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This paper aims to present the critical top tension for static equilibrium configurations of a steel catenary riser（SCR） by using the finite element method. The critical top tension is the minimum top tension that can maintain the equilibrium of the SCR. If the top tension is smaller than the critical value, the equilibrium of the SCR does not exist. If the top tension is larger than the critical value, there are two possible equilibrium configurations. These two configurations exhibit the nonlinear large displacement. The configuration with the smaller displacement is stable, while the one with larger displacement is unstable. The numerical results show that the increases in the riser＇s vertical distances, horizontal offsets, riser＇s weights, internal flow velocities, and current velocities increase the critical top tensions of the SCR. In addition, the parametric studies are also performed in order to investigate the limit states for the analysis and design of the SCR. 相似文献
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Effects of rainfall intensity and slope gradient on the application of vetiver grass mulch in soil and water conservation 总被引：3，自引：1，他引：2
The objective of this study is to investigate the effect of rainfall intensity and slope gradient on the performance ofvetiver grass mulch (VGM) in soil and water conservation.The study involved field ... 相似文献
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Free vibrations of three-dimensional extensible marine cables with specified top tension via a variational method 总被引：1，自引：0，他引：1
This paper presents a model formulation that can be used for analyzing the three-dimensional vibration behaviours of an inclined extensible marine cable. The virtual work-energy functional, which involves strain energy due to axial stretching of the cable and virtual work done by external hydrostatic forces is formulated. The coupled equations of motion in the Cartesian coordinates of global systems are obtained by taking into account the difference between Euler’s equations and equilibrium equations. The method of Galerkin finite element is used to obtain the mass and stiffness matrices which are transformed into the local coordinate systems. Then the eigenvalue problem is solved to determine its natural frequencies and corresponding mode shapes. The model formulation developed herein is conveniently applied for the cases of specified top tension. The numerical investigations are carried out to demonstrate the validity of the model and to explore in details the influence of various parameters on the behaviours of marine cables. Results for the frequency avoidance phenomenon, maximum dynamic tension and coupled transverse mode shapes are presented and discussed. 相似文献
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This paper aims to present the critical top tension for static equilibrium configurations of a steel catenary riser (SCR) by using the finite element method. The critical top tension is the minimum top tension that can maintain the equilibrium of the SCR. If the top tension is smaller than the critical value, the equilibrium of the SCR does not exist. If the top tension is larger than the critical value, there are two possible equilibrium configurations. These two configurations exhibit the nonlinear large displacement. The configuration with the smaller displacement is stable, while the one with larger displacement is unstable. The numerical results show that the increases in the riser’s vertical distances, horizontal offsets, riser’s weights, internal flow velocities, and current velocities increase the critical top tensions of the SCR. In addition, the parametric studies are also performed in order to investigate the limit states for the analysis and design of the SCR. 相似文献
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Drought is a significant natural hazard in Herat Province, Afghanistan. The objective of this study was to explore farmers’ perceptions of the drought’s prevalence and characteristics, its socioeconomic and environmental impacts, their strategies for coping with and mitigating it, and types of conflicts and resolution mechanisms. A questionnaire was completed by 147 farming households. The results indicate that farmers' perceptions regarding drought are in line with the results obtained using the precipitation data. Even though the respondents have religious belief in interpreting the weather related issues, they also perceived drought as the climatic and environmental factors such as increased temperature, decreased precipitation, and other factors like war, financial weakness, deforestation, over-exploitation of groundwater, lack of electricity supply etc. The results show that drought has had serious economic impacts, including loss of employment and reduction in crop yield and livestock production, which have reduced farmers’ livelihood options and weakened their financial situation. Social impacts have included migration, a sense of hopelessness and loss, conflicts over water, health problems, impacts on the schooling of children, malnutrition, and limits to food options. Significant environmental impacts such as an increase in temperature, pasture and forest degradation, deterioration of water quality, damage to fish and wildlife habitats, and groundwater depletion were also reported. Farmers used local techniques to adapt to drought and lessen its effects. Farmers perceived irrigation water to be a major source of conflict. Local elders, water-user associations, and formal courts were reported to be the most successful conflict resolution methods. It is expected that the results of this study will support policy makers within government and development agencies in Afghanistan to develop future drought adaptation policies. 相似文献
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Cherdvong Saengsupavanich Somchai Chonwattana Thitima Naimsampao 《Ocean & Coastal Management》2009,52(6):307-316
