This paper deals with the problem of limit cycles for the whirling pendulum equation x=y,y=sin x(cosx-r)under piecewise smooth perturbations of polynomials of cos x,sin x and y of degree n with the switching line x=0....This paper deals with the problem of limit cycles for the whirling pendulum equation x=y,y=sin x(cosx-r)under piecewise smooth perturbations of polynomials of cos x,sin x and y of degree n with the switching line x=0.The upper bounds of the number of limit cycles in both the oscillatory and the rotary regions are obtained using the Picard-Fuchs equations,which the generating functions of the associated first order Melnikov functions satisfy.Furthermore,the exact bound of a special case is given using the Chebyshev system.At the end,some numerical simulations are given to illustrate the existence of limit cycles.展开更多
Nonlinear dynamics of a cracked rotor with whirling were analyzed and were compared to a rotor without whirling. Distinct differences have been found in bifurcation, amplitude, orbit and Poincare map when carrying on ...Nonlinear dynamics of a cracked rotor with whirling were analyzed and were compared to a rotor without whirling. Distinct differences have been found in bifurcation, amplitude, orbit and Poincare map when carrying on this comparison. Complicated dynamics may be found when a cracked rotor has its whirling speed. The results revealed may be useful in crack-early-detection and diagnosis.展开更多
Blade rubbing faults cause detrimental impact on the operation of aeroengines. Most of the existing studies on blade rubbing in the shaft-disk-blade-casing(SDBC) system have overlooked the elastic deformation of the b...Blade rubbing faults cause detrimental impact on the operation of aeroengines. Most of the existing studies on blade rubbing in the shaft-disk-blade-casing(SDBC) system have overlooked the elastic deformation of the blade, while some only consider the whirl of the rotor, neglecting its spin. To address these limitations, this paper proposes a dynamic model with large rotation for the SDBC system. The model incorporates the spin and whirl of the rotor, enabling the realistic reproduction of multiblade rubbing faults. To verify the accuracy of the SDBC model with large rotation and demonstrate its capability to effectively consider the rotational effects such as the centrifugal stiffening and gyroscopic effects, the natural characteristics and dynamic responses of the proposed model are compared with those obtained from reported research and experimental results. Furthermore, the effects of the rotating speed, contact stiffness,and blade number on the dynamic characteristics of the SDBC system with multi-blade rubbing are investigated. The results indicate that the phase angle between the rotor deflection and the unbalance excitation force increases with the increasing rotating speed,which significantly influences the rubbing penetration of each blade. The natural frequency of the SDBC system with rubbing constrain can be observed in the acceleration response of the casing and the torsional response of the shaft, and the frequency is related to the contact stiffness. Moreover, the vibration amplitude increases significantly with the product of the blade number under rubbing, and the rotating frequency approaches the natural frequency of the SDBC system. The proposed model can provide valuable insight for the fault diagnosis of rubbing in bladed rotating machinery.展开更多
Whirling has been adopted for the cost-effective machining of blade-shape components in addition to traditional end milling and flank milling processes.To satisfy the requirements of rotary forming in the blade whirli...Whirling has been adopted for the cost-effective machining of blade-shape components in addition to traditional end milling and flank milling processes.To satisfy the requirements of rotary forming in the blade whirling process,the workpiece must be clamped at both ends in suspension and rotated slowly during machining,which complicates the dynamics.This study aims to identify the dynamic characteristics within the blade whirling operation and present strategies for stability prediction.In this study,the dynamic characteristics of a whirling system are modeled by assuming symmetric and asymmetric parameters.Theoretical prediction frequency response function(FRF)results are compared with experimental results.Moreover,semi-discretization stability lobe diagrams(SLDs)obtained using the dynamic parameters of these models are investigated experimentally.The results show that the asymmetric model is more suitable for describing the whirling system,whereas the symmetric model presents limitations associated with the frequency range and location of measuring points.Finally,a set of airfoil propeller blade whirling operations is conducted to verify the prediction accuracy.展开更多
