A beam approximation method for dynamic analysis of launch vehicles modelled as stiffened cylindrical shells is proposed.Firstly,an initial beam model of the stiffened cylindrical shell is established based on the cro...A beam approximation method for dynamic analysis of launch vehicles modelled as stiffened cylindrical shells is proposed.Firstly,an initial beam model of the stiffened cylindrical shell is established based on the cross-sectional area equivalence principle that represents the shell skin and its longitudinal ribs as a beam with annular cross-section,and the circumferential ribs as lumped masses at the nodes of the beam elements.Then,a fine finite element model(FE model)of the stiffened cylindrical shell is constructed and a modal analysis is carried out.Finally,the initial beam model is improved through model updating against the natural frequencies and mode shapes of the fine FE model of the shell.To facilitate the comparison between the mode shapes of the fine FE model of the stiffened shell and the equivalent beam model,a weighted nodal displacement coupling relationship is introduced.To prevent the design parameters used in model updating from converging to incorrect values,a pre-model updating procedure is added before the proper model updating.The results of two examples demonstrate that the beam approximation method presented in this paper can build equivalent beam models of stiffened cylindrical shells which can reflect the global longitudinal,lateral and torsional vibration characteristics very well in terms of the natural frequencies.展开更多
The first International Symposium on Dynamics,Monitoring,and Diagnostics was held in Chongqing,China,in April 2022.The Symposium,which was attended both virtually and in person,had an audience of 2000 and was aimed at...The first International Symposium on Dynamics,Monitoring,and Diagnostics was held in Chongqing,China,in April 2022.The Symposium,which was attended both virtually and in person,had an audience of 2000 and was aimed at enhancing the intelligence of condition monitoring for engineering systems.During the Symposium,five keynote addresses were delivered by world leading experts,and this paper is comprised of summaries of these addresses to ensure that the important messages of these speakers are properly on record and readily able to be referenced.展开更多
In this work,a comparative study is performed to investigate the influence of time-varying normal forces on the friction properties and friction-induced stick-slip vibration(FIV)by experimental and theoretical methods...In this work,a comparative study is performed to investigate the influence of time-varying normal forces on the friction properties and friction-induced stick-slip vibration(FIV)by experimental and theoretical methods.In the experiments,constant and harmonic-varying normal forces are applied,respectively.The measured vibration signals under two loading forms are compared in both time and frequency domains.In addition,mathematical tools such as phase space reconstruction and Fourier spectra are used to reveal the science behind the complicated dynamic behavior.It can be found that the friction system shows steady stick-slip vibration,and the main frequency does not vary with the magnitude of the constant normal force,but the size of limit cycle increases with the magnitude of the constant normal force.In contrast,the friction system under the harmonic normal force shows complicated behavior,for example,higher-frequency larger-amplitude vibration occurs and looks chaotic as the frequency of the normal force increases.The interesting findings offer a new way for controlling FIV in engineering applications.展开更多
For years,friction-induced vibration and noise(FIVN)has puzzled many researchers in academia and industry.Several mechanisms have been proposed for explaining its occurrence and quantifying its frequencies,notably for...For years,friction-induced vibration and noise(FIVN)has puzzled many researchers in academia and industry.Several mechanisms have been proposed for explaining its occurrence and quantifying its frequencies,notably for automotive brake squeal,clutch squeal,and even rail corrugation.However,due to the complex and complicated nature of FIVN,there is not yet one fundamental mechanism that can explain all phenomena of FIVN.Based on experimental results obtained on a simple test structure and corresponding numerical validation using both complex eigenvalue analysis(CEA)and transient dynamic analysis(TDA),this study attempts to propose a new fundamental mechanism for FIVN,which is the repeated cycles of partial detachment and then reattachment of the contact surfaces.Since friction is ubiquitous and FIVN is very common,the insight into FIVN reported in this paper is highly significant and will help establish effective means to control FIVN in engineering and daily life.展开更多
