Unified Wind Wave Growth and Spectrum Functions for All Water Depths: Field Observations and Model Results

Wind wave development is governed by the fetch- or duration-limited growth principle that is expressed as a pair of similarity functions relating the dimensionless elevation variance (wave energy) and spectral peak frequency to fetch or duration. Combining the pair of similarity funtions the fetch or duration variable can be removed to form a dimensionless function of elevation variance and spectral peak frequency, which is interepreated as the wave enegry evolution with wave age. The relationship is initially developed for quasi-neural stability and quasi-steady wind forcing conditions. Further analyses show that the same fetch, duration, and wave age similarity functions are applicable to unsteady wind forcing conditions, including rapidly accelerating and decelerating mountain gap wind episodes and tropical cyclone (TC) wind fields. Here it is shown that with the dimensionless frequency converted to dimensionless wavenumber using the surface wave dispersion relationship, the same similarity function is applicable in all water depths. Field data collected in shallow to deep waters and mild to TC wind conditions, and synthetic data generated by spectrum model computations are assembled to illustrate the applicability. For the simulation work, the finite-depth wind wave spectrum model and its shoaling function are formulated for variable spectral slopes. Given wind speed, wave age, and water depth, the measrued and spectrum-computed significant wave heights and the associated growth parameters are in good agreement in forcing conditions from mild to TC winds and in all depths from deep ocean to shallow lake.

Dynamic Behavior Study of Functionally Graded Porous Nanoplates

This paper introduces the analytical solutions of complex behavior analysis utilizing high-order shear deformation plate theory of functionally graded FGM nano-plate content consisting of a mixture of metal and ceramics with porosity. To incorporate the small-scale effect, the non-local principle of elasticity is used. The impact of variance of material properties such as thickness-length ratio, aspect ratio, power-law exponent and porosity factor on natural frequencies of FG nano-plate is examined. Compared to those achieved from other researchers, the latest solutions are. Using the simulated displacements theory, equilibrium equations are obtained. Current solutions of the dimensionless frequency are compared with those of the finite element method. The effect of geometry, material variations of nonlocal FG nano-plates and the porosity factor on their natural frequencies are investigated in this review. The results are in good agreement with those of the literature.

Unsteady cavities near the hydrofoil with a small aspect ratio

Using digital processing of high-speed visualization data on a cavitation flow near NACA hydrofoil with critically low aspect ratio, the frequencies of the formation and separation of cavities in the flow are identified. It is shown that in the case of development of cloud cavitation the main dimensionless frequency varies within 0.4, which corresponds to the type of internal instability. The Strouhal number corresponds to the frequency of attached cavity occurrence and varies in range from 0.6 to 0.8. The Strouhal numbers calculated in third mode exceed 1. This mode corresponds to the forming of very small cavities near the leading edge of hydrofoil.

Impedance of Inner Saturated Soil to Horizontally Vibrating Large-Diameter Pipe Piles

An analytical solution for the inner soil impedance of saturated soil to a horizontally vibrating large-radius pipe pile was presented. Based on the porous media theory and the assumption that the vertical normal stress is zero, the closed solution of the inner soil impedance of the saturated soil to the movement of the large-diameter pipe pile is obtained. This analytical solution considers the influence of saturated soil parameters on the impedance of the core soil of large-diameter pipe piles. Through numerical examples, the variation law of the inner soil impedance with pile radius, pile length, dimensionless frequency, compression coefficient, effective permeability coefficient, and porosity was analyzed and the pile radius corresponding to effective inner soil impedance is determined.

