Influence of microbubble diameter and distribution on frictional resistance reduction

2002 ◽  
Vol 7 (2) ◽  
pp. 79-85 ◽  
Author(s):  
Yasuhiro Moriguchi ◽  
Hiroharu Kato
Keyword(s):  
Frictional Resistance ◽  
Resistance Reduction

scholarly journals Resistance reduction on trimaran ship model by biopolymer of eel slime

2015 ◽  
Vol 12 (2) ◽  
pp. 95-102
Author(s):  
Y. Yanuar ◽  
G. Gunawan ◽  
M. A. Talahatu ◽  
R. T. Indrawati ◽  
A. Jamaluddin
Keyword(s):  
Drag Reduction ◽  
Frictional Resistance ◽  
Skin Surface ◽  
Fish Skin ◽  
Total Drag ◽  
Towing Tank ◽  
Ship Model ◽  
Resistance Reduction ◽  
Towing Tank Test ◽  
Tank Test

Resistance reduction in ship becomes an important issue to be investigated. Energy consumption and its efficiency are related toward drag reduction. Drag reduction in fluid flow can be obtained by providing polymer additives, coating, surfactants, fiber and special roughness on the surface hull. Fish skin surface coated with biopolymers viscous fluid (slime) is one method in frictional resistance reduction. The aim of this is to understanding the effect of drag reduction using eel slime biopolymer in unsymmetrical trimaran ship model. The Investigation was conducted using towing tank test with variation of velocity. The dimension of trimaran model are L = 2 m, B = 0.20 m and T = 0.065 m. The ship model resistance was precisely measured by a load cell transducer. The comparison of resistance on trimaran ship model coated and uncoated by eel slime are shown on the graph as a function of the total drag coefficient and Froude number. It is discovered the trimaran ship model by eel slime has higher drag reduction compared to trimaran with no eel slime at similar displacement. The result shows the drag reduction about 11 % at Fr 0.35.

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.

Experimental Investigation on Resistance Reduction by Means of Air-Bubbling Technique

2018 ◽  
Author(s):  
Enrico Ravina ◽  
Sofia Guidomei
Keyword(s):  
Flow Rate ◽  
Low Cost ◽  
Frictional Resistance ◽  
Flat Plates ◽  
Research Activity ◽  
Frictional Drag ◽  
Towing Tank ◽  
Resistance Reduction ◽  
The University ◽  
Different Levels

The paper refers on a research activity, focused at DREAMS Lab of the University of Genoa (Italy) and still under development, oriented to experimental application of air-bubbling techniques on flat plates and hull models. In this study the reduction in the frictional resistance by air bubbling generated by customized pneumatic circuits is tested, both on the lower surfaces of flat plates characterized of different geometries of holes and on a hull model tested in towing tank. The effective shape of air bubbles is observed, and changes in the local frictional drag are measured, using flexible and low cost thin sensors at different levels of flow rate and pressure of injected air. In towing tank tests the experiments compare hull without and with holes on the bottom, modifying the characteristics of speed, pressure, flow rate and areas interested to the air injection. Systematic tests campaign has been developed, using also actuation pneumatic workbenches expressly designed for the experiments.

scholarly journals Research on Ship Hull Optimisation of High-Speed Ship Based on Viscous Flow/Potential Flow Theory

2020 ◽  
Vol 27 (1) ◽  
pp. 18-28
Author(s):  
Zhang Baoji
Keyword(s):  
High Speed ◽  
Design Method ◽  
Frictional Resistance ◽  
Linear Wave ◽  
Total Resistance ◽  
Friction Resistance ◽  
Resistance Reduction ◽  
Before And After ◽  
Reduction Effect ◽  
Cfd Method

AbstractIn order to quickly obtain practical ship forms with good resistance performance, based on the linear wave-making resistance theory, the optimal design method of ship forms with minimum total resistance is discussed by using the non-linear programming (NLP) method. Taking the total resistance as the objective function (the Michell integral is used to calculate the wave-making resistance and the equivalent plate friction resistance formula is used to calculate the frictional resistance), the hull surface offset as the design variable and appropriate displacement as the basic constraints, and considering the additional constraints, the hull bow shape and the whole ship are optimised, and an improved hull form is obtained. The resistance of the ship before and after optimisation is calculated by the CFD method to further evaluate the resistance reduction effect and performance after optimisation. Finally, an example of optimisation calculation of an actual high-speed ship is given. The obvious resistance reduction results confirm the reliability of the optimisation design method.

