The sagging shape of shoreline formed on downdrift side of the structures due to seasonal oblique wave incidence

Downdrift coastal erosion has occurred at natural or man-made groynes on Korea’s eastern coast, caused by oblique high waves in winter months. The resulting shoreline planform has a sagging shape with a maximum indentation point within the eroded shoreline. This study focused on solving the frequent and severe coastal erosion problem of this type at the Jeongdongjin review of wave data over 40 years from the National Oceanic and Atmospheric Administration (NOAA), as well as analyzing shoreline monitoring images for identifying the yielding line of maximum indentation points. An analytical method was developed to verify the eroding shoreline in a sagging shape and its maximum indentation by applying the conservation principle of sediment transport and the empirical model of equilibrium shoreline. To examine how well the empirical formula is suitable for the Jeongdongjin coast, the annual directional spectrum of the observed wave data was applied to the simple diffraction wave model for the gamma breakwater, and satisfactory agreement was obtained by comparing it with the shoreline results. Breaking wave height and angle, duration, longshore sediment transport coefficient, and protruding length of the groyne were the inputs. The theoretical results are in good agreement with those of the shoreline monitoring program. The factors mitigating downdrift coastal erosion of this type were identified by applying the obtained theoretical solution, and the engineering solutions were examined via factor analysis.

Noise reduction of Parallel barrier integrated with compact flexible panel device

Erection of parallel barriers to control environmental noise such as traffic noise and construction noise is commonly seen in community. Owing to the formation of multiple reflection waves between the parallel barriers, their performance may be worse than a single barrier. To improve the performance of parallel barriers, a small piece of flush-mounted panels backed by a slender cavity in an otherwise rigid wall of barriers is proposed. With the excitation of the incident wave from a sound source inside parallel barriers, the flexible panel vibrates and sound is radiated out to undergo acoustics interference with sound field between the parallel barriers so that the sound intensity in this space and diffraction wave at the barrier top edge is reduced over a broadband in the low-frequency regime. The use of the panel provides flexibility in controlling range of stopband with high insertion loss by varying mass and bending stiffness. A semi-analytical model for dealing with vibroacoustic coupling between the open cavity and vibrating panel in a two-dimensional configuration is established in order to understand the sound suppression mechanism within the shadow zone. With the optimal structural properties of the panel, the extra averaged insertion loss of about 5dB in the frequencies ranging from 50 to 1000 Hz is reached for the parallel barrier.

Wave field reconstruction and phase imaging by electron diffractive imaging

In electron diffractive imaging, the phase image of a sample is reconstructed from its diffraction intensity through iterative calculations. The principle of this method is based on the Fourier transform relation between the real-space wave field transmitted by the sample and its Fraunhofer diffraction wave field. Since Gerchberg’s experimental work in 1972, various advancements have been achieved, which have substantially improved the quality of the reconstructed phase images and extended the applicable range of the method. In this review article, the principle of diffractive imaging, various experimental processes using electron beams and application to specific samples are explained in detail.

Moment of Wave Energy Model in Water of Finite Depth

In this work, we have consider a particular wave energy device to create electrical energy in water. The device contains a submerged cylindrical obstacle placed above a plate which is also assume as a cylindrical structure. Also the diffracted potentials are derived by applying several mathematical model for each region of the fluid. Due to continuous flow of the fluid, we have introduce a system of equation for some unknown constants which are involve in potentials expression. Finally, we derived moment of the device due to diffraction wave field and present graphically.