The leakage and diffusion characteristics of natural gas were investigated in the condition of the leakage of liquefied natural gas(LNG) in the storage tank.Fluent was adopted to simulate the process in a series of th...The leakage and diffusion characteristics of natural gas were investigated in the condition of the leakage of liquefied natural gas(LNG) in the storage tank.Fluent was adopted to simulate the process in a series of three-dimension unsteady state calculations.The effects of different heights of the cofferdam(1.0 m, 2.0 m and 3.0 m),wind directions,ambient temperature,leakage location,leakage volume on the diffusion process of natural gas were investigated.The diffusion characteristics of the natural gas clouds over cofferdam were found.Under windless condition,when the gas clouds met,the gas clouds rose due to the collision,which made them easier to cross the cofferdam and spread out.The higher the ambient temperature was,the higher the gas concentration around the cofferdam was,and the smaller the gas concentration difference was.When the leakage occurred,the higher coffe rdam was more beneficial to delay the outward diffusion of gas clouds.However,when the leaka ge stopped,the higher cofferdam went against the dissipation of gas clouds.Under windy condition,the time to form stable leakage flow field was faster than that of windless,and the lower cofferdam further reduced this time.Therefore,considering the effect of barrier and dissipation,it was suggested that the rational height of cofferdam should be designed in the range of 1.0 m to 2.0 m.In case of emergency,the leakage of gas should be deduced reasonably by combining the measurement of gas concentration with the rolling of gas clouds.When windless,the leakage area should be entered between the overflows of gas clouds.展开更多
Suaeda salsa is an important local species in the intertidal beach of the Western Pacific coast. However,under the artificial cofferdam and Spartina alterniflora expansion,Suaeda marsh has degraded seriously. Therefor...Suaeda salsa is an important local species in the intertidal beach of the Western Pacific coast. However,under the artificial cofferdam and Spartina alterniflora expansion,Suaeda marsh has degraded seriously. Therefore,using Yancheng Nature Reserve as a case study area,taking ETM+images in 2000,2006 and 2011 as the basic data sources,we revealed the evolution characteristics of Salsa marsh which was impacted. The research results are as follows. From 2000 to 2011,Salsa marsh area in the artificial area tempestuously degraded,decreasing by 87. 158%,more than 22% than those in the natural area. The landscape was fragmentized. Landscape polymerization degree index dropped from 95. 780 to 65. 455,more than 16% than those in the natural area. The mean patch area fell down to 21. 429 ha from 389. 333 ha,more than 11% that in the natural area. Compared to the steady change in natural conditions,the area was reduced by 118. 167 ha/a from 2000 to 2006,while during 2006-2011,it was only 51. 500 ha/a in artificial area. As for spatial change of landscape,in artificial area,the Salsa marsh centroid moved forward to the southeast with 666. 350 m,but that in natural area moved forward to the north with 1 042. 710 m from 2000 to 2006. From 2006 to 2011,the centroid moved forward to east and north respectively. Artificial cofferdam transformed the area into freshwater ecosystem,and meanwhile the freshwater was beneficial to Reed marsh. During 2000 to 2006,in the artificial area,539 ha Salsa marsh controlled by cofferdam transferred into reed marsh and aquaculture ponds,of which the transformation rate was nearly 4% higher than that in natural area. From 2006 to 2011,178 ha Salsa marsh was transferred into reed marsh,the transformation rate was 20% higher than that in natural area. With rapid spreading and strong competition of Spartina species,the coastal wetland has formed the pattern of " Salsa – Spartina marshes". From 2000 to 2006,in artificial area,15. 24% of Salsa marsh was transferred into Spartina marsh,of which the transformation rate was13% higher than that in natural area. And from 2006 to 2011,30. 07% Salsa marsh was replaced by the Spartina marsh in artificial area,the rate was almost 10% higher than that in the natural area.展开更多
This study presented a novel circular cofferdam for offshore bridges consisting of ring segments and investigated its structural behaviors using ANSYS Mechanical. Because the bottom segment of the cofferdam which has ...This study presented a novel circular cofferdam for offshore bridges consisting of ring segments and investigated its structural behaviors using ANSYS Mechanical. Because the bottom segment of the cofferdam which has a double sleeve cross-section was installed by suction, contact behaviors of the cofferdam wall and the lid plate during installation are important for design and the behaviors were also analyzed. Prior to numerical investigation of the bottom segment and complete cofferdam after dewatering, a suction modeling for structural analysis was proposed and evaluate by seepage analysis. Hydrodynamic loads applied to the cofferdam