Advances in Marine Propulsion

Ship type identification is an important basis for ship management and monitoring. The paper proposed a new method of ship type identification by combining characteristic parameters from the energy difference between high and low frequencies and the sensitive IMF variance mean value based on the modal decomposition of the underwater radiated noise signals using the Ensemble Empirical Mode Decomposition (EEMD) method. The comparison shows that the characteristic parameters of different types of ship, underwater radiated noises are different, whereas those of the same types of ship, underwater radiated noises fall in close range. Validation experiments based on randomly selected ship underwater radiated noise samples manifest that the method is of good separability for the four types of ship underwater radiated noises in the Deepship dataset. It has a higher identification rate than other methods within the distance range of ship underwater radiated noise detection in the dataset. The accuracy of this method tends to decrease with distance in the classification experiments of the ship underwater radiated noises at different distances. Full article

The use of gas energy includes a wide range of applications to directly accelerate the liquid in a pipeline without the aid of mechanical equipment, such as marine gas-liquid jet propulsion. To clarify the characteristics of energy transfer by interphase forces for gas-liquid flows in variable cross-section tubes, two-fluid models of annular flow, bubbly flow and homogeneous flow were adopted, respectively, along with four newly elaborated coefficients, which are the work factor of gas $f_g$, reflecting the relative ability of gas to power liquid, the interface work transfer coefficient $k_g$ (representing the relative magnitude of mechanical work received by liquid from gas), the interphase work-to-energy conversion coefficient $k_l$ (denoting the capability of energy transfer through work performed by interphase forces) and the interphase mechanical efficiency ${\eta }_w$. The results reveal the interphase work transfer is strongly influenced by the structural parameters of the tubes (or nozzles), and an optimized design is necessary to improve the performance. The higher the degree of gas dispersion in the liquid, the more advantageous the conversion of gas work into the liquid’s mechanical energy. Of these three flow patterns, annular flow has the lowest $k_l$ and ${\eta }_w$ ($k_l$ = 0.0797, ${\eta }_w$ = 0.9885 in present example), while homogeneous flow displays the limit of interphase mechanical energy conversion because the gas-liquid momentum coupling reaches the maximum ($k_l$ = 0.9979, ${\eta }_w$ = 1). Full article

Taking advantage of end-plate effects to enhance propeller efficiency is engaging. This paper applied a 4-order B-spline curve to design the rake distribution of Kappel propellers using five types of Kappel propellers that each possesses different tip rakes, and one type has no constructed end-plate. The RANS method coupled with the γ transition model was utilized to analyze the open-water performance of the six propellers, considering cavitating flow. It was found that the tip rake is conducive to the thrust capacity of the Kappel propellers, mostly improving the propulsion efficiency by 2.5% at a designed advance speed with the appropriate tip rake. The increase in the tip rake will magnify the low-pressure value and area on the suction side blade surface, together with the phenomenon of the stretching tip vortex and the inhibition of wake vortex contraction, which are both beneficial to the elevation of propulsion efficiency. However, the sheet cavitation behavior of the six propellers aggravates as the tip rake rises. Accordingly, the reasonable range of a tip rake for the design of a Kappel propeller in favor of the propulsion performance is suggested in this paper, exhibiting the promising potential of energy savings for the application to marine vehicles. Full article

The composition characteristics and working principle of the hydraulic rotary system of the azimuth thruster were analyzed. The mathematical model of the rotary dynamic system of the pump-controlled hydraulic motor driving the gear reduction mechanism was established. Additionally, a fast tracking method for the azimuth angle of the azimuth thruster was proposed to analyze the rotary azimuth angle, angular velocity and dynamic response characteristics of the hydraulic system for different desired azimuth angles. The simulation results show that the established dynamic model can simulate the rotary motion response process of the real thruster, and can realize the rapid and accurate tracking of the azimuth angle. At the same time, the physical constraints of the rotary dynamic response were established. It provides an important reference for research on the motion control methods of dynamic positioning vessels. Full article

