The low field nuclear magnetic resonance (NMR), as a nondestructive and noninvasive technique, was employed to investigate the water distribution and content in cement paste with different water-to-cement ratio (w/c r...The low field nuclear magnetic resonance (NMR), as a nondestructive and noninvasive technique, was employed to investigate the water distribution and content in cement paste with different water-to-cement ratio (w/c ratio) during early and later hydration stages. From the water distribution spectrum deduced from relaxation time distribution in paste, it is suggested that the water fills in the capillary pores at initial period, and then diffuses to the mesopores and gel pores in hydration products with the hydration proceeding. The decrease of peak area in water distribution spectrum reflects the transformation from physically bound water to chemically bound water. In addition, based on the connection between relaxation time and pore size, the relative content changes of water in various states and constrained in different types of pores were also measured. The results demonstrate that it is influenced by the formation of pore system and the original water-to-cement ratio in the paste. Consequently, the relative content of capillary water is dropped to less than 2% in the paste with low w/c ratio of 0.3 when being hydrated for 1 d, while the contents are still 16% and 36% in the pastes with w/c ratios of 0.4 and 0.5, respectively.展开更多
A new methodology was proposed for contamination source identification using information provided by consumer complaints from a probabilistic view.Due to the high uncertainties of information derived from users,the ob...A new methodology was proposed for contamination source identification using information provided by consumer complaints from a probabilistic view.Due to the high uncertainties of information derived from users,the objective of the proposed methodology doesn't aim to capture a unique solution,but to minimize the number of possible contamination sources.In the proposed methodology,all the possible pollution nodes are identified through the CSA methodology firstly.And then based on the principle of total probability formula,the probability of each possible contamination node is obtained through a series of calculation.According to magnitude of the probability,the number of possible pollution nodes is minimized.The effectiveness and feasibility of the methodology is demonstrated through an application to a real case of ZJ City.Four scenarios were designed to investigate the influence of different uncertainties on the results in this case.The results show that pollutant concentration,injection duration,the number of consumer complaints nodes used for calculation and the prior probability with which consumers would complaint have no particular effect on the identification of contamination source.Three nodes were selected as the most possible pollution sources in water pipe network of ZJ City which includes more than 3 000 nodes.The results show the potential of the proposed method to identify contamination source through consumer complaints.展开更多
Sixteen priority polycyclic aromatic hydrocarbons(PAHs) in surface water samples were analyzed by gas chromatograph-mass spectrometer(GC-MS) to study their distribution and characterizing sources.The water samples wer...Sixteen priority polycyclic aromatic hydrocarbons(PAHs) in surface water samples were analyzed by gas chromatograph-mass spectrometer(GC-MS) to study their distribution and characterizing sources.The water samples were collected from five sites(J1-J5) in the Jialing River of Chongqing downtown area from September 2009 to August 2010.The results demonstrate that the concentration of total PAHs in three samples upstream are relatively higher than those in other two sites downstream,with average concentration of total PAHs for each site ranging from 811.5 ng/L to 1585.8 ng/L.The 2,3 and 4-ring PAHs for sampling stations account for 13.0%,56.6% and 28.6%,respectively,in total PAHs.There are obvious tendencies of seasonal change for PAHs concentration in surface water.The PAHs concentration in April of wet season is 1 301.6 ng/L,which is 1.3 times the lowest amount of total PAHs in August of flood season.Ratios of specific PAH compounds were used to characterize the possible pollution sources.Experimental results indicate that the PAHs in surface water samples are primarily from pyrolytic PAHs because of factories along these sites,while the direct leakage of petroleum products may be significant for two sites,Jiahua Bridge(J4) and Huanghuayuan Bridge(J5),because of the wharf boat nearby.展开更多
The optimal operation of water distribution networks under local pipe failures, such as water main breaks, was proposed. Based on a hydraulic analysis and a simulation of water distribution networks, a macroscopic mod...The optimal operation of water distribution networks under local pipe failures, such as water main breaks, was proposed. Based on a hydraulic analysis and a simulation of water distribution networks, a macroscopic model for a network under a local pipe failure was established by the statistical regression. After the operation objectives under a local pipe failure were determined, the optimal operation model was developed and solved by the genetic algorithm. The program was developed and examined by a city distribution network. The optimal operation alternative shows that the electricity cost is saved approximately 11%, the income of the water corporation is increased approximately 5%, and the pressure in the water distribution network is distributed evenly to ensure the network safe operation. Therefore, the proposed method for optimal operation under local pipe failure is feasible and cost-effective.展开更多
