The Catenary Calculator is taken from within the program STA CHAINLENGTH and is part of the STA in-house library of software.

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Hydrodynamic analysis with OrcaFlex is used to confirm and improve upon closed form analytical solutions developed by STA.

Designs have been developed for cruise ships up to 333m length with gross tonnage 150,000 and a starting collision velocity  of 6 knots.

Efforts on the project were interrupted in September 2017, by Hurricanes Harvey, which effected our Houston office, and Irma, which effected our Caribbean interests.

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Specializing in marine and offshore structures, fluid dynamics and related disciplines, here are just a few of the services that our marine consultants at Stewart Technology Associates can provide:

1) Hydrodynamic Analysis

Hydrodynamic analysis is used to accurately simulate the forces at work on a structure in a marine environment. This includes the movement of the waves, the action of the tides, the effects of undersea pressures, turbulence from structures or seafloor features, and the effect of high winds and inclement weather. By learning how these forces affect a structure, its design can be improved to eliminate possible failure points and to reduce costs and maintenance requirements. Hydrodynamic analysis can be used to examine both new and existing designs, and it can also be used after a maritime accident to help determine the cause of the problem.

2) Finite Element Analysis

Finite element analysis can be used to model how real-world conditions will affect the operation of a product or of a component of a larger system when subjected to forces such as vibration, heat, high pressures, fluid flow or other physical challenges. The results of the modeling can be used to improve the product’s design, reducing component failures and wear that can shorten its lifespan or lead to increased maintenance costs. Finite element analysis can also make a product safer, and help to determine the cause of failure in an existing design.

3) Structural Design and Analysis

STA can help design and analyze marine structures, such as drilling rigs, jack-ups and liftboats, to make sure that they will perform efficiently and safely in a specified environment. They can work directly with a client to create a structure that will withstand the forces in a particular marine or sub-sea environment safely, while increasing productivity and reducing long-term costs. They can also analyze existing designs to improve their structural performance, productivity and safety.

4) Riser Design and Analysis

Risers are one of the most critical components in an offshore oil drilling or production platform. They carry mud and drilling fluids to the well during drilling operations and carry oil and gas to the surface during production operations. To operate safely while maximizing production, they must be able to withstand the movement and pressure below the surface, while moving fluids efficiently. Engineer consultants can be used to design an efficient riser system for production or drilling operations, determining what type of riser will be needed, rigid, flexible or hybrid, effective mooring solutions, what equipment will be required and other factors. They can also improve the efficiency of fluid moment withing the riser, increasing production, and analyze existing designs to suggest structural, efficiency and safety improvements.

5) Anchor Performance Analysis

Anchors are critical to securing marine vessels and other structures in place temporarily, permanently or semi-permanently, and if they fail to perform adequately, they can allow vessels to drift off course or to collide with other structures, leading to injuries, property damage, productivity losses or environmental concerns. To perform effectively, the design of an anchor must take into account the weight and movement of the vessel, the surface conditions and the composition of the sea floor. With an anchor analysis, engineer consultants can model the forces at work on the anchor and suggest improvements that will make it stronger, safer and more effective.

6) Mooring Design and Analysis

Mooring systems in the offshore oil industry are critical to keep the platform in place during operation, to secure tankers while transferring oil and gas and to secure other vessels as needed. They must be able to withstand the weight of the vessel or platform, while compensating for motion at the surface of the sea and keeping transfer pipes and equipment safe. Engineering consultants can analyze the design of a mooring system, including the anchors, mooring lines and surface structure, ensuring that it can perform both safely and effectively. They can also create new designs for specific applications and analyze the performance of transfer systems.

7) Oil Spill Clean-Up and Containment

Oil spills can have far-reaching consequences, from polluting the water supply and harming animal and plant life, to making beaches less inviting and hurting economies that depend on fishing or tourism. When the worst does happen, the key to minimizing the damage is to contain the oil as close as possible to the source and to clean it up as quickly as possible. Engineering consultants can help to design effective measures for both containing the oil and cleaning it up, including effective boom systems to contain the oil and techniques that can adequately model the currents and conditions at the site to make clean-up more successful and efficient.

8) Forensic Analysis

After a maritime accident or an oil spill, the original cause of the accident can be difficult to determine and, often, there are many contributing factors that make the origin even less clear. Engineer consultants can use hydrodynamic analysis, finite element analysis and other techniques, along with advanced software and extensive knowledge of marine systems, to analyze the events leading up to the accident, as well as the accident itself and its effects, to help determine the original cause. This information can be used to determine liabilities in the aftermath of the accident, to improve designs to prevent future accidents and to establish new safety protocols and programs that can help avoid or mitigate such incidents in the future.

Sources:

https://stewart-usa.com

https://stewart-usa.com/overview.php

http://usa.oceana.org/sites/default/files/tourism_impacts_fact_sheet_9-8-15.pdf

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Sewol Salvage: Stewart Technology Associates worked as Technical Advisors to Shanghai Salvage Company using STA software and were responsible for all dynamic analysis of the complex lifts in the open ocean environment.  All lifts are dynamically sensitive and involved cutting edge marine salvage dynamics. Analyses were performed with waves in the time domain using FEA (OrcaFlex).

Marine Salvage Dynamics of Sewol Salvage raised with ZPMC 12,000 ton floating crane and 1,200 ton lifting frame.

32 HMPE upper slings, 8 balance slings, 34 pairs of steel lower slings.

Fully coupled 6 DOF time-domain dynamic analyses in OrcaFlex with diffraction forces on the Sewol and ZPMC crane barge.  All individual sling tensions computed during all stages of the Sewol Salvage.

