The vibration analysis of Kirchhoff plates requires robust mass lumping schemes to guarantee numerical stability and accuracy.However,existing methods fail to generate symmetric and positive definite mass matrices whe...The vibration analysis of Kirchhoff plates requires robust mass lumping schemes to guarantee numerical stability and accuracy.However,existing methods fail to generate symmetric and positive definite mass matrices when handling rotational degrees of freedom,leading to compromised performance in both time and frequency domains analyses.This study proposes a manifold-based mass lumping scheme that systematically resolves the inertia matrix formulas for rotational/torsional degrees of freedom.By reinterpreting the finite element mesh as a mathematical cover composed of overlapping patches,Hermitian interpolations for plate deflection are derived using partition of unity principles.The manifold-based mass matrix is constructed by integrating the virtual work of inertia forces over these patches,ensuring symmetry and positive definiteness.Numerical benchmarks demonstrate that the manifold-based mass lumping scheme performance can be comparable or better than the consistent mass scheme and other existing mass lumping schemes.This work establishes a unified theory for mass lumping in fourth order plate dynamics,proving that the widely used row-sum method is a special case of the manifold-based framework.The scheme resolves long-standing limitations in rotational/torsional inertia conservation and provides a foundation for extending rigorous mass lumping to 3D shell and nonlinear dynamic analyses.展开更多
The torsional low strain integrity test(TLSIT),known for its advantages such as a smaller detection blind zone,improved identification of shallowly buried defects,stable phase velocity for signal interpretation,and be...The torsional low strain integrity test(TLSIT),known for its advantages such as a smaller detection blind zone,improved identification of shallowly buried defects,stable phase velocity for signal interpretation,and better adaptability for existing pile testing.However,it lacks a comprehensive understanding of the authentic three-dimensional(3D)strain wave propagation mechanism,particularly wave reflection and transmission at defects.To address this gap,a novel 3D theoretical framework is introduced in this context to model the authentic 3D wave propagation during the TLSIT.The proposed approach is validated by comparing its results with those obtained from 3D finite element method(FEM)simulations and simplified 1D(one-dimensional)and 3D analytical solutions.Additionally,a parametric study is conducted to enhance insights into the formation mechanism of high-frequency interference observed during the TLSIT.Finally,a defect identification study is performed to provide guidance for interpreting the wave spectrum in terms of defect characteristics.展开更多
It is well known that there are some torsional damages in earthquakes. In Taibai park, Jiangyou city, Sichuan province, most of the stone statues, which were placed upon the banisters of one zigzag bridge, exhibited d...It is well known that there are some torsional damages in earthquakes. In Taibai park, Jiangyou city, Sichuan province, most of the stone statues, which were placed upon the banisters of one zigzag bridge, exhibited different torsional phenomena in 2008 Wenchuan earthquake. This paper introduces the torsional phenomena of all the statues on the zigzag bridge firstly. Then one eccentric- ity model is established and the equivalent rotational accelerations are calculated in order to analyze the causes of the torsional damage. In addition, the torsional components are synthesized by using translation accelerations recorded at Jiangyou station in the Wenchuan earthquake. The results show that the equivalent rotational acceleration is larger than the synthesized rotational components, which sug- gests that the torsional phenomena of the statues on the zigzag bridge might mainly come from its eccentricity. The comparison between the estimated torsional component at Jiangyou and that presented by Trifunac shows that they are in the same order. The research im- plies that the torsional phenomena in earthquakes are very complicated, and not only caused by torsional motions.展开更多
A pushover procedure with a load pattern based on the height-wise distribution of the combined modal story shear and torsional moment is proposed to estimate the seismic response of 3D asymmetric-plan building frames....A pushover procedure with a load pattern based on the height-wise distribution of the combined modal story shear and torsional moment is proposed to estimate the seismic response of 3D asymmetric-plan building frames. Contribution of the higher modes and torsional response of asymmetric-plan buildings are incorporated into the proposed load pattern. The proposed pushover method is a single-run procedure, which enables tracing the nonlinear response of the structure during the analysis and averts the elusiveness of conducting multiple pushover analyses. The proposed method has been used to estimate the response of two moment-resisting building frames with 9 and 20 stories. The obtained results indicate the appropriate accuracy and efficiency of the proposed procedure in estimating the trend of the drift profiles of the structures resulted from nonlinear time history analyses.展开更多
With numerous applications coilable masts in high-precision astronomical observations,such as X-ray source observations,it is important to investigate mast stiffness.To date,there have been many studies on the bending...With numerous applications coilable masts in high-precision astronomical observations,such as X-ray source observations,it is important to investigate mast stiffness.To date,there have been many studies on the bending stiffness of coilable masts,but few studies on their torsional stiffness,especially regarding the nonlinear characteristics of torsional stiffness of coilable masts under large torsional deformation.In this paper,a nonlinear analysis method is presented to examine the torsional stiffness of coilable masts with triangular sections.Based on the second-order bending buckling hypothesis of battens under large torsion deformation,the nonlinear relationship between torsional torque and torsional angle is obtained by analyzing torsional deformation and force of coilable masts.This method is used to analyze the torsional stiffness nonlinearity of a certain type of coilable mast which will be used in a practical application in the future and the results are verified by simulation and testing.The comparison results show that the error is within the acceptable range,which proves the effectiveness of the proposed method.展开更多