Water invasion is a common phenomenon in gas reservoirs with active edge-and-bottom aquifers.Due to high reservoir heterogeneity and production parameters,carbonate gas reservoirs feature exploitation obstacles and lo...Water invasion is a common phenomenon in gas reservoirs with active edge-and-bottom aquifers.Due to high reservoir heterogeneity and production parameters,carbonate gas reservoirs feature exploitation obstacles and low recovery factors.In this study,combined core displacement and nuclear magnetic resonance(NMR)experiments explored the reservoir gas−water two-phase flow and remaining microscopic gas distribution during water invasion and gas injection.Consequently,for fracture core,the water-phase relative permeability is higher and the co-seepage interval is narrower than that of three pore cores during water invasion,whereas the water-drive recovery efficiency at different invasion rates is the lowest among all cores.Gas injection is beneficial for reducing water saturation and partially restoring the gas-phase relative permeability,especially for fracture core.The remaining gas distribution and the content are related to the core properties.Compared with pore cores,the water invasion rate strongly influences the residual gas distribution in fracture core.The results enhance the understanding of the water invasion mechanism,gas injection to resume production and the remaining gas distribution,so as to improve the recovery factors of carbonate gas reservoirs.展开更多
The improved weighted-least-square model was used for state simulation of water distribution networks. And DFP algorithm was applied to get the model solution. In order to fit DFP algorithm,the initial model was trans...The improved weighted-least-square model was used for state simulation of water distribution networks. And DFP algorithm was applied to get the model solution. In order to fit DFP algorithm,the initial model was transformed into a non-constrained optimization problem using mass conservation. Then,through one dimensional optimization and scale matrix establishment,the feasible direction of iteration was obtained,and the values of state variables could be calculated. After several iterations,the optimal estimates of state variables were worked out and state simulation of water distribution networks was achieved as a result. A program of DFP algorithm is developed with Delphi 7 for verification. By running on a designed network,which is composed of 55 nodes,94 pipes and 40 loops,it is proved that DFP algorithm can quickly get the convergence. After 36 iterations,the root mean square of all nodal head errors is reduced by 90.84% from 5.57 to 0.51 m,and the maximum error is only 1.30 m. Compared to Marquardt algorithm,the procedure of DFP algorithm is more stable,and the initial values have less influences on calculation accuracy. Therefore,DFP algorithm can be used for real-time simulation of water distribution networks.展开更多
To study the effect of soil water and salt environment factors on the root growth of cotton under different moisture control,three different emergence water volumes(60,105,and 150 m^(3)/hm^(2)),two different frequenci...To study the effect of soil water and salt environment factors on the root growth of cotton under different moisture control,three different emergence water volumes(60,105,and 150 m^(3)/hm^(2)),two different frequencies(high frequency and low frequency)and one double film cover winter irrigation control treatment(CK:2250 m^(3)/hm^(2))were set up to analyze the spatial distribution patterns of soil water and salt environment and root density in dry sown and wet emerged cotton fields under diffe-rent moisture control conditions.The results show that the soil water content and water infiltration range gradually become larger with the increase of seedling water quantity,and the larger the seedling water quantity,the higher the soil water content.With the same seedling water quantity,the soil water content of the high-frequency(HF)treatment becomes obviously larger.The soil conductivity of each treatment tends to decrease gradually with the increase of seedling water and drip frequency,among which the distribution of soil conductivity of S6 treatment is closest to that of CK.With the increase in soil depth,the soil conductivity tends to increase first and then decrease.Compared with the low-frequency(LF)treatment,the high-frequency treatment shows a significantly deeper soil salt accumulation layer.The root length density(RLD)of cotton gradually increases with the amount of seedling water and the frequency of dripping.The soil layer of root distribution gradually deepens with the amount of seedling water in the vertical direction,and the RLD value in the horizontal direction is significantly greater in the mulched area than that in the bare area between films.This research can serve as a solid scientific foundation for the use of dry sowing and wet emergence techniques in cotton fields in southern Xinjiang.展开更多
