Journal of Marine Science and Technology最新文献

The Circulating Water Channel (CWC) is a device commonly utilized in maritime engineering for hydrodynamic experiments. The ability to generate a high-quality flow field is a critical criterion for evaluating the device, and thus, improving key parts of the CWC device can significantly increase this ability. In this paper, a numerical model based on the RANS method is established to investigate the hydrodynamic performance of the circulating water channel’s finite section. First, associated analyses and optimizations for the turning vanes and contraction section are performed. Following confirmation that adding a honeycomb can greatly improve the flow field, the hole type and length diameter ratio are investigated further. After integrating the components, the flow field properties are examined at various flow velocities. The main findings demonstrate that flow field’s uniformity can be enhanced using the right number of turning vanes. Applying the Witozinsky transition curve to the contraction section can produce a better pressure gradient and increase the efficiency of contraction selection. The best rectification result is achieved by a honeycomb with a square shape and a slenderness ratio of 9. By varying flow velocities, the most uniform flow field area occurs at 4 m to 16 m from the outlet of the contraction section. This model can better simulate the dynamic characteristics of the flow field in the 3D CWC and serve as the foundation for the design of multifunctional CWC equipment for wind, wave, and flow.

Numerous accidents caused by parametric rolling have been reported on container ships and pure car carriers (PCCs). Considering this dangerous phenomenon, the parametric rolling in irregular seas is examined in this paper based on the stability of the systems origin, which corresponds to the upright condition of the vessel. It provides a novel theoretical explanation of the instability mechanism for two cases: white-noise parametric excitation and colored-noise parametric excitation. Moreover, the authors confirm the usefulness of the previously provided formulae by Roberts and Dostal by means of numerical examples.

Propeller cavitation is one of the main causes of pressure fluctuation and noise around marine propellers, and tip vortex cavitation is one of the main causes of high-frequency underwater radiated noise. To predict tip vortex cavitation, it is necessary to correctly describe the radius of the vortex core and the vortex circulation of the tip vortex. Therefore, in this study, non-cavitating flow field measurements around the tip of model propellers were made for the 0.75 m diameter working section of the large cavitation tunnel at the National Maritime Research Institute, Japan (NMRI) using 2D-PIV. Identification procedures were investigated to develop a tip vortex model. The vortex properties (radius of vortex core and vortex circulation) of the tip vortex were obtained by applying by a Rankine vortex model and a Burgers vortex model. The measured velocity and vorticity values around the tip vortex as identified by the Burgers vortex model were in better agreement than those given by the Rankine vortex model. The Burgers vortex model was suitable for obtaining vortex properties from the measured flow field around the tip vortex. The vortex properties obtained from the identification using the Burgers vortex model showed the Reynolds number demonstrated a greater effect on the radius of the vortex core and vortex circulation. The higher the Reynolds numbers, the smaller the radius of the vortex core and the smaller vortex circulation tends to be. It is also shown that this Reynolds number effect differs depending on the blade shape of the propellers.

This paper proposes and demonstrates a simulator-based approach for testing and assessing human operators’ ability and performance in supervising autonomous ships. In the autonomy concept studied here, it is assumed that the autonomous navigation system is capable of detecting and notifying the human operator prior to entering a challenging situation. The system will attempt to resolve the situation with a proposed evasive maneuver, but the system may occasionally make errors or select sub-optimal solutions. When the human operator is notified about a challenging situation, the operator should closely assess the situation, and intervene if (and only if) necessary. The proposed approach allows us to test and quantify the human operators’ abilities and performances in supervising an autonomously navigated ship. The approach is demonstrated on 56 simulator experiments, involving seven different navigators that perform eight different traffic scenarios. The scenarios are all based on real traffic data collected from a Norwegian ferry-crossing. The demonstration shows that the candidates are successful in supervising the autonomous ship in low-complexity traffic scenarios where it is easy for the operator to interpret the system’s decisions. The operators’ ability to intervene when and only when needed does, however, decline in more complex scenarios, and their performance is highly dependent on the traffic scenario and vary significantly between the candidates.

The present numerical investigation evaluates the significance of seabed undulations on the efficiency of an oscillating water column (OWC) device. The proposed physical problem is formulated in a two-dimensional Cartesian coordinate system under the framework of linearized potential flow theory. The numerical model based on the dual-boundary integral equation method (DBEM) is employed to solve the boundary value problem (BVP), and the study presents the hydrodynamic coefficients of the OWC device in the presence of a composite wavy seabed. Various effects such as the effect of seabed undulations, OWC configuration, chamber spacing, partial rotation of lip-wall, and lip-wall draft on the system radiation coefficients (i.e., wave energy capturing efficiency, radiation susceptance, and conductance) and wall force coefficient is presented against the relative wave frequency. The numerical results indicate that the efficiency of OWC is a trivariate function, which depends upon incident wave frequency, lip-wall rotation, and chamber spacing. The comparative study between various types of OWC devices (i.e., lip-wall configurations) is reported against relative wave frequency in the presence of bottom undulations. The peak performance of OWC is plausible using the resonance mechanism concept when the chamber spacing is moderate and lip-wall is either seaside horizontal or seaside partially inclined.

