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1.
This paper presents a potential based boundary element method for solving a nonlinear free surface flow problem for a ship moving with a uniform speed in finite depth of water. The free surface boundary condition is linearized by the systematic method of perturbation in terms of a small parameter up to third order. The surfaces are discretized into flat quadrilateral elements and the influence coefficients are calculated by Morino's analytical formula. Dawson's upstream finite difference operator is used in order to satisfy the radiation condition. The second order solution gives better result than the first or third order solution. So the present method with the second order solution can be adopted as a powerful tool for the hydrodynamic analysis of the thin ship in finite depth of water. 相似文献
2.
A time dependent model for the flow of gas in a spicule is studied. In this model, the flow occurs in a magnetic flux sheath. Starting from hydrostatic equilibrium, the flux sheath is allowed to collapse normal to itself. The collapse induces a flow of gas along the magnetic field and this flow is identified as a spicule. A variety of sheath geometries and velocity patterns for the normal flow have been studied. It is observed that a large curvature in the field geometry and a large initial value for the normal flow are necessary to achieve spicule-like velocities. The duration for which a large velocity of normal flow is required is much shorter than the average lifetime of a spicule. It is proposed that the initial rapid collapse occurs during an impulsive spicule phase and it is the subsequent gradual relaxation of the flow which is observed as a spicule. 相似文献
3.
Md. Sirajul Islam G. M. Jahid Hasan Md. Aktarul Islam Chowdhury 《International Journal of Environmental Science and Technology》2006,2(4):301-308
Indiscriminate cutting of hills in the Sylhet region has become a major environmental issue. The nature and life style of Sylhet intimately related with the hills are thus under the threat of a drastic imbalance in its ecosystem. Due to such hill cutting the mostly affected sectors of this region will be its weather and climate, geomorphology and hydrology, and the indigenous flora and fauna. As a result the frequency of natural calamities like earthquake, flash flooding etc may increase considerably. Deforestation and resulting increased soil erosion, decreased ground water recharge and deteriorated water quality might also be as consequences of such hill cutting. This paper investigates the cause and extent of the problem along with its probable impact and finally suggests actions for conservation of hills for ecological balance of the region. 相似文献
4.
The impact of Southern Oscillation on thecyclogenesis over the Bay of Bengal duringthe summer monsoon has been investigated.The analysis of correlation coefficients(CCs) between the frequency of monsoondepressions and the Southern OscillationIndex (SOI) reveals that more depressionsform during July and August of El Niñoyears. Due to this, the seasonal frequencyof monsoon depressions remains little higherduring El Niño epochs even though thecorrelations for June and September are notsignificant. The CCs for July and August aresignificant at the 99% level.The El Niño-Southern Oscillation (ENSO)is known to affect Indian MonsoonRainfall (IMR) adversely. The enhancedcyclogenesis over the Bay of Bengal duringJuly and August is an impact of ENSO whichneeds to be examined closely. Increasedcyclogenesis over the Bay of Bengal may bereducing the deficiency in IMR duringEl Niño years by producing more rainfallover the eastern parts of India duringJuly and August. Thus there is a considerablespatial variation in the impact of ENSOon the monsoon rainfall over India and El Niñoneed not necessarily imply a monsoonfailure everywhere in India.The area of formation of monsoon depressionsshifts eastward during El Niño years.Warmer sea surface temperature (SST) anomaliesprevail over northwest and adjoiningwestcentral Bay of Bengal during premonsoon andmonsoon seasons of El Niño years.May minus March SOI can provide useful predictionsof monsoon depression frequencyduring July and August. 相似文献
5.
