scholarly journals Performance Comparison of Bow and Stern Rudder for High-Speed Supercavitating Vehicles

2020 ◽  
Vol 2020 ◽  
pp. 1-17
Author(s):  
Chuang Huang ◽  
Kai Luo ◽  
Kan Qin ◽  
Daijin Li ◽  
Jianjun Dang
Keyword(s):  
High Speed ◽  
Lift Force ◽  
Turbulence Models ◽  
Performance Comparison ◽  
Hydrodynamic Characteristics ◽  
Control Force ◽  
Supercavitating Vehicles ◽  
Wetted Area ◽  
Control Surfaces ◽  
Rudder Angle

To predict the hydrodynamic characteristics and supercavity shape of supercavitation flows, the numerical model including VOF, cavitation model, and turbulence models is presented and validated by a well-established empirical correlation. The numerical method is then employed to simulate the high-speed supercavitating vehicles with two different types of control surfaces: bow rudders and stern rudders. The hydrodynamic characteristics and influences on the supercavity are compared. By contrast with the stern rudder, the bow rudder with the same wetted area is capable of generating a larger control force and moment. Also, the bow rudder introduces a considerable deformation to the forepart of the supercavity, while the stern rudder provides a negligible influence on the supercavity before it. In addition, the bow rudder is fully wetted, and the lift force only changes with the rudder angle. However, the stern rudder is partly wetted; the lift force is not only determined by the rudder angle but also related to the actual wetted status.

Heading control of a novel finless high-speed supercavitating vehicle with an internal oscillating pendulum

2020 ◽  
pp. 107754632094834
Author(s):  
Mojtaba Mirzaei ◽  
Hossein Taghvaei
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
Sliding Mode ◽  
Six Degrees Of Freedom ◽  
Supercavitating Vehicles ◽  
Supercavitating Vehicle ◽  
High Speeds ◽  
Heading Control ◽  
Heading Angle ◽  
Control Surfaces

High-speed supercavitating vehicles are surrounded by a huge cavity of gas and only a small portion of the nose and the tail of the vehicle are in contact with the water which leads to a considerable reduction in skin friction drag and reaching very high speeds. High-speed supercavitating vehicles are usually controlled by the cavitator at the nose which controls the pitch and depth of the vehicle and the control surfaces or fins which control the roll and heading angle of the vehicle using the bank-to-turn maneuvering method. However, control surfaces have disadvantages such as the high drag force and ineffectiveness due to the supercavity. Therefore, the purpose of the present study is to eliminate the fins from high-speed supercavitating vehicles and propose a new bank-to-turn heading control of this novel finless high-speed supercavitating vehicle which is composed of the cavitator at the nose and an oscillating pendulum as the internal actuator. Sliding mode control as a robust method is used for the six-degrees-of-freedom model of this finless high-speed vehicle against exposed disturbances. Some design criteria for the design of the internal pendulum in this finless supercavitating vehicle are presented for the damping coefficient, pendulum mass, and radius.

Aerodynamic and hydrodynamic aspects of high-speed water surface craft

1987 ◽  
Vol 91 (906) ◽  
pp. 241-268 ◽  
Author(s):  
R. K. Nangia
Keyword(s):  
Water Surface ◽  
High Speed ◽  
Dynamic Pressure ◽  
Hydrodynamic Characteristics ◽  
Stability Margins ◽  
High Speeds ◽  
Wetted Area ◽  
The Stability ◽  
Safety And Stability ◽  
Aerodynamic Lift

Summary High speeds on water are being attained in racing sport and in attempts on world speed records in various classes. Success, safety and stability of these craft depends upon the favourable interaction of their aerodynamic and hydrodynamic characteristics under the influence of two media, one about 800 times denser than the other. Speed on the straight course and in turns is important. As its velocity increases, a craft experiences increasing dynamic pressure in water and to maintain the balance, the ‘wetted’ area of the craft reduces as it rises up (‘planing’). Modern fast craft have ‘tunnel-hulls’ and lifting areas to generate aerodynamic lift and to assist the craft to attain planing attitudes rapidly. The ‘lifting’ areas may not necessarily be in the correct locations however. An example often seen is that of a power boat riding virtually on its propeller and ‘wallowing’ in an unstable manner. In this case the variation in riding height alters the relative positions of centres of aero- and hydro-lift such that the ‘stability-margins’ are near critical in both the longitudinal and the lateral sense.

