scholarly journals Kinematics of the Ship’s Wake in the Presence of a Shear Flow

2020 ◽  
Vol 9 (1) ◽  
pp. 7
Author(s):  
Igor Shugan ◽  
Yang-Yih Chen
Keyword(s):  
Shear Flow ◽  
Kinematic Model ◽  
Wedge Angle ◽  
Transverse Waves ◽  
Ship Waves ◽  
Ship Wake ◽  
Shear Current ◽  
The Difference ◽  
Wake Model ◽  
Subsurface Current

We present the kinematic model of the ship wake in the presence of horizontal subsurface current linearly varying with the depth of water. An extension of the Whitham–Lighthill theory for calm water is developed. It has been established that the structure of ship waves under the action of a shear flow can radically differ from the classical Kelvin ship wake model. Co propagating ship and shear current lead to increasing the total wedge angle up to full one 180° and decreases for the counter shear current. At relatively large unidirectional values of the shear current, cusp waves in the vicinity of the wedge boundary are represented by transverse waves and, conversely, by diverging waves directed almost perpendicular to the ship track for the opposite shear current. The presence of a shear flow crossing the direction of the ship’s movement gives a strong asymmetry of the wake. An increase in the perpendicular shear flow leads to an increase in the difference between the angles of the wake arms. The limiting value of the shear current corresponds to one or both arms angles equal to 90°. Transverse and divergent edge waves for this limiting case coincide.

scholarly journals Ship waves in the presence of uniform vorticity

2014 ◽  
Vol 742 ◽  
Author(s):  
Simen Å. Ellingsen
Keyword(s):  
Shear Flow ◽  
Finite Depth ◽  
Critical Value ◽  
Wave Problem ◽  
Transverse Waves ◽  
Ship Waves ◽  
Striking Result ◽  
Constant Vorticity ◽  
Shear Current ◽  
Half Angle

AbstractLord Kelvin’s result that waves behind a ship lie within a half-angle $\phi _{\mathit{K}}\approx 19^{\circ }28'$ is perhaps the most famous and striking result in the field of surface waves. We solve the linear ship wave problem in the presence of a shear current of constant vorticity $S$, and show that the Kelvin angles (one each side of wake) as well as other aspects of the wake depend closely on the ‘shear Froude number’ $\mathit{Fr}_{\mathit{s}}=VS/g$ (based on length $g/S^2$ and the ship’s speed $V$), and on the angle between current and the ship’s line of motion. In all directions except exactly along the shear flow there exists a critical value of $\mathit{Fr}_{\mathit{s}}$ beyond which no transverse waves are produced, and where the full wake angle reaches $180^\circ $. Such critical behaviour is previously known from waves at finite depth. For side-on shear, one Kelvin angle can exceed $90^\circ $. On the other hand, the angle of maximum wave amplitude scales as $\mathit{Fr}^{-1}$ ($\mathit{Fr}$ based on size of ship) when $\mathit{Fr}\gg 1$, a scaling virtually unaffected by the shear flow.

scholarly journals ANALYSIS OF ACOUSTIC ANISOTROPY PARAMETERS OF PYROXENE-MAGNETITE ROCKS OF THE PISCHANKA STRUCTURE

2020 ◽  
pp. 40-45
Author(s):  
I. Bezrodna ◽  
V. Svystov ◽  
D. Bezrodny
Keyword(s):  
Acoustic Properties ◽  
Significant Heterogeneity ◽  
Depth Range ◽  
Transverse Waves ◽  
Acoustic Anisotropy ◽  
Micro Cracks ◽  
Acoustic Tensor ◽  
Transverse Isotropic ◽  
Different Depths ◽  
The Difference

