Ship Propeller Research Articles

Automatic offline path planning of robots grinding multi-curved surfaces on large ship propellers – A human-in-the-loop approach

Multi-curved components represent a particular challenge when machining with robots, as the machining is subject to a wide range of technical limits depending on the robot system used. An example of such a multi-curved component can be found in the ship propeller, which is one of the most important components of a ship and represents a relatively complex part in the production process. Manufacturing in the casting process is resource- and time-consuming and requires extensive finishing, which also includes grinding to final size. Technologically, this operation is still performed manually or mechanically assisted and requires employees with a high level of experience in the operation and handling of grinding technology. In order to prevent the increasing shortage of skilled workers and to make the finishing process independent from employee-specific knowledge, it is necessary to develop an automatic grinding process. In this context, offline path planning for multi-curved surfaces has emerged as a particular challenge, since existing approaches do not sufficiently consider the robot axis positions nor the pose limits of the end effectors. This work starts by presenting the current state of research and then introduces a human-in-the-loop approach that solves the problem of 3D trajectory planning using two-dimensional viewing planes. The trajectories thus found are projected onto the surface of the propeller and analyzed for potential collisions with the robot, grinding efficiency and reachability. Furthermore, it is possible to calculate an automatic removal characteristic by overlaying a simplified casting model and ideal model of a propeller.

Designing a Computer Simulation Model to Study the Failure Mechanism in Rotating Shaft

The phenomenon of the failure of rotating mechanical structures is considered one of the dangerous phenomena that researchers are trying to study to find effective ways to avoid it. Many mathematical models describing the mechanism of crack formation in structures and the occurrence of failure in them have been adopted. In this paper, a computer simulation model of the failure mechanism in the intermediate conduction shaft of the ship's propeller (oil shuttle tanker) was designed based on the mathematical model that describes the stages of failure according to the number of revolutions that the shaft bears and the dimensions of fatigue cracks in it. In the beginning, a detailed mathematical model of the crack propagation mechanism was deduced as an initial stage, through which the differential equations that express the failure of the shaft were described. In the second stage, numerical simulations were implemented using the Euler and Rung-Kutta numerical methods used in solving ordinary differential equations. Also, for both methods using the Matlab language to reach the results and accurate graphs and analyze them. In this way it is possible to predict the number of cycles that the column will bear before the collapse, and this will reduce the occurrence of sudden collapses and save time, effort, and costs.

Construction and Analysis of New Mathematical Models of the Operation of Ship Propellers in Different Maneuvering Modes

Construction and Analysis of New Mathematical Models of the Operation of Ship Propellers in Different Maneuvering Modes

Research on self-propulsion simulation of a polar ship in a brash ice channel based on body force model

Main engine power prediction is important for polar ships operating in brash ice channels, which is one of the most important concerns of shipowners. Self-propulsion simulation is an efficient method to predict the developed power. At present, such models as the discretized propeller model (DPM) and the body force model (BFM) are used for self-propulsion simulation. However, these models are often limited to open water. There is little research on self-propulsion calculations in ice-infested water. This paper presents the BFM to carry out self-propulsion simulations in a brash ice channel. Research on simulation strategy for open water performance based on the BFM is carried out. Ship–ice–water interactions are simulated using computational fluid dynamics-discrete element method (CFD-DEM) coupling method. Both loaded and ballast conditions are considered in the model-scale self-propulsion simulations. Numerical results based on the BFM are compared with the simulation results based on the DPM, as well as model test results. Ship–propeller–ice interactions and propeller suction effects are also compared with photographs taken at an ice tank test. The results show that the differences of the developed power based on the BFM for both loaded and ballast conditions are 8.94% and 15.25%, respectively. The prediction accuracies of the developed power based on the BFM for both loaded and ballast conditions are 1.56% and 7.01%, respectively; lower than those based on the DPM. However, the computation efficiency based on the BFM is 12 times higher than that based on the DPM. To conclude, the proposed BFM could be used as an effective means to calculate the developed power and to evaluate the trend of hull-line optimization at the development stage.