scholarly journals The Prediction of the Performance of a Twisted Rudder

2021 ◽  
Vol 11 (15) ◽  
pp. 7098
Author(s):  
Ilryong Park ◽  
Bugeun Paik ◽  
Jongwoo Ahn ◽  
Jein Kim
Keyword(s):  
Lift Force ◽  
Twist Angle ◽  
Hydrodynamic Characteristics ◽  
Total Drag ◽  
Reference Design ◽  
Drag And Lift ◽  
Correction Step ◽  
Rudder Angle ◽  
Ship Speed ◽  
Good Agreement

A new design approach using the concept of a twisted rudder to improve rudder performances has been proposed in the current paper. A correction step was introduced to obtain the accurate inflow angles induced by the propeller. Three twisted rudders were designed with different twist angle distributions and were tested both numerically and experimentally to estimate their hydrodynamic characteristics at a relatively high ship speed. The improvement in the twisted rudders compared to a reference flat rudder was assessed in terms of total cavitation amount, drag and lift forces, and moment for each twin rudder. The total amount of surface cavitation on the final optimized twin twisted rudder at a reference design rudder angle decreased by 43% and 34.4% in the experiment and numerical prediction, respectively. The total drag force slightly increased at zero rudder angle than that for the twin flat rudder but decreased at rudder angles higher than 4° and 6° in the experiment and numerical simulation, respectively. In the experimental measurements, the final designed twin twisted rudder gained a 5.5% increase in the total lift force and a 37% decrease in the maximum rudder moment. Regarding these two performances, the numerical results corresponded to an increase of 3% and a decrease of 66.5%, respectively. In final, the present numerical and experimental results of the estimation of the twisted rudder performances showed a good agreement with each other.

scholarly journals Systematic Performance Comparison of (Duobinary)-PAM-2,4 Signaling under Light and Strong Opto-Electronic Bandwidth Conditions

Photonics ◽  
2021 ◽  
Vol 8 (3) ◽  
pp. 81
Author(s):  
Ramón Gutiérrez-Castrejón ◽  
Md Ghulam Saber ◽  
Md Samiul Alam ◽  
Zhenping Xing ◽  
Eslam El-Fiky ◽  
...  
Keyword(s):  
Optical Networks ◽  
High Speed ◽  
Performance Comparison ◽  
Sampling Point ◽  
Bit Rate ◽  
Performance Limits ◽  
Specific System ◽  
Rate System ◽  
Modulation Formats ◽  
Modulation Format

We present a systematic comparison of PAM-2 (NRZ), Duobinary-PAM-2, PAM-4, and Duobinary-PAM-4 (duo-quaternary) signaling in the context of short-reach photonic communications systems using a Mach–Zehnder modulator as transmitter. The effect on system performance with a relaxed and constrained system’s opto-electronic bandwidth is analyzed for bit rates ranging from 20 to 116 Gb/s. In contrast to previous analyses, our approach employs the same experimental and simulation conditions for all modulation formats. Consequently, we were able to confidently determine the performance limits of each format for particular values of bit rate, system bandwidth, transmitter chirp, and fiber dispersion. We demonstrate that Duobinary-PAM-4 is a good signaling choice only for bandwidth-limited systems operating at relatively high speed. Otherwise, PAM-4 represents a more sensible choice. Moreover, our analysis put forward the existence of transition points: specific bit rate values where the BER versus bit rate curves for two different formats cross each other. They indicate the bit rate values where, for specific system conditions, switching from one modulation to another guarantees optimum performance. Their existence naturally led to the proposal of a format-selective transceiver, a component that, according to network conditions, operates with the most adequate modulation format. Since all analyzed modulations share similar implementation details, signaling switching is achieved by simply changing the sampling point and threshold count at the receiver, bringing flexibility to IM/DD-based optical networks.

A Benchmark Control Problem for Supercavitating Vehicles and an Initial Investigation of Solutions

2003 ◽  
Vol 9 (7) ◽  
pp. 791-804 ◽  
Author(s):  
John Dzielski ◽  
Andrew Kurdila
Keyword(s):  
High Speed ◽  
Linear Models ◽  
The Body ◽  
Control Surface ◽  
Force Model ◽  
Entire Body ◽  
Benchmark Problem ◽  
Supercavitating Vehicles ◽  
Forcing Function ◽  
Natural Cavitation

