Self-propelled Condition Research Articles

A Study on the Propulsion Performance of Hybrid-Driven Underwater Glider Equipped with a Kappel Tip Rake Propeller

In order to solve the problem of the lack of maneuverability of the conventional underwater glider, this paper proposes a hybrid-driven underwater glider equipped with a Kappel tip rake propeller, analyzes the propulsion performance of different types of Kappel tip rake propellers in the wake field of the hybrid-driven underwater glider, optimizes the overall propulsion performance of the hybrid-driven underwater glider, and realizes self-propulsion and gliding with high efficiency and low energy consumption. In the research process, the Schnerr–Sauer cavitation model and the cavitation simulation strategy of VOF two-phase flow were adopted, coupled with the SST k-ω and γ transition turbulence model, and the control calculation error was not more than 3%. Based on the hydrodynamic performance study of the Kappel tip rake propeller, the self-propelled simulation was carried out under the working conditions of 6 kn, 5 kn, 4 kn, and 3 kn, and the gliding simulation was carried out under the working conditions of 1 kn, 0.5 kn, and a glide angle of 12°. The propulsion performance of the hybrid-driven underwater glider with different models of Kappel tip rake propellers was analyzed. It was found that the maximum open water propulsion efficiency of the propeller Kap05 had the largest improvement, which was 3.07% higher than that of the reference base propeller. Under the self-propelled condition, the hybrid-driven underwater glider with the propeller Kap05 had the lowest wake fraction, and the propellers Kap04 and Kap05 had the best propulsion performance in the wake field of the hybrid-driven underwater glider. In the gliding condition, the form of the folding paddle can reduce the gliding resistance generated by the propeller by more than 45% and the gliding negative lift by more than 68%. A moderate tip rake can effectively improve the propulsion efficiency of the Kappel tip rake propeller in the wake field of the hybrid-driven underwater glider, reduce energy loss, and improve the overall performance of the hybrid-driven underwater glider.

Working mechanism of pre-swirl stator based on stereoscopic particle image velocimetry

The pre-swirl stator (PSS), as a type of energy-saving device, has garnered increasing attention due to efforts aimed at global energy-saving and emission reduction. Owing to the influence of the stern profile, the wake field at the stern is complex, and the installation of such energy-saving appendages further increases its complexity. To explore the flow mechanism of a ship's wake field and the working principles of energy-saving appendages, this study used a scale model of a bulk carrier as its research object and conducted a wake field experiment with the help of the large underwater stereoscopic particle image velocimetry system at Harbin Engineering University. The wake field data of several sections were obtained, including the axial velocity, tangential velocity, average kinetic energy, vorticity, swirl strength, streamline, pulsating velocity, turbulent kinetic energy, and axial velocity at different radii. The wake field data with or without a PSS in the bare hull condition and with or without a PSS in the self-propelled condition were compared. The time-averaged flow field clearly demonstrated a “hook-like” velocity profile, bilge vortex, hub cap vortex, and other flow structures, as well as the flow details around the PSS. The results showed that the PSS could destroy the contour structure of the axial velocity, which mainly affects the range of 0.5–0.8R, making the flow field more uniform. The PSS has a certain influence on the flow field on the side without the stator blade and a great influence on the tangential velocity by producing a pre-swirl flow in a direction opposite to the propeller rotation in front of the propeller plane. This pre-swirl flow can increase the inflow of the propeller disk and improve the working conditions of the propeller. The PSS also has an influence on radial velocity; however, the influence degree and range are smaller than that on the tangential velocity. The PSS changed the water inflow direction, increased the interaction angle between the water flow and propeller blade, improved the wake conditions and propulsion performance, and was conducive to improving the working efficiency of the propeller. Moreover, the existence of a PSS reduced the local pulsating velocity and turbulent kinetic energy, benefiting the structural strength of the propeller.

Vertical zigzag maneuver of a generic submarine

A study of a 10/10 vertical zigzag maneuver of the generic submarine Joubert BB2 is presented. CFD simulations, involving moving planes and rotating propeller using a dynamic overset technique, are performed at constant propeller rotational speed in model scale on four systematically refined grids and compared against experimental data for depth, pitch, pitch rate, vertical drift, vertical velocity, absolute velocity, and propeller thrust and torque coefficients. A grid study is also performed for the self-propelled approach condition before starting the maneuver, used to obtain the propeller rotational speed, controller vertical and horizontal commands, and boat attitude. The maneuver is also analyzed in full scale at 6, 10 and 15 knots. Results indicate that CFD matches very well the experimental data, even for the coarsest grid, with the propeller RPS converging slowest in grid. By comparing model and full scale results, it can be concluded that model scale simulations are a good surrogate for full scale for parameters related to motions, but as expected forces are strongly affected by scale and the propeller operational point changes considerably. Analysis of forces and moments affecting vertical control from hull, sail and stern planes, propeller and hull help understand the response of the vehicle.

