This paper shows an asymptotic expansion of Green's function for a two-layered acoustic halfspace. In general, an asymptotic expansion is able to give a brief overview for the physical phenomena at the far field from a source point by indicating the decaying factor, although, there is a difficulty to represent the asymptotic form due to the complicated modification of the wavenumber integral. In this paper, a proper modification of the wavenumber integral path is carried out to apply Watson's lemma, namely the wavenumber integration is transformed into Laplace transform. The asymptotic expansion obtained here is applicable to a generalized layered medium because of incorporating the representation of Green's function in terms of eigenvalues and takes some properties that are not found out through Green's function directly.

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The present paper proposes a macro-micro analysis to predict a possible strong motion distribution in a metropolis. The macro-micro analysis takes advantage of the singular perturbation expansion and the bounding media theory, such that required numerical computation is reduced due to the multi-scale analysis and the uncertainty of the ground and geological structures are accounted for. Hence, optimistic and pessimistic evaluation in a most high spatial and time resolution can be obtained; A prototype of a numerical code is developed. An actual earthquake is simulated, and the comparison with measured data are made. The results support the basic validity of the proposed method.

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We simulate the strong ground motion of Kobe earthquake by means of 3D finite difference method and studied the strong motion distribution and waveforms in some points. The dynamic faulting model is used in order to represent natural rupture process. Simulated distribution of maximum velocityalmost matches to that of damaged area, including Nishinomiya, and simulated waveforms in heavily damaged region have pulse like wave in common. We also executed 3D simulation including new seismic fault Akashi Kaikyo fault, which was recently revealed to have ruptured uring the Kobe earthquake, and studied its effect on the strong motion near the fault.

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The purpose of this research is to derive the spectral representation of Green's function for an acoustic layered medium by means of the concept of the Hyperfunction. The concept of the Hyperfunction used here is that the Hyperfunction is the result of the difference of the boundary values of the wave function on the spectrum in the complex wavenumber plane. The eigenfunction for the continuous spectrum is assumed to be the Hyperfunction due to Green's functi oni n the resolvent set. Green's function in the resolvent set satisfies the radiation condition, so that the definition and calculation for the energy integral for the continuous spectrum is carried out without any difficulty. As a result, the kernel of the integral for the continuous spectrum is decomposed into eigenfunctions. The decompoesd form agrees with the previous result which the author showed.

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A substructure method is introduced into the theoretical synthesis of free field ground motions resulting from the propagating seismic waves in earth crustal and surface soil layers, which originate from an extended fault rupturing. The proposed method is derived from the stiffness based formulation of the synthesis of seismic ground motions. The proposed method will make it possible to drastically reduce the high capacity computer memory that is often required in the high quality synthesis of ground motoin accelerations at frequency beyond about 1.0 Hz.

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This paper describes the method to identify the location of earthquake fault after the eventusing the records of maximum amplitude of ground accelerations. First the identification of longitude and latitude of both ends of the fault line is formulated using the method of least squares, in which attenuation equation of peak acceleration is used. Numerical analysis of identification has been carried out. Subsequently the method to evaluate the estimation error is described, and its validity as well as the effect of the number and location of records has been demonstrated by Monte Carlo Simulation. Finally, this method has been applied to 1995 Hyogoken-Nanbu eathquake.

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In this paper, it is shown that the elasto-plastic effective input energy E_ef may become a important index for dynamic collapse of a steel bridge pier modelled as a SDOF vibration system with bilinear restoring hysteretic property. Moreover, the correlation between various kinds of energy indices and the elasto-plastic dynamic response displacements is investigated. From these results, some methods to estimate the elasto-plastic dynamic response displacement from the maximum displacement and/or energy input rate in elastic analysis are considered.