Estimating the effect of biofouling on ship shaft power based on sensor measurements

ABSTRACT Marine biofouling on a ship's hull and propeller increases the resistance of the ship moving through water and reduces the propulsion efficiency of the ship. Estimating the effect of fouling is difficult, as the biomass is rarely measured. In this paper, we present a new data-driven model for the total shaft power use of a large containership, in order to estimate the unobserved effect of fouling. Due to the limitations of both physical models and machine learning models, we develop a Bayesian generalized additive model for our purpose. We discuss issues of representative training data for the model. Further, we subset and subsample the data to a representative sample. Models are compared by out-of-sample predictive quality, physical appropriateness, and through autocorrelation of residuals. The Bayesian generalized additive model combined with computational inference using integrated nested Laplace approximations gives a robust estimate of the biofouling effect over time. It also allows a decomposition of the total shaft power use into effects of speed, weather, and other conditions. This model can be used to understand the effectiveness and timing of different hull and propeller treatments.

Parameterization of the propeller thrust for modelling ship braking in ice channel behind icebreaker

Abstract Cargo ship sailing within the ice channel that an assisting icebreaker tracks in the compact ice cover is the usual navigation practice for difficult ice conditions in freezing seas and Arctic water areas. When the icebreaker or an ahead vessel stops before the insuperable ice obstacle or because of engine trouble, the danger of an emergency appears, namely of collision with the icebreaker or the ahead ship, if the interval between them is not sufficient for effective braking and stopping. The paper presents the equation that describes the ship braking process within an ice channel and includes the thrust of the propeller that works under the reverse regime. The specific of this regime is the following: the ship continues the motion ‘forwards' and the propeller rotates ‘backwards’. An analytical method for description of the ship propeller work on the reverse regime is absent because of the detached flow on its blades. The paper describes the developed empirical method of this regime parameterization on the basis of serial models of propeller testing. The outcomes of this investigation are applied to a ship braking process simulation and the evaluation of the safe interval between the ship and the icebreaker.

Design of a hydro sound intensity probe for quantification and localization of acoustic sources — Applied to a hubless marine rim drive

The reduction of hydro noise emission by ship propulsion systems is of importance since background noise levels in the oceans have increased by 21 dB in the past decades. Thus, the acoustical improvement of ship propulsion systems is a necessary and challenging task. It involves not only the ship propeller but also the components of the entire drive train like diesel or electrical engines, electrical inverters as well as gearboxes. Acoustical measurement systems for the quantification and localization of noise sources are essential for any kind of optimization and are state of the art in the airborne noise field. This is not the case in the hydro acoustic field and measurements are mostly limited to the recording of the hydro sound pressure using single hydrophones. The objective of this paper is the presentation of a new three dimensional hydro sound intensity probe capable of acoustical sound power quantification and noise source localization. The probe can be used for the determination of the hydro sound pressure, the 3D sound intensity vector and the sound power. Furthermore, the probe can be utilized for hydro sound source localization purposes using beamforming methods based on virtual acoustical arrays. The developed probe was used for hydro acoustic investigations of a full scale marine rim drive during a measurement campaign in the river Warnow in Rostock, Germany. The results indicate the different hydro sound generating mechanism of the rim drive.

Microstructure and Mechanical Properties of Nickel-Aluminum Bronze Coating on 17-4PH Stainless Steel by Laser Cladding

Bimetallic copper-steel composite could be an effective structural material to improve the performance of traditional nickel-aluminum bronze (NAB) ship propeller due to its high structural strength and corrosion resistance. In this work, the defect-free NAB coatings has been successfully fabricated by laser direct depositing technique on the 17-4PH stainless steel substrate. The phase constitution, microstructure characteristics and hardness properties were investigated in details. The XRD results showed that the coatings mainly consisted of α-Cu, Fe and intermetallic κ phases despite the diffraction peaks shifted more than 0.5°, which may due to the influence of the Ni, Fe and Al atoms dissolved into Cu-matrix. The microstructures of the coatings were affected significantly by laser energy density according to SEM and EDS results. The top region of the coating was more undercooled during solidification, therefore the grains at this region was much finer than that at the bottom region. The higher energy input would lead to coarser grains. Fe-rich dendrites and spherical particles were found in the Cu matrix, which could be a result of liquid separation. The hardness of the coating is in the range of 204 HV0.2–266 HV0.2 which is higher than traditional as- cast NAB. The uneven distribution of Fe-rich phases as well as the hard κ phases could be the main reasons for the fluctuations of the hardness value. Tensile fracture occurred at bronze side, not at transition zone, which shows there is a good interfacial bonding between the two metals produced by laser cladding.