This study presents how Thailand applied an integrated approach to tackle erosion problems by using a case study in Nakorn Si Thammarat province. Communities along 36 km of coastline suffered from continual erosion. Community members believed the erosion was a natural phenomenon that was intensified by human actions. Historical erosion rate estimated by overlaying aerial photographs was about 5 m per year, while LITPROF simulations suggested that approximately 5 m of beach dune would be eroded by storm waves. Stakeholders were identified based on power and legitimacy criteria. Their past attempts to mitigate the erosion were analyzed. Conflicts arose from how they selected erosion protection methods. Lessons learnt from previous management failures taught that addressing needs of the stakeholders and consulting them throughout the design process were of importance. Finally, a combination of detached nearshore breakwaters and beach nourishment was the selected protection measure and was welcome by the communities. 相似文献
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FLOW PATTERNS AND DAMAGE OF DIKE OVERTOPPING 总被引：1，自引：0，他引：1
Damage of a dike may result in severe damage and suffering. To reduce downstream damage and loss of life, it is important to study the process of breaching of the damaged dike. It is not possible to understand the damage process without a clear understanding of the flow patterns encountered. In the present study, data obtained from nine experimental runs are analyzed. The flow patterns and progressive damage of dike overtopping are investigated. Two types of phenomena at the dike surface: erosion; and erosion and sliding, are observed during the overtopping event. Four stages of dike damage can be distinguished. The degradation rate of the dike crest is found to be dependent on the downstream slope of the dike. The degradation rate is higher when the downstream slope is steeper. 相似文献
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Based on the Princeton Ocean Model （POM）, the seasonal thermohaline feature and the ocean circulation in the Gulf of Thailand （GOT）, situated between 6°N to 14°N latitude and 99°E to 105°E longitude, were studied numerically with 37 × 97 orthogonal curvilinear grid and 10 vertical sigma levels conforming to a realistic bottom topography. A spin-up phase of the first model run was executed using wind stress calculated from climatological monthly mean wind, restoring-type surface heat and salt, and climatological monthly mean fresh water flux data. In this paper, the temperature and salinity fields taken from Levitus94 data sets and the calculated temperature and salinity from the model run for 12-month mean and for each season are presented where the winter, summer, rainy, and end of the rainy seasons of Thailand are represented by the months January, April, July, and October, respectively. The simulated circulations are also described. The results show that the temperature in the GoT is warmer than the temperature of the other parts connected to the South China Sea （SCS）. At any depth of inflow from SCS into the GoT, the salinity is high, but in the outflow from the GoT at the surface, the salinity is low. The strong circulations are clockwise during summer and the rainy seasons of Thailand, which are the East Asian monsoon periods, northeasterly and southwesterly during summer. They occur near Pattani and Narathiwat provinces during summer and in the central GoT during the rainy seasons. Sensitivity experiments were designed to investigate the effects of wind forcing and open boundary conditions. Wind forcing is shown to be the important factor for generating the circulation in the GoT. The lateral velocity at the open boundaries is of considerable importance to current circulation for the rainy and end of the rainy seasons, with insignificant effect for the winter and summer seasons of Thailand. 相似文献
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Akira Imai Kotaro Yonezu Kenzo Sanematsu Takashi Ikuno Shingo Ishida Koichiro Watanabe Visut Pisutha‐Arnond Somchai Nakapadungrat Jarupong Boosayasak 《Resource Geology》2013,63(1):84-98
Geochemical studies were conducted on the hydrothermally altered granitic rocks in the Ranong and Takua Pa tin‐fields in southern Thailand in order to investigate the mode of occurrence of REE (rare earth elements), with emphasis placed on a potential REE resource associated with granitic rocks in the Southeast Asian Tin Belt. The total REE (ΣREE) content of altered granitic rocks ranges from 130 to 350 ppm at Haad Son Paen (which is presently mined for kaolin clay) in the Ranong tin‐field, and that of altered granitic rocks and kaolinite veinlets reaches up to 424 ppm and 872 ppm, respectively, at Nok Hook in the Takua Pa tin‐field. Rare earth elements in the altered granitic rocks and kaolinite veinlets show a relatively flat chondrite‐normalized pattern, thus enriched in heavy REE compared with the original granitic rocks and their weathered crusts. At Nok Hook (Takua Pa), the ΣREE content of kaolinite separated from an altered granitic rock by elutriation is 1313 ppm, a ΣREE amount about four times higher than that of whole‐rock composition of the altered granitic rock. Chondrite‐normalized REE patterns of the elutriated kaolinite and of the altered granite are relatively flat. Sequential extraction experiments suggest that 41 and 85 percent of REE are present as ion exchangeable‐form in the altered granitic rock, and in the kaolinite veinlets, respectively. In addition, more than 90% of REE in the kaolinite veinlets are present as the acid‐soluble state. On the other hand, the ΣREE content of kaolinite veinlets and of the kaolinite concentrated by elutriation from an altered granitic rock at Haad Som Paen (Ranong) is 70 ppm and 75 ppm, respectively, thus enrichment of REE in kaolinite was not confirmed. In addition, by the sequential extraction experiments, 23% and 4% of REE were extracted from the altered granitic rock and the kaolinite veinlets at Haad Som Paen. In the altered granitic rocks at Haad Som Paen, REE are present as refractory phases, and REE in the acid‐soluble states had been leached by hydrothermal fluid. 相似文献
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