Propeller Forces Research Articles

Structural vibration and acoustic radiation of coupled propeller-shafting and submarine hull system due to propeller forces

This paper investigates the structural and acoustic responses of a coupled propeller-shafting and submarine pressure hull system under different propeller force excitations. The entire system, which consists of a rigid propeller, a main shaft, two bearings and an orthogonally stiffened pressure hull, is submerged in a heavy fluid. The shaft is elastically connected to the pressure hull by a radial bearing and a thrust bearing. The theoretical model of the structural system is formulated based on a modified variational method, in which the propeller, the main shaft and the bearings are treated as a lumped mass, an elastic beam and spatially distributed spring-damper systems, respectively. The rings and stringers in the pressure hull are modeled as discrete structural elements. The acoustic field generated by the hull is calculated using a spectral Kirchhoff-Helmholtz integral formulation. A strongly coupled structure-acoustic interaction analysis is employed to achieve reasonable solutions for the coupled system. The displacement of the pressure hull and the sound pressure of the fluid are expanded in the form of a double mixed series using Fourier series and Chebyshev orthogonal polynomials, providing a flexible way for the present method to account for the individual contributions of circumferential wave modes to the vibration and acoustic responses of the pressure hull in an analytical manner. The contributions of different circumferential wave modes of the pressure hull to the structural and acoustic responses of the coupled system under axial, transversal and vertical propeller forces are investigated. Computed results are compared with those solutions obtained from the coupled finite element/boundary element method. Effects of the ring and the bearing stiffness on the acoustic responses of the coupled system are discussed.

Effects of a duct before a propeller on propulsion performance

We numerically investigated the effect of a duct on propeller performance. Numerical simulations were performed for a wide range of diameters (0.7D≤DD≤1.0D) and angles of attack of the duct (0°≤θ≤20°), where D is the propeller diameter. The duct profile is NACA0015 whose chord length is 0.3D and trailing edge is located 0.2D upstream from the center of the propeller. The propeller force coefficients presented the same increasing pattern and the rate of the propeller efficiency with the duct to the bare propeller augments with increasing θ, irrelevant to DD. However, the net thrust reflecting the total drag, including the duct, depends on the duct size. Hence, there is a critical value of θ such that the magnitude of the total drag becomes maximum for a relatively large duct size. A certain size of duct leads two regions of the inflow into the propeller, which is originated by the duct. One is the inner region of the duct where the high-speed flow exists because of the contraction of the duct. Another is the outer region of the duct where the flow decelerates due to the duct wake. The circumferential locality of the axial velocity becomes weaker with increasing θ due to the accelerated flow along the axial direction. Eventually, lower and higher pressure coefficients on the suction- and pressure-side surfaces, respectively, cover a much wider area than those of the case without the duct, leading to greater thrust and torque.

Maneuverability prediction for a ship with full-revolving twin propellers

To predict the maneuverability of full-revolving propeller ships, this paper analyzes the propeller force and establishes MMG equations for controlling motion mathematical models that are suited to the full-revolving propeller model, in accordance with the modeling method of the separating ship motion model and taking into account the special nature of the force and flexibility of a full rotation in the horizontal plane of a full-revolving propeller. Secondly, hydrodynamic force derivatives for the ship model are obtained by simulating the model's PMM movement, and the controlling Ordinary Differential Equation (ODE) is solved using the four-stage Rung-Kuta method. Finally, the numerical simulation of a certain ship's rotating motion and its zigzag test in still water is obtained, and the prediction results are compared with that of a self-running model. It is found that the simulation results agree well with the trial results, and the effectiveness of the ship motion model for the full-revolving propeller model is validated. In brief, this paper provides a reliable and effective method of predicting the maneuverability of full-revolving propeller ships.

