Polyurethane polymer grouting materials were studied with conventional triaxial tests via the particle flow code in two dimensions（PFC^（2D）） method, and the simulation results agreed with the experimental data. Th...Polyurethane polymer grouting materials were studied with conventional triaxial tests via the particle flow code in two dimensions（PFC^（2D）） method, and the simulation results agreed with the experimental data. The particle flow code method can simulate the mechanical properties of the polymer. The triaxial cyclic loading tests of the polymer material under different confining pressures were carried out via PFC^（2D） to analyze its mechanical performance. The PFC^（2D） simulation results show that the value of the elastic modulus of the polymer decreases slowly at first and fluctuated within a narrow range near the value of the peak strength; the cumulative plastic strain increases slowly at first and then increases rapidly; the peak strength and elastic modulus of polymer increase with the confining pressure; the PFC^（2D） method can be used to quantitatively evaluate the damage behavior of the polymer material and estimate the fatigue life of the materials under fatigue load based on the number and the location of micro-cracks. Thus, the PFC^（2D） method is an effective tool to study polymers.展开更多
The HTR-10 is a small modular high-temperature reactor located in Tsinghua University,in China.After the reactor ran continuously for 72 h at full power in the commissioning stage,a full load rejection test was conduc...The HTR-10 is a small modular high-temperature reactor located in Tsinghua University,in China.After the reactor ran continuously for 72 h at full power in the commissioning stage,a full load rejection test was conducted by manually disconnecting the generator from the grid.In this study,reactor transients were analyzed using the THERMIX model.Some of the important thermal–fluid phenomena that occurred after the test initiation are discussed here,including the natural convection of helium in the core and the temperature redistribution in the reactor.Temperatures reproduced for the measuring points arranged in the internals were in agreement with the test data.This demonstrated that the code and calculation model are suitable for posttest analysis applications.Regarding the safety features of the reactor,there was a large margin between the predicted maximum fuel temperature of 997℃and the safety limit of 1620℃.展开更多
Failure of rock under impact loadings involves complex micro-fracturing and progressive damage. Strength increase and splitting failure have been observed during dynamic tests of rock materials. However, the failure m...Failure of rock under impact loadings involves complex micro-fracturing and progressive damage. Strength increase and splitting failure have been observed during dynamic tests of rock materials. However, the failure mechanism still remains unclear. In this work, based on laboratory tests, numerical simulations with the particle flow code(PFC) were carried out to reproduce the micro-fracturing process of granite specimens. Shear and tensile cracks were both recorded to investigate the failure mode of rocks under different loading conditions. At the same time, a dynamic damage model based on the Weibull distribution was established to predict the deformation and degradation behavior of specimens. It is found that micro-cracks play important roles in controlling the dynamic deformation and failure process of rock under impact loadings. The sharp increase in the number of cracks may be the reason for the strength increase of rock under high strain rates. Tensile cracks tend to be the key reason for splitting failure of specimens. Numerical simulation of crack propagation by PFC can give vivid description of the failure process. However, it is not enough for evaluation of material degradation. The dynamic damage model is able to predict the stress-strain relationship of specimens reasonably well, and can be used to explain the degradation of specimens under impact loadings at macro-scale. Crack and damage can describe material degradation at different scales and can be used together to reveal the failure mechanism of rocks.展开更多
This paper presents some aspects of the load-settlement behavior for large diameter bored piles using four different international codes, namely: ECP 202 [1], DIN 4014 [2], AASHTO [3] and French Code [4]. Ultimate cap...This paper presents some aspects of the load-settlement behavior for large diameter bored piles using four different international codes, namely: ECP 202 [1], DIN 4014 [2], AASHTO [3] and French Code [4]. Ultimate capacities for 38 pile load tests founded in realistic multi-layered soils in Delta and Port Saidareas atEgyptare evaluated using modified Chin (1970) method and compared to ultimate load predictions obtained by the aforementioned codes. Many statistical analyses were conducted on the total pile loads and individual contributions of tip and skin resistances. Based on code predictions of ultimate pile loads, an empirical modified load-settlement model is proposed. This model will simplify to a great extent the analysis of piled-raft systems as it can effortlessly predict pile settlement due to the load on pile itself. Comparisons showed that the pile load test is an irreplaceable process for determining the ultimate capacity of piles.展开更多