The negative DC corona discharge in air at atmospheric pressure was investigated in a needle-to-water system to obtain the pressure distribution of corona ionic wind.The deformation of water surface was measured and t...The negative DC corona discharge in air at atmospheric pressure was investigated in a needle-to-water system to obtain the pressure distribution of corona ionic wind.The deformation of water surface was measured and the distribution of wind pressure over the water surface was calculated.The effects of varying discharge parameters,such as applied voltage,gap spacing,tip radius of needle,and the shape of grounded electrode,on the wind pressure were studied.The measured wind pressure ranges from several Pa to several tens of Pa and up to 33 Pa over a small area;the pressure is comparatively large in the center and decreases quickly outwards.In the experiment system,a higher voltage on a 3 mm gap resulted in a stronger pressure of the ionic wind;around the onset voltage,using a needle with tip radius of 50μm obtained a larger wind pressure than using a needle with 100μm tip radius,but the latter one can produce larger pressure at higher voltages.Plus,the shape of the grounded electrode only influences the wind pressure a little.展开更多
While the moisture content of soil affects significantly the blast impulse of shallow buried explosives,the role of surface-covering water(SCW)on soil in such blast impulse remains elusive.A combined experimental and ...While the moisture content of soil affects significantly the blast impulse of shallow buried explosives,the role of surface-covering water(SCW)on soil in such blast impulse remains elusive.A combined experimental and numerical study has been carried out to characterize the effect of SCW on transferred impulse and loading magnitude of shallow buried explosives.Firstly,blast tests of shallow buried explosives were conducted,with and without the SCW,to quantitatively assess the blast loading impulse.Subsequently,finite element(FE)simulations were performed and validated against experimental measurement,with good agreement achieved.The validated FE model was then employed to predict the dynamic response of a fully-clamped metallic circular target,subjected to the explosive impact of shallow buried explosives with SCW,and explore the corresponding physical mechanisms.It was demonstrated that shallow buried explosives in saturated soil generate a greater impulse transferred towards the target relative to those in dry soil.The deformation displacement of the target plate is doubled.Increasing the height of SCW results in enhanced center peak deflection of the loaded target,accompanied by subsequent fall,due to the variation of deformation pattern of the loaded target from concentrated load to uniform load.Meanwhile,the presence of SCW increases the blast impulse transferred towards the target by three times.In addition,there exists a threshold value of the burial depth that maximizes the impact impulse.This threshold exhibits a strong sensitivity to SCW height,decreasing with increasing SCW height.An empirical formula for predicting threshold has been provided.Similar conclusions can be drawn for different explosive masses.The results provide technical guidance on blast loading intensity and its spatial distribution considering shallow buried explosives in coast-land battlefields,which can ultimately contribute to better protective designs.展开更多
The aim of this work is to evaluate how the building distribution influences the cooling effect of water bodies. Different turbulence models, including the S-A, SKE, RNG, Realizable, Low-KE and RSM model, were evaluat...The aim of this work is to evaluate how the building distribution influences the cooling effect of water bodies. Different turbulence models, including the S-A, SKE, RNG, Realizable, Low-KE and RSM model, were evaluated, and the CFD results were compared with wind tunnel experiment. The effects of the water body were detected by analyzing the water vapor distribution around it. It is found that the RNG model is the most effective model in terms of accuracy and computational economy. Next, the RNG model was used to simulate four waterfront planning cases to predict the wind, thermal and moisture environment in urban areas around urban water bodies. The results indicate that the building distribution, especially the height of the frontal building, has a larger effect on the water vapor dispersion, and indicate that the column-type distribution has a better performance than the enclosed-type distribution.展开更多
