Masaki Sawamoto

Experiments on transition to turbulence in an oscillatory pipe flow

Experiments on transition to turbulence in a purely oscillatory pipe flow were performed for values of the Reynolds number R δ , defined using the Stokes-layer thickness δ = (2ν/ω) ½ and the cross-sectional mean velocity amplitude U, from 19 to 1530 (or for values of the Reynolds number R e , defined using the pipe diameter d and U , from 105 to 5830) and for values of the Stokes parameter λ = ½ d (ω/ 2ν ) ½ ( ν = kinematic viscosity and ω = angular frequency) from 1·35 to 6·19. Three types of turbulent flow regime have been detected: weakly turbulent flow, conditionally turbulent flow and fully turbulent flow. Demarcation of the flow regimes is possible on R λ , λ or R e , λ diagrams. The critical Reynolds number of the first transition decreases as the Stokes parameter increases. In the conditionally turbulent flow, turbulence is generated suddenly in the decelerating phase and the profile of the velocity distribution changes drastically. In the accelerating phase, the flow recovers to laminar. This type of partially turbulent flow persists even at Reynolds numbers as high as R e = 5830 if the value of the Stokes parameter is high.

Regionalization of lumped water balance model parameters based on multiple regression

This study establishes a method for evaluating the coefficients of tank model. First, the model coefficients were optimized using the Standardized Powell Method at 12 watersheds. Then 16 characteristics were derived from geographical information on topography, soil type, geology, and land-use of the basins. Finally, a multiple linear regression model was applied to the relationship between the model coefficients and the basin characteristics. Trial application of the regression equations worked successfully at two different watersheds, suggesting that the coefficients of the tank model could be evaluated based solely on the geographical characteristics of the basin.

Assessment of water conflict in Mae Chaem River Basin, Northern Thailand

For this study, we conducted a quantitative water resources assessment of the Mae Chaem River Basin, Thailand, an area with dry season water scarcity and water use conflicts between upstream and downstream inhabitants. The block-wise TOPMODEL with the Muskingum–Cunge flow routing method (BTOPMC) was used to predict run-off in 21 sub-basins and Geographic Information System (GIS) was employed to collect information for crop water demand evaluation. Four sub-basins exhibited critical water conditions in 2000. The conversion of forestlands into agricultural lands during the past decade has engendered water scarcity in the dry season and flooding in the wet season.

INTERACTIONS BETWEEN A SAND BARRIER AND FLOOD TERRACE AT THE ABUKUMA RIVER MOUTH

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

Topography Change Due to Floods and Recovery Process at the Abukuma River Mouth

ABSTRACTThe river mouth process is investigated for the Abukuma River which drains into the Pacific Ocean. Firstly, a topography change process of long time scales is discussed by analyzing maps si...

MEASUREMENTS OF TURBULENCE OVER VORTEX-RIPPLE

The cost of many coastal projects is often increased by the expensive beach repair and maintenance required to remedy the destabilising effects of structures on the adjoining coastline. Physical and/or mathematical models have been developed for use in planning these projects in order to predict and quantify the effects of marine sediment transport on the coastal topography. Such models need to be calibrated against prototype data and one method of gauging volumetric sediment movement is by successive bathymetric/ topographic profiting surveys which are performed seasonally and annually. Since large quantities of sediment are related to small changes in bed elevation it is clear that this profiling needs to be done with the utmost precision* The areas most affected extend from the beach through the surf zone to water depths of about 25 metres. The surf zone in particular is a dynamic and hostile area which falls outside the traditional activities of both the hydrographic and land surveyors. Consequently innovative methods, deficient in sound survey principle and practice, have often been pursued in this area without any attempt being made to assess the tolerance on the data. This paper attempts to show that it is possible to produce reliable and verifiable results to the required accuracy by using conventional survey equipment and techniques, also by taking the necessary precautions against the many possible sources of survey error. The procedures and techniques described have evolved from NRIOs involvement over the past decade in major projects at Richards Bay, Durban, Koeberg and in False Bay. The results of a recent verification investigation are fully reported in this paper.Besides wave impact forces, erosion of the inner side of a sea dike is a serious cause of destruction. Therefore, wave run-up and overtopping effects have to be considered with respect to the safety of a dike. Strong relations were found between both these influences (TAUTENHAIN et.al., 1980, 1981, 1982), based on experiments in a wave flume and using an energy conservation concept. However, under natural conditions, an oblique wave approach has to be considered. This paper deals with the influence of wave direction on wave runup on a smooth dike slope in order to provide a basis for calculating the overtopping rates for both regular and irregular waves.This paper describes a study carried out at Port Taranaki, New Plymouth, New Zealand to determine ships track and motions at the port entrance. The results of the study being used to establish the extent (plan area) and optimum depth of proposed capital dredging works. The time lapse photographic technique, incorporating reference levels and bearings in each frame, used to record vessels entering and leaving the port is described, Maximum increases in ships draft due to sea conditions are given.N.S.L. program is a finite-difference code for two dimensionnal flows with a free surface in a vertical plane. Basic equations are Navier-Stokes Equations with a simple simulation of turbulent effects by an eddy viscosity coefficient related to the mixing length and the mean velocity gradient. Theses equations are solved in a variable domain in time. The main features of the numerical method are presented. Some comparisons with theoretical solutions give a good validation of the code both in linear and non linear cases. Other examples of application are given.The design of the coal unloading terminal in an unprotected environment created the need to develop design criteria as well as operational and structural systems that will respond toproblems arising from unloading bulk in the open sea. As there was no known precedent of an unprotected unloading terminal, the criteria was based on experience in existing offshore loadina terminals, laboratory tests and engineering judgement.A large number of man-made tidal swimming pools (two examples are shown in Figure 1) exist along the South African coast. They are usually situated on rocky outcrops in the close vicinity of popular sandy bathing beaches to provide protected bathing conditions in these areas mainly for children and elderly people. Some tidal pools, especially along rocky coast, provide the only safe bathing facilities. Besides affording protection against waves and surfzone currents the pools provide protection from sharks. A large number of tidal pools were built during the early 1950s along the Natal South Coast after the occurrence of a relatively large number of shark attacks on bathers on that coast. The semi-diurnal tide with a range of about 1,5 m along the South African coast makes it possible for pools to be built such that water replenishment can occur during every high-water (approximately every 12 hours) during both neap and spring tide periods. Presently, there exists a great need for more tidal pools as part of the demand for more recreational facilities along the South African coast. However, no information on design criteria could be found in the literature.The objective of this research is to study the prediction method of hurricane waves around this island, especially in the Taiwan Strait. The paper describes the prediction of hurricane waves used by Bretchneiders (1976) Method and finds out the predicted waves are different from measured waves, therefore the Bretchneider predicted model is modified by the authors and then the modified model is applied to predict waves again. It is found out that predicted waves match well with the measured waves. The results of the modified Bretchneider model are compared with those of the Ijima tracing method and find out the former is better than the latter. The second part is to apply the modified model to predict the extreme value of wave heights and compute the worse hurricane wave condition of the surrounding sea area around island, within recent score year (1959-1978). The calculated sites are Chu-Wei, Nan-Liaw, Ta-Shih, Cheng-Kung, Pu-Tai, Tung-Kang, Nan-Wan as shown in Fig.1 and Shiau Liu- Chieu totally 8 stations. Then use the Gumbel Distribution TYPE 1 to predict the extreme wave height of each returned period.In the design and construction of waterfront bulkhead systems, it is essential to consider the coastal effects of tides, waves, boat wakes, currents, bottom sediment movement and bottom scour. Many improperly designed bulkhead systems experience severe loss of backfill and toe materials with the bulkhead eventually failing if it is not corrected in time. Inadequate drainage, joint connections, and/or inadequate toe protection are typically the causes of failure. This paper describes an investigation of a bulkhead system supporting a large waterfront development in southern California which was experiencing widespread sinkhole development in the bulkheads backfill and was on the verge of losing toe material. The objective of this investigation was to determine the extent and cause of ongoing subsurface erosion, to evaluate its effect on the bulkhead stability, and to recommend and design mitigative measures. The cause of the erosion was determined to be piping of fine grained soils due to inadequate backfill drainage. A remedial drainage scheme was designed and field-tested, and several structural repair schemes were suggested for portions of the bulkhead where accumulated damage affected the integrity of the structure.

