Ship Hull Drag Reduction Using Bottom Air Injection

2007 ◽  
Author(s):  
Ahmad Fakhraee ◽  
Manoucher Rad ◽  
Hamid Amini ◽  
Mehdi Rishehri
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Frictional Resistance ◽  
Air Injection ◽  
Hydrodynamic Resistance ◽  
Alternative Form ◽  
Hydrodynamic Characteristics ◽  
Air Cavity ◽  
Marine Vehicles ◽  
Wetted Surface Area

Air cavity ship concept has received some interest due to its potential on viscous resistance reduction for high speed craft. Air-cavity ships (ACS) are advanced marine vehicles that use air injection at the wetted hull surfaces to improve a vessel’s hydrodynamic characteristics. Air is supplied through nozzles under a profiled bottom to generate an air cavity beneath such a ship, so that a steady air layer separates a part of the bottom from contact with water, consequently reducing hydrodynamic resistance. Resistance tests were conducted with two forms: first of which was planning catamaran hull form, and second one was an alternative form with an air cavity injection under its bottom which was tested both without any air injection and with three different air injection ranges. Dead rise angle was fixed to 23 degree during both model tests. Frictional resistance was calculated from wetted surface area and compared with total resistance. It is clear from these results that improvements in high speed planning catamarans can be realized by using bottom air injection. Drag reduction achieved on these model is within 13–23 percent.

Supersonic Bi-Directional Flying Wing Wave Drag Optimization Based on Alternative Form of CST Method

2013 ◽  
Vol 477-478 ◽  
pp. 240-245
Author(s):  
Xiaohui Guan
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Wave Drag ◽  
Alternative Form ◽  
Shape Transformation ◽  
Flat Bottom ◽  
Symmetric Configuration ◽  
Shape Parameterization ◽  
Wave Drag Reduction ◽  
Sufficient Precision

Bi-directional Flying Wing (BFW) is a new supersonic civil transport shape concept that aims to meet the conflict requirements of high speed cruise and low speed take-off/landing missions. In this paper the Class-Shape-Transformation (CST) shape parameterization method is modified to represent the BFW shape, and new basis functions suitable for the BFW airfoil representation are constructed. The Far-field Composite Element (FCE) wave drag optimization is performed on both the flat bottom and symmetric BFW configurations, and the drag reduction effects and result precision are surveyed. It is suggested that significant wave drag reduction can be achieved by the FCE optimization for both the flat bottom and the symmetric BFW configurations. The wave drag coefficients with sufficient precision can be obtained in the FCE optimization of the symmetric configuration; while the FCE optimization results of the flat bottom one are not accurate enough.

Stability Enhancement of Supercavitating Projectiles by Unsteady Air Injection

2005 ◽  
Author(s):  
Yasmin Khakpour ◽  
Miad Yazdani
Keyword(s):  
Numerical Simulation ◽  
Drag Reduction ◽  
High Speed ◽  
The Body ◽  
Air Injection ◽  
Cavity Surface ◽  
The Stability ◽  
Stability Enhancement

In this work, numerical simulation is used to study the stability enhancement of high speed supercavitating hydrofoils. Although supercavitation is known as one of the most effective methods for drag reduction, producing the cavity, either by ventilation or by cavitator at front of the body, may cause some instabilities on cavity surface and thus on the projectile’s motion. Therefore removing these instabilities comes as an important point of discussion. First of all, we calculate the sources of instabilities and measure respective forces and then present some approaches that significantly reduce these instabilities. One of these methods that could produce more stable supercavities is injecting of the air into the cavity unsteadily which varies through the projectile’s surface. This approach is provided by arrays of slots distributed on the projectile’s surface and unsteady injection is modeled over the surface. Furthermore, the position of ventilation, dramatically affects the stability like those in aerodynamics. In all approaches it is assumed that the supercavity covers the whole of the body, however the forces caused by the wakes, formed behind the body are taken into account. The calculation is performed at three cavitation numbers with respective velocities of 40 m/s, 50 m/s, 60 m/s.

