A numerical study on drag reduction of underwater vehicles using hydrophobic surfaces

2017 ◽  
Vol 233 (1) ◽  
pp. 301-309 ◽  
Author(s):  
Morteza Anbarsooz
Keyword(s):  
Skin Friction ◽  
Numerical Study ◽  
Slip Flow ◽  
Numerical Procedure ◽  
Underwater Vehicle ◽  
Underwater Vehicles ◽  
Flow Profile ◽  
Friction Drag ◽  
Hydrophobic Surfaces ◽  
Novel Approach

During last decades, many investigations have been done to find suitable solutions to reduce the drag force of underwater vehicles. These attempts can be divided into two main categories: supercavitating vehicles and unseparated flow patterns. In this study, a novel approach is introduced which uses hydrophobic surfaces for an underwater vehicle with an unseparated flow body profile. Fluid slippage on hydrophobic walls can lead to a considerable reduction of skin friction drag. The effectiveness of this approach for underwater hulls has been examined numerically. In this regard, first, the numerical procedure is validated by comparing the numerical results for the slip flow over a micron-sized spherical particle with the analytical results available in the literature. Next, numerical simulations are performed for an unseparated flow profile at various values of the sliding coefficients. Results show that the principal drag of such profiles is the skin friction drag which can be drastically reduced using hydrophobic surfaces. For the sliding coefficients smaller than 10, the drag coefficient of the underwater vehicle with an unseparated flow profile can be even lower than that of a supercavitating hull.

Skin-friction drag reduction in the turbulent regime using random-textured hydrophobic surfaces

2014 ◽  
Vol 26 (8) ◽  
pp. 085108 ◽  
Author(s):  
Rahul A. Bidkar ◽  
Luc Leblanc ◽  
Ambarish J. Kulkarni ◽  
Vaibhav Bahadur ◽  
Steven L. Ceccio ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Skin Friction ◽  
Turbulent Regime ◽  
Friction Drag ◽  
Hydrophobic Surfaces ◽  
Friction Drag Reduction

scholarly journals Reduction of turbulent skin-friction drag by passively rotating discs

2021 ◽  
Vol 923 ◽  
Author(s):  
Paolo Olivucci ◽  
Daniel J. Wise ◽  
Pierre Ricco
Keyword(s):  
Skin Friction ◽  
Friction Drag ◽  
Rotating Discs

Abstract

Effects of the air layer of an idealized superhydrophobic surface on the slip length and skin-friction drag

2016 ◽  
Vol 790 ◽  
Author(s):  
Taeyong Jung ◽  
Haecheon Choi ◽  
John Kim
Keyword(s):  
Drag Reduction ◽  
Skin Friction ◽  
Superhydrophobic Surface ◽  
Slip Length ◽  
Joint Probability ◽  
Turbulent Channel Flow ◽  
Water Interface ◽  
Friction Drag ◽  
Recirculating Flow ◽  
Air Water Interface

The anisotropy of the slip length and its effect on the skin-friction drag are numerically investigated for a turbulent channel flow with an idealized superhydrophobic surface having an air layer, where the idealized air–water interface is flat and does not contain the surface-tension effect. Inside the air layer, both the shear-driven flow and recirculating flow with zero net mass flow rate are considered. With increasing air-layer thickness, the slip length, slip velocity and percentage of drag reduction increase. It is shown that the slip length is independent of the water flow and depends only on the air-layer geometry. The amount of drag reduction obtained is in between those by the empirical formulae from the streamwise slip only and isotropic slip, indicating that the present air–water interface generates an anisotropic slip, and the streamwise slip length ($b_{x}$) is larger than the spanwise one ($b_{z}$). From the joint probability density function of the slip velocities and velocity gradients at the interface, we confirm the anisotropy of the slip lengths and obtain their relative magnitude ($b_{x}/b_{z}=4$) for the present idealized superhydrophobic surface. It is also shown that the Navier slip model is valid only in the mean sense, and it is generally not applicable to fluctuating quantities.

