Propeller Forces Research Articles

Confined geometry and laser energy affect laser plasma propulsion.

The interaction of plasma (or shock waves) with the uniform sphere shape of polystyrene particles was investigated in this study to observe the effects of confined geometry and energy fluence on propulsion efficiency. The measurements indicate that propulsion efficiency first increases with energy fluence until reaching a maximum at 0.46 J/cm2, then decreases as energy fluency continues to increase. Compared to polystyrene particle propulsion without confined geometry, the propulsion efficiency of polystyrene particles improved due to multiple laser-induced shock wave reflections among the confined geometry internal face; the plasma propelling force also increased perpendicular to the target surface under confined geometry conditions. The results also show that the energy deposited on the plasma affects the energy distribution between the plasma and polystyrene particle. Moreover, a series of experiments was performed to roughly estimate the shock wave expansion shape through the motion direction of the polystyrene particle swarm, where the shock wave was observed to expand spherically.

Vibro-acoustic responses of a coupled propeller-shaft-hull system due to propeller forces

The vibro-acoustic responses of a submerged propeller-shaft-hull coupled system under propeller forces in different directions are investigated by the coupled finite element/boundary element method. In the analysis, the acoustic transfer vector (ATV) approach is utilized to study the acoustic contribution from the elastic propeller and the hull. By applying the modal decomposition technology, the effects of the stern bearing on the acoustic response of the coupled system under transversal propeller force are observed. The numerical results are compared with those obtained from a hydroacoustic experiment of the propeller-shaft-hull coupled system. The effects of the decreasement of the stiffness of the thrust bearing on the acoustic response of the coupled system are discussed.

System-based prediction of maneuvering performance of twin-propeller and twin-rudder ship using a modular mathematical model

The turning circle and zigzag maneuvering performance of surface combatant, DTMB 5415 have been investigated by using system-based method. Unsteady Reynolds averaged Navier Stokes (URANS) approach is utilized to estimate hydrodynamic derivatives and hull-propeller-rudder interactions. DTMB 5415 is a twin-propeller / twin-rudder ship and there are some studies on the derivation of maneuvering coefficients in the literature but none of them took into account the propeller and rudder forces. In this study, static drift, pure yaw, combined yaw and drift, self-propulsion and rudder tests of DTMB 5415 hull have been simulated in calm and deep water condition. Bare hull PMM simulations were carried out for a fixed Froude number of Fr=0.28, while the simulations related to rudder and propeller were performed at Fr=0.25. Computational results were used by MMG (Maneuvering Modeling Group) model to estimate the maneuvering performance of the ship. Hydrodynamic derivatives from numerically generated forces and moment data were obtained by single-run and multiple-run methods. The results from both methods were tested in an in-house maneuvering simulation code (MANSIM) that solves for ship motions and they were compared with computed turning circle and zigzag maneuvering performances. Although it is known a priori that the multiple-run method would give better solution in overall, it was found that the single-run method can be a good alternative in some specific cases. For the zigzag and turning circle tests, the results from single-run method were found satisfactory when correct PMM test conditions were adopted.

Dynamic Characteristics Analysis of Marine Propulsion Shafting Using Multi‐DOF Vibration Coupling Model

This paper mainly focuses on the elastic support of thrust bearings. The dynamic characteristics of the shafting system are studied. Firstly, the multi‐DOF transfer matrix expressions of the simplified mass element and spring element are derived. A three‐DOF transfer matrix‐coupling model in XOZ plane is established by using force coupling conditions at thrust bearings. Then, a test rig is built to test the propulsion shafting. The bending vibration characteristics of the shafting under the support conditions of thrust bearings are studied. And finally, the transmission characteristics of vertical and longitudinal forces of propellers under different support conditions of thrust bearings are emphatically analyzed.

Lateral vibration transmission suppression of a shaft-hull system with active stern support

This paper presents an active control method for reducing the lateral vibration transmission in a shaft-hull coupled system of submerged vehicles under the excitation of propeller forces. In this method, a 6-DOF (degree of freedom) active stern support and the local velocity feedback control strategy are employed to suppress vibration transmission from the shaft to the hull. The dynamic model of the shaft-hull system embedded with the active stern support is established with the FRF (frequency response function)-based synthesis method and the FEM/BEM (finite element method/boundary element method). The six-channel local velocity feedback control strategy is employed to suppress vibrations of the strut-hull interface. Numerical results indicate that a noticeable attenuation of vibration and sound radiation can be achieved by the active stern support. In addition, the combination control at the stern support and the thrust bearing is able to obtain better attenuation at some critical frequencies. Suppression of the mean square velocity and radiated sound power of the hull surface are observed.

