Reynolds-averaged Navier–Stokes simulation of hydrofoil effects on hydrodynamic coefficients of a catamaran in forced oscillation

2016 ◽  
Vol 231 (2) ◽  
pp. 364-383
Author(s):  
Amin Najafi ◽  
Mohammad Saeed Seif
Keyword(s):  
High Speed ◽  
Experimental Approach ◽  
Navier Stokes ◽  
Hydrodynamic Coefficients ◽  
Laboratory Equipment ◽  
Factors Affecting ◽  
High Frequencies ◽  
Frequency Independent ◽  
Reynolds Averaged Navier Stokes

Determination of high-speed crafts’ hydrodynamic coefficients will help to analyze the dynamics of these kinds of vessels and the factors affecting their dynamic stabilities. Also, it can be useful and effective in controlling the vessel instabilities. The main purpose of this study is to determine the coefficients of longitudinal motions of a planing catamaran with and without a hydrofoil using Reynolds-averaged Navier–Stokes method to evaluate the foil effects on them. Determination of hydrodynamic coefficients by experimental approach is costly and requires meticulous laboratory equipment; therefore, utilizing the numerical methods and developing a virtual laboratory seem highly efficient. In this study, the numerical results for hydrodynamic coefficients of a high-speed craft are verified against Troesch’s experimental results. In the following, after determination of hydrodynamic coefficients of a planing catamaran with and without foil, the foil effects on its hydrodynamic coefficients are evaluated. The results indicate that most of the coefficients are frequency-independent especially at high frequencies.

A METHOD FOR COMPUTING THE TOTAL MAGNETIZATION VECTOR AND THE DIMENSIONS OF A RECTANGULAR BLOCK‐SHAPED BODY FROM MAGNETIC ANOMALIES

Geophysics ◽  
1966 ◽  
Vol 31 (1) ◽  
pp. 74-96 ◽  
Author(s):  
B. K. Bhattacharyya
Keyword(s):  
High Speed ◽  
Magnetization Vector ◽  
The Body ◽  
Total Field ◽  
Unknown Parameters ◽  
Factors Affecting ◽  
Vertical Derivative ◽  
Correct Location ◽  
Unit Of Length

In this paper is presented a new method for determining the following parameters of a uniformly magnetized body of rectangular prismatic shape: (i) horizontal dimensions, (ii) depths to the top and bottom of the body, and (iii) intensity and direction of magnetization. Accuracy in the computation of these parameters is highly dependent on the correct location of the center and on the determination of the major and minor axes of the body. An iterative method of calculations is used. This method is considerably aided not only by the second vertical derivative map of the observed total field but also by the total field reduced to the pole and its second vertical derivative map. The horizontal dimensions are determined by noting the location of the maximum of the odd component of the second vertical derivative about the center of the body. These dimensions are estimated with high accuracy when they are greater than the depth to the top of the body. The remaining unknown parameters of the body are calculated with the help of the first horizontal and vertical derivatives and the total field at the origin in the plane of observation which is directly above the center of the body. The present method also requires the total‐field value at the point one‐half unit of length above the origin. The factors affecting the accuracy in the calculation of the parameters are discussed in detail. With the help of high‐speed digital computers, this method can be used with great advantage for computation of the above parameters of magnetized bodies giving rise to a number of anomalies over a particular area.

Factors affecting the accurate determination of cerebrovascular blood flow using high-speed droplet imaging

1998 ◽  
Author(s):  
Stephen Rudin ◽  
Afshin Divani ◽  
Ajay K. Wakhloo ◽  
Baruch B. Lieber ◽  
William Granger ◽  
...  
Keyword(s):  
Blood Flow ◽  
High Speed ◽  
Accurate Determination ◽  
Factors Affecting

Calculation of Debris Trajectories During High-Speed Snowplowing

2002 ◽  
Author(s):  
H. K. Nakhla ◽  
B. E. Thompson
Keyword(s):  
Particle Tracking ◽  
High Speed ◽  
Turbulence Modeling ◽  
Stokes Equations ◽  
Cutting Edge ◽  
Navier Stokes ◽  
Engineering Model ◽  
Navier Stokes Equations ◽  
Snow Plowing ◽  
Reynolds Averaged Navier Stokes

An engineering model is presented to calculate the trajectory of airborne debris that adversely affects visibility during high-speed snow plowing. Reynolds-averaged Navier-Stokes equations are solved numerically with turbulence-modeling, particle-tracking, and cutting-edge approximations. Results suggest snow can be divided into splash and snow-cloud when designing treatments to improve visibility for snowplow drivers and following traffic. Calculated results confirm the findings of windtunnel and road tests, specifically that the trap angle of overplow deflectors should be less than 50 degrees to eliminate snow debris blowing over top of the plow onto the windscreen.

scholarly journals Experimental application of contour method for determination of residual stress in subsurface layers of milled sample