Thermal Analysis of Solid/Liquid Phase Change in a Cavity with One Wall at Periodic Temperature

In this study, heat transfer in a square cavity filled with a Phase Change Material (PCM) under a sinusoidal wall temperature during solidification and melting is analyzed. All surfaces of the cavity are insulated except one surface, which is under the sinusoidal temperature change. The governing equations and boundary conditions are made dimensionless to reduce the number of governing parameters into two as dimensionless frequency and Stefan number. The governing equations were solved numerically by using Finite Volume Method for a wide range of Stefan number (0.1 < Ste < 1.0) and dimensionless frequency (0.23 < < 2.04). Based on the obtained results, a chart in terms of Stefan number and dimensionless frequency is obtained to divide the heat transfer process in the cavity into three regions as uncompleted, completed, and overheated phase-change processes. For the uncompleted process, some parts of the cavity are inactive, and no phase change occurs in those parts of the cavity during the melting and freezing process. For the overheated phase change, the temperature of the cavity highly increases (or decreases), causing the sensible heat storage to compete with latent thermal storage. In the completed process, almost all thermal storage is done by the utilization of latent heat. The suggested graph helps thermal designers to avoid wrong designs and predict the type of thermal storage (sensible or latent) in the cavity without doing any computations.

Electrokinetic energy conversion of electro-magneto-hydro-dynamic nanofluids through a microannulus under the time-periodic excitation

In this work, the effects of externally applied axial pressure gradients and transverse magnetic fields on the electrokinetic energy conversion (EKEC) efficiency and the streaming potential of nanofluids through a microannulus are studied. The analytical solution for electro-magneto-hydro-dynamic (EMHD) flow is obtained under the condition of the Debye-Hückel linearization. Especially, Green’s function method is used to obtain the analytical solutions of the velocity field. The result shows that the velocity distribution is characterized by the dimensionless frequency Ω, the Hartmann number Ha, the volume fraction of the nanoparticles φ, the geometric radius ratio a, and the wall ζ potential ratio b. Moreover, the effects of three kinds of periodic excitations are compared and discussed. The results also show that the periodic excitation of the square waveform is more effective in increasing the streaming potential and the EKEC efficiency. It is worth noting that adjusting the wall ζ potential ratio and the geometric radius ratio can affect the streaming potential and the EKEC efficiency.

DESIGN OF THE BOUNDARIES OF THE STABILITY REGIONS THE STATIONARY ROTATION MODE OF A ROTARY SYSTEM WITH A LIQUID, THE AXLE OF WHICH IS LOCATED IN ANISOTROPIC FIXINGS

Earlier, the authors generalized the original method for studying the stability of stationary rotation of rotor systems containing a viscous incompressible fluid, the axis of which is located in isotropic anchors, in the case when the viscoelastic anchors of the axis of the rotor system are anisotropic. The generalization is based on two theorems that say that finding the stability conditions of such systems is associated with the possibility of elliptical precession-type motion, and with such motion there is a special non-inertial reference frame in which the hydrodynamic elements of the system periodically change in time. The study of such movements allows us to construct the boundaries of regions with different degrees of instability, in particular, the boundaries of the stability regions of the stationary rotation regime in the parameter space of the problem. The boundaries of the stability regions are constructed for cases when the anchoring of the rotor axis is anisotropic. In the space of the anchorage parameters, a parametrically defined D-curve is obtained as a function of the dimensionless frequency of the rotor precession. The two most interesting cases are considered – anisotropic stiffness of anchors (damping is isotropic in this case) and the opposite situation: isotropic stiffness of anchors with anisotropic damping. The obtained results are compared with the known results for the case of isotropic anchoring of the rotor axis. It is shown that the anisotropy of anchors, which is always present in real rotary systems due to the imperfection of technologies for the production of anchors, does not lead to negative effects. Moreover, using the obtained D-curves, it is possible to obtain technological tolerances for the production of fasteners, using what is known as the permissible deviation of the stiffness or damping value along the axes.

Nonlinear ultrasonic waves in a magneto-flexo-thermally actuated single walled armchair carbon nanotube embedded on polymer matrix

