An experimental study on a bare flexible cylinder as well as cylinders fitted with two types of cross-sectioned helical strakes was carried out in a towing tank. The main purpose of this paper is to investigate the ef...An experimental study on a bare flexible cylinder as well as cylinders fitted with two types of cross-sectioned helical strakes was carried out in a towing tank. The main purpose of this paper is to investigate the effects of strakes’ cross-section on the vortex-induced vibrations （VIV） suppression of a flexible cylinder. The square-sectioned and round-sectioned helical strakes were selected in the experimental tests. The uniform current was generated by towing the cylinder models along the tank using a towing carriage. The Reynolds number was in the range of 800–16000. The strain responses were measured by the strain gages in cross-flow （CF） and in-line （IL） directions. A modal analysis method was adopted to obtain the displacement responses using the strain signals in different measurement positions. The comparison of the experimental results among the bare cylinder, square-sectioned straked cylinder and round-sectioned straked cylinder was performed. The helical strakes can effectively reduce the strain amplitude, displacement amplitude, response frequencies and dominant modes of a flexible cylinder excited by VIV. And the mean drag coefficients of straked cylinders were approximately consistent with each other. In addition, the square-sectioned and round-sectioned strakes nearly share the similar VIV reduction behaviors. Sometimes, the strakes with round-section represent more excellent effects on the VIV suppression of response frequency than those with square-section.展开更多
This paper describes a new method for simulation of the cross section shape of log. The self-developed MQK3102 log shape recognizing machine was used to acquire the finite discrete sampling points on the cross section...This paper describes a new method for simulation of the cross section shape of log. The self-developed MQK3102 log shape recognizing machine was used to acquire the finite discrete sampling points on the cross section of log and those points were fitted with the quadratic B-spline parametric curve. This method can clearly stimulate the real shape of the log cross section and is characterized by limited sampling points and high speed computing. The computed result of the previous curve does not affect the next one, which may avoid the graphic distortion caused by the accumulative error. The method can be used to simulate the whole body shape of log approximately by sampling the cross sections along the length direction of log, thus providing a reference model for optimum saw cutting of log.展开更多
This study evaluated the efficacy and safety of ＂J＂-shaped uterine incision for caesarean section for patients diagnosed with placenta previa. A total of 55 consecutive cases of placenta previa treated in Union Hosp...This study evaluated the efficacy and safety of ＂J＂-shaped uterine incision for caesarean section for patients diagnosed with placenta previa. A total of 55 consecutive cases of placenta previa treated in Union Hospital were retrospectively analyzed over a period of two years and 10 months. The subjects were divided into two groups with respect to the uterine incision. Twenty-four pregnant women with placenta previa who were indicated for caesarean section underwent the procedure using a new ＂J＂-shaped uterine incision and 31 pregnant women with placenta previa received caesarean section that used the traditional transverse incision. The two groups were compared in terms of operation time, estimated blood loss, infant expulsion time, exhaust time and postoperative recovery. Meanwhile, comparison was also made in neonatal clinical data between the two groups. Compared with the ＂J＂-shaped incision group, the traditional incision group had a lower Apgar scores （P〈0.05）. However, there existed no statistically significant differences in the overall time of operation and postoperative period of breaking wind （P〉0.05）. It is concluded that, with caesarean section for placenta previa patients, the ＂J＂-shaped uterine incision significantly decreases intraoperative blood loss and facilitates the fetal delivery.展开更多
Rolling process plays an important role in the manufacture of Bi-based high temperature superconductor tapes, and the plastic flow regularities of the superconducting wires during deformation will directly affect the ...Rolling process plays an important role in the manufacture of Bi-based high temperature superconductor tapes, and the plastic flow regularities of the superconducting wires during deformation will directly affect the ultimate quality of the tapes. In order to investigate the effect of cross-sectional shapes before fiat rolling on the performance and homogeneity of the tapes, some numerical models of Bi-2223/Ag wires with different cross-sectional shapes including circular, square, elliptical and racetrack cross-sections are constructed during the rolling process. By comparing the relative density, logarithmic strain ratio and length-width ratio on the filaments, it is revealed that Bi-2223/Ag wire with special-shaped cross-section can achieve better conductivity than the round wire, in particular, the racetrack cross-sectional wire has the second best performance among four wires. Based on material processability and experimental condition, tri-pass racetrack drawing technique is employed to optimize the process and obtain racetrack cross-sectional wire. The rolling process of Bi-2223/Ag wire with racetrack cross-section causes more intensive deformation of filaments in the center of the tape and achieves the filaments with larger length-width ratio. Also, the deformation distribution of filaments verifies the numerical results. Consequently, the racetrack drawing technique can be utilized for a reference during the mechanical processing and to increase the current transmission capacities of Bi-2223/Ag tapes.展开更多