Актуальные вопросы изучения реверса движителей

Object and purpose of research. This paper discusses crash-stop of ship propellers. The puspose of the study was to investigate a number of relevant challenges in this process, i.e. to refine the methods of crash-stop distance calculation, to update the scenarios for which crash-stop strength of propeller blades has to be verified, as well as to determine operational parameters and algorithms for automatic control systems of electric power plants in crash-stop conditions. Subject matter and methods. The study was based on the results of quasi-crash-stop model tests, as well as on previous publications about crash-stop maneuvers of ships and operations of their propulsion systems in these conditions. Main results. To obtain more accurate crash-stop distance estimates, it was suggested to use an alternative, bollard-pull system of propeller-hull interaction coefficients for crash-stop conditions. It was also suggested to perform crash-stop strength check of propellers not only for the scenarios with maximum hydrodynamic load, but also for the moment of propeller rotation direction reversal because it might be accompanied by considerable inertial loads. It is shown that model testing is not helpful in determination of operational parameters and automatic control system algorithms for electric power plants because shaft lines cannot be simulated correctly. These parameters can be obtained through calculations, but this will require more refined expressions for shaft line friction moments. Conclusion. The actual problems of ship reverse propulsion theory is presented in the paper. The possible approaches to their solution are proposed.

Study on dynamic response of underwater towed system in ship propeller wakes using a new hydrodynamic model

The dynamic analysis of underwater towed systems is challenging considering complex flow disturbances such as ship propeller wakes. This paper proposed a new fully-coupled three-dimensional hydrodynamic model for the dynamic analysis of an underwater towed system under complex flow disturbances. The hydrodynamic characteristics of the towed vehicle and the flow field behind the towing ship and propeller were simulated using computational fluid dynamics (CFD). The fluid forces on the towing cable were determined by combining the Morison formula and the CFD method. A dynamic analysis of an underwater towed system in a towing ship propeller wake under typical uncontrolled towing and depth regulation operations was conducted. The simulation results indicated that the proposed method was reasonable. Moreover, the time-averaged position and posture of the underwater towed system and its hydrodynamic characteristics vary with the rotation rate of the ship propeller in uncontrolled towing operation under a fixed towing speed. Furthermore, the fluid forces on the towing system and the cable tension in the depth regulation operation changed more drastically than in the uncontrolled towing operation. The proposed method can be easily extended to simulate other marine cable systems.

Experimental Study of Cavitation Damage to Marine Propellers Based on the Rotational Speed in the Coastal Waters

Cavitation in a propeller causes erosion, accelerating corrosion, and tearing off blades in severe cases. Despite the maintenance requirements caused by cavitation, few studies have investigated the cavitation resistance of small ship propellers. Therefore, in this study, these characteristics were investigated through a demonstration test in the coastal waters of South Korea. Cavitation erosion characteristics were analyzed according to the low- and high-rotational speed of the propeller, and the weight was measured every 10 h for 100 h of sailing. The erosion pits were qualitatively compared through liquid penetrant testing (PT) and quantitatively compared by image processing with color edge detection. The results showed that propeller weight loss at high speed was double that at low speed. The cavitation erosion exhibited one cycle each of incubation, acceleration, deceleration, and steady state at low speed, while the acceleration and deceleration periods repeated at high speed. According to PT and color edge detection, the concentration of pits in the low- and high-speed conditions increased towards the trailing and leading edges, respectively. Further, in the radial direction, the trend was similar in both conditions, and the largest number of pits were detected in the region of 0.7–0.9R, where R is the propeller radius.

Intelligent Collision Avoidance Method for Ships Based on COLRGEs and Improved Velocity Obstacle Algorithm

Collision prevention is critical for navigational safety at sea, which has developed rapidly in the past decade and attracted a lot of attention. In this article, an improved velocity obstacle (IVO) algorithm for intelligent collision avoidance of ocean-going ships is proposed in various operating conditions, taking into count both a ship’s manoeuvrability and Convention on the International Regulations for Preventing Collisions at Sea (COLREGs). An integrated model combines a three-degree-of-freedom manoeuvring model with ship propeller characteristics to provide a precise prediction of ships in various manoeuvring circumstances. In the given case, what is different to present studies, this improved algorithm allows for decision-making in two ways: altering course and changing speed. The proposed technique is demonstrated in a variety of scenarios through simulation. The findings reveal that collision-avoidance decision-making can intelligently avoid collisions with the target ships (TSs) in multi-ship situations.