The stress state around circular openings,such as boreholes,shafts,and tunnels,is usually needed to be evaluated.Solutions for stresses,strains and ultimate bearing capacities of pressurized hollow cylinder are common...The stress state around circular openings,such as boreholes,shafts,and tunnels,is usually needed to be evaluated.Solutions for stresses,strains and ultimate bearing capacities of pressurized hollow cylinder are common cases.Stress analytical method for plane problem of a double-layered thick-walled cylinder subjected to a type of non-uniform pressure on the outer surface and uniform radial pressure on the inner surface is given.The power series method of complex function is used.The stress analytical solution is obtained with the assumption that two layers of a cylinder are fully contacted.The distributions of normal and tangential contact stress along the interface,tangential stress on the inner boundary and stresses in the radial direction at θ=0°,45° and 90°,are obtained.An example indicates that,when the elastic modulus of the inner layer of a double-layered thick-walled cylinder is smaller than that of the outer layer,the tangential stress is smaller than that in the corresponding point for a traditional cylinder composed of homogeneous materials.In that way,stress concentration at the inner surface can be alleviated and the stress distribution is more uniform.This is a capable way to enhance the elastic ultimate bearing capacity of thick-walled cylinder.展开更多
Combining vacuum preloading technology and electroosmosis can improve the treatment effect of soft soil foundation by utilizing the advantages of both methods.Many studies indicate that the soil electrical potential i...Combining vacuum preloading technology and electroosmosis can improve the treatment effect of soft soil foundation by utilizing the advantages of both methods.Many studies indicate that the soil electrical potential is non-linearly distributed in the treatment process by the combined method.However,in the previous theoretical study,the non-linear-distribution impacts of soil’s electrical potential on soft soil foundation treatment have not been considered.It is always assumed to be linear distribution,which is different from the experimental results.In this paper,the coupling consolidation model of this technology under the two-dimensional plane strain condition is initially established;and the well resistance effect,the vacuum load decreasing along the soil depth and the non-linear variation of electrical potential in the soil are considered.Then,the analytical solutions of the average excess pore water pressure and soil’s consolidation degree in the anode affected area are acquired based on the soil’s electrical potential distribution.Finally,the rationality of the analytical solution is testified by conducting an experimental model test,which proves the scientificity of the analytical solution.The analytical solution is adopted to better predict the dissipation of excess pore water pressure and soil consolidation degree when using the combined technology.This study can provide a reference with more accuracy for the engineering practices of this combined technology in the future.展开更多
As one of the major projects of GAME (GEWEX Asian Monsoon Experiment), the GAME\|Tibet aimed to mainly examine the energy and water cycle in Tibetan Plateau and its effects on Asian monsoon. In this paper, based on th...As one of the major projects of GAME (GEWEX Asian Monsoon Experiment), the GAME\|Tibet aimed to mainly examine the energy and water cycle in Tibetan Plateau and its effects on Asian monsoon. In this paper, based on the in\|situ high\|resolution observation data of GAME\|Tibet, the soil energy\|moisture distribution and the melting\|freezing progresses and their effects on seasonal shift were preliminarily discussed.The soil energy\|water distribution and freezing\|melting processes varied at different sites in northern part of Tibetan Plateau. The temporal and spatial variation of the soil moisture content is more complex than that of temperature. The soil moisture content increased with depth in certain layers but decreased in other layers. The freezing and melting processes and the temperature distribution were largely influenced by the existence of higher soil moisture content layer. During summer monsoon, the soil moisture at 10cm at all sites is relatively high, but the spatial difference existed. Generally speaking, the shallow layers start to freeze in October and to melt from April at all sites, with about 6 months frozen period. However, the beginning time of freezing\|melting and frozen period varied at different sites.展开更多
Buried high explosive(HE) charges represent a high threat to military vehicles. The detonation of these charges can lead to significant momentum transfer onto vehicles and their occupants. A detailed understanding of ...Buried high explosive(HE) charges represent a high threat to military vehicles. The detonation of these charges can lead to significant momentum transfer onto vehicles and their occupants. A detailed understanding of the physical processes involved in the loading of vehicle structures is necessary for an optimization of effective countermeasures and protection systems. A quantitative description of the local momentum distribution on the vehicle underbody due to the detonation process is of special importance. In the following, a new test setup is presented that allows the experimental determination of the specific impulse distribution. It is based on a ring arrangement where the elements are nested into each other and the velocity of each ring is correlated with the local specific impulse at its position.The momentum transfer to a vehicle depends on a number of influencing factors such as: charge mass,embedding material(e.g. sand, gravel, clay), density, water content, saturation, depth of burial, ground clearance and vehicle shape. The presented technology is applied to quantify the influence of the embedding material(alluvial sand, quartz sand), the burial depth and the water content on the local specific impulse distribution. The obtained data can be used as initial condition for the numerical simulation of occupant safety assessment and as input for empirical modeling of momentum transfer on structures.展开更多