This paper introduces physical models of drill string whirling and torsional vibrations and analyses the physical models in V.I.Gulyayev's three papers on drill string whirling and torsional vibrations:“V.I.Gulya...This paper introduces physical models of drill string whirling and torsional vibrations and analyses the physical models in V.I.Gulyayev's three papers on drill string whirling and torsional vibrations:“V.I.Gulyayev,L.V.Shevchuk,Drill string bit whirl simulation with the use of frictional and nonholonomic models,Journal of Vibration and Acoustics 138(1)(2016)011021”,“V.I.Gulyayev,L.V.Shevchuk,Nonholonomic dynamics of drill string bit whirling in a deep bore-hole,J Multi-body Dynamics 227(3)(2013)234–244”and“V.I.Gulyayev,SN Hudoliy,O.V.Glushakova,Simulation of torsion relaxation auto-oscillations of drill string bit with viscous and coulombic friction moment models,J Multi-body Dynamics 225(2011)139–152”.This work finds that the physical models described in these three papers are clearly incorrect.展开更多
Fire whirls cause an increase in fire damage. This study clarified the unsteady behavior of fire whirls, considering that instantaneous changes in the temperature and flame shape of fire whirls can affect the damage t...Fire whirls cause an increase in fire damage. This study clarified the unsteady behavior of fire whirls, considering that instantaneous changes in the temperature and flame shape of fire whirls can affect the damage to the surrounding area. Numerical simulations of a lab-scale flame that simulates a fire whirl were performed to investigate the changes in gas temperature and velocity fields under various fuel inflow velocities. The flow field was obtained by solving a continuity equation and a three-dimensional Navier-Stokes equation, and the turbulence was resolved using a large eddy simulation. A chemical equilibrium partially premixed combustion model was used, and radiation effects were considered. The time-averaged gas temperature distribution along the burner central axis revealed that the gas temperature decreased monotonically from upstream to downstream. The time-averaged velocity distribution along the burner central axis showed that the velocity decreased as one moved downstream, but the decrease was uneven. The time variation of the gas temperature demonstrated that the higher the fuel inflow velocity, especially near the burner, the greater the gas temperature flutter. Furthermore, the larger the fuel inflow velocity, the larger the flame swell and wobble. The results showed that the fuel inflow velocity affected temperature fluctuation and flame undulating movement.展开更多
中间表示对编译器的性能、效率和可扩展性都起着决定性作用.Open64编译器采用一种树型结构的中间表示WHIRL,能表示各种高级控制流结构,但不能显式的提供数据流信息.本文基于WHIRL对SSA(Static Single Assignment)进行扩展,提出了一个新...中间表示对编译器的性能、效率和可扩展性都起着决定性作用.Open64编译器采用一种树型结构的中间表示WHIRL,能表示各种高级控制流结构,但不能显式的提供数据流信息.本文基于WHIRL对SSA(Static Single Assignment)进行扩展,提出了一个新的优化结构WHIRL SSA.WHIRL SSA通过将SSA信息标注在WHIRL节点上,显式的为数据流分析提供使用-定义(UD)信息.相比于传统的数据流信息构建方法,WHIRL SSA提供了更精确、有效的数据流信息.本文讨论了WHIRL SSA的设计与实现和基于WHIRL SSA的优化.展开更多
This paper deals with the theoretic simulation of a drill bit whirling under conditions of its contact interaction with the bore-hole bottom rock plane. The bit is considered to be an absolutely rigid ellipsoidal body...This paper deals with the theoretic simulation of a drill bit whirling under conditions of its contact interaction with the bore-hole bottom rock plane. The bit is considered to be an absolutely rigid ellipsoidal body with uneven surface. It is attached to the lower end of a rotating elastic drill string. In the perturbed state, the bit can roll without sliding on the bore-hole bottom, performing whirling vibrations (the model of dynamic equilibrium with pure rolling when maximum cohesive force does not exceed the ultimate Coulombic friction). To describe these motions, a nonholonomic dynamic model is proposed, constitutive partial differential equations are deduced. With their use, the whirling vibrations of oblong and oblate ellipsoidal bits are analyzed, the functions of cohesive (frictional) forces are calculated. It is shown that the system of elastic drill string and ellipsoidal bit can acquire stable or unstable whirl modes with approaching critical Eulerian values by the parameters of axial force, torque and angular velocity. The analogy of the found modes of motions with ones of the Celtic stones is established. It is shown that the ellipsoidal bits can stop their whirling vibrations and change directions of their circumferential motions in the same manner as the ellipsoidal Celtic stones do. As this takes place, the trajectories of the oblate ellipsoidal bits are characterized by more complicated paths and irregularities.展开更多
