Shape memory alloy(SMA)bars are currently preferred over elastomeric seismic isolators due to the elimination of degradation within effective damping and stiffness factors during the cyclic response of an isolation sy...Shape memory alloy(SMA)bars are currently preferred over elastomeric seismic isolators due to the elimination of degradation within effective damping and stiffness factors during the cyclic response of an isolation system.These bars could also be used to prevent the functionality of the isolator units from failing due to large deformations.This study aims to investigate the performance of a high damping rubber bearing(HDRB)isolator that is combined with two different types of SMA bars,i.e.,Nickel-Titanium(Ni-Ti)and Copper-Aluminum-Beryllium(Cu-Al-Be),subjected to near-fault ground motions that are characterized with forward directivity and fling step effects.To achieve this objective,a self-centering material with flag-shape,force-deformation hysteresis was utilized to simulate the behavior of SMA bars in OpenSees.A single degree of freedom(SDOF)system representing an isolated one-story shear building was developed to conduct nonlinear analysis under selected ground motions.The SMA bars were introduced as an X-shape within the model and were connected diagonally to the top and bottom of the isolator.Results showed that the HDRB system’s hysteretic response under near-fault ground accelerations experiences significant degradation,especially when near-fault motions involve the fling step effect.It was demonstrated that SMA bars effectively reduce large displacement observed in HDRB systems under near-fault earthquakes.Comparing the results of the base-isolated HDRB and SMA-HDRB subjected to selected ground motions demonstrated that maximum displacement was found to be significantly reduced by an average of 79%when SMA bars were used.Incorporating SMA bars with a larger diameter significantly improves the efficiency of SMA HDRB systems,and a reduction in maximum displacements is more pronounced for fling step,near-fault ground motions.展开更多
This study experimentally investigates the hydrodynamic characteristics,geometric configurations,fluttering motions of the codend,and the instantaneous flow fields inside and around the codend,with and without a liner...This study experimentally investigates the hydrodynamic characteristics,geometric configurations,fluttering motions of the codend,and the instantaneous flow fields inside and around the codend,with and without a liner,under varying catch sizes and inflow velocities.A proper orthogonal decomposition method is employed to extract phase-averaged mean properties of unsteady turbulent flows from flow measurement data obtained using an electromagnetic current velocity meter inside and around the codend.The results reveal that as catch size increases,the drag force,codend motion,Reynolds number,and codend volume increase while the drag coefficient decreases.Owing to the codend shape and pronounced motion,a complex fluid–structure interaction occurs,demonstrating a strong correlation between drag force and codend volume.The oscillation amplitudes of the hydrodynamic forces and codend motions increase with increasing catch size,and their oscillations mainly involve low-frequency activity.A significant reduction in the flow field occurs inside and around the unlined codend without a catch.The flow field is 5.81%,14.39%,and 27.01%lower than the unlined codend with a catch,the codend with a liner but without a catch,and the codend with both a liner and a catch,respectively.Fourier analysis reveals that the codend motions and hydrodynamic forces are mainly characterized by low-frequency activity and are synchronized with the unsteady turbulent flow street.Furthermore,the proper orthogonal decomposition results reveal the development of unsteady turbulent flow inside and around the codend,driven by flow passage blockage caused by the presence of the liner,intense codend motions,and the catch.Understanding the hydrodynamic characteristics and flow instabilities inside and around the codend,particularly those associated with its fluttering motions,is crucial for optimizing trawl design and improving trawl selectivity.展开更多
This study employed a computational fluid dynamics model with an overset mesh technique to investigate the thrust and power of a floating offshore wind turbine(FOWT)under platform floating motion in the wind–rain fie...This study employed a computational fluid dynamics model with an overset mesh technique to investigate the thrust and power of a floating offshore wind turbine(FOWT)under platform floating motion in the wind–rain field.The impact of rainfall on aerodynamic performance was initially examined using a stationary turbine model in both wind and wind–rain conditions.Subsequently,the study compared the FOWT’s performance under various single degree-of-freedom(DOF)motions,including surge,pitch,heave,and yaw.Finally,the combined effects of wind–rain fields and platform motions involving two DOFs on the FOWT’s aerodynamics were analyzed and compared.The results demonstrate that rain negatively impacts the aerodynamic performance of both the stationary turbines and FOWTs.Pitch-dominated motions,whether involving single or multiple DOFs,caused significant fluctuations in the FOWT aerodynamics.The combination of surge and pitch motions created the most challenging operational environment for the FOWT in all tested scenarios.These findings highlighted the need for stronger construction materials and greater ultimate bearing capacity for FOWTs,as well as the importance of optimizing designs to mitigate excessive pitch and surge.展开更多
