Study of Drag Reduction on Ship Hull by Expansion of Entrained Air in Water Flow.

In this paper, artificial bee colony (ABC) algorithms are introduced to optimize ship hull forms for reduced drag. Two versions of ABC algorithm are used: one is the basic ABC algorithm, and the other is an improved artificial bee colony (IABC) algorithm. A recently developed fast flow solver based on the Neumann-Michell theory is used to evaluate the drag of the ship in the optimization process. The ship hull surface is represented by discrete triangular panels and modified using radial basis function interpolation method. The developed optimization algorithms are first validated by benchmark mathematical functions with different dimensions. They are then applied to the optimization of DTMB Model 5415 for reduced drag. Two optimal hull forms are obtained by the ABC and the IABC algorithms. A large drag reduction is obtained by both of the algorithms. The optimal hull form obtained by the IABC algorithm has larger drag reduction than that of the hull form from the ABC algorithm. The results show that two ABC algorithms can be used for optimizing ship hull forms and the IABC algorithm has better performance than the ABC algorithm for the tested case in ship hull form optimization.

Download Full-text

Drag Reduction with Biopolymer-Synthetic Polymer Mixtures in Oil-Water Flows: Effect of Synergy

Engineering Journal ◽

10.4186/ej.2020.24.6.1 ◽

2020 ◽

Vol 24 (6) ◽

pp. 1-10

Author(s):

Lawrence Chukwuka Edomwonyi-Otu ◽

Muhammed Muhammed Gimba ◽

Nurudeen Yusuf

Keyword(s):

Reynolds Number ◽

Pressure Drop ◽

Pressure Gradient ◽

Drag Reduction ◽

Water Flow ◽

Transport Systems ◽

Test Fluid ◽

Polymer Mixture ◽

Water Flows ◽

Oil Water

The search for lower cost materials that reduce pressure drop in fluid transport systems in oil and gas industries to conserve pumping energy is of paramount importance. Polymers are known to reduce pressure drop in pipeline oil-water flows in a process referred to as drag reduction (DR). The effect of partially hydrolysed polyacrylamide, polyethylene oxide, Aloe Vera mucilage and their mixtures as drag reducing polymers (DRPs) on pressure gradient (pressure drop; Δp) in pipeline oil-water flows were studied. The experiment was carried out in flow rig with 0.02-m diameter straight unplasticised polyvinylchloride (uPVC) pipe, two centrifugal pumps, control valves and two storage tanks. Tap water (ρ = 997 kg/m3 and µ = 0.89 cP) and diesel (ρ = 832 kg/m3 and µ = 1.66 cP) were used as the test fluid at ambient condition. The polymer mixture total concentration (MTC) of 30 and 400 ppm at different mixing proportion, mixture Reynolds number (Remix) and oil input volume were investigated. The results show increase in pressure gradient with increase in oil input volume in both single-phase water flow and oil-water flow before adding drag reducing polymers (DRPs). However, Δp decreased after adding DRPs with increase in Reynolds number (Re) or Remix and decrease in the oil-phase Re, and vice versa. The results further showed higher reduction in pressure drop by the polymer mixture than in each of the polymer used at the same conditions. The rigidness of the biopolymer was improved by adding synthetic polymers which resulted to increase in DR efficiency.

Download Full-text

A Controllable Microbubble Emitter

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2005-77140 ◽

2005 ◽

Author(s):

Neal A. Brown ◽

Martin Wosnik

Keyword(s):

Boundary Layer ◽

Drag Reduction ◽

Water Flow ◽

Bubble Diameter ◽

Proof Of Concept ◽

Surface Drag ◽

Frictional Drag ◽

Micro Holes ◽

Bubble Number ◽

Theoretical Analyses

Controlled emission of microbubbles into a water flow boundary layer appears to be a promising means to significant reduction of frictional drag on ships. Theoretical analyses and hypotheses require that particularly small (∼ 100 micrometers or less) gas bubbles be emitted and retained in particular laminae close to the wetted surface. Drag reduction economy requires that the quantity of gas emitted be very small. Here a design of a controllable microbubble emitter which meets both demands above is put forth. The two key requirements governing the design are pulsed operation, which expels a known volume of air during each cycle, and a known number of uniformly-sized micro-holes, which determines bubble number and therefore bubble diameter. A first, proof-of-concept experiment with a modified pulsed-pressure design of the proposed microbubble emitter was carried out and shows promise.

Download Full-text