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.

A Statistical Study of Process Variables to Optimize a High Speed Curtain Coater: Part I

TAPPI Journal ◽  
2009 ◽  
Vol 8 (1) ◽  
pp. 20-26 ◽  
Author(s):  
PEEYUSH TRIPATHI ◽  
MARGARET JOYCE ◽  
PAUL D. FLEMING ◽  
MASAHIRO SUGIHARA
Keyword(s):  
Boundary Layer ◽  
Experimental Design ◽  
High Speed ◽  
Statistical Study ◽  
Process Variables ◽  
High Speeds ◽  
The Stability ◽  
Air Removal ◽  
Removal System

Using an experimental design approach, researchers altered process parameters and material prop-erties to stabilize the curtain of a pilot curtain coater at high speeds. Part I of this paper identifies the four significant variables that influence curtain stability. The boundary layer air removal system was critical to the stability of the curtain and base sheet roughness was found to be very important. A shear thinning coating rheology and higher curtain heights improved the curtain stability at high speeds. The sizing of the base sheet affected coverage and cur-tain stability because of its effect on base sheet wettability. The role of surfactant was inconclusive. Part II of this paper will report on further optimization of curtain stability with these four variables using a D-optimal partial-facto-rial design.

Stability of Water-Lubricated, Hydrostatic, Conical Bearings With Spiral Grooves for High-Speed Spindles

2001 ◽  
Vol 124 (2) ◽  
pp. 398-405 ◽  
Author(s):  
S. Yoshimoto ◽  
S. Oshima ◽  
S. Danbara ◽  
T. Shitara
Keyword(s):  
High Speed ◽  
Water Pressure ◽  
Rotating Shaft ◽  
Pressurized Water ◽  
High Speeds ◽  
Theoretical Predictions ◽  
The Stability ◽  
Stability Of Water ◽  
Spiral Grooves ◽  
Good Agreement

In this paper, the stability of water-lubricated, hydrostatic, conical bearings with spiral grooves for high-speed spindles is investigated theoretically and experimentally. In these bearing types, pressurized water is first fed to the inside of the rotating shaft and then introduced into spiral grooves through feeding holes located at one end of each spiral groove. Therefore, water pressure is increased due to the effect of the centrifugal force at the outlets of the feeding holes, which results from shaft rotation. In addition, water pressure is also increased by the viscous pumping effect of the spiral grooves. The stability of the proposed bearing is theoretically predicted using the perturbation method, and calculated results are compared with experimental results. It was consequently found that the proposed bearing is very stable at high speeds and theoretical predictions show good agreement with experimental data.

scholarly journals Hydroelastic effects during the fast lifting of a disc from a water surface

2019 ◽  
Vol 869 ◽  
pp. 726-751 ◽  
Author(s):  
P. Vega-Martínez ◽  
J. Rodríguez-Rodríguez ◽  
T. I. Khabakhpasheva ◽  
A. A. Korobkin
Keyword(s):  
Water Surface ◽  
High Speed ◽  
Hydrodynamic Force ◽  
Early Stage ◽  
The Body ◽  
Plate Motion ◽  
Elastic Behaviour ◽  
Simple Extension ◽  
Wetted Area ◽  
Water Exit

Here we report the results of an experimental study where we measure the hydrodynamic force acting on a plate which is lifted from a water surface, suddenly starting to move upwards with an acceleration much larger than gravity. Our work focuses on the early stage of the plate motion, when the hydrodynamic suction forces due to the liquid inertia are the most relevant ones. Besides the force, we measure as well the acceleration at the centre of the plate and the time evolution of the wetted area. The results of this study show that, at very early stages, the hydrodynamic force can be estimated by a simple extension of the linear exit theory by Korobkin (J. Fluid Mech., vol. 737, 2013, pp. 368–386), which incorporates an added mass to the body dynamics. However, at longer times, the measured acceleration decays even though the applied external force continues to increase. Moreover, high-speed recordings of the disc displacement and the radius of the wetted area reveal that the latter does not change before the disc acceleration reaches its maximum value. We show in this paper that these phenomena are caused by the elastic deflection of the disc during the initial transient stage of water exit. We present a linearised model of water exit that accounts for the elastic behaviour of the lifted body. The results obtained with this new model agree fairly well with the experimental results.