基金Project(2009CB623105) supported by the National Basic Research Program of ChinaProject(51108341) supported by the National Natural Science Foundation of ChinaProjects(20110490703, 2012T50437) supported by China Postdoctoral Science Foundation
文摘The low field nuclear magnetic resonance (NMR), as a nondestructive and noninvasive technique, was employed to investigate the water distribution and content in cement paste with different water-to-cement ratio (w/c ratio) during early and later hydration stages. From the water distribution spectrum deduced from relaxation time distribution in paste, it is suggested that the water fills in the capillary pores at initial period, and then diffuses to the mesopores and gel pores in hydration products with the hydration proceeding. The decrease of peak area in water distribution spectrum reflects the transformation from physically bound water to chemically bound water. In addition, based on the connection between relaxation time and pore size, the relative content changes of water in various states and constrained in different types of pores were also measured. The results demonstrate that it is influenced by the formation of pore system and the original water-to-cement ratio in the paste. Consequently, the relative content of capillary water is dropped to less than 2% in the paste with low w/c ratio of 0.3 when being hydrated for 1 d, while the contents are still 16% and 36% in the pastes with w/c ratios of 0.4 and 0.5, respectively.
基金Project(50908165) supported by the National Natural Science Foundation of China
文摘A new methodology was proposed for contamination source identification using information provided by consumer complaints from a probabilistic view.Due to the high uncertainties of information derived from users,the objective of the proposed methodology doesn't aim to capture a unique solution,but to minimize the number of possible contamination sources.In the proposed methodology,all the possible pollution nodes are identified through the CSA methodology firstly.And then based on the principle of total probability formula,the probability of each possible contamination node is obtained through a series of calculation.According to magnitude of the probability,the number of possible pollution nodes is minimized.The effectiveness and feasibility of the methodology is demonstrated through an application to a real case of ZJ City.Four scenarios were designed to investigate the influence of different uncertainties on the results in this case.The results show that pollutant concentration,injection duration,the number of consumer complaints nodes used for calculation and the prior probability with which consumers would complaint have no particular effect on the identification of contamination source.Three nodes were selected as the most possible pollution sources in water pipe network of ZJ City which includes more than 3 000 nodes.The results show the potential of the proposed method to identify contamination source through consumer complaints.
基金Project(41101457) supported by the National Natural Science Foundation of ChinaProject(2009-122) supported by the Fund of Chongqing Municipal Construction Commission, China
文摘Sixteen priority polycyclic aromatic hydrocarbons(PAHs) in surface water samples were analyzed by gas chromatograph-mass spectrometer(GC-MS) to study their distribution and characterizing sources.The water samples were collected from five sites(J1-J5) in the Jialing River of Chongqing downtown area from September 2009 to August 2010.The results demonstrate that the concentration of total PAHs in three samples upstream are relatively higher than those in other two sites downstream,with average concentration of total PAHs for each site ranging from 811.5 ng/L to 1585.8 ng/L.The 2,3 and 4-ring PAHs for sampling stations account for 13.0%,56.6% and 28.6%,respectively,in total PAHs.There are obvious tendencies of seasonal change for PAHs concentration in surface water.The PAHs concentration in April of wet season is 1 301.6 ng/L,which is 1.3 times the lowest amount of total PAHs in August of flood season.Ratios of specific PAH compounds were used to characterize the possible pollution sources.Experimental results indicate that the PAHs in surface water samples are primarily from pyrolytic PAHs because of factories along these sites,while the direct leakage of petroleum products may be significant for two sites,Jiahua Bridge(J4) and Huanghuayuan Bridge(J5),because of the wharf boat nearby.
