NUMERICAL PREDICTION OF SLAMMING LOADS DURING WATER ENTRY OF BOW-FLARED SECTIONS

The two-dimensional water entry of bow-flared sections is studied by using a Multi-Material Arbitrary Lagrangian- Eulerian (MMALE) formulation and a penalty-coupling algorithm. A convergence study is carried out, considering the effects of mesh size, the dimension of fluids domain, and fluid leakage phenomenon through the structure. The predicted results on the wetted surface of a bow-flared section are compared with published experimental values in terms of vertical slamming force, pressure distributions at different time instances and the pressure histories at different points. Comparisons between the numerical results and measured values show satisfactory correlation. An approximation method is adopted to estimate the sectional slamming force showing good consistency for the peak forces.

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Numerical Simulation of Free-Air Explosion Using LS-DYNA

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.553.780 ◽

2014 ◽

Vol 553 ◽

pp. 780-785 ◽

Cited By ~ 1

Author(s):

S.K. Hashemi ◽

Mark A. Bradford

Keyword(s):

Computational Modelling ◽

Mesh Size ◽

Arbitrary Lagrangian Eulerian ◽

Empirical Methods ◽

Large Structures ◽

Pressure Distributions ◽

Free Air ◽

Charge Shape ◽

Air Explosion ◽

Parameter Values

The development of advanced computational technologies in recent years has seen studies of the effects of explosions on large structures becoming feasible and, as a consequence, the number of destructive tests and their high cost can be reduced significantly. This paper presents a study of air-burst explosion wave propagation using computational modelling based on LS-DYNA. Incident and reflected pressure waves are investigated, as well as the mesh sensitivity, different scaled distances and the charge shape. The Multi-Material Arbitrary Lagrangian-Eulerian (MM-ALE) representation is used to model the blast, and the results are validated by empirical methods. The effects of parameter values adopted in these methods are studied. The results show that LS-DYNA can effectively simulate an air-burst explosion. Additionally, the mesh size and explosive weight have a large influence on the peak incident and reflected pressures. It is observed that there is an optimum range of the mesh size in relation to the explosive weight, material properties and the scaled distance which can significantly reduce the CPU usage while having reasonable accuracy. Different charge shapes cause different pressure distributions over the air domain.

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The Departure from Equilibrium of Turbulent Boundary Layers

Aeronautical Quarterly ◽

10.1017/s0001925900004418 ◽

1968 ◽

Vol 19 (1) ◽

pp. 1-19 ◽

Cited By ~ 8

Author(s):

H. McDonald

Keyword(s):

Boundary Layer ◽

Shear Stress ◽

Kinetic Energy ◽

Stress Distribution ◽

Boundary Layers ◽

Turbulent Boundary Layers ◽

Two Dimensional ◽

Pressure Distributions ◽

Momentum Integral ◽

State Examination

SummaryRecently two authors, Nash and Goldberg, have suggested, intuitively, that the rate at which the shear stress distribution in an incompressible, two-dimensional, turbulent boundary layer would return to its equilibrium value is directly proportional to the extent of the departure from the equilibrium state. Examination of the behaviour of the integral properties of the boundary layer supports this hypothesis. In the present paper a relationship similar to the suggestion of Nash and Goldberg is derived from the local balance of the kinetic energy of the turbulence. Coupling this simple derived relationship to the boundary layer momentum and moment-of-momentum integral equations results in quite accurate predictions of the behaviour of non-equilibrium turbulent boundary layers in arbitrary adverse (given) pressure distributions.

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Three-dimensional flow in cavities

Journal of Fluid Mechanics ◽

10.1017/s0022112063001014 ◽

1963 ◽

Vol 16 (4) ◽

pp. 620-632 ◽

Cited By ~ 126

Author(s):

D. J. Maull ◽

L. F. East

Keyword(s):

Static Pressure ◽

Three Dimensional ◽

Two Dimensional ◽

Three Dimensional Flow ◽

Large Span ◽

Dimensional Flow ◽

Pressure Distributions ◽

Oil Flow ◽

Two Dimensional Flow

The flow inside rectangular and other cavities in a wall has been investigated at low subsonic velocities using oil flow and surface static-pressure distributions. Evidence has been found of regular three-dimensional flows in cavities with large span-to-chord ratios which would normally be considered to have two-dimensional flow near their centre-lines. The dependence of the steadiness of the flow upon the cavity's span as well as its chord and depth has also been observed.

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Measurements of Apparent Mass Torque Coefficients of Two-Dimensional Centrifugal Impellers

Journal of Fluids Engineering ◽

10.1115/1.3242596 ◽

1986 ◽

Vol 108 (4) ◽

pp. 407-413

Author(s):

Y. Tsujimoto ◽

K. Imaichi ◽

T. Moritani ◽

K. Kim

Keyword(s):

Angular Velocity ◽

Flow Rate ◽

Potential Flow ◽

Rotational Velocity ◽

Apparent Mass ◽

Two Dimensional ◽

Drag Torque ◽

Mean Flow ◽

Experimental Values

Apparent mass torque coefficients for fluctuations of flow rate and angular velocity are determined experimentally for two-dimensional centrifugal impellers. Nearly sinusoidal fluctuations of flow rate and angular velocity are produced by using crank mechanisms, and the resulting unsteady torque on the impeller is measured. The torque is divided into components in-phase and out-of-phase with the displacements. The in-phase components are used to determine the apparent mass coefficients. Drag torque coefficients are defined and used to represent the out-of-phase components. The tests are conducted under various frequencies and amplitudes of the fluctuations with zero mean flow rate and rotational velocity. The apparent mass torque coefficients are compared with theoretical values obtained under the assumption of a two-dimensional potential flow. The experimental values are 5 to 20 percent larger than the theoretical ones and no appreciable effects of the frequency and the amplitude are observed within the range of the experiments.