Vector of diagnostic signs(VDS)using torsional vibration(TV)signal on the main propulsion plant(MPP)is the vector of z maxima(or minima)values of the TV signal in accordance with the cylinder firing orders.The technic...Vector of diagnostic signs(VDS)using torsional vibration(TV)signal on the main propulsion plant(MPP)is the vector of z maxima(or minima)values of the TV signal in accordance with the cylinder firing orders.The technical states of the marine diesel engine(MDE)include R=z+1 classes and are presented in z-dimensional space coordinate of VDS.The presentation of Dk,k=1÷R using z diagnostic signs(Vi,i=1÷z)is nonfigurative and quite complicated.This paper aims to develop a new method for converting VDS from z-dimensional to 2-dimensional space(two-axes)based on the firing orders of the diesel cylinders,as an equivalent geometrical sign of the all diagnostic signs.The proposed model is useful for presenting a technical state Dk in two-dimensional space(x,y)for better visualization.The paper verifies the simulation of the classification illustration of the 7–state classes for the MDE 6S46-MCC,installed on the motor vessel(MV)34000DWT,using the new above mentioned method.The seven technical state classes(for 6-cylinder MDE,z=6)are drawn separately and visually in the Descartes.The received results are valuable to improve smart diagnostic system for analyzing normal/misfire states of cylinders in operation regimes.展开更多
The jointed shaft in the drivelines of the rolling mill, with its angle continuously varying in the production, has obvious impact on the stability of the main drive system. Considering the effect caused by the joint ...The jointed shaft in the drivelines of the rolling mill, with its angle continuously varying in the production, has obvious impact on the stability of the main drive system. Considering the effect caused by the joint angle and friction force of roller gap, the nonlinear vibration model of the main drive system which contains parametric excitation stiffness and nonlinear friction damping was established. The amplitude-frequency characteristic equation and bifurcation response equation were obtained by using the method of multiple scales. Depending on the bifurcation response equation, the transition set and the topology structure of bifurcation curve of the system were obtained by using the singularity theory. The transition set can separate the system into seven areas, which has different bifurcation forms respectively. By taking the 1 780 rolling mill of Chengde Steel Co for example, the simulation and analysis were performed. The amplitude-frequency curves under different joint angles, damping coefficients, and nonlinear stiffness were given. The variations of these parameters have strong influences on the stability of electromechanical resonances and the characteristic of the response curves. The best angle of the jointed shaft is 4.761 3° in this rolling mill.展开更多
Torsional vibration generally causes serious instability and damage problems in many rotating machinery parts. The global dynamic characteristic of nonlinear torsional vibration system with nonlinear rigidity and nonl...Torsional vibration generally causes serious instability and damage problems in many rotating machinery parts. The global dynamic characteristic of nonlinear torsional vibration system with nonlinear rigidity and nonlinear friction force is investigated. On the basis of the generalized dissipation Lagrange＇s equation, the dynamics equation of nonlinear torsional vibration system is deduced. The bifurcation and chaotic motion in the system subjected to an external harmonic excitation is studied by theoretical analysis and numerical simulation. The stability of unperturbed system is analyzed by using the stability theory of equilibrium positions of Hamiltonian systems. The criterion of existence of chaos phenomena under a periodic perturbation is given by means of Melnikov＇s method. It is shown that the existence of homoclinic and heteroclinic orbits in the unperturbed system implies chaos arising from breaking of homoclinic or heteroclinic orbits under perturbation. The validity of the result is checked numerically. Periodic doubling bifurcation route to chaos, quasi-periodic route to chaos, intermittency route to chaos are found to occur due to the amplitude varying in some range. The evolution of system dynamic responses is demonstrated in detail by Poincare maps and bifurcation diagrams when the system undergoes a sequence of periodic doubling or quasi-periodic bifurcations to chaos. The conclusion can provide reference for deeply researching the dynamic behavior of mechanical drive systems.展开更多
Torsional impact drilling is a new technology which has the advantages of high rock-breaking efficiency and a high rate of penetration(ROP).So far,there is no in-depth understanding of the rock-breaking mechanism for ...Torsional impact drilling is a new technology which has the advantages of high rock-breaking efficiency and a high rate of penetration(ROP).So far,there is no in-depth understanding of the rock-breaking mechanism for the ROP increase from torsional impact tools.Therefore,it has practical engineering significance to study the rock-breaking mechanism of torsional impact.In this paper,discrete element method(DEM)software(PFC2 D)is used to compare granite breaking under the steady and torsional impacting conditions.Meanwhile,the energy consumption to break rock,microscopic crushing process and chip characteristics as well as the relationship among these three factors for granite under different impacting frequencies and amplitudes are discussed.It is found that the average cutting force is smaller in the case of torsional impact cutting(TIC)than that in the case of steady loading.The mechanical specific energy(MSE)and the ratio of brittle energy consumption to total energy are negatively correlated;rock-breaking efficiency is related to the mode of action between the cutting tooth and rock.Furthermore,the ROP increase mechanism of torsional impact drilling technology is that the ratio of brittle energy consumption under the TIC condition is larger than that under a steady load;the degree of repeated fragmentation of rock chips under the TIC condition is lower than that under the steady load,and the TIC load promotes the formation of a transverse cracking network near the free surface and inhibits the formation of a deep longitudinal cracking network.展开更多
