Month: August 2018

How to control uncertainty in water current profile when designing oceanographic moorings

Image of the Rockland Nemo uncertainty in water current profile

Rockland Scientific’s Nemo MicroRider turbulence measurement platform (photo courtesy of Rockland Scientific)

When you get something different than you expect, it’s a sign that uncertainty has reared its head

“Just make sure that it’s good!” It was the last thing I heard from my wife as I bolted out the front door. On a twilight dash to the supermarket down the road, I’d still handily get there before closing time for critical essentials – coffee, milk, and ice cream.

Making quick work of the aisles, I stopped short and hesitated in front of the freezer. Some of the cartons had frost on the labels, but I could tell there was some strange choices: cinnamon dust, citrus tea, and chocolate chip; who doesn’t like chocolate chip?

I was back home with time to spare. “You realize of course,” my wife said, brushing frost off the label of the carton, “you bought the only ice cream that tastes like toothpaste?” It was mint chocolate chip. Frost had covered up part of the name.

I ended up with something I didn’t expect

When deploying oceanographic moorings, there’s a lot to do on a tight schedule. There are many factors that can affect results. Uncertainty can cause something that’s different than expected.

Image of Ice Cream Freezers for uncertainty in water current profil blog

Mint Chocolate Chip and Chocolate Chip are definitely not the same

Uncertainty and risk will cost you

Oceanographic sensors ($) collect data from the ocean and are specifically designed to survive for long periods of time in harsh conditions. With the ocean covering 70% of the planet at an average depth of 4000m, these sensors are often submerged, under high pressure, in very remote locations and need ships and crew ($$) to deploy, and hopefully, recover them.

These devices collect measurements of pressure, salinity, current, and any other number of parameters, at precise locations in the ocean and potentially for many years at a time. This data is worth far more than the cost of the equipment and its deployment ($+$$ = $$$), not to mention the loss of years worth of data when sensors are invalid or lost. So how does uncertainty in the water current profile cost you?

It’s a serious drag

The force from water drag grows with the square of the current speed. This force can be a severe challenge in designing a mooring because of how quickly the forces increase and deflect the mooring. More deflection means more sensor tilt and greater knockdown.

With too much tilt, some sensors stop working, and every bit of knockdown is an error from the intended position. Much like the frost covering the ice cream label, it means you might not know what you’re going to end up with. But is there a way to control the risk?

Rockland Scientific’s Nemo MicroRider platform as seen in ProteusDS

Bounds can control uncertainty

Understand the problem accurately at the boundaries, and you know the answer is somewhere in the middle. Using a dynamic analysis program like ProteusDS, a mooring design can be checked with both a conservative and optimistic current profile.

Using the bounds allows adjustment of the design to understand the forces, and their effect on tilt, and knock down to protect the data that is acquired at great cost.

But how does dynamic analysis complement field experience and intuition?

There’s always new combinations of equipment and conditions in the environment. Field experience has value and is based on real equipment in specific configurations in a set of environmental conditions.

Dynamic analysis software like ProteusDS helps systematically evaluate both new and existing combinations of equipment, confirming a hypothesis and trends in design behaviour, and broadens a mooring designer’s intuition and knowledge.

Example: 30m Nemo mooring

Rockland Scientific produces the MicroRider sensor package that continuously measures turbulence in the water at a specific depth. To measure at the desired depth in the water, the turbulence sensor is mounted on a streamlined float hull, called Nemo, that minimizes drag forces, so it is less affected by the wide range of flow speeds.

Mooring analysis in ProteusDS shows the effect of conservative and optimistic bounds of the water current profile on knockdown, which highlights the potential error in the data from the target measurement depth. Mooring designers can plan for effects at the optimistic bound and assess implications at the conservative bound.

In this example, the Nemo float is moored in 100m water depth on a 30m mooring. A power law current profile with 1.5m/s and 2.5m/s surface current was used to find the steady-state deflection in ProteusDS. The excursion was 4.6m and 11m in low and high speed flows, respectively, and knock down was 0.4m and 2.5m in low and high speed flows, respectively.