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The effect of stress drop process of fault on ground motion near fault is investigated numerically by dynamic model. The shear stress on the fault is assumed to decay exponentially toward residual stress with slip after rupture multiplied by A and 1/A is used as an index of slip needed for stress drop. Resultsof calculation of the prototypic fault model (10km wide and 20km long strike slip fault with stress drop 10MPa in a homogeneous medium and constant rupture velocity) show the stress drop process has little effect on 1.5Hz low pass filtered seismic waves near fault, if the index is equal or less than 20cm. The maximum velocity on the ground surface becomes about 6% small if the index is 30cm, and about 20% small if the index is 40cm.The value of the index that has effects on ground motion is proportional to the stress drop.

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The structure design method which takes into consideration the influence of the earthquake faults on the ground has not yet been established. This is true, especially, in designing linear structures, such as roads, tunnels, and bridges. The purpose of this paper is to examine the deformation of model grounds, shear zones and bedrock stress, and to compare the position of shear zones reaching the ground surface in the model tests with the ones in the prototype. This paper presents the results of a series of laboratory model tests, in which the effects of the reverse dip-slip faults in the bedrock are measured through the aluminum rods set on the subsurface ground. The results suggest the significance of considering the deformation and stress of the ground in designing linear structures.

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The present paper deals with an effect of vertical seismic motion on soil liquefaction. A new DEM program was proposed for this study by considering an effect of vertical motions in the equation of motion. Detailed approaches of calculating the volume change of pores and excessive pore water pressure were given. The results of simulation indicated that the excess pore water pressure could rise in case of only vertical shaking. The numerical simulation made it possible to explain microscopically an effect of vertical motion on soil liquefaction. The results in this study agreed to those of the shaking table tests done by the authors.

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We propose a new simulation method for elastic deformation based on a finite difference. The most remarkable feature of this method is to combine the finite difference of the fundamental equation of elastic body with a spring-block system. We derived a procedure, called continuous cellular automaton, for calculation of deformation of spring-block system as an approximation of deformation of continuous elastic body. Using the method, we obtain final shapes of the deformed body under some conditions. The results show qualitatively good agreement with expected shapes. Because local fracturing can be corresponded to breaking of springs, this method may have a potentiality for describing fracturing.

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Three dimensional computations were performed using the KIVA-3 code to investigate the unsteady compressible turbulent flows about a practical train passing through a single-track tunnel. Both length of the traintunnel and speed of the train were considered to investigate their effects on the train-tunnel interaction. In order to understand the whole process of the train-tunnel aerodynamic interaction, we studied the formation and propagation of the pressure waves, the reflection and radiation of the waves at the tunnel portals and the histories of aerodynamic forces on the train. The experimental results were compared well with the computational data. The code can be used to predict the aerodynamic phenomena of the train-tunnel system.

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The purpose of this paper is to investigate treatments of boundary condition and modeling for a flow analysis around parallel configurated rectangular cylinders. Wind tunnel experiments that had been investigated for noises from handrail caused by wind flow using real scale lightweight handrails made by the aluminum are referred to the present computation. The flow field is assumed to be the two-dimensional incompressible viscous flow at the Reynolds number 500, and the finite element method is used for the discretization. To investigate the treatments of the domain, the number of rectangular cylinders was changed, and two types of side face boundary conditions that are periodic and slip conditions were compared

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Numerical simulations of the flow around rectangular cross-sections are carried out to examinecharacteristics of aeroacoustic sources caused by the unsteady separated shear flows around the cross-sections.The aeroacoustic sources are identified by second derivative of pressure fluctuation in the incompressible flow around the cross-sections. It is shown that the locations of the aeroacoustic sources are not necessarily corresponding to those of high pressure fluctuation. Furthermore, it is found that reattachment of the separated shear flows to the solid surface near the trailing edges has significant effects on the intensity of the aeroacoustic sources.

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Stably stratified flows past a two-dimensional hill in a channel of finite depth are analyzed numerically by using a Direct Numerical Simulation (DNS) with a third-order upwind difference scheme at Re=2000. To simulate the flow around the hill with high accuracy, a collocated grid in curvilinear coordinates is employed. Attention is focused on the occurrence of local severe winds which are induced downstream of the hill. A strong wind area with a wind speed greater than 1.29-2.21, which represents a ratio of the local streamwise wind speed to the uniform approaching one of U=1 in the non-dimensional unit, is caused by the downward flow in.the lee wave motion and is located near the first trough behind the hill. A few factors which have an effect on the generation of local severe winds are also discussed.

