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The October 4 2018 COPRI Houston Conference lecture Breakwater Caisson Design was presented a few days before the first Nador Caisson was loaded out in Morocco.

This video illustrates a success story.  The loading out the 3,000 tonne caisson (that had been slipformed on land) is shown onto a semi-submersible barge.  The barge is towed to relatively deep water and ballasted down, until the caisson can be floated off.  The caisson is then towed to a moderate water depth where it is ballasted down and stored until all caissons are ready for final installation.

All phases of the operation required naval architecture calculations for the hydrostatic stability of the caisson and barge. About 100 Caissons make up the breakwater for the new harbor at Port Nador.

The post 1st Nador Caisson Floated appeared first on Stewart Technology Associates.

The full lecture can be viewed at CAISSON DESIGN VERIFICATION.  This lecture was presented at the ASCE COPRI 2018 Houston Chapter Conference.

A cross section through the main breakwater is shown below:

Wave forces and safety factors against sliding and overturning are computed with Excel and shown in the Excel chart below:

The installation requires afloat stability checks as the caisson is removed from the semi-submersible barge.

The Excel package goes on to calculate motions of the floating structure in waves, based on closed form analytical solutions.

For each degree of freedom, the diffraction and Froude-Krilov forces are discretely calculated for wave attack in the primary plane of motion, at a range of wave periods.  Mechanical admittance is calculated and dynamic response is computed.  Response at intermediate attack angles is interpolated.

This paper describes coastal civil engineering and naval architecture good practices applied to design optimization of concrete caissons, typically constructed by slipforming.

Always check results with experienced engineers and naval architects.  It is easy to make mistakes in input data.

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Boom Backwards Recoil Collapse in Marine Salvage

Some of the sections from the video are shown below, beginning with an amateur video of a crawler crane boom backwards collapse on a barge during a salvage operation in 2018.

The next clip illustrates the crane boom recoil issue with a 1/12th scale model.  In the first part a heavy load is dropped when the model boom stops are not connected.  in the second part, the boom stops (which have springs in the model) are connected.

The Excel analysis finds both a closed form analytical solution to the maximum boom recoil angle and also provides a time domain integration of the boom pendant wire sudden tension reduction from the lost load.

The next clip shows the close comparison of the boom pendant wire tension change in the first 0.5 seconds after the load is dropped.  Both Excel and OrcaFlex predict that the tension becomes zero after 0.22 seconds.  During this time the pendant tension is accelerating the boom’s angular velocity.

The time domain motion of the boom angle is compared in the next clip, then the Excel closed form solutions for a range of dropped load sizes and initial boom angles is shown, for two different pendant wire sizes.

Floating Service Load Chart

A Floating Service Load Chart is required by US Army Corps of Engineers (USACE) Manual EM-385-1-1, Safety and Health Requirements, November 2014, for all mobile cranes mounted on barges, pontoons, etc.  This can be provided by the Load Handling Equipment (LHE) manufacturer.

Naval Architectural Analysis

If a manufacturer’s Floating Load Service Chart is not available, a floating service load chart may be developed and provided by a qualified registered engineer or naval architect, competent in the field of floating cranes.  STA provides the NAA Service.

Additional Codes and Standards

In developing a Floating Service Load Chart and de-rating any floating crane, the following codes and standards must be considered:

• CFR 173.005: Vessels Equipped to Lift Cargo or Other Loads
• CFR 173.020: Intact Stability Standards
• CFR 1915.115: Hoisting and Hauling Equipment, OSHA
• CFR 1926.1433-1434: Design, Construction and Testing (cranes) OSHA
• CFR 1926.1501(f)&(g), OSHA
• ASME B30.5-2015: Mobile and Locomotive Cranes
• ASME B30.8-2018: Floating Cranes and Floating Derricks
• USACE EM-385-1-1, 2014
• NAVCRANECEN INSTRUCTION 11450.2, March 2013: 2-1.7 Design of Floating Cranes
• NAVFAC P-307, Weight Handling Program Management, 2016

The relevant FRs do not mention crane boom recoil or boom stops.  ASME 30.5 specifies that boom stops shall be provided on mobile cranes to resist the boom falling backwards.  No design guidelines are given.  ASME 30.8 has similar wording.  P-307 requires boom stops to be checked, but does not mention precautions to be taken if the crane does not have boom stops. Similarly, EM-385 notes that a crane should have boom stops.  NAVCRANECEN Instruction 11450.2 gives a specific analysis to be performed to check if crane boom recoil will result in contact with the boom stops.  The load to be used in the analysis is stated with reference to the Floating Service Load Chart.

An example of a Floating Service Load Chart is shown below, with the crane boom recoil limitation on maximum hook loads also included.

An example of a safe lift at a high (77º) boom angle, on a barge mounted mobile crawler crane without boom stops is shown below.

A detailed structural dynamic analysis of the boom and the boom stops can be performed using OrcaFlex, as shown in the next example clip.

SUMMARY

• Calculation of maximum crane boom recoil angle from closed-form analysis equations in Excel
• Calculation of maximum safe loads at high boom angles
• Prevent backwards crane boom recoil accidents
• Time domain “instant” solutions in Excel
• Detailed time domain simulations relatively quick with OrcaFlex
• Structural checks using non-linear dynamic analysis of boom stops and booms performed in OrcaFlex
• Low cost, high value, advanced structural engineering calculations save lives and save money.

The post Crane Boom Recoil from Sudden Loss of Load appeared first on Stewart Technology Associates.

A rigging failure resulted in sudden release of the hook load.  The boom was raised high and crane was on a barge.  The boom collapsed backwards over the cab.  Late 2017, BVI.

