Effects Of Wave Frequency Research Articles

Dynamic stress from a cylindrical inclusion buried in a functionally graded piezoelectric material layer under electro-elastic waves

This paper presents a theoretical method to investigate the multiple scattering of electro-elastic waves and dynamic stress around a subsurface cylindrical inclusion in a functionally graded piezoelectric material layer bonded to homogeneous piezoelectric materials. The analytical solutions of wave fields are expressed by employing wave function expansion method, and the expanded mode coefficients are determined by satisfying the boundary conditions around the inclusion. The image method is used to satisfy the mechanical and electrically short conditions at the free surface of the structure. Through the numerical solutions of dynamic stress concentration factors around the inclusion, it is found that when the cylindrical inclusion possesses higher rigidity and greater piezoelectric constant than the two phases of functionally graded materials, the dynamic stress around the inclusion increases greatly. When the distance between the surface of the structure and the inclusion is smaller, the effect of the properties of the inclusion becomes greater. When the cylindrical inclusion possesses lower rigidity and smaller piezoelectric constant than the two phases of functionally graded materials, the maximum dynamic stress shows little difference; however, the variation of the distribution of the dynamic stress around the inclusion is greater. The effect of the properties of the inclusion on the dynamic stress around the inclusion is greater than that on the electric field. The effects of wave frequency on the dynamic stress and electric field are also examined.

The Vibratory Response of High-Speed Catamarans to Slamming Investigated by Hydroelastic Segmented Model Experiments

Hydroelastic segmented model tests have been undertaken in head-seas to investigate the parameters affecting the whipping vibratory response of high-speed catamaran vessels subject to slamming. The first longitudinal modal frequency measured on full-scale INCAT catamaran vessels is used as a basis for predicting the flexural response frequency of the hydroelastic segmented model. Wet and dry vibration tests at zero speed are used to investigate the influence of variations in stiffness and mass of the model on the flexural bending frequency and damping ratio. The flexural frequencies are predicted using a three degree of freedom theoretical model based on measured inertias and predicted added water mass. The effects of forward speed on the whipping response of the segmented model are also investigated as well as the effects of wave frequency and wave height on the flexural response frequency. © 2009: The Royal Institution of Naval Architects.

Quasisteady state interpulse plasmas

The generation of quasisteady state plasmas in the power off phase, by short pulses [pulse duration (τp)∼0.5–1.2μs] of intense (60–100kW) microwaves in the X band (9.45GHz) is observed experimentally. The steady state is sustained from a few to tens of microseconds and depends upon the ionization processes in the interpulse phase and the characteristic diffusion length. The results are explained by a model, which considers the electron acceleration effects by the large amplitude of the field, the energy losses, and the characteristic electromagnetic field decay time. The effects of wave frequency, microwave power density, and particle diffusion on the steady state are investigated. A striking difference with conventional afterglows of pulsed discharges is pointed out.

Effects of frequency and grouted length on the behavior of guided ultrasonic waves in rock bolts

Experiments were conducted to study the behavior of guided waves in free and grouted rock bolts. Ultrasonic waves with frequencies from 25 to 100 kHz were used as excitation inputs. Tests were first conducted on free bolts to help understand the behavior of guided waves in non-grouted bolts. The effects of wave frequency and grouted length on the group velocity and attenuation of the guided ultrasonic waves were then evaluated. The test results indicated clear but different trends for the group velocity in the free and the grouted bolts. The attenuation in free bolts was not affected by bolt length and frequency. However, in grouted bolts it increased with frequency and grouted length. It was also found that the two main sources of attenuation are the setup energy loss, which has a fixed quantity for a specific type of test setup, and the dispersive and spreading energy loss which varies with frequency and bolt length.