Building Code is a legal document that provides a minimum level of safety and health for the constructions to make the public live in safe buildings. People recognize the importance of constructing the buildings in sa...Building Code is a legal document that provides a minimum level of safety and health for the constructions to make the public live in safe buildings. People recognize the importance of constructing the buildings in safe conditions, since the dawn of civilization. Many countries around the world were facing different kind of disasters such as fires, earthquakes, etc. These disasters made builders develop methods for safe construction to avoid any disaster. Later, these developments became codes and standards. Since the middle of the last century many countries established its local codes. This research represented a review of the importance of the codes with a short history for them. Furthermore, reviews for some national codes (Egyptian, Syrian and Arabia Saudi) were done as well as comparison between load’s correction factors, geotechnical requirements and materials used in concrete. Most of the national codes were highly based on the ACI, British and Germany codes and standards. In addition, a review and comparison were presented for International codes (American (ACI) and European (EC)) through a case study. EC code is becoming more common for the world. Eurocode gives more flexibility to the user to employ their own standards (national annex). To find the best suitable foundation design to be used in Iraq and the differences when using the American and European codes, a building model was designed and analyzed using STAAD Pro., and SAFE softwares for three locations (Mosul, Baghdad and Basrah). The combination loads used in the two softwares were for ACI and EC codes. Results obtained were very similar. The type of foundation to be chosen for Mosul location is spread or continuous. For Baghdad location the suitable type is raft and for Basrah the choice is raft and piles. In view of the fact that Iraq has no national code, engineers and designers were depending on the ACI and British codes and standards. It is very important to have an Iraqi code because it will improve the quality and safety of the design and construction of buildings as well as its economic value.展开更多
The emerging ultra-wideband (UWB) system offers a great potential for the design of high-speed short-range communications.Compared with great progress at physical layer,the corresponding medium access control (MAC) la...The emerging ultra-wideband (UWB) system offers a great potential for the design of high-speed short-range communications.Compared with great progress at physical layer,the corresponding medium access control (MAC) layer designs are naturally placed on the schedules.We focus on the optimal power load scheme,which is an integral part of the MAC layer protocol design,for UWB space-time coded (STC) orthogonal frequency-division multiplexing (OFDM) transmissions.Assumed the transmitter has perfect or partial channel stage information (CSI).Based on the optimization criteria of maximizing capacity,three kinds of power load schemes were presented with different tradeoff among performance,complexity and feedback bandwidth overhead.The proposed schemes are verified and compared under the channel prototype proposed by IEEE 802.15.3a Task Group.展开更多
在大规模分布式存储系统的广泛应用背景下,传统容错编码方案在单盘和双盘故障修复过程中面临读取资源消耗高、修复效率不足等技术难题,提出一种具有局部修复特性的混合校验编码方案——VC-code(vertical central symmetric code)。VC-c...在大规模分布式存储系统的广泛应用背景下,传统容错编码方案在单盘和双盘故障修复过程中面临读取资源消耗高、修复效率不足等技术难题,提出一种具有局部修复特性的混合校验编码方案——VC-code(vertical central symmetric code)。VC-code通过融合横纵式阵列码的快速修复与负载均衡特性,设计了一种局部水平校验与对角校验交叉融合的结构,并采用纵向中心对称校验布局优化数据依赖关系。该设计将单盘和双盘故障修复的数据读取量显著降低,同时通过缩短修复链提升整体效率。理论分析表明,在单双盘故障恢复时大幅降低了数据读取开销。实验结果进一步验证了其性能优势,与RDP码、LRRDP码以及DRDP码相比,VC-code在单盘故障修复时间上减少了10.45%~29.57%,在双盘故障修复时间上减少了6.35%~33.24%。展开更多
基金the National Key R&D Program of China(No.2017YFC0405002)
文摘Polyurethane polymer grouting materials were studied with conventional triaxial tests via the particle flow code in two dimensions（PFC^（2D）） method, and the simulation results agreed with the experimental data. The particle flow code method can simulate the mechanical properties of the polymer. The triaxial cyclic loading tests of the polymer material under different confining pressures were carried out via PFC^（2D） to analyze its mechanical performance. The PFC^（2D） simulation results show that the value of the elastic modulus of the polymer decreases slowly at first and fluctuated within a narrow range near the value of the peak strength; the cumulative plastic strain increases slowly at first and then increases rapidly; the peak strength and elastic modulus of polymer increase with the confining pressure; the PFC^（2D） method can be used to quantitatively evaluate the damage behavior of the polymer material and estimate the fatigue life of the materials under fatigue load based on the number and the location of micro-cracks. Thus, the PFC^（2D） method is an effective tool to study polymers.
基金supported by the Chinese National S&T Major Project(No.ZX069)
文摘The HTR-10 is a small modular high-temperature reactor located in Tsinghua University,in China.After the reactor ran continuously for 72 h at full power in the commissioning stage,a full load rejection test was conducted by manually disconnecting the generator from the grid.In this study,reactor transients were analyzed using the THERMIX model.Some of the important thermal–fluid phenomena that occurred after the test initiation are discussed here,including the natural convection of helium in the core and the temperature redistribution in the reactor.Temperatures reproduced for the measuring points arranged in the internals were in agreement with the test data.This demonstrated that the code and calculation model are suitable for posttest analysis applications.Regarding the safety features of the reactor,there was a large margin between the predicted maximum fuel temperature of 997℃and the safety limit of 1620℃.