Unconfined propeller scour in waterways: The role of flow intensity

Flow intensity represents an important input to be investigated in the ship propeller jet scouring process in ship maneuvering areas, waterways path, and mooring in navigation channels. Although the still water condition is not realistic, since it induces modifications in the canonical propeller jet scouring process in waterways, several studies were based on this assumption and only a few papers focused on the influence of the flow intensity are present in the technical literature. In this work, an experimental campaign aimed at exploring the flow intensity effects on the propeller jet and related scour was carried out. In particular, three flow intensities combined with different propeller submergence depths were tested. The experimental results are shown in terms of longitudinal and cross-sectional scoured bed profiles, and empirical equations to compute the main scour hole dimensions are proposed. Moreover, scour hole bathymetries were analyzed by spectral analysis to estimate characteristics length scales. In order to increase the detail on the fluid mechanics analysis to explain the influence of the flow intensity on the evolution of the scour hole and obtain an insight into the influence of the boundary effect on the flow field, Reynolds-Averaged Navier–Stokes simulations were performed over the three-dimensional scoured bathymetry, acquired at the equilibrium stage, and over the horizontal boundary, representing the earliest stages of the scouring process. The good agreement between the numerical results and the measured velocities at the equilibrium stage allowed also the simulations over a flat bed in the same hydraulic conditions. These represent the beginning of the scour process in the case in which the propeller blades are close to the bottom. As to the authors' knowledge, the last configurations were never simulated before, owing to the difficulties in managing the computation of a moving mesh close to a solid boundary. The results show, for the first time numerically, the plane boundary effects on the characteristics of propeller jets with and without an incoming flow.

Cavitation Detection on Hydraulic Machines

This paper gives an engineering review of the phenomenon of cavitation on hydraulic machines: turbines, pumps and ships propellers. The types of cavitation and its consequences are presented by the cabinet study of the results of relevant researches on models and real plants. In the special focus of this paper are the techniques of exploration of cavitation erosion: visual examination, measurements of pressures and vibrations and CFD methods.

Jetting mechanisms in bubble-pair interactions

Jetting mechanisms in cavitation bubbles play a crucial role in the destructive forces of cavitation. Depending on the application, these forces can have desirable effects like in medical treatments or catastrophic effects like in the erosion of ship propellers. Still today, thorough understanding of all details in complex bubble collapse scenarios is lacking. Hence, in this work, we numerically investigate the jetting mechanisms for air bubble pairs in water following a recent experimental setup. We apply a finite-volume approach with fifth-order low-dissipation shock-capturing weighted essentially non-oscillatory reconstruction. The interface interaction is described by a conservative sharp-interface level-set method. For time integration, a third-order total-variation-diminishing Runge–Kutta scheme is employed. Complementing experimental observations, our simulations reveal the presence of dominating gas jets and new types of jetting mechanisms.

New Results Regarding the Cavitation Destruction Behavior of Heat-Treated CuZn39Pb3 Brass with Different Parameters

Among other parts made of brass there are also the blades and the rotors of the hydraulic machines, respectively ship propellers, which during operation are degraded by cavitation erosion. As a result, most of the researches, including the most recent ones, are focused on the morphological analysis of structures eroded under the impact of micro-jets and shock waves, produced by cavitation hydrodynamics. The goal is to create new materials, but also to use new treatment technologies to increase cavitation resistance. As the literature is quite poor in studies related to the materials resistance to cavitation erosion, respectively treatments and technological procedures of it’s improvement, this paper presents the research results on the behavior of vibration cavitation erosion, carried out on three sets of CuZn39Pb3 brass samples, subjected to volumetric heat treatments of hardening for putting in solution at 800°C, followed by tempering at 250°C, 400°C and 600°C. The characterization of the behavior and the cavitation resistance of the structures resulting from the applied heat treatments is performed based on macroscopic images, taken at different representative periods, SEM images at the end of the test duration and values ​​of specific parameters recommended by ASTM G32-2016. The analysis highlights the differences caused by the change in structure by varying the temperature, but also the hardness of the surface exposed to the cavity. Thus, of the three treatments, it is found that the best resistance to cavitation is conferred by the structure resulting from hardening at 800°C, with tempering at 250°C.