Research on Propeller Force and Oil Film Thickness of Stern Tube Bearing

Research on Propeller Force and Oil Film Thickness of Stern Tube Bearing

Gemi Pervanelerinde Kavitasyon Kaynaklı Gürültü ve Farklı İz Alanlarının Pervane Performansına Etkisinin İncelenmesi

The fact that the inflow to the marine propeller is not uniform and cavitation phenomenon which is likely to develop on propeller blades may lead to undesirable effects (performance loss, erosion, vibration, and noise) with respect to hydrodynamic performance. Particularly, periodically changing of the sheet cavitation size on the propeller blades leads to unsteady propeller force, vibration, underwater radiated noise as well as noise in the ship. In this study, prediction of sheet cavitation induced noise of a marine propeller whose geometry and wake distribution are known, were examined. Cavitation was present in all given operating conditions. Further investigations were carried out for the target propeller to observe the effect of five different wake distributions on propeller performance, thrust values on the propeller blade for one rotation, and changing of propeller induced pressure pulse at a point on the hull. By changing skew value (two different skew angle), which is one of the geometric characteristics of original propeller, the effect on the cavitation induced noise was analyzed parametrically. The current study includes a discussion for only the original propeller in terms of performance (thrust, torque and efficiency). A numerical approach, based on Brown’s method and lifting surface method, was used to predict noise calculations. Noise levels obtained from calculations were compared to the other noise predictions in literature. It can be seen that skew has an effect in cases where the inflow is non-uniform. It can be concluded that vibration and noise levels can be reduced significantly by increasing the skew value of the propeller in these operating conditions

Biomechanical and bioenergetical evaluation of swimmers using fully-tethered swimming: A qualitative review

It is presented a qualitative review of the specialized literature on fully-tethered swimming, with the scopes of summarizing and highlighting published knowledge, identifying its gaps and limitations, and motivate future research. The major research conclusions can be summarized as follows: (i) tethered swimming is a reliable test to evaluate force exerted in water by swimmers; (ii) higher maximum values of force are obtained in breaststroke and butterfly, while average values are higher in front crawl; (iii) tethered forces present moderate to strong relationships with swimming velocity, and associations between forces diminish as swimming distance increases; (iv) 30 s maximal tethered swimming may be used as an adaptation of Wingate test for swimming; (v) differences in stroke mechanics can occur in tethered swimming but there is no evidence to suggest that they affect swimming performance; (vi) Tethered swimming is a valid methodology to evaluate aerobic energy contribution in swimming and recent investigations concluded that it can also provide information on the anaerobic contribution. Based on and stimulated by current knowledge, further research should focus on the following topics: (i) the usefulness of tethered swimming as a valid tool to evaluate other swimming techniques; (ii) differences in force parameters induced by gender or competitive level; (iii) defining accurate variables for estimation of anaerobic power and/or capacity using tethered swimming; (iv) bilateral asymmetries in exerted forces, and corresponding influence of breathing; (v) relative contribution of arms and legs for whole-body propelling forces.

空気噴射型能動スコープカメラの性能評価実験

Active Scope Camera (ASC) is the robot video scope that can move by itself to probe narrow gaps for rescue missions. ASC has the ciliary vibration drive mechanism which generates a propellant force to travel in rubble. We had proposed a method to lift up the tip of the ASC stably by using air jet and a flexible passive parallel mechanism, which enabled ASC to climb over steps. However, enough evaluation of the mobility, especially quantitative evaluation, had not been done yet. In this paper, the quantitative evaluation of the mobility in terms of turning motion and step climbing is conducted. In addition, the mobility on rubble is also evaluated through the experiments. These evaluations make It clear that the air-jet-type ASC has higher mobility than the previous non air-jet-type ASC.

An unsteady free wake model for aerodynamic performance of cycloidal propellers

A new unsteady three-dimensional aerodynamic performance prediction approach is established to achieve fast and accurate prediction of the unsteady aerodynamics of cycloidal propellers. This model is developed by the coupling of momentum theory, lifting-line method, free wake model, and the Leishman–Beddoes semi-empirical dynamic stall model. The overall calculation process includes two parts. Firstly, to reduce the computational time and improve the computational convergence, the momentum theory is coupled with the Leishman–Beddoes semi-empirical dynamic stall model to predict a uniform inflow velocity through the cycloidal propeller disc, which is set as the initial induced velocity for iterations in the subsequent process. Then, the blade aerodynamic model, which couples the unsteady lifting-line method with the Leishman–Beddoes dynamic stall model, is used to calculate the unsteady aerodynamic response of blades. The wake of cycloidal propeller is represented by a serious of finite-length shed and trailing vortex elements, and the free wake model is utilized to model the dynamics of cycloidal propeller wake. Predictions from the present model are shown to be agreed reasonably well with the overall experimental data and the computational fluid dynamics results, both in terms of the aerodynamic performance prediction of cycloidal propeller and instantaneous blade force variations.