This study investigates the effect of nacelle motions on the rotor performance and drivetrain dynamics of floating offshore wind turbines(FOWTs)through fully coupled aero-hydro-elastic-servo-mooring simulations.Using ...This study investigates the effect of nacelle motions on the rotor performance and drivetrain dynamics of floating offshore wind turbines(FOWTs)through fully coupled aero-hydro-elastic-servo-mooring simulations.Using the National Renewable Energy Laboratory 5 MW monopile-supported offshore wind turbine and the OC4 DeepCwind semisubmersible wind turbine as case studies,the research addresses the complex dynamic responses resulting from the interaction among wind,waves,and turbine structures.Detailed multi-body dynamics models of wind turbines,including drivetrain components,are created within the SIMPACK framework.Meanwhile,the mooring system is modeled using a lumped-mass method.Various operational conditions are simulated through five wind-wave load cases.Results demonstrate that nacelle motions significantly influence rotor speed,thrust,torque,and power output,as well as the dynamic loads on drivetrain components.These findings highlight the need for advanced simulation techniques for the design and optimization of FOWTs to ensure reliable performance and longevity.展开更多
To improve the resilience of railway stations,a typical station was selected as the research object,and an isolation design was introduced.Twenty-four groups of near-fault pulse-like ground motions were selected.The s...To improve the resilience of railway stations,a typical station was selected as the research object,and an isolation design was introduced.Twenty-four groups of near-fault pulse-like ground motions were selected.The seismic resilience of the no-isolation railway stations(NIRS)and the isolation railway stations(IRS)were compared to provide a numerical result of the improvement in resilience.The results show that in the station isolation design,the station's functional requirements and structural characteristics should be considered and the appropriate placement of isolation bearings is under the waiting room.Under the action of a rare earthquake,the repair cost,repair time,rate of harm and death of the IRS were decreased by 8.04 million,18.30 days,6.93×10^(-3)and 1.21×10^(-3),respectively,when compared to the NIRS.The IRS received a seismic resilience grade of three-stars and the NIRS only one-star,indicating that rational isolation design improves the seismic resilience of stations.Thus,for the design of stations close to earthquake faults,it is suggested to utilize appropriate isolation techniques to improve their seismic resilience.展开更多
To analyze the correlation between the input energy parameters(V_(E))and typical intensity measures(IMs)of offshore ground motions,based on 273 earthquake events recorded by the K-NET in Japan,892 offshore ground moti...To analyze the correlation between the input energy parameters(V_(E))and typical intensity measures(IMs)of offshore ground motions,based on 273 earthquake events recorded by the K-NET in Japan,892 offshore ground motion records with moment magnitudes from 4.0 to 7.0 were used in this study.Residuals obtained through a ground motion model were calculated and analyzed for the correlation between V_(E) and amplitude,duration,frequency content and cumulative IMs.The results indicate that PGV and PGD have strong correlation with the V_(E)(T>0.2 s and T>0.4 s),the duration IMs have weakly negative correlation with the V_(E),Sd_(1) has a strong correlation with the V_(E) in the periods of T>0.4 s,T_(g) has a weak correlation with V_(E) and the cumulative IMs have strong correlation with the V_(E).The parametric predictive equations between typical IMs and V_(E) was proposed,and the differences between the prediction equations from the onshore ground motion records were compared.The differences in parametric predicted equations between offshore and onshore ground motions were confirmed in this study.Proposed correlation equations can be applied to offshore probabilistic seismic hazard analysis and the selection of ground motion records by generalized conditional intensity measures.展开更多
This study is aimed at developing statistical equations to estimate the inelastic displacement ratio of singledegree-of-freedom systems subjected to far fault repeated earthquakes. In the study, peak ground motion par...This study is aimed at developing statistical equations to estimate the inelastic displacement ratio of singledegree-of-freedom systems subjected to far fault repeated earthquakes. In the study, peak ground motion parameters are used to define the scatter of the original data. The ratio of peak ground acceleration to peak ground velocity, and peak ground velocity of the ground motion records and structural parameters such as period of vibration and lateral strength ratio are used in the proposed equations. For the development of the equations, nonlinear time history analyses of single-degree-offreedom systems are conducted. Then, the results are used in a multivariate regression procedure. The equations are verified by comparing the estimated results with the calculated results. The average error and coefficient of variation of the proposed equations are presented. The analyses results revealed that the direct use of peak ground motion parameters for the estimation of inelastic displacement ratio significantly reduced the scatter in the original data and yielded accurate results. From the comparative results it is also observed that results obtained using equations specific to peak ground velocity or peak ground acceleration to peak ground velocity ratio are similar.展开更多
