The failure of the key parts, such as gears, in cutter head driving system of tunneling boring machine has not been properly solved under the interaction of driving motors asynchronously and wave tunneling torque load...The failure of the key parts, such as gears, in cutter head driving system of tunneling boring machine has not been properly solved under the interaction of driving motors asynchronously and wave tunneling torque load. A dynamic model of multi-gear driving system is established considering the inertia effects of driving mechanism and cutter head as well as the bending-torsional coupling. By taking into account the nonlinear coupling factors between ring gear and multiple pinions, the influence for meshing angle by bending-torsional coupling and the dynamic load-sharing characteristic of multiple pinions driving are analyzed. Load-sharing coefficients at different rotating cutter head speeds and input torques are presented. Numerical results indicate that the load-sharing coefficients can reach up to 1.2-1.3. A simulated experimental platform of the multiple pinions driving is carried out and the torque distributions under the step load in driving shaft of pinions are measured. The imbalance of torque distribution of pinions is verified and the load-sharing coefficients in each pinion can reach 1.262. The results of simulation and test are similar, which shows the correctness of theoretical model. A loop coupling control method is put forward based on current torque master slave control method. The imbalance of the multiple pinions driving in cutter head driving system of tunneling boring machine can be greatly decreased and the load-sharing coefficients can be reduced to 1.051 by using the loop coupling control method. The proposed research provides an effective solution to the imbalance of torque distribution and synchronous control method for multiple pinions driving of TBM.展开更多
On the basis of capacity flow model, a new model is developed for a load-sharing k-out-of-n： G system consisting of different components, to describe the increase of the same component＇s failure rates under differen...On the basis of capacity flow model, a new model is developed for a load-sharing k-out-of-n： G system consisting of different components, to describe the increase of the same component＇s failure rates under different loads. All components have exponential life distributions and are nonrepairable in the system. Reliability of load- sharing 2-out- of-3： G system is calculated and some special cases for the system are discussed. The calculation and discussions show that the model is right and practical.展开更多
BACKGROUND Many classification systems of thoracolumbar spinal fractures have been proposed to enhance treatment protocols,but none have achieved universal adoption.AIM To develop a new patient scoring system for case...BACKGROUND Many classification systems of thoracolumbar spinal fractures have been proposed to enhance treatment protocols,but none have achieved universal adoption.AIM To develop a new patient scoring system for cases with thoracolumbar injury classification and severity score(TLICS)=4,namely the load-sharing thoracolumbar injury score(LSTLIS).METHODS Based on thoracolumbar injury classification and severity score,this study proposes the use of the established load-sharing classification(LSC)to develop an improved classification system(LSTLIS).To prove the reliability and reproducibility of LSTLIS,a retrospective analysis for patients with thoracolumbar vertebral fractures has been conducted.RESULTS A total of 102 cases were enrolled in the study.The scoring trend of LSTLIS is roughly similar as the LSC scoring,however,the average deviation based on the former method is relatively smaller than that of the latter.Thus,the robustness of the LSTLIS scoring method is better than that of LSC.LSTLIS can further classify patients with TLICS=4,so as to assess more accurately this particular circumstance,and the majority of LSTLIS recommendations are consistent with actual clinical decisions.LSTLIS is a scoring system that combines LSC and TLICS to compensate for the lack of appropriate inclusion of anterior and middle column compression fractures with TLICS.Following preliminary clinical verification,LSTLIS has greater feasibility and reliability value,is more practical in comprehensively assessing certain clinical circumstances,and has better accuracy with clinically significant guidelines.展开更多
In complex systems,functional dependency and physical dependency may have a coupling effect.In this paper,the reliability of a k-out-of-n system is analyzed considering load-sharing effect and failure mechanism(FM)pro...In complex systems,functional dependency and physical dependency may have a coupling effect.In this paper,the reliability of a k-out-of-n system is analyzed considering load-sharing effect and failure mechanism(FM)propagation.Three types of FMs are considered and an accumulative damage model is proposed to illustrate the system behavior of the k-out-of-n system and the coupling effect between load-sharing effect and FM propagation effect.A combinational algorithm based on Binary decision diagram(BDD)and Monte-Carlo simulation is presented to evaluate the complex system behavior and reliability of the k-out-of-n system.A current stabilizing system that consists of a 3-out-of-6 subsystem with FM propagation effect is presented as a case to illustrate the complex behavior and to verify the applicability of the proposed method.Due to the coupling effect change,the main mechanism and failure mode will be changed,and the system lifetime is shortened.Reasons are analyzed and results show that different sensitivity factors of three different FMs lead to the change of the development rate,thus changing the failure scenario.Neglecting the coupling effect may lead to an incomplete and ineffective measuring and monitoring plan.Design strategies must be adopted to make the FM propagation insensitive to load-sharing effect.展开更多