Air Lubrication Influence on Frictional Resistance Reduction of Multi-Purpose Amphibious Vehicle

2015 ◽  
Vol 74 (5) ◽  
Author(s):  
M. Nakisa ◽  
A. Maimun ◽  
Yasser M. Ahmed ◽  
F. Behrouzi ◽  
Jaswar Jaswar ◽  
...  
Keyword(s):  
Frictional Resistance ◽  
Hydrodynamic Resistance ◽  
Marine Vehicles ◽  
Resistance Reduction ◽  
Ansys Cfx ◽  
Lubrication Layer ◽  
Air Lubrication ◽  
Layer Effect ◽  
Air Cushion ◽  
Pump Compressor

The presentarticle focuses on the hydrodynamic resistance reduction of Multipurpose Amphibious Vehicles (MAV) usingthe air lubrication layer effect. The use of air cushions to support marine vehicles, heavy floating structures and in other operation is well known. The main problem in Multi-purpose Amphibious Vehicles (MAV) is the amount of power needed in order to overcome the hydrodynamic resistance acting on the hull which is included the frictional and pressure resistances. Therefore, more power is needed to move the MAV forward. In this respect, more fuel will be required to operate the amphibious vehicles. This problem could be effectively reduced by the introduction of the air cushion concept. With the air being drawn from top of craft to the cavity below the hull will produce some cushioning effect and also help to reduce skin friction drag. In this paper, air cushion effect will be studied in rigid surface cavity instead of using flexible skirts. This would avoid the problem of high maintenance due to replacement of damaged skirts. Finally, the MAV will be supported using air cavity and bubbles generated by an air pump (compressor and air pressure vessel) to pushes the hull of multi-purpose amphibious vehicle up and reduce the frictional resistance due to draft and wetted surface reduction and layer of air between hull surface and water. This research would be done via CFD (ANSYS-CFX 14.0) and analyzed the hydrodynamic resistance.

scholarly journals Analysis of trimaran-pentamaran side hull location based on clearance and staggers with stern form variations

2018 ◽  
Vol 67 ◽  
pp. 04003
Author(s):  
Yanuar ◽  
Wiwin Sulistyawati ◽  
R. Joshua Yones ◽  
Samodero Mahardika
Keyword(s):  
Surface Area ◽  
Optimum Design ◽  
High Speed ◽  
Frictional Resistance ◽  
Experimental Tests ◽  
Hull Form ◽  
Negative Interference ◽  
Friction Resistance ◽  
Resistance Reduction ◽  
Wetted Surface Area

An optimum design of ship is to achieve the required speed with minimum power requirements. On multihull, sidehull position against to mainhull influences the friction resistance and its stability. Frictional resistance of multi-hull increases due to the addition of wetted surface area of hull, but wave making resistance can be lowered by a slender hull form. This research are experimental tests of trimaran with five Wigley hulls on a combination transom and without transom. The test varied on stagger, clearance and trim at several speeds. A ship with formation arrow tri-hull on forward was given to prove the resistance reduction due to cancellation wave which was indicated by negative interference. The influence diverse position of sidehull has shown that model non-transom (NT) stern moreover give beneficial resistance than model with transom (WT) at high speed. Similarly, in the trim conditions that NT more favorable on trim specifically for high speed depending on the position of the sidehull to the mainhull.

Hydrodynamic Resistance Reduction of Multi-Purpose Amphibious Vehicle due to Air Bubble Effect

2016 ◽  
Vol 819 ◽  
pp. 335-340 ◽  
Author(s):  
Adi Maimun ◽  
Mehdi Nakisa ◽  
Yasser M. Ahmed ◽  
Fatemeh Behrouzi ◽  
Koh K. Koh ◽  
...  
Keyword(s):  
Frictional Resistance ◽  
Hydrodynamic Resistance ◽  
Operating Life ◽  
Air Bubble ◽  
Marine Vehicles ◽  
Ansys Cfx ◽  
Flat Shape ◽  
Air Cushion ◽  
Comparative Results ◽  
Pump Compressor