This paper presents an efficient numerical scheme for calculating the periodic motion of a harmonically forced piecewise linear oscillator very accurately. The scheme is based on the shooting technique with the tradi...This paper presents an efficient numerical scheme for calculating the periodic motion of a harmonically forced piecewise linear oscillator very accurately. The scheme is based on the shooting technique with the traditional numerical Poincare mapping and its Jacobian replaced by the piecewise analytic ones. Thus, the scheme gets rid of the requirement of the current schemes for an assumed order of the oscillator trajectory passing through different linear regions. The numerical examples in the paper demonstrate that the new scheme, compared with the current schemes, enables one to cope with more complicated dynamics of harmonically forced piecewise linear oscillators.展开更多
Parallel robots with SCARA（selective compliance assembly robot arm） motions are utilized widely in the field of high speed pick-and-place manipulation. Error modeling for these robots generally simplifies the parall...Parallel robots with SCARA（selective compliance assembly robot arm） motions are utilized widely in the field of high speed pick-and-place manipulation. Error modeling for these robots generally simplifies the parallelogram structures included by the robots as a link. As the established error model fails to reflect the error feature of the parallelogram structures, the effect of accuracy design and kinematic calibration based on the error model come to be undermined. An error modeling methodology is proposed to establish an error model of parallel robots with parallelogram structures. The error model can embody the geometric errors of all joints, including the joints of parallelogram structures. Thus it can contain more exhaustively the factors that reduce the accuracy of the robot. Based on the error model and some sensitivity indices defined in the sense of statistics, sensitivity analysis is carried out. Accordingly, some atlases are depicted to express each geometric error’s influence on the moving platform’s pose errors. From these atlases, the geometric errors that have greater impact on the accuracy of the moving platform are identified, and some sensitive areas where the pose errors of the moving platform are extremely sensitive to the geometric errors are also figured out. By taking into account the error factors which are generally neglected in all existing modeling methods, the proposed modeling method can thoroughly disclose the process of error transmission and enhance the efficacy of accuracy design and calibration.展开更多
In this study, a new mathematical model is developed composed of two parts, including harmonic and polynomial expressions for simulating the dominant velocity pulse of near fault ground motions. Based on a proposed ve...In this study, a new mathematical model is developed composed of two parts, including harmonic and polynomial expressions for simulating the dominant velocity pulse of near fault ground motions. Based on a proposed velocity function, the corresponding expressions for the ground acceleration and displacement time histories are also derived. The proposed model is then fitted using some selected pulse-like near fault ground motions in the Next Generation Attenuation （NGA） project library. The new model is not only simple in form but also simulates the long-period portion of actual velocity near fault records with a high level of precision. It is shown that the proposed model-based elastic response spectra are compatible with the near fault records in the neighborhood of the prevailing frequency of the pulse. The results indicate that the proposed model adequately simulates the components of the time histories. Finally, the energy of the proposed pulse was compared with the energy of the actual record to confirm the compatibility.展开更多
This paper presents a novel approach to model and simulate the multi-support depth-varying seismic motions（MDSMs） within heterogeneous offshore and onshore sites.Based on 1 D wave propagation theory,the three-dimens...This paper presents a novel approach to model and simulate the multi-support depth-varying seismic motions（MDSMs） within heterogeneous offshore and onshore sites.Based on 1 D wave propagation theory,the three-dimensional ground motion transfer functions on the surface or within an offshore or onshore site are derived by considering the effects of seawater and porous soils on the propagation of seismic P waves.Moreover,the depth-varying and spatial variation properties of seismic ground motions are considered in the ground motion simulation.Using the obtained transfer functions at any locations within a site,the offshore or onshore depth-varying seismic motions are stochastically simulated based on the spectral representation method（SRM）.The traditional approaches for simulating spatially varying ground motions are improved and extended to generate MDSMs within multiple offshore and onshore sites.The simulation results show that the PSD functions and coherency losses of the generated MDSMs are compatible with respective target values,which fully validates the effectiveness of the proposed simulation method.The synthesized MDSMs can provide strong support for the precise seismic response prediction and performance-based design of both offshore and onshore large-span engineering structures.展开更多