Determining the Hydrodynamic Loads of the Marine Propeller Forces in Oblique Flow and Off-Design Condition

This paper evaluates hydrodynamic force and moments applied to a marine propeller in oblique and off-design conditions. When a marine propeller operates at an off-design condition, the propeller is usually subjected to unsteady flows which can significantly change the hydrodynamic performance of the propeller. The effect of oblique angles on propeller performance is considered by implementing the numerical simulations. For the purposes of this research, a DTMB propeller is analyzed in different oblique angles. The unsteady calculations are made by applying a Reynolds-averaged Navier–Stokes solver and the sliding mesh method. The method is first verified by a propeller in straight inflow condition. The performance curves of the propellers obtained by numerical method are compared and verified by the experimental results. In the next step, the flow around the propeller in oblique conditions is simulated. The results show, in non-symmetric flow condition, the hydrodynamic forces and moment generated by the propeller become considerably larger.

Classification of point-group-symmetric orientational ordering tensors.

The concept of symmetry breaking has been a propelling force in understanding phases of matter. While rotational-symmetry breaking is one of the most prevalent examples, the rich landscape of orientational orders breaking the rotational symmetries of isotropic space, i.e., O(3), to a three-dimensional point group remain largely unexplored, apart from simple examples such as ferromagnetic or uniaxial nematic ordering. Here we provide an explicit construction, utilizing a recently introduced gauge-theoretical framework, to address the three-dimensional point-group-symmetric orientational orders on a general footing. This unified approach allows us to enlist order parameter tensors for all three-dimensional point groups. By construction, these tensor order parameters are the minimal set of simplest tensors allowed by the symmetries that uniquely characterize the orientational order. We explicitly give these for the point groups {C_{n},D_{n},T,O,I}⊂SO(3) and {C_{nv},S_{2n},C_{nh},D_{nh},D_{nd},T_{h},T_{d},O_{h},I_{h}}⊂O(3) for n,2n∈{1,2,3,4,6,∞}. This central result may be perceived as a road map for identifying exotic orientational orders that may become more and more in reach in view of rapid experimental progress in, e.g., nanocolloidal systems and novel magnets.

Bank of controllers and virtual thrusters for fault-tolerant control of autonomous underwater vehicles

This paper proposes a fault-tolerant control based on a virtual thruster approach for autonomous underwater vehicles (AUVs) with four horizontal and two vertical thrusters. This methodology defines that, in case of partial fault or complete fault (failure) in horizontal thrusters located in different action planes (which defines the axis or plane where component(s) of forces are actuating in this plane), horizontal propelling forces are calculated through the allocation matrix, used in the pseudo-inverse method, without any change, and a modified weighted matrix. Then, the resultant forces of the remaining working thrusters are calculated by using virtual forces. These forces correspond to the failing thruster forces projection into the forces of the remaining thrusters located in the same action plane. Additionally, we use a bank of controllers to reconfigure the controller against the fault, which improves the performance. Simulation results of a real vehicle show that this is an effective method to cope with the problem of fault tolerant control of AUVs.

Design and characteristic evaluation of a novel amphibious spherical robot

This paper presents a new type of amphibious spherical robots. The robot includes four drive units. Each drive unit consists of two servo motors, a water-jet propeller, a DC motor and a wheel. The robot can constitute three movement structure ways according to the environment. When the robot enters water, it adopts water jet propulsion. According to different land conditions, there are two movement patterns to switch. One is a quadruped movement pattern which is available to climb over obstacles; the other is a driving wheel movement pattern which is used to speed up the movement of robot under the flat terrain. Characteristic evaluation experiments on land for a novel amphibious spherical robot were conducted. Underwater motions of the robot mainly rely on the four water-jet propellers, it is necessary to measure relationship between actuating force of the water-jet propeller and the duty ratio. Gambit software is employed to establish and mesh the water-jet propulsion model. Simulation analysis of the models is implemented by FLUENT software. Localization control of the robot and wireless control of the robot were conducted. Finally, experiment results indicated that the developed novel amphibious spherical robot is feasible to develop marine resources and implement marine missions.