On the High-Speed Porpoising Instability of a Prismatic Hull

1984 ◽  
Vol 28 (02) ◽  
pp. 77-89 ◽  
Author(s):  
Peter R. Payne
Keyword(s):  
Skin Friction ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Transient Solution ◽  
Delta Wings ◽  
Closed Form Solutions ◽  
Wetted Area ◽  
The Stability ◽  
Transient Forces ◽  
Vertical Impact

Simple closed-form solutions are obtained for the steady-state and transient forces and moments on a prismatic hull at speeds high enough for hydrostatic forces to be negligible and the chines to be above the undisturbed water surface ("chines dry"). We first show that this solution can be transformed to get the correct results for other hydrodynamic problems, such as the vertical impact of a wedge, a slender foil, or the two-dimensional planing of a flat plate. We then show that the full transient solution is essentially identical with Ribner's [1]2 equations for delta wings, except for terms which depend on the reduction in wetted width with heave. These results are employed to study the stability of such a hull on the assumption that only heave and pitch degrees of freedom are important, following the reasoning of Per̂ing [2]. In contradistinction to all four previous studies [2–5], the effect of skin friction is included and is found to be very powerful. If the center of gravity is above the centroid of the wetted area (which it generally is), then the effect of skin friction is stabilizing.

Hydrodynamic Characteristics of a Hydrofoil-assisted Amphibious Vehicle

2017 ◽  
Vol 61 (01) ◽  
pp. 15-22
Author(s):  
Seung-Jae Lee ◽  
Tae-il Lee ◽  
Jong-Jin Lee ◽  
Wonki Nam ◽  
Jung-Chun Suh
Keyword(s):  
Deleterious Effect ◽  
High Speed ◽  
Control Device ◽  
Hydrodynamic Characteristics ◽  
Towing Tank ◽  
Operational Capability ◽  
High Speeds ◽  
Important Requirement ◽  
Field Of Vision ◽  
Military Services

For amphibious vehicles that are utilized in military services, high-speed ship-to-shore movement is an important requirement for enhancement of the operational capability in tactical environments. At high speeds, such a vehicle begins to sink at the stern, causing the bow to rise out of the water. Moreover, excessive trim has a deleterious effect on forward field of vision and powering performance. In this study, a hydrofoil was considered as a trim-control device to decrease the significant bow rise without compromising the performance. Experiments were conducted in a towing tank to investigate the running attitude and powering performance of a box-shaped amphibious vehicle at high speeds. Results for the hydrodynamic features show that a fixed hydrofoil under the stern of the vehicle successfully achieved an improved trim. It was also found that the interaction between the waterjet and hydrofoil can enhance the dynamic lift of the hydrofoil.

Design of Propulsion Systems for High-Speed Craft

1997 ◽  
Vol 34 (04) ◽  
pp. 276-292
Author(s):  
Donald L. Blount ◽  
Robert J. Bartee
Keyword(s):  
High Speed ◽  
Hydrodynamic Characteristics ◽  
Power Demand ◽  
Propulsion Systems ◽  
Performance Requirements ◽  
High Speeds ◽  
Operational Profile ◽  
Mode Of Operation ◽  
Very High ◽  
Vessel Speed

The demand for increased speed in medium and large craft challenges the designer to select propulsion systems which meet performance requirements economically throughout ever-widening operational profiles. The combined hydrodynamic characteristics of hull and propulsors result in a speed-thrust relationship for the environment in which the vessel operates. This speed-thrust relationship requires unique values of power and RPM input for each type and number of propulsors. Power and RPM are also sensitive to the mode of operation of the vessel whether at constant speed, accelerating to a greater speed or towing an object. Most vessels utilize fixed-pitch submerged propellers. Surface propellers are fitted to vessels designed to perform at very high speeds and waterjetpropulsors are being utilized with increasing frequency on larger vessels with high-speed operational profile. This paper discusses brake horsepower (BHP) and propulsor RPM relationships for vessel speed requirements based on the hydrodynamic characteristics of three types of propulsors: submerged propellers, surface propellers and waterjets. An example of predicted vessel performance regarding speed, power and propulsor RPM is presented which includes engine characteristics and BHP versus RPM. This latter format depicts the differences in power demand for three types of propulsors on a monohull vessel with regard to engine characteristics.