were also evaluated using panel method based on the potential flow theory. Through numerical analyses, structural behaviors of the cofferdam during installation were then investigated. First, contact behaviors between the lid plate and the wall were analyzed using different contact conditions imposed on the interface. Sharp stress increases were shown while the stress jumps were limited to contact area. Next, structural behaviors were investigated by considering seepage pressure. Using an axisymmetric seepage model, the total water pressure considering seepage was estimated and applied to structural analysis. The analysis results showed that strong effects of seepage on the stress change in cofferdam occurred and the seepage effects are necessary to be considered in design of the cofferdam induced by suction.展开更多
Phase Ⅲ Rolled Compacted Concrete(RCC) cofferdam construction belongs to Phase Ⅲ diversion works. It is a key item to ensure an achievement in the reservoir impoundment, navigation and power generation in 2003 and a...Phase Ⅲ Rolled Compacted Concrete(RCC) cofferdam construction belongs to Phase Ⅲ diversion works. It is a key item to ensure an achievement in the reservoir impoundment, navigation and power generation in 2003 and a guarantee to the safety construction of the follow up right bank intake dam section and the powerhouse. Restrained by conditions for construction, navigation, the worksite and the duration, both the concreting intensity and the height of Phase Ⅲ RCC cofferdam exceed the current construction level. In view of these difficulties, a great deal of research work performed by relevant departments is described in the paper.展开更多
In order to ensure the stable water supply in cities and villages, many water conservancy projects for water storage, transportation and transportation need to be built. During the construction of water conservancy pr...In order to ensure the stable water supply in cities and villages, many water conservancy projects for water storage, transportation and transportation need to be built. During the construction of water conservancy projects, various scientific and advanced construction technologies need to be adopted. On this basis, the construction quality of water conservancy projects will be continuously improved to better meet the needs of economic and social development and people's life and production. Therefore, in the process of water conservancy project construction, the diversion construction technology should be reasonably applied and the appropriate diversion method should be selected to ensure the orderly development of water conservancy project construction. This paper analyzes the application of different types of diversion technology, hoping to give full play to the role of diversion technology and lay a solid foundation for future water conservancy construction.展开更多
With the continuous development of China's social economy, water conservancy and hydropower infrastructure is particularly important, and cofferdam diversion technology is an important technical measure in the con...With the continuous development of China's social economy, water conservancy and hydropower infrastructure is particularly important, and cofferdam diversion technology is an important technical measure in the construction of water conservancy projects. cofferdam diversion technology has the characteristics of fast flow rate and large flow, which slows down the impact of water flow on construction projects and plays a guiding role in water flow. As the most common and used construction method of water conservancy and hydropower engineering, in order to improve the stability and impact resistance, each construction process should be accurately coordinated. During the construction of the construction of water conservancy engineering, the comprehensive analysis of cofferdam diversion technology is conducted to facilitate the development of water conservancy and hydropower engineering in China.展开更多
With the continuous development and progress of the times, water conservancy engineering has become the cornerstone of national economic development. It is of great significance to explore the application and developm...With the continuous development and progress of the times, water conservancy engineering has become the cornerstone of national economic development. It is of great significance to explore the application and development of water conservancy engineering technology. As an important technology in the construction of water conservancy projects, the application of cofferdam technology plays a very important role in the economic, social and environmental benefits of water conservancy projects, which is more worthy of our research and discussion. From the perspective of case engineering, this paper explores the application method of cofferdam construction technology in hydraulic engineering construction.展开更多