基金Projects(51274254,51322403)supported by the National Natural Science Foundation of ChinaProject(NCET-11-0528)supported by theProgram for New Century Excellent Talents in University,ChinaProject(2013SK2011)supported by Hunan Province Science andTechnology Plan,China
文摘Failure of rock under impact loadings involves complex micro-fracturing and progressive damage. Strength increase and splitting failure have been observed during dynamic tests of rock materials. However, the failure mechanism still remains unclear. In this work, based on laboratory tests, numerical simulations with the particle flow code(PFC) were carried out to reproduce the micro-fracturing process of granite specimens. Shear and tensile cracks were both recorded to investigate the failure mode of rocks under different loading conditions. At the same time, a dynamic damage model based on the Weibull distribution was established to predict the deformation and degradation behavior of specimens. It is found that micro-cracks play important roles in controlling the dynamic deformation and failure process of rock under impact loadings. The sharp increase in the number of cracks may be the reason for the strength increase of rock under high strain rates. Tensile cracks tend to be the key reason for splitting failure of specimens. Numerical simulation of crack propagation by PFC can give vivid description of the failure process. However, it is not enough for evaluation of material degradation. The dynamic damage model is able to predict the stress-strain relationship of specimens reasonably well, and can be used to explain the degradation of specimens under impact loadings at macro-scale. Crack and damage can describe material degradation at different scales and can be used together to reveal the failure mechanism of rocks.
文摘This paper presents some aspects of the load-settlement behavior for large diameter bored piles using four different international codes, namely: ECP 202 [1], DIN 4014 [2], AASHTO [3] and French Code [4]. Ultimate capacities for 38 pile load tests founded in realistic multi-layered soils in Delta and Port Saidareas atEgyptare evaluated using modified Chin (1970) method and compared to ultimate load predictions obtained by the aforementioned codes. Many statistical analyses were conducted on the total pile loads and individual contributions of tip and skin resistances. Based on code predictions of ultimate pile loads, an empirical modified load-settlement model is proposed. This model will simplify to a great extent the analysis of piled-raft systems as it can effortlessly predict pile settlement due to the load on pile itself. Comparisons showed that the pile load test is an irreplaceable process for determining the ultimate capacity of piles.
文摘Building Code is a legal document that provides a minimum level of safety and health for the constructions to make the public live in safe buildings. People recognize the importance of constructing the buildings in safe conditions, since the dawn of civilization. Many countries around the world were facing different kind of disasters such as fires, earthquakes, etc. These disasters made builders develop methods for safe construction to avoid any disaster. Later, these developments became codes and standards. Since the middle of the last century many countries established its local codes. This research represented a review of the importance of the codes with a short history for them. Furthermore, reviews for some national codes (Egyptian, Syrian and Arabia Saudi) were done as well as comparison between load’s correction factors, geotechnical requirements and materials used in concrete. Most of the national codes were highly based on the ACI, British and Germany codes and standards. In addition, a review and comparison were presented for International codes (American (ACI) and European (EC)) through a case study. EC code is becoming more common for the world. Eurocode gives more flexibility to the user to employ their own standards (national annex). To find the best suitable foundation design to be used in Iraq and the differences when using the American and European codes, a building model was designed and analyzed using STAAD Pro., and SAFE softwares for three locations (Mosul, Baghdad and Basrah). The combination loads used in the two softwares were for ACI and EC codes. Results obtained were very similar. The type of foundation to be chosen for Mosul location is spread or continuous. For Baghdad location the suitable type is raft and for Basrah the choice is raft and piles. In view of the fact that Iraq has no national code, engineers and designers were depending on the ACI and British codes and standards. It is very important to have an Iraqi code because it will improve the quality and safety of the design and construction of buildings as well as its economic value.
基金This work was partially supported by NSF under Grant 60496315 and national "863" projects under Grant2003AA12331005
文摘The emerging ultra-wideband (UWB) system offers a great potential for the design of high-speed short-range communications.Compared with great progress at physical layer,the corresponding medium access control (MAC) layer designs are naturally placed on the schedules.We focus on the optimal power load scheme,which is an integral part of the MAC layer protocol design,for UWB space-time coded (STC) orthogonal frequency-division multiplexing (OFDM) transmissions.Assumed the transmitter has perfect or partial channel stage information (CSI).Based on the optimization criteria of maximizing capacity,three kinds of power load schemes were presented with different tradeoff among performance,complexity and feedback bandwidth overhead.The proposed schemes are verified and compared under the channel prototype proposed by IEEE 802.15.3a Task Group.
文摘在大规模分布式存储系统的广泛应用背景下,传统容错编码方案在单盘和双盘故障修复过程中面临读取资源消耗高、修复效率不足等技术难题,提出一种具有局部修复特性的混合校验编码方案——VC-code(vertical central symmetric code)。VC-code通过融合横纵式阵列码的快速修复与负载均衡特性,设计了一种局部水平校验与对角校验交叉融合的结构,并采用纵向中心对称校验布局优化数据依赖关系。该设计将单盘和双盘故障修复的数据读取量显著降低,同时通过缩短修复链提升整体效率。理论分析表明,在单双盘故障恢复时大幅降低了数据读取开销。实验结果进一步验证了其性能优势,与RDP码、LRRDP码以及DRDP码相比,VC-code在单盘故障修复时间上减少了10.45%~29.57%,在双盘故障修复时间上减少了6.35%~33.24%。