Erkan Aydar Alain Gourgaud Inan Ulusoy Fabrice Digonnet Philippe Labazuy Erdal Sen Hasan Bayhan Turker Kurttas Arif Umit Tolluoglu 《Journal of Volcanology and Geothermal Research》2003,123(3-4):301-312
Mount Nemrut, an active stratovolcano in eastern Turkey, is a great danger for its vicinity. The volcano possesses a summit caldera which cuts the volcano into two stages, i.e. pre- and post-caldera. Wisps of smoke and hot springs are to be found within the caldera. Although the last recorded volcanic activity is known to have been in 1441, we consider here that the last eruption of Nemrut occurred more recently, probably just before 1597. The present active tectonic regime, historical eruptions, occurrence of mantle-derived magmatic gases and the fumarole and hot spring activities on the caldera floor make Nemrut Volcano a real danger for its vicinity. According to the volcanological past of Nemrut, the styles of expected eruptions are well-focused on two types: (1) occurrence of water within the caldera leads to phreatomagmatic (highly energetic) eruptions, subsequently followed by lava extrusions, and (2) effusions–extrusions (non-explosive or weakly energetic eruptions) on the flanks from fissures. To predict the impact area of future eruptions, a series of morphological analyses based on field observations, Digital Elevation Model and satellite images were realized. Twenty-two valleys (main transport pathways) were classified according to their importance, and the physical parameters related to the valleys were determined. The slope values in each point of the flanks and the Heim parameters H/L were calculated. In the light of morphological analysis the possible impact areas around the volcano and danger zones were proposed. The possible transport pathways of the products of expected volcanic events are unified in three main directions: Bitlis, Guroymak, Tatvan and Ahlat cities, the about 135 000 inhabitants of which could be threatened by future eruptions of this poorly known and unsurveyed volcano. 相似文献
6.
A Turkish Airlines (THY) Boeing 737-400 plane crashed into alluvial soils creating an approximately 13 m deep and 30 m wide crater near the village of Adatepe, Ceyhan in southern Turkey. Effects of the impact on the soils in and around the crater were investigated from both the geological and soil mechanics point of view.
The results show that the impact caused severe deformations in the soils in and around the crater. The soils deformed similar to metamorphic rocks seen at many terrestrial hypervelocity impact craters around the world and became overconsolidated up to a distance of about 10 m from the crater wall as a result of the impact.
Also, the crash was recorded as a 2.7 magnitude earthquake by a nearby microtremor seismograph which provided both the location (epicenter) and time of the crash which was not known immediately after the crash. 相似文献
7.
8.
Umair Hasan Amin Chegenizadeh Mochamad Arief Budihardjo Hamid Nikraz 《Geotechnical and Geological Engineering》2016,34(6):1707-1722
In this study, the effect of ground granulated blast furnace slag (GGBFS) and recycled construction waste (CW) on bentonite clay stabilisation were investigated. The unconfined compressive strength (UCS) of specimens was evaluated with different combinations of GGBFS and CW over various curing periods. A series of micro analysis tests consisting of scanning electron microscope, energy dispersive spectrometer and X-ray diffraction were also conducted to determine the microstructural arrangement and mineralogical effect of the stabilisation treatment. The UCS results showed an increment in strength after introduction of GGBFS and CW and the longer curing period produced more pronounced results. The optimum additive ratio was calculated as 5 % of slag and 20 % of construction waste under all curing conditions. The micro analytical results also indicated formation of structural bonds between admixtures and bentonite in stabilised specimens, as slag crystals and bentonite particles were observed to occupy the cavities and vesicles on the construction waste grains. However, the experimental data shows that the strength improvement is not significant with the addition of only construction waste. 相似文献
9.
M. A. F. M. Rashidul Hasan M. M. Keramat S. Shahid R. Yasmin M. Mohsenipour Golam Shabbir Sattar 《Geotechnical and Geological Engineering》2016,34(5):1395-1411
Barind Tract, located north western part of Bangladesh, is one of the most diversified physiographic units of the country. The surface water supply in this part is particularly limited, so the irrigation is almost entirely depends on groundwater. However, over exploitation indicates falling groundwater heads in this area. The objective of present study is to examine the nature of the aquifer system Barind Tract of Bangladesh in order to assess the sustainability of groundwater yield. Borehole lithology data were collected, processed and analyzed for this purpose. Representative panel diagram, 3-D stratigraphic and cross-sectional views were also prepared for necessary assessment of the variation of individual subsurface stratum in different locations. The study identified three subsurface geologic formations namely, a top clay layer, sand layer of different grain size and at the bottom an impermeable clay zone. Maps of formation thickness and index revealed that aquifer thickness is low in the north-western corner and in some places of middle of south-western corner. The thickness of sand formation in other places is recorded above 20 m. It is expect that the finding of the study will help groundwater resources development, planning and management in the area. 相似文献
10.