A new model to simulate spatially correlated earthquake ground motions is developed. In the model, the main factors that characterize three distinct effects of spatial variability, namely, the incoherency effect, the ...A new model to simulate spatially correlated earthquake ground motions is developed. In the model, the main factors that characterize three distinct effects of spatial variability, namely, the incoherency effect, the wave-passage effect and the site-response effect, are taken into account, and corresponding terms/parameters are incorporated into the well known model of uniform ground motions. Some of these terms/parameters can be determined by the root operation, and others can be calculated directly. The proposed model is first verified theoretically, and examples of ground motion simulations are provided as a further illustration. It is proven that the ensemble expected value and the ensemble auto-/cross-spectral density functions of the simulated ground motions are identical to the target spectral density functions. The proposed model can also be used to simulate other correlated stochastic processes, such as wave and wind loads.展开更多
The numerical prediction of added resistance and vertical ship motions of one ITTC （Intemational Towing Tank Conference） S-175 containership in regular head waves by our own in-house unsteady RANS solver naoe-FOAM-S...The numerical prediction of added resistance and vertical ship motions of one ITTC （Intemational Towing Tank Conference） S-175 containership in regular head waves by our own in-house unsteady RANS solver naoe-FOAM-SJTU is presented in this paper. The development of the solver naoe-FOAM-SJTU is based on the open source CFD tool, OpenFOAM. Numerical analysis is focused on the added resistance and vertical ship motions （heave and pitch motions） with four very different wavelengths （ 0.8Lpp 〈 2 〈 1.5L ） in regular head waves. Once the wavelength is near the length of the ship model, the responses of the resistance and ship motions become strongly influenced by nonlinear factors, as a result difficulties within simulations occur. In the paper, a comparison of the experimental results and the nonlinear strip theory was reviewed and based on the findings, the RANS simulations by the solver naoe-FOAM-SJTU were considered competent with the prediction of added resistance and vertical ship motions in a wide range of wave lengths.展开更多
The forming of elliptic motions on the modal conversion ultrasonic motors （MCUMs） is discussed. The principles of the modal conversion are investigated based on the coupling with the stator and the rotor, and using ...The forming of elliptic motions on the modal conversion ultrasonic motors （MCUMs） is discussed. The principles of the modal conversion are investigated based on the coupling with the stator and the rotor, and using an independent coupler. The elliptical locus observed on the longitudinal-torslonal vibration converter with oblique slits is analyzed by using vibration theory. A method for the modal conversion is proposed by using the local mode of a substructure On a main structure. The method can be used to design the modal conversion type ultrasonic motors.展开更多
Features of near-inertial motions on the shelf （60 m deep） of the northern South China Sea were observed under the passage of two typhoons during the summer of 2009. There are two peaks in spectra at both sub-inerti...Features of near-inertial motions on the shelf （60 m deep） of the northern South China Sea were observed under the passage of two typhoons during the summer of 2009. There are two peaks in spectra at both sub-inertial and super-inertial frequencies. The super-inertial energy maximizes near the surface, while the sub-inertial energy maximizes at a deeper layer of 15 m. The sub-inertial shift of frequency is induced by the negative background vorticity. The super-inertial shift is probably attributed to the near-inertial wave propagating from higher latitudes. The near-inertial currents exhibit a two-layer pattern being separated at mid-depth （25-30 m）, with the phase in the upper layer being nearly opposite to that in the lower layer. The vertical propagation of phase implies that the near-inertial energy is not dominantly downward. The upward flux of the near-inertial energy is more evident at the surface layer （〈17 m）. There exist two boundaries at 17 and 40 rn, where the near-inertial energy is reflected upward and downward. The near-inertial motion is intermittent and can reach a peak of as much as 30 cm/s. The passage of Typhoon Nangka generates an intensive near-inertial event, but Typhoon Linfa does not. This difference is attributed to the relative moor- ing locations, which is on the right hand side of Nangka＇s path （leading to a wind pattern rotating clockwise with time） and is on the left hand side of Linfa＇s path （leading to a wind pattern rotating anti-clockwise with time）.展开更多
With the increase of system scale, time delays have become unavoidable in nonlinear power systems, which add the complexity of system dynamics and induce chaotic oscillation and even voltage collapse events. In this p...With the increase of system scale, time delays have become unavoidable in nonlinear power systems, which add the complexity of system dynamics and induce chaotic oscillation and even voltage collapse events. In this paper, coexisting phenomenon in a fourth-order time-delayed power system is investigated for the first time with different initial conditions.With the mechanical power, generator damping factor, exciter gain, and time delay varying, the specific characteristic of the time-delayed system, including a discontinuous ＂jump＂ bifurcation behavior is analyzed by bifurcation diagrams, phase portraits, Poincar′e maps, and power spectrums. Moreover, the coexistence of two different periodic orbits and chaotic attractors with periodic orbits are observed in the power system, respectively. The production condition and existent domain of the coexistence phenomenon are helpful to avoid undesirable behavior in time-delayed power systems.展开更多
