Magnetorheological(MR)bearings,with their field-controllable rheological properties,offer new possibilities for control of rotor instabilities.However,their nonlinear dynamic behaviors and the underlying physical mech...Magnetorheological(MR)bearings,with their field-controllable rheological properties,offer new possibilities for control of rotor instabilities.However,their nonlinear dynamic behaviors and the underlying physical mechanisms governing these instabilities remain insufficiently understood.This work develops a coupled MR bearingrotor system model,where the oil film force is derived from a novel bilinear constitutive equation to capture the field-sensitive shear behaviors of MR fluids.Complex nonlinear dynamic behaviors including period doubling,quasi-period,and chaos are revealed,which emerge from the interaction between oil film vortex dynamics and magnetic excitation.The critical instability mechanism is identified from the evolution of intrinsic dynamic characteristics of MR bearings.When the whirl speed within the oil film reaches approximately half of the rotor speed,the damping force balances the destabilizing force,thereby defining a critical threshold beyond which the system transitions to instability.This threshold can be effectively tuned by adjusting the excitation current,which modifies the yield stress of MR fluids and consequently regulates the damping force.As a result,the nonlinear vibrations of oil whirl and whip can be suppressed,and the system stability can be significantly enhanced.These findings provide both theoretical insight and practical guidance for the design and control of MR bearing supported rotor systems.展开更多
Fluid lubricated bearings have been widely adopted as support components for high-end equipment in metrology,semiconductor devices,aviation,strategic defense,ultraprecision manufacturing,medical treatment,and power ge...Fluid lubricated bearings have been widely adopted as support components for high-end equipment in metrology,semiconductor devices,aviation,strategic defense,ultraprecision manufacturing,medical treatment,and power generation.In all these applications,the equipment must deliver extreme working performances such as ultraprecise movement,ultrahigh rotation speed,ultraheavy bearing loads,ultrahigh environmental temperatures,strong radiation resistance,and high vacuum operation,which have challenged the design and optimization of reliable fluid lubricated bearings.Breakthrough of any related bottlenecks will promote the development course of high-end equipment.To promote the advancement of high-end equipment,this paper reviews the design and optimization of fluid lubricated bearings operated at typical extreme working performances,targeting the realization of extreme working performances,current challenges and solutions,underlying deficiencies,and promising developmental directions.This paper can guide the selection of suitable fluid lubricated bearings and optimize their structures to meet their required working performances.展开更多
Based on the nonlinear characiers of the discrete problems of some ellipticalvariational inequalities, this paper presents a numerical iterative method, the schemesof which are pithy and converge rapidly The new metho...Based on the nonlinear characiers of the discrete problems of some ellipticalvariational inequalities, this paper presents a numerical iterative method, the schemesof which are pithy and converge rapidly The new method possesses a high efficiency. insolving such applied engineering problems as obstacle problems and .free boundary.problems arising in fluid lubrications.展开更多
Effects of time-dependent deformation（TDD） on a tunnel constructed using the micro-tunneling technique in Queenston shale（QS） are investigated employing the finite element method. The TDD and strength parameters o...Effects of time-dependent deformation（TDD） on a tunnel constructed using the micro-tunneling technique in Queenston shale（QS） are investigated employing the finite element method. The TDD and strength parameters of the QS were measured from tests conducted on QS specimens soaked in water and lubricant fluids（LFs） used in micro-tunneling such as bentonite and polymer solutions. The numerical model was verified using the results of TDD tests performed on QS samples, field measurements of some documented projects, and the closed-form solutions to circular tunnels in swelling rock. The verified model was then employed to