To create an autonomous surface vehicle, the microcontroller that will be responsible for the vessel’ s response will have access to both engine thrust controls and steering controls. In the case of a vehicle with waterjet propulsion, the term “controls” refers to engine RPM and nozzle angle. The latter allows the thrust vectoring. Having performed the mathematical modelling of the surface vessel, a method must be found such that the microcontroller actions on the controls create the desired outputs, based on predefined performance objectives. A commonly selected control algorithm considered an industry standard for control applications—at least from the perspective of classical control methods—is the PID control scheme. Many times, a PID control scheme is sufficient for achieving the required performance. There are also many methods that extend the functionality of the PID to robust control schemes, to accomplish more specific targets, such as noise rejection. The vast majority of all these implementations, will have to be implemented using a digital microcontroller or an FPGA. This paper assists theoretically in implementing PID controllers digitally, by elaborating on the discrete-time perspective of PID control. It also provides a test method for evaluating the algorithmic implementation. Full article

In order to identify the natural frequency of ship propulsion shafting under the running condition, a multi-method approach that combines Duffing Oscillator, harmonic wavelet packet transform, and probability density function is proposed. An experimental investigation on the natural frequency of running propulsion shafting is conducted on the ship propulsion shafting test bench, and the natural frequency response of running propulsion shafting under different alignment states is obtained from the measured bearing vibration signal. The results show that the natural frequency of propulsion shafting can be excited under the running condition, but its response is feeble. When the alignment state of the propulsion shafting gradually changes with the elevation of the front stern bearing, the identified natural frequency of the propulsion shafting shows an upward trend. In contrast, its amplitude shows a downward trend. Therefore, the proposed approach can identify the natural frequency of the ship propulsion shafting from the measured bearing vibration signal under the running condition. Full article

A new type of marine transportation engine, the pulsed detonation hydroramjet (PDH), which was first designed, manufactured, and tested by the present authors, has been further investigated in terms of the potential improvement of its propulsive performance. PDH is composed of a pulsed detonation tube (DT) inserted in the flow-through water guide. Thrust is developed by shock-induced pulsed water jets which are periodically emitted from the water guide nozzle. The measured values of the time-averaged thrust and specific impulse in the first operation cycle were shown to always be considerably higher than those in subsequent cycles, indicating the possibility of improving the overall thrust performance. The present manuscript is aimed at clarifying the reasons for, and eliminating, cycle-to-cycle variability during PDH operation, as well as optimization of the PDH design. An experimental model of the PDH with an optically transparent water guide was designed and manufactured. The cycle-to-cycle variability was found to be caused by the overexpansion of gaseous detonation products in the DT due to the inertia of water column in the water guide. Gas overexpansion caused the reverse flow of the gas–water mixture which filled the water guide and penetrated the DT, thus exerting a strong effect on PDH operation. To eliminate the cycle-to-cycle variability, a new PDH model was developed, manufactured, and tested. The model was equipped with a passive flap valve and active rotary valve and operated on the stochiometric propane–oxygen mixture. Its test firing showed that use of the valves made it possible to eliminate the cycle-to-cycle variability and nearly double the time-averaged thrust and specific impulse reaching 40 N and 550 s, respectively. Full article

The acceleration characteristics of a water jet-propelled ship during startup are related to its performance under mooring conditions. Water jet propulsion cavitation during startup increases the vibration and noise of the whole ship. Therefore, accurately predicting and analyzing the performance, hydrodynamics and flow field characteristics of water jet-propelled ships under mooring conditions can help elucidate the startup characteristics of the ships and optimize their acceleration strategies. In this study, the hydrodynamic and flow field characteristics of water jet propulsion and water jet propulsion ships under mooring conditions were studied using three-dimensional numerical modeling. First, the hydrodynamic performance of the water jet propeller was analyzed, and the relevant flow field law was derived. Then, the hydrodynamic performance, internal and external flow field characteristics, pulsation pressure and flow rate at the nozzle, and pulsation pressure at the monitoring points around the impeller of the water jet propulsion ship model were analyzed under mooring conditions. We obtained the open-water law for the water jet propeller and the hydrodynamic force and flow field law for a two-pump water jet propulsion ship. The ship model developed in this study provides a good theoretical foundation for further research on water jet propulsion. Full article

