A study is performed about the water entry of a flat-bottom structure by use of the FE software MSC Dytran. The aim of the study is to find out the effect of the air cushion and structural mass on the impact peak pres...A study is performed about the water entry of a flat-bottom structure by use of the FE software MSC Dytran. The aim of the study is to find out the effect of the air cushion and structural mass on the impact peak pressure and the role of splash in the course of water entry. Some FE models are built up and some cases including the flat-bottom structure with different masses impacting water at some constant or initial velocities are calculated. The calculation shows that air plays an important role in the course of water entry of a flat-bottom structure and the compression of the air captured by the flat- bottom structure produces the first peak pressure. And the mass of the structure has a great effect on the peak value of impact pressure. The structure with different masses will produce different impact pressures even at the same impact velocity. Splash will occur a long time after the impact pressure reaches the peak value. A formula is given for the calculation of the peak value of impact pressure in this paper.展开更多
The frequency and consequences of extreme flood events have increased in recent times, having huge impact on the socio-economic well-being of nations with the most significant impact being felt at the community level....The frequency and consequences of extreme flood events have increased in recent times, having huge impact on the socio-economic well-being of nations with the most significant impact being felt at the community level. Flooding is the most common environmental hazard in Nigeria, particularly Lokoja, with the frequency, intensity, and extent likely to increase due to the effects of global warming leading to climate change such as sea level rise, more intensive precipitation levels, and higher river discharges. While destructive impacts of flood events continue to increase, flood managers in Nigeria have continued to implement a top-down approach towards mitigating these impacts, without involving affected communities in planning and implementation of mitigation strategies. This study therefore employed a participatory approach to determine the causes and impact of flooding in the study area. Participatory research tools such as key informant interviews, focus group discussions, and questionnaire surveys using the purposive sampling method were deployed to elicit data on the perception of the communities about the causes and impact of flood events. Descriptive statistical analysis was performed to elucidate the major causes and areas of impact while qualitative analysis was carried out to corroborate the results and to make for a robust outcome. The Chi Square Test analysis was performed to empirically establish a relationship between the impacts and flooding. Results show that major causes of flooding are the release of water from dams (83% in Adankolo, 97% in Gadumo, and 100% in Ganaja), overflow of rivers, and heavy rainfall while flooding affects economic concerns, property and basic amenities. The Chi Square Test analysis determined empirically that a relationship exists between several areas of impact and flood occurrence. The research concludes that participatory flood research approach can provide flood managers and decision makers a bottom-up approach for effective and robust flood mitigation strategies.展开更多
The use of coal fly ash（CFA）, municipal solid waste incinerator bottom ash（MSWIBA） and flue gas desulfurization residue（FGDR） in road construction has become very common owing to its economical advantages. Howev...The use of coal fly ash（CFA）, municipal solid waste incinerator bottom ash（MSWIBA） and flue gas desulfurization residue（FGDR） in road construction has become very common owing to its economical advantages. However, these residues may contain toxic constituents that pose an environmental risk if they leach out and flow through the soil, surface water and groundwater.Therefore, it is necessary to assess the ecotoxicity and groundwater impact of these residues before decisions can be made regarding their utilization for road construction. In this study,the physico-chemical characteristics, leaching and phytotoxicity of these residues were investigated. Specifically, multivariate analyses were used to evaluate the contributions of the leaching constituents of the CFA, MSWIBA and FGDR leachates to the germination index of wheat seeds. B, Ba, Cr, Cu, Fe and Pb were found to be more toxic to the wheat seeds than the other heavy metals. Furthermore, the leached concentrations of the constituents from the CFA, MSWIBA and FGDR were below the regulatory threshold limits of the Chinese identification standard for hazardous wastes. Analyses conducted using a numerical groundwater model（Wisc LEACH） indicated that the predicted field concentrations of metals from the CFA, MSWIBA and FGDR increased with time up to about 30 years at the point of compliance, then decreased with time and distance. Overall, this study demonstrated that the risks resulting from MSWIBA, CFA and FGDR leaching could be assessed before its utilization for road construction, providing crucial information for the adoption of these alternative materials.展开更多
采用现场调查的方法,于2002年4月—2003年1月对哑铃湾2个不同养殖年限的网箱养殖区、对照海区和网箱周围海区底层水化学进行了四季采样和结果分析。哑铃湾网箱养殖使底层海水中TO C、SS、有机污染物和溶解态氮磷营养盐都有不同程度的增...采用现场调查的方法,于2002年4月—2003年1月对哑铃湾2个不同养殖年限的网箱养殖区、对照海区和网箱周围海区底层水化学进行了四季采样和结果分析。哑铃湾网箱养殖使底层海水中TO C、SS、有机污染物和溶解态氮磷营养盐都有不同程度的增加,春、夏、秋3季D O有不同程度的下降,SS、C O D M n、N H4+、D IN、D IP的增加相对更显著,而对pH值、盐度、水温和冬季D O的影响较小;在水质状况上,D O、B O D5受影响最大,其次是D IP;养殖期较长的网箱区底层海水在春、秋2季已达到富营养化水平。短期网箱养殖对底层海水的水质影响较小,长期养殖影响较明显。A N O V A分析结果显示养殖期较短的网箱邻近海区底层海水营养盐含量与对照点无明显的差异,网箱养殖对底层海水的影响范围主要局限于网箱下。养殖过程中应提高饵料的利用率、采取轮养或休养等措施,以利于海水网箱养殖业的可持续发展。展开更多
文摘A study is performed about the water entry of a flat-bottom structure by use of the FE software MSC Dytran. The aim of the study is to find out the effect of the air cushion and structural mass on the impact peak pressure and the role of splash in the course of water entry. Some FE models are built up and some cases including the flat-bottom structure with different masses impacting water at some constant or initial velocities are calculated. The calculation shows that air plays an important role in the course of water entry of a flat-bottom structure and the compression of the air captured by the flat- bottom structure produces the first peak pressure. And the mass of the structure has a great effect on the peak value of impact pressure. The structure with different masses will produce different impact pressures even at the same impact velocity. Splash will occur a long time after the impact pressure reaches the peak value. A formula is given for the calculation of the peak value of impact pressure in this paper.