Bil Stewart produces Naval Architectural Reports (NAA) and Floating Service Load Charts for mobile cranes used on barges.  The video above, was not one of STA’s projects.

The above Floating Service Load Chart is for a crane and barge unit in Greece.

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Maleo Producer, a mat-supported Jack-Up rig converted to a gas production platform (MOPU) owned by Global Production Systems, with structural design and foundation dynamic analysis by Stewart Technology Associates.  The platform is shown during a dry tow to the site in Indonesia on board the heavy lift vessel Black Marlin.

There are many challenges in the off-shore oil and gas industry, from operating in an unforgiving marine environment safely, to offloading oil and gas efficiently and designing drilling rigs, risers, moorings and other equipment that can withstand the punishing environmental forces at play. No matter how well-rounded and diverse your team is, eventually, you will run into an engineering problem or situation beyond your knowledge and expertise, or something that requires a different discipline or skill set.

While expanding your team is one option, finding someone with the necessary skills can be difficult, time-consuming, and potentially costly, and it may not be worth the effort if you need only temporary or intermittent assistance. In these situations, the most convenient, cost-effective option is to use outside engineer consultants who can work closely with your team to achieve the desired results, while bringing a unique set of skills and fresh viewpoints to the task at hand.

Here are a few of the ways that engineer consultants, like the team at Stewart Technology Associates, can help your off-shore exploration or production operation:

#1 Structural Design and Analysis

Designing equipment and structures that can stand up to the rigors of a marine environment, including forces such as rain, snow, wind, wave action, tidal forces, deep sea pressures, corrosion and chemical reactions, can be a difficult process. It can include thousands of hours of design, simulation, prototyping, testing and analysis work. Even with a highly-qualified team and large budget, it can be a grueling process fraught with pitfalls and mistakes. By working with experienced engineer consultants, you can eliminate guess work and get the project finished and into production in a timely manner. Some of the structural projects that engineer consultants can help you with include:

• Fixed platforms
• Tension-leg platforms
• Jack-ups
• Liftboats
• Semi-submersible platforms
• Drillships
• Barges
• Bouys
• Moorings
• Single-point moorings
• Pipelines
• Risers
• Anchors
• Foundations

Engineer consultants can help throughout the design process; from the initial planning of the structure, to creating the final design and selecting the appropriate materials and construction methods. Using software such as ORCAFLEX, ASAS or ABAQUS can employ finite element analysis and model how your structure will behave in real-world conditions by simulating the effects of vibration, heat, fluid movements and other variables. This will determine where likely failure points are, allowing design to be improved before production. The software can also be used to improve existing designs and model previous failures to avoid future incidents.

By working with engineering consultants during the design process, you can avoid common problems that lead to structural failure, safety problems and increased maintenance, and you can develop a reliable, long-lasting structure that will serve your needs more thoroughly.

#2 Hydrodynamic Analysis

Anything in a marine environment is bombarded by waves, tidal forces, inclement weather, high pressures, corrosion and electrochemical processes. These forces cause wear and stress on marine structures and equipment, leading to increased maintenance requirements, higher operational costs and structural failures or safety issues. Engineer consultants use hydrodynamic analysis tools, like OrcaFlex, to model the hydrodynamic forces at work on your structure, allowing you to improve the design, increasing durability and reducing maintenance costs. Hydrodynamic analysis improves the performance of equipment and marine structures, including:

• Drilling rigs
• Production platforms
• Mooring systems
• Anchors
• Anchor points
• Mooring lines
• Anchoring hardware
• Underwater pipelines
• Floating pipelines
• Risers
• Tankers

Engineer consultants can help your marine equipment and structures perform as expected, and keep workers safe.

#3 Fluid Dynamics Analysis

Systems designed to store and transport fluids like oil must be designed to avoid leaks, eliminate bottlenecks that reduce transfer efficiency and move fuel safely. Engineer consultants use software like OrcaFlex to model the behavior of liquids in equipment like risers, pipelines, pumps, swivels and tanker ships, leading to improved designs.

For pipelines, risers, and swivels, the software determines where there are impediments to flow, allowing you to create a design with higher flow rates. It also shows the forces at work on the seals, allowing you to design seals that are more resistant to leaks and other failures.

An analysis of fluid dynamics can also be used on pumps to increase flow rates and to make them operate more efficiently, reducing energy usage and costs. In tankers, it can help design holds that minimize the movement of oil and prevent sloshing, leading to greater ship stability during transit, increased safety and reduced fuel costs.

#4 Other Areas

In addition to these basics, there are other ways engineer consultants can improve your oil and gas operations:

• Risk Assessment: Engineer consultants can examine your overall operations and suggest improvements to increase safety, efficiency and financial health. They can also report to insurance agencies to evaluate your operation and so that a project can move forward.
• Emergency Preparedness: Engineer consultants can design safety systems, equipment and strategies that keep employees protected and minimize liability during emergency events, like inclement weather or fire.
• Marine Simulation and Training: Engineering consultants can design training programs, software and equipment that helps employees learn to use marine equipment safely, effectively and efficiently, including systems like jack-ups or liftboats.
• Forensic Analysis: Engineer consultants use tools like hydrodynamic and finite element analysis to determine the cause of an accident, and how to prevent it in the future.
• Oil Cleanup: Engineer consultants can develop effective oil cleanup procedures and equipment that minimize costs and environmental damage in the event of a leak or a spill.

Engineer consultants offer a wide range of valuable knowledge and skills that help your oil and gas operation design better structures and equipment, improve operations, enhance safety and increase profits.

Sources:

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