As a frequently used technical type in water conservancy projects at the present stage, cofferdam technology plays a very important role in technical support. It has a great impact on both hydropower industry and the ...As a frequently used technical type in water conservancy projects at the present stage, cofferdam technology plays a very important role in technical support. It has a great impact on both hydropower industry and the whole project. However, it should be noted that although most enterprises have selectively integrated some cofferdam technology into water conservancy project construction in recent years, cofferdam technology can not give full play to its application advantages due to the careless construction process and the neglect of water conservancy construction principles. Therefore, it is of great practical value to clarify the application principles of cofferdam technology and make an in-depth analysis of the main cofferdam technology from multiple angles.展开更多
In the construction of long-span sea crossing bridge, it is often necessary to build huge pier foundation in deep water, which often uses steel cofferdam to block water, forming dry construction conditions. Under the ...In the construction of long-span sea crossing bridge, it is often necessary to build huge pier foundation in deep water, which often uses steel cofferdam to block water, forming dry construction conditions. Under the condition of silt layer exceeding 40m and deep water, the construction technology of double wall steel cofferdams is adopted for the steel cofferdams of bridge caps. Baiteng river section of Jinhai super large bridge between Zhuhai and Jinan is adjacent to Jinhai highway bridge (Baitenghe bridge). The left and right sections of the highway are located on both sides of the railway. The main pier 129 # - 130 # (corresponding to the left and right sections of the highway) crosses the main channel of Baitenghe river with a span of 180m, and the stratum is mainly composed of two layers. The average thickness of the muddy layer is about 45m, and the highway and railway are adjacent to each other, so it is difficult to construct the cofferdam. According to the construction characteristics of this project, this paper studies the construction technology of steel sheet pile combined cofferdam and underwater concrete bottom sealing.展开更多
The protection of downstream concrete slab is a key issue for the stability of overflow earth-rock cofferdam. The coupling effect between bedding layer and concrete slab was taken into account when the stability of do...The protection of downstream concrete slab is a key issue for the stability of overflow earth-rock cofferdam. The coupling effect between bedding layer and concrete slab was taken into account when the stability of downstream concrete slab was researched. The characteristics of overflow and seepage over the downstream concrete slab were investigated when floodwater passes over the cofferdam. Firstly a limit equation of seepage failure for the bedding layer was derived with the consideration of geometric and mechanical factors, and a reliability model was established and numerically simulated. Then based on the reliability calculation for the bedding layer, the coupling effect between bedding layer and downstream concrete slab was analyzed. Under the most unfavorable pressure condition for the concrete slab, its instability criterion was put forward, which offers a structural design tool of downstream concrete slab for overflow earth-rock cofferdam. Compared with model tests, it shows that the model of reliability calculation of bedding layer and the stability analysis of downstream concrete slab are effective.展开更多
基金supported by the Funding for post-doctoral research in Foshan City。
文摘The leakage and diffusion characteristics of natural gas were investigated in the condition of the leakage of liquefied natural gas(LNG) in the storage tank.Fluent was adopted to simulate the process in a series of three-dimension unsteady state calculations.The effects of different heights of the cofferdam(1.0 m, 2.0 m and 3.0 m),wind directions,ambient temperature,leakage location,leakage volume on the diffusion process of natural gas were investigated.The diffusion characteristics of the natural gas clouds over cofferdam were found.Under windless condition,when the gas clouds met,the gas clouds rose due to the collision,which made them easier to cross the cofferdam and spread out.The higher the ambient temperature was,the higher the gas concentration around the cofferdam was,and the smaller the gas concentration difference was.When the leakage occurred,the higher coffe rdam was more beneficial to delay the outward diffusion of gas clouds.However,when the leaka ge stopped,the higher cofferdam went against the dissipation of gas clouds.Under windy condition,the time to form stable leakage flow field was faster than that of windless,and the lower cofferdam further reduced this time.Therefore,considering the effect of barrier and dissipation,it was suggested that the rational height of cofferdam should be designed in the range of 1.0 m to 2.0 m.In case of emergency,the leakage of gas should be deduced reasonably by combining the measurement of gas concentration with the rolling of gas clouds.When windless,the leakage area should be entered between the overflows of gas clouds.