자항상태 VPMM 시험을 통한 무인잠수정 조종성능 추정에 관한 연구

The present study aims to improve the accuracy of the maneuvering simulations based on captive model test results. To derive the hydrodynamic coefficients in a self-propelled condition, a mathematical maneuvering model using a whole vehicle model was established. Captive model tests were carried out using the Vertical Planar Motion Mechanism (VPMM) equipment. A motor controller was used to control the constant propeller revolution rate during pure motion tests. The resistance tests, self-propulsion tests, static drift tests, and VPMM tests were performed in the towing tank of Seoul National University. When the vertical drift angle changes, the gravity load on the sensors were changed. The hydrodynamic forces were deduced by subtracting the gravity load from the measured forces. The hydrodynamic coefficients were calculated using the least-square method. The simulation of the turning circle test was compared with the free-running model test result, and the error of the turning radius was 8.3 % compared to the free-running model test.

Linear Acceleration of an Undulatory Robotic Fish with Dynamic Morphing Median Fin under the Instantaneous Self-propelled Condition

Fish commonly execute rapid linear accelerations initiated during steady swimming, yet the function of the median fins during this process is less understood. We find that the erection/folding time (from the starting time of the linear acceleration (0 s) to the starting time of the folding movement of the fin), as well as the spreading area of the median fins, actively change during the linear acceleration of the live largemouth bass (Micropterus salmoides). To better understand the influence of the folding time and the area change of the median fins on the linear acceleration, we implemented an undulatory biomimetic robotic fish with soft median fins that can be programmed to erect and fold, just like a live fish. To characterize the acceleration performance of the robotic fish, we developed a “self-propelled” experiment technique based on the Kalman filter and Proportional-Integral-Derivative (PID) control algorithm. The experiments on the robotic fish show the acceleration induced by fully-erected median fins increases by 46.3%. Fully-erected median fins positively contribute to propulsion primarily at the onset stage of the linear acceleration while result in a significant decrease in steady swimming speed by 25%, which suggests a large drag force is induced at the steady swimming stage due to the enlarged wetted area. Parametric sweeping experiments on erection/folding time and spreading area demonstrate a proper combination of the erection/folding time and the spreading area enhances the mean linear acceleration by up to 85%. Particle Image Velocimetry (PIV) results reveal that the vortexes shed by the erected dorsal fin are stronger than those shed by the folded fin. As the acceleration process progresses, the thrust generated by the dorsal fins gradually is weakened until only resistance is generated in the end. Our findings may shed light on the realization of controllable surfaces on high performance fish-inspired robotic systems in the future.

Towed underwater PIV measurement of propeller wake in self-propelled condition

A series of particle image velocimetry measurements was conducted in a towing tank to analyze the propeller wake dynamics of a fully appended very large crude oil carrier model. The Froude number and the Reynolds number of the test condition based on the model length and towing speed were 0.142 and 2.32 × 106, respectively. The propeller wake dynamics was investigated in terms of vortical structure and wake acceleration. It was found that the propeller loading on the starboard side was larger than that on the port side, as upward component of the propeller inflow resulted in a higher inflow speed on that side. The different propeller loading deformed the wake structure and bent it towards the port side. Between neighboring tip vortices, the local maxima of the turbulence kinetic energy and corresponding local turbulence structure were found. The rudder effects on the propeller wake were also investigated, proving that the rudder blocked the progress of the hub vortex and straightened the propeller wake.

Large-Eddy Simulations of a notional submarine in towed and self-propelled configurations

The present study reports results of Large Eddy Simulations (LES) in towed and self-propelled conditions for the DARPA SUBOFF (DSub), a notional submarine geometry, at a Reynolds number, based on the model length, L, and the free-stream velocity, U∞, equal to ReL=1.2×106. An Immersed-Boundary (IB) method was adopted to enforce no-slip boundary conditions on the surface of the body. The approach (LES with IB) was validated by the authors in earlier studies on the towed DSub, as well as on the INSEAN E1619 propeller in open-water conditions. Comparisons between towed and propelled configurations are presented here. Results show that the development of the boundary layer over the cylindrical mid-body is almost unaffected by propeller suction. Instead, the effect over the stern is dramatic, modifying substantially the flow ingested by the same propeller. In the wake the bimodal distribution of the turbulent stresses for the towed case, due to the adverse pressure gradient induced by the tapered geometry of the stern, is replaced in self-propulsion by an axial peak of turbulent kinetic energy, mainly due to instability of the hub vortex.