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.

Analysis of the Effect the Modal-Parameter on the Milling Stability

2013 ◽  
Vol 372 ◽  
pp. 459-462
Author(s):  
Ming Chang Tsai ◽  
Te Ching Hsiao ◽  
Shyh Chour Huang
Keyword(s):  
Natural Frequency ◽  
High Precision ◽  
High Speed ◽  
Damping Ratio ◽  
Chatter Stability ◽  
Modal Parameter ◽  
High Speeds ◽  
Stability Lobe ◽  
The Stability ◽  
Chatter Stability Lobes

In the past few years, it has become a tendency to develop machinery of high speeds and high precision. In order to meet the need for high-speed manufacturing of high precision components, the machine tools structure must be very stiff and have high cutting stability levels. Should the process of the firsthand milling be unstable, the effects include cutting tool breakages, decrease in surface accuracy and could even shorten the machine tolls lifespan. Thus, in the manufacturing of milling, chattering often causes problems for the manufacturer. To prevent cases of milling chattering, there is a need to use a chatter stability lobe to predict the chatter stability and to analyze the effect the modal-parameter has on the stability of milling. This research paper uses the Zero-Order Analytical Method (ZOA) to analyze and compare the effects modal-parameter (natural frequency, damping ratio, modal stiffness) has on the stability of the milling system. The results show that level of stiffness and the damping ratio influences the vertical shape of the chatter stability lobes while the natural frequency affects the lateral shape of the lobes.

Evolutionary Topology Optimization Design of Rotary Lobe of Roots Vacuum Pumps

2013 ◽  
Vol 798-799 ◽  
pp. 365-368 ◽  
Author(s):  
Xiao Ming Chen ◽  
Xi De Lai ◽  
Xiang Zhang ◽  
Xiang Zhou
Keyword(s):  
Mass Flow ◽  
High Speed ◽  
Optimization Design ◽  
Optimization Method ◽  
Operation Conditions ◽  
Evolutionary Structural Optimization ◽  
The Stability ◽  
Material Utilization ◽  
Safety And Stability ◽  
Volume Decrease

Aiming at the mass flow and high speed operating condition of roots pumps, the evolutionary structural optimization method was used to optimize rotary lobe of roots vacuum pumps. During the optimization process, filtering and removing algorithm based on the join traits of distortion elements were proposed for solving the structural mutation phenomenon. In this way, the ESO method was improved to ensure the stability and continuity when optimizing. Optimizing respectively with 5 different initial rejection ratios, then a reasonable structure was obtained by finite elements contrastive analysis. Results of finite element comparative analysis indicate that the new structures have better stress distribution, and the material utilization is maximized when applying the inertial load. The maximal stress, strain and deformation of new structure decrease by 17.7%, 17.5% and 18.7%, respectively, and the volume decrease by 55% comparing with primary structures, thus the safety and stability of roots pumps have a significant improvement at the high speed and mass flow operation conditions.

RED CUT COBALT

Alloy Digest ◽  
1980 ◽  
Vol 29 (8) ◽  
Keyword(s):  
Fracture Toughness ◽  
Cast Iron ◽  
High Speed ◽  
Elevated Temperatures ◽  
High Speed Steel ◽  
Heat Treating ◽  
High Speeds ◽  
Red Hardness ◽  
Nonferrous Alloys ◽  
Cutting Point

Abstract RED CUT COBALT steel is made by adding 5% cobalt to the conventional 18% tungsten -4% chromium-1% vanadium high-speed steel. Cobalt increases hot or red hardness and thus enables the tool to maintain a higher hardness at elevated temperatures. This steel is best adapted for hogging cuts or where the temperature of the cutting point of the tool in increased greatly. It is well adapted for tools to be used for reaming cast-iron engine cylinders, turning alloy steel or cast iron and cutting nonferrous alloys at high speeds. This datasheet provides information on composition, physical properties, and hardness as well as fracture toughness. It also includes information on forming, heat treating, and machining. Filing Code: TS-367. Producer or source: Teledyne Vasco.

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