Purpose The purpose of this paper is concerned with the study of nonlinear ultrasonic waves in a magneto-flexo-thermo (MFT) elastic armchair single-walled carbon nanotube (ASWCNT) resting on polymer matrix. Design/methodology/approach A mathematical model is developed for the analytical study of nonlinear ultrasonic waves in a MFT elastic armchair single walled carbon nanotube rested on polymer matrix using Euler beam theory. The analytical formulation is developed based on Eringen’s nonlocal elasticity theory to account small scale effect. After developing the formal solution of the mathematical model consisting of partial differential equations, the frequency equations have been analysed numerically by using the nonlinear foundations supported by Winkler-Pasternak model. The solution is obtained by ultrasonic wave dispersion relations. Findings From the literature survey, it is evident that the analytical formulation of nonlinear ultrasonic waves in an MFT elastic ASWCNT embedded on polymer matrix is not discussed by any researchers. So, in this paper the analytical solutions of nonlinear ultrasonic waves in an MFT elastic ASWCNT embedded on polymer matrix are studied. Parametric studies is carried out to scrutinize the influence of the nonlocal scaling, magneto-electro-mechanical loadings, foundation parameters, various boundary condition and length on the dimensionless frequency of nanotube. It is noticed that the boundary conditions, nonlocal parameter and tube geometrical parameters have significant effects on dimensionless frequency of nanotubes. Originality/value This paper contributes the analytical model to find the solution of nonlinear ultrasonic waves in an MFT elastic ASWCNT embedded on polymer matrix. It is observed that the increase in the foundation constants raises the stiffness of the medium and the structure is able to attain higher frequency once the edge condition is C-C followed by S-S. Further, it is noticed that the natural frequency is arrived below 1% in both local and nonlocal boundary conditions in the presence of temperature coefficients. Also, it is found that the density and Poisson ratio variation affects the natural frequency with below 2%. The results presented in this study can provide mechanism for the study and design of the nano devices such as component of nano oscillators, micro wave absorbing, nano-electron technology and nano-electro--magneto-mechanical systems that make use of the wave propagation properties of ASWCNTs embedded on polymer matrix.

Nonlinear magneto-thermo-elastic vibration of mass sensor armchair carbon nanotube resting on an elastic substrate

The present paper aims at studying the nonlinear ultrasonic waves in a magneto-thermo-elastic armchair single-walled (SW) carbon nanotube (CNT) with mass sensors resting on a polymer substrate. The analytical formulation accounts for small scale effects based on the Eringen’s nonlocal elasticity theory. The mathematical model and its differential equations are solved theoretically in terms of dimensionless frequencies while assuming a nonlinear Winkler-Pasternak-type foundation. The solution is obtained by means of ultrasonic wave dispersion relations. A parametric work is carried out to check for the effect of the nonlocal scaling parameter, together with the magneto-mechanical loadings, the foundation parameters, the attached mass, boundary conditions and geometries, on the dimensionless frequency of nanotubes. The sensitivity of the mechanical response of nanotubes investigated herein, could be of great interest for design purposes in nano-engineering systems and devices.

Active Control of Unsteady Cavitating Flows Over Hydrofoil

A preliminary two-dimensional (2D) numerical investigation of the active control of unsteady cavitation by means of one single synthetic jet actuator (SJA) is presented. The investigation involves the cloud-cavitating flow of water around a NACA 0015 hydrofoil with an angle of attack of 8-deg and ambient conditions. The SJA locates on the suction side at a distance of 16% of the chord from the leading edge; it has been modeled by means of a user-defined velocity boundary conditions based on a sinusoidal waveform. A Eulerian homogeneous mixture model has been used, coupled with an extended Schnerr–Sauer cavitation model and a volume of fluid interface tracking method. As first, a sensitivity analysis allowed to evaluate the influence of the main control parameters, namely, the momentum coefficient Cμ, the dimensionless frequency F+, and the jet angle αjet. As a result, the best performing SJA configuration was retrieved at Cμ=0.0002, F+=0.309, and αjet=90 deg, which led to a reduction of both the average vapor content and the average torsional load in the measure of 34.6% and 17.8%. The analysis of the coupled dynamics between vapor cavity–vorticity and their proper orthogonal decomposition (POD)-based modal structures highlighted the benefit of the SJA lies in preventing the growth of a thick sheet cavity, which causes the development of the highly cavitating cloud dynamics after the cavity breakup. This is mainly due to an additional vorticity close to the hydrofoil surface just downstream the SJA, as well as a local pressure modification close the SJA during the blowing stroke.