Ship Speed Meter Using Multi-Depth Current Velocity Analysis
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Solution Overview
Problem
Existing ship speed meters, both electromagnetic and acoustic, face inaccuracies in measuring ship speed relative to water due to the assumption of a constant boundary layer thickness, which varies with factors like hull fouling, pitching, and sea currents, leading to incorrect measurement points within the boundary layer.
Innovation Solution
A ship speed meter that measures the change rate of current velocity at multiple depths and calculates the speed based on a predetermined threshold, using a wave transmitter, wave receiver, and arithmetic processing unit to determine the accurate speed by analyzing frequency differences and electromotive force, ensuring measurements are taken outside the boundary layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed measurement point is used based on assumed boundary layer thickness, then the device structure is simple, but measurement precision deteriorates because the measurement point may be inside the boundary layer
Solution Approach 1:
The measurement point is made dynamic by automatically adjusting its depth based on real-time boundary layer thickness measurements. The system continuously monitors boundary layer characteristics and repositions the measurement point outside the boundary layer, transforming a static measurement system into an adaptive one that maintains accuracy under varying operational conditions.
Solution Approach 2:
The system incorporates feedback mechanisms where measurement data from multiple points is analyzed to determine boundary layer thickness, which then feeds back to adjust the measurement point position. This closed-loop control ensures the measurement point remains outside the boundary layer, improving accuracy without requiring complex manual intervention.
2Measurement precision
If multiple measurement points are used to account for boundary layer variation, then measurement precision improves, but device complexity increases
Solution Approach 1:
The measurement system is segmented into multiple sensor units positioned at different depths, each measuring current velocity independently. This segmentation allows the system to capture vertical variations in current velocity and identify the measurement point outside the boundary layer, improving accuracy while maintaining manageable system complexity through modular sensor design.
3Reliability
If measurement point is fixed at a constant depth, then ease of operation is high, but reliability deteriorates under dynamic conditions like hull fouling and pitching
Solution Approach 1:
The system transitions from a fixed-depth measurement approach to a dynamic measurement system that automatically adjusts measurement point depth in response to changing boundary layer conditions caused by hull fouling, pitching, and rolling. This dynamic adaptation maintains measurement reliability without requiring manual system reconfiguration.
Solution Approach 2:
The measurement system performs self-adjustment by automatically detecting boundary layer thickness changes and repositioning the measurement point accordingly. This self-service capability eliminates the need for manual intervention to maintain measurement accuracy under varying operational conditions, preserving ease of operation while improving reliability.
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
This approach allows for a more accurate determination of ship speed relative to water by accounting for varying boundary layer thickness, providing reliable measurements even under dynamic conditions.
Implementation Method 1
the acoustic ship's speed meter (sometimes called 'Doppler log') measures a ship's speed relative to the water using the Doppler effect
Implementation Method 2
the wave transmitter emits sound waves to the bottom of water and the wave receiver detects sound waves reflected by the bottom of water or by suspended matter in water
Implementation Method 3
the electromagnetic ship's speed meter measures a ship's speed relative to the water using the law of electromagnetic induction
Data Source
AI summary
A ship's speed meter for measuring a speed relative to the water of a ship 10, the ship's speed meter including a wave transmitter 1 for emitting a sound wave toward a sea bottom 20, a wave receiver 2 for detecting a plurality of reflected waves, which are reflected waves of the sound wave having been emitted from the wave transmitter 1, reflected by a plurality of reflecting objects 30 positioned at different water depths, and an arithmetic processing unit 4 for calculating a ship's speed relative to the water of the ship 10 based on a frequency difference of the sound wave and the reflected wave. The arithmetic processing unit 4 obtains a change rate of a current velocity in a water depth direction by obtaining current velocities at a plurality of different water depths based on a frequency difference between the sound wave and the plurality of reflected waves, and calculates a current velocity at a water depth at which the change rate is smaller than or equal to a threshold value as the ship's speed relative to the water of the ship 10.