This study considers the torsional vibration of a pipe pile in a transversely isotropic saturated soil layer. Based on Biot＇s poroelastic theory and the constitutive relations of the transversely isotropic medium, th...This study considers the torsional vibration of a pipe pile in a transversely isotropic saturated soil layer. Based on Biot＇s poroelastic theory and the constitutive relations of the transversely isotropic medium, the dynamic governing equations of the outer and inner transversely isotropic saturated soil layers are derived. The Laplace transform is used to solve the governing equations of the outer and inner soil layers. The dynamic torsional response of the pipe pile in the frequency domain is derived utilizing 1D elastic theory and the continuous conditions at the interfaces between the pipe pile and the soils. The time domain solution is obtained by Fourier inverse transform. A parametric study is conducted to demonstrate the influence of the anisotropies of the outer and inner soil on the torsional dynamic response of the pipe pile.展开更多
Torsional properties are important performance parameters for bone screw applications,but they are seldom studied,especially for newly developed biodegradable Mg alloys.In this study,WE43 Mg alloy with different micro...Torsional properties are important performance parameters for bone screw applications,but they are seldom studied,especially for newly developed biodegradable Mg alloys.In this study,WE43 Mg alloy with different microstructures was achieved by equal channel angular pressing(ECAP)and heat treatment,and their torsional properties were studied.In addition,tensile properties were also tested as a comparison.The results indicated that grain refinement led to higher torsional strength and ductility,while the second phases improved the torsional strength but reduced the ductility.The texture was strengthened after ECAP,as a result the tensile strength increased,but the torsional strength did not increase and even decreased,especially for 2-pass ECAP sample with a typical basal fiber texture.The basal plane orientation deviation from the extrusion direction after 4-pass ECAP resulted in higher torsional strength and lower torsional ductility,but lower tensile strength and higher tensile ductility were obtained.This implied that a strong fiber texture would reduce the torsional strength but improve the torsional ductility,which was different from its effect on tensile properties.展开更多
AIM:To compare and evaluate the phacoemulsification parameters and postoperative endothelial cell changes of two different phacoemulsification machines, each with different modes, but also to assess the relationship b...AIM:To compare and evaluate the phacoemulsification parameters and postoperative endothelial cell changes of two different phacoemulsification machines, each with different modes, but also to assess the relationship between postoperative endothelial cell loss and the phacoemulsification parameters, as well as the other factors in both groups.METHODS:This prospective observational study was comprised of consecutive eligible cataract patients operated with phacoemulsification technique performed by the same surgeon using either a WHITESTAR Signature Ellips FX(transversal, group 1) or Infiniti OZil IP(torsional, group 2) machine.RESULTS:The study included 86 patients. Baseline characteristics in the groups were similar. The median nuclear sclerosis grade was 3(2-4) in the first group and2(2-4) in the second group(P =0.265). Both groups had similar phacoemulsification needle times(group 1: 60.63±36 s; group 2: 55.98±30 s; P =0.789). The percentage of endothelial cell loss 30 d after surgery ranged from 3% to15% with a median of 7% in group 1, and from 2% to13% with a median of 6% in group 2; however, there was no statistically significant difference between the groups(P =0.407). Hexagonality(P =0.794) and the coefficient of variation(CV; P =0.142) did not differ significantly between the groups before and 30 d after surgery. Asignificant positive correlation was found between the endothelial cell loss and nuclear sclerosis grade(group1: P 【0.001; group 2: P 【0.001) and between the endothelial cell loss and average phacoemulsification power(group 1: P =0.007; group 2: P =0.008).CONCLUSION:Both of these machines were efficient,with similar endothelial cell loss. This endothelial cell loss was related to the increased nuclear sclerosis grade and increased phacoemulsification power.展开更多
For the purpose of analyzing the torsional vibration caused by the gravitational unbalance torque arisen in a spindle system when it is machining heavy work piece,a 10-DOF lumped parameter model was made for the machi...For the purpose of analyzing the torsional vibration caused by the gravitational unbalance torque arisen in a spindle system when it is machining heavy work piece,a 10-DOF lumped parameter model was made for the machine tool spindle system with geared transmission.By using the elementary method and Runge-Kutta method in Matlab,the eigenvalue problem was solved and the pure torsional vibration responses were obtained and examined.The results show that the spindle system cannot operate in the desired constant rotating speed as far as the gravitational unbalance torque is engaged,so it may cause bad effect on machining accuracy.And the torsional vibration increases infinitely near the resonant frequencies,so the spindle system cannot operate normally during these spindle speed ranges.展开更多
The torsional fretting wear tests of 7075 aluminum alloy flat against 52100 steel ball in dry condition were carried out on a new high-precision torsional fretting-wear tester.The kinetics behaviors and damage mechani...The torsional fretting wear tests of 7075 aluminum alloy flat against 52100 steel ball in dry condition were carried out on a new high-precision torsional fretting-wear tester.The kinetics behaviors and damage mechanism of 7075 aluminum alloy under different angular displacement amplitudes were investigated in detail.The results show that the torsional fretting running behaviors of 7075 aluminum alloy can be defined by three fretting regimes(i.e.partial slip regime(PSR),mixed fretting regime(MFR) and slip regime(SR)) with the increase of angular displacement amplitudes.In PSR,the damage occurs at the lateral portion of the contact zone with a slight annular shape.However,in MFR and SR,more severe damages are observed and the debris layer covers the wear scars.Friction torque and dissipation energy which are strongly dependent upon the imposed angular displacement amplitudes and presented in three stages were discussed in detail.The mechanisms of torsional fretting wear of aluminum alloy are mainly oxidative wear,abrasive wear and delamination in the three fretting regimes.In addition,the oxidative debris plays an important role during the torsional fretting wear processes.展开更多
