• 한국항만학회지
• /
• 제12권1호
• /
• pp.75-86
• /
• 1998

To design a coastal structure in the nearshore region, engineers must have means to estimate wave climate. Waves, approaching the surf zone from offshore, experience changes caused by combined effects of bathymetric variations, interference of man-made structure, and nonlinear interactions among wave trains. This paper has attempted to find out the effects of two of the more subtle phenomena involving nonlinear shallow water waves, amplitude dispersion and secondary wave generation. Boussinesq-type equations can be used to model the nonlinear transformation of surface waves in shallow water due to effect of shoaling, refraction, diffraction, and reflection. In this paper, generalized Boussinesq equations under the complex bottom condition is derived using the depth averaged velocity with the series expansion of the velocity potential as a product of powers of the depth of flow. A time stepping finite difference method is used to solve the derived equation. Numerical results are compared to hydraulic model results. The result with the non-linear dispersive wave equation can describe an interesting transformation a sinusoidal wave to one with a cnoidal aspect of a rapid degradation into modulated high frequency waves and transient secondary waves in an intermediate region. The amplitude dispersion of the primary wave crest results in a convex wave front after passing through the shoal and the secondary waves generated by the shoal diffracted in a radial manner into surrounding waters.

• Advances in nano research
• /
• 제13권5호
• /
• pp.465-474
• /
• 2022

Based on the nonlocal strain gradient (NSG) theory and considering the influence of moment of inertia, the governing equations of motion of porous functionally graded (FG) nanoplates with four edges clamped are established; The Galerkin method is applied to eliminate the spatial variables of the partial differential equation, and the partial differential governing equation is transformed into an ordinary differential equation with time variables. By satisfying the boundary conditions and solving the characteristic equation, the dispersion relations of the porous FG strain gradient nanoplates with four edges fixed are obtained. It is found that when the wave number is very small, the influences of nonlocal parameters and strain gradient parameters on the dispersion relation is very small. However, when the wave number is large, it has a great influence on the group velocity and phase velocity. The nonlocal parameter represents the effect of stiffness softening, and the strain gradient parameter represents the effect of stiffness strengthening. In addition, we also study the influence of power law index parameter and porosity on guided wave propagation.

• Steel and Composite Structures
• /
• 제32권2호
• /
• pp.213-223
• /
• 2019

For the first time, longitudinal and transverse wave propagation of triclinic nanobeam is investigated via a size-dependent shear deformation theory including stretching effect. Furthermore, the influence of initial stress is studied. To consider the size-dependent effects, the nonlocal strain gradient theory is used in which two small scale parameters predict the behavior of wave propagation more accurately. The Hamiltonian principle is adopted to obtain the governing equations of wave motion, then an analytic technique is applied to solve the problem. It is demonstrated that the wave characteristics of the nanobeam rely on the wave number, nonlocal parameter, strain gradient parameter, initial stress, and elastic foundation. From this paper, it is concluded that the results of wave dispersion in isotropic and anisotropic nanobeams are almost the same in the presented case study. So, in this case, triclinic nanobeam can be approximated with isotropic model.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2013년도 춘계학술대회 논문집
• /
• pp.102-107
• /
• 2013

It is important to understand the vibrating behavior of plate structures for many engineering applications. In this study, vibration characteristics of strip plates which have finite width and infinite length are investigated theoretically and numerically. The waveguide finite element approach is used in this study which is known as an effect tool for waveguide structures. WFE method requires only cross-sectional FE model and uses theoretical harmonic solutions for the wave propagation along the longitudinal direction. First of all for a simple strip plate, WFE results are compared with theoretical ones such as the dispersion diagrams, point mobilities, etc. to validate the numerical model. Then in the numerical analysis, the several different types of longitudinal stiffeners are included to the plate model to investigate the effects of the stiffeners in terms of the dispersion curves and mobilities.

• 한국대기환경학회지
• /
• 제15권6호
• /
• pp.767-777
• /
• 1999

In the coastal region air flow changes due to the abrupt change of surface temperature between land and sea. So a numerical simulation for atmospheric flow fields must be considered the correct fields of sea surface temperature(SST). In this study, we used variables such as latent heat flux, sensible heat flux, short and long wave radiation of ocean and atmosphere which exchanged across the sea surface between atmosphere and ocean model. We found that this consideration simulated the more precise SST fields by comparing with those of the observated results. Simulated horizontal SST differences in season were 2.5~4$^{\circ}C$. Therefore we simulated the more precise atmospheric flow fields and the movement and dispersion of the pollutants with the Lagrangian particle dispersion model. In the daytime dispersion pattern of the pollutants emitted from ship sources moved toward inland, in the night time moved toward sea by land/sea breeze criculation. But air pollutants dispersion can be affected by inland topography, especially Yangsan and coastal area because of nocturnal wind speed decrease.