Multipurpose Amphibious Vehicles (MAV) and other blunt shaped floating vehicles encounter the problem of a large bow wave forming and hydrodynamic resistance at high speeds. This wave formation is accompanied by higher resistance and at a critical speed results in bow submerging or swamping. Three new shapes of hull bow design for the multipurpose amphibious vehicle were conducted at several speeds to investigate the hydrodynamic phenomena using Computational Fluid Dynamics (CFD, RANS code), which is applied by Ansys-CFX14.0 and Maxsurf. The vehicle’s hydrodynamic bow shapes were able to break up induced waves and avoid swamping. Comparative results with the vehicle fitted with U-shape, V-shape and Flat-shape of hull bow, showed that the U-shape of the hull bow has reduced the total resistance to 20.3% and 13.6% compared with the V-shape and flat shape respectively. Though, the U-shape of hull bow is capable to increase the amphibious operating life and speed of vehicle. Also it has ability to reduce the vehicle’s required power, fossil fuel consumption and wetted hull surface. On the other hand, the use of air cushions to support marine vehicles, heavy floating structures and in other operation is well known. The main problem in Multi-purpose Amphibious Vehicles (MAV) is the amount of power needed in order to overcome the hydrodynamic resistance acting on the hull which is included the frictional and pressure resistances. Therefore, more power is needed to move the MAV forward. In this respect, more fuel will be required to operate the amphibious vehicles. This problem could be effectively reduced by the introduction of the air cushion concept. With the air being drawn from top of craft to the cavity below the hull will produce some cushioning effect and also help to reduce skin friction drag. In this paper, air cushion effect will be studied in rigid surface cavity instead of using flexible skirts. This would avoid the problem of high maintenance due to replacement of damaged skirts. Finally, the MAV will be supported using air cavity and bubbles generated by an air pump (compressor and air pressure vessel) to pushes the hull of multi-purpose amphibious vehicle up and reduce the frictional resistance due to draft and wetted surface reduction and layer of air between hull surface and water. This research would be done via CFD (ANSYS-CFX 14.0) and analyzed the hydrodynamic resistance

scholarly journals Influence of Characteristics of the Melted Basalt on the Process of Formation of Fibers

2020 ◽  
Vol 6 (6) ◽  
pp. 15-24
Author(s):  
Zh. Aydaraliev ◽  
Yu. Ismanov ◽  
A. Kainazarov
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Viscosity Coefficient ◽  
Mineral Wool ◽  
Fiber Formation ◽  
Hydrodynamic Resistance ◽  
Hydrodynamic Characteristics ◽  
Mineral Fibers ◽  
The Relationship

In any production of products based on mineral fibers, one of the main types of equipment included in the line for the production of fiber products is installations for forming a basalt carpet, or the so-called fiberizing chambers. The quality of finished products depends on their perfection. Currently, there are several widely used in industry methods for producing mineral fibers from melt, which determine the various types and designs of fiberization chambers. In all chambers, the formation of mineral wool carpet occurs under the influence of hydrodynamic forces. Therefore, the study of such hydrodynamic characteristics as the rate of fall of individual fibers and clumps of these fibers and the hydrodynamic resistance of the carpet are of paramount importance in the design of new and reconstruction of old chambers. In this paper, we study the relationship between the strain rate and the viscosity coefficient of basaltic melt during fiber formation using a blow head developed by the authors. The substantiation of the process of fiber formation using a blowing head is given. Relations are obtained that establish the dependence of the strain rate in the fiber stream on the viscosity of the melt. Experimental data have been obtained that can be used to evaluate the effect of a basalt deposit on the dependence of the strain rate on the viscosity of a basalt melt. It was found that high-speed deformation of the melt greatly affects the quality of the fibers and the amount of waste in the production of fibers.

Hydrodynamic Characteristics of the Surface-Piercing Propeller for the Planing Craft

2009 ◽  
Author(s):  
Hassan Ghassemi ◽  
Roya Shademani ◽  
Abdollah Ardeshir
Keyword(s):  
Numerical Method ◽  
Weber Number ◽  
High Speed ◽  
Hydrodynamic Characteristics ◽  
Propulsive Efficiency ◽  
Planing Craft ◽  
Marine Vehicles ◽  
Pitch Ratio ◽  
Advance Ratio ◽  
Surface Piercing Propeller

Market demands for high-speed marine vehicles (HSMVs) are high in both commercial and naval branches. It is the naval architects’ task to design the hull and propulsion system to diminish drag, improve the propulsive efficiency, higher safety and better maneuverability. Surface Piercing Propellers (SPPs) may provide those possessions for the vehicles. Unlike immersed propellers, behavior of the SPPs is susceptible to immersed depth, Weber number and shaft inclination angle. This paper uses a specially practical and numerical method to predict the hydrodynamic characteristics of the SPPs. Critical advance ratio is obtained by practical formula, using Weber number and pitch ratio in the transition mode. Numerical method employs the potential based boundary element method (BEM) on the engaged surfaces. Two models of three and six bladed of the SPPs (SPP-1 and SPP-2) are selected and some results are shown.