At very high speeds, underwater bodies develop cavitation bubbles at the trailing edges of sharp corners or from contours where adverse pressure gradients are sufficient to induce flow separation. Coupled with a properly designed cavitator at the nose of a vehicle, this natural cavitation can be augmented with gas to induce a cavity to cover nearly the entire body of the vehicle. The formation of the cavity results in a significant reduction in drag on the vehicle and these so-called high-speed supercavitating vehicles (HSSVs) naturally operate at speeds in excess of 75 m s-1. The first part of this paper presents a derivation of a benchmark problem for control of HSSVs. The benchmark problem focuses exclusively on the pitch-plane dynamics of the body which currently appear to present the most severe challenges. A vehicle model is parametrized in terms of generic parameters of body radius, body length, and body density relative to the surrounding fluid. The forebody shape is assumed to be a right cylindrical cone and the aft two-thirds is assumed to be cylindrical. This effectively parametrizes the inertia characteristics of the body. Assuming the cavitator is a flat plate, control surface lift curves are specified relative to the cavitator effectiveness. A force model for a planing afterbody is also presented. The resulting model is generally unstable whenever in contact with the cavity and stable otherwise, provided the fin effectiveness is large enough. If it is assumed that a cavity separation sensor is not available or that the entire weight of the body is not to be carried on control surfaces, limit cycle oscillations generally result. The weight of the body inevitably forces the vehicle into contact with the cavity and the unstable mode; the body effectively skips on the cavity wall. The general motion can be characterized by switching between two nominally linear models and an external constant forcing function. Because of the extremely short duration of the cavity contact, direct suppression of the oscillations and stable planing appear to present severe challenges to the actuator designer. These challenges are investigated in the second half of the paper, along with several approaches to the design of active control systems.

Application of several turbulence models for high speed shear layer flows

1999 ◽  
Author(s):  
Yildirim Suzen ◽  
Klaus Hoffmann ◽  
James Forsythe
Keyword(s):  
Shear Layer ◽  
High Speed ◽  
Turbulence Models

Transonic Hull: Theory, Validation, Breakthroughs and Applications to Ships

2015 ◽  
Author(s):  
Alberto A. Calderon ◽  
Brian Maskew
Keyword(s):  
High Speed ◽  
Feasibility Studies ◽  
Hydrodynamic Characteristics ◽  
Large Magnitude ◽  
Transverse Waves ◽  
Triangular Shape ◽  
Bow Wave ◽  
Linear Drag ◽  
Speed Function ◽  
Displacement Regime

Froude laws are inductive therefore not universally applicable. The relation between Froude and Kelvin, and Froude and Wigley are made explicit. Transonic Hull (TH) has hydrodynamic characteristics not predictable by Froude’s laws. In Transonic Hydrofield (THF) Theory TH’s 3-D triangular shape induces a submerged current - subduction effect - that replaces and substantially precludes bow wave, reducing or eliminating wave making drag growth. TH’s ability to transverse waves without diminishing their energy eliminates slam. TH’s unprecedented breakthroughs with large magnitude are: substantially no bow or stern wave; full displacement regime and near zero pitch independent of speed; linear drag-speed function with greatly reduced wave making (residual) drag; accelerations in a sea that decrease with increasing speed; no slam at any speed and sea conditions. CFD studies of TH-900 vs. Fastship and TH-4022 vs. Axe Bow 4103 shows reduction of drag from 20% to 37% with gains of weight/drag from 33% to 59%. Gains originate from much smaller residual drag. Pre-feasibility studies demonstrate that TH’s triangular waterplanes houses same contents and payloads as conventional vessels provided TH has larger length and beam. TH-1200 Strategic Lift with full payload and range has exceptional high L/D at high speed in Von-Karman-Gabrielli chart.

RANS Study on Hydrodynamic Characteristics of Flapped Rudders

2018 ◽  
Author(s):  
Jialun Liu ◽  
Robert Hekkenberg ◽  
Bingqian Zhao
Keyword(s):  
Yangtze River ◽  
Area Ratio ◽  
Hydrodynamic Characteristics ◽  
Hydrodynamic Coefficients ◽  
Sectional Area ◽  
The Yangtze River ◽  
Long Distance ◽  
Ansys Fluent ◽  
Rans Simulations ◽  
Rudder Angle

Ships that equipped with flapped rudders have better manoeuvring performance than ships fitted with traditional spade rudders. Moreover, this advantage is achieved without significantly affecting the ship’s resistance during normal cruising. Flapped rudders are, therefore, favourable for ships that require high manoeuvring performance and sail long distance. Nowadays, there is a trend of using twin flapped rudders on newly built inland vessels in the Yangtze River. To properly design these ships and analyse their manoeuvring performance, the hydrodynamic characteristics of the flapped rudders are required. In this paper, a RANS study is performed to analyse the impacts of the three main properties of a flapped rudder on its hydrodynamic coefficients. The target properties are the rudder profile, the flap-linkage ratio (the flapped angle relative to the rudder chord line divided by the applied rudder angle), and the flap-area ratio (the sectional area of the flap divided by the total sectional area). The RANS simulations are carried out with commercial meshing tool ANSYS Meshing and CFD solver ANSYS Fluent.

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