Tham khảo tài liệu 'basic coastal engineering part 2', kỹ thuật - công nghệ, kiến trúc - xây dựng phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 24 Basic Coastal Engineering A wave propagating through a porous structure for example where the water depth is the same on both sides of the structure will have the same period and wave length on both sides. Thus a reduction of wave energy because of reflection from the structure and viscous dissipation within the structure will result in a decrease in the wave height. A 50 reduction in wave energy would result in only a 29 decrease in the wave height because the wave energy is proportional to the wave height squared. Both the kinetic and potential energies are variable from point to point along a wave length. However a useful concept is the average energy per unit surface area given by E fgH- E - L1 iT 2 36 This is usually known as the energy density or specific energy of a wave. Equations and apply for deep to shallow water within the limits of the small-amplitude wave theory. Wave Power Wave power P is the wave energy per unit time transmitted in the direction of wave propagation. Wave power can be written as the product of the force acting on a vertical plane normal to the direction of wave propagation times the particle flow velocity across this plane. The wave-induced force is provided by the dynamic pressure total pressure minus hydrostatic pressure and the flow velocity is the horizontal component of the particle velocity. Thus p - T Ị J p rgz udzdt where the term in parentheses is the dynamic pressure. Inserting the dynamic pressure from Eq. and the horizontal component of velocity from Eq. and integrating leads to P - PgH2L 2kd 16T V sinh2kdj or P - 4 1 2-37 2T sinh 2kd Letting n - 1 1 j 2-3S 2 sinh 2kd Two-Dimensional Wave Equations and Wave Characteristics 25 Equation becomes nE T The value of n increases as a wave propagates toward the shore from in deep water to in shallow water. Equation indicates that n can be interpreted as the fraction of the mechanical energy in a wave that is transmitted forward each .
