minimize casualties, and to take further action to protect the safety of ship personnel and minimize liability issues.

Other Applications

These are just a few of the ways that hydrodynamic analysis can be employed in real-world applications. It can also be used to improve the designs of sea-faring vessels, mooring systems, sub-sea pipelines, floating pipelines, drilling risers, anchors, mooring lines, liquid-storage systems, buoys, marine weapon systems, off-shore wind turbines and wave power generators. Furthermore, it can be used to help during oil spill cleanup or containment operations, for forensic analysis, marine training simulations, risk assessments, financial assessments, emergency preparedness and accident prevention. Hydrodynamic analysis is a versatile tool, and it has many critical applications across multiple industries, including oil and gas production, energy production, shipping services, defense, maritime entertainment and oceanography.

With so many applications, hydrodynamic analysis is very important to any marine based-operation, and through its accurate modeling, it can help improve the design and operation of many marine-based structures, tools and equipment. It can help cut design costs and minimize production delays, and improve the safety of marine-based personnel.

Sources:

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During off-shore oil and gas production operations, single point moorings provide a safe way to offload petroleum products to tankers, operating as both a buoy system to keep the ship in position and as a connection to the sub-sea pipeline and riser system to move the petroleum products from the production platform to the tanker.

Single point mooring systems have several critical parts, and they must all operate together properly to safely and efficiently load the tanker. They must also be able to withstand large forces from the movement of the ship on the ocean, wave action, tidal forces, surface weather, undersea pressures and both horizontal and vertical movements.

Here are some of the most important parts of single point moorings, and how they help to complete the off-loading process successfully:

#1 The Buoy

The buoy typically consists of a set of legs that connect it to the sea floor and a body section, which is located at the surface. The body can freely spin around the leg section, due to a roller-bearing system that permits free rotation. This allows ships that are moored to the buoy to freely move around it, according to the movements of the ocean.

Without this ability to rotate, ships attached to the buoy would exert large amounts of extra force on the buoy system, potentially resulting in a failure of the lines anchoring the ship to the buoy, or the lines anchoring the buoy to the sea floor. During loading operations, this could cause safety problems, as the ship breaks free and moves unexpectedly, or environmental consequences if it causes a spill of petroleum products.

A properly-designed buoy system should be able to handle all the horizontal, vertical and rotational forces exerted on it while safely delivering oil or gas to the tanker.

#2 The Anchoring System

The buoy is attached to the seafloor with either anchors or a pile system, in most cases. Anchors provide a temporary attachment system by sinking a large mass, such as concrete, to the sea floor to provide a stationary weight, by embedding into the seafloor itself, or by attaching to an existing sub sea feature, such as a large mass of rock or a crevice. For a more permanent attachment system, piles can be driven into the seafloor to provide a solid anchoring system.

Once the anchor and the buoy are in place, anchor chain, or sometimes synthetic or metal cables, are run from the anchors or piles on the seafloor up to the buoy itself, providing a secure attachment.

Each of the components in the anchoring system must be able to withstand the corrosive effects of salt water, as well as the natural forces of the ocean, including waves, weather, and pressure. Most anchoring systems are built to withstand some small amounts of movement, which helps prevent fatigue and the structural failures that can result from the forces acting against the system.

#3 The Petroleum Loading System

The buoy is connected to a pipeline system that is located on the seafloor. This pipeline carries oil or gas from the well and distributes it through a pipeline end manifold to a system of risers that bring it to the surface of the ocean. These risers are typically flexible, allowing them to move along with the ocean currents and the movements of the buoy.

At the surface, the risers connect to the buoy, and the oil and gas is routed through a swivel system in the buoy’s body, allowing the output connections for the petroleum products to swivel along with the moments of the ship. The final connection from the buoy to the tanker is typically made with a floating hose system, which features breakaway connectors that prevent oil spills if the ship moves too far away from the buoy.

The swivel system contains a number of valves and seals that prevent oil or gas leaks, as well as supplemental connections for power, data or electrical signals in many cases. All of the seals and electrical connections are constantly subjected to rotational forces, friction and some horizontal and vertical movement. They must be carefully designed to withstand all of the stresses experienced during operation while minimizing the amount of maintenance required and the associated costs.

#4 Ship Mooring System

The deck of the buoy features a mooring point, to which one or two synthetic ropes are attached, depending on the size of the ship. The ropes are extended out to the tanker, where they are connected to a chafe chain that is extended from the tanker. The connection allows the ship to rotate around the buoy, and the floating hose system moves along with the ship. Each component must be carefully designed to handle the weight of the ship and the forces exerted on it by the movement of the ocean.

Optional Components

Typically, the buoy will have a boat dock for personnel to easily access the deck, as well as fenders or bumpers to prevent damage to the buoy. It may also have an integrated power system, weather equipment, navigation aids, or cranes and other equipment for maneuvering large loads, as well as safety equipment.

Improving the Design of Single Point Moorings

To design a long-lasting and structurally-sound single point mooring system, it is wise to invest in both a structural design analysis and a hydrodynamic analysis. By scrutinizing the structural components and modeling how each behaves under the conditions present in a marine environment, including wave action, high pressures, tidal forces, variable weather and corrosive forces, the design of each component can be optimized to ensure that it will perform well under the worst conditions, with a suitable design life and minimal maintenance. With hydrodynamic analysis, every possible component can be modeled and improved, from the shackles connecting the mooring lines to the anchoring system, to the buoy itself.

With a properly-designed single point mooring system, operational costs can be significantly reduced, production efficiency can be increased, safety can be improved and the environment can be better protected.

Sources:

https://stewart-usa.com/mooring-analysis.php
https://stewart-usa.com/hydrodynamic-analysis.php
http://petrofed.winwinhosting.net/upload/18Sep10/1.pdf
http://www.rigzone.com/training/insight.asp?insight_id=308&c_id=17

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