The analysis of the results of acoustic properties of rocks study of Pischans`ka iron-ore structure is presented. The aim of the work is to establish the features of the distribution of acoustic properties and parameters of acoustic anisotropy in samples of core rocks selected from the well No. 3 of the Pischans`ka structure to determine the nature of its occurrence. A sample of 35 samples from the depth range 144-273 m is divided into 3 groups of rocks, namely: magnetite-pyroxene, quartz-magnetitepyroxene and biotite-amphibole crystalline shales. Based on an invariant polarization method, a number of acoustic laboratory measurements have been carried out. The values of the measured phase velocities "quasi-longitudinal" and two "quasi-transverse" waves at the stage of measurements showed significant acoustic anisotropy of the rocks. The ranges of the measured speeds of the collection samples are 7661 ÷ 5046 m / s for longitudinal waves and 4232 ÷ 2648 m/s for transverse ones. The difference in values measured for each of the sides of the cubic rhombic dodecahedron is from 100 to 800 m / s and from 0 to 500 m/s for Vp and Vs, respectively. The parameters of an acoustic ellipsoid were calculated, on the basis of which the division of samples into 3 main groups has been performed, according to the acoustic texture: acoustically linear, shale and rhombic. Separately, a group of samples with a more complex texture was discovered. The analysis of coefficients of anisotropy by different methods is carried out: longitudinal, transverse and relative acoustic anisotropy. Most of the samples are characterized by low or average acoustic anisotropy (from 2 to 7 %). A group of highly anisotropic rocks (11–14 %), represented by samples of biotite-amphibole crystalline silicates, is singled out. According to the parameters of the acoustic tensor of most samples, the transverse isotropic type of symmetry inherent to samples from the depth intervals 174–220 m and 222–232 m, while the smaller part is rhombic, is inherent. Differences in the parameters of anisotropy of samples can be explained by the significant heterogeneity of their textures, namely: micro cracks, minerals of various sizes, shapes and orientations. The results of the research show that the acoustic properties of the samples are quite heterogeneously distributed along the investigated depth range. This indicates the difficult conditions for the formation of rocks at different depths and the presence of different types of deformations, which accompanied the formation of the Pischans`ka structure.

scholarly journals A Study on the Ship Wake Model under the Ocean Environment

2021 ◽  
Vol 24 (1) ◽  
pp. 22-30
Author(s):  
Ho Seuk Bae ◽  
Won-Ki Kim ◽  
Su-Uk Son ◽  
Woo-Shik Kim ◽  
Joung-Soo Park
Keyword(s):  
Ship Wake ◽  
Wake Model ◽  
Ocean Environment

A Note on the Design of Wake-Adapted Propellers

1980 ◽  
Vol 24 (04) ◽  
pp. 227-231
Author(s):  
Gilbert Dyne
Keyword(s):  
Vortex Theory ◽  
The Difference ◽  
Wake Model ◽  
Effective Wake ◽  
Leveling Effect

Problems associated with the design of wake-adapted propellers are illustrated by results obtained from a simple propeller and wake model. It is shown that the widely used approach of the vortex theory gives much-too-low induced axial velocities at the inner radii of the propeller, which results in too-low blade pitch ratios. The reason for this is that no regard is paid to the fact that the vorticity of the approaching flow is changed by the propeller. If this changing vorticity is introduced in the vortex theory, its shortcomings are eliminated. An effect of the improvement is that the effective wake at the propeller plane differs from the nominal wake. The difference depends upon the propeller load. The propeller is shown to have a leveling effect on a nonuniform axisymmetric nominal wake.

DIFFERENCE FREQUENCY HARMONIC ION HEATING

1967 ◽  
Vol 45 (5) ◽  
pp. 1771-1781 ◽  
Author(s):  
C. R. James ◽  
W. B. Thompson
Keyword(s):  
High Frequency ◽  
Collision Frequency ◽  
Difference Frequency ◽  
Fourth Power ◽  
Heating Process ◽  
Ion Heating ◽  
Frequency Signal ◽  
Transverse Waves ◽  
The Difference ◽  
Frequency Harmonic

The heating of a magnetized hot diffuse plasma using the difference frequency signal generated from two high-frequency (35 GHz) transverse waves is examined. The plasma is described by the cold plasma model and a series expansion of harmonics is used to obtain a solution to the equations. It is shown that the energy absorbed by the ions can be made inversely proportional to the collision frequency and the fourth power of the driven frequency and proportional to the fourth power of the driven electric field intensity. An investigation of the sensitivity of the heating process to fluctuations in frequency, density, and d-c. magnetic field is carried out.

scholarly journals Observation of surface wave patterns modified by sub-surface shear currents