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Effect of Compressibility on Gaseous Flows in a Micro-Tube

Heat Transfer: Volume 1 ◽

10.1115/ht2003-47166 ◽

2003 ◽

Cited By ~ 2

Author(s):

Yutaka Asako ◽

Kenji Nakayama

Keyword(s):

Reynolds Number ◽

Mach Number ◽

Pressure Distribution ◽

Flow Characteristics ◽

Fused Silica ◽

Two Dimensional ◽

Arbitrary Lagrangian Eulerian ◽

Gaseous Flow ◽

Gaseous Flows ◽

Energy Equations

The product of friction factor and Reynolds number (f·Re) of gaseous flow in the quasi-fully developed region of a micro-tube was obtained experimentally and numerically. The tube cutting method was adopted to obtain the pressure distribution along the tube. The fused silica tubes whose nominal diameters were 100 and 150 μm, were used. Two-dimensional compressible momentum and energy equations were solved to obtain the flow characteristics in micro-tubes. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The both results agree well and it was found that (f·Re) is a function of Mach number.

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Water entry of an expanding wedge/plate with flow detachment

Journal of Fluid Mechanics ◽

10.1017/jfm.2016.291 ◽

2016 ◽

Vol 797 ◽

pp. 322-344 ◽

Cited By ~ 4

Author(s):

Yuriy A. Semenov ◽

Guo Xiong Wu

Keyword(s):

Free Surface ◽

General Solution ◽

Water Entry ◽

Hodograph Method ◽

Fixed Length ◽

Pressure Distributions ◽

Initial Stage ◽

Special Cases ◽

Wedge Plate ◽

Special Case

A general similarity solution for water-entry problems of a wedge with its inner angle fixed and its sides in expansion is obtained with flow detachment, in which the speed of expansion is a free parameter. The known solutions for a wedge of a fixed length at the initial stage of water entry without flow detachment and at the final stage corresponding to Helmholtz flow are obtained as two special cases, at some finite and zero expansion speeds, respectively. An expanding horizontal plate impacting a flat free surface is considered as the special case of the general solution for a wedge inner angle equal to ${\rm\pi}$. An initial impulse solution for a plate of a fixed length is obtained as the special case of the present formulation. The general solution is obtained in the form of integral equations using the integral hodograph method. The results are presented in terms of free-surface shapes, streamlines and pressure distributions.

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Flow Fields in a Two-Dimensional Diffuser With Extraction of Fluid on the Diverging Walls

Journal of Engineering for Power ◽

10.1115/1.3445677 ◽

1972 ◽

Vol 94 (3) ◽

pp. 226-232

Author(s):

D. O. Rockwell

Keyword(s):

Experimental Verification ◽

Static Pressure ◽

Flow Fields ◽

Hydrogen Bubble ◽

Two Dimensional ◽

Stagnation Region ◽

Pressure Distributions

A theory is developed to describe the inviscid core in two-dimensional unstalled diffusers with suction (extraction) on the diverging walls. Experimental wall static pressure distributions and streamline patterns agree well with those predicted theoretically. Under appropriate extraction conditions, a stagnation region is located downstream of the diverging wall extraction station. Experimental verification of the streamline patterns and of the location of this stagnation region was achieved via hydrogen bubble visualization. In addition, the possible stall conditions, which result if improper extraction is employed, are described qualitatively.

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Aerodynamic Performance of the NREL S826 Airfoil in Icing Conditions

10.5194/wes-2017-39 ◽

2017 ◽

Cited By ~ 3

Author(s):

Julie Krøgenes ◽

Lovisa Brandrud ◽

Richard Hann ◽

Jan Bartl ◽

Tania Bracchi ◽

...

Keyword(s):

Wind Farm ◽

Aerodynamic Performance ◽

Cold Climate ◽

Navier Stokes ◽

Computational Results ◽

Energy Potential ◽

Pressure Distributions ◽

Wind Energy Potential ◽

Experimental Values ◽

Lift And Drag

Abstract. The demand for wind power is rapidly increasing, creating opportunities for wind farm installations in more challenging climates. Cold climate areas, where ice accretion can be an issue, are often sparsely populated and have high wind energy potential. Icing may lead to severely reduced aerodynamic performance and thereby reduced power output. To reach a greater understanding of how icing affects the aerodynamics of a wind turbine blade, three representative icing cases; rime ice, glaze ice and a mixed ice, were deﬁned and investigated experimentally and computationally. Experiments at Re = 1.0 × 105–4.0 × 105 were conducted in the low-speed wind tunnel at NTNU on a two dimensional wing with applied 3D-printed ice shapes, determining lift, drag and surface pressure distributions. Computational results, obtained from the Reynolds Averaged Navier–Stokes ﬂuid dynamics code FENSAP, complement the experiments. Measured and predicted data show a reduction in lift for all icing cases. Most severe is the mixed ice case, with a lift reduction of up to 30 % in the linear lift area, compared to a clean reference airfoil. Computational results show an under-prediction in maximum lift of 7–18 % compared to experimental values. Curvature and tendencies for both lift and drag show good agreement between simulations and experiment.

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