In this work,the correlations between spatial distributions of landslide point density(LPD)and strong ground motions of the three strong earthquakes are qualitatively investigated.Meanwhile the qualitative relationshi...In this work,the correlations between spatial distributions of landslide point density(LPD)and strong ground motions of the three strong earthquakes are qualitatively investigated.Meanwhile the qualitative relationship between the distribution of LPD and the fault rupture process is also characterized.Three strong events are the Lushan,Wenchuan,and Jiuzhaigou earthquakes.In order to reconstruct the near filed strong ground motions and the fault processes of these earthquakes,the broadband ground simulation method of University of California Santa Barbara(UCSB)and the simplified crustal layer structures are applied.To show the rationality of the UCSB method,the fault slip distributions of the three earthquakes reconstructed by the kinematic rupture generator model in the UCSB method are compared with those by inversed.Furthermore,the validation of the UCSB method for the three earthquakes is also carried according to the validation exercise of the Southern California Earthquake Center(SCEC)Broadband Platform(BBP).Lastly,the fields of peak ground acceleration(PGA)and peak ground velocity(PGV)in three mutually perpendicular directions of the three earthquakes are achieved.Generally,the landslide distribution length of large LPD values along the fault strike is less than the fault strike length.Therefore,the slip modes of earthquake faults affect the distributions of landslides.For the strike slip earthquakes,the distributions of large LPD values relate well to PGA and PGV components of the parallel and normal to the fault strike.For the reverse slip earthquakes,distributions of LPD relate to ground motion components in all directions.Moreover,distributions of landslides in near fields of earthquakes are significantly affected by the focus parameters and fault scales.展开更多
A domain decomposition and matching method in the time-domain is outlined for simulating the motions of ships advancing in waves. The flow field is decomposed into inner and outer domains by an imaginary control surfa...A domain decomposition and matching method in the time-domain is outlined for simulating the motions of ships advancing in waves. The flow field is decomposed into inner and outer domains by an imaginary control surface, and the Rankine source method is applied to the inner domain while the transient Green function method is used in the outer domain. Two initial boundary value problems are matched on the control surface. The corresponding numerical codes are developed, and the added masses, wave exciting forces and ship motions advancing in head sea for Series 60 ship and S175 containership, are presented and verified. A good agreement has been obtained when the numerical results are compared with the experimental data and other references. It shows that the present method is more efficient because of the panel discretization only in the inner domain during the numerical calculation, and good numerical stability is proved to avoid divergence problem regarding ships with flare.展开更多
基金Open Access funding enabled and organized by CAUL and its Member Institutions。
文摘Shape memory alloy(SMA)bars are currently preferred over elastomeric seismic isolators due to the elimination of degradation within effective damping and stiffness factors during the cyclic response of an isolation system.These bars could also be used to prevent the functionality of the isolator units from failing due to large deformations.This study aims to investigate the performance of a high damping rubber bearing(HDRB)isolator that is combined with two different types of SMA bars,i.e.,Nickel-Titanium(Ni-Ti)and Copper-Aluminum-Beryllium(Cu-Al-Be),subjected to near-fault ground motions that are characterized with forward directivity and fling step effects.To achieve this objective,a self-centering material with flag-shape,force-deformation hysteresis was utilized to simulate the behavior of SMA bars in OpenSees.A single degree of freedom(SDOF)system representing an isolated one-story shear building was developed to conduct nonlinear analysis under selected ground motions.The SMA bars were introduced as an X-shape within the model and were connected diagonally to the top and bottom of the isolator.Results showed that the HDRB system’s hysteretic response under near-fault ground accelerations experiences significant degradation,especially when near-fault motions involve the fling step effect.It was demonstrated that SMA bars effectively reduce large displacement observed in HDRB systems under near-fault earthquakes.Comparing the results of the base-isolated HDRB and SMA-HDRB subjected to selected ground motions demonstrated that maximum displacement was found to be significantly reduced by an average of 79%when SMA bars were used.Incorporating SMA bars with a larger diameter significantly improves the efficiency of SMA HDRB systems,and a reduction in maximum displacements is more pronounced for fling step,near-fault ground motions.