This paper presents real-time monitoring data and analysis results of the non-stationary vibrations of an operational wind turbine. The advanced time-frequency spectrum analysis reveals varied non-stationary vibration...This paper presents real-time monitoring data and analysis results of the non-stationary vibrations of an operational wind turbine. The advanced time-frequency spectrum analysis reveals varied non-stationary vibrations with timevarying frequencies, which are correlated with certain system natural modes characterized by finite element analysis. Under the effects of strong wind load, the wind turbine system exhibits certain resonances due to blade passing excitations. The system also exhibits certain instabilities due to the coupling of the tower bending modes and blade flapwise mode with blade passing excitations under the variation of wind speed. An analytical model is used to elaborate the non-stationary and instability phenomena observed in experimental results. The properties of the nonlinear instabilities are evaluated by using Lyapunov exponent estimation.展开更多
Under the sliding bearing support for the rotor-bearing system, the dynamic model of a rotor-bearing system is established under the action of non-linear oil film force. The rotor-bearing system has been studied by th...Under the sliding bearing support for the rotor-bearing system, the dynamic model of a rotor-bearing system is established under the action of non-linear oil film force. The rotor-bearing system has been studied by the application of nonlinear dynamics theory, and the system's response was obtained by the numerical integration approach. The effects of eccentricity, speed, lubricant viscosity, radius gap, bearing length and journal radius on the system's response have been studied by using an amplitude-frequency curve, three-dimensional spectrum and bifurcation, which provides a theoretical basis for the diagnosis of the oil whirl fault effectively in the rotor-bearing system supported by a sliding bearing.展开更多
Based on the mechanized mathematics and WU Wen-tsun elimination method, using oil film forces of short-bearing model and Muszynska's dynamic model, the dynamical behavior of rotor-beating system and its stability ...Based on the mechanized mathematics and WU Wen-tsun elimination method, using oil film forces of short-bearing model and Muszynska's dynamic model, the dynamical behavior of rotor-beating system and its stability of motion are investigated. As example, the concept of Wu characteristic set and Maple software, whirl parameters of short-bearing model, which is usually solved by the numerical method, are analyzed. At the same time, stability of zero solution of Jeftcott rotor whirl equation and stability of self-excited vibration are studied. The conditions of stable motion are obtained by using theory of nonlinear vibration.展开更多
An experimental method is presented to analyze the dynamic stability of the gas bearing for small cryogenic turbo-expanders. The rotation imbalance response and the shape of the rotor orbit were obtained for different...An experimental method is presented to analyze the dynamic stability of the gas bearing for small cryogenic turbo-expanders. The rotation imbalance response and the shape of the rotor orbit were obtained for different speeds up to 110,000 rpm, and the critical speed of the rotor-bearing system was determined by a Bode diagram. An FFT signal analytical method was applied to identify the resonance frequency, and the waterfall plot was presented. During the whole process of speeding up to the designed speed of 110,000 rpm, the rotor-bearing works stably with no whirl instability, which is validated in a waterfall plot. Also, the tested rotor-bearing model was analyzed theoretically. It was proved that the experimental results were highly consistent with those of theoretical calculations. Thus the experimental method proposed here to analyze the dynamic stability of the gas bearing is feasible.展开更多
The general features of the Great Whirl(GW)off the Somali Coast in 2017 and its influences on chlorophyll a(Chl a)concentration were studied by using satellite data and model outputs.Results show that GW,which initiat...The general features of the Great Whirl(GW)off the Somali Coast in 2017 and its influences on chlorophyll a(Chl a)concentration were studied by using satellite data and model outputs.Results show that GW,which initiated at7°N,53°E on June 13,had a lifetime of 153 d with an average amplitude of 16 cm and an average radius of 205 km.After the formation of GW,the concentration of Chl a in the interior of GW showed a downward trend throughout its life cycle,except in early July and mid-October.In early July,the Chl a blooms in the interior of GW were attributed to the combined effect of three processes.They are eddy horizontal transportation,the deepening of the mixed layer caused by the monsoon and eddy pumping,and the upward transportation of nutrients caused by eddy-induced Ekman pumping.In October,the Chl a blooms were probably due to the weakening of GW.During the period,water exchange occurred more frequently across the eddy,thus phytoplanktons were imported into the interior of GW.展开更多