Prediction of Performance of a Cavitating Propeller in Oblique Inflow

A cavitating propeller subject to an oblique inflow in a cavitating tunnel is simulated using potential flow methods coupled with a Reynolds-averaged Navier-Stokes (RANS) solver. The propeller is mainly modelled using a panel method, while the inflow to the propeller is evaluated by coupling a Vortex-Lattice Method (VLM) with the RANS solver. The effects of the tunnel wall are incorporated into the calculated effective inflow to the propeller. The predicted propeller forces and cavity pattern are correlated with experiment. The fully wetted open water characteristics of the propeller predicted by the panel method are presented as well.

Tow Forces for Emergency Towing of Containerships

For a series of five containerships of differing capacities (707, 3400, 5300, 14,000, and 18,000 TEU), systematic computations were performed to estimate the tow force required in an emergency. Time-average ship positions with respect to the given waves, wind, and current directions and the corresponding time-average forces were considered. Current speed was considered to include also towing speed. Directionally aligned as well as not aligned wind and waves were investigated. Wave height, wind speed, and wave and wind direction relative to current direction were systematically varied. Wind speeds based on the Beaufort wind force scale corresponded to significant wave heights for a fully arisen sea. Waves were assumed to be irregular short-crested seaways described by a Joint North Sea Wave Observation Project (JONSWAP) spectrum with peak parameter 3.3 and cosine squared directional spreading. For each combination of current speed, wave direction, significant wave height, and peak wave period, the required tow force and the associated drift angle were calculated. Tow force calculations were based on the solution of equilibrium equations in the horizontal plane. A Reynolds-Averaged Navier–Stokes (RANS) solver obtained current and wind forces and moments; and a Rankine source-patch method, drift forces and moments in waves. Tow forces accounted for steady (calm-water) hydrodynamic forces and moments, constant wind forces and moments, and time-average wave drift forces and moments. Rudder and propeller forces and towline forces were neglected.

Memoryless self-reinforcing directionality in endosomal active transport within living cells.

In contrast to Brownian transport, the active motility of microbes, cells, animals and even humans often follows another random process known as truncated Lévy walk. These stochastic motions are characterized by clustered small steps and intermittent longer jumps that often extend towards the size of the entire system. As there are repeated suggestions, although disagreement, that Lévy walks have functional advantages over Brownian motion in random searching and transport kinetics, their intentional engineering into active materials could be useful. Here, we show experimentally in the classic active matter system of intracellular trafficking that Brownian-like steps self-organize into truncated Lévy walks through an apparent time-independent positive feedback such that directional persistence increases with the distance travelled persistently. A molecular model that allows the maximum output of the active propelling forces to fluctuate slowly fits the experiments quantitatively. Our findings offer design principles for programming efficient transport in activematerials.

Submarine Maneuvers Using Direct Overset Simulation of Appendages and Propeller and Coupled CFD/Potential Flow Propeller Solver

This article presents two approaches to simulate maneuvers of a model radio-controlled submarine. In the direct simulation approach, rudders, stern planes, and propellers are gridded and treated as moving objects using dynamic overset technology. The second approach couples the overset computational fluid dynamics (CFD) solver and a potential flow propeller code, with both codes exchanging velocities at the propeller plane and wake, body forces, and propeller forces and moments, whereas rudders and stern planes are still explicitly resolved. It is shown that during the maneuvers, the range of advance coefficients does not deviate much from the design point, making a coupled approach a valid choice for standard maneuvering simulations. By allowing time steps about an order of magnitude larger than for the direct simulation approach, the coupled approach can run about five times faster. The drawback is a loss of resolution in the wake as the direct propeller simulation can resolve blade vortical structures. Open water propeller curves were simulated with both the direct propeller approach and the coupled approach, showing that the coupled approach can match the direct approach performance curves for a wide range of advance coefficients. Simulations of a horizontal overshoot maneuver at two approach speeds were performed, as well as vertical overshoot and controlled turn maneuvers at high speed. Results show that both CFD approaches can reproduce the experimental results for all parameters, with errors typically within 10%.