Sewol wreck transfered to semi-submerged floating dry dock in open ocean.  OrcaFlex time domain dynamic analysis of three main vessels, lifting frame and all slings.

The following video describes how STA has examined the issues of unusually low freeboard and trapped water on the pontoon deck.

The video provides a description of how OrcaFlex is used to cope with time domain calculations of the wave motions of the floating dry dock when the deck becomes submerged and the buoyancy of the wing tanks is of critical importance.

More details of the accident can be found at:

gCaptain

Wikipedia

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

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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.

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Dynamically positioned drill ship in storm conditions.
Riser tensioners seen actively tensioning riser until 7:50 on the timer.
Riser emergency disconnected, EDS activated at the BOP at 7:50 and the top end raised about 3 meters.
Moonpool with hung-off riser shown after EDS activated.

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

View list of STA software.

Drilling Riser Analysis Services

View our Drilling Riser Analysis section.

In the offshore oil and gas industry, risers connect drilling and production platforms to the sea floor. They transport oil and gas from the well to the platform or inject fluids into the well to facilitate drilling or production. Risers are critical to the operation of the platform, and any failure could mean a loss of production capabilities and a serious loss of profit.

Risers enable the platform to move up and down, or side to side during production and drilling operations. They also must efficiently transfer fluids to and from the sea floor. The impact of wave action, tidal action, high pressures, low temperatures, and corrosion must not affect the platform’s movement. In order to do the job properly, with minimal maintenance and downtime, an extremely efficient and reliable riser design is required.

In the past, the main way to evaluate a riser design was through building prototypes, testing them extensively in real-world conditions and redesigning the riser until it met all the requirements and specifications necessary. This could be a tedious and expensive process, and it could still yield sub-standard designs, in some cases.

Today, riser analysis takes out some of the guesswork. Using special software packages and talented engineers, riser analysis can model the forces at work on a potential riser design. It looks at waves, tides, temperature, pressure, vortex forces and vibration to determine the strong and weak points of a design, and improves them to avoid structural fatigue, leaks, inefficient fluid transfer and other common problems. This can reduce design and prototyping costs, and lead to a final product that is efficient, durable, safe and low-maintenance.

Riser analysis is now a critical tool for improving the performance of drilling and production operations, and here are a few of the ways it can help to improve riser design:

1) Determining the Right Type of Riser for the Job

The type of riser used for a particular application will depend on the type of platform, the depth of the seafloor, the depth of the well and the sub-sea conditions. Riser analysis can be used to determine the best type of riser for the application, and help perfect the design and adapt it to particular equipment. The most common types of risers include:

• Top-tensioned riser: A rigid riser that is held in place vertically through tension, and allows both lateral and vertical movement through a flexible connection between the riser and the platform.
• Steel centenary riser: A curved riser used to connect two platforms, or to connect the platform to the sea floor, it can withstand some motion and is used on spars, tension-leg platforms and floating production storage and offloading platforms.
• Flexible riser: Made from flexible pipe, these risers can withstand horizontal and vertical motion.
• Pull-tube riser: A hollow tube attached to the center of the platform, it houses a pipeline or flowline that is pulled from the seafloor with a cable, and is used primarily on fixed platforms.
• Attached riser: Used on fixed platforms, compliant towers, and concrete gravity structures, these risers clamp to the side of the platform and are connected to the sea floor with an export pipeline or a flowline.
• Riser tower: A combination of a steel tower and riser that is used for deepwater drilling, a buoyancy tank is used near the surface to keep it in place through tension and flexible lines connect it to the platform
• Drilling riser: Transfers drilling mud and other fluids to the seafloor during drilling operations and is only a temporary connection.

With riser analysis, you can choose the best riser for the situation, adapt an existing design for use with your equipment, or create an entirely new or hybrid design, then test and improve the riser before it goes into production.

2) Improving Riser Structure

The overall structure of the riser must be able to withstand the waves, the tides, the high pressures and the low temperatures present below the ocean surface. Riser analysis can be used to model these forces at work on your riser design, determining how they affect individual areas and structures of the riser and how they affect maintenance requirements and the longevity of the system. Using the resulting data, the design can be improved to make the riser stronger, more stable and safer.

3) Determining Insulation Efficacy

In deep water, the temperature can drop significantly, reducing the viscosity of oil and drilling fluid and slowing down production and drilling operations. To combat this, many risers incorporate insulation to keep the fluids at a more desirable temperature so that they can flow properly. Riser analysis can be used to design and test the insulation, and find problems that may reduce the temperature and fluid flow within the riser. By improving the design of the insulation, riser analysis can help to increase production efficiency, leading to higher profits.

4) Designing and Testing Valves

Valves in the riser help control the flow of oil, hydraulic fluid, and other substances through the system, and they must operate in cold, high-pressure conditions without frequent failures or maintenance. Riser analysis can be used to model the flow of fluids through the valves and to find failure points and other problems that can reduce their life cycle or cause leaks. With the data, the valve can be reengineered to promote longevity and efficient fluid flow.

5) Designing Buoyancy Tanks

Buoyancy tanks are critical to keeping a riser stable and accessible in sub-surface conditions, and if they malfunction, oil spills or other problems could occur. Riser analysis can help to design and test the buoyancy tanks, improving their design so that they are safer and more stable, regardless of the sub-surface conditions.

6) Improving Riser Flow

Production risers must carry fuel to the surface efficiently to meet production goals and maintain the platform’s earnings. Riser analysis can be used to model how oil and drilling fluids flow through the riser, determining points of turbulence or restriction. By improving the design of the riser and eliminating these problems, production rates, and profits can be increased.

Riser analysis is a powerful tool that can make an oil platform safer, more efficient, and more productive by improving every aspect of riser design, from the seals to the valves and the overall structure.

Sources:

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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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