Depending on the level of risk for the specific application, a larger current speed or more conservative current profile could be used, and the mooring design can be adjusted to reduce excursion and knock down.

A ProteusDS PDS Image of the Rockland Nemo.

Bounding the Nemo mooring deflection A) in 1.5m/s current (optimistic estimate) and B) 2.5m/s current (pessimistic estimate)

Designers design, tools help

The costs of oceanographic data are very high because of the specialized equipment and remote access to sites of interest. Uncertainty from factors like water current profile can introduce serious risks, like loss of equipment, gaps in data, or erroneous results from too much sensor movement. However, mooring designers can control risk by bounding the problem with a tool like ProteusDS, and then everybody gets the ice cream flavour they expected.

Next step

At DSA, we have created ProteusDS to help oceanographic mooring designers. License the software to check for yourself how current profile assumptions affect your designs and oceanographic data.

Check out this video tutorial on how to quickly assess an oceanographic mooring deflection to a current profile in ProteusDS.

Thanks to Rockland Scientific

Thanks to Rockland Scientific‘s Fabian Wolk, Jeremy Hancyk, and Peter Stern for sharing technical pointers, information, and pictures of the Nemo MicroRider.

What the History of Flight Can Teach Marine Renewable Energy

In 1903 the Wright brothers changed how the world experienced travel by inventing aircraft controls that made fixed-wing powered flight possible. Initially, the Wright brothers struggled to get their aircraft off the ground, and that first flight may never have happened without a piece of well-placed advice from Octave Chanute.

Chanute, a French-born, Chicago-based engineer, was quite possibly the first independent aeronautical consultant at the time, and the Wright brothers often sought his expertise. Many of Chanute’s ideas were incorporated into the Wright brothers designs leading up to their first successful flight in 1903. Chanute provided the Wright brothers with specific technical expertise, and according to Roger D. Launius,

“It was the Wright brothers that taught the world to fly without question, but it was Chanute who taught the Wrights to fly.”

The Wright brothers recognized the value that outside expertise offered in helping them reach their goals, and ensure success. This is why Aquatera, DSA, and Orcades Marine have partnered to launch the third-party verification service called “360 TPV”.  In this article, we’ll discover what 360 TPV is, how it works, and why we think it could help you.

A JOINT SERVICE PROVIDED BY

Image of the partner company logos

“I’ve heard about third party verification, but what is 360 TPV?”

360 TPV allows our team of experts in marine operations, engineering, and environmental and resource assessment to provide you with strategic advice at critical milestones during your marine renewables project lifecycle. We call these milestones value assurance gates, and they are implemented after each significant stage of the project life-cycle.

Image of the 360TPV-Value Assurance Process Gates

At each assurance gate, our team identifies opportunities for success, minimize uncertainty, and manages risk. By providing you with prompt feedback, we help you avoid potential hazards common to marine projects, such as:

Typical RisksPotential Consequences
Cost constraintsUnder-resourcing, unsafe acts, inadequate equipment
Unrealistic schedulesPoor planning, hazardous operations, delays, escalated costs
Limited marine experienceHigh operational risk, escalated costs, sub-optimal design
New and challenging operationsHigh marine installation and O&M costs, unsafe operations
Inadequate change controlHigher operational risks, cost escalation, project failure
Inappropriate met-ocean dataUnder design: equipment failure: Over design: excess costs
Flawed design inputHigh installation costs, early failures, re-working costs

360 TPV is your commitment to due diligence when it comes to engineering design, locational suitability, operability, regulatory and license compliance, as well as cost-effectiveness and invest-ability. 360 TPV is designed to be used in part, or as a whole, to meet your specific requirements providing the independent oversight that regulatory bodies, investors, governments, and other key stakeholders value.

“But I have an experienced team, why do I need to hire you?” Good question!

During the development and execution of a marine renewables project, many of the details can become overwhelming, and there may be times when those closest to the project are blinded to opportunities, obstacles, and risks that are in front of them. 360 TPV is a safety net that provides you with the assurance that you are unlikely to miss a golden opportunity, and that risks will be mitigated.