A numerical method for the solution of the three-dimensional acoustic wave equation in a marine environment considering complex sources

The need to understand how complex acoustic sources propagate noise in a realistic environment is of growing interest. In this work, we propose a numerical model for the simulation of noise generated by sources with directivity and propagating in ocean waveguides. The numerical model solves the wave equation for the acoustic pressure in the physical space using a second-order accurate finite difference method (FDTD). The source is implemented using an improved form of the hard-source method, which implicitly takes into consideration the reflection of acoustic waves associated to the presence of the ocean free surface, through the use of the method of images. This novel method is shown to improve the results with respect to the standard hard source implementation. We first validate the numerical method considering both analytical solutions and benchmark cases for the case of a monopole and then explore the acoustic energy patterns developed in the case of dipole and quadrupole sources. Specifically, the algorithm and the implementation of complex sources are evaluated first in a semi-infinite fluid layer and then considering two classical waveguides: the Ideal one and the Pekeris one. The comparison with analytical results shows the numerical method’s accuracy and that incorporating free surface effects in the hard source implementation improves results. In addition, the study shows that the acoustic response in the near field, of the order of few kilometers from the source, is strongly influenced by the source’s directivity and orientation relative to the free surface. The results of this paper have implications for future research aimed at characterizing and quantifying ship propeller noise in realistic waveguides. Indeed, this preliminary work is necessary to proceed to more complex numerical experiments, such as considering a real propeller signal as a source or considering stratification of the medium or propagation in confined domains such as experimental tanks.

Validation of a partitioned fluid-structure interaction simulation for turbo machine rotors

ABSTRACT A partitioned solution approach for the fluid-structure interaction (FSI) simulations of turbo machine rotors is presented. The in-house developed boundary element method solver panMARE is used for the fluid simulation, while the structural side is treated with the commercial finite element method solver ANSYS. The generic in-house multiphysics coupling library comana is used for the management of the implicit coupling procedure. As the first example, the KRISO container ship propeller is considered. The simulation is validated for open water test conditions assuming a rigid propeller based on the thrust and torque coefficients. Simulation results for a flexible propeller in open water are also presented. In the second example, the validation of the FSI simulation is conducted for a multilayered flexible submersible mixer based on thrust and torque coefficients and local strains. The results show a good agreement between the simulations and the experimental data for both examples.

Investigation of the Effect of Rope Cutter on Water Flow behind Ship Propellers Based on CFD Analysis

Small vessels operating in coastal waters are susceptible to propeller failure because of the entanglement of marine debris. Secondary accidents such as the injury of divers may also occur when removing entangling material. Rope cutters are devices used to prevent marine litter from entangling the propeller of small ships. However, installing rope cutters on propeller shafts might affect the working of the propeller. In this study, three-dimensional simulations were performed to investigate the effect of a rope cutter on flow characteristics behind the propeller. The Computational fluid dynamics (CFD) models were validated by particle image velocimetry (PIV) experiments performed in a rope cutter performance testing tank. The study results showed that the installation of a rope cutter on the propeller shaft led to an insignificant reduction in water flow velocity magnitude behind the propeller. Additionally, the effects of the rope cutter on the reductions of thrust (0.87%) and torque (0.76%) of the propeller were also negligible. However, it is very interesting to note that rope cutter installation resulted in a lower vortex formation, leading to a significant reduction in the turbulence intensity behind the propeller by 27.12%, 37.50%, and 47.29% at 100, 150, and 200 rpm propeller speed, respectively. Based on the study results, it can be concluded that rope cutters help to reduce propeller entanglements without significantly affecting the propeller’s working.

Numerical prediction of cavitation phenomena on marine vessel: Effect of the water environment profile on the propulsion performance

Abstract Energy-saving and emission reduction are crucial since shipping activity due to the global maritime trade has increased exponentially. Several agreements have been engaged to optimize ship energy efficiency composed of ship design and shipping operation planning. However, most up-to-date studies focused on speed and route optimization. The interaction analysis between speed and route efficiency below varied environmental conditions is limited. To attain energy and cost efficiency, a study of cavitation on the propeller that considers the ocean environmental condition will be discussed in this work. Although researchers have previously observed cavitation phenomena, the predictability of simulations is not yet such that problems can be eliminated. Since the multiphase flow of water and vapor is sensitive to environmental conditions, it leads to varying observation accuracy. Thus, the current paper proposes a new performance indicator of the ship propeller under cavitation predicted by computational fluid dynamics (CFD). CFD-based simulation to observe the propeller cavitation was used to model the Zwart cavitation and Kunz cavitation models under two turbulence models of K−ε at different flow conditions and operating environments. Initial validation tests between experimental and numerical simulation show good agreement with a mean error of 4.7% in the Zwart model and 3.7% in the Kunz model, where the k−ε turbulence model provides an almost higher relative error. It is revealed from the result that the increase in temperature causes the rise in the cavitation problem. It is revealed from the result that the increase of temperature causes the increase in cavitation problem.