文摘The frequency and consequences of extreme flood events have increased in recent times, having huge impact on the socio-economic well-being of nations with the most significant impact being felt at the community level. Flooding is the most common environmental hazard in Nigeria, particularly Lokoja, with the frequency, intensity, and extent likely to increase due to the effects of global warming leading to climate change such as sea level rise, more intensive precipitation levels, and higher river discharges. While destructive impacts of flood events continue to increase, flood managers in Nigeria have continued to implement a top-down approach towards mitigating these impacts, without involving affected communities in planning and implementation of mitigation strategies. This study therefore employed a participatory approach to determine the causes and impact of flooding in the study area. Participatory research tools such as key informant interviews, focus group discussions, and questionnaire surveys using the purposive sampling method were deployed to elicit data on the perception of the communities about the causes and impact of flood events. Descriptive statistical analysis was performed to elucidate the major causes and areas of impact while qualitative analysis was carried out to corroborate the results and to make for a robust outcome. The Chi Square Test analysis was performed to empirically establish a relationship between the impacts and flooding. Results show that major causes of flooding are the release of water from dams (83% in Adankolo, 97% in Gadumo, and 100% in Ganaja), overflow of rivers, and heavy rainfall while flooding affects economic concerns, property and basic amenities. The Chi Square Test analysis determined empirically that a relationship exists between several areas of impact and flood occurrence. The research concludes that participatory flood research approach can provide flood managers and decision makers a bottom-up approach for effective and robust flood mitigation strategies.
基金supported by the National Basic Research Program (973) of China (No. 2011CB201500)the National Natural Science Foundation of China (No. 21277096)+1 种基金the Collaborative Innovation Center for Regional Environmental Qualitythe China Scholarship Council (CSC), Ministry of Education, China (No. 2011GXZT67)
文摘The use of coal fly ash（CFA）, municipal solid waste incinerator bottom ash（MSWIBA） and flue gas desulfurization residue（FGDR） in road construction has become very common owing to its economical advantages. However, these residues may contain toxic constituents that pose an environmental risk if they leach out and flow through the soil, surface water and groundwater.Therefore, it is necessary to assess the ecotoxicity and groundwater impact of these residues before decisions can be made regarding their utilization for road construction. In this study,the physico-chemical characteristics, leaching and phytotoxicity of these residues were investigated. Specifically, multivariate analyses were used to evaluate the contributions of the leaching constituents of the CFA, MSWIBA and FGDR leachates to the germination index of wheat seeds. B, Ba, Cr, Cu, Fe and Pb were found to be more toxic to the wheat seeds than the other heavy metals. Furthermore, the leached concentrations of the constituents from the CFA, MSWIBA and FGDR were below the regulatory threshold limits of the Chinese identification standard for hazardous wastes. Analyses conducted using a numerical groundwater model（Wisc LEACH） indicated that the predicted field concentrations of metals from the CFA, MSWIBA and FGDR increased with time up to about 30 years at the point of compliance, then decreased with time and distance. Overall, this study demonstrated that the risks resulting from MSWIBA, CFA and FGDR leaching could be assessed before its utilization for road construction, providing crucial information for the adoption of these alternative materials.
文摘采用现场调查的方法,于2002年4月—2003年1月对哑铃湾2个不同养殖年限的网箱养殖区、对照海区和网箱周围海区底层水化学进行了四季采样和结果分析。哑铃湾网箱养殖使底层海水中TO C、SS、有机污染物和溶解态氮磷营养盐都有不同程度的增加,春、夏、秋3季D O有不同程度的下降,SS、C O D M n、N H4+、D IN、D IP的增加相对更显著,而对pH值、盐度、水温和冬季D O的影响较小;在水质状况上,D O、B O D5受影响最大,其次是D IP;养殖期较长的网箱区底层海水在春、秋2季已达到富营养化水平。短期网箱养殖对底层海水的水质影响较小,长期养殖影响较明显。A N O V A分析结果显示养殖期较短的网箱邻近海区底层海水营养盐含量与对照点无明显的差异,网箱养殖对底层海水的影响范围主要局限于网箱下。养殖过程中应提高饵料的利用率、采取轮养或休养等措施,以利于海水网箱养殖业的可持续发展。