Contact Force Measurement in an Operational Thrust Bearing using PVDF Film at the Blade and Pad Passing Frequencies.

A major contributor to longitudinal vibration in marine propulsion systems is propeller induced excitation. This constitutes a key source of underwater acoustical radiation through excitation of the hull. Understanding this hydrodynamic force at the interface of the thrust bearing is important in order to develop an accurate vibrational model of the propulsion system and in determining potential control mechanisms. In order to investigate the thrust force during operation of a propulsion system, Polyvinylidene Fluoride (PVDF) was embedded into the stationery collar inside a custom thrust bearing in a scaled model of a typical propulsion system. The number of blades of the propeller and its rotational speed were altered to obtain an understanding of the characteristic vibrations of the shaft propulsion system. The rig comprised of the propeller, shaft, journal bearings and a thrust bearing. A two and three blade propeller and a four, five and six pad bearing were tested. A strain gauge and accelerometer were used to infer the propeller force and enable comparison with the PVDF signals. As a result of the asymmetrical flow around the propeller, the blade passing frequencies (BPF) are clearly observed. This frequency contribution was present at all speeds tested. The PVDF signal also showed significant pad passing frequency (PPF) and BPF and modulation of both.

The Effect of Transient Eccentric Propeller Forces on Shaft Behavior Measured Using the Strain Gauge Method During Starboard Turning of a 4,700 DWT Ship

The Effect of Transient Eccentric Propeller Forces on Shaft Behavior Measured Using the Strain Gauge Method During Starboard Turning of a 4,700 DWT Ship

Beating of grafted chains induced by active Brownian particles.

We study the interplay between active Brownian particles (ABPs) and a "hairy" surface in two-dimensional geometry. We find that the increase of propelling force leads to and enhances inhomogeneous accumulation of ABPs inside the brush region. Oscillation of chain bundles (beating like cilia) is found in company with the formation and disassembly of a dynamic cluster of ABPs at large propelling forces. Meanwhile chains are stretched and pushed down due to the effective shear force by ABPs. The decrease of the average brush thickness with propelling force reflects the growth of the beating amplitude of chain bundles. Furthermore, the beating phenomenon is investigated in a simple single-chain system. We find that the chain swings regularly with a major oscillatory period, which increases with chain length and decreases with the increase of propelling force. We build a theory to describe the phenomenon and the predictions on the relationship between the period and amplitude for various chain lengths, and propelling forces agree very well with simulation data.

Numerical Prediction of Added Power in Seaway

The paper describes a numerical approach to predict required added power for propulsion in waves. Such predictions are important to address fuel consumption in seaway and define suitable operating point and sea margin, as well as for routing optimization and hull performance monitoring. Added resistance and, in general, drift forces and moments due to waves are key input parameters for added power requirements. The three-dimensional Rankine source-patch method was used to compute them. The method solves the problem in the frequency domain, linearizing wave-induced motions around the fully nonlinear steady flow. The added power software combines added resistance and drift forces and moments in irregular waves with wind forces and moments, calm-water maneuvering forces and moments, rudder and propeller forces, and propulsion and engine model and provides associated resistance and power as well as changes in ship propulsion in waves. The approach is demonstrated for a container ship to compare predictions with full-scale data.

Application of strain gauge method for investigating influence of ship shaft movement by hydrodynamic propeller forces on shaft alignment

