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11.
This study has been undertaken to quantify the tank wall effects on resistance estimation of ship models. Given the finite width of a tank, the flow around a ship model has been numerically modelled and the pressure and pressure related drag have been estimated.Since the model runs at speeds essentially in the laminar and transient speed range, an inviscid model has been chosen for obtaining the pressure drag component in the numerical studies. Grid dependency study has been done to optimize the mesh in the control volume for the numerical studies. An unstructured grid consisting of hexahedral cells has been used in the volume of fluid (VOF) model. The model chosen is a medium speed, ocean going barge and the residuary resistance has been obtained for different tank width conditions. The tank width has been defined using a non-dimensionalized parameter W/B (tank width W, model width B) ratio. The study shows that the residuary resistance obtained at W/B=5.0 is free from tank wall influence for the chosen model. The findings of the study have been compared by testing two geosim models under the same tank width conditions. The residuary resistance values have been compared with numerical results. The combined numerical experimental approach provides interesting results of consistency for comparison. The tank wall influences suggested by the numerical study are well quantified in the experimental study and give useful guideline for limiting wall influences. 相似文献
12.
Subdivision and fragmentation of land holdings and their implication in desertification in the Thar Desert, India 总被引：1，自引：0，他引：1
Analysis of data at the household level in Khabra Kalan village in the Thar desert of India revealed that the land holding size is halved every 20–30 years due to subdivision of land holdings. The subdivision is caused by the equal sharing among sons at the time of inheritance based on the succession laws, and attributed to the increase in the village population. The shrinking land holdings resulted in a shortfall of food on small farms; 12% in cereals and 42% in pulses, promoted continuous cultivation and the increase of monoculture, and deteriorated the land productivity through its effect on the soil fertility and land management. 相似文献
13.
D Anantha Rao Pradeep K Naik Sunil K Jain K Vinod Kumar E N Dhanamjaya Rao 《Journal of Earth System Science》2018,127(4):49
Assessment of groundwater vulnerability to pollution is an essential pre-requisite for better planning of an area. We present the groundwater vulnerability assessment in parts of the Yamuna Nagar District, Haryana State, India in an area of about \(800 \hbox { km}^{2}\), considered to be a freshwater zone in the foothills of the Siwalik Hill Ranges. Such areas in the Lower Himalayas form good groundwater recharge zones, and should always be free from contamination. But, the administration has been trying to promote industrialization along these foothill zones without actually assessing the environmental consequences such activities may invite in the future. GIS-DRASTIC model has been used with field based data inputs for studying the vulnerability assessment. But, we find that inclusion electrical conductivity (EC) as a model parameter makes it more robust. Therefore, we rename it as GIS-DRASTIC-EC model. The model identifies three vulnerability zones such as low, moderate and high with an areal extent of 5%, 80% and 15%, respectively. On the basis of major chemical parameters alone, the groundwater in the foothill zones apparently looks safe, but analysis with the help of GIS-DRASTIC-EC model gives a better perspective of the groundwater quality in terms of identifying the vulnerable areas. 相似文献
14.
Kaushal K. Garg K. H. Anantha A. Venkataradha Sreenath Dixit Ramesh Singh Ragab Ragab 《Ground water》2021,59(6):839-855
Agricultural water management (AWM) interventions play an important role in ensuring sustainable food production and mitigating climate risks. This study was carried out in a watershed located in a low rainfall (400–600 mm) region of western India. The Soil and Water Assessment Tool model was calibrated using surface runoff, soil loss, and reservoir storage levels, between the year 2000 and 2006. The investigation indicated that the various AWM interventions increased groundwater recharge from 30 mm/year to 80 mm/year and reduced surface runoff from 250 mm/year to 100 mm/year. The intervention structures were refilled two to three times during the monsoon season depending on rainfall intensity and duration. The interventions have the advantage of building a resilient system by enhancing groundwater availability even in dry years, stimulating crop intensification and protecting the landscape from severe erosion. The results indicate that soil erosion has been reduced by more than 75% compared to the nonintervention situation. Moreover, the AWM interventions led to the cultivation of 100–150 ha of fallow land with high-value crops (horticulture, vegetables, and fodder). Household income increased by several folds compared to the nonintervention situation. The study showed about 50% reduction in downstream water availability, which could be a major concern. However, there are a number of ecosystem trade-offs such as improved base flow to the stream and reduction in soil loss that should be considered. The study is of great importance to stakeholders to decide on the optimal design for AWM interventions to achieve sustainable development goals. 相似文献
15.
Matthew P. Peters Stephen N. Matthews Louis R. Iverson Anantha M. Prasad 《International journal of geographical information science》2014,28(8):1547-1560
Species distribution models (SDM) are commonly used to provide information about species ranges or extents, and often are intended to represent the entire area of potential occupancy or suitable habitat in which individuals occur. While SDMs can provide results over various geographic extents, they normally operate within a grid and cannot delimit distinct, smooth boundaries. Additionally, there are instances where a zone of primary occupancy (i.e., a mostly continuous region where species exists, excluding outliers) is better suited for particular analyses, such as when examining source/sink population dynamics or modeling movement into new habitats. We present a semi-automated method to delineate a generalized species boundary (GSB) from SDM output, which provides a practical alternative to digitizing. This preliminary boundary is then manually updated based on inventory data and historical ranges. We used the method to generate contemporary boundaries for 132 tree species of the eastern United States, which are complementary to the ranges generated by Elbert Little for North America during the 1970s, but are not replacements. The methods we present can broadly be applied to other grid-based SDM to generate GSBs. 相似文献