Curved twin I-girder bridges (CTIGBs) have low torsional stiffness that makes them vulnerable to dynamic loads. This study investigates the effects of bottom bracings on the torsional dynamic characteristics of CTIGBs...Curved twin I-girder bridges (CTIGBs) have low torsional stiffness that makes them vulnerable to dynamic loads. This study investigates the effects of bottom bracings on the torsional dynamic characteristics of CTIGBs. Five types of bottom bracings are designed to investigate their effects on the dynamic characteristics of CTIGBs with different curvatures under free and forced vibrations. To perform numerical investigations, three-dimensional (3-D) finite element (FE) bridge and vehicle models are established using commercial ANSYS code, and then a vehicle-bridge interaction analysis approach is proposed. Road roughness profiles generated from power spectral density and cross spectral functions are also taken into account in the analyses. The numerical results show that torsional frequencies increase significantly after providing bottom bracings, and the increasing rate depends on the type of bottom bracings and their locations of installation. Bottom bracings can act as load transmitting members from one main girder to the others. Large negative bearing forces that have occurred in bridges with small radii of curvatures can be remarkably reduced by providing bottom bracing systems. It is found that the performances of several bottom bracing systems are effective in improving the torsional dynamic characteristics of the bridges in this study.展开更多
It is pointed out in this paper that the offshore platform could be controlled by means of the Tuned Mass Damper (TMD) if there is torsional vibration in the system. The effectiveness of the location of TMD is quantif...It is pointed out in this paper that the offshore platform could be controlled by means of the Tuned Mass Damper (TMD) if there is torsional vibration in the system. The effectiveness of the location of TMD is quantified with the help of the response ratio between the peak responses of the system in the presence and in the absence of TMD. In addition, the parameters of frequency and damping ratio of TMD are optimized.展开更多
In order to investigate the effect of sample size on the dynamic torsional behaviour of the 2A12 aluminium alloy. In this paper, torsional split Hopkinson bar tests are conducted on this alloy with different sample di...In order to investigate the effect of sample size on the dynamic torsional behaviour of the 2A12 aluminium alloy. In this paper, torsional split Hopkinson bar tests are conducted on this alloy with different sample dimensions. It is found that with the decreasing gauge length and thickness, the tested yield strength increases. However, the sample innerlouter diameter has little effect on the dynamic torsional behaviour. Based on the finite element method, the stress states in the alloy with different sample sizes are analysed. Due to the effect of stress concentration zone （SCZ）, the shorter sample has a higher yield stress. Furthermore, the stress distributes more uniformly in the thinner sample, which leads to the higher tested yield stress. According to the experimental and simulation analysis, some suggestions on choosing the sample size are given as well.展开更多
Torsional instability of an incompressible thermo-hyperelastic cylindrical rod, subjected to axial stretching and large torsions, is examined within the framework of finite elasticity. When the cylinder is stretched a...Torsional instability of an incompressible thermo-hyperelastic cylindrical rod, subjected to axial stretching and large torsions, is examined within the framework of finite elasticity. When the cylinder is stretched and twisted by a sufficiently large degree, a knot may form suddenly at one point. This inherent elastic instability is analyzed with the minimum potential energy principle and the critical values of torsion are obtained. The distribution of stresses as well as the tensile force and the torque are studied. Effect of tem- perature change is specifically discussed.展开更多
Crankshaft assembly failure is one of the main factors that affects the reliability and service life of engines.The linear lumped mass method,which has been universally applied to the dynamic modeling of engine cranks...Crankshaft assembly failure is one of the main factors that affects the reliability and service life of engines.The linear lumped mass method,which has been universally applied to the dynamic modeling of engine crankshaft assembly,reveals obvious simulation errors.The nonlinear dynamic characteristics of a crankshaft assembly are instructionally significant to the improvement of modeling correctness.In this paper,a general expression for the non-constant inertia of a crankshaft assembly is derived based on the instantaneous kinetic energy equivalence method.The nonlinear dynamic equations of a multi-cylinder crankshaft assembly are established using the Lagrange rule considering nonlinear factors such as the non-constant inertia of reciprocating components and the structural damping of shaft segments.The natural frequency and mode shapes of a crankshaft assembly are investigated employing the eigenvector method.The forced vibration response of a diesel engine crankshaft assembly taking into account the non-constant inertia is studied using the numerical integral method.The simulation results are compared with a lumped mass model and a detailed model using the system matrix method.Results of non-linear torsional vibration analysis indicate that the additional excitation torque created by non-constant inertia activates the 2nd order rolling vibration,and the additional damping torque resulting from the non-constant inertia is the main nonlinear factor.The increased torsional angular displacement evoked by the high order excitation torque relates to the non-constant inertia.This research project is aimed at improving nonlinear dynamics theory,and the confirmed nonlinear parameters can be used for the structure design of a crankshaft assembly.展开更多
基金supported by National Natural Science Foundation of China(Grant Nos.42107214 and 52130905)the Natural Science Foundation of Chongqing(No.CSTB2024NSCQMSX0740)the Henan Province Science and Technology Research Projects(No.252102220050).