To ensure the stability of marine propulsion shafting system, series of studies regarding shaft alignment have been performed under quasi-static conditions. In the shaft system of a ship, the increase of local load in the stern tube bearing, which supports a propeller shaft, occurs prominently due to the influence of the propeller weight at the shaft end, similar to the case of the cantilever beam. In particular, the aft stern tube bearing is likely to receive a concentrated load in the bottom of aft side. While such magnitude and distribution of local load are determined by the relative inclination angle between the shaft and bearing, the aft bottom of aft stern tube bearing is more severely affected by the local load than other bearings. Such local load can significantly deflect towards the aft end of aft stern tube bearing in case that the shaft sags down, when the eccentric thrust force acts downward due to the propeller force in the hydrodynamic transient status. In this paper, the dynamic behaviour of the propeller shaft is evaluated for a medium-sized oil/chemical product carrier with 50,000 dead weight tonnage acknowledged as a highly efficient eco-friendly ship type. As a result of the analysis, it is confirmed that shaft behaviour would be affected by hydrodynamic propeller forces by the variation of ship draught and main engine load. Further, it is found that the propeller forces during ship acceleration acted as a force lifting the propeller shaft from the aft stern tube bearing and it reduced the possibility of damage to the aft stern tube bearing, thereby, contributing to improving the reliability of the shaft system. This paper deals with the new application of strain gauge method to evaluate the shaft stability. The research results are consistent with those from the previous studies based on the direct measurement in the vicinity of the propeller. The Research findings demonstrate that this new application would be excellent and practical as an alternative to the direct measurement method performed at the propeller position.

Prediction of the Open-Water Performance of Ducted Propellers with a Panel Method

In the present work, a comparison between the results obtained by a panel code with a Reynolds-averaged Navier-Stokes (RANS) code is made to obtain a better insight on the viscous effects of the ducted propeller and on the limitations of the inviscid flow model, especially near bollard pull conditions or low advance ratios, which are important in the design stage. The analysis is carried out for propeller Ka4-70 operating inside duct 19A. From the comparison, several modelling aspects are studied for improvement of the inviscid (potential) flow solution. Finally, the experimental open-water data is compared with the panel method and RANS solutions. A strong influence of the blade wake pitch, especially near the blade tip, on the ducted propeller force predictions is seen. A reduction of the pitch of the gap strip is proposed for improvement of the performance prediction at low advance ratios.

Multicopter With Series Connected Propeller Drives

This study considered a tethered multicopter, powered from ground by electrical cables integrated in the tether. For a low tether mass and diameter, but high-efficient and simple propeller drives, a higher tether voltage than the rated voltage of the propeller drives was considered. To avoid additional power converters to step-down the tether voltage, the propeller drives were proposed to be connected partly in series. A control method was developed to stabilize the voltages and simultaneously achieve the requested propeller forces and moments. The feasibility of the proposed concept and the effectiveness of the developed control method were demonstrated by experiments. The proof-of-principle demonstrator was a tethered octocopter with 48 V tether voltage, wherein two or four voltage levels were created by a series connection. The demonstrator flew stably for several minutes until a test flight was completed successfully. During flight, the voltage control errors were always less than 0.75 V. A possible application of such a system with a scaled-up voltage is crosswind kite power, where the kite is equipped with small onboard turbines and the electricity is transmitted to the ground via electrical cables. During launching and landing, the turbines are used as propellers, i.e., the kite is a tethered multicopter and hovers from ground into a launching position, or vice versa.

Investigation of the effects of a fan-shaped Mewis duct before a propeller on propulsion performance

To define the guidelines for the design of a Mewis duct for a small bulk cargo ship, a numerical study was carried out to investigate the effects of a fan-shaped Mewis duct on propeller performance of a 38,000 t bulk cargo ship with a three-blade propeller. Calculations were performed using the STAR-CCM+ software based on the solution of the Reynolds averaged Navier–Stokes (RANS) equation. Computations were carried out for a wide range of locations from 0.11D to 0.21D upstream from the propeller disc, a radius of trailing edge from 0.65R to 1.05R, and angle of attack of the inner fins, where from 0° to 10° of the fan-shaped Mewis duct, where D is the diameter of the propeller and R is the radius of the propeller. With the installation of the duct, the axial mean wake fraction on the propeller disc decreased, while the tangential mean wake fraction increased significantly. As the installation position was far away from the propeller, the axial mean wake fraction varied in a wave pattern, while the tangential mean wake fraction increased. With the increase of the radius and the angle of attack of the inner fins of the duct, the axial mean wake fraction first decreased and then increased, while the tangential mean wake fraction increased gradually. Correspondingly, the propeller force coefficients and efficiencies with the duct were all more than those without the duct and changed with the variations of the duct parameters. When the propeller and duct were taken as a propulsion system, the efficiency of the system was less than that of only the propeller. At the same time, with variations of the location, radius, and angle of attack of the inner fins of the duct, the efficiency of the system first increased and then decreased gradually, which indicates that there was an optimum design value for all of the duct parameters. Moreover, only when the design of these duct parameters are reasonable can energy savings be achieved; otherwise, the opposite effect is produced. Eventually, with the installation of the fan-shaped Mewis duct, the wake harmonic degree on the propeller disc can be significantly improved.