基金Supported by National Natural Science Foundation of China(41771199)Basic Research Project of Jiangsu Province,China(BK20171277)
文摘Suaeda salsa is an important local species in the intertidal beach of the Western Pacific coast. However,under the artificial cofferdam and Spartina alterniflora expansion,Suaeda marsh has degraded seriously. Therefore,using Yancheng Nature Reserve as a case study area,taking ETM+images in 2000,2006 and 2011 as the basic data sources,we revealed the evolution characteristics of Salsa marsh which was impacted. The research results are as follows. From 2000 to 2011,Salsa marsh area in the artificial area tempestuously degraded,decreasing by 87. 158%,more than 22% than those in the natural area. The landscape was fragmentized. Landscape polymerization degree index dropped from 95. 780 to 65. 455,more than 16% than those in the natural area. The mean patch area fell down to 21. 429 ha from 389. 333 ha,more than 11% that in the natural area. Compared to the steady change in natural conditions,the area was reduced by 118. 167 ha/a from 2000 to 2006,while during 2006-2011,it was only 51. 500 ha/a in artificial area. As for spatial change of landscape,in artificial area,the Salsa marsh centroid moved forward to the southeast with 666. 350 m,but that in natural area moved forward to the north with 1 042. 710 m from 2000 to 2006. From 2006 to 2011,the centroid moved forward to east and north respectively. Artificial cofferdam transformed the area into freshwater ecosystem,and meanwhile the freshwater was beneficial to Reed marsh. During 2000 to 2006,in the artificial area,539 ha Salsa marsh controlled by cofferdam transferred into reed marsh and aquaculture ponds,of which the transformation rate was nearly 4% higher than that in natural area. From 2006 to 2011,178 ha Salsa marsh was transferred into reed marsh,the transformation rate was 20% higher than that in natural area. With rapid spreading and strong competition of Spartina species,the coastal wetland has formed the pattern of " Salsa – Spartina marshes". From 2000 to 2006,in artificial area,15. 24% of Salsa marsh was transferred into Spartina marsh,of which the transformation rate was13% higher than that in natural area. And from 2006 to 2011,30. 07% Salsa marsh was replaced by the Spartina marsh in artificial area,the rate was almost 10% higher than that in the natural area.
文摘This study presented a novel circular cofferdam for offshore bridges consisting of ring segments and investigated its structural behaviors using ANSYS Mechanical. Because the bottom segment of the cofferdam which has a double sleeve cross-section was installed by suction, contact behaviors of the cofferdam wall and the lid plate during installation are important for design and the behaviors were also analyzed. Prior to numerical investigation of the bottom segment and complete cofferdam after dewatering, a suction modeling for structural analysis was proposed and evaluate by seepage analysis. Hydrodynamic loads applied to the cofferdam were also evaluated using panel method based on the potential flow theory. Through numerical analyses, structural behaviors of the cofferdam during installation were then investigated. First, contact behaviors between the lid plate and the wall were analyzed using different contact conditions imposed on the interface. Sharp stress increases were shown while the stress jumps were limited to contact area. Next, structural behaviors were investigated by considering seepage pressure. Using an axisymmetric seepage model, the total water pressure considering seepage was estimated and applied to structural analysis. The analysis results showed that strong effects of seepage on the stress change in cofferdam occurred and the seepage effects are necessary to be considered in design of the cofferdam induced by suction.
文摘Phase Ⅲ Rolled Compacted Concrete(RCC) cofferdam construction belongs to Phase Ⅲ diversion works. It is a key item to ensure an achievement in the reservoir impoundment, navigation and power generation in 2003 and a guarantee to the safety construction of the follow up right bank intake dam section and the powerhouse. Restrained by conditions for construction, navigation, the worksite and the duration, both the concreting intensity and the height of Phase Ⅲ RCC cofferdam exceed the current construction level. In view of these difficulties, a great deal of research work performed by relevant departments is described in the paper.