A boundary control problem for the steady self-propelled motion of a rigid body in a Navier–Stokes fluid

Consider a rigid body S⊂R3 immersed in an infinitely extended Navier–Stokes fluid. We are interested in self-propelled motions of S in the steady state regime of the system rigid body-fluid, assuming that the mechanism used by the body to reach such a motion is modeled through a distribution of velocities v⁎ on ∂S. If the velocity V of S is given, can we find v⁎ that generates V? We show that this can be solved as a control problem in which v⁎ is a six-dimensional control such that either Suppv⁎⊂Γ, an arbitrary nonempty open subset of ∂Ω, or v⁎⋅n|∂Ω=0. We also show that one of the self-propelled conditions implies a better summability of the fluid velocity.

Hydrodynamic Performance of an Undulatory Robot: Functional Roles of the Body and Caudal Fin Locomotion

Both body undulation and caudal fin flapping play essential locomotive roles while a fish is swimming, but how these two affect the swimming performance and hydrodynamics of fish individually is yet to be known. We implemented a biomimetic robotic fish that travel along a servo towing system, which can be regarded as “treadmill” of the model. Hydrodynamics was studied as a function of the principal kinetic parameters of the undulatory body and caudal fin of the model in a self-propelled condition, under which the time-averaged measured axial net force becomes zero. Thrust efficiency was estimated from two-dimensional digital particle image velocimetry (DPIV) measurements in the horizontal and mid-caudal fin plane. The Single-Row Reverse Karman wake (2S) is commonly observed in many previous studies of live fish swimming. However, we show that a Double-Row Two-Paired vortices (2P) wake was generated by the robotic model for most kinetic parameter combinations. Interestingly, the 2S wake emerged within the results of a narrow range of robotic caudal fin pitch angles (0<0<10°), occurring concurrently with enhanced thrust efficiency. We also show that, compared with the effect of body wavelength ( ?), the wake structure behind the robotic swimmer is more sensitive to the Strouhal number ( St) and caudal fin pitch angle ( θ).

Further study of the method of approach to testing the performance of extraterrestrial rovers/rover wheels on earth

The current practice for experimentally evaluating the performance of extraterrestrial rovers/rover wheels is to conduct tests on earth on a soil simulant, appropriate to the regolith on the extraterrestrial body of interest. In the tests, the normal load (force) applied by the rover/rover wheel to the soil simulant is set identical to that expected on the extraterrestrial surface, taking into account its acceleration due to gravity. It should be pointed out, however, that the soil simulant used in the tests is subject to earth gravity, while the regolith on the extraterrestrial surface is subject to a different gravity. Thus, it is uncertain whether the performance of the rover/rover wheel obtained from tests on earth represents that on the extraterrestrial surface. This issue has been explored previously. A method has been proposed for conducting tests of the rover/rover wheel on earth with identical mass to that on the extraterrestrial surface, instead of with identical normal load used in the current practice [1]. This paper provides further evidence to substantiate the merits of the proposed method, based on a detailed analysis of the test data obtained under various gravity conditions, produced in an aircraft undergoing parabolic flight manoeuvres [8]. In the study, the effect of slip on wheel sinkage has been evaluated. It is found that gravity has little effect on the slip and sinkage relationship of the rover wheel under self-propelled conditions.

Computational Study of the Embedded Engine Static Pressure Thrust Propulsion System

Drag reduction is being pursued for next generation aircraft to reduce fuel consumption and pollutant production. Drag reduction of fuselages is now receiving more consideration, since the fuselage represents 30% of the drag of the entire aircraft. This paper presents numerical simulations of earlier experimental studies using aft suction slots and embedded propulsor systems to reduce fuselage drag. Detailed grid refinement studies were conducted, and different turbulence models were evaluated. A simulation of an airship with a boundary layer suction slot and an embedded engine with aft injection of the ingested flow for propulsion was conducted. The simulations require significantly more propulsor power to achieve a self-propelled condition than reported in the experiments, which were subject to large experimental uncertainties. The computational fluid dynamics flow field can be interrogated in detail, leading to improved understanding of the performance and integration of all system components. The particular arrangement studied in the experiments was shown to be limited by significant internal flow losses. This study provides the basis for the much improved integration of an embedded engine and gives the starting point for a wider analysis of more slender bodies operating in a transonic flow field for application to modern transport aircraft

Young children with autism spectrum disorder use predictive eye movements in action observation.

