選擇卷期
- 期刊
During the conceptual design of a high speed craft, the most important element of the process is resistance and drag prediction. To increase efficiency in high speed craft design, the prediction of total resistance must be increasingly accurate. To achieve this objective, model towing tank tests were used. Although testing will always be necessary, the growing field of computational fluid dynamics (CFD) is gaining interest, considering the experimental costs. This paper investigates both the experimental and numerical methods of total resistance prediction for a high speed hull, including comparison of the trim and sinkage measurements. Additionally, the model tests were compared to CFD methods when considering the numerical ventilation problem (NVP) and were also validated with full-scale test results. It was shown that at high speeds, the numerical solution of the ventilation problem may lead to an erroneous drag reduction of 27%. To overcome this, replacing the air phase with the water phase under the hull provides an efficient solution. For the numerical solutions with Froude number (Fn) ＞ 0.50 after resolving the NVP, the calculated total resistance shows quite good agreement with the experimental data, with a margin of 2.86%.
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The flow characteristics and velocity fields of swirling double-concentric jets at a high central jet Reynolds number were studied. The central jet Reynolds numbers varied from 700 ＜ Re_c ＜ 1000. The flow behaviors of the swirling double-concentric jets were observed using a laser light sheet assisted by a smoke-wire flow visualization technique. The time-averaged velocity vectors and streamlines, normalized velocity contours, fluctuation intensity contours, and vorticity contours were carried out using particle image velocimeter (PIV). Two characteristic flow modes are classified: the central jet-dominated radial flow occurs at a low annular jet Reynolds number while the high-turbulence swirling wake appears at a high annular jet Reynolds number. The flow feature of the central jet-dominated radial flow presents a wide-open shear layer because of the effect of a high-speed deflected central jet. A large dual-ring vortex in the wake and two pairs of vortices in the gap between the control disk and primary disk in the high-turbulence swirling wake mode appear. The turbulence intensity in the high-turbulence swirling wake were significantly larger than those in the central jet-dominated radial flow.
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The issue of data completion is important for the elliptic type partial differential equation. In the inverse Cauchy problem, we need to complete the boundary data by over-specifying Dirichlet and Neumann data on a portion of the boundary. In this paper, we numerically solve the generalized inverse boundary value problems of Laplace equation in a rectangle with one boundary function and two boundary functions missing, which are more difficult than the inverse Cauchy problem. By using the technique of a boundary integral equation method together with a specially designed Trefftz test function, we can complete the boundary data by requiring minimal extra data. Then solving the Laplace equation with the given data and recovered data by the multiple-scale Trefftz method, we can find the numerical solution in the interior nodal points.
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This paper investigates a mixed H_2/Passivity performance control problem of uncertain stochastic systems. Based on Itô stochastic equation, the considered system is described by a linear difference equation with multiplicative noise term. To minimize output energy and guarantee asymptotical stability, the H_2 scheme is employed. Moreover, passivity theory is applied to constrain the effect of external disturbance on the system. According to the passivity theory, a general and flexible mixed performance controller design method is proposed. Based on Lyapunov function, some sufficient conditions are derived into extended Linear Matrix Inequality (LMI) form which reduces conservatism of finding the feasible solutions. Furthermore, the derived conditions can be directly solved by convex optimization algorithm to establish a controller such that asymptotical stability and mixed H_2/Passivity performance of the uncertain stochastic system are achieved. At last, an inverted pendulum system is used to show effectiveness and applicability of the proposed method.
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In this paper, the performance of a 2000-ton hybrid AIP system submarine is investigated by analyzing the weight, volume and efficiency of its propulsion system. The engine of the investigated AIP system employs a low temperature polymer electrolyte membrane fuel cell which makes use of the hydrogen and oxygen as the reactants. More specifically, the reactants of fuel cell in this study are considered from the combination of three fuel storage systems, methanol (MeOH), liquid hydrogen (LH_2) and metal hydride (MH_2), and two oxidant storage systems, liquid oxygen (LOX) and compressed oxygen (O_2). Based on the assumed various daily propulsion load consumptions, a propulsion system of a 3500 kW diesel generator, a 300 kW fuel cell, and a 7500 kWh energy capacity Li-ion battery bank is determined. With the system installed in the submarine, the maximum designed endurance can reach a total of 26 days for the fuel cell using the combination of reactant LH_2+LOX, and the minimum designed endurance can be up to 10 days for using the reactant MH_2+O2. For submarine cruising at zero speed, the submerged endurance of the AIP system using reactant LH2 LOX plus battery bank is 22.8 times of that using battery bank alone. This value will increase to 25.0 times for submarine cruising at 7.4 knots. At the cruising speed of 5.5 knots, the maximum submerged range of submarine increases a factor of 24.1 for fuel cell using the reactant of LH_2+LOX as compared with operation on battery bank alone. Therefore, the submerged endurance is substantial enhanced for using the combination of fuel cell and battery. In addition, the indiscretion ratio is zero for the AIP system submarine with a cruising speed below 7.1 knots; this can greatly reduce the submarine vulnerability. Based on the weight and volume analysis of the submarine equipped with a hybrid AIP system, the usage of the reactant LH_2+LOX is well suited for a small- to medium-sized 2000-ton submarine with a fuel cell system. Furthermore, using the reactant MeOH+LOX has the advantage for large-sized LT-PEMFC AIP system submarines.