文摘The vibration analysis of Kirchhoff plates requires robust mass lumping schemes to guarantee numerical stability and accuracy.However,existing methods fail to generate symmetric and positive definite mass matrices when handling rotational degrees of freedom,leading to compromised performance in both time and frequency domains analyses.This study proposes a manifold-based mass lumping scheme that systematically resolves the inertia matrix formulas for rotational/torsional degrees of freedom.By reinterpreting the finite element mesh as a mathematical cover composed of overlapping patches,Hermitian interpolations for plate deflection are derived using partition of unity principles.The manifold-based mass matrix is constructed by integrating the virtual work of inertia forces over these patches,ensuring symmetry and positive definiteness.Numerical benchmarks demonstrate that the manifold-based mass lumping scheme performance can be comparable or better than the consistent mass scheme and other existing mass lumping schemes.This work establishes a unified theory for mass lumping in fourth order plate dynamics,proving that the widely used row-sum method is a special case of the manifold-based framework.The scheme resolves long-standing limitations in rotational/torsional inertia conservation and provides a foundation for extending rigorous mass lumping to 3D shell and nonlinear dynamic analyses.
基金supported by the National Natural Science Foundation of China(Grant Nos.52408407 and 52478373)the‘CUG Scholar’Scientific Research Funds at China University of Geosciences(Grant No.2023082).
文摘The torsional low strain integrity test(TLSIT),known for its advantages such as a smaller detection blind zone,improved identification of shallowly buried defects,stable phase velocity for signal interpretation,and better adaptability for existing pile testing.However,it lacks a comprehensive understanding of the authentic three-dimensional(3D)strain wave propagation mechanism,particularly wave reflection and transmission at defects.To address this gap,a novel 3D theoretical framework is introduced in this context to model the authentic 3D wave propagation during the TLSIT.The proposed approach is validated by comparing its results with those obtained from 3D finite element method(FEM)simulations and simplified 1D(one-dimensional)and 3D analytical solutions.Additionally,a parametric study is conducted to enhance insights into the formation mechanism of high-frequency interference observed during the TLSIT.Finally,a defect identification study is performed to provide guidance for interpreting the wave spectrum in terms of defect characteristics.
基金supported by the National Natural Science Foundation of China (No. 50578125)
文摘It is well known that there are some torsional damages in earthquakes. In Taibai park, Jiangyou city, Sichuan province, most of the stone statues, which were placed upon the banisters of one zigzag bridge, exhibited different torsional phenomena in 2008 Wenchuan earthquake. This paper introduces the torsional phenomena of all the statues on the zigzag bridge firstly. Then one eccentric- ity model is established and the equivalent rotational accelerations are calculated in order to analyze the causes of the torsional damage. In addition, the torsional components are synthesized by using translation accelerations recorded at Jiangyou station in the Wenchuan earthquake. The results show that the equivalent rotational acceleration is larger than the synthesized rotational components, which sug- gests that the torsional phenomena of the statues on the zigzag bridge might mainly come from its eccentricity. The comparison between the estimated torsional component at Jiangyou and that presented by Trifunac shows that they are in the same order. The research im- plies that the torsional phenomena in earthquakes are very complicated, and not only caused by torsional motions.
文摘A pushover procedure with a load pattern based on the height-wise distribution of the combined modal story shear and torsional moment is proposed to estimate the seismic response of 3D asymmetric-plan building frames. Contribution of the higher modes and torsional response of asymmetric-plan buildings are incorporated into the proposed load pattern. The proposed pushover method is a single-run procedure, which enables tracing the nonlinear response of the structure during the analysis and averts the elusiveness of conducting multiple pushover analyses. The proposed method has been used to estimate the response of two moment-resisting building frames with 9 and 20 stories. The obtained results indicate the appropriate accuracy and efficiency of the proposed procedure in estimating the trend of the drift profiles of the structures resulted from nonlinear time history analyses.
文摘With numerous applications coilable masts in high-precision astronomical observations,such as X-ray source observations,it is important to investigate mast stiffness.To date,there have been many studies on the bending stiffness of coilable masts,but few studies on their torsional stiffness,especially regarding the nonlinear characteristics of torsional stiffness of coilable masts under large torsional deformation.In this paper,a nonlinear analysis method is presented to examine the torsional stiffness of coilable masts with triangular sections.Based on the second-order bending buckling hypothesis of battens under large torsion deformation,the nonlinear relationship between torsional torque and torsional angle is obtained by analyzing torsional deformation and force of coilable masts.This method is used to analyze the torsional stiffness nonlinearity of a certain type of coilable mast which will be used in a practical application in the future and the results are verified by simulation and testing.The comparison results show that the error is within the acceptable range,which proves the effectiveness of the proposed method.