The bifurcation of a shaft with hysteretic internal friction of material was analysed. Firstly, the differential motion equation in complex form was deduced using Hamilton principle. Then averaged equations in primary...The bifurcation of a shaft with hysteretic internal friction of material was analysed. Firstly, the differential motion equation in complex form was deduced using Hamilton principle. Then averaged equations in primary resonances were obtained using the averaging method. The stability of steady_state responses was also determined.Lastly, the bifurcations of both normal motion (synchronous whirl) and self_excited motion (non_synchronous whirl) were investigated using the method of singularity. The study shows that by a rather large disturbance, the stability of the shaft can be lost through Hopf bifurcation in case the stability condition is not satisfied. The averaged self_excited response appears as a type of unsymmetrical bifurcation with high orders of co_dimension. The second Hopf bifurcation, which corresponds to double amplitude_modulated response, can occur as the speed of the shaft increases. Balancing the shaft carefully to decrease its unbalance level and increasing the external damping are two effective methods to avoid the appearance of the self_sustained whirl induced by the hysteretic internal friction of material.展开更多
We report a case of cecal volvulus in an 11-year-old girl who had been diagnosed with Cornelia de Lange syndrome. She had undergone operative fundoplication several years earlier and was referred to our institute for ...We report a case of cecal volvulus in an 11-year-old girl who had been diagnosed with Cornelia de Lange syndrome. She had undergone operative fundoplication several years earlier and was referred to our institute for treatment of intestinal obstruction. A severely dilated colon was detected on abdominal roentgenogram, and abdominal CT and colonic enema strongly suggested cecal volvulus. Emergency operation was performed and cecal volvulus with mobile cecum was ascertained;the volvulus was corrected and the mobile cecum was fixed to the peritoneum on the right side. Neurologically handicapped patients sometimes suffer from cecal volvulus, and patients with Cornelia de Lange syndrome are at especially high risk. Moreover, operative fundoplication promotes intestinal dilatation and it may be another risk factor for cecal volvulus.展开更多
Objective: Intermittent gastric volvulus is a rare disease that requires high index of suspicion for diagnosis and treatment. The incidence and prevalence is unknown, may be due to under reporting or under diagnosis. ...Objective: Intermittent gastric volvulus is a rare disease that requires high index of suspicion for diagnosis and treatment. The incidence and prevalence is unknown, may be due to under reporting or under diagnosis. Gastric volvulus may be transient producing few symptoms. The Borchardt’s Triad may be present only during an acute presentation. Common symptoms may mislead to diagnose a nonsurgical disease if an evaluation is not done, keeping in mind a possibility of gastric volvulus, even if a UGI scopy is normal. Cases may be submerged in the community being undiagnosed. Case Series: CASE 1: 21 yrs old male with intermittent abdominal pain for 1(1/2) yrs with marfanoid habitus, MVP and a normal UGI scopy. BMS revealed an Organo-Axial Volvulus and ligament laxity per-operatively. CASE 2: 65 yrs old diabetic female with vomiting and abdominal pain for 3 months and left sided pneumonitis. UGI scopy showed twisted gastric folds immediately below OGJ and inability to visualise antrum. BMS revealed mixed volvulus with paraesophageal herniation of distal stomach. Per-operatively there was laxity of ligaments with omental content alone within the diaphragmatic rent. Posterior retrocolic sub-mucosal gastrojejunostomy(pexy) was done for all cases. Conclusion: Gastric volvulus should be thought of in a case of chronic intermittent abdominal pain with normal baseline evaluation. A Chest X-ray and BMS should be done, at the time of symptoms.展开更多