Usually, the need for research arises when there is a discrepancy between the theoretical and practical data. For example, the RINA (Registro Italiano Navale) Rules describe two navigation areas for yachts: unrestricted navigation and a navigation area with a significant wave height of not more than 4 m. In the GL (Germanischer Lloyd) Rules, it is proposed to assign the maximum wave height that a ship can meet, taking into account its speed and design features. The CCS (China Classification Society) Rules consider five categories of yachts for different navigational conditions. The significant wave height range is from 0.5 m to 6 m, and the distance from the place of refuge is from 5 to 200 nautical miles or more. Directive of the European Parliament and of the Council does not consider the distance from the place of refuge for the ship, and significant wave heights from 0.3 m to 4 m or more are proposed. In practice, the following situations may arise: it is necessary to determine the maximum value of the wave height at which the ship will be able to move against the wave or a possible decrease in the speed of the ship; to determine the height of the wave at which the wetness of the deck will begin; to study the relationship between the allowable values of the design accelerations and technical characteristics of the ship; to determine the distance from the emergency ship to the mooring place of the rescue ship; and calculate the minimum time to render assistance to people. These four situations will be considered in the article by using the energy wave criterion $EWC$, the recommendations of classification societies, and modeling the behavior of a vessel on a head wave. Full article

Ducted propeller is a kind of special propeller widely used in unmanned underwater vehicles, its flow characteristics and hydrodynamic noise are very important for marine environmental protection and equipment concealment. The hybrid techniques based on the acoustic analogy theory are adopted in the present study to calculate the unsteady flow field and sound field characteristics of a ducted propeller. The full scale flow filed and hydro-acoustic sources of the propulsion system are simulated by Detached-Eddy computational fluid dynamics (CFD) method. Hydrodynamic noise are calculated by FWH equation based on the CFD results. The frequency domain and directivity of sound pressure level at different sound field monitoring points are analyzed at four navigational speeds. The results show that the navigational speed that is in the inflow condition of the ducted propeller play important roles in the flow structure and underwater radiated noise. Under the fixed impeller rotational speed, the propulsion efficiency of ducted propeller increases first and then decreases with the raise of navigational speed. The maximum errors of thrust and power between simulation and experiment values are 0.5% and 0.1% respectively, which means that the adopted DES numerical simulation method has high credibility in calculating the acoustic source. At impeller rotational speed of 2000 r/min, the best state of flow field distribution is at the navigational speed of 1.54 m/s, which is corresponding to the highest propulsion efficiency condition. The propeller noise presents dipole characteristic in all working conditions, and at the obvious blade passing frequency, multiple characteristics are presented; most of the noise contribution is also concentrated below four times of the blade passing frequency. The total sound pressure level of the hydrodynamic noise is the smallest at the optimal efficiency condition (the navigational speed is 1.54 m/s). At high navigational speed, the low frequency characteristics below blade passing frequency increase and the amplitude becomes larger. This indicates that the component of turbulent noise becomes more important with the increase of navigational speed. The research focuses on analyzing the relationship between the energy loss of the ducted propeller wake field and the noise level, and it is found that the vortex at the tail makes a certain contribution to the noise. The research conclusions could provide some reference for the acoustic performance evaluation and noise reduction optimization of ducted propeller design as well as the improvement of UUV stealth performance. Full article

The pressure distribution of a misaligned elastomeric journal bearing is crucial for analyzing the uneven excessive wearing of the propulsion shaft bearing. However, analysis of the misaligned bearing is usually mainly based on the finite element method (FEM), which lacks a convenient and effective calculation method. This paper uses the influence coefficient factors (ICs) method to analyze the contact pressure of the misaligned bearing. First, the elastic displacement of the cylindrical shell subjected to a single point of concentrated force is derived and used to attain the new influence coefficient factors. Then, the geometric boundary conditions of planar conformal cylindrical contact are extended to the case of non-planar contact. Finally, the proposed method is applied and compared with other methods. The results show that the influence coefficient factors are greatly affected by the shape and constraints of the contact object. The proposed method is suitable for cylindrical shell contact analysis and has the same accuracy as FEM with half of the time consumption. In addition, the bearing capacity and contact stiffness are decreased as the effective contact area decreases due to misalignment. Full article