To achieve the goal of a 50% reduction of CO₂ emission in the maritime industry by 2050, different systems and solutions were proposed by researchers. Rigid wind sails, rotor sails, suction wings, and kites were developed to contribute to cleaner and environment-friendly transportation by reducing total fuel and energy consumption. In the present study, a ship dynamics model of KVLCC2 consisting of hull, rudder, propeller, and sailing system was built considering the effects of wind and wave. Firstly, the amount of energy consumption reduction of both systems was examined under different wind directions and wind speeds. It was found that a single sailing system can reduce total energy consumption by up to 10%. Then, the effects of the ship speed, the position of the sailing system, and the number of sails on the reduction of energy consumption were examined. It was found that the amount of overall energy reduction reaches around 23% and 16% when the number of sails was increased to 10 rigid wind sails and 10 rotor sails, respectively. The effects of waves were also investigated, and it was revealed that wave forces decrease the percent energy reduction more when environmental conditions become more severe, starting from the Beaufort scale of 7.

Underwater communication is one of the most important and difficult challenges facing researchers due to the high attenuation of the signal, communication with the surface because of the harsh medium of water, and data transmission performance degradation as a result of various effects. Underwater acoustic communication (UWA) has a low data rate, which describes the disadvantage of this type of communication. In addition, it has a low bandwidth range and high latency but has a long transmission range as an advantage. Multicarrier wireless transmission systems increase the data rate by sending the data using more than one carrier. We proposed a noncoherent orthogonal frequency division multiplexing (OFDM) method to increase the data rate in UWA communication systems. In addition, doubling the data rate in the OFDM using Subcarrier Power Modulation (OFDM-SPM) system can save half of the bandwidth. The MATLAB simulation program was used to implement the system in the underwater acoustic environment to increase its throughput. The proposed design uses Differential Phase Shift Keying (DPSK) with power control, and the data stream is transmitted through two-dimensional modulation schemes, the DPSK, and the power level of each subcarrier in the OFDM system with cyclic prefix (CP). The underwater channel was designed using a Rician fading multipath with a spreading loss formula as a function of distance and frequency. We designed an equalizer at the receiver side to recover the original signal as a function of three parameters which are: the channel effect as a rate between transmitting and receiving symbols, the Rician channel response, and the UWA spreading loss. OFDM-Subcarrier Power Modulation (OFDM-SPM) using the proposed equalizer performed better than the theoretical OFDM-SPM in the Rayleigh channel. The designed equalizer increased the performance of the OFDM-SPM system by 25% which helped to enhance the system’s throughput and doubled the data rate compared with the OFDM system, doubling the data rate using OFDM-SPM had been validated in laboratory experiments in the Time domain.

In maritime transportation systems, the stability and structural integrity of ship-mounted tanks subjected to sloshing phenomenon are critical due to economic considerations and to ensure ecological safety. During the voyage, the ships are subjected to external excitations, which induce sloshing in fluid in partially filled tanks mounted on the ship’s deck. This article investigates the effect of rotational axis configurations on the slosh dynamics of a 24,000 TEU water tank mounted on an Ever-Ace container ship. Sloshing phenomena caused by different combinations of piecewise sinusoidal rotational excitations have been compared. The fluid domain was simulated using ANSYS Fluent, coupled with transient structural analysis in ANSYS Mechanical, to analyze the structural integrity of the container. The fluid pressure loads were imported on the tank structure using a one-way FSI approach. The numerical results have been validated with the experimental data available in the literature. It has been found that the effects of viscous sub-layer are insignificant on the slosh dynamics of the tank. Moreover, the transient response of the air–water interface, impact pressure, and wall moment have been presented. Wave fluctuation is observed to be small when the axis of rotation is perpendicular to the free surface. Maximum impact pressure of 7 kPa has been observed for combination of roll and pitch motions. The range of amplitude of moment is maximum for combination of roll and pitch motions that varies from − 95.6 to 92.3 kN m. Furthermore, the frequency of the moment differed from the excitation frequency depending on the configuration of the rotational axis.

To achieve energy conservation and improve ship maneuverability, a new type of collaborative spoiled rudder (CSR) is proposed by absorbing the advantages of existing ship rudders. This study investigates the non-stationary characteristics of the hydrodynamic forces of CSR section in depth, and carries out structural optimization based on numerical simulations. First, the effects of rudder angle and spoiler open angles on the non-stationary characteristics of the hydrodynamic forces of the CSR, and the appropriate maximum value of the spoiler open angle is determined. The results show that the unsteady pulsation amplitude of the hydrodynamic forces of the CSR is directly proportional to the spoiler open angle and inversely proportional to the rudder angle, and the upper limit of the spoiler open angle is set to 30°. Then, the hydrodynamic characteristics of the CSR with different spoiler widths are investigated in further. The maximum lift of the CSR increases as the spoiler width increases. The target lift method is used for efficiency evaluation. The ranges of the favorable rudder angle and the favorable spoiler open angle for different CSR configurations are determined, and the optimal spoiler width is further determined based on the non-stationary characteristics of the hydrodynamic forces.

Ocean thermal energy conversion (OTEC) is a heat engine application that utilizes the Rankine cycle to extract energy from the thermal gradient between surface seawater and deep seawater. Hybrid cycle OTEC (H-OTEC) is a combination of an open cycle desalination system and a closed-cycle power generation system that leverages the features of both cycles. Unlike other desalination technologies that require extensive energy to operate, H-OTEC relies entirely on renewable energy. In addition, a desalination plant can be coupled with the H-OTEC system (H-OTEC + D) to improve its performance. Conventionally, the total heat transfer area of heat exchangers per net power is used as an objective function to achieve optimal performance with the lowest capital expenditure cost. The proposed objective function, unlike the conventional one, considers both power and water. In this study, the optimization of H-OTEC + D and H-OTEC is carried out by minimizing the proposed objective function, considering several independent variables. The performance of both systems is evaluated in terms of the objective function, power consumption, seawater flow rates, and desalination ratio. The findings also indicate the effectiveness of the proposed objective function over the conventional one as an effective tool for maximizing power and desalinated water generation.