RESPONSE CHARACTERISTICS OF RIVER MOUTH TOPOGRAPHY IN WIDE TIME SCALE RANGE

A special reflecting wall 12 m long and 2.1 m high was built off the beach at Reggio Calabria, and 30 wave gauges were assembled before the wall and were connected to an electronic station on land. It was possible to observe the reflection of wind waves generated by a very stable wind over a fetch of 10 Km. The experiment aimed to verify the general closed solution for the wave group mechanics (Boccotti, 1988, 1989), for the special case of the wave reflection.Significant features on Wadden Sea wave climate are evaluated in respect of the state of the art. Main emphasis was laid on an analysis of the governing boundary conditions of local wave climate in island sheltered Wadden Sea areas with extensions being sufficient for local wind wave growth. Explanatory for significant wave heights a reliable parametrization of local wave climate has been evaluated by using generally available data of water level and wind measurements.

Snow area detection by using AVHRR/NOAA

Comparing the AVHRR/NOAA data with snow information on the ground, a scheme for the detection of snow covered area is discussed. The studied area is the Tohoku district, northern Japan, where 169 ground truth data points are located. Firstly, an image on 15 February 1989 is analyzed in detail. A scheme of snow area detection is obtained and some mismatch points are explained. Secondly, parameter change is studied from January to April 1989. It is confirmed that a set of threshold parameters varies under the influence of the solar elevation.<<ETX>>

Study on Pneumatic Wave Power Conversion System with Water Valve Rectifier

We experimentally and theoretically studied the energy conversion characteristics on a new type of wave power conversion system with water valves. The hydraulic model experiment was performed in regular waves using a nozzle as a dummy load with some parameters of submerged depth of the water valve, nozzle ratio, height of incident wave and wave period. It was proved from the experimental results that the efficiency of the water valve is equal to or higher than that of such a mechanical valve as conventional flap valves, that the influences of wave period and load change to the new system is less than to the conventional oscillating water column type wave power converter. In addition, it was confirmed that the water valve was effective as a safety system.

Sensitivity Analysis of Distributed Rainfall-Runoff Models

Two Monte Carlo based methods were applied in a mountainous watershed. The methods covered were the Generalized Likelihood Uncertainty Estimation Technique (GLUE) and the variance based Sobol’ technique. The former assess the likelihood of a model to describe a system recognizing that model and data are subject to uncertainty; the latter statistically evaluates the uncertainty in the estimation of model parameter values. Both are commonly used in model predictive uncertainty. This paper analyzed their applicability to distributed rainfall-runoff schemes. The methods were found to be complimentary: GLUE technique contributed the criteria for rejection/acceptance of behavioral models, and Sobol’ indices described the relative variance contribution of model parameters on total discharge. Bayesian updating within GLUE, and the spatial distribution of sensitivity indices were not covered, and can be the key to extend the analysis into fully distributed schemes.