2012 ◽  
Vol 60 (5) ◽  
pp. 79-88
Author(s):  
Karel Horák ◽  
Michal Černý ◽  
Petr Dostál
Keyword(s):  
Residual Stress ◽  
High Speed ◽  
Diffraction Method ◽  
Sample Surface ◽  
Contour Method ◽  
Hole Drilling ◽  
Laboratory Equipment ◽  
Hole Drilling Method ◽  
Drilling Method

Determination of residual stress close to the sample surface is in the most cases performed by hole-drilling method, X-Ray diffraction or neutron diffraction. Each of these methods has its benefits and disadvantages. In case of diffraction methods the measurement speed is the main disadvantage. It is also very problematic to apply diffraction method in case of sample with mechanically deformed surface, for example by standard machining operations. Therefore, determined results are very often confusing and hard to interpret. On the other side, hole drilling method is less sensitive to quality of sample surface than diffraction methods, but measurement realization is quite expensive and equipment demanding (strain gage rosettes, miniature milling cutter, high speed milling machine, pc equipment,…).Recently introduce contour method used for determination of residual stress inside the sample is very fast, can be performed with almost common laboratory equipment and combines traditional stance with modern numerical methods by FEM. Contour method was selected for determination of residual stress below the milled surface and the dependency of milling process quality on residual stress value is demonstrated.

Determination of Hydrodynamic Coefficients in Roll Motion of High-Speed Planing Hulls

2015 ◽  
Author(s):  
Sasan Tavakoli ◽  
Parviz Ghadimi ◽  
Abbas Dashtimanesh ◽  
Prasanta K. Sahoo
Keyword(s):  
High Speed ◽  
Transverse Motion ◽  
Roll Motion ◽  
Hydrodynamic Coefficients ◽  
Mathematical Study ◽  
Sea Trial ◽  
Conceptual Design Phase ◽  
Interesting Study ◽  
Linear And Nonlinear

Observations by crew of high-speed planing boats and sea trial tests have indicated that high-speed planing hulls suffer poor longitudinal and transverse instabilities, and boat may experience unfavorable motions due to any small environmental excitation. In this regard, dynamic motions of planing boats have been investigated over the last thirty years, during which innovative linear and nonlinear methods have been developed .In these studies, different method s have been developed by various authors to determine forces and moments acting on the hull. However, majority of investigators have focused on vertical motions of planning boats in waves (such as Zarnick [1978], Hicks and Troesch [1994] etc.) and few researchers have only attempted to model motions in transverse and horizontal planes including sway, yaw and roll motions. Furthermore, most of researches dealing with transverse and horizontal planning motions, were experimentally conducted (such as Judge [2010], Morabito et al [2014] etc). There exist only few articles, in which mathematical models for transverse motion have been developed. Therefore, it is needed to develop as implemathematical models for prediction of transverse motions of planing boats for use in conceptual design phase. During the last five years, there has been an increased interesting study of transverse motions, and in the current paper, an attempt has been made for a mathematical study of roll motion of planning hulls.

Reynolds-Averaged Navier-Stokes Simulations for High-Speed Wigley Hull in Deep and Shallow Water

2007 ◽  
Vol 51 (03) ◽  
pp. 187-203
Author(s):  
Nobuaki Sakamoto ◽  
Robert Vance Wilson ◽  
Frederick Stern
Keyword(s):  
Shallow Water ◽  
Message Passing ◽  
High Speed ◽  
High Performance ◽  
Message Passing Interface ◽  
Iterative Solvers ◽  
Verification And Validation ◽  
Navier Stokes ◽  
Wigley Hull ◽  
Reynolds Averaged Navier Stokes

Reynolds-averaged Navier-Stokes simulations and verification and validation studies for a high-speed Wigley hull in deep and shallow water are presented using CFD-SHIP-IOWA Version 4.00, which is a general-purpose ship hydrodynamics computational fluid dynamics code: single-phase level set free surface and k-w turbulence modeling; higher-order conservative discretization, embedded overset grids, advanced iterative solvers, and implicit coupling flow field and predicted motions numerical methods; and high-performance computing for message-passing interface (MPI)-based domain decomposition. The results are presented for low to high speed and deep to shallow water. The investigation is exploratory in nature using an idealized geometry and relatively coarse grids. Based on the verification and validation results, modifications for increased grid resolution at the bow for high speed and improved grid orthogonality for shallow water are made to obtain better solutions. The flow physics observations provide both integral and differential views of the highspeed and shallow-water flow fields, including resistance, pressure variation, wave pattern, boundary layer, and vortices.

