Regional study of mode-2 internal solitary waves in the Pacific coast of Central America using marine seismic survey data

In this paper, a regional study of the mode-2 internal solitary waves (ISWs) in the Pacific coast of Central America is carried out by using seismic reflection method. The observed relationship between the dimensionless phase velocity and the dimensionless amplitude (DA) of the mode-2 ISWs was analysed. When DA < 1, the dimensionless phase velocity increases with the increasing dimensionless amplitude, divided into two parts with different growth rates. When DA > 1, the dimensionless phase velocity increases with the increasing dimensionless amplitude at a relatively small growth rate. We suggest that the influences of seawater depth (submarine topography), pycnocline depth, and pycnocline thickness on the phase velocity of the mode-2 ISWs in the study area, cause the relationship between the dimensionless phase velocity and the dimensionless amplitude diversified. The observed relationship between the dimensionless wavelength and the dimensionless amplitude of the mode-2 ISWs was also analysed. When DA < 1 and DA > 2, the dimensionless wavelength decreases and increases with the increasing dimensionless amplitude, respectively. Additionally, the seawater depth has a great influence on the wavelength of the mode-2 ISWs in the study area, and overall the wavelength increases with the increasing seawater depth. As for the vertical structure of the amplitude of the mode-2 ISWs in the study area, we find that it is affected by the nonlinearity of the ISWs and the pycnocline deviation (especially the downward pycnocline deviation).

Asymptotic Analysis of Nonlinear Resonance Interaction of Capillary Waves of Arbitrary Symmetry on Moving Charged Jet at Multimode Initial Deformation

The problem of research of a nonlinear resonance between capillary waves on a surface of the charged jet at multimode initial deformation moving regarding the material environment is considered. It is shown in analytical asymptotic calculations of the second order on the dimensionless amplitude of oscillations that on a surface of a jet an internal nonlinear resonant interaction of capillary waves of any symmetry, both degenerate and secondary combinational, takes place. Positions of resonances depend on physical parameters of the system: the values of the coefficient of a surface tension and of the radial electric field at a surface of a jet, the velocity of its movement regarding the material environment, the values of the wave and azimuthal numbers of the interacting waves, a range of the waves defining initial deformation.

Parametric Analysis of an Energy-Harvesting Device for a Riser Based on Vortex-Induced Vibrations

An energy-harvesting device for a riser based on vortex-induced vibration is proposed to overcome the power supply problem for a marine deep-water riser-monitoring device. To estimate the upper limit of its energy-capture efficiency, as well as the weight and size of the device designed, a discrete model of the riser was configured. With the experimental settings of Stappenbelt and Blevins, vortex-induced vibrations of the discrete cylinder with two degrees of freedom were simulated, and the parameters affecting the energy-acquisition efficiency of the riser were analyzed. The analysis of the dimensionless amplitude ratio showed that this ratio for the system decreased with increasing mass ratio and damping ratio. An analysis showed that the influences of the damping ratio on the energy-capture efficiency were different under medium and low-mass-ratio conditions. A maximum value of 38.44% was achieved when the mass ratio was 2.36 and the damping ratio was 0.05.

Heat transfer behavior caused by temperature difference in reciprocating sliding contact

In order to study the heat transfer characteristics between two rough surfaces of two contacting blocks with different bulk temperatures and sliding reciprocating motion, a two-dimensional heat transfer model was used to analyze the dimensionless average heat flux, considering thermal contact conductance. The results of a series simulations were presented, covering a wide range of operating parameters including dimensionless amplitude [Formula: see text], dimensionless frequency [Formula: see text], and measurements of interface conductance [Formula: see text]. The results show that the dimensionless average heat flux increases with the increase of dimensionless frequency and amplitude, and the dimensionless average heat flux rises sharply in the low range of [Formula: see text] and approaches to a steady state approximation when [Formula: see text] and [Formula: see text].

Richtmyer–Meshkov instability of an unperturbed interface subjected to a diffracted convergent shock

The Richtmyer–Meshkov (RM) instability is numerically investigated on an unperturbed interface subjected to a diffracted convergent shock created by diffracting an initially cylindrical shock over a rigid cylinder. Four gas interfaces are considered with Atwood number ranging from $-0.18$ to 0.67. Results indicate that the diffracted convergent shock increases its strength gradually and reduces its amplitude quickly when it propagates towards the convergence centre. After the strike of the diffracted convergent shock, the initially unperturbed interface deforms with a bulge structure at the centre and two interface steps at both sides, which can be ascribed to the non-uniformity of the pressure distribution behind the diffracted convergent shock. With the decrease of Atwood number, the bulge structure becomes more pronounced. Quantitatively, the interface amplitude experiences a fast but short growing stage and then enters a linear stage. A good collapse of the dimensionless amplitude is found for all cases, which indicates a weak dependence of the growth rate on Atwood number in the deformed shock-induced RM instability. Then the impulsive theory is modified by eliminating the Atwood number and considering the geometry convergence, which well predicts the amplitude growth for the deformed shock-induced RM instability. Finally, the underlying mechanism is decoupled into three parts, and it is found that both the impulsive pressure perturbation and the geometry convergence promote the growth of interface perturbation while the continuous pressure perturbation inhibits the growth. As the Atwood number decreases, the impulsive perturbation plays an increasingly important role, which suggests that the impulsive perturbation dominates the deformed shock-induced RM instability at the linear stage.