文摘Vector of diagnostic signs(VDS)using torsional vibration(TV)signal on the main propulsion plant(MPP)is the vector of z maxima(or minima)values of the TV signal in accordance with the cylinder firing orders.The technical states of the marine diesel engine(MDE)include R=z+1 classes and are presented in z-dimensional space coordinate of VDS.The presentation of Dk,k=1÷R using z diagnostic signs(Vi,i=1÷z)is nonfigurative and quite complicated.This paper aims to develop a new method for converting VDS from z-dimensional to 2-dimensional space(two-axes)based on the firing orders of the diesel cylinders,as an equivalent geometrical sign of the all diagnostic signs.The proposed model is useful for presenting a technical state Dk in two-dimensional space(x,y)for better visualization.The paper verifies the simulation of the classification illustration of the 7–state classes for the MDE 6S46-MCC,installed on the motor vessel(MV)34000DWT,using the new above mentioned method.The seven technical state classes(for 6-cylinder MDE,z=6)are drawn separately and visually in the Descartes.The received results are valuable to improve smart diagnostic system for analyzing normal/misfire states of cylinders in operation regimes.
基金Item Sponsored by National Natural Science Foundation of China(51005196)Natural Science Foundation of Hebei Province of China(F2010001317,E2012203194)
文摘The jointed shaft in the drivelines of the rolling mill, with its angle continuously varying in the production, has obvious impact on the stability of the main drive system. Considering the effect caused by the joint angle and friction force of roller gap, the nonlinear vibration model of the main drive system which contains parametric excitation stiffness and nonlinear friction damping was established. The amplitude-frequency characteristic equation and bifurcation response equation were obtained by using the method of multiple scales. Depending on the bifurcation response equation, the transition set and the topology structure of bifurcation curve of the system were obtained by using the singularity theory. The transition set can separate the system into seven areas, which has different bifurcation forms respectively. By taking the 1 780 rolling mill of Chengde Steel Co for example, the simulation and analysis were performed. The amplitude-frequency curves under different joint angles, damping coefficients, and nonlinear stiffness were given. The variations of these parameters have strong influences on the stability of electromechanical resonances and the characteristic of the response curves. The best angle of the jointed shaft is 4.761 3° in this rolling mill.
基金supported by National Key Technologies R&D Program of the 10th Five-year Plan of China (Grant No. ZZ02-13B-02-03-1)Hebei Provincial Natural Science Foundation of China (Grant No. F2008000882)Hebei Provincial Education Office Scientific Research Projects of China (Grant No. ZH2007102, 2007496)
文摘Torsional vibration generally causes serious instability and damage problems in many rotating machinery parts. The global dynamic characteristic of nonlinear torsional vibration system with nonlinear rigidity and nonlinear friction force is investigated. On the basis of the generalized dissipation Lagrange＇s equation, the dynamics equation of nonlinear torsional vibration system is deduced. The bifurcation and chaotic motion in the system subjected to an external harmonic excitation is studied by theoretical analysis and numerical simulation. The stability of unperturbed system is analyzed by using the stability theory of equilibrium positions of Hamiltonian systems. The criterion of existence of chaos phenomena under a periodic perturbation is given by means of Melnikov＇s method. It is shown that the existence of homoclinic and heteroclinic orbits in the unperturbed system implies chaos arising from breaking of homoclinic or heteroclinic orbits under perturbation. The validity of the result is checked numerically. Periodic doubling bifurcation route to chaos, quasi-periodic route to chaos, intermittency route to chaos are found to occur due to the amplitude varying in some range. The evolution of system dynamic responses is demonstrated in detail by Poincare maps and bifurcation diagrams when the system undergoes a sequence of periodic doubling or quasi-periodic bifurcations to chaos. The conclusion can provide reference for deeply researching the dynamic behavior of mechanical drive systems.
基金supported by the National Natural Science Foundation of China(Grant No.51674214)International Cooperation Project of Sichuan Science and Technology Plan(2016HH0008)+1 种基金Youth Science and Technology Innovation Research Team of Sichuan Province(2017TD0014)Applied Basic Research of Sichuan Province(Free Exploration-2019YJ0520)
文摘Torsional impact drilling is a new technology which has the advantages of high rock-breaking efficiency and a high rate of penetration(ROP).So far,there is no in-depth understanding of the rock-breaking mechanism for the ROP increase from torsional impact tools.Therefore,it has practical engineering significance to study the rock-breaking mechanism of torsional impact.In this paper,discrete element method(DEM)software(PFC2 D)is used to compare granite breaking under the steady and torsional impacting conditions.Meanwhile,the energy consumption to break rock,microscopic crushing process and chip characteristics as well as the relationship among these three factors for granite under different impacting frequencies and amplitudes are discussed.It is found that the average cutting force is smaller in the case of torsional impact cutting(TIC)than that in the case of steady loading.The mechanical specific energy(MSE)and the ratio of brittle energy consumption to total energy are negatively correlated;rock-breaking efficiency is related to the mode of action between the cutting tooth and rock.Furthermore,the ROP increase mechanism of torsional impact drilling technology is that the ratio of brittle energy consumption under the TIC condition is larger than that under a steady load;the degree of repeated fragmentation of rock chips under the TIC condition is lower than that under the steady load,and the TIC load promotes the formation of a transverse cracking network near the free surface and inhibits the formation of a deep longitudinal cracking network.