Does a dysfunction in the mirror neuron system (MNS) underlie the social symptoms defining autism spectrum disorder (ASD)? Research suggests that the MNS matches observed actions to motor plans for similar actions, and that these motor plans include directions for predictive eye movements when observing goal-directed actions. Thus, one important question is whether children with ASD use predictive eye movements in action observation. Young children with ASD as well as typically developing children and adults were shown videos in which an actor performed object-directed actions (human agent condition). Children with ASD were also shown control videos showing objects moving by themselves (self-propelled condition). Gaze was measured using a corneal reflection technique. Children with ASD and typically developing individuals used strikingly similar goal-directed eye movements when observing others' actions in the human agent condition. Gaze was reactive in the self-propelled condition, suggesting that prediction is linked to seeing a hand-object interaction. This study does not support the view that ASD is characterized by a global dysfunction in the MNS.

Predictive Eye Movements Are Driven by Goals, Not by the Mirror Neuron System

The importance of a mirror neuron system (MNS) as a mechanism for understanding the actions of others has been established (e.g., Rizzolatti, Fadiga, Gallese, & Fogassi, 1996). Neurons in the primate premotor cortex fire both when a monkey performs an action (e.g., grasping) and when the monkey observes someone else performing the same action. It has also been proposed that the MNS is the starting point for understanding the intentions and goal-directed behavior of others (Fogassi et al., 2005; Gallese & Goldman, 1998). Consistent with this view, Falck-Ytter, Gredeback, and von Hofsten (2006) argued that the MNS is implicated in proactive goal-directed (predictive) eye movements. In a series of eye-tracking studies, participants observed a toy object moving along a trajectory toward a container. Adults and 1-year-old infants looked ahead of the toy and toward the goal container only when a hand was observed moving the toy (the human-agent condition). Proactive goaldirected eye movements were not found in two further conditions: a self-propelled condition, in which a toy with rudimentary facial features moved along the trajectory by itself, or a mechanical motion condition, in which a ball with no distinctive features moved along the trajectory. Falck-Ytter et al. interpreted these data as evidence that the MNS is necessary for proactive goal-directed eye movements. Moreover, the absence of proactive goal-directed eye movements in 6-month-old infants (who are too young to perform the actions themselves) is taken as further support for the MNS account. These claims are premature. The conditions run by FalckYtter et al. (2006) do not discriminate between predicted human motion tied to intention and predicted agent goals tied to intention. Consistent with the mirror neuron hypothesis, movement of the hand may necessarily involve the simulation of motion via the MNS, and proactive goal-directed eye movements may therefore only occur when a hand is shown to move the object. Alternatively, a hand moving an object involves the intention of an agent to place the object in the goal container, and the expectation that the agent intends for the object to end up in a goal location may cause the proactive eye movements (consistent with teleological stance theory; Gergely & Csibra, 2003). To arbitrate between these accounts, it is necessary to run a human-agent condition without human movement. Therefore, we set out to test the claims of Falck-Ytter, et al. (2006), but with the addition of a new critical condition missing in the original study. We ran three movement conditions: the human-agent condition, in which a human agent was shown moving a toy frog toward a goal container (i.e., [1human agent, 1human motion]); the self-propelled condition, in which no human agent was shown moving the frog (i.e., [ human agent, human motion]); and the new condition, in which a human agent was shown with hand behind the starting point of the frog, flicking it so as to propel it along a trajectory (as in the game ‘‘Tiddlywinks’’; i.e., [1human agent, human motion]; see Fig. 1a). In the latter condition, the human-agent intention is matched to that of the human-agent condition, but human motion is not shown along the trajectory. This allows a clean test of the MNS versus goal-intention explanations for the proactive eye-movement data. We also ran each condition in two ways. In the original humanagent condition run by Falck-Ytter et al. (2006), when the toy object reached the bucket, a sound was played and a smiley face on the bucket was animated. This could serve to heighten the desirability of the goal state, encouraging proactive eye movements in a manner consistent with teleological stance theory. Therefore, we ran each of the three conditions with and without end effects. For the conditions with end effects, when the toy The order of authorship is arbitrary; all authors contributed equally to the work reported. Address correspondence to Kenny R. Coventry, Cognition and Communication Research Centre, Northumbria University, Northumberland Building, Northumberland Rd., Newcastle Upon Tyne NE1 8ST, United Kingdom, e-mail: kenny.coventry@ northumbria.ac.uk. PSYCHOLOGICAL SCIENCE

