Effect of Surface Curvature on the Hydrodynamics of Water Entry at High Horizontal Velocity

Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics ◽

10.1115/omae2018-78438 ◽

2018 ◽

Author(s):

Alessandro Iafrati

Keyword(s):

Flat Plate ◽

Body Surface ◽

Air Entrainment ◽

Maximum Load ◽

Water Entry ◽

The Body ◽

Horizontal Velocity ◽

Scaling Effects ◽

Research Activity ◽

Convex Shape

The role played by the curvature of the body surface on the hydrodynamics of water entry with high horizontal velocity component is investigated experimentally. The study is a part of a research activity finalized at the understanding of the aircraft ditching problem. In order to avoid scaling effects which may prevent the development of ventilation/cavitation phenomena, the study is carried out at full scale velocity. Measurements are presented in terms of pressures and loads whereas some underwater visualizations are used for the interpretation of the data. Both a convex and concave body surface are considered and comparisons with the flat plate data are established. In the case of a concave shape, a quite complicated flow with large air entrainment develops beneath the plate. The air entrainment causes a general reduction of the pressure peak at the middle, whereas the pressure peaks recorded at the side probes are about in line with those found for the flat plate in the same conditions. The total hydrodynamic load acting normal to the plate grows more regularly but the maximum load is essentially the same as that measured in the flat plate case. For the convex shape, the pressure probes located in the middle of the plate get wetted well before the ones at the side and the pressure peaks at the sides are much lower than those in the middle. The reduced pressures at the sides cause a reduction of the total loading in the normal direction compared to flat and concave plates.

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Water entry of a wedge with rolled-up vortex sheet

Journal of Fluid Mechanics ◽

10.1017/jfm.2017.766 ◽

2017 ◽

Vol 835 ◽

pp. 512-539 ◽

Cited By ~ 5

Author(s):

Yuriy A. Semenov ◽

G. X. Wu

Keyword(s):

Free Surface ◽

Pressure Distribution ◽

Body Surface ◽

Vortex Shedding ◽

Vortex Sheet ◽

Water Entry ◽

The Body ◽

Surface Shape ◽

Force Coefficients ◽

Local Singularity

The problem of asymmetric water entry of a wedge with the vortex sheet shed from its apex is considered within the framework of the ideal and incompressible fluid. The effects due to gravity and surface tension are ignored and the flow therefore can be treated as self-similar, as there is no length scale. The solution for the problem is sought through two mutually dependent parts using two different analytic approaches. The first one is due to water entry, which is obtained through the integral hodograph method for the complex velocity potential, in which the streamline on the body surface remains on the body surface after passing the apex, leading to a non-physical local singularity. The second one is due to a vortex sheet shed from the apex, and the shape of the sheet and the strength distribution of the vortex are obtained through the solution of the Birkhoff–Rott equation. The total circulation of the vortex sheet is obtained by imposing the Kutta condition at the apex, which removes the local singularity. These two solutions are nonlinearly coupled on the unknown free surface and the unknown vortex sheet. This poses a major challenge, which distinguishes the present formulation of the problem from the previous ones on water entry without a vortex sheet and ones on vortex shedding from a wedge apex without a moving free surface. Detailed results in terms of pressure distribution, vortex sheet, velocity and force coefficients are presented for wedges of different inner angles and heel angles, as well as the water-entry direction. It is shown that the vortex shedding from the tip of the wedge has a profound local effect, but only weakly affects the free-surface shape, overall pressure distribution and force coefficients.

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An Examination of Efficiency during Walking in Children and Adults

Pediatric Exercise Science ◽

10.1123/pes.4.1.36 ◽

1992 ◽

Vol 4 (1) ◽

pp. 36-49 ◽

Cited By ~ 19

Author(s):

Christine J. Ebbeling ◽

Joseph Hamill ◽

Patty S. Freedson ◽

Thomas W. Rowland

Keyword(s):

Heart Rate ◽

Oxygen Consumption ◽

Surface Area ◽

Body Surface ◽

Walking Speed ◽

The Body ◽

Biomechanical Analysis ◽

Scaling Effects ◽

The Subject ◽

Work Done

This study compared metabolic, kinematic, and efficiency parameters in 10 boys and 10 men while walking at speeds of similar relative intensities. Heart rate and oxygen consumption were monitored throughout the exercise and a sagittal view of the subject was filmed for biomechanical analysis. Angles of the hip, knee, and ankle changed with an increase in walking speed. There were kinematic differences between children and adults at the hip and knee. Heart rate and oxygen consumption (ml•kg−1•min−1) were greater in the children. There were no significant differences between children and adults when VO2 was normalized by body surface area rather than body mass. The work done by the body was greater in the adults, whereas the energy used was greater in the children. Therefore the children appeared less efficient. The reasons for the efficiency difference are not well documented. Scaling effects may be involved and therefore should be taken into consideration when comparing children and adults.