基金The 111 Project under Grant No.B13024the National Natural Science Foundation of China under Grant Nos.U1134207 and 51378177the Program for New Century Excellent Talents in University under Grant No.NCET-12-0843
文摘This study considers the torsional vibration of a pipe pile in a transversely isotropic saturated soil layer. Based on Biot＇s poroelastic theory and the constitutive relations of the transversely isotropic medium, the dynamic governing equations of the outer and inner transversely isotropic saturated soil layers are derived. The Laplace transform is used to solve the governing equations of the outer and inner soil layers. The dynamic torsional response of the pipe pile in the frequency domain is derived utilizing 1D elastic theory and the continuous conditions at the interfaces between the pipe pile and the soils. The time domain solution is obtained by Fourier inverse transform. A parametric study is conducted to demonstrate the influence of the anisotropies of the outer and inner soil on the torsional dynamic response of the pipe pile.
基金supported financially by the Key Program of China on Biomedical Materials Research and Tissue and Organ Replacement(Nos.2016YFC11018 and 2016YFC1100604)the Shenyang Key R&D and Technology Transfer Program(No.Z18-0-027)the National Natural Science Foundation of China(No.51801220)。
文摘Torsional properties are important performance parameters for bone screw applications,but they are seldom studied,especially for newly developed biodegradable Mg alloys.In this study,WE43 Mg alloy with different microstructures was achieved by equal channel angular pressing(ECAP)and heat treatment,and their torsional properties were studied.In addition,tensile properties were also tested as a comparison.The results indicated that grain refinement led to higher torsional strength and ductility,while the second phases improved the torsional strength but reduced the ductility.The texture was strengthened after ECAP,as a result the tensile strength increased,but the torsional strength did not increase and even decreased,especially for 2-pass ECAP sample with a typical basal fiber texture.The basal plane orientation deviation from the extrusion direction after 4-pass ECAP resulted in higher torsional strength and lower torsional ductility,but lower tensile strength and higher tensile ductility were obtained.This implied that a strong fiber texture would reduce the torsional strength but improve the torsional ductility,which was different from its effect on tensile properties.
文摘AIM:To compare and evaluate the phacoemulsification parameters and postoperative endothelial cell changes of two different phacoemulsification machines, each with different modes, but also to assess the relationship between postoperative endothelial cell loss and the phacoemulsification parameters, as well as the other factors in both groups.METHODS:This prospective observational study was comprised of consecutive eligible cataract patients operated with phacoemulsification technique performed by the same surgeon using either a WHITESTAR Signature Ellips FX(transversal, group 1) or Infiniti OZil IP(torsional, group 2) machine.RESULTS:The study included 86 patients. Baseline characteristics in the groups were similar. The median nuclear sclerosis grade was 3(2-4) in the first group and2(2-4) in the second group(P =0.265). Both groups had similar phacoemulsification needle times(group 1: 60.63±36 s; group 2: 55.98±30 s; P =0.789). The percentage of endothelial cell loss 30 d after surgery ranged from 3% to15% with a median of 7% in group 1, and from 2% to13% with a median of 6% in group 2; however, there was no statistically significant difference between the groups(P =0.407). Hexagonality(P =0.794) and the coefficient of variation(CV; P =0.142) did not differ significantly between the groups before and 30 d after surgery. Asignificant positive correlation was found between the endothelial cell loss and nuclear sclerosis grade(group1: P 【0.001; group 2: P 【0.001) and between the endothelial cell loss and average phacoemulsification power(group 1: P =0.007; group 2: P =0.008).CONCLUSION:Both of these machines were efficient,with similar endothelial cell loss. This endothelial cell loss was related to the increased nuclear sclerosis grade and increased phacoemulsification power.
基金Project(10033135-2009-11) supported by the Korean Ministry of Knowledge Economy (MKE) through HNK. Co,Ltd.
文摘For the purpose of analyzing the torsional vibration caused by the gravitational unbalance torque arisen in a spindle system when it is machining heavy work piece,a 10-DOF lumped parameter model was made for the machine tool spindle system with geared transmission.By using the elementary method and Runge-Kutta method in Matlab,the eigenvalue problem was solved and the pure torsional vibration responses were obtained and examined.The results show that the spindle system cannot operate in the desired constant rotating speed as far as the gravitational unbalance torque is engaged,so it may cause bad effect on machining accuracy.And the torsional vibration increases infinitely near the resonant frequencies,so the spindle system cannot operate normally during these spindle speed ranges.
