Model test of the surface and submerged vehicles with the micro-bubble drag reduction     

Sheng-Ju Wu  Cheng-Hsing Hsu  Tsung-Te Lin 《Ocean Engineering》2007,34(1):83-93

This study is based on the effective experiment observation and measuring technology to discuss the interaction influence between liquid turbulent boundary layer and a crowded group micro-bubbles. It is in order to understand and quantify the micro-bubbles clouds inside the turbulent boundary layer to eliminate the capacity of skin friction drag. Whenever the micro-bubbles are over supplied, pile up effect happened which makes micro-bubbles to integrate to each other as a large-size air film. Although they still have the drag reduction effect, the efficiency of drag reduction slowed down at this transition period. In the experiment of vertical type circulating water tunnel, when 1 μm porous medium is at 7 m/s flow speed, the C_v value at 0.056 has the best drag reduction efficiency of 26%. While 10 μm porous medium is at the same flow speed, the drag reduction efficiency is only around 23%.  相似文献   

Nonlinear wave effect on the slow drift motion of a floating body   总被引：1，自引：0，他引：1  

Takumi Ohyama  John R. C. Hsu 《Applied Ocean Research》1995,17(6):349-362

The slow drift motion of a floating body in a two-dimensional wave field has been investigated using a time-domain, fully nonlinear numerical model with non-reflective open boundaries. Preliminary computations were conducted for incident bichromatic waves, in which wave theories with different orders were applied in generating the waves required. The results show that the use of low-order theories generates undesirable free waves, and that fourth-order terms contribute markedly to low-frequency input. The motion of a rectangular floating body in response to nonlinear bichromatic waves was computed. The numerical results for small-amplitude incident waves agree reasonably well with the second-order approximation for both the steady and difference-frequency (Δσ) components in the body's motion. For relatively large waves, however, the 2Δσ component becomes predominant compared with the Δσ component. The motion of the body in irregular waves with different wave parameters has also been presented in order to discuss the validity range of a second-order approximation.  相似文献   

Coastal erosion in Eastern Black Sea Region, Turkey, by Ö. Yüksek et al.: comments     

Richard Silvester  John R. C. Hsu 《Coastal Engineering》1997,30(3-4)

  相似文献   

Trends of precipitation extreme indices over a subtropical semi-arid area using PERSIANN-CDR     

Pari-Sima?Katiraie-BoroujerdyEmail author  Hamed?Ashouri  Kuo-lin?Hsu  Soroosh?Sorooshian 《Theoretical and Applied Climatology》2017,130(1-2):249-260

In this study, satellite-based daily precipitation estimation data from precipitation estimation from remotely sensed information using artificial neural networks (PERSIANN)-climate data record (CDR) are being evaluated in Iran. This dataset (0.25°, daily), which covers over three decades of continuous observation beginning in 1983, is evaluated using rain-gauge data for the period of 1998–2007. In addition to categorical statistics and mean annual amount and number of rainy days, ten standard extreme indices were calculated to observe the behavior of daily extremes. The results show that PERSIANN-CDR exhibits reasonable performance associated with the probability of detection and false-alarm ratio, but it overestimates precipitation in the area. Although PERSIANN-CDR mostly underestimates extreme indices, it shows relatively high correlations (between 0.6316–0.7797) for intensity indices. PERSIANN-CDR data are also used to calculate the trend in annual amounts of precipitation, the number of rainy days, and precipitation extremes over Iran covering the period of 1983–2012. Our analysis shows that, although annual precipitation decreased in the western and eastern regions of Iran, the annual number of rainy days increased in the northern and northwestern areas. Statistically significant negative trends are identified in the 90th percentile daily precipitation, as well as the mean daily precipitation from wet days in the northern part of the study area. The positive trends of the maximum annual number of consecutive dry days in the eastern regions indicate that the dry periods became longer in these arid areas.  相似文献   

Cymrite: new occurrence and stability   总被引：2，自引：0，他引：2  

L. C. Hsu 《Contributions to Mineralogy and Petrology》1994,118(3):314-320

The rare mineral cymrite, BaAl₂Si₂O₈·H₂O, was discovered in Nevada in a Cambrian bedded barite sequence that exhibits low-grade metamorphism. The mineral occurs exclusively in thin-bedded siliceous rock containing anhedral pyrite crystals up to 1 cm. Cymrite forms rectangular grains ca 40 m across, distributed throughout the chalcedonic quartz matrix. An SEM image of one such blocky grain shows that it is filled by tiny aggregates, instead of a single crystal of cymrite. This cymrite may have replaced a pre-existing rectangular mineral, most likely barite. The Nevada occurrence of cymrite prompted a restudy of its stability relations. Conventional hydrothermal techniques were adopted in the experimental work with run durations up to 7 months. The univariant curve for the dehydration reaction: BaA1₂Si₂O₈· H₂O -BaA1₂Si₂O₈ +H₂O passes the following reversed brackets: 300–315° C at 3 kbar, 290–300° C at a 2 kbar, 270–285° C at 1 kbar, and 240–270° C at 0.5 kbar. These results indicate that cymrite can be stable at much lower pressures than those previously reported. The replacement of barite by cymrite was experimentally demonstrated with an alkaline solution as depicted by the reaction: BaSO₄+2OH^-+A1₂O₃-2SiO₂=BaA1₂Si₂O₈·H₂O+SO ₄ ² Such replacement failed to take place when an acidic solution was used instead.  相似文献   

Generalities on static equilibrium bays     

J.R.C. Hsu  R. Silvester  Y.M. Xia 《Coastal Engineering》1989,12(4)