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In the southern part of Kyushu Island, Japan, slope failures often occur due to heavy rainfalls when it is rainy season (from June to September). The most part of slope failure are classified as the surface slip failure whose depth is commonly less than 1m. The phase change of pore-fluid in soil with the change of temperature and humidity in atmosphere should be investigated to make clear the mechanism of surface slip failure because the phase change is deeply related to the change of effective stress in soil near the surface ground. In this paper the in-situ measuring system of suction and temperature in soil is explained and the obtained measuring data are shown. Then the numerical model is proposed to simulate the mechanical behavior of unsaturated soil and then the numerical experiment is carried out to prove the validity of proposed model by using obtained data.

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A few basic studies on Direct Numerical Simulation (DNS) using upwind difference scheme and regular mesh have been executed to investigate its applicability to complex boundary and high Reynolds number flows. In this paper, one-dimensional linear advection equation was calculated by use of the upwind scheme in combination with the time marching schemes. The result showed that 5th-order accurate upwind scheme for convective term and 3rd-order Adams-Bashforth method for time stepgave the superior accuracy and stability in the combinations selected. Moreover, fully developed turbulent flows between parallel plates were analyzed to clarify the influence of different difference schemes for convective term on computational accuracy. Comparison with the spectral method proved that thehigh order upwind DNS is sufficiently accurate with respect to turbulence statistics.

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General applicability of recently-developed low-Reynolds number two-equation turbulence models using isotropic eddy viscosity, are examined by conducting calculations of flows past a backward-facing step and over a rectangular cavity in the bottom bed of open channels, by comparing with recent direct simulation results. These flows contain features of many general complex flows, such as separation and stagnation and are suited for the present purpose. Models that appropriately incorporate the low-Reynolds number effects near solid walls are found to perform fairly well in the test flows and it is expected that these simple models can further be improved to be a practical method of prediction with wide enough applicability if the effects of the Reynolds stress anisotropy can be taken into account.

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Rivers have various conditions of flows. Open channel flows with pressure gradients can be regarded as an example of those flows. Therefore to make clear turbulent structures in such flows is important to consider complex water environments. Pressure gradients are classified into adverse pressure gradients and favorable pressure gradients. In this paper, the discussion is limited on open channel flows with favorable pressure gradients. Many researches have been carried out on relaminarization and bursting phenomena in boundary layers with favorable pressure gradients. Little investigation, however, has been conducted concerning open channel flows. In this study, we have examined turbulent and coherent structures in open channel flows with different favorable pressure gradients with a laser Doppler anemometer (LDA) and hydrogen-bubble technique. The results of our experiments clealy showed that turbulent structures in open channel flows are greatly affected by the favorable pressure gradients.

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Image analysis method has come to be an efficient tool to measure turbulent flows and several commercial systems are available at present. Most of the systems utilize a particle image velocimetry (PIV) technique based on a pattern matching technique. However, the accuracy of this technique becomes not sufficient under a flow with highly shearing deformation. Thus, in this study, the particle tracking velocimetry (PTV), which has a higher spatial resolution and accuracy than PTV, is used instead for measuring mean and turbulent quantities of open-channel flows. The experiments were performed using a transparent open-channel flume having a width of 0.15m and a high-speed video camera (HAS 200R) with 200fps was used for imaging. As a preliminary experiment, velocity distribution at a longitudinal vertical section of a uniform flow was measured by two PTV techniques and their accuracy and efficiency were verified. Three-dimensional measurement was performed for the flow around a rectangular obstacle placed on one side of the channel wall. Here the three-dimensional information was obtained by combining 2-D PTV results for the laser light sheets (LLS) separately placed in seven horizontal and fourteen vertical planes. It was made clear that two and three dimensional mean and turbulent velocity fields can be obtained with a reasonable accuracy by the presented PTV procedure.