This paper investigates the self-loosening of threaded fasteners subjected to dynamic shear load. Three kinds of typical coatings, PTFE, MoS_2, and TiN applied to bolts and nuts, are tested in this investigation. The ...This paper investigates the self-loosening of threaded fasteners subjected to dynamic shear load. Three kinds of typical coatings, PTFE, MoS_2, and TiN applied to bolts and nuts, are tested in this investigation. The study experimentally examines the loosening mechanisms of fasteners and assesses the anti-loosening performance of the three tested coatings based on their tightening characteristics, loosening curves, and the damage of thread surface. Additionally, the anti-loosening performance of the three coatings is compared under different load forms. The results indicate that the PTFE and MoS_2 coatings have significant anti-loosening effect, whereas the anti-loosening performance of Ti N coating is not satisfactory. It is also found that an appropriate increase of the initial tightening torque can significantly improve the anti-loosening effect. In addition, the microscopic analyses of PTFE and MoS2 coating reveal that a reduced initial tightening torque leads to fretting wear on the thread contact surfaces of fasteners, thereby aggravating the damage.展开更多
In this study,piezoelectric elements were added to a reciprocating friction test bench to harvest friction‐induced vibration energy.Parameters such as vibration acceleration,noise,and voltage signals of the system we...In this study,piezoelectric elements were added to a reciprocating friction test bench to harvest friction‐induced vibration energy.Parameters such as vibration acceleration,noise,and voltage signals of the system were measured and analyzed.The results show that the piezoelectric elements can not only collect vibration energy but also suppress friction‐induced vibration noise(FIVN).Additionally,the wear of the friction interface was examined via optical microscopy(OM),scanning electron microscopy(SEM),and white‐light interferometry(WLI).The results show that the surface wear state improved because of the reduction of FIVN.In order to analyze the experimental results in detail and explain them reasonably,the experimental phenomena were simulated numerically.Moreover,a simplified two‐degree‐of‐freedom numerical model including the original system and the piezoelectric system was established to qualitatively describe the effects,dynamics,and tribological behaviors of the added piezoelectric elements to the original system.展开更多
基金the National Natural Science Foundation of China(11672060,11672052).
文摘A beam approximation method for dynamic analysis of launch vehicles modelled as stiffened cylindrical shells is proposed.Firstly,an initial beam model of the stiffened cylindrical shell is established based on the cross-sectional area equivalence principle that represents the shell skin and its longitudinal ribs as a beam with annular cross-section,and the circumferential ribs as lumped masses at the nodes of the beam elements.Then,a fine finite element model(FE model)of the stiffened cylindrical shell is constructed and a modal analysis is carried out.Finally,the initial beam model is improved through model updating against the natural frequencies and mode shapes of the fine FE model of the shell.To facilitate the comparison between the mode shapes of the fine FE model of the stiffened shell and the equivalent beam model,a weighted nodal displacement coupling relationship is introduced.To prevent the design parameters used in model updating from converging to incorrect values,a pre-model updating procedure is added before the proper model updating.The results of two examples demonstrate that the beam approximation method presented in this paper can build equivalent beam models of stiffened cylindrical shells which can reflect the global longitudinal,lateral and torsional vibration characteristics very well in terms of the natural frequencies.
基金supported in part by the Australian Government through the Australian Research Council Discovery Project DP160103501.
文摘The first International Symposium on Dynamics,Monitoring,and Diagnostics was held in Chongqing,China,in April 2022.The Symposium,which was attended both virtually and in person,had an audience of 2000 and was aimed at enhancing the intelligence of condition monitoring for engineering systems.During the Symposium,five keynote addresses were delivered by world leading experts,and this paper is comprised of summaries of these addresses to ensure that the important messages of these speakers are properly on record and readily able to be referenced.
基金The authors would like to acknowledge the support from the National Natural Science Foundation of China(11672052 and 51822508)111 Project(B20008)and Natural Science Foundation of Zhejiang province(LQ22E050012).