Previous methods of determining the curved waterlines of bays which form on the coasts around the world have involved the logarithmic spiral. This has been applied to unstable bays which could erode back to a limit termed “static equilibrium” for which the constant in the spiral could be related to the obliquity of the wave crests to the control line, joining the upcoast headland to the downcoast extremity of the bay. It is shown that this applies mainly to the shadow zone behind the upcoast headland and not to the full bay periphery and does not have a fixed centre. A new method is proposed utilising arcs from the point of wave diffraction to the shoreline, whose lengths and angles to the wave crest line are related to those of the control line. Data and curves are presented for the static equilibrium shape by which the stability can be tested. They thus predict the waterline for the case of no sediment supply either from littoral drift or rivers debouching into the bay. An indentation ratio can also be derived to test stability.  相似文献   

A Simple Eddy Viscosity Model of Rough Turbulent Wave Boundary Layer     

Hsu Tai-Wen  Lin Hwung-Yui Associate Professor 《中国海洋工程》1996,(3)

- A one-layer time-invariant eddy viscosity model is specified to develop a mathematical model for describing the essential features of the turbulent wave boundary layer over a rough bed. The functional form of the eddy viscosity is evaluated based on computational results from a two-equation turbulence model in which the eddy viscosity varies with time and space. The present eddy viscosity model simplifies much of the mathematical complexity in many existing models. Predictions from the present model have been compared with a wide range of experimental data. It is found that the eddy viscosity model adopted in the present study is physically reasonable.  相似文献   

Transition between the Okinawa trough backarc extension and the Taiwan collision: New insights on the southernmost Ryukyu subduction zone   总被引：4，自引：0，他引：4  

Shu-Kun Hsu  Jean-Claude Sibuet  Serge Monti  Chuen-Tien Shyu  Char-Shine Liu 《Marine Geophysical Researches》1996,18(2-4):163-187

Located between the Okinawa trough (OT) backarc basin and the collisional zone in Taiwan, the southernmost Ryukyu subduction zone is investigated. This area, including the southwestern portions of the OT and Ryukyu island arc (RA) and located west of 123.5° E, is named the Taiwan-Ryukyu fault zone (TRFZ). West of 123.5° E, the OT displays NNW-SSE structural trends which are different in direction from the ENE-WSW trending pattern of the rest of the OT. Using joint analysis of bathymetric, magnetic, gravity and earthquake data, three major discontinuities, that we interpret as right-lateral strike-slip faults (Faults A, B and C), have been identified. These faults could represent major decouplings in the southern portion of the Ryukyu subduction zone: each decoupling results in a decrease of the horizontal stress on the portion of the RA located on the eastern side of the corresponding fault, which allows the extension of the eastern side of OT to proceed more freely.We demonstrate that the 30° clockwise bending of the southwestern RA and the consecutive faulting in the TRFZ are mainly due to the collision of the Luzon arc with the former RA. After the formation of Fault C, the counterclockwise rotated portion of the ancient RA located west of the Luzon arc was more parallel to the Luzon arc. This configuration should have increased the contact surface and friction between the Luzon arc and the ancient RA, which could have reduced the northward subduction of the Luzon are. Thus, the westward component of the compressive stress from the collision of the Luzon arc should become predominant in the collisional system resulting in the uplift of Taiwan. Presently, because the most active collision of the Luzon arc has migrated to the central Taiwan (at about 23° N; 121.2° E), the southwestern OT has resumed its extension. In addition, the later resistent subduction of the Gagua ridge could have reactivated the pre-existing faults A and B at 1 M.y. ago and present, respectively. From 9 to 4 M.y., a large portion of the Gagua ridge probably collided with the southwestern RA. Because of its large buoyancy, this portion of the ridge resisted to subduct beneath the Okinawa platelet. As a result, we suggest that a large exotic terrane, named the Gagua terrane, was emplaced on the inner side of the present Ryukyu trench. Since that period, the southwestern portion of the Ryukyu trench was segmented into two parallel branches separated by the Gagua ridge: the eastern segment propagated westward along the trench axis while the western segment of the trench retreated along the trench axis.  相似文献   

A two-point method for estimating wave reflection over a sloping beach     

H. -K. Chang  T. -W. Hsu 《Ocean Engineering》2003,30(14):1833-1847

This work presents a frequency-domain method for estimating incident and reflected waves when normally incident waves’ propagating over a sloping beach in a wave flume is considered. Linear wave shoaling is applied to determine changes of the wave amplitude and phase due to variations of the bathymetry. The wave reflection coefficient is estimated using wave heights measured at two fixed wave gauges with a distance. The present model demonstrates a high capacity of estimating reflection and shoaling coefficients from synthetic wave-amplitude data. Sensitivity tests for the present model due to measurement errors of wave amplitudes and distance of two probes can more accurately predict the reflection coefficients. The measurement error of wave amplitude affects more significantly than measurement error of distance of two probes on calculating reflection coefficient of waves over a sloping bed.  相似文献   

Development of roughness updating based on artificial neural network in a river hydraulic model for flash flood forecasting     

J C Fu  M H Hsu  Y Duann 《Journal of Earth System Science》2016,125(1):115-128

Flood is the worst weather-related hazard in Taiwan because of steep terrain and storm. The tropical storm often results in disastrous flash flood. To provide reliable forecast of water stages in rivers is indispensable for proper actions in the emergency response during flood. The river hydraulic model based on dynamic wave theory using an implicit finite-difference method is developed with river roughness updating for flash flood forecast. The artificial neural network (ANN) is employed to update the roughness of rivers in accordance with the observed river stages at each time-step of the flood routing process. Several typhoon events at Tamsui River are utilized to evaluate the accuracy of flood forecasting. The results present the adaptive n-values of roughness for river hydraulic model that can provide a better flow state for subsequent forecasting at significant locations and longitudinal profiles along rivers.  相似文献