基金sponsored by the National Natural Science Foundation of China(Grant No.32373187)the Research Fund for International Scientists of the National Natural Science Foundation of China(Grant No.32350410404)the Natural Science Foundation of Shanghai(Grant No.23ZR1427000).
文摘This study experimentally investigates the hydrodynamic characteristics,geometric configurations,fluttering motions of the codend,and the instantaneous flow fields inside and around the codend,with and without a liner,under varying catch sizes and inflow velocities.A proper orthogonal decomposition method is employed to extract phase-averaged mean properties of unsteady turbulent flows from flow measurement data obtained using an electromagnetic current velocity meter inside and around the codend.The results reveal that as catch size increases,the drag force,codend motion,Reynolds number,and codend volume increase while the drag coefficient decreases.Owing to the codend shape and pronounced motion,a complex fluid–structure interaction occurs,demonstrating a strong correlation between drag force and codend volume.The oscillation amplitudes of the hydrodynamic forces and codend motions increase with increasing catch size,and their oscillations mainly involve low-frequency activity.A significant reduction in the flow field occurs inside and around the unlined codend without a catch.The flow field is 5.81%,14.39%,and 27.01%lower than the unlined codend with a catch,the codend with a liner but without a catch,and the codend with both a liner and a catch,respectively.Fourier analysis reveals that the codend motions and hydrodynamic forces are mainly characterized by low-frequency activity and are synchronized with the unsteady turbulent flow street.Furthermore,the proper orthogonal decomposition results reveal the development of unsteady turbulent flow inside and around the codend,driven by flow passage blockage caused by the presence of the liner,intense codend motions,and the catch.Understanding the hydrodynamic characteristics and flow instabilities inside and around the codend,particularly those associated with its fluttering motions,is crucial for optimizing trawl design and improving trawl selectivity.
基金Supported by the National Natural Science Foundation of China(51679080 and 51379073)the Fundamental Research Funds for the Central Universities(B230205020).
文摘This study employed a computational fluid dynamics model with an overset mesh technique to investigate the thrust and power of a floating offshore wind turbine(FOWT)under platform floating motion in the wind–rain field.The impact of rainfall on aerodynamic performance was initially examined using a stationary turbine model in both wind and wind–rain conditions.Subsequently,the study compared the FOWT’s performance under various single degree-of-freedom(DOF)motions,including surge,pitch,heave,and yaw.Finally,the combined effects of wind–rain fields and platform motions involving two DOFs on the FOWT’s aerodynamics were analyzed and compared.The results demonstrate that rain negatively impacts the aerodynamic performance of both the stationary turbines and FOWTs.Pitch-dominated motions,whether involving single or multiple DOFs,caused significant fluctuations in the FOWT aerodynamics.The combination of surge and pitch motions created the most challenging operational environment for the FOWT in all tested scenarios.These findings highlighted the need for stronger construction materials and greater ultimate bearing capacity for FOWTs,as well as the importance of optimizing designs to mitigate excessive pitch and surge.
基金Supported by the Scientific and Technological Research Program of Chongqing Municipal Education Commission of China(Grant No.:KJQN202301105,KJQN202101550)Scientific Research Fund of Chongqing University of Technology(grant No.2021ZDZ015)National Nature Science Foundation of China(No.:52205052).
文摘This study investigates the effect of nacelle motions on the rotor performance and drivetrain dynamics of floating offshore wind turbines(FOWTs)through fully coupled aero-hydro-elastic-servo-mooring simulations.Using the National Renewable Energy Laboratory 5 MW monopile-supported offshore wind turbine and the OC4 DeepCwind semisubmersible wind turbine as case studies,the research addresses the complex dynamic responses resulting from the interaction among wind,waves,and turbine structures.Detailed multi-body dynamics models of wind turbines,including drivetrain components,are created within the SIMPACK framework.Meanwhile,the mooring system is modeled using a lumped-mass method.Various operational conditions are simulated through five wind-wave load cases.Results demonstrate that nacelle motions significantly influence rotor speed,thrust,torque,and power output,as well as the dynamic loads on drivetrain components.These findings highlight the need for advanced simulation techniques for the design and optimization of FOWTs to ensure reliable performance and longevity.