Over the last few decades,the research on the effect of bristle pack position on the rotordynamic characteristics of the brush-labyrinth seals is not sufficient.To this end,two kinds of brush-labyrinth seals for the b...Over the last few decades,the research on the effect of bristle pack position on the rotordynamic characteristics of the brush-labyrinth seals is not sufficient.To this end,two kinds of brush-labyrinth seals for the bristle pack element installed upstream of the labyrinth teeth named BSU and installed downstream of the labyrinth teeth called BSD were used to investigate the effect of bristle pack position on the rotordynamic characteristics of the brush-labyrinth seals.Using the numerical model combining the porous medium model and the whirling rotor method,the rotordynamic characteristics of the BSU and BSD at various operating conditions including four kinds of pressure ratios,five kinds of inlet preswirl speeds and four kinds of rotor spinning speeds were conducted.The obtained results show that the effects of operating conditions on rotordynamic coefficients for the different seal configurations are different.The direct stiffness,cross-coupled stiffness and direct damping of the BSU are lower than those of the BSD.The rotordynamic coefficients of the BSU are more insensitive to the operating conditions variation.From the perspective of the seal stability,the BSU is a better brush-labyrinth seal configuration at high pressure ratio,high positive preswirl or high rotor spinning speed conditions.While in the case of low pressure ratio,low positive preswirl or low rotor spinning speed conditions,the BSD is a better choice.展开更多
基金supported by the Natural Science Foundation of Ningxia(2022AAC05044)the National Natural Science Foundation of China(12161069)。
文摘This paper deals with the problem of limit cycles for the whirling pendulum equation x=y,y=sin x(cosx-r)under piecewise smooth perturbations of polynomials of cos x,sin x and y of degree n with the switching line x=0.The upper bounds of the number of limit cycles in both the oscillatory and the rotary regions are obtained using the Picard-Fuchs equations,which the generating functions of the associated first order Melnikov functions satisfy.Furthermore,the exact bound of a special case is given using the Chebyshev system.At the end,some numerical simulations are given to illustrate the existence of limit cycles.
文摘Nonlinear dynamics of a cracked rotor with whirling were analyzed and were compared to a rotor without whirling. Distinct differences have been found in bifurcation, amplitude, orbit and Poincare map when carrying on this comparison. Complicated dynamics may be found when a cracked rotor has its whirling speed. The results revealed may be useful in crack-early-detection and diagnosis.
基金Project supported by the National Science and Technology Major Project of China (No. 2017-V-0009)the National Natural Science Foundation of China (Nos. 12032015 and 12121002)the National Funding Program for Postdoctoral Researchers of China (No. GZC20231586)。
文摘Blade rubbing faults cause detrimental impact on the operation of aeroengines. Most of the existing studies on blade rubbing in the shaft-disk-blade-casing(SDBC) system have overlooked the elastic deformation of the blade, while some only consider the whirl of the rotor, neglecting its spin. To address these limitations, this paper proposes a dynamic model with large rotation for the SDBC system. The model incorporates the spin and whirl of the rotor, enabling the realistic reproduction of multiblade rubbing faults. To verify the accuracy of the SDBC model with large rotation and demonstrate its capability to effectively consider the rotational effects such as the centrifugal stiffening and gyroscopic effects, the natural characteristics and dynamic responses of the proposed model are compared with those obtained from reported research and experimental results. Furthermore, the effects of the rotating speed, contact stiffness,and blade number on the dynamic characteristics of the SDBC system with multi-blade rubbing are investigated. The results indicate that the phase angle between the rotor deflection and the unbalance excitation force increases with the increasing rotating speed,which significantly influences the rubbing penetration of each blade. The natural frequency of the SDBC system with rubbing constrain can be observed in the acceleration response of the casing and the torsional response of the shaft, and the frequency is related to the contact stiffness. Moreover, the vibration amplitude increases significantly with the product of the blade number under rubbing, and the rotating frequency approaches the natural frequency of the SDBC system. The proposed model can provide valuable insight for the fault diagnosis of rubbing in bladed rotating machinery.
基金the Shandong Provincial Natural Science Foundation,China(Grant No.ZR2017MEE021)for the financial support toward this research.