conduct a parametric study considering important micro-tunneling design parameters, such as depth and diameter of the tunnel, in situ stress ratio（K;）, and the time lapse prior to replacing LFs with permanent cement grout around the tunnel. It was revealed that the time lapse plays a vital role in controlling deformations and associated stresses developed in the tunnel lining.The critical case of a pipe or tunnel in which the maximum tensile stress develops at its springline occurs when it is constructed at shallow depths in the QS layer. The results of the parametric study were used to suggest recommendations for the construction of tunnels in QS employing micro-tunneling.展开更多
Lubrication is an important prerequisite and foundation for the organism to protect biological tissues from mechanical friction damage and to maintain their normal life functions[1,2].After mechanical friction trauma,...Lubrication is an important prerequisite and foundation for the organism to protect biological tissues from mechanical friction damage and to maintain their normal life functions[1,2].After mechanical friction trauma,the lubrication matrix repairs damaged tissue by protecting the host from external impact and promotes the restoration of lubrication balance in the body.The process of lubrication typically unfolds in a series of events,beginning with a rapid response phase where lubricating fluids flow within the organism,reducing wear between tissues.This is followed by a gradual transition into a lubrication phase involving various lubrication mechanisms,such as fluid lubrication(The load is fully sustained by lubricant due to viscous forces in the space or gap between the components that are moving in relation to another object,while preventing solid-to-solid contact),boundary lubrication(The load is carried by surface high points rather than by lubricant),hydration lubrication(Hydration layers are tightly bound by the surrounding charges,allowing them to withstand significant pressure without being displaced,while also being able to quickly relax,resulting in a fluid-like response to shear forces),and mixed lubrication(This regime exists between full film lubrication and boundary lubrication,where the lubricant film generated is inadequate to fully separate the surfaces in contact,yet the hydrodynamic effect is significant)[3-5].Thus,lubrication plays a vital role in protecting living beings.However,if this well-coordinated wear reduction process is disrupted,lubrication can become uncontrolled or deteriorate,potentially leading to a range of lubrication-related diseases,including osteoarthritis,tendon adhesion,intervertebral disc degeneration,femoral head necrosis,cardiovascular blockages,tooth wear,and implant infections[1].展开更多
基金Project supported by the National Natural Science Foundation of China(Nos.52575093 and 12202229)the China Postdoctoral Science Foundation(No.2025M771368)the Fundamental Research Funds for the Central Universities of China(Nos.buctrc202405 and JD2522)。
文摘Magnetorheological(MR)bearings,with their field-controllable rheological properties,offer new possibilities for control of rotor instabilities.However,their nonlinear dynamic behaviors and the underlying physical mechanisms governing these instabilities remain insufficiently understood.This work develops a coupled MR bearingrotor system model,where the oil film force is derived from a novel bilinear constitutive equation to capture the field-sensitive shear behaviors of MR fluids.Complex nonlinear dynamic behaviors including period doubling,quasi-period,and chaos are revealed,which emerge from the interaction between oil film vortex dynamics and magnetic excitation.The critical instability mechanism is identified from the evolution of intrinsic dynamic characteristics of MR bearings.When the whirl speed within the oil film reaches approximately half of the rotor speed,the damping force balances the destabilizing force,thereby defining a critical threshold beyond which the system transitions to instability.This threshold can be effectively tuned by adjusting the excitation current,which modifies the yield stress of MR fluids and consequently regulates the damping force.As a result,the nonlinear vibrations of oil whirl and whip can be suppressed,and the system stability can be significantly enhanced.These findings provide both theoretical insight and practical guidance for the design and control of MR bearing supported rotor systems.