Few studies were focused on the load-sharing characteristics of double-row planetary gear(DRPG)systems with bearings.Meanwhile,the supported bearing has an important influence on the transmission characteristics of th...Few studies were focused on the load-sharing characteristics of double-row planetary gear(DRPG)systems with bearings.Meanwhile,the supported bearing has an important influence on the transmission characteristics of the entire system.To overcome this problem,a multi-body dynamic(MBD)model of the DRPG system fully considering the influences of bearing parameters is established.Dynamic loads among contacting gear pairs have been obtained to calculate the load-sharing coefficient(LSC)of the system.The LSC of each gear tooth pair has been compared to study the effect of the supported bearing clearance on the load-sharing characteristics.These methods are based on Hertz contact theory.The liner stiffness and damping are used in the model.The results show that the supported bearing clearance has a greatly effect on the LSC of the DRPG system.Choosing appropriate clearance parameters of supported bearing can help suppress the uneven load distribution of the DRPG system.The results can provide some guidance to find new method to study the LSC and increase the service life of planetary gear systems.展开更多
To solve a real problem:how to calculate the reliability of a system with time-varying failure rates in industry systems,this paper studies a model for the load-sharing parallel system with time-varying failure rates,...To solve a real problem:how to calculate the reliability of a system with time-varying failure rates in industry systems,this paper studies a model for the load-sharing parallel system with time-varying failure rates,and obtains calculating formulas of reliability and availability of the system by solving differential equations.In this paper,the failure rates are expressed in polynomial configuration.The constant,linear and Weibull failure rate are in their special form.The polynomial failure rates provide flexibility in modeling the practical time-varying failure rates.展开更多
A set of serf-developed apparatus for foundation physical model were utilized to conduct model tests of the multi-element composite foundation with a steel pipe pile and several gravel piles. Some load-bearing charact...A set of serf-developed apparatus for foundation physical model were utilized to conduct model tests of the multi-element composite foundation with a steel pipe pile and several gravel piles. Some load-bearing characteristics of the multi-element Composite foundation, including the curves of foundation settlement, stresses of piles, pile-soil stress ratio, and load-sharing ratio of piles and soil, were obtained to study its working performances in silty sand soil. The experimental results revealed that the multi-element composite foundation with steel pipe pile and gravel pile contributed more than the gravel pile composite foundation in improving the bearing capacity of the silty fine sand.展开更多
基金supported by National Basic Research Program of China(973 Program, Grant No. 2013CB035402)
文摘The failure of the key parts, such as gears, in cutter head driving system of tunneling boring machine has not been properly solved under the interaction of driving motors asynchronously and wave tunneling torque load. A dynamic model of multi-gear driving system is established considering the inertia effects of driving mechanism and cutter head as well as the bending-torsional coupling. By taking into account the nonlinear coupling factors between ring gear and multiple pinions, the influence for meshing angle by bending-torsional coupling and the dynamic load-sharing characteristic of multiple pinions driving are analyzed. Load-sharing coefficients at different rotating cutter head speeds and input torques are presented. Numerical results indicate that the load-sharing coefficients can reach up to 1.2-1.3. A simulated experimental platform of the multiple pinions driving is carried out and the torque distributions under the step load in driving shaft of pinions are measured. The imbalance of torque distribution of pinions is verified and the load-sharing coefficients in each pinion can reach 1.262. The results of simulation and test are similar, which shows the correctness of theoretical model. A loop coupling control method is put forward based on current torque master slave control method. The imbalance of the multiple pinions driving in cutter head driving system of tunneling boring machine can be greatly decreased and the load-sharing coefficients can be reduced to 1.051 by using the loop coupling control method. The proposed research provides an effective solution to the imbalance of torque distribution and synchronous control method for multiple pinions driving of TBM.
基金the Natural Science Foundation of the Education Department of Sichuan Province([2006]A067)the Talent Introduction Foundation of Sichuan Normal University.
文摘On the basis of capacity flow model, a new model is developed for a load-sharing k-out-of-n： G system consisting of different components, to describe the increase of the same component＇s failure rates under different loads. All components have exponential life distributions and are nonrepairable in the system. Reliability of load- sharing 2-out- of-3： G system is calculated and some special cases for the system are discussed. The calculation and discussions show that the model is right and practical.
基金Supported by Multicenter Clinical Trial of hUC-MSCs in the Treatment of Late Chronic Spinal Cord Injury,No.2017YFA0105404the Project of Shanghai Science and Technology Commission,No.19441901702.