Wheel slip measurement in 2WD tractor

A microcontroller-based slip sensor was developed for a 2WD tractor to indicate slip values during on-farm use. The ‘zero condition’ considered for the development of slip sensor was – tractor supplied with a driving torque to propel any device across a tarmacadam surface while delivering zero net traction (self-propelled condition). This sensor comprised of four components: power supply; sensing of throttle position, gear position, and wheel rpm; processing of collected data; and display unit. Power was taken from the tractor battery. Rotary potentiometer and proximity switches were installed on the tractor to measure throttle position and wheel revolution, respectively. The performance of developed slip sensor was evaluated both on tarmacadam surface as well as in the field. The variations between indicated and actual slip were found to be within 0–5% for both the surfaces, thus indicating the accuracy of slip measurement by the developed slip sensor.

Flow measurement around a model ship with propeller and rudder

For the design of hull forms with better resistance and propulsive performance, it is essential to understand flow characteristics, such as wave and wake development, around a ship. Experimental data detailing the local flow characteristics are invaluable for the validation of the physical and numerical modeling of computational fluid dynamics (CFD) codes, which are recently gaining attention as efficient tools for hull form evaluation. This paper describes velocity and wave profiles measured in the towing tank for the KRISO 138,000 m3 LNG carrier model with propeller and rudder. The effects of propeller and rudder on the wake and wave profiles in the stern region are clearly identified. The results contained in this paper can provide an opportunity to explore integrated flow phenomena around a model ship in the self-propelled condition, and can be added to the International Towing Tank Conference benchmark data for CFD validation as the previous KCS and KVLCC cases.

The Wake of Self-Propelled and Over-Thrusted Slender Bodies Near a Simulated Free Surface

Measurements were performed in the turbulent wake of a propeller-driven axisymmetric body with a plane of symmetry. A flat plate strut was attached to the upper surface of the axisymmetric body, giving a configuration like that of a SWATH-type ship, with the free surface replaced by the plane of symmetry. All mean flow and turbulent flow parameters were measured at three streamwise stations. The measurements were performed for the self-propelled condition and 100 percent over-thrust condition. In the far wake, the center of the wake was found to migrate towards the plane of symmetry. Some interactions were noted between the wakes of the propeller-driven axisymmetric body and that of the flat plate strut—yielding lower axial velocities, higher turbulence intensities and larger static pressure changes compared to regions free of such interference. Comparisons of these effects in the self-propelled case, 100 percent over-thrust case and a previous unpropelled case are given. Spectral measurements were also performed in both near-wake and far-wake regions.

Modeling motion resistance of rigid wheels

A mathematical model was developed to describe the motion resistance of rigid wheels under self-propelled conditions where no drawbar pull is developed. The modeling was based on the concept that the work required to overcome the motion resistance is equal to the energy dissipated in compacting the soil beneath the wheel. Slippage of the wheel was also considered in the modeling. Finally the validity of the proposed model was discussed.

On the Optimization of Overall Performance of Rudders (Second Report)

In this Second Report, results are presented and discussed of a study of rudder optimisation from the resistance and propulsion points of view. A synthetic method of approach is used in contrast to the analytic method of the First Report. On the basis of Kumano's finding (in 1960-61) that the rudder occupies a near optimum position as a stern bulb aimed at stern wave cancellation, the Authors investigate, by towing tests and wave analysis, several unconventional rudder configurations. Also, possible improvement of self-propulsion factors is investigated in propulsion tests. Up to 7% improvement in propulsive performance is obtained; this is mainly attributable to stern wave cancellation. Viscous scale effects upon the main hull stern wave system are studied in the towed and self-propelled conditions with tow geosim models (L = 2.5 m and 10 m). Order from BSRA as No. 51,914.

Measurement of the velocity of the slip stream behind a ship model, and its application to the design of the reaction rudder

To utilize the energy of the rotation, existing in the slip stream behind a ship, the reaction rudder has been used commonly. But it seems that there is no reasonable method of designing this rudder. To improve the propulsive efficiency of single-screw ship still more, we investigated the action of the reaction rudder, and obtained a theoretical method of determining the chief character of this rudderRelating to this investigation we measured the distribution of the direction and velocity of the slip stream behind a ship model at a self-propelled condition, and as a example, by means of the above-mentioned method, the optimum reaction rudder is designed for that condition.