The Effect of Air Lubrication on a Flat Plate at Varying Angles of Trim With Regard to Drag Reduction

2013 ◽  
Author(s):  
Sean P. Murphy ◽  
Colin T. Spillane
Keyword(s):  
Drag Reduction ◽  
Flat Plate ◽  
Fuel Consumption ◽  
Technological Development ◽  
Frictional Resistance ◽  
Flow Volume ◽  
Resistance Reduction ◽  
Flow Speeds ◽  
Air Lubrication ◽  
Air Layer Drag Reduction

One of the driving factors of technological development in ship design is the reduction of fuel consumption. One way to reduce fuel consumption is to reduce the total resistance experienced by a vessel. The methods of resistance reduction covered in this document are Air-layer-drag-reduction (ALDR) and Bubble Drag Reduction (BDR). This research, conducted in Webb Institute’s circulating flow channel, investigates the applications of ALDR and BDR to a flat plate. These tests measured frictional resistance at varying air flow volume and angles of trim over a range of flow speeds. Results from these tests offer compelling evidence that ALDR is an effective method of reducing frictional resistance.

Numerical Simulation of Trim Optimization on Resistance Performance Based on CFD Method

2019 ◽  
Author(s):  
Wenyang Duan ◽  
Hongsen Zhang ◽  
Limin Huang ◽  
Jianyu Liu ◽  
Wenbo Shao ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Frictional Resistance ◽  
Total Resistance ◽  
Residual Resistance ◽  
Model Method ◽  
Resistance Reduction ◽  
Fixed Model ◽  
Reduction Effect ◽  
Wetted Surface Area ◽  
Resistance Performance

Abstract In response to the gradually stringent carbon emission requirements of the International Maritime Organization (IMO), the energy-saving methods of the shipping industry have received increasing attention. Today how to reduce fuel consumptions so as to lower carbon emissions to improve the economic and environmental benefits of ships has become a hot topic. As one of the most easily implemented energy-saving methods, trim optimization has caught more and more researchers’ eyes. In this paper, a commercial CFD software STAR-CCM+ was adopted to analyze the influence of trim on the resistance performance of VLCC ship mainly with fixed model method under various typical conditions of the design draft and the ballast draft respectively. The grid convergence was studied at the design draft and the typical numerical simulations were verified by the experimental results before carrying out various numerical simulations of trim optimization. Seven different kinds of trim conditions, which correspond to the changing process of the full scale ship from trimming by stern 4m to bow 4m, were simulated with 3 different speeds of design draft and ballast draft. The changes of total resistance, frictional resistance and residual resistance were analyzed to explore the effect of trims on the ship’s resistance. The variation of ship’s wetted surface area and waterplane area under different trim angles were studied. It was found that under the condition of low Froude number, both the simulation of free trim and sink method and the fixed model method can achieve good accuracy with the method of fixed model reducing the simulation time obviously. Both conditions of the design draft and ballast draft had a certain reduction effect of total resistance for trimming by bow properly, of which the change of frictional resistance is dominant in the decrease of total resistance at design draft while the change of residual resistance is the main cause at ballast draft. The optimum trims were found and the optimal total resistance reduction effects were evaluated. The optimal total resistance reduction effect increased with speed whether at the design or the ballast draft and the reduction effects were more obvious at ballast draft. Meanwhile, it was found that the changes of wetted surface area and the waterplane area with different trims were close to the variation tendency of the frictional resistance.

scholarly journals Numerical Simulation on flow characteristics of the supercritical fluid in Micro-Fin Tube

2021 ◽  
Vol 257 ◽  
pp. 03082
Author(s):  
Peng-Fei Chen ◽  
Kang Chen ◽  
Gao-xiang Ma ◽  
Xiao Wang ◽  
Long Wen
Keyword(s):  
Supercritical Fluid ◽  
Fluid Velocity ◽  
Flow Characteristics ◽  
Frictional Resistance ◽  
Bottom Layer ◽  
Flow Process ◽  
Resistance Reduction ◽  
Fin Tube ◽  
Fin Tubes ◽  
And Control

The flow characteristics of the supercritical fluid in the micro-fin tube is the theoretical basis for the development of heat transfer enhancement and flow resistance reduction in the micro-fin tube. For micro-fin tubes with different fin shapes, this paper considered the physical properties of nitrogen in the supercritical state and adopted the enhanced wall function, reasonable turbulence equations, and control equations, etc., to numerically simulate the flow of nitrogen in a 2 mm micro-fin tube under supercritical pressure. The distribution of velocity field, turbulence and pressure field of supercritical nitrogen in the micro-fin tube was analyzed. The turbulent flow mechanism of the micro-fins was obtained, and it is found that the existence of the viscous bottom layer slows down the inter-costal fluid velocity and increases the frictional resistance during the flow process.

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