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Experimental investigation of the water entry of a rectangular plate at high horizontal velocity

Journal of Fluid Mechanics ◽

10.1017/jfm.2016.374 ◽

2016 ◽

Vol 799 ◽

pp. 637-672 ◽

Cited By ~ 17

Author(s):

A. Iafrati

Keyword(s):

Rectangular Plate ◽

Velocity Component ◽

Propagation Velocity ◽

Velocity Ratio ◽

Water Entry ◽

The Body ◽

Horizontal Velocity ◽

Initial Growth ◽

Test Conditions ◽

Pressure Peak

The water entry of a rectangular plate with a high horizontal velocity component is investigated experimentally. The test conditions are representative of those encountered by aircraft during emergency landing on water and are given in terms of three main parameters: horizontal velocity, approach angle, i.e. vertical to horizontal velocity ratio, and pitch angle. Experimental data are presented in terms of pressure, spray root shape, pressure peak propagation velocity and total loads acting on the plate. A theoretical solution of the plate entry problem based on two-dimensional and potential flow assumptions is derived and is used to support the interpretation of the experimental measurements. The results indicate that, as the plate penetrates and the ratio between the plate breadth and the wetted length measured on the longitudinal plane diminishes, the role of the third dimension becomes dominant. The increased possibility for the liquid to escape from the lateral sides yields a reduction of the pressure peak propagation velocity and, consequently, of the corresponding pressure peak intensity. In particular, it is shown that, at the beginning of the entry process, the pressure peak moves much faster than the geometric intersection between the body and the free surface, but at a later stage the two points move along the body at the same speed. Furthermore, it is shown that the spray root develops a curved shape which is almost independent of the specific test conditions, even though the initial growth rate of the curvature is higher for larger pitch angles. The loads follow a linear increase versus time, as predicted by the theoretical model, only in a short initial stage. Next, for all test conditions examined here, they approach a square-root dependence on time. It is seen that, if the loads are scaled by the square of the velocity component normal to the plate, the data are almost independent of the test conditions.

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Water entry of an expanding body with and without splash

Journal of Fluid Mechanics ◽

10.1017/jfm.2018.922 ◽

2019 ◽

Vol 862 ◽

pp. 924-950 ◽

Cited By ~ 1

Author(s):

Y. A. Semenov ◽

G. X. Wu

Keyword(s):

Free Surface ◽

Body Surface ◽

Water Entry ◽

The Body ◽

Surface Shape ◽

Cylinder Surface ◽

Hodograph Method ◽

Expansion Speed ◽

Attached Flow ◽

Self Similar

A self-similar flow generated by water entry of an expanding two-dimensional smooth and curved body is studied based on the incompressible velocity potential theory, with gravity and surface tension effects being ignored. At each expansion speed, mathematical solutions for detached flow with a splash jet and attached flow with jet leaning on the body surface are obtained, both of which have been found possible in experiment, corresponding to hydrophobic and hydrophilic bodies, respectively. The problem is solved using the integral hodograph method, which converts the governing Laplace equations into two integral equations along the half real and imaginary axes of a parameter plane. For the detached flow, the conditions for continuity and finite spatial derivative of the velocity at the point of flow departing form the body surface are imposed. It is found that the Brillouin–Villat criterion for flow detachment of steady flow is also met in this self-similar flow, which requires the curvatures of the free surface and the body surface to be the same at the detachment point. Solutions for the detached flow have been obtained in the whole range of the expansion speeds, from zero to infinity, relative to the water entry speed. For the attached flow there is a minimal expansion speed below which no solution cannot be obtained. Detailed results in terms of pressure distribution, free surface shape and streamlines and tip angle of the jet are presented. It is revealed that when solutions for both detached and attached flows exist, the pressure distributions on the cylinder surface are almost the same up to the point near the jet root. Beyond that point, the pressure relative to the ambient one drops to zero at the detachment point in the former, while it drops below zero in the jet attached on the body and then returns to zero at the contact point in the latter.

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A Generalized Wagner Method for Three-Dimensional Slamming

Journal of Ship Research ◽

10.5957/jsr.2005.49.4.279 ◽

2005 ◽

Vol 49 (04) ◽

pp. 279-287

Author(s):

O. M. Faltinsen ◽

M. Chezhian

Keyword(s):