2019 ◽  
Vol 873 ◽  
pp. 508-530 ◽  
Author(s):  
Benjamin K. Smeltzer ◽  
Eirik Æsøy ◽  
Simen Å. Ellingsen
Keyword(s):  
Surface Wave ◽  
Empirical Support ◽  
Surface Flow ◽  
Recent Theory ◽  
Transient Effects ◽  
Surface Shear ◽  
Ship Waves ◽  
Shear Current ◽  
Wave Patterns ◽  
Good Agreement

We report experimental observations of two canonical surface wave patterns – ship waves and ring waves – skewed by sub-surface shear, thus confirming effects predicted by recent theory. Observed ring waves on a still surface with sub-surface shear current are strikingly asymmetric, an effect of strongly anisotropic wave dispersion. Ship waves for motion across a sub-surface current on a still surface exhibit striking asymmetry about the ship’s line of motion, and large differences in transverse wavelength for upstream versus downstream motion are demonstrated, all of which is in good agreement with theoretical predictions. Neither of these phenomena can occur on a depth-uniform current. A quantitative comparison of measured versus predicted average phase shift for a ring wave is grossly mispredicted by no-shear theory, but in good agreement with predictions for the measured shear current. A clear difference in wave frequency within the ring wave packet is observed in the upstream versus downstream direction for all shear flows, while wave dispersive behaviour is identical to that for quiescent water for propagation normal to the shear current, as expected. Peak values of the measured two-dimensional Fourier spectrum for ship waves are shown to agree well with the predicted criterion of stationary ship waves, with the exception of some cases where results are imperfect due to the limited wavenumber resolution, transient effects and/or experimental noise. Experiments were performed on controlled shear currents created in two different ways, with a curved mesh and beneath a blocked stagnant-surface flow. Velocity profiles were measured with particle image velocimetry, and surface waves with a synthetic schlieren method. Our observations lend strong empirical support to recent predictions that wave forces on vessels and structures can be greatly affected by shear in estuarine and tidal waters.

Development of a representative operation cycle characterized by dual time series for bulldozers

2017 ◽  
Vol 231 (13) ◽  
pp. 1818-1828 ◽  
Author(s):  
Baodi Zhang ◽  
Xin Zhang ◽  
Lihe Xi ◽  
Chuanyang Sun
Keyword(s):  
Fuel Consumption ◽  
Probability Distributions ◽  
Kinematic Model ◽  
Substantial Effect ◽  
Area Network ◽  
Driving Cycles ◽  
Operating Process ◽  
The Difference ◽  
Operation Cycle ◽  
Two Parameters

Driving cycles have been developed for various types of vehicle by different nations and in different areas, as they have a substantial effect on analysis of the fuel economy and the emissions. As the concern about the fuel consumption and the emissions of engineering machinery increases continuously, it has become necessary to develop corresponding operation cycles for engineering machinery. However, a typical operation cycle for bulldozers and the methods for its development is still lacking. Therefore, a representative operation cycle for bulldozers was developed in this study. By taking advantage of readily available data from the Controller Area Network (CAN), large amounts of cycle experimental data were acquired in a typical bulldozing process. Two parameters, namely the bulldozing resistance and the speed, were employed to represent the operation cycle. The values of these parameters were calculated on the basis of the dynamic model and the kinematic model combined with system identification methods. Experimental cycles were divided into operation segments according to the respective operating processes, and characteristic parameters for the operation segments were chosen and calculated accordingly. The optimal representative operation cycle was finally selected on the basis of the smallest Mahalanobis distance. The fuel consumption and the probability distributions of the representative operation cycle were also compared with the average fuel consumption and probability distributions of all the operation cycles and analysed. The average correlation coefficient of the probability distributions was 0.936, whereas the difference in the fuel consumptions was only 1.786%. This indicates that the developed cycle is indeed appropriate for representing the operating process of the bulldozer.

scholarly journals Effect of manual reduction and indirect decompression on thoracolumbar burst fracture: a comparison study

2020 ◽  
Author(s):  
Jian Huang ◽  
Limin Zhou ◽  
Zhaodong Yan ◽  
Zongbo Zhou ◽  
Xuejian Gou
Keyword(s):  
Burst Fracture ◽  
Wedge Angle ◽  
Control Group ◽  
Thoracolumbar Burst Fracture ◽  
Manual Reduction ◽  
Significant Difference ◽  
Indirect Decompression ◽  
The Difference ◽  
Experimental Group

