LNG Cargo Sloshing Mitigation via Compartment Period Separation

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Solution Overview

Problem

LNG cargo sloshing during loading and unloading at offshore terminals causes damage to cargo containment systems due to vessel motions driven by wave conditions, limiting terminal operability and feasibility.

Innovation Solution

Distributing liquid cargo to multiple storage compartments at different fill levels to separate their natural periods, reducing the coupling effect between vessel and cargo motions and thereby minimizing sloshing impacts.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If LNG carrier performs cargo operations at offshore terminals exposed to waves, then terminal operability and feasibility are improved, but cargo sloshing damage to containment system increases

Engineering Contradiction:

Improveterminal operabilityVSAvoidcargo sloshing damage

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The cargo containment system is divided into multiple separate storage compartments instead of using a single large tank. This segmentation allows each compartment to have different natural periods, preventing resonant sloshing across the entire cargo load while maintaining total cargo capacity for offshore terminal operations.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each storage compartment is designed with different fill levels and/or dimensions to create locally distinct natural periods. By making the local characteristics (fill level, compartment size) different, the system prevents uniform resonant sloshing patterns that would occur in a single-compartment design, thereby reducing overall sloshing damage while enabling offshore operations.

Inventive Principle:

Principle #3Local quality

2Ease of operation

If storage compartments are filled to the same level, then loading/unloading operations are simplified, but natural periods of compartments become coupled increasing sloshing

Engineering Contradiction:

Improveloading/unloading operation simplicityVSAvoidcargo motion coupling

Core Design Contradiction:

Ease of operationVSStability of the object's composition

Solution Approach 1:

The system intentionally creates local quality differences by filling storage compartments to different levels or designing them with different dimensions. This results in different natural periods for each compartment, which decouples the cargo motion and prevents resonant sloshing, while still allowing standardized loading/unloading procedures to be used across all compartments.

Inventive Principle:

Principle #3Local quality

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

Significantly reduces roll and sway motions, decreasing the risk of cargo sloshing damage and enhancing the operational availability of offshore LNG terminals.

Implementation Method 1

distributing liquid cargo to multiple storage compartments at different fill levels to separate their natural periods, reducing the coupling effect between vessel and cargo motions and thereby minimizing sloshing impacts

Methodology Applied

Scientific EffectNatural period separation:

Implementation Method 2

Methodology Applied

Scientific EffectSloshing reduction:

Data Source

PatentUS8915203B2Transporting liquefied natural gas (LNG)

Publication Date: 2014.12.23 EXXONMOBIL UPSTREAM RESEARCH COMPANY(US)

AI summary

There is provided a method for loading or unloading a liquid cargo for a water-borne vehicle. An exemplary method comprises distributing liquid cargo to a first storage compartment of the water-borne vehicle to a first level. The exemplary method additionally comprises distributing liquid cargo to a second storage compartment of the water-borne vehicle to a second level different from the first level so that a natural period of the first storage compartment is separated relative to a natural period of the second storage compartment to reduce sloshing of the liquid cargo. An exemplary water-borne vehicle and method of producing hydrocarbons are also provided.