The collective experience and marine industry knowledge of Aquatera, DSA, and Orcades Marine is extensive. We are proud of our track record working with small startups to large oil and gas companies.  Our team adds essential but often missing elements to ocean energy developments by:

  • Providing direct access to experienced sector experts who know what can happen, what has happened and what can be done
  • Delivering rapid feedback to enable any adaptations can be made promptly
  • Contributing independent and unbiased expert review
  • Analyzing up-side opportunities as well as down-side risks
  • Building in a multidisciplinary approach from the outset
  • Ensuring the right inputs are used from beginning to end
  • Thinking about solutions rather than solely identifying problems
  • Helping the sector progress rather than merely selling a service

“What specific things are your team going to do?”

Looking in depth at an example of a tidal energy device deployed for six months at a test site where 360 TPV was used to de-risk the deployment can likely help answer this question.

Image courtesy of Marine Renewables Canada

The tidal developer had a two-turbine floating structure, with a four-point mooring system that they wanted to test. A third-party review was desired to ensure compliance with appropriate standards and where necessary perform independent design calculations to verify critical components along the load path from the turbine and the floating structure to the anchors. Towards this end, our team conducted the following:

Reviewed environmental conditions and design basis
Environmental conditions used in the design were reviewed, and it was determined whether they covered a representative range of conditions for the planned deployment.

It was determined that the location was exposed to tidal eddies that produce greater cross-flow, resulting in multiple nonobvious design cases. The team provided assurance that the site was also sheltered in specific directions that limited the exposure to waves and tidal flow and interaction between these.

Operational weather forecasting processes and site condition limits were reviewed.

Investigated regulatory compliance
The navigation risk assessment (NRA) completed for the deployment was reviewed for completeness.

Analysed mooring designs and checked the structural integrity
Critical structural points were analyzed to ensure acceptable design limits and fatigue life.

In this example, no structural integrity calculations of the hull were performed as a review of the design documentation were deemed satisfactory. However, it was emphasized to the developer that visual inspection before deployment by an experienced third party is required.

A review of the mooring analysis and design was completed to ensure that the mooring design followed industry accepted practices and standards and utilized the specific environmental characteristics of the site. It was determined that no additional numerical modelling of the mooring was required.

Checked installation and marine operation plans and limits
Operational environmental limits for marine operations were reviewed and established along with alpha factors to account for weather uncertainty based on relevant standards.

Documented the independent review
At the end of the review, the client received a professional report which included:

reference documents
description of conditions, limitations and assumptions taken
review of design and considerations
appropriate appendixes

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The tasks completed during 360 TPV depend very much on the needs of the client, but the case above is typical of many projects.

“Should I be worried about sharing our trade secrets?”

All projects are completed with the utmost respect for privacy and confidentiality. Non-disclosure agreements are always step-one in any 360 TPV project.  Our success depends on your success, and we understand you must protect your trade secrets and business advantages. Everything that is shared is confidential.  

What the history of flight can teach marine renewable energy

360 TPV is designed to provide your company with the same wrap-around technical expertise that Octave Chanute provided the Wright brothers. Chanute was fascinated by flight and capitalized on his engineering knowledge to solve the problems of flight making him a valued and trusted resource.

360 TPV provides independent third party oversight to your engineering design, location suitability, operability, regulatory and license compliance, as well as cost-effectiveness and invest-ability. It is an integrated, holistic and formalized service delivered by Orcades, DSA, and Aquaterra.

Whether it’s 1903 and you’re the Wright brothers, or it’s 2018 and you’re a technology developer, consulting with industry experts brings confidence to project developers, insurers, investors, authorizing bodies, customers, test facilities, and government. 360 TPV provides an opportunity for you to benefit from the experience of those who have gone before and it delivers independent, sharp insight, improving your likelihood of success.

Minimize Risk and Maximize Opportunity with 360 TPV

Meet our Team

Aquatera

Orcades Marine Consultants