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With the increase of the sea disaster caused by ship capsizing, self-rescuing ability of damaged ship has attracted much attention among ship designers, ship owners, classification societies and authorities. Damaged ship righting optimization remains a very complicated problem due to the feasible combinations of counter-flooding approaches with different compartments and loads are numerous. The effectiveness and efficiency of the artificial bee colony (ABC) algorithm has been demonstrated on the combinatorial optimization problem. In this paper, an ABC algorithm-based righting plan optimization method for damaged ship is proposed. In this method, the objective is to minimize the inclination angle under a group of constraints regarding stability, floatation and available compartments and loads. The functions of damage stability and floatation calculation are integrated into the proposed method to evaluate the righting effect of each single counter-flooding measure. The proposed method in this paper is validated through a case study of finding optimal righting plan of a train ferry with two different damage scenarios, and provides a foundation for the adoption of emergency response technologies in ship operation.
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The active heave compensation (AHC) system on an offshore supply vessel (OSV) plays a pivotal role in offshore installation operations by minimizing the heave motion of suspended subsea equipment, regardless of the OSV motion. In order to successfully perform its function, the AHC system should have a suitable control algorithm, and its performance must be evaluated in advance of operation. Performance analysis of the AHC system requires complicated testing procedures, and a great deal of associated equipment. In particular, such analysis is often very costly and time-consuming, and realistic conditions are typically impossible to establish in a testing environment. To solve this problem, the Hardware-In-the-Loop Simulation (HILS) concept can be used as an effective method to test an AHC system prior to its final installation. In this study, we have constructed the HILS environment for an AHC system for an OSV, and conducted a performance analysis of the AHC system. To do so, a virtual model of the OSV was first created from a multibody system that can represent realistic motion in waves. Then, a controller of the AHC system with a control algorithm for heave compensation was implemented on real hardware. Next, an integrated simulation interface was implemented to efficiently connect the virtual model and the controller, and a visualization model was developed to verify simulation results by immersive and realistic views. Finally, a performance analysis of the AHC system was conducted within the proposed HILS environment. A numerical example is a deadweight 3,500 ton OSV to install a subsea manifold in regular and irregular waves. A comparative study between uncontrolled and controlled results of the AHC system was further performed. As a result, the performance of the AHC system could be evaluated effectively within the HILS environment.
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Shipbuilding, a significant sector of the international shipping market, shows fluctuations and periodicity typical of variations in supply and demand. However, it takes a significant amount of time to build a ship, and the influencing factors are complex. Therefore, attempts to understand the market's fluctuations by directly analyzing these influencing factors suffer from high inaccuracy, necessitating a quantitative analysis of shipbuilding's periodic features. In this paper, we used wavelet analysis, an efficient way to analyze time series data, to analyze the unit price of a Panamax bulk ship's compensated gross tonnage and get the periodical features of the market. Choosing a significantly periodic wavelet coefficient curve yields three different cycle lengths: a 1-year seasonal cycle, a 3.5-year short-term cycle, and a 13-year medium-to-long-term cycle. Finally, we analyzed the accumulated wavelet coefficient curve, and forecasted that the market should reach its next prosperity phase around 2023 in the medium-to-long-term cycle. The present study is in the direct interest of maritime practitioners, because it helps to more precisely forecast shipbuilding market fluctuations, allowing them to make informed decisions.
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In this study, a sound and vibration analysis of a marine diesel engine was conducted. The vibration and sound signals of the engine under various operating conditions were measured and analyzed by applying a spectrum analysis and an order-tracking analysis. In addition, a finite-element model of the engine was constructed via reverse engineering from a 3D scan. The main causes of engine vibration and noise were clarified and identified individually through the experiments and the engine model. Finally, the biodiesel-blended diesel fuel was used for the engine for comparing sound and vibration performance with the ultra-low sulfur diesel (ULSD). In mid to high-range speeds, the biodiesel-blended diesel fuel does reduce the engine exhaust noise and vibration amplitude caused by the constant engine combustion explosion.
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This study applied a time series of fully polarimetric synthetic aperture radar (SAR) images using RADARSAT-2 to analyze the polarimetric responses of the west coast of Taiwan. A total of seven images were acquired from 2009 and 2012, covering the low, high, and similar tide levels. A four-component target decomposition algorithm was used to investigate the tidal effects and dynamic ocean interactions of sandbanks near the coast. The experimental results showed that the Yamaguchi four-component decomposition can extract different features in the coastal area efficiently and effectively. From the target decomposition image constructed using the Yamaguchi four-component model, strong double-bounce scattering and weak volume scattering were favorable indicators of oyster farms, whether they were densely arranged or rugged, and surface scattering delineated the water boundaries of sandbanks. Using the extracted water boundaries and tidal-level information from different times, a sandbank elevation model was estimated. The experimental results also revealed that a small offshore sandbank had a displacement of approximately 1.5 km under a tidal level of -1.14 m. Furthermore, large sandbanks had a counterclockwise displacement on the west coast and moved eastward on the eastern coast.