基金National Natural Science Foundation of China under Grant No.52278534Sichuan Provincial Natural Science Foundation of China under Grant No.2022NSFSC0423。
文摘To improve the resilience of railway stations,a typical station was selected as the research object,and an isolation design was introduced.Twenty-four groups of near-fault pulse-like ground motions were selected.The seismic resilience of the no-isolation railway stations(NIRS)and the isolation railway stations(IRS)were compared to provide a numerical result of the improvement in resilience.The results show that in the station isolation design,the station's functional requirements and structural characteristics should be considered and the appropriate placement of isolation bearings is under the waiting room.Under the action of a rare earthquake,the repair cost,repair time,rate of harm and death of the IRS were decreased by 8.04 million,18.30 days,6.93×10^(-3)and 1.21×10^(-3),respectively,when compared to the NIRS.The IRS received a seismic resilience grade of three-stars and the NIRS only one-star,indicating that rational isolation design improves the seismic resilience of stations.Thus,for the design of stations close to earthquake faults,it is suggested to utilize appropriate isolation techniques to improve their seismic resilience.
基金National Natural Science Foundation of China under Grant No.52478568National Key R&D Program of China under Grant Nos.2021YFC3100701 and 2022YFC3003503the Nature Science Foundation of Hubei Province under Grant No.2023AFA030。
文摘To analyze the correlation between the input energy parameters(V_(E))and typical intensity measures(IMs)of offshore ground motions,based on 273 earthquake events recorded by the K-NET in Japan,892 offshore ground motion records with moment magnitudes from 4.0 to 7.0 were used in this study.Residuals obtained through a ground motion model were calculated and analyzed for the correlation between V_(E) and amplitude,duration,frequency content and cumulative IMs.The results indicate that PGV and PGD have strong correlation with the V_(E)(T>0.2 s and T>0.4 s),the duration IMs have weakly negative correlation with the V_(E),Sd_(1) has a strong correlation with the V_(E) in the periods of T>0.4 s,T_(g) has a weak correlation with V_(E) and the cumulative IMs have strong correlation with the V_(E).The parametric predictive equations between typical IMs and V_(E) was proposed,and the differences between the prediction equations from the onshore ground motion records were compared.The differences in parametric predicted equations between offshore and onshore ground motions were confirmed in this study.Proposed correlation equations can be applied to offshore probabilistic seismic hazard analysis and the selection of ground motion records by generalized conditional intensity measures.
文摘This study is aimed at developing statistical equations to estimate the inelastic displacement ratio of singledegree-of-freedom systems subjected to far fault repeated earthquakes. In the study, peak ground motion parameters are used to define the scatter of the original data. The ratio of peak ground acceleration to peak ground velocity, and peak ground velocity of the ground motion records and structural parameters such as period of vibration and lateral strength ratio are used in the proposed equations. For the development of the equations, nonlinear time history analyses of single-degree-offreedom systems are conducted. Then, the results are used in a multivariate regression procedure. The equations are verified by comparing the estimated results with the calculated results. The average error and coefficient of variation of the proposed equations are presented. The analyses results revealed that the direct use of peak ground motion parameters for the estimation of inelastic displacement ratio significantly reduced the scatter in the original data and yielded accurate results. From the comparative results it is also observed that results obtained using equations specific to peak ground velocity or peak ground acceleration to peak ground velocity ratio are similar.
文摘This paper presents an efficient numerical scheme for calculating the periodic motion of a harmonically forced piecewise linear oscillator very accurately. The scheme is based on the shooting technique with the traditional numerical Poincare mapping and its Jacobian replaced by the piecewise analytic ones. Thus, the scheme gets rid of the requirement of the current schemes for an assumed order of the oscillator trajectory passing through different linear regions. The numerical examples in the paper demonstrate that the new scheme, compared with the current schemes, enables one to cope with more complicated dynamics of harmonically forced piecewise linear oscillators.