Free Surface ◽

Body Surface ◽

Surface Condition ◽

Three Dimensional ◽

Water Entry ◽

The Body ◽

Experimental Results ◽

Vertical Force ◽

Free Surface Condition ◽

Drop Tests

Impact between the water and ship, that is, slamming, can cause important global and local effects. A numerical method has been applied to predict water entry loads on three-dimensional bodies. The problem is solved as an initial value problem using the boundary element method. The Green second identity is used to represent the velocity potential as a distribution of Rankine sources and dipoles over the body surface and free surface. The problem is stepped up in time using the information from the boundary conditions. The kinematic free-surface condition is used to determine the intersection between the body surface and free surface at each time step. The exact body boundary condition is used, whereas the dynamic free-surface condition, φ = 0, is approximated on to a horizontal line and not on the exact free-surface profile. The approach presented by Zhao et al (1996) for two-dimensional water entry problems was extended to arbitrary three-dimensional bodies in this presented work. An idealized shape, which consists of cylindrical mid-body and hemispherical ends, was studied. The wetted body surface is calculated with great detail and is considered to be more important than the free-surface elevation away from the body. Drop tests have been carried out to verify and validate the numerical simulation. The effect of the angle between the free surface and the body surface has also been studied. The agreement between theory and experiments is good, and the effect of three-dimensionality is documented. The presented computational method is found to be robust for engineering use and computationally less demanding. The experimental results for vertical force have a strong oscillatory nature, and this has been analyzed using a simplified hydroelastic model. The hydroelastic model gives reasonable representation of the dynamic oscillations found in the vertical force. Reasons for the observed deviations between the numerical and the experimental results are documented. Recommendations for conducting drop tests with minimal dynamic effects are also presented.

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Cavity Formation during Asymmetric Water Entry of Rigid Bodies

Applied Sciences ◽

10.3390/app11052029 ◽

2021 ◽

Vol 11 (5) ◽

pp. 2029

Author(s):

Riccardo Panciroli ◽

Giangiacomo Minak

Keyword(s):

Velocity Component ◽

Water Entry ◽

Rigid Bodies ◽

Rigid Body Dynamics ◽

The Body ◽

Horizontal Velocity ◽

Cavity Formation ◽

Fluid Structure ◽

Horizontal Velocity Component ◽

The Stability

This work numerically evaluates the role of advancing velocity on the water entry of rigid wedges, highlighting its influence on the development of underpressure at the fluid–structure interface, which can eventually lead to fluid detachment or cavity formation, depending on the geometry. A coupled FEM–SPH numerical model is implemented within LS-DYNA, and three types of asymmetric impacts are treated: (I) symmetric wedges with horizontal velocity component, (II) asymmetric wedges with a pure vertical velocity component, and (III) asymmetric wedges with a horizontal velocity component. Particular attention is given to the evolution of the pressure at the fluid–structure interface and the onset of fluid detachment at the wedge tip and their effect on the rigid body dynamics. Results concerning the tilting moment generated during the water entry are presented, varying entry depth, asymmetry, and entry velocity. The presented results are important for the evaluation of the stability of the body during asymmetric slamming events.

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The Role of Computer Modeling in Electrocardiography

Methods of Information in Medicine ◽

10.1055/s-0038-1634809 ◽

1990 ◽

Vol 29 (04) ◽

pp. 282-288 ◽

Cited By ~ 2

Author(s):

A. van Oosterom

Keyword(s):

Electrical Activity ◽

Computer Modeling ◽

Body Surface ◽

Electrical Current ◽

The Body ◽

Volume Conductor ◽

Current Generator ◽

Cardiac Electrical Activity ◽

Source Models

AbstractThis paper introduces some levels at which the computer has been incorporated in the research into the basis of electrocardiography. The emphasis lies on the modeling of the heart as an electrical current generator and of the properties of the body as a volume conductor, both playing a major role in the shaping of the electrocardiographic waveforms recorded at the body surface. It is claimed that the Forward-Problem of electrocardiography is no longer a problem. Several source models of cardiac electrical activity are considered, one of which can be directly interpreted in terms of the underlying electrophysiology (the depolarization sequence of the ventricles). The importance of using tailored rather than textbook geometry in inverse procedures is stressed.

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The use of Body Surface Index as a Better Clinical Health indicators Compare to Body Mass Index and Body Surface Area for Clinical Application

International Journal of Scientific Research in Science Engineering and Technology ◽

10.32628/ijsrset2184117 ◽

2018 ◽

pp. 131-136

Author(s):

Shirazu I. ◽

Theophilus. A. Sackey ◽

Elvis K. Tiburu ◽

Mensah Y. B. ◽

Forson A.

Keyword(s):

Surface Area ◽

Body Surface Area ◽

Clinical Application ◽

Body Surface ◽

Body Height ◽

Health Indicators ◽

The Body ◽

Body Parameters ◽

The Relationship ◽

Individual Body

The relationship between body height and body weight has been described by using various terms. Notable among them is the body mass index, body surface area, body shape index and body surface index. In clinical setting the first descriptive parameter is the BMI scale, which provides information about whether an individual body weight is proportionate to the body height. Since the development of BMI, two other body parameters have been developed in an attempt to determine the relationship between body height and weight. These are the body surface area (BSA) and body surface index (BSI). Generally, these body parameters are described as clinical health indicators that described how healthy an individual body response to the other internal organs. The aim of the study is to discuss the use of BSI as a better clinical health indicator for preclinical assessment of body-organ/tissue relationship. Hence organ health condition as against other body composition. In addition the study is `also to determine the best body parameter the best predict other parameters for clinical application. The model parameters are presented as; modeled height and weight; modelled BSI and BSA, BSI and BMI and modeled BSA and BMI. The models are presented as clinical application software for comfortable working process and designed as GUI and CAD for use in clinical application.

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