Effects of step configuration on hydrodynamic performance of one- and doubled-stepped planing flat plates: A numerical simulation

2019 ◽  
Vol 234 (1) ◽  
pp. 181-195 ◽  
Author(s):  
Abbas Dashtimanesh ◽  
Fatemeh Roshan ◽  
Sasan Tavakoli ◽  
Ahmadreza Kohansal ◽  
Bahare Barmala
Keyword(s):  
Numerical Simulation ◽  
High Speed ◽  
Critical Role ◽  
Pressure Coefficient ◽  
Numerical Data ◽  
Hydrodynamic Performance ◽  
Step Height ◽  
Hydrodynamic Characteristics ◽  
Flat Plates ◽  
Marine Vehicles

Categorized as one of high-speed marine vehicles, stepped planing hulls have the potential to reach relatively high speed in the sea by decreasing wetted surface. There were and still are some challenges in modeling of these vessels and design of ideal situation of steps. In the current study, a numerical-based method has been used to provide understanding about the effect of step height and its location on hydrodynamic characteristics of double-stepped planing plates. At the first step, one-stepped planing plate is numerically simulated. Results are compared against exiting numerical data, suggesting that results of the current numerical simulation are similar to results of previous numerical simulations. Then, double-stepped planing plates are modeled and pressure distribution, wetted length, free surface elevation and drag over lift ratio are computed. It is seen that, ventilation length behind the step and pressure coefficient are increased when step height of one- and a double-stepped planing plates are increased. It has been shown that, unlike an one-stepped planing plate, drag coefficient of a double-stepped planing plate can be increased when the step height is increased. The effects of the location of the second step on the performance of the planing plate have been explored, showing that this position plays a critical role on hydrodynamic forces. It is demonstrated that when the smallest possible lift force is produced by the middle-body, the plate shows the best performance (highest lift over drag ratio).

scholarly journals Numerical Investigation on the Influence of the Streamlined Structures of the High-Speed Train’s Nose on Aerodynamic Performances

2021 ◽  
Vol 11 (2) ◽  
pp. 784
Author(s):  
Zhenxu Sun ◽  
Shuanbao Yao ◽  
Lianyi Wei ◽  
Yongfang Yao ◽  
Guowei Yang
Keyword(s):  
Drag Reduction ◽  
Pressure Distribution ◽  
Flow Separation ◽  
High Speed ◽  
Leeward Side ◽  
Detached Eddy Simulation ◽  
Side Force ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Asymmetrical Design

The structural design of the streamlined shape is the basis for high-speed train aerodynamic design. With use of the delayed detached-eddy simulation (DDES) method, the influence of four different structural types of the streamlined shape on aerodynamic performance and flow mechanism was investigated. These four designs were chosen elaborately, including a double-arch ellipsoid shape, a single-arch ellipsoid shape, a spindle shape with a front cowcatcher and a double-arch wide-flat shape. Two different running scenes, trains running in the open air or in crosswind conditions, were considered. Results reveal that when dealing with drag reduction of the whole train running in the open air, it needs to take into account how air resistance is distributed on both noses and then deal with them both rather than adjust only the head or the tail. An asymmetrical design is feasible with the head being a single-arch ellipsoid and the tail being a spindle with a front cowcatcher to achieve the minimum drag reduction. The single-arch ellipsoid design on both noses could aid in moderating the transverse amplitude of the side force on the tail resulting from the asymmetrical vortex structures in the flow field behind the tail. When crosswind is considered, the pressure distribution on the train surface becomes more disturbed, resulting in the increase of the side force and lift. The current study reveals that the double-arch wide-flat streamlined design helps to alleviate the side force and lift on both noses. The magnitude of side force on the head is 10 times as large as that on the tail while the lift on the head is slightly above that on the tail. Change of positions where flow separation takes place on the streamlined part is the main cause that leads to the opposite behaviors of pressure distribution on the head and on the tail. Under the influence of the ambient wind, flow separation occurs about distinct positions on the train surface and intricate vortices are generated at the leeward side, which add to the aerodynamic loads on the train in crosswind conditions. These results could help gain insight on choosing a most suitable streamlined shape under specific running conditions and acquiring a universal optimum nose shape as well.

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