文摘In order to ensure the stable water supply in cities and villages, many water conservancy projects for water storage, transportation and transportation need to be built. During the construction of water conservancy projects, various scientific and advanced construction technologies need to be adopted. On this basis, the construction quality of water conservancy projects will be continuously improved to better meet the needs of economic and social development and people's life and production. Therefore, in the process of water conservancy project construction, the diversion construction technology should be reasonably applied and the appropriate diversion method should be selected to ensure the orderly development of water conservancy project construction. This paper analyzes the application of different types of diversion technology, hoping to give full play to the role of diversion technology and lay a solid foundation for future water conservancy construction.
文摘With the continuous development of China's social economy, water conservancy and hydropower infrastructure is particularly important, and cofferdam diversion technology is an important technical measure in the construction of water conservancy projects. cofferdam diversion technology has the characteristics of fast flow rate and large flow, which slows down the impact of water flow on construction projects and plays a guiding role in water flow. As the most common and used construction method of water conservancy and hydropower engineering, in order to improve the stability and impact resistance, each construction process should be accurately coordinated. During the construction of the construction of water conservancy engineering, the comprehensive analysis of cofferdam diversion technology is conducted to facilitate the development of water conservancy and hydropower engineering in China.
文摘With the continuous development and progress of the times, water conservancy engineering has become the cornerstone of national economic development. It is of great significance to explore the application and development of water conservancy engineering technology. As an important technology in the construction of water conservancy projects, the application of cofferdam technology plays a very important role in the economic, social and environmental benefits of water conservancy projects, which is more worthy of our research and discussion. From the perspective of case engineering, this paper explores the application method of cofferdam construction technology in hydraulic engineering construction.
文摘As a frequently used technical type in water conservancy projects at the present stage, cofferdam technology plays a very important role in technical support. It has a great impact on both hydropower industry and the whole project. However, it should be noted that although most enterprises have selectively integrated some cofferdam technology into water conservancy project construction in recent years, cofferdam technology can not give full play to its application advantages due to the careless construction process and the neglect of water conservancy construction principles. Therefore, it is of great practical value to clarify the application principles of cofferdam technology and make an in-depth analysis of the main cofferdam technology from multiple angles.
文摘In the construction of long-span sea crossing bridge, it is often necessary to build huge pier foundation in deep water, which often uses steel cofferdam to block water, forming dry construction conditions. Under the condition of silt layer exceeding 40m and deep water, the construction technology of double wall steel cofferdams is adopted for the steel cofferdams of bridge caps. Baiteng river section of Jinhai super large bridge between Zhuhai and Jinan is adjacent to Jinhai highway bridge (Baitenghe bridge). The left and right sections of the highway are located on both sides of the railway. The main pier 129 # - 130 # (corresponding to the left and right sections of the highway) crosses the main channel of Baitenghe river with a span of 180m, and the stratum is mainly composed of two layers. The average thickness of the muddy layer is about 45m, and the highway and railway are adjacent to each other, so it is difficult to construct the cofferdam. According to the construction characteristics of this project, this paper studies the construction technology of steel sheet pile combined cofferdam and underwater concrete bottom sealing.
基金supported by the National Natural Science Foundation of China (Grant No. 50579056)the Joint Fund of Yalong River Hydropower Development Researchthe National Natural Science Foundation of China(Grant No. 50539120)
文摘The protection of downstream concrete slab is a key issue for the stability of overflow earth-rock cofferdam. The coupling effect between bedding layer and concrete slab was taken into account when the stability of downstream concrete slab was researched. The characteristics of overflow and seepage over the downstream concrete slab were investigated when floodwater passes over the cofferdam. Firstly a limit equation of seepage failure for the bedding layer was derived with the consideration of geometric and mechanical factors, and a reliability model was established and numerically simulated. Then based on the reliability calculation for the bedding layer, the coupling effect between bedding layer and downstream concrete slab was analyzed. Under the most unfavorable pressure condition for the concrete slab, its instability criterion was put forward, which offers a structural design tool of downstream concrete slab for overflow earth-rock cofferdam. Compared with model tests, it shows that the model of reliability calculation of bedding layer and the stability analysis of downstream concrete slab are effective.