文摘Whirling has been adopted for the cost-effective machining of blade-shape components in addition to traditional end milling and flank milling processes.To satisfy the requirements of rotary forming in the blade whirling process,the workpiece must be clamped at both ends in suspension and rotated slowly during machining,which complicates the dynamics.This study aims to identify the dynamic characteristics within the blade whirling operation and present strategies for stability prediction.In this study,the dynamic characteristics of a whirling system are modeled by assuming symmetric and asymmetric parameters.Theoretical prediction frequency response function(FRF)results are compared with experimental results.Moreover,semi-discretization stability lobe diagrams(SLDs)obtained using the dynamic parameters of these models are investigated experimentally.The results show that the asymmetric model is more suitable for describing the whirling system,whereas the symmetric model presents limitations associated with the frequency range and location of measuring points.Finally,a set of airfoil propeller blade whirling operations is conducted to verify the prediction accuracy.
基金The paper is supported by the National Natural Science Foundation of China(Grants Nos.51674220,and 51490653).
文摘This paper introduces physical models of drill string whirling and torsional vibrations and analyses the physical models in V.I.Gulyayev's three papers on drill string whirling and torsional vibrations:“V.I.Gulyayev,L.V.Shevchuk,Drill string bit whirl simulation with the use of frictional and nonholonomic models,Journal of Vibration and Acoustics 138(1)(2016)011021”,“V.I.Gulyayev,L.V.Shevchuk,Nonholonomic dynamics of drill string bit whirling in a deep bore-hole,J Multi-body Dynamics 227(3)(2013)234–244”and“V.I.Gulyayev,SN Hudoliy,O.V.Glushakova,Simulation of torsion relaxation auto-oscillations of drill string bit with viscous and coulombic friction moment models,J Multi-body Dynamics 225(2011)139–152”.This work finds that the physical models described in these three papers are clearly incorrect.
文摘Fire whirls cause an increase in fire damage. This study clarified the unsteady behavior of fire whirls, considering that instantaneous changes in the temperature and flame shape of fire whirls can affect the damage to the surrounding area. Numerical simulations of a lab-scale flame that simulates a fire whirl were performed to investigate the changes in gas temperature and velocity fields under various fuel inflow velocities. The flow field was obtained by solving a continuity equation and a three-dimensional Navier-Stokes equation, and the turbulence was resolved using a large eddy simulation. A chemical equilibrium partially premixed combustion model was used, and radiation effects were considered. The time-averaged gas temperature distribution along the burner central axis revealed that the gas temperature decreased monotonically from upstream to downstream. The time-averaged velocity distribution along the burner central axis showed that the velocity decreased as one moved downstream, but the decrease was uneven. The time variation of the gas temperature demonstrated that the higher the fuel inflow velocity, especially near the burner, the greater the gas temperature flutter. Furthermore, the larger the fuel inflow velocity, the larger the flame swell and wobble. The results showed that the fuel inflow velocity affected temperature fluctuation and flame undulating movement.
文摘This paper deals with the theoretic simulation of a drill bit whirling under conditions of its contact interaction with the bore-hole bottom rock plane. The bit is considered to be an absolutely rigid ellipsoidal body with uneven surface. It is attached to the lower end of a rotating elastic drill string. In the perturbed state, the bit can roll without sliding on the bore-hole bottom, performing whirling vibrations (the model of dynamic equilibrium with pure rolling when maximum cohesive force does not exceed the ultimate Coulombic friction). To describe these motions, a nonholonomic dynamic model is proposed, constitutive partial differential equations are deduced. With their use, the whirling vibrations of oblong and oblate ellipsoidal bits are analyzed, the functions of cohesive (frictional) forces are calculated. It is shown that the system of elastic drill string and ellipsoidal bit can acquire stable or unstable whirl modes with approaching critical Eulerian values by the parameters of axial force, torque and angular velocity. The analogy of the found modes of motions with ones of the Celtic stones is established. It is shown that the ellipsoidal bits can stop their whirling vibrations and change directions of their circumferential motions in the same manner as the ellipsoidal Celtic stones do. As this takes place, the trajectories of the oblate ellipsoidal bits are characterized by more complicated paths and irregularities.