scholarly journals Efficiency of disengaged wet brake packs

2018 ◽  
Vol 233 (6) ◽  
pp. 1562-1569 ◽  
Author(s):  
M Leighton ◽  
Nicholas Morris ◽  
Gareth Trimmer ◽  
Paul D King ◽  
Homer Rahnejat
Keyword(s):  
High Speed ◽  
Experimental Approach ◽  
Fuel Efficiency ◽  
Operating Conditions ◽  
Squeeze Film ◽  
Navier Stokes ◽  
Fluid Viscosity ◽  
Fluid Inertia ◽  
Systems Model ◽  
High Fluid

Key objectives in off-highway vehicular powertrain development are fuel efficiency and environmental protection. As a result, palliative measures are made to reduce parasitic frictional losses while sustaining machine operational performance and reliability. A potential key contributor to the overall power loss is the rotation of disengaged wet multi-plate pack brake friction. Despite the numerous advantages of wet brake pack design, during high-speed manoeuvre in highway travel or at start-up conditions, significant frictional power losses occur. The addition of recessed grooves on the brake friction lining is used to dissipate heat during engagement. These complicate the prediction of performance of the system, particularly when disengaged. To characterise the losses produced by these components, a combined numerical and experimental approach is required. This paper presents a Reynolds-based numerical model including the effect of fluid inertia and squeeze film transience for prediction of performance of wet brake systems. Model predictions are compared with very detailed combined Navier–Stokes and Rayleigh-Plesset fluid dynamics analysis to ascertain its degree of conformity to representative physical operating conditions, as well the use of a developed experimental rig. The combined numerical and experimental approach is used to predict significant losses produced during various operating conditions. It is shown that cavitation becomes significant at low temperatures due to micro-hydrodynamic action, enhanced by high fluid viscosity. The magnitude of the losses for these components under various operating conditions is presented. The combined numerical-experimental study of wet multi-plate brakes of off-highway vehicles with cavitation flow dynamics has not hitherto been reported in the literature.

scholarly journals Desenvolvimento de um modelo numérico para a predição de um escoamento em bocal do tipo H.O.M.E.R

2019 ◽  
Vol 5 (1) ◽  
pp. 129-137
Author(s):  
Elizaldo Domingues dos Santos
Keyword(s):  
High Speed ◽  
Navier Stokes ◽  
Reynolds Averaged Navier Stokes

No presente estudo é desenvolvido um modelo numérico para a abordagem de escoamentos turbulentos no regime permanente em bocais do tipo H.O.M.E.R (do inglês: High-speed Orienting Momentum with Enhanced Reversibility) que consiste na mistura de dois jatos incidentes sobre superfícies de Coanda. Essa superfície causa uma deflexão no escoamento permitindo que o bocal atue como um dispositivo de manobra em aplicações aeronáuticas. O principal objetivo é avaliar o modelo numérico desenvolvido comparando com resultados numéricos da literatura. As equações de conservação de massa e quantidade de movimento médias no tempo são resolvidas numericamente através do método de volumes finitos. Para resolver o problema do fechamento da turbulência foi empregada modelagem clássica (RANS – do inglês: Reynolds Averaged Navier Stokes) com modelo k – ε. Primeiramente, um teste de independência de malha será realizado, com o intuito de dispender menos recursos computacionais e obter resultados precisos. Em seguida, serão feitas as simulações em regime permanente, com o objetivo de obter os ângulos de deflexão (α) gerados com a diferença das vazões mássicas injetadas em cada um dos canais do bocal H.O.M.E.R (m*). Posteriormente, esses resultados são comparados com os obtidos numericamente na literatura. Os resultados obtidos tiveram o mesmo comportamento obtido na literatura, onde o aumento da diferença entre os jatos de entrada conduziu a um aumento no ângulo de deflexão do jato no bocal. Com exceção de um valor específico (m* = 0.2) os resultados obtidos no presente trabalho apresentaram uma boa concordância com os preditos numericamente na literatura.

The Evolution of Computational Methods in Aerodynamics

1983 ◽  
Vol 50 (4b) ◽  
pp. 1052-1070 ◽  
Author(s):  
A. Jameson
Keyword(s):  
Euler Equations ◽  
Computational Methods ◽  
High Speed ◽  
Stokes Equations ◽  
Inviscid Flow ◽  
Flow Equation ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Electronic Computers ◽  
Reynolds Averaged Navier Stokes

This paper surveys the evolution of computational methods in aerodynamics. Improvements in high-speed electronic computers have made it feasible to attempt numerical calculations of progressively more complex mathematical models of aerodynamic flows. Numerical approximation methods for a hierarchy of models are examined in ascending order of complexity, ranging from the linearized potential flow equation to the Reynolds averaged Navier Stokes equations, with the inclusion of some previously unpublished material on implicit and multigrid methods for the Euler equations. It is concluded that the solution to the Euler equations for inviscid flow past a complete aircraft is a presently attainable objective, while the solution to the Reynolds averaged Navier Stokes equations is a possibility clearly visible on the horizon.

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