Vibration transmission suppression for propeller-shaft system by hub-embedded damping ring under broadband propeller force

To suppress the vibration of propeller blades and vibration transmission from the blades to bearings under broadband propeller force, a damping ring placed under the propeller hub is proposed. The configuration of the damping ring is introduced first. Then the analytical dynamic model of the damping ring is established. The dynamic model of the propeller-shaft-multiple bearings system with and without the damping ring is developed based on the modal properties of the propeller-shaft-multiple bearings system, the damping ring and friction interface characteristics between them. Node-to-node contact elements are introduced with both normal and tangential relative displacements. The dynamic model is solved by the Duhamel integration of single-degree-of-freedom system and then by employing the superposition method. It is shown that the damping ring can suppress the responses of the propeller blades and the force transmitted to the foundation at the in-phase blade modes of an integrated forming propeller and the longitudinal mode of the propeller-shaft-bearings system. The suppression mechanism is energy dissipation due to the friction phenomena on the interface. The time histories of the contact variables (tangential relative forces) of given contact points on the hub/ring interface are given to illustrate the local behavior of the contact interface. Parametric analysis is carried out to investigate the influence of the inherent damping of the coupled system, rotation speed, tangential stiffness and friction coefficient on the interface. It is shown that the tangential stiffness and friction coefficient on the interface are two key parameters. The theoretical study will provide some references on designing the damping ring for propellers.

Effects of non-axisymmetric structures on vibro-acoustic signatures of a submerged vessel subject to propeller forces

Wave localization effects of concentrated mass in a cylindrical shell at high frequencies have been proved to increase the sound radiation of the shell, but the effects of non-axisymmetric substructures on the low-frequency vibro-acoustic responses of a propeller-shafting-hull system are more complicated due to the strong coupling between the propulsion system and the hull. To investigate the influences of the non-axisymmetric substructures on the structural and acoustic behaviors of submerged vessels, fully coupled finite element/boundary element models are developed for vessels with/without added mass and keel. The propeller-shafting system is connected to the pressure hull of the vessel through an irregularly shaped foundation. Large-scale underwater vibro-acoustic experiments are performed, and the numerical solutions are verified by the experimental results. The physical insight into the effects of the substructures on the acoustic responses of the propeller-shafting-hull system are discussed by examining the normal velocity distribution of the hull in the wavenumber space and the modal contributions of the modes of the substructures to the vibro-acoustic responses of the system. A passive control method is proposed to efficiently suppress the structural and acoustic responses of the system under both axial and lateral propeller excitations.

Design of a safety operational envelope protection system for a submarine

A safety operational envelope (SOE) is an area that guarantees the safety of a submarine from accidents, such as jamming and flooding. In this study, a submarine envelope protection system (EPS) was designed to prevent submarine excursion from the SOE. Modeling of the hull force, propeller force, and main ballast tank blowing was performed. The SOE was established based on a crash stop and emergency rising maneuver simulation. In the estimation model, a linear compensator and neural network are employed to estimate the submarine dynamics. The command limit is calculated using the estimation model and the dynamic trim algorithm, and it is restricted by the limit avoidance. The EPS was applied to a submarine maneuvering simulation program and its performance was verified by a depth change simulation. The designed EPS prevents the submarine from exceeding the limit boundary and the control system can thereby enhance the operational stability.

A BEM/RANS interactive method for predicting contra-rotating propeller performance

This paper introduces a BEM/RANS interactive scheme to predict the contra-rotating propeller (CRP) performance. In this scheme, the forward propeller and the aft propeller are handled by two separate BEM models while the interactions between them are achieved by coupling them with a RANS solver. By using the body force field and mass source field to represent the propeller in the RANS model, the number of RANS cells and the number of required RANS iterations reduce significantly. The method provides an efficient way to predict the effective wake, the steady/unsteady propeller forces, etc. The BEM/RANS interactive scheme is first applied to a CRP in both an axisymmetric manner and a non-axisymmetric manner. Results are shown in good agreement with the experimental data in moderate to high advance ratios. It is proved that the difference between the axisymmetric scheme and the non-axisymmetric scheme mainly comes from the non-axisymmetric bodies. It is also found that the error is larger at lower advance ratios. Possible explanations are given. Finally, some additional cases are tested which justifies that the non-axisymmetric BEM/RANS scheme is able to handle a podded CRP working at given inclination angles.

