Semantic Segmentation in Underwater Ship Inspections: Benchmark and Data Set
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In this article, we present the first large-scale data set for underwater ship lifecycle inspection, analysis and condition information (LIACI). It contains 1893 images with pixel annotations for ten object categories: defects, corrosion, paint peel, marine growth, sea chest gratings, overboard valves, propeller, anodes, bilge keel and ship hull. The images have been collected during underwater ship inspections and annotated by human domain experts. We also present a benchmark evaluation of state-of-the-art semantic segmentation approaches based on standard performance metrics. Consequently, we propose to use U-Net with a MobileNetV2 backbone for the segmentation task due to its balanced tradeoff between performance and computational efficiency, which is essential if used for real-time evaluation. Also, we demonstrate its benefits for in-water inspections by providing quantitative evaluations of the inspection findings. With a variety of use cases, the proposed segmentation pipeline and the LIACI data set create new promising opportunities for future research in underwater ship inspections.Keywords:
Benchmark (surveying)
Underwater image segmentation is an important technique for underwater machine vision and underwater resources exploration. For the complexity of imagery underwater image segmentation is more difficult that that for common images. Methods on underwater image segmentation are studied. The advantages and limitations of each algorithm are discussed. Future searching trends for underwater image segmentation are given.
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A method for calculating the hydrodynamic forces acting on an obliquely sailing ship with helm angle is developed, in which the mutual interaction among hull, propeller and rudder is taken into account. The hull and rudder are treated by the surface panel method, and the propeller is expressed by a simplified propeller theory. The hull to be calculated is not limited to slender or thin because of the use of the surface panel method. A wake vortex model of an obliquely sailing hull is proposed to save computer time after an iteration procedure for determining the wake vortex shape completed. To express hydrodynamic interaction between hull and propeller-rudder system, new interaction coefficients are introduced.
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Model tests have been performed in the deep water towing tank and large cavitation tunnel of the NSMB to study the propeller generated hydrodynamic hull forces of a Great Lakes bulk carrier, which suffered from severe vibrations. The investigation also comprised propulsion, wake, flow and cavitation tests. High speed movies were made to study in detail propeller-hull vortex cavitation and to investigate the correlation between this cavitation phenomenon and the pressure fluctuations on the hull. Further, pressure measurements on full scale were performed and a good agreement with the results from model tests was found. It is shown that a stern tunnel fitted to the hull above the propeller reduced the excitation forces more than a modified propeller design. Application of vertical fins, to avoid propeller-hull vortex cavitation, showed an increase of average excitation level.
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This paper considers inadequacies in the formulas for ship global hull strength currently approved by members of the International Associations of Classification Societies (IACS). Citing the results of several experimental and numerical studies, the author proposes modifications to the Rules formulas on ship hull vertical bending moments. Wave loading on the hull under steady wave conditions is studied for long-term ship operations, and the existing fatigue strength standards for hull longitudinals are also examined.
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An outstanding problem in naval architecture is the selection of the propeller geometry and the location of the propeller in the aperture in order to reduce the sum of the propeller-induced vibratory bearing forces and moments and the hull surface forces and moments to an acceptable minimum. This paper presents a reliable method for calculating these net excitations for arbitrary stern and propeller configurations. A computer solution for the propeller and hull excitations has been developed and assessed by comparison with two independent sets of model measurments. The paper describes the physical mechanisms involved in visualisation of the velocity field and outlines the mathematical models employed to represent the propeller in the hull wake and the hull surface. Although the method is currently limited to non-cavitating propellers, it can embrace the dominating excitations arising from intermittent blade cavitation. Order from BSRA as No. 54,391.
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A practical method for the prediction of cavitation on a propeller operating in a ship wake and hull surface pressure induced by a cavitating propeller is presented.In this method, the following items are applied : i) propeller part : the combination of Hanaoka-Koyama's unsteady lifting surface theory and corresponding 2-D wing theory ii) cavitation part : linearized 2-D cavity theory applying the angle of attack and the local cavitation number derived form i) iii) hull surface pressure part : the application of the method of periodic source in place of cavity volume variation while a propeller blade is turning behind hull, moreover blade loading and blade thickness are includedIn order to stand the practical use, correction factors on the cavitation part are adopted from 2-D cavitation test and actual ship observations. The predicted results on blade cavitation and hull surface pressure are compared with measured one, and the advantages of the method are discussed.
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High-amplitude fluctuations in hull-surface pressures induced by unsteady propeller cavitation (with consequent hull vibration) are mainly the result of the nature of the wake field, but it must be accepted that the propeller loading distribution associated with maximum propulsive efficiency makes it difficult, if not impossible, to control cavitation under adverse flow conditions. Experience with unusual propeller-loading distributions associated with suppression of noise from warship propellers has led to a consideration of non-optimum, or arbitrary, loading distributions as a more general means of controlling pressure amplitudes, and a research programme has accordingly been carried out in which a design method for an arbitrarily-loaded wake-adapted propeller was developed. The Authors describe this design method, which, because of the uncertainties of such a propeller being successful, was put together from components of existing methods without undue expenditure of effort on the preparation of computer programs. The application of the method to the re-design of a propeller (for a single-screw container-ship) is also described, and an account is given of the associated tests, carried out on models of a 100% tip-unloaded propeller at the National Maritime Institute and consisting of open-water tests, self-propulsion tests with the model hull, and, in the cavitation tunnel, cavitation viewing and pressure measurements behind a partial-hull model. The results of the model tests, and comparisons with results from earlier experiments on models of the as-fitted propeller, are presented and discussed in some detail. It is concluded that, while the design process requires refinement, this research has clearly demonstrated the possibility of controlling hull surface pressure forces by varying the radial distribution of loading on the propeller. The advantages and disadvantages of tip unloading have been clearly defined, and the shipowner is presented with the choice between (i) maximum propulsive efficiency with the risk of severe vibration, and (ii) vibration-free running with reduced efficiency. Reports from the first full-scale application of this research, a retrofit on a large gas-carrier, are good.
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Naval architecture
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An outstanding problem in regard to the design of ships is the selection of the propeller geometry and the location of the propeller in the aperture in order to reduce the sum of the propeller-induced vibratory bearing forces and moments and the hull surface forces and moments to an acceptable minimum. This paper presents a reliable method to predict these net excitations for quite arbitrary stern and propeller configurations. A computer solution for the propeller and hull excitations has been developed and assessed for its adequacy by comparisons with two sets of model measurements.
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This paper describes the hydrodynamic performance prediction of ship hull with propeller by using CFD techniques. As an attempt in investigating the flow features around ship hull equipped with a rotating propeller, open water test, resistance test, and self-propulsion test were conducted. The paper discusses also the applicability of different turbulence models which are used to predict the hydrodynamic performance of the propeller, the hull, and the interaction hull-propeller. The hydrodynamic performance prediction method was gotten and was validated. The computational results were validated against the existing experimental data.
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