文摘This paper presents real-time monitoring data and analysis results of the non-stationary vibrations of an operational wind turbine. The advanced time-frequency spectrum analysis reveals varied non-stationary vibrations with timevarying frequencies, which are correlated with certain system natural modes characterized by finite element analysis. Under the effects of strong wind load, the wind turbine system exhibits certain resonances due to blade passing excitations. The system also exhibits certain instabilities due to the coupling of the tower bending modes and blade flapwise mode with blade passing excitations under the variation of wind speed. An analytical model is used to elaborate the non-stationary and instability phenomena observed in experimental results. The properties of the nonlinear instabilities are evaluated by using Lyapunov exponent estimation.
文摘Under the sliding bearing support for the rotor-bearing system, the dynamic model of a rotor-bearing system is established under the action of non-linear oil film force. The rotor-bearing system has been studied by the application of nonlinear dynamics theory, and the system's response was obtained by the numerical integration approach. The effects of eccentricity, speed, lubricant viscosity, radius gap, bearing length and journal radius on the system's response have been studied by using an amplitude-frequency curve, three-dimensional spectrum and bifurcation, which provides a theoretical basis for the diagnosis of the oil whirl fault effectively in the rotor-bearing system supported by a sliding bearing.
基金Foundation items:the National Key Basic Research Foundation of China(G1998020317)the National Natural Science Foundation of China(19990510)
文摘Based on the mechanized mathematics and WU Wen-tsun elimination method, using oil film forces of short-bearing model and Muszynska's dynamic model, the dynamical behavior of rotor-beating system and its stability of motion are investigated. As example, the concept of Wu characteristic set and Maple software, whirl parameters of short-bearing model, which is usually solved by the numerical method, are analyzed. At the same time, stability of zero solution of Jeftcott rotor whirl equation and stability of self-excited vibration are studied. The conditions of stable motion are obtained by using theory of nonlinear vibration.
基金supported by the Knowledge Innovation Program of the Chinese Academy of Sciences(No.KJCX2-YW-N16)
文摘An experimental method is presented to analyze the dynamic stability of the gas bearing for small cryogenic turbo-expanders. The rotation imbalance response and the shape of the rotor orbit were obtained for different speeds up to 110,000 rpm, and the critical speed of the rotor-bearing system was determined by a Bode diagram. An FFT signal analytical method was applied to identify the resonance frequency, and the waterfall plot was presented. During the whole process of speeding up to the designed speed of 110,000 rpm, the rotor-bearing works stably with no whirl instability, which is validated in a waterfall plot. Also, the tested rotor-bearing model was analyzed theoretically. It was proved that the experimental results were highly consistent with those of theoretical calculations. Thus the experimental method proposed here to analyze the dynamic stability of the gas bearing is feasible.
基金The National Natural Science Foundation of China under contract Nos 41830538 and 42090042the Chinese Academy of Sciences Fund under contract Nos XDA15020901,133244KYSB20190031,ZDRW-XH-2019-2,ISEE2021PY02 and ISEE2021ZD01+1 种基金Guangdong Basic and Applied Basic Research Fund under contract No.2020A1515010498the Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)Fund under contract Nos GML2019ZD0303 and 2019BT02H594。
文摘The general features of the Great Whirl(GW)off the Somali Coast in 2017 and its influences on chlorophyll a(Chl a)concentration were studied by using satellite data and model outputs.Results show that GW,which initiated at7°N,53°E on June 13,had a lifetime of 153 d with an average amplitude of 16 cm and an average radius of 205 km.After the formation of GW,the concentration of Chl a in the interior of GW showed a downward trend throughout its life cycle,except in early July and mid-October.In early July,the Chl a blooms in the interior of GW were attributed to the combined effect of three processes.They are eddy horizontal transportation,the deepening of the mixed layer caused by the monsoon and eddy pumping,and the upward transportation of nutrients caused by eddy-induced Ekman pumping.In October,the Chl a blooms were probably due to the weakening of GW.During the period,water exchange occurred more frequently across the eddy,thus phytoplanktons were imported into the interior of GW.