文摘In this work,a comparative study is performed to investigate the influence of time-varying normal forces on the friction properties and friction-induced stick-slip vibration(FIV)by experimental and theoretical methods.In the experiments,constant and harmonic-varying normal forces are applied,respectively.The measured vibration signals under two loading forms are compared in both time and frequency domains.In addition,mathematical tools such as phase space reconstruction and Fourier spectra are used to reveal the science behind the complicated dynamic behavior.It can be found that the friction system shows steady stick-slip vibration,and the main frequency does not vary with the magnitude of the constant normal force,but the size of limit cycle increases with the magnitude of the constant normal force.In contrast,the friction system under the harmonic normal force shows complicated behavior,for example,higher-frequency larger-amplitude vibration occurs and looks chaotic as the frequency of the normal force increases.The interesting findings offer a new way for controlling FIV in engineering applications.
基金the National Natural Science Foundation of China(No.11672052)Natural Science Foundation of Zhejiang Province(LQ22E050012)are gratefully acknowledged.
文摘For years,friction-induced vibration and noise(FIVN)has puzzled many researchers in academia and industry.Several mechanisms have been proposed for explaining its occurrence and quantifying its frequencies,notably for automotive brake squeal,clutch squeal,and even rail corrugation.However,due to the complex and complicated nature of FIVN,there is not yet one fundamental mechanism that can explain all phenomena of FIVN.Based on experimental results obtained on a simple test structure and corresponding numerical validation using both complex eigenvalue analysis(CEA)and transient dynamic analysis(TDA),this study attempts to propose a new fundamental mechanism for FIVN,which is the repeated cycles of partial detachment and then reattachment of the contact surfaces.Since friction is ubiquitous and FIVN is very common,the insight into FIVN reported in this paper is highly significant and will help establish effective means to control FIVN in engineering and daily life.
基金the financial support provided by the National Science Funds for Distinguished Young Scholars(No.51025519)the Changjiang Scholarships and Innovation Team Development Plan(No.IRT1178)the Self-Topic Fund of Traction Power State Key Laboratory(No.2016TPL-Z03)
文摘This paper investigates the self-loosening of threaded fasteners subjected to dynamic shear load. Three kinds of typical coatings, PTFE, MoS_2, and TiN applied to bolts and nuts, are tested in this investigation. The study experimentally examines the loosening mechanisms of fasteners and assesses the anti-loosening performance of the three tested coatings based on their tightening characteristics, loosening curves, and the damage of thread surface. Additionally, the anti-loosening performance of the three coatings is compared under different load forms. The results indicate that the PTFE and MoS_2 coatings have significant anti-loosening effect, whereas the anti-loosening performance of Ti N coating is not satisfactory. It is also found that an appropriate increase of the initial tightening torque can significantly improve the anti-loosening effect. In addition, the microscopic analyses of PTFE and MoS2 coating reveal that a reduced initial tightening torque leads to fretting wear on the thread contact surfaces of fasteners, thereby aggravating the damage.
基金This project was supported by the National Natural Science Foundation of China(Nos.51822508 and 11672052)the Sichuan Province Science and Technology Support Program(No.2020JDTD0012).
文摘In this study,piezoelectric elements were added to a reciprocating friction test bench to harvest friction‐induced vibration energy.Parameters such as vibration acceleration,noise,and voltage signals of the system were measured and analyzed.The results show that the piezoelectric elements can not only collect vibration energy but also suppress friction‐induced vibration noise(FIVN).Additionally,the wear of the friction interface was examined via optical microscopy(OM),scanning electron microscopy(SEM),and white‐light interferometry(WLI).The results show that the surface wear state improved because of the reduction of FIVN.In order to analyze the experimental results in detail and explain them reasonably,the experimental phenomena were simulated numerically.Moreover,a simplified two‐degree‐of‐freedom numerical model including the original system and the piezoelectric system was established to qualitatively describe the effects,dynamics,and tribological behaviors of the added piezoelectric elements to the original system.