In industrial plants, ships, and buildings, a large amount of gas and air ducts are applied for equipment connection, HVAC, medium transport, and exhaust, etc. These ducts can be designed in varied cross-sectional sha...In industrial plants, ships, and buildings, a large amount of gas and air ducts are applied for equipment connection, HVAC, medium transport, and exhaust, etc. These ducts can be designed in varied cross-sectional shapes, such as round or rectangle. The author reveals through geometric calculation of the duct cross-sectional shapes and engineering experiences that the round cross-section is an optimal shape in the duct system. The round duct has the shorter perimeter than the other cross-sectional shape ducts and the stronger structure in the same working condition. The material saving of the round duct due to the shorter perimeter is quantitatively determined. In the pater, it is shown that the round duct is economically attractive. The economic analysis for the material cost saving is illustrated by an example. For a long duct system, the material and material cost savings are significant. It is suggested that the round duct in the gas and air duct system should have priority as long as the field conditions are allowed. In the paper, the material cost saving is also converted to PW, AW, and FW used for LCC economic analysis.展开更多
中大型船舶的建造正常都是以分段为单位按区域进行建造。考虑到船体线型、内部结构的布置和施工的方便性,分段划分的形状各异,建造方式也不同。分段建造完毕需要移送冲砂房进行抛丸除锈、根据船舶保护涂层标准(Performance Standard of ...中大型船舶的建造正常都是以分段为单位按区域进行建造。考虑到船体线型、内部结构的布置和施工的方便性,分段划分的形状各异,建造方式也不同。分段建造完毕需要移送冲砂房进行抛丸除锈、根据船舶保护涂层标准(Performance Standard of Protective Coatings,PSPC)保护、喷涂防锈漆等,再运送至船台进行合拢。此过程中的安全起吊、侧翻和翻身等需要考虑的因素很多,特别是特殊形状的异形分段,这就要求分段吊码的设计必须非常谨慎。根据历来多种船型分段吊码的理论设计和现场经验进行分析,并归纳总结异形分段吊码设计的要点。研究结果可为后续不同建造方式和不同结构外形的分段吊码设计提供一定的参考依据。展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.51479135,51525803 and 51679167)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(Grant No.51621092)+1 种基金the Major State Basic Research Development Program of China(973 Program,Grant No.2014CB046801)the Natural Science Foundation of Tianjin(Grant No.15JCQNJC07700)
文摘An experimental study on a bare flexible cylinder as well as cylinders fitted with two types of cross-sectioned helical strakes was carried out in a towing tank. The main purpose of this paper is to investigate the effects of strakes’ cross-section on the vortex-induced vibrations （VIV） suppression of a flexible cylinder. The square-sectioned and round-sectioned helical strakes were selected in the experimental tests. The uniform current was generated by towing the cylinder models along the tank using a towing carriage. The Reynolds number was in the range of 800–16000. The strain responses were measured by the strain gages in cross-flow （CF） and in-line （IL） directions. A modal analysis method was adopted to obtain the displacement responses using the strain signals in different measurement positions. The comparison of the experimental results among the bare cylinder, square-sectioned straked cylinder and round-sectioned straked cylinder was performed. The helical strakes can effectively reduce the strain amplitude, displacement amplitude, response frequencies and dominant modes of a flexible cylinder excited by VIV. And the mean drag coefficients of straked cylinders were approximately consistent with each other. In addition, the square-sectioned and round-sectioned strakes nearly share the similar VIV reduction behaviors. Sometimes, the strakes with round-section represent more excellent effects on the VIV suppression of response frequency than those with square-section.
基金The research is supported by Project of National Natural Science Foundation of China(30571455)and National "948" Project(2005-4-62)
文摘This paper describes a new method for simulation of the cross section shape of log. The self-developed MQK3102 log shape recognizing machine was used to acquire the finite discrete sampling points on the cross section of log and those points were fitted with the quadratic B-spline parametric curve. This method can clearly stimulate the real shape of the log cross section and is characterized by limited sampling points and high speed computing. The computed result of the previous curve does not affect the next one, which may avoid the graphic distortion caused by the accumulative error. The method can be used to simulate the whole body shape of log approximately by sampling the cross sections along the length direction of log, thus providing a reference model for optimum saw cutting of log.