Submarine Maneuvers Using Direct Overset Simulation of Appendages and Propeller and Coupled CFD/Potential Flow Propeller Solver

This article presents two approaches to simulate maneuvers of a model radio-controlled submarine. In the direct simulation approach, rudders, stern planes, and propellers are gridded and treated as moving objects using dynamic overset technology. The second approach couples the overset computational fluid dynamics (CFD) solver and a potential flow propeller code, with both codes exchanging velocities at the propeller plane and wake, body forces, and propeller forces and moments, whereas rudders and stern planes are still explicitly resolved. It is shown that during the maneuvers, the range of advance coefficients does not deviate much from the design point, making a coupled approach a valid choice for standard maneuvering simulations. By allowing time steps about an order of magnitude larger than for the direct simulation approach, the coupled approach can run about five times faster. The drawback is a loss of resolution in the wake as the direct propeller simulation can resolve blade vortical structures. Open water propeller curves were simulated with both the direct propeller approach and the coupled approach, showing that the coupled approach can match the direct approach performance curves for a wide range of advance coefficients. Simulations of a horizontal overshoot maneuver at two approach speeds were performed, as well as vertical overshoot and controlled turn maneuvers at high speed. Results show that both CFD approaches can reproduce the experimental results for all parameters, with errors typically within 10%.

선박의 직진과 선회 시의 프로펠러 하중이 프로펠러 축 베어링에 미치는 영향

In the beginning of the 1990's, numerous shaft bearing damages, especially in aft stern tube bearing, were reported. The main reasons of bearing damages were estimated that hull deflections have been increased by more flexible hulls and propeller dynamic loads have not been considered in shaft alignment. After that time, studies to take into account hull deflections in shaft alignment have been actively carried out, but for the latter leave much to be desired. In this study, the effects of the propeller forces on the propeller shaft bearing have been investigated by estimating thrust eccentricity as reasonable as possible although some assumptions to simulate turning of ship were introduced. Three dimensional nominal wake to estimate thrust eccentricity have been calculated by using CFD analysis and model test in the towing tank. This study presents the procedure to estimate the propeller eccentric forces and their influence on the stern tube bearing for a container carrier. As a result, it has been found that the lateral propeller forces in turning condition should be considered in shaft alignment to prevent shaft bearing damages.

Dynamics of CMEs in the LASCO Field of View

A large set (16 000) of coronal mass ejections (CMEs) observed during 1996 – 2011 was selected to study their dynamics in the LASCO field of view (LFOV). These events were selected based on the criterion that at least three height–time measurements were available for each CME. The height–time measurements included in the SOHO/LASCO catalog were used to determine velocities and accelerations of the respective CMEs at successive distances from the Sun. Next, these parameters were sorted into 30 subsamples depending on the distance from the Sun at which they were determined. The mean velocities and accelerations calculated for the successive distance-dependent subsamples of CMEs were used to study their dynamics. We demonstrate that CMEs in the LFOV manifest three distinct phases of propagation: (i) The propelling Lorentz force dominates the dynamics of CMEs in the inner (C2 LASCO) FOV, (ii) a stable propagation occurs as a result of the balance between the propelling and drag forces, (iii) the drag force dominates at the outer edge of the LFOV. When we considered different categories of CME separately, we found different acceleration–distance profiles for different categories.

Reduction of vibration and noise radiation of an underwater vehicle due to propeller forces using periodically layered isolators

Abstract Using periodic structure theory, the suppression of vibration and noise radiation from an underwater vehicle due to excitation from propeller forces is investigated. The underwater vehicle is modelled in two parts (the hull and the propeller/shafting system). A model of the propeller/shafting system is constructed using a modular approach and considers the propeller, shaft, thrust bearing, isolation structure and foundation. Different forms of isolator are considered – a simple spring-damper system, a continuous rod and a periodically layered structure. The dynamic properties of the underwater vehicle and the isolation performances of various isolators are compared and analysed. The stop band properties of the periodic isolator are used to enhance the passive control performance. Furthermore, an integrated isolation device is proposed that consists of the periodic isolator and a dynamic absorber, and its isolation performance is investigated. The effects of the absorber parameters on the performance of the integrated device are also analysed. Finally, the radiated sound pressure is calculated to verify the attenuation. The numerical results show that the vibration and noise radiation are greatly attenuated in the stop bands. By optimising the design of the periodic isolators and its integrated structures, the suppression of the vibration and noise radiation can be improved effectively.