基金Project(50278062) supported by the National Natural Science Foundation of ChinaProject(003611611)supported by the Natural Science Foundation of Tianjin, China
文摘The optimal operation of water distribution networks under local pipe failures, such as water main breaks, was proposed. Based on a hydraulic analysis and a simulation of water distribution networks, a macroscopic model for a network under a local pipe failure was established by the statistical regression. After the operation objectives under a local pipe failure were determined, the optimal operation model was developed and solved by the genetic algorithm. The program was developed and examined by a city distribution network. The optimal operation alternative shows that the electricity cost is saved approximately 11%, the income of the water corporation is increased approximately 5%, and the pressure in the water distribution network is distributed evenly to ensure the network safe operation. Therefore, the proposed method for optimal operation under local pipe failure is feasible and cost-effective.
基金Project(2016ZX05017)supported by the China National Science and Technology Major Project
文摘Water invasion is a common phenomenon in gas reservoirs with active edge-and-bottom aquifers.Due to high reservoir heterogeneity and production parameters,carbonate gas reservoirs feature exploitation obstacles and low recovery factors.In this study,combined core displacement and nuclear magnetic resonance(NMR)experiments explored the reservoir gas−water two-phase flow and remaining microscopic gas distribution during water invasion and gas injection.Consequently,for fracture core,the water-phase relative permeability is higher and the co-seepage interval is narrower than that of three pore cores during water invasion,whereas the water-drive recovery efficiency at different invasion rates is the lowest among all cores.Gas injection is beneficial for reducing water saturation and partially restoring the gas-phase relative permeability,especially for fracture core.The remaining gas distribution and the content are related to the core properties.Compared with pore cores,the water invasion rate strongly influences the residual gas distribution in fracture core.The results enhance the understanding of the water invasion mechanism,gas injection to resume production and the remaining gas distribution,so as to improve the recovery factors of carbonate gas reservoirs.
基金Project(IRT0853) supported by Changjiang Scholars and Innovative Research Team in UniversityProject(DB03086) supported by Talents Fund of Xi’an University of Architecture and TechnologyProject(50978213) supported by National Natural Science Foundation
文摘The improved weighted-least-square model was used for state simulation of water distribution networks. And DFP algorithm was applied to get the model solution. In order to fit DFP algorithm,the initial model was transformed into a non-constrained optimization problem using mass conservation. Then,through one dimensional optimization and scale matrix establishment,the feasible direction of iteration was obtained,and the values of state variables could be calculated. After several iterations,the optimal estimates of state variables were worked out and state simulation of water distribution networks was achieved as a result. A program of DFP algorithm is developed with Delphi 7 for verification. By running on a designed network,which is composed of 55 nodes,94 pipes and 40 loops,it is proved that DFP algorithm can quickly get the convergence. After 36 iterations,the root mean square of all nodal head errors is reduced by 90.84% from 5.57 to 0.51 m,and the maximum error is only 1.30 m. Compared to Marquardt algorithm,the procedure of DFP algorithm is more stable,and the initial values have less influences on calculation accuracy. Therefore,DFP algorithm can be used for real-time simulation of water distribution networks.
基金National Key Research and Development Plan(2021YFD1900805)Funded Project of Basic Scientific Research Business of Public Welfare Research Institutes in Autonomous Region(KY2022127)。
文摘To study the effect of soil water and salt environment factors on the root growth of cotton under different moisture control,three different emergence water volumes(60,105,and 150 m^(3)/hm^(2)),two different frequencies(high frequency and low frequency)and one double film cover winter irrigation control treatment(CK:2250 m^(3)/hm^(2))were set up to analyze the spatial distribution patterns of soil water and salt environment and root density in dry sown and wet emerged cotton fields under diffe-rent moisture control conditions.The results show that the soil water content and water infiltration range gradually become larger with the increase of seedling water quantity,and the larger the seedling water quantity,the higher the soil water content.With the same seedling water quantity,the soil water content of the high-frequency(HF)treatment becomes obviously larger.The soil conductivity of each treatment tends to decrease gradually with the increase of seedling water and drip frequency,among which the distribution of soil conductivity of S6 treatment is closest to that of CK.With the increase in soil depth,the soil conductivity tends to increase first and then decrease.Compared with the low-frequency(LF)treatment,the high-frequency treatment shows a significantly deeper soil salt accumulation layer.The root length density(RLD)of cotton gradually increases with the amount of seedling water and the frequency of dripping.The soil layer of root distribution gradually deepens with the amount of seedling water in the vertical direction,and the RLD value in the horizontal direction is significantly greater in the mulched area than that in the bare area between films.This research can serve as a solid scientific foundation for the use of dry sowing and wet emergence techniques in cotton fields in southern Xinjiang.