基金supported by the National Natural Science Foundations of China under Grant Nos.52206123,52075506,52205543,52322510,52275470 and 52105129Science and Technology Planning Project of Sichuan Province under Grant No.2021YJ0557+2 种基金Natural Science Foundation of Sichuan Province under Grant No.2023NSFSC1947Presidential Foundation of China Academy of Engineering PhysicsGrant No.YZJJZQ2022009。
文摘Fluid lubricated bearings have been widely adopted as support components for high-end equipment in metrology,semiconductor devices,aviation,strategic defense,ultraprecision manufacturing,medical treatment,and power generation.In all these applications,the equipment must deliver extreme working performances such as ultraprecise movement,ultrahigh rotation speed,ultraheavy bearing loads,ultrahigh environmental temperatures,strong radiation resistance,and high vacuum operation,which have challenged the design and optimization of reliable fluid lubricated bearings.Breakthrough of any related bottlenecks will promote the development course of high-end equipment.To promote the advancement of high-end equipment,this paper reviews the design and optimization of fluid lubricated bearings operated at typical extreme working performances,targeting the realization of extreme working performances,current challenges and solutions,underlying deficiencies,and promising developmental directions.This paper can guide the selection of suitable fluid lubricated bearings and optimize their structures to meet their required working performances.
文摘Based on the nonlinear characiers of the discrete problems of some ellipticalvariational inequalities, this paper presents a numerical iterative method, the schemesof which are pithy and converge rapidly The new method possesses a high efficiency. insolving such applied engineering problems as obstacle problems and .free boundary.problems arising in fluid lubrications.
基金Ward and Burke Microtunneling Ltd. for its excellent technical and financial support
文摘Effects of time-dependent deformation（TDD） on a tunnel constructed using the micro-tunneling technique in Queenston shale（QS） are investigated employing the finite element method. The TDD and strength parameters of the QS were measured from tests conducted on QS specimens soaked in water and lubricant fluids（LFs） used in micro-tunneling such as bentonite and polymer solutions. The numerical model was verified using the results of TDD tests performed on QS samples, field measurements of some documented projects, and the closed-form solutions to circular tunnels in swelling rock. The verified model was then employed to conduct a parametric study considering important micro-tunneling design parameters, such as depth and diameter of the tunnel, in situ stress ratio（K;）, and the time lapse prior to replacing LFs with permanent cement grout around the tunnel. It was revealed that the time lapse plays a vital role in controlling deformations and associated stresses developed in the tunnel lining.The critical case of a pipe or tunnel in which the maximum tensile stress develops at its springline occurs when it is constructed at shallow depths in the QS layer. The results of the parametric study were used to suggest recommendations for the construction of tunnels in QS employing micro-tunneling.
基金supported by the Noncommunicable Chronic Diseases-National Science and Technology Major Project(2023ZD0500700)the National Natural Science Foundation of China(52305206)the Shanghai Pujiang Programme(23PJD056)。
文摘Lubrication is an important prerequisite and foundation for the organism to protect biological tissues from mechanical friction damage and to maintain their normal life functions[1,2].After mechanical friction trauma,the lubrication matrix repairs damaged tissue by protecting the host from external impact and promotes the restoration of lubrication balance in the body.The process of lubrication typically unfolds in a series of events,beginning with a rapid response phase where lubricating fluids flow within the organism,reducing wear between tissues.This is followed by a gradual transition into a lubrication phase involving various lubrication mechanisms,such as fluid lubrication(The load is fully sustained by lubricant due to viscous forces in the space or gap between the components that are moving in relation to another object,while preventing solid-to-solid contact),boundary lubrication(The load is carried by surface high points rather than by lubricant),hydration lubrication(Hydration layers are tightly bound by the surrounding charges,allowing them to withstand significant pressure without being displaced,while also being able to quickly relax,resulting in a fluid-like response to shear forces),and mixed lubrication(This regime exists between full film lubrication and boundary lubrication,where the lubricant film generated is inadequate to fully separate the surfaces in contact,yet the hydrodynamic effect is significant)[3-5].Thus,lubrication plays a vital role in protecting living beings.However,if this well-coordinated wear reduction process is disrupted,lubrication can become uncontrolled or deteriorate,potentially leading to a range of lubrication-related diseases,including osteoarthritis,tendon adhesion,intervertebral disc degeneration,femoral head necrosis,cardiovascular blockages,tooth wear,and implant infections[1].
