Ship Bottom Coating Friction Estimation via Roughness Wavelength Filtering
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Solution Overview
Problem
Evaluating the frictional resistance increase in ship bottom coatings is challenging due to the influence of various factors like wave-making resistance, wind, and tidal currents, and existing methods are insufficient for accurately determining the optimal evaluation length and cut-off wavelength, limiting the effectiveness of surface roughness measurements.
Innovation Solution
A method involving the measurement of roughness parameters such as Rz, Rc, Ra, Rq, and RZJIS in a specific range, combined with a frictional resistance testing method using a double cylinder device and high-pass filtering, to calculate the frictional resistance increase rate using formulas like FIR (%)=C*R2RSm, where C is a previously determined coefficient based on the roughness and testing conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If surface roughness is measured using conventional methods (BSRA roughness meter with 50mm evaluation length), then the measurement process is simple, but the measurement precision and reliability of frictional resistance estimation is insufficient
Solution Approach 1:
The patent changes the key parameter of evaluation length from the conventional 50mm to 1000mm, and introduces a new parameter RSm (mean length of roughness profile elements) with a specific range (2-10mm). This parameter transformation allows for more accurate frictional resistance estimation by capturing the relevant wavelength range that actually influences drag, while maintaining measurement feasibility through standardized procedures.
2Reliability
If the evaluation length is extended to improve measurement accuracy, then the frictional resistance estimation becomes more reliable, but the measurement time and complexity increase
Solution Approach 1:
By extending the evaluation length parameter from 50mm to 1000mm and defining a specific wavelength range (2-10mm) for RSm, the patent captures the hydrodynamically significant roughness features that conventional methods miss. This parameter change improves reliability without excessive time cost because the measurement focuses on the most relevant wavelength range rather than measuring all scales equally.
Solution Approach 2:
The patent extracts and isolates the specific wavelength range (2-10mm) that is most relevant to frictional resistance using high-pass filtering with a cutoff wavelength of 10mm. This extraction allows the measurement system to focus only on the hydrodynamically significant roughness components, improving reliability while avoiding measurement of irrelevant longer wavelengths that would increase measurement time.
3Measurement precision
If multiple roughness parameters are measured to improve accuracy, then the estimation becomes more precise, but the ease of operation and simplicity are reduced
Solution Approach 1:
The patent identifies and focuses on the critical parameter RSm (mean length of roughness profile elements) within the 2-10mm range, combined with roughness height parameters (Rz, Rc, Ra, Rq, RZJIS). By specifying the wavelength range for RSm, the patent reduces the complexity of measuring all possible roughness parameters while maintaining precision, as this specific wavelength range is what primarily influences frictional resistance.
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 simple and accurate estimation of frictional resistance increase, enabling quick selection of antifouling coatings and evaluating coating performance, applicable in dockyards, with an economically viable evaluation device that fixes the wavelength range for precise measurements.
Implementation Method 1
measuring any one of Rz (maximum height roughness), Rc (mean height of roughness profile elements), Ra (arithmetic mean roughness), Rq (root mean square roughness) and RZJIS (ten-point mean roughness) as a roughness height R in a mean length RSm of roughness profile elements
Implementation Method 2
determining a torque T, which acts on an internal cylinder coated with a ship bottom coating paint when the rotation is carried out under the same condition, and determining the frictional resistance increase rate FIR (%)
Data Source
AI summary
A method of estimating a frictional resistance of a ship bottom coating film, the method including measuring any one of Rz (maximum height roughness), Rc (mean height of roughness profile elements), Ra (arithmetic mean roughness), Rq (root mean square roughness) and RZJIS (ten-point mean roughness) as a roughness height R in a mean length RSm of roughness profile elements in the range of 2,000 to 10,000 μm according to JIS B 0601:2001 (ISO4287:1997) on a coating film formed by applying a ship bottom coating paint on a substrate and calculating a frictional resistance increase rate FIR (%) from a mirror surface by the following formula (1), wherein coefficient C is a constant depending on the kind of the roughness height R and a frictional resistance testing method, and is previously determined in such a manner that plural ship bottom coating films each having different roughness are subjected to a roughness measurement and a frictional resistance test in a definite evaluation length, and then the coefficient C is determined by the formula (1) using the roughness height R, the mean length RSm of roughness profile elements and the frictional resistance increase rate FIR (%), which have been measured.