文摘BACKGROUND Many classification systems of thoracolumbar spinal fractures have been proposed to enhance treatment protocols,but none have achieved universal adoption.AIM To develop a new patient scoring system for cases with thoracolumbar injury classification and severity score(TLICS)=4,namely the load-sharing thoracolumbar injury score(LSTLIS).METHODS Based on thoracolumbar injury classification and severity score,this study proposes the use of the established load-sharing classification(LSC)to develop an improved classification system(LSTLIS).To prove the reliability and reproducibility of LSTLIS,a retrospective analysis for patients with thoracolumbar vertebral fractures has been conducted.RESULTS A total of 102 cases were enrolled in the study.The scoring trend of LSTLIS is roughly similar as the LSC scoring,however,the average deviation based on the former method is relatively smaller than that of the latter.Thus,the robustness of the LSTLIS scoring method is better than that of LSC.LSTLIS can further classify patients with TLICS=4,so as to assess more accurately this particular circumstance,and the majority of LSTLIS recommendations are consistent with actual clinical decisions.LSTLIS is a scoring system that combines LSC and TLICS to compensate for the lack of appropriate inclusion of anterior and middle column compression fractures with TLICS.Following preliminary clinical verification,LSTLIS has greater feasibility and reliability value,is more practical in comprehensively assessing certain clinical circumstances,and has better accuracy with clinically significant guidelines.
基金This work was supported by the National Natural Science Foundation of China(61503014).
文摘In complex systems,functional dependency and physical dependency may have a coupling effect.In this paper,the reliability of a k-out-of-n system is analyzed considering load-sharing effect and failure mechanism(FM)propagation.Three types of FMs are considered and an accumulative damage model is proposed to illustrate the system behavior of the k-out-of-n system and the coupling effect between load-sharing effect and FM propagation effect.A combinational algorithm based on Binary decision diagram(BDD)and Monte-Carlo simulation is presented to evaluate the complex system behavior and reliability of the k-out-of-n system.A current stabilizing system that consists of a 3-out-of-6 subsystem with FM propagation effect is presented as a case to illustrate the complex behavior and to verify the applicability of the proposed method.Due to the coupling effect change,the main mechanism and failure mode will be changed,and the system lifetime is shortened.Reasons are analyzed and results show that different sensitivity factors of three different FMs lead to the change of the development rate,thus changing the failure scenario.Neglecting the coupling effect may lead to an incomplete and ineffective measuring and monitoring plan.Design strategies must be adopted to make the FM propagation insensitive to load-sharing effect.
基金National Natural Science Foundation of China(No.51975068)。
文摘Few studies were focused on the load-sharing characteristics of double-row planetary gear(DRPG)systems with bearings.Meanwhile,the supported bearing has an important influence on the transmission characteristics of the entire system.To overcome this problem,a multi-body dynamic(MBD)model of the DRPG system fully considering the influences of bearing parameters is established.Dynamic loads among contacting gear pairs have been obtained to calculate the load-sharing coefficient(LSC)of the system.The LSC of each gear tooth pair has been compared to study the effect of the supported bearing clearance on the load-sharing characteristics.These methods are based on Hertz contact theory.The liner stiffness and damping are used in the model.The results show that the supported bearing clearance has a greatly effect on the LSC of the DRPG system.Choosing appropriate clearance parameters of supported bearing can help suppress the uneven load distribution of the DRPG system.The results can provide some guidance to find new method to study the LSC and increase the service life of planetary gear systems.
文摘To solve a real problem:how to calculate the reliability of a system with time-varying failure rates in industry systems,this paper studies a model for the load-sharing parallel system with time-varying failure rates,and obtains calculating formulas of reliability and availability of the system by solving differential equations.In this paper,the failure rates are expressed in polynomial configuration.The constant,linear and Weibull failure rate are in their special form.The polynomial failure rates provide flexibility in modeling the practical time-varying failure rates.
基金The National Natural Science Foundation of China (No.50478090)
文摘A set of serf-developed apparatus for foundation physical model were utilized to conduct model tests of the multi-element composite foundation with a steel pipe pile and several gravel piles. Some load-bearing characteristics of the multi-element Composite foundation, including the curves of foundation settlement, stresses of piles, pile-soil stress ratio, and load-sharing ratio of piles and soil, were obtained to study its working performances in silty sand soil. The experimental results revealed that the multi-element composite foundation with steel pipe pile and gravel pile contributed more than the gravel pile composite foundation in improving the bearing capacity of the silty fine sand.