基金supported by a grant from the National Natural Sciences Foundation of China (No. 30872776)
文摘This study evaluated the efficacy and safety of ＂J＂-shaped uterine incision for caesarean section for patients diagnosed with placenta previa. A total of 55 consecutive cases of placenta previa treated in Union Hospital were retrospectively analyzed over a period of two years and 10 months. The subjects were divided into two groups with respect to the uterine incision. Twenty-four pregnant women with placenta previa who were indicated for caesarean section underwent the procedure using a new ＂J＂-shaped uterine incision and 31 pregnant women with placenta previa received caesarean section that used the traditional transverse incision. The two groups were compared in terms of operation time, estimated blood loss, infant expulsion time, exhaust time and postoperative recovery. Meanwhile, comparison was also made in neonatal clinical data between the two groups. Compared with the ＂J＂-shaped incision group, the traditional incision group had a lower Apgar scores （P〈0.05）. However, there existed no statistically significant differences in the overall time of operation and postoperative period of breaking wind （P〉0.05）. It is concluded that, with caesarean section for placenta previa patients, the ＂J＂-shaped uterine incision significantly decreases intraoperative blood loss and facilitates the fetal delivery.
基金supported by Major Program of National Natural Science Foundation of China (Grant No. 50635050)National Natural Science Foundation of China (Grant No. 50575124)
文摘Rolling process plays an important role in the manufacture of Bi-based high temperature superconductor tapes, and the plastic flow regularities of the superconducting wires during deformation will directly affect the ultimate quality of the tapes. In order to investigate the effect of cross-sectional shapes before fiat rolling on the performance and homogeneity of the tapes, some numerical models of Bi-2223/Ag wires with different cross-sectional shapes including circular, square, elliptical and racetrack cross-sections are constructed during the rolling process. By comparing the relative density, logarithmic strain ratio and length-width ratio on the filaments, it is revealed that Bi-2223/Ag wire with special-shaped cross-section can achieve better conductivity than the round wire, in particular, the racetrack cross-sectional wire has the second best performance among four wires. Based on material processability and experimental condition, tri-pass racetrack drawing technique is employed to optimize the process and obtain racetrack cross-sectional wire. The rolling process of Bi-2223/Ag wire with racetrack cross-section causes more intensive deformation of filaments in the center of the tape and achieves the filaments with larger length-width ratio. Also, the deformation distribution of filaments verifies the numerical results. Consequently, the racetrack drawing technique can be utilized for a reference during the mechanical processing and to increase the current transmission capacities of Bi-2223/Ag tapes.
文摘In industrial plants, ships, and buildings, a large amount of gas and air ducts are applied for equipment connection, HVAC, medium transport, and exhaust, etc. These ducts can be designed in varied cross-sectional shapes, such as round or rectangle. The author reveals through geometric calculation of the duct cross-sectional shapes and engineering experiences that the round cross-section is an optimal shape in the duct system. The round duct has the shorter perimeter than the other cross-sectional shape ducts and the stronger structure in the same working condition. The material saving of the round duct due to the shorter perimeter is quantitatively determined. In the pater, it is shown that the round duct is economically attractive. The economic analysis for the material cost saving is illustrated by an example. For a long duct system, the material and material cost savings are significant. It is suggested that the round duct in the gas and air duct system should have priority as long as the field conditions are allowed. In the paper, the material cost saving is also converted to PW, AW, and FW used for LCC economic analysis.
文摘中大型船舶的建造正常都是以分段为单位按区域进行建造。考虑到船体线型、内部结构的布置和施工的方便性,分段划分的形状各异,建造方式也不同。分段建造完毕需要移送冲砂房进行抛丸除锈、根据船舶保护涂层标准(Performance Standard of Protective Coatings,PSPC)保护、喷涂防锈漆等,再运送至船台进行合拢。此过程中的安全起吊、侧翻和翻身等需要考虑的因素很多,特别是特殊形状的异形分段,这就要求分段吊码的设计必须非常谨慎。根据历来多种船型分段吊码的理论设计和现场经验进行分析,并归纳总结异形分段吊码设计的要点。研究结果可为后续不同建造方式和不同结构外形的分段吊码设计提供一定的参考依据。