Numerical Investigation of Ductile Fracture in Pipelines Under Complex Loading Using a Phenomenological Damage Model

2021 ◽  
Author(s):  
Iago S. Santos ◽  
Diego F. B. Sarzosa
Keyword(s):  
Ductile Fracture ◽  
Mechanical Response ◽  
Numerical Study ◽  
Damage Model ◽  
Stress Triaxiality ◽  
Numerical Procedure ◽  
Complex Loading ◽  
Experimental Tests ◽  
Compact Tension ◽  
Axial Tensile

Abstract This paper presents a numerical study on pipes ductile fracture mechanical response using a phenomenological computational damage model. The damage is controlled by an initiation criterion dependent on the stress triaxiality and the Lode angle parameter, and a post-initiation damage law to eliminate each finite element from the mesh. Experimental tests were carried out to calibrate the elastoplastic response, damage parameters and validate the FEM models. The tested geometries were round bars having smooth and notched cross-section, flat notched specimens under axial tensile loads, and fracture toughness tests in deeply cracked bending specimens SE(B) and compact tension samples C(T). The calibrated numerical procedure was applied to execute a parametric study in pipes with circumferential surface cracks subjected to tensile and internal pressure loads simultaneously. The effects of the variation of geometric parameters and the load applications on the pipes strain capacity were investigated. The influence of longitudinal misalignment between adjacent pipes was also investigated.

scholarly journals Optimal design of nose and tail of an autonomous underwater vehicle hull to reduce drag force using numerical simulation

2019 ◽  
Vol 234 (1) ◽  
pp. 76-88 ◽  
Author(s):  
Mohammad Saghafi ◽  
Roham Lavimi
Keyword(s):  
Energy Consumption ◽  
Drag Force ◽  
Autonomous Underwater Vehicle ◽  
Turbulence Modeling ◽  
Stokes Equations ◽  
Autonomous Underwater Vehicles ◽  
Three Dimensional ◽  
Underwater Vehicle ◽  
Underwater Vehicles ◽  
Navier Stokes

In this research, the flow around the autonomous underwater vehicles with symmetrical bodies is numerically investigated. Increasing the drag force in autonomous underwater vehicles increases the energy consumption and decreases the duration of underwater exploration and operations. Therefore, the main objective of this research is to decrease drag force with the change in geometry to reduce energy consumption. In this study, the decreasing or increasing trends of the drag force of axisymmetric bare hulls have been studied by making alterations in the curve equations and creating the optimal geometric shapes in terms of hydrodynamics for the noses and tails of autonomous underwater vehicles. The incompressible, three-dimensional, and steady Navier–Stokes equations have been used to simulate the flow. Also, k-ε Realizable with enhanced wall treatment was used for turbulence modeling. Validation results were acceptable with respect to the 3.6% and 1.4% difference with numerical and experimental results. The results showed that all the autonomous underwater vehicle hulls designed in this study, at an attack angle of 0°, had a lower drag force than the autonomous underwater vehicle hull used for validation except geometry no. 1. In addition, nose no. 3 has been selected as the best nose according to the lowest value of stagnation pressure, and also tail no. 3 has been chosen as the best tail due to the production of the lowest vortex. Therefore, geometry no. 5 has been designed using nose and tail no. 3. The comparison made here showed that the maximum drag reduction in geometry no. 5 was equal to 26%, and therefore, it has been selected as the best bare hull in terms of hydrodynamics.

scholarly journals Report on Research with Biomimetic Autonomous Underwater Vehicle — Low Level Control

2018 ◽  
Vol 212 (1) ◽  
pp. 105-123
Author(s):  
Tomasz Praczyk ◽  
Piotr Szymak ◽  
Krzysztof Naus ◽  
Leszek Pietrukaniec ◽  
Stanisław Hożyń
Keyword(s):  
Research And Development ◽  
Autonomous Underwater Vehicle ◽  
Autonomous Underwater Vehicles ◽  
Underwater Vehicle ◽  
Underwater Vehicles ◽  
Swimming Pool ◽  
Final Report ◽  
Level Control ◽  
Low Level

Abstract The paper presents the first part of the final report on all the experiments with biomimetic autono-mous underwater vehicle (BAUV) performed within the confines of the project entitled ‘Autonomous underwater vehicles with silent undulating propulsion for underwater ISR’, financed by Polish National Center of Research and Development. The report includes experiments in the swimming pool as well as in real conditions, that is, both in a lake and in the sea. The tests presented in this part of the final report were focused on low-level control.

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