Abstract Study designRetrospective cohort study.ObjectiveTo evaluate the effect of manual reduction and indirect decompression on thoracolumbar burst fracture.Methods60 patients with thoracolumbar burst fracture who were hospitalized from January 2018 to October 2019 were selected and divided into experimental group (33 cases) and control group (27 cases) according to different treatment methods. The experimental group was treated with manual reduction and indirect decompression, while the control group was not treated with manual reduction. The operation time and intraoperative blood loss were recorded. VAS score was used to evaluate the improvement of pain. The anterior height of injured vertebra, wedge angle of injured vertebral body, encroachment ratio of injured vertebral canal were used to evaluate spinal canal decompression and fracture reduction. JOA score was used to evaluate the improvement of spinal function.ResultsThere was no significant difference in operation time and intraoperative blood loss between the two groups. Compared with the control group, the VAS score and the wedge angle of injured vertebral body of the experimental group on 3 days after operation and the last follow-up were significantly lower than that of the control group, and the difference was statistically significant. The ratio of anterior height of injured vertebra of the experimental group on 3 days after operation and the last follow-up were significantly higher than that of the control group, and the difference was statistically significant. The difference of the encroachment ratio of injured vertebral canal between preoperation and 3 days after operation was significantly higher than that of the control group, and the difference was statistically significant. The bladder function of JOA on 3 days after operation of the experimental group was significantly higher than that of the control group, and the difference was statistically significant. And the rest aspect of JOA on 3 days after operation and last follow-up of the experimental group were no significant difference Compared with the control group.ConclusionManipulative reduction and indirect decompression can obtain better clinical effect in the treatment of thoracolumbar burst fractures.

scholarly journals Structural and kinematic analysis of a stirred tank planetary drive

2018 ◽  
Vol 226 ◽  
pp. 01012 ◽  
Author(s):  
Alexander A. Prikhodko
Keyword(s):  
Kinematic Model ◽  
Planetary Gear ◽  
Output Shaft ◽  
Mixing Efficiency ◽  
Reciprocating Motion ◽  
Stirred Tanks ◽  
Input Shaft ◽  
Variable Transmission ◽  
The Difference ◽  
Physical And Chemical

Stirred tanks are used in many industries to intensify various physical and chemical processes. Currently, one of the most promising areas of research is the creation of rotationally reciprocating stirred tanks (RRST), which realize high mixing efficiency due to the difference in the velocities of the stirred liquid. As the actuator of RRST, we proposed to use a planetary gear with elliptical gears. Due to the variable transmission ratio of elliptical gearwheels, the rotationally reciprocating motion of the output shaft is ensured with rotational motion of the input shaft. We conducted a structural analysis of the planetary gear by means of the structural mathematical model of mechanisms and machines. A kinematic model of planetary gear has been constructed and studied, resulting in velocity analogue function of the mechanism output shaft.

Effect of Anisotropic Shape on Ship Wakes in Presence of Shear Current of Uniform Vorticity

2016 ◽  
Author(s):  
Yan Li ◽  
Simen Å. Ellingsen
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Ship Waves ◽  
Aspect Ratios ◽  
Asymptotic Expressions ◽  
Shear Current ◽  
Ship Wakes ◽  
Surface Disturbance ◽  
Dimensional Shape ◽  
Three Dimensional Shape

We analyze the interactions between a subsurface shear current of uniform vorticity and a moving surface disturbance of anisotropic shape which generates surface gravity waves. The problem extends previous analysis of ship waves in the presence of a shear current varying linearly with depth, now also accounting for the three dimensional shape of real ships, in order to study the interplay of aspect ratio and the shear current. Based on general solutions derived previously, we apply an elliptical Gaussian pressure disturbance at the surface moving at constant velocity as a model for a real “ship”. Wave contributions in the far field and expressions for the Mach angle (of maximum wave amplitude) based on asymptotic expressions for high Froude numbers, are derived thereafter. Through numerical calculations we present wave patterns, as well as Kelvin and Mach angles, at moderate Froude numbers under different shear strenghts and aspect ratios. Results show that the aspect ratio has negligible effect on the value of the critical shear vorticity and Kelvin angle, whereas a subtle interplay of aspect ratio and shear strenght is found to affect the Mach angle at moderate Froude numbers.

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