A further study of P-wave attenuation across parallel fractures with linear deformational behaviour

When a wave propagates through fractured rock masses, it is greatly attenuated (and slowed) due to the presence of fractures. In the situation where dynamic responses are induced by a far field explosion or vibration, the magnitude of the stress wave is generally too small to mobilize nonlinear deformation of the fractures, so linear deformational behaviour is adopted in studying wave attenuation. Cai and Zhao [Effects of multiple parallel fractures on apparent wave attenuation in rock masses. Int J Rock Mech Min Sci 2000;37(4): 661–82.] used the method of characteristics to study P-wave attenuation across linear deformational fractures by considering interfracture wave reflections. However, the frequency characteristic of the incident wave (a one-cycle sinusoidal wave) was overlooked in their previous study. The present study treats the incident wave as the sum of a series of harmonic waves in the frequency domain. Results and wave phenomena in the previous study are improved and better understood. When the incident wavelength is substantially greater than fracture spacing, an equivalent medium method is developed to explain the wave phenomena in such a situation. In addition, the uncertainty of back analyzing fractured structures and the effects of wave frequency are examined. These results are in accordance with conclusions in the field of geophysics.

자유표면 아래의 타원형 실린더에 대한 비선형 운동

The motion response analysis of a submerged elliptic cylinder in waves is presented and the elliptic cylinder is a simplification of the section of submarine in this paper. The method is based on boundary integral method and two-dimensional 3 degree motions are calculated in regular harmonic waves. The fully nonlinear free surface boundary condition is assumed in an numerical domain and this solution is matched along an assumed boundary as a linear solution composed of transient Green function, The large amplitude motions of an elliptic cylinder are directly simulated and effects of wave frequency, wave amplitude and the distance from buoyancy center to gravity center are discussed.

Effect of wave frequency on the nonlinear interaction between Görtler vortices and three-dimensional Tollmien-Schlichting waves

The nonlinear interaction between Görtler vortices (GV) and three-dimensional Tollmien-Schlichting (TS) waves nonlinear interaction is studied with a spatial, nonparallel model based on the Parabolized Stability Equations (PSE). In this investigation the effect of TS wave frequency on the nonlinear interaction is studied. As verified in previous investigations using the same numerical model, the relative amplitudes and growth rates are the dominant parameters in GV/TS wave interaction. In this sense, the wave frequency influence is important in defining the streamwise distance traveled by the disturbances in the unstable region of the stability diagram and in defining the amplification rates that they go through.

The influence of wave frequency and wave height on the behaviour of rainbow trout ( Oncorhynchus mykiss) in cages

The understanding of the behaviour of fish in cages is limited, yet is important for the efficient management of farmed fish. The feeding, swimming and social activity of rainbow trout, Oncorhynchus mykiss, in two cage types (rigid-cage and bag-cage), was video-taped under various wave conditions in a large wave tank. Results indicated that the amount of time spent swimming and the number of interactions between fish were significantly positively correlated with wave frequency and height. The effect of wave frequency and height on the distance between individuals and their distribution patterns was also significantly correlated. The effect of wave frequency on all the variables was stronger than the effect of wave height, and appears to be important in modifying behaviour. The influence of wave frequency and height on swimming and social interaction was higher in the bag-cage than in the rigid-cage, probably because the rigid structure of the cage dissipated some of the wave energy which resulted in less stress on the fish.

Shortwave and microwave diathermy for deep-tissue heating

A theory is developed to describe the heating of a planary skin-fat-muscle tissue combination by electromagnetic wave diathermy. Both shortwaves and microwaves are treated. All mechanisms of heat dissipation are taken into account. The effects of wave frequency, power input, ambient conditions, vasodilation and core boundary conditions on the thermal distributions in the tissues are determined. The theoretical results agree well within vivo temperatures recorded in human thighs. It is concluded that (a) microwaves at 2450 MHz yield peak temperatures in the skin layer, a superficial heating agent, (b) 900MHz radiation has a pronounced temperature rise and the highest peak value in the musculature, most attractive for deep issue heating, and (c) shortwaves at 27·12 MHz produce a wide plateau of elevated temperature in the muscle layer using a high power intensity.