基金Project supported by National Key Laboratory of Science and Technology on Electro-mechanical Dynamic Control of China(2011C3606)
文摘The negative DC corona discharge in air at atmospheric pressure was investigated in a needle-to-water system to obtain the pressure distribution of corona ionic wind.The deformation of water surface was measured and the distribution of wind pressure over the water surface was calculated.The effects of varying discharge parameters,such as applied voltage,gap spacing,tip radius of needle,and the shape of grounded electrode,on the wind pressure were studied.The measured wind pressure ranges from several Pa to several tens of Pa and up to 33 Pa over a small area;the pressure is comparatively large in the center and decreases quickly outwards.In the experiment system,a higher voltage on a 3 mm gap resulted in a stronger pressure of the ionic wind;around the onset voltage,using a needle with tip radius of 50μm obtained a larger wind pressure than using a needle with 100μm tip radius,but the latter one can produce larger pressure at higher voltages.Plus,the shape of the grounded electrode only influences the wind pressure a little.
基金supported by the National Natural Science Foundation of China(Grant Nos.12002156,11972185,12372136)Research Fund of State Key Laboratory of Mechanics and Control for Aerospace Structures(Grant No.MCMS-I-0222K01)。
文摘While the moisture content of soil affects significantly the blast impulse of shallow buried explosives,the role of surface-covering water(SCW)on soil in such blast impulse remains elusive.A combined experimental and numerical study has been carried out to characterize the effect of SCW on transferred impulse and loading magnitude of shallow buried explosives.Firstly,blast tests of shallow buried explosives were conducted,with and without the SCW,to quantitatively assess the blast loading impulse.Subsequently,finite element(FE)simulations were performed and validated against experimental measurement,with good agreement achieved.The validated FE model was then employed to predict the dynamic response of a fully-clamped metallic circular target,subjected to the explosive impact of shallow buried explosives with SCW,and explore the corresponding physical mechanisms.It was demonstrated that shallow buried explosives in saturated soil generate a greater impulse transferred towards the target relative to those in dry soil.The deformation displacement of the target plate is doubled.Increasing the height of SCW results in enhanced center peak deflection of the loaded target,accompanied by subsequent fall,due to the variation of deformation pattern of the loaded target from concentrated load to uniform load.Meanwhile,the presence of SCW increases the blast impulse transferred towards the target by three times.In addition,there exists a threshold value of the burial depth that maximizes the impact impulse.This threshold exhibits a strong sensitivity to SCW height,decreasing with increasing SCW height.An empirical formula for predicting threshold has been provided.Similar conclusions can be drawn for different explosive masses.The results provide technical guidance on blast loading intensity and its spatial distribution considering shallow buried explosives in coast-land battlefields,which can ultimately contribute to better protective designs.
基金Project(51438005)supported by the National Natural Science Foundation of China
文摘The aim of this work is to evaluate how the building distribution influences the cooling effect of water bodies. Different turbulence models, including the S-A, SKE, RNG, Realizable, Low-KE and RSM model, were evaluated, and the CFD results were compared with wind tunnel experiment. The effects of the water body were detected by analyzing the water vapor distribution around it. It is found that the RNG model is the most effective model in terms of accuracy and computational economy. Next, the RNG model was used to simulate four waterfront planning cases to predict the wind, thermal and moisture environment in urban areas around urban water bodies. The results indicate that the building distribution, especially the height of the frontal building, has a larger effect on the water vapor dispersion, and indicate that the column-type distribution has a better performance than the enclosed-type distribution.