• Advances in nano research
• /
• 제7권5호
• /
• pp.325-335
• /
• 2019

In the present study, nonlocal strain gradient theory (NSGT) is developed for wave propagation of functionally graded (FG) nanoscale plate in the thermal environment by considering the porosity effect. $Si_3N_4$ as ceramic phase and SUS304 as metal phase are regarded to be constitutive material of FG nanoplate. The porosity effect is taken into account on the basis of the newly extended method which considers coupling influence between Young's modulus and mass density. The motion relation is derived by applying Hamilton's principle. NSGT is implemented in order to account for small size effect. Wave frequency and phase velocity are obtained by solving the problem via an analytical method. The effects of different parameters such as porosity coefficient, gradient index, wave number, scale factor and temperature change on phase velocity and wave frequency of FG porous nanoplate have been examined and been presented in a group of illustrations.

• 한국소음진동공학회논문집
• /
• 제21권3호
• /
• pp.248-257
• /
• 2011

It was reported recently that railpads can be included as a continuous elastic support of the rail and the model was justified from experiments. In general, however, railpads are installed discretely on sleepers with a regular span. The effect of the discrete railpad was not clearly examined so far in such a high frequency range. In this paper, the effect of the railpads in track modelling for high frequencies is investigated by means of the finite element analysis. To do that, the railpads are regarded as 'a continuous elastic support' and 'a discrete elastic support' in this paper. The dispersion relations and decaying features are predicted and compared between the two models up to 80 kHz.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2000년도 추계학술대회 논문집
• /
• pp.196-203
• /
• 2000

In this study, the evaluation method of diffusion characteristics of Suspended Soli&SS) and the generation limit(source and thick) are investigated, which is significantly affecting on marine examined by construction works such as dredging and reclamation. Dispersion characteristics of SS is examined by hydraulic tests and numerical works in consideration with the Pusan Port. Hydraulic model test was performed in 2-D wave flume to find the limit wave conditon of re-suspension of solid as well as the time dependent characteristics of settlement The results obtainded in the study are as follows; 1) The quantituative evaluation af SS is the basic parameter of marine environmental impact assessment in related with the port development The SS increases as the water content of sea bed solid increases and the density decreases. 2) The sea bed solid in Sinsundai area, Pusan Port has the water content range of 83~157% 3) The ratio of suspension velocity against settlement velocity is about 0.25 and SS concentration converges as the wave heigh. 4) The SS increases 2 time when time step increases 3 time(10 sec to 30 sec) in numerical simulation It means that the effect of the time step should be checked in detail to stable. The diffusion The diffusion coefficient are Affiected senstively in the dispersion process while sea ved friction coefficinet have not strong relation in the simulated area

• Structural Engineering and Mechanics
• /
• 제75권4호
• /
• pp.435-444
• /
• 2020

Ultrasonic guided wave testing is a very promising non-destructive testing method for rails, which is of great significance for ensuring the safe operation of railways. On the basis of the semi-analytical finite element (SAFE) method, a analytical model of 59R2 grooved rail was proposed, which is commonly used in the ballastless track of modern tram. The dispersion curves of ultrasonic guided waves in free rail and supported rail were obtained. Sensitivity analysis was then undertaken to evaluate the effect of rail elastic modulus on the phase velocity and group velocity dispersion curves of ultrasonic guided waves. The optimal guided wave mode, optimal excitation point and excitation direction suitable for detecting rail integrity were identified by analyzing the frequency, number of modes, and mode shapes. A sinusoidal signal modulated by a Hanning window with a center frequency of 25 kHz was used as the excitation source, and the propagation characteristics of high-frequency ultrasonic guided waves in the rail were obtained. The results show that the rail pad has a relatively little influence on the dispersion curves of ultrasonic guided waves in the high frequency band, and has a relatively large influence on the dispersion curves of ultrasonic guided waves in the low frequency band below 4 kHz. The rail elastic modulus has significant influence on the phase velocity in the high frequency band, while the group velocity is greatly affected by the rail elastic modulus in the low frequency band.

• ETRI Journal
• /
• 제28권5호
• /
• pp.607-614
• /
• 2006

This paper presents a new class of microstrip slow-wave open-loop resonator filters with reduced size and improved stopband characteristics. A comprehensive treatment of both ends loaded with triangular and rectangular ends is described, leading to the invention of a microstrip slow-wave open-loop resonator. Two-resonator and four-resonator bandpass filters are designed at the operating frequency of about 2 GHz, and a bandwidth of 60 MHz. The size of the slow-wave open-loop resonator is optimized from the standpoint of the unloaded Q-factor. The filters are not only compact in size due to the slow-wave effect, but also have a wider upper stopband resulting from the dispersion effect. The filter designs of this type are described in details. The experimental results are demonstrated and discussed.