基金Project(2007CB714704) supported by the National Basic Research Program of ChinaProjects(50775192,50821063) supported by the National Natural Science Foundation of China
文摘The torsional fretting wear tests of 7075 aluminum alloy flat against 52100 steel ball in dry condition were carried out on a new high-precision torsional fretting-wear tester.The kinetics behaviors and damage mechanism of 7075 aluminum alloy under different angular displacement amplitudes were investigated in detail.The results show that the torsional fretting running behaviors of 7075 aluminum alloy can be defined by three fretting regimes(i.e.partial slip regime(PSR),mixed fretting regime(MFR) and slip regime(SR)) with the increase of angular displacement amplitudes.In PSR,the damage occurs at the lateral portion of the contact zone with a slight annular shape.However,in MFR and SR,more severe damages are observed and the debris layer covers the wear scars.Friction torque and dissipation energy which are strongly dependent upon the imposed angular displacement amplitudes and presented in three stages were discussed in detail.The mechanisms of torsional fretting wear of aluminum alloy are mainly oxidative wear,abrasive wear and delamination in the three fretting regimes.In addition,the oxidative debris plays an important role during the torsional fretting wear processes.
文摘Curved twin I-girder bridges (CTIGBs) have low torsional stiffness that makes them vulnerable to dynamic loads. This study investigates the effects of bottom bracings on the torsional dynamic characteristics of CTIGBs. Five types of bottom bracings are designed to investigate their effects on the dynamic characteristics of CTIGBs with different curvatures under free and forced vibrations. To perform numerical investigations, three-dimensional (3-D) finite element (FE) bridge and vehicle models are established using commercial ANSYS code, and then a vehicle-bridge interaction analysis approach is proposed. Road roughness profiles generated from power spectral density and cross spectral functions are also taken into account in the analyses. The numerical results show that torsional frequencies increase significantly after providing bottom bracings, and the increasing rate depends on the type of bottom bracings and their locations of installation. Bottom bracings can act as load transmitting members from one main girder to the others. Large negative bearing forces that have occurred in bridges with small radii of curvatures can be remarkably reduced by providing bottom bracing systems. It is found that the performances of several bottom bracing systems are effective in improving the torsional dynamic characteristics of the bridges in this study.
文摘It is pointed out in this paper that the offshore platform could be controlled by means of the Tuned Mass Damper (TMD) if there is torsional vibration in the system. The effectiveness of the location of TMD is quantified with the help of the response ratio between the peak responses of the system in the presence and in the absence of TMD. In addition, the parameters of frequency and damping ratio of TMD are optimized.
基金Financial support is from the NSFC(Grant Nos.11602257,11472257,11272300,11572299)funded by the key subject"Computational Solid Mechanics"of the China Academy of Engineering Physics
文摘In order to investigate the effect of sample size on the dynamic torsional behaviour of the 2A12 aluminium alloy. In this paper, torsional split Hopkinson bar tests are conducted on this alloy with different sample dimensions. It is found that with the decreasing gauge length and thickness, the tested yield strength increases. However, the sample innerlouter diameter has little effect on the dynamic torsional behaviour. Based on the finite element method, the stress states in the alloy with different sample sizes are analysed. Due to the effect of stress concentration zone （SCZ）, the shorter sample has a higher yield stress. Furthermore, the stress distributes more uniformly in the thinner sample, which leads to the higher tested yield stress. According to the experimental and simulation analysis, some suggestions on choosing the sample size are given as well.
基金The project supported by the National Natural Science Foundation of China （10402018, 10272069） and Shanghai Key Project Program （Y0103） The English text was polished by Keren Wang.
文摘Torsional instability of an incompressible thermo-hyperelastic cylindrical rod, subjected to axial stretching and large torsions, is examined within the framework of finite elasticity. When the cylinder is stretched and twisted by a sufficiently large degree, a knot may form suddenly at one point. This inherent elastic instability is analyzed with the minimum potential energy principle and the critical values of torsion are obtained. The distribution of stresses as well as the tensile force and the torque are studied. Effect of tem- perature change is specifically discussed.
基金supported by National Natural Science Foundation of China (Grant No. 50975026)Ministerial Eleventh Five-Year Plan Basic Product Pre-research Project of China (Grant No. D2220062905)
文摘Crankshaft assembly failure is one of the main factors that affects the reliability and service life of engines.The linear lumped mass method,which has been universally applied to the dynamic modeling of engine crankshaft assembly,reveals obvious simulation errors.The nonlinear dynamic characteristics of a crankshaft assembly are instructionally significant to the improvement of modeling correctness.In this paper,a general expression for the non-constant inertia of a crankshaft assembly is derived based on the instantaneous kinetic energy equivalence method.The nonlinear dynamic equations of a multi-cylinder crankshaft assembly are established using the Lagrange rule considering nonlinear factors such as the non-constant inertia of reciprocating components and the structural damping of shaft segments.The natural frequency and mode shapes of a crankshaft assembly are investigated employing the eigenvector method.The forced vibration response of a diesel engine crankshaft assembly taking into account the non-constant inertia is studied using the numerical integral method.The simulation results are compared with a lumped mass model and a detailed model using the system matrix method.Results of non-linear torsional vibration analysis indicate that the additional excitation torque created by non-constant inertia activates the 2nd order rolling vibration,and the additional damping torque resulting from the non-constant inertia is the main nonlinear factor.The increased torsional angular displacement evoked by the high order excitation torque relates to the non-constant inertia.This research project is aimed at improving nonlinear dynamics theory,and the confirmed nonlinear parameters can be used for the structure design of a crankshaft assembly.
