Sloshing Alert System for LNG Tank Resonance

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Solution Overview

Problem

Sloshing of liquid cargo in LNG tanks during ship motion can cause severe damage due to resonance with ship movements, especially in partially filled tanks, leading to unpredictable and varying impact magnitudes, which existing computational fluid dynamics and regulations struggle to accurately predict and mitigate.

Innovation Solution

A sloshing alert and advisory system (SAAS) that calculates the natural period of liquid cargo based on tank configuration and fill percentage, receives ship motion data, and provides alerts and advisories to operators on changing conditions such as heading, speed, route, draft, and trim to minimize sloshing risks, using real-time motion sensors and predictive analysis.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If LNG tanks are partially filled to increase flexibility in dispensing partial loads, then cargo flexibility is improved, but the risk of sloshing damage increases due to resonance with ship motions

Engineering Contradiction:

Improvecargo flexibilityVSAvoidsloshing damage risk

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The system calculates the natural period of the liquid cargo before shipping and compares it with the ship's roll and pitch periods. By performing this analysis in advance, operators can identify resonance risks before they materialize, allowing proactive adjustments to cargo operations or vessel routing to avoid dangerous conditions while maintaining flexible partial loading capabilities

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system continuously monitors ship motion data and compares it with the calculated natural period of the liquid cargo. When the ship's motion period approaches the liquid's natural period (within a threshold value), an alert is generated. This feedback mechanism enables real-time detection of resonance conditions and allows operators to take corrective actions to prevent sloshing damage while maintaining cargo flexibility

Inventive Principle:

Principle #23Feedback

2Measurement precision

If computational fluid dynamics are used to predict sloshing, then prediction capability is improved, but reliability is worsened due to inability to consider entrapped bubbles

Engineering Contradiction:

Improvesloshing prediction capabilityVSAvoidprediction accuracy

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent replaces complex computational fluid dynamics simulations with a simplified mechanical approach based on natural period calculations. By using the natural period formula for liquid in tanks and comparing it with ship motion periods, the system achieves reliable predictions without the computational complexity and limitations of CFD, particularly regarding entrapped bubbles. This substitution maintains sufficient accuracy for practical maritime operations

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 system effectively reduces the risk of sloshing damage by providing real-time alerts and decision support to operators, allowing for proactive measures to avoid resonance conditions, thereby minimizing cargo and structural damage.

Implementation Method 1

The cargo tank is particularly susceptible to damage when it is partially filled, and further susceptible to damage when the natural period of the liquid in the tank is in resonance with (near or equal to) roll or pitch motion periods of the ship.

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS8643509B1Methods and systems for providing sloshing alerts and advisories

Publication Date: 2014.02.04 THE BOEING CO

AI summary

A method is described for providing an alert when the motion of a ship indicates a potential of sloshing damage from liquid cargo being transported by the ship. The method includes calculating, with a processing device, a natural period for the tanks holding the liquid cargo based on the configuration and fill levels of the tanks, receiving, at the processing device, data describing the actual or predicted motion of the ship with respect to three orthogonal axes, determining, with the processing device, a proximity of the natural period of the tanks to a period defined by the actual or predicted motion of the ship, and providing an alert to a user if the proximity in periods is within a threshold value.