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Vegetation in a curved river is considered to influence the local flow structures and bed configuration by changing a pressure gradient and a momentum transport. In this study, three-dimensional mean flow structures were measured in curved open channels with various vegetation arrangements. Secondary flows are generated only in the region outside the vegetation zones and their strength indicates similar developing/decaying process. In order to investigate the effects of vegetation on momentum transport, two-dimensional depth-averaged momentum equations are used in an orthogonal, curvilinear coordinate system. The lateral momentum transport due to the secondary flow is modeled from an examination of the previous experimental data. The mean flow distributions and water surface profiles in curved channels with vegetation are well predicted by using this model.

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An investigation on three-dimensional turbulent structures accompanied with secondary currents and large-scale horizontal vortices in compound open-channel flows is very important in basic hydraulics as well as in river environment engineering to evaluate the friction law of the flow and sedimentransport in compound river.
In this study, secondary currents and three-dimensional (3-D) turbulent structures were experimentally revealed by making use of a fiber-optic laser Doppler anemometer (LDA). These experimental data were compared with the numerical calculations using threedimensional algebraic stress model (3-D ASM). Next, instantaneous structures were analyzed by making use of Particle-Image Velocimetry (PIV) which can measure the simultaneous velocity components at all points in laser-light-sheet (LLS). These results revealed effects of the floodplain depth on the turbulent structures in compound open-channel flows.

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Around a plate with footing in an open channel flow, vortexes separate from the edge of the plate and are carried away, and horse-shoe vortex and secondary flow can be observed. In this paper these phenomena are discussed by experimental results. The secondary flow is very strong and influences on vortex stretching of the separated vortexes. This secondary flow also has a close relation with local scour around the plate. The influence of the secondary flow on the vortex stretching is studied by flow visualization and velocity measurements. The results show that the secondary flow stretches the vortexes vertically, and makes them strong and stable. Another experiments are carried out for investigating the relation between the secondary flow and local scour in a channel with movable bed. The results show that the horse-shoe vortex is not dominant around the plate with footing, but the secondary flow is dominant there. In this case, the deepest scouring hole is formed apart from the footing.

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Recent studies have shown that a group of submerged groynes can provide a valuable habitat for fishes and macro invertebrates in addition to the function to establish a more desirable river for a flood, navigation and bank erosion.
In this study, we investigated experimentally the effects of submerged groynes on bank erosion, secondary currents and bed configuration in the cases that groynes were positioned facing upstream, downstream and normal to the main flow. The results showed that the groynes facing upstream caused minimum scour along the bank, the maximum scour depth in the main channel bed, and the groynes facing downstream led to the maximum scour along the bank, the minimum one in the main channel bed. In addition, it was found that these bed topography was determined by the momentum transport between the main flow region and submerged groynes region which was characterized by secondary currents.

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It is important in modeling of global gas circulation to predict gas transfer across the air-water interface accurately. In the previous studies, reaeration in rivers is calculated as a funcurtion of stream flow parameters, such as bed shear stress. In contrast, gas transfer rates in lake and ocean are estimated as a funcution of surface wind velocity. However, in the actual water environments, the flow condition is influenced by both the water current and the surface wind simultaneously. So, the difference about the conditions of wind-shear induced turbulence, bottom-shear induced turbulence, and combined wind/stream-shear induced turbulence are considered in this study. A laser Doppler anemometer (LDA) and DO (dissolved oxygen) meter were used to examine the influence of turbulent structures near the air-water interface on gas transfer process.

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Performance of a new water quality improvement system in a reservoir is experimentally examined by using a hydraulic model. The facility is such that anaerobic and polluted bottom water is pumped up and showered on the water surface. Although some projects of this system are running in several reservoirs, their performance are not well known. The target of this study is to find how the discharged water is transported in a reservoir and how much water quality mixing is expected to occur. In order to focus on hydrodynamics of the system, fresh and salt waters are used as working fluids to simulate warm surface water and cold bottom water, respectively.
Hydrodynamic behavior of the diffusing plume are examined based on a dimensional argument. The result would provide information in developing a high-performance system for reservoir water purification.

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