文摘The bifurcation of a shaft with hysteretic internal friction of material was analysed. Firstly, the differential motion equation in complex form was deduced using Hamilton principle. Then averaged equations in primary resonances were obtained using the averaging method. The stability of steady_state responses was also determined.Lastly, the bifurcations of both normal motion (synchronous whirl) and self_excited motion (non_synchronous whirl) were investigated using the method of singularity. The study shows that by a rather large disturbance, the stability of the shaft can be lost through Hopf bifurcation in case the stability condition is not satisfied. The averaged self_excited response appears as a type of unsymmetrical bifurcation with high orders of co_dimension. The second Hopf bifurcation, which corresponds to double amplitude_modulated response, can occur as the speed of the shaft increases. Balancing the shaft carefully to decrease its unbalance level and increasing the external damping are two effective methods to avoid the appearance of the self_sustained whirl induced by the hysteretic internal friction of material.
文摘We report a case of cecal volvulus in an 11-year-old girl who had been diagnosed with Cornelia de Lange syndrome. She had undergone operative fundoplication several years earlier and was referred to our institute for treatment of intestinal obstruction. A severely dilated colon was detected on abdominal roentgenogram, and abdominal CT and colonic enema strongly suggested cecal volvulus. Emergency operation was performed and cecal volvulus with mobile cecum was ascertained;the volvulus was corrected and the mobile cecum was fixed to the peritoneum on the right side. Neurologically handicapped patients sometimes suffer from cecal volvulus, and patients with Cornelia de Lange syndrome are at especially high risk. Moreover, operative fundoplication promotes intestinal dilatation and it may be another risk factor for cecal volvulus.
文摘Objective: Intermittent gastric volvulus is a rare disease that requires high index of suspicion for diagnosis and treatment. The incidence and prevalence is unknown, may be due to under reporting or under diagnosis. Gastric volvulus may be transient producing few symptoms. The Borchardt’s Triad may be present only during an acute presentation. Common symptoms may mislead to diagnose a nonsurgical disease if an evaluation is not done, keeping in mind a possibility of gastric volvulus, even if a UGI scopy is normal. Cases may be submerged in the community being undiagnosed. Case Series: CASE 1: 21 yrs old male with intermittent abdominal pain for 1(1/2) yrs with marfanoid habitus, MVP and a normal UGI scopy. BMS revealed an Organo-Axial Volvulus and ligament laxity per-operatively. CASE 2: 65 yrs old diabetic female with vomiting and abdominal pain for 3 months and left sided pneumonitis. UGI scopy showed twisted gastric folds immediately below OGJ and inability to visualise antrum. BMS revealed mixed volvulus with paraesophageal herniation of distal stomach. Per-operatively there was laxity of ligaments with omental content alone within the diaphragmatic rent. Posterior retrocolic sub-mucosal gastrojejunostomy(pexy) was done for all cases. Conclusion: Gastric volvulus should be thought of in a case of chronic intermittent abdominal pain with normal baseline evaluation. A Chest X-ray and BMS should be done, at the time of symptoms.
基金co-supported by the National Key R&D Program of China(No.2017YFB0601804)the National Natural Science Foundation of China(No.51776152)。
文摘Over the last few decades,the research on the effect of bristle pack position on the rotordynamic characteristics of the brush-labyrinth seals is not sufficient.To this end,two kinds of brush-labyrinth seals for the bristle pack element installed upstream of the labyrinth teeth named BSU and installed downstream of the labyrinth teeth called BSD were used to investigate the effect of bristle pack position on the rotordynamic characteristics of the brush-labyrinth seals.Using the numerical model combining the porous medium model and the whirling rotor method,the rotordynamic characteristics of the BSU and BSD at various operating conditions including four kinds of pressure ratios,five kinds of inlet preswirl speeds and four kinds of rotor spinning speeds were conducted.The obtained results show that the effects of operating conditions on rotordynamic coefficients for the different seal configurations are different.The direct stiffness,cross-coupled stiffness and direct damping of the BSU are lower than those of the BSD.The rotordynamic coefficients of the BSU are more insensitive to the operating conditions variation.From the perspective of the seal stability,the BSU is a better brush-labyrinth seal configuration at high pressure ratio,high positive preswirl or high rotor spinning speed conditions.While in the case of low pressure ratio,low positive preswirl or low rotor spinning speed conditions,the BSD is a better choice.