A Generalized Potential/RANS Interactive Method for the Prediction of Propulsor Performance

This article introduces a generalized potential/Reynolds-averaged Navier-Stokes (RANS) interactive method for the prediction of propulsor performance with an emphasis on the calculation of the steady (axisymmetric) or the time-averaged (non-axisymmetric) effective wake fields. In the RANS solver, the propeller boundary is represented by local source terms. Therefore, this method can be used to efficiently handle different types of propulsor-related multicomponent interaction problems. The scheme is first validated by an open propeller application with a uniform inflow and then applied to a vortical-inflow-propeller interaction case, a contra-rotating propeller case, as well as a hull-rudder-propeller interaction case. Results are compared with RANS (with the propeller modeled as wall boundaries) and experiments. 1. Introduction Predictions of propeller efficiency, propeller forces, and propeller cavitation patterns are of great importance in maritime and offshore industry. These predictions are directly related to fuel efficiency, structural vibration analysis, and noise control. To accurately evaluate the propeller performance, it is essential to consider the mutual influence between the ship hull and the propeller, between different propellers if multiple propellers are used, and between different rows of a propeller if multirow propulsion is employed. To predict the flow field around multiple bodies, finite volume methods are commonly used. In these methods, the fluid domain is usually split into one static domain and one (or several) revolving domain(s) and a mixing plane condition is applied to the sliding interfaces between different domains (Zhuang et al. 2004; Sanchez-Caja et al. 2009). The mixing plane condition circumferentially averages certain fluid quantities on each side of the interface and uses these averaged quantities as the boundary condition to the other side. This treatment neglects the unsteady component of the interaction effect between different bodies (between ship hull/propeller or between different rows of the propeller) so that the problem can be solved as steady. The computational cost of this method can range from several hours to several days depending on the size of the mesh, the type of the propeller, and the computing power (Kinnas et al. 2015). In fact, when the mixing plane condition is applied to the sliding interfaces, the Reynolds-averaged Navier-Stokes method (RANS) actually solves for the mean performance of the propeller. On the other hand, if the mixing plane condition is not applied, RANS can be solved as unsteady, but the computational cost will be much higher.

5만톤급 석유화학제품 운반선의 선박 가속 시 엔진 부하에 따른 프로펠러 힘이 추진축계에 미치는 영향 연구

5만톤급 석유화학제품 운반선의 선박 가속 시 엔진 부하에 따른 프로펠러 힘이 추진축계에 미치는 영향 연구

Effects of an Organic‐inorganic Nanocomposite Additive on the Combustion and Erosion Performance of High Energy Propellants Containing RDX

AbstractA nanocomposite microsphere consisting of solid paraffin, nano‐TiO2, nano‐BN, zeolitic imidazolate framework‐67 particles and polymethyl methacrylate was prepared and applied as a functional additive for high energy propellants (with about 23 wt % RDX) to reduce the barrel erosion and improve its combustion performance as well. High energy propellants modified with the nanocomposite were manufactured by a solvent extrusion technique. According to the scanning electron microscope and differential scanning calorimetry results, there exists a good compatibility between the nanocomposite and propellant matrix. The energy and combustion performance as well as erosion of the modified propellants were studied by a closed bomb test and an erosion tube device, respectively. Results showed that compared with the unmodified propellant, both the erosion and energy performance of modified high energy propellant gradually decreased with the increase of nanocomposites contents. When the content of nanocomposites was 5.1 %, the erosion mass of the modified propellant reduced to 37.0 % while the propellant force only decreased 5.7 %, indicating that the nanocomposite has enormous ability to improve gun erosion resistance while barely affect energy performance of propellant. Furthermore, the closed bomb burning curves of the samples showed that addition of nanocomposites to propellant matrix could prolong the combustion time, efficiently inhibit the initial generation rate of combustion gas, and further achieve the progressive burning of the propellants.