Об устойчивости сильно заряженной капли, подвешенной в суперпозиции гравитационного и электростатического полей

For strongly charged drop suspended in a fixed status in superposition gravitational and electrostatic fields, critical conditions of realization of its instability in relation to own and induced charges are found. All calculations are carried out in the fourth order of smallness on value of stationary deformation of spherical shape of a drop and first order on the dimensionless amplitude of its capillary oscillations. Dependences of values of critical parameters of Rayleigh and Taylor on radius, density, coefficient of surface tension, acceleration of the field of gravity and from number of a mode of oscillations, other than those for the free drop are found. With increase mode number the critical value of parameter of Rayleigh grows and comes to an asymptotic , and the critical value of Taylor parameter decreases and comes to an asymptotic . The specified changes and are explained by existence of a condition of immobility of the center of masses in a suspension connecting , and acceleration of the field of gravity.

For an incompressible lubricant in the bearing sliding surfaces of the spherical segments with the adjusted surfaces

A mechanism consisting of a deformable surface and a gear unit with a curve is considered. An incompressible viscous liquid is applied to the surface. The gear unit rotates or moves along the surface. Under the influence of the load, the gear unit can deform the surface. Such a mechanism can be considered as a sliding bearing. Using the tensor analysis apparatus, it is proved that in all cases a thin layer of incompressible lubricant is formed. The results of the following studies are presented: The effect of the lubricant with harmonic oscillations of the gear unit is normal to the surface. With the harmonic oscillations of the gear unit, the velocity distribution of the liquid in a thin liquid layer depends only on the dimensionless amplitude of the oscillations. The incompressible fluid flows out beyond the edges of the gear unit when the thickness of the layer (the movement of the tooth to the surface) decreases between it and the surface and flows from outside with the increasing thickness (removing the tooth from the surface). The appearance of the bearing capacity of such a mechanism is associated with the forces of friction and inertia inside the fluid.

Structure Optimization of a Vibration Suppression Device for Underwater Moored Platforms Using CFD and Neural Network

We only consider the underwater mooring platform (UMP) and the plate moving in the transverse direction, and the plate can be relative to the UMP free rotation. In the case of constant flow rate (U=1 m/s), the effect of different dimensionless plate length (Lp/D) and damping value (c) on the UMP was studied. We get the sample data point set by computational fluid dynamics (CFD) simulation with changing the dimensionless plate length (Lp/D=0.3, 0.5, 0.75, 1.0, 1.25, 1.5) and damping value (c=50, 75, 100, 125, 175, 250, 300 (N × s/m)). The optimal value of the vibration suppression rate is obtained by backpropagation (BP) neural network and genetic algorithm. The optimal vibration suppression rate is Py=0.9878 and the corresponding variable value is Lp/D=1.0342, c=57.9631 (N × s/m). In order to verify the accuracy of the optimization, we perform the CFD numerical simulation with the optimized parameters and compare the theoretical optimization results with the CFD simulation result. The absolute error between CFD simulation and optimal Py is only 0.0037. Finally, we compare the results of CFD simulation based on optimal parameter with the bare UMP and analyze their dimensionless amplitude, wake structure, and lift coefficient. It is shown that BP neural network and generic algorithm are effective.

Isothermal Rectangular Roughness Elements in a Rectangular Cavity Heated at Bottom

The purpose of the present research was to explore the role of rectangular roughness elements during natural convection in a two-dimensional rectangular cavity. The computational algorithm was developed based on the single relaxation time Bhatnagr-Gross and Krook (BGK) model of lattice Boltzmann method (LBM). Rectangular roughness elements were located on the horizontal walls. The computational algorithm was validated against benchmark studies using different numerical techniques, and a good agreement was found to exist. The range of the Rayleigh (Ra) number was explored from 103 to 106 for a Newtonian fluid of Prandtl number equal to 1.0. The dimensionless amplitude (h/H) of roughness elements was fixed to 0.1, while the spacing between these elements was equal to twice their height. The maximum reduction in the average heat transfer was calculated to be 27 percent at Ra number 1×106.