基金Projects(50874047,51074014,51174014)supported by the National Natural Science Foundation of China
文摘The stress state around circular openings,such as boreholes,shafts,and tunnels,is usually needed to be evaluated.Solutions for stresses,strains and ultimate bearing capacities of pressurized hollow cylinder are common cases.Stress analytical method for plane problem of a double-layered thick-walled cylinder subjected to a type of non-uniform pressure on the outer surface and uniform radial pressure on the inner surface is given.The power series method of complex function is used.The stress analytical solution is obtained with the assumption that two layers of a cylinder are fully contacted.The distributions of normal and tangential contact stress along the interface,tangential stress on the inner boundary and stresses in the radial direction at θ=0°,45° and 90°,are obtained.An example indicates that,when the elastic modulus of the inner layer of a double-layered thick-walled cylinder is smaller than that of the outer layer,the tangential stress is smaller than that in the corresponding point for a traditional cylinder composed of homogeneous materials.In that way,stress concentration at the inner surface can be alleviated and the stress distribution is more uniform.This is a capable way to enhance the elastic ultimate bearing capacity of thick-walled cylinder.
基金Project(51979087)supported by the National Natural Science Foundation of ChinaProject(BK20180776)supported by the Jiangsu Natural Science Foundation,ChinaProject(202006710002)supported by the China Scholarship Council。
文摘Combining vacuum preloading technology and electroosmosis can improve the treatment effect of soft soil foundation by utilizing the advantages of both methods.Many studies indicate that the soil electrical potential is non-linearly distributed in the treatment process by the combined method.However,in the previous theoretical study,the non-linear-distribution impacts of soil’s electrical potential on soft soil foundation treatment have not been considered.It is always assumed to be linear distribution,which is different from the experimental results.In this paper,the coupling consolidation model of this technology under the two-dimensional plane strain condition is initially established;and the well resistance effect,the vacuum load decreasing along the soil depth and the non-linear variation of electrical potential in the soil are considered.Then,the analytical solutions of the average excess pore water pressure and soil’s consolidation degree in the anode affected area are acquired based on the soil’s electrical potential distribution.Finally,the rationality of the analytical solution is testified by conducting an experimental model test,which proves the scientificity of the analytical solution.The analytical solution is adopted to better predict the dissipation of excess pore water pressure and soil consolidation degree when using the combined technology.This study can provide a reference with more accuracy for the engineering practices of this combined technology in the future.
文摘As one of the major projects of GAME (GEWEX Asian Monsoon Experiment), the GAME\|Tibet aimed to mainly examine the energy and water cycle in Tibetan Plateau and its effects on Asian monsoon. In this paper, based on the in\|situ high\|resolution observation data of GAME\|Tibet, the soil energy\|moisture distribution and the melting\|freezing progresses and their effects on seasonal shift were preliminarily discussed.The soil energy\|water distribution and freezing\|melting processes varied at different sites in northern part of Tibetan Plateau. The temporal and spatial variation of the soil moisture content is more complex than that of temperature. The soil moisture content increased with depth in certain layers but decreased in other layers. The freezing and melting processes and the temperature distribution were largely influenced by the existence of higher soil moisture content layer. During summer monsoon, the soil moisture at 10cm at all sites is relatively high, but the spatial difference existed. Generally speaking, the shallow layers start to freeze in October and to melt from April at all sites, with about 6 months frozen period. However, the beginning time of freezing\|melting and frozen period varied at different sites.
文摘Buried high explosive(HE) charges represent a high threat to military vehicles. The detonation of these charges can lead to significant momentum transfer onto vehicles and their occupants. A detailed understanding of the physical processes involved in the loading of vehicle structures is necessary for an optimization of effective countermeasures and protection systems. A quantitative description of the local momentum distribution on the vehicle underbody due to the detonation process is of special importance. In the following, a new test setup is presented that allows the experimental determination of the specific impulse distribution. It is based on a ring arrangement where the elements are nested into each other and the velocity of each ring is correlated with the local specific impulse at its position.The momentum transfer to a vehicle depends on a number of influencing factors such as: charge mass,embedding material(e.g. sand, gravel, clay), density, water content, saturation, depth of burial, ground clearance and vehicle shape. The presented technology is applied to quantify the influence of the embedding material(alluvial sand, quartz sand), the burial depth and the water content on the local specific impulse distribution. The obtained data can be used as initial condition for the numerical simulation of occupant safety assessment and as input for empirical modeling of momentum transfer on structures.
