OTEC Cold Water Pipe Stress Relief via Compliant Ropes

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Solution Overview

Problem

Ocean Thermal Energy Conversion (OTEC) systems face significant stress on cold water pipes due to severe weather and wave action, leading to potential catastrophic failure at the joint between the pipe and the platform, with forces reaching up to 3E9 Newtons in 40 meter peak to peak waves.

Innovation Solution

The implementation of a surge volume tank, two floatation systems, a vertical sliding/rolling joint with large rollers, and a compliant mounting system using multiple, large diameter ropes to alleviate stress and prevent water hammer, allowing for stress relief and mitigation of six degrees of freedom motion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If the cold water pipe is hard mounted to the OTEC platform, then the structural support is strong, but the stress from wave action and severe weather causes catastrophic failure

Engineering Contradiction:

Improvestructural supportVSAvoidresistance to wave action stress

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent changes the mechanical parameters of the mounting system by replacing rigid connections with compliant ropes that have specific elasticity and strength properties. The ropes are designed with particular diameter and material characteristics to provide both support and stress absorption, transforming the mounting from rigid to flexibly compliant.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs flexible mounting elements in the form of large diameter ropes that act as compliant mountings. These flexible elements replace rigid structural connections, allowing the system to accommodate wave-induced motions while maintaining structural support through the elasticity and tensile strength of the rope material.

Inventive Principle:

Principle #30Flexible shells and thin films

2Ease of manufacture

If the cold water pipe is rigidly connected to the platform, then installation is simple, but the pipe experiences water hammer and catastrophic failure under wave action

Engineering Contradiction:

Improveinstallation simplicityVSAvoidwater hammer and stress

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent introduces compliant ropes as intermediary elements between the cold water pipe and the OTEC platform. These ropes serve as a mediating mounting system that simplifies installation compared to rigid structural connections while simultaneously providing stress absorption and water hammer protection through their compliant nature.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The compliant rope mounting system provides beforehand cushioning by being pre-designed to absorb stress and mitigate water hammer effects before they can cause damage. The elasticity and damping properties of the ropes are selected to cushion against anticipated wave-induced forces and pressure transients.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Reliability

If the cold water pipe is supported by floatation systems, then stress on the pipe is reduced, but the system complexity increases

Engineering Contradiction:

Improvestress reliefVSAvoidmounting system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent employs floatation systems that provide buoyant forces to counteract the weight of the cold water pipe. This anti-weight approach reduces the stress on the pipe by having the floatation devices support the pipe's weight through buoyancy, thereby decreasing the load on the mounting ropes and improving reliability.

Inventive Principle:

Principle #8Anti-weight (Counterweight)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The described system effectively reduces stress on OTEC cold water pipes, preventing catastrophic failure by avoiding water hammer and distributing forces, thereby enhancing the structural integrity and operational reliability of the OTEC system.

Implementation Method 1

The first floatation system can be placed at some depth below the platform and can support most of the weight of the cold water pipe

Methodology Applied

Scientific EffectBuoyancy: Archimedes' Principle (Buoyancy)

Implementation Method 2

The second floatation system can be placed above the pipe in the moon well, can support the remainder of the weight of the pipe, and also can contribute some amount of reserve buoyancy

Methodology Applied

Scientific EffectBuoyancy: Archimedes' Principle (Buoyancy)

Implementation Method 3

One advantage to this design is the avoidance of water hammer, a condition that can occur in pipes where a slug of liquid inside the pipe is propelled at a high velocity or is subjected to a quick high pressure spike

Methodology Applied

Scientific EffectWater hammer prevention: Fluid Hammer

Data Source

PatentUS7735321B2OTEC cold water pipe system

Publication Date: 2010.06.15 LOCKHEED MARTIN CORP

AI summary

A system for relieving the stress on an Ocean Thermal Energy Conversion (OTEC) cold water pipe includes a slidable joint that couples the OTEC cold water pipe to a surge tank at an opening in the surge tank. The system can further include a first flotation device that is coupled to the OTEC cold water pipe below the surge tank, and a second flotation device that is coupled to the OTEC cold water pipe within the surge tank.