基金Supported by National Natural Science Foundation of China(Grant No.51305222)National Key Scientific and Technological Program of China(Grant No.2013ZX04001-021)
文摘Parallel robots with SCARA（selective compliance assembly robot arm） motions are utilized widely in the field of high speed pick-and-place manipulation. Error modeling for these robots generally simplifies the parallelogram structures included by the robots as a link. As the established error model fails to reflect the error feature of the parallelogram structures, the effect of accuracy design and kinematic calibration based on the error model come to be undermined. An error modeling methodology is proposed to establish an error model of parallel robots with parallelogram structures. The error model can embody the geometric errors of all joints, including the joints of parallelogram structures. Thus it can contain more exhaustively the factors that reduce the accuracy of the robot. Based on the error model and some sensitivity indices defined in the sense of statistics, sensitivity analysis is carried out. Accordingly, some atlases are depicted to express each geometric error’s influence on the moving platform’s pose errors. From these atlases, the geometric errors that have greater impact on the accuracy of the moving platform are identified, and some sensitive areas where the pose errors of the moving platform are extremely sensitive to the geometric errors are also figured out. By taking into account the error factors which are generally neglected in all existing modeling methods, the proposed modeling method can thoroughly disclose the process of error transmission and enhance the efficacy of accuracy design and calibration.
文摘In this study, a new mathematical model is developed composed of two parts, including harmonic and polynomial expressions for simulating the dominant velocity pulse of near fault ground motions. Based on a proposed velocity function, the corresponding expressions for the ground acceleration and displacement time histories are also derived. The proposed model is then fitted using some selected pulse-like near fault ground motions in the Next Generation Attenuation （NGA） project library. The new model is not only simple in form but also simulates the long-period portion of actual velocity near fault records with a high level of precision. It is shown that the proposed model-based elastic response spectra are compatible with the near fault records in the neighborhood of the prevailing frequency of the pulse. The results indicate that the proposed model adequately simulates the components of the time histories. Finally, the energy of the proposed pulse was compared with the energy of the actual record to confirm the compatibility.
基金National Key R&D Program of China under Grant No.2016YFC0701108the State Key Program of National Natural Science Foundation of China under Grant No.51738007
文摘This paper presents a novel approach to model and simulate the multi-support depth-varying seismic motions（MDSMs） within heterogeneous offshore and onshore sites.Based on 1 D wave propagation theory,the three-dimensional ground motion transfer functions on the surface or within an offshore or onshore site are derived by considering the effects of seawater and porous soils on the propagation of seismic P waves.Moreover,the depth-varying and spatial variation properties of seismic ground motions are considered in the ground motion simulation.Using the obtained transfer functions at any locations within a site,the offshore or onshore depth-varying seismic motions are stochastically simulated based on the spectral representation method（SRM）.The traditional approaches for simulating spatially varying ground motions are improved and extended to generate MDSMs within multiple offshore and onshore sites.The simulation results show that the PSD functions and coherency losses of the generated MDSMs are compatible with respective target values,which fully validates the effectiveness of the proposed simulation method.The synthesized MDSMs can provide strong support for the precise seismic response prediction and performance-based design of both offshore and onshore large-span engineering structures.
基金National Natural Science Foundation of China Under Grant No.90815020 and No.50639010
文摘A new model to simulate spatially correlated earthquake ground motions is developed. In the model, the main factors that characterize three distinct effects of spatial variability, namely, the incoherency effect, the wave-passage effect and the site-response effect, are taken into account, and corresponding terms/parameters are incorporated into the well known model of uniform ground motions. Some of these terms/parameters can be determined by the root operation, and others can be calculated directly. The proposed model is first verified theoretically, and examples of ground motion simulations are provided as a further illustration. It is proven that the ensemble expected value and the ensemble auto-/cross-spectral density functions of the simulated ground motions are identical to the target spectral density functions. The proposed model can also be used to simulate other correlated stochastic processes, such as wave and wind loads.
基金Foundation item： Supported by the National Natural Science Foundation of China （Grant No. 50739004 and 11072154）
文摘The numerical prediction of added resistance and vertical ship motions of one ITTC （Intemational Towing Tank Conference） S-175 containership in regular head waves by our own in-house unsteady RANS solver naoe-FOAM-SJTU is presented in this paper. The development of the solver naoe-FOAM-SJTU is based on the open source CFD tool, OpenFOAM. Numerical analysis is focused on the added resistance and vertical ship motions （heave and pitch motions） with four very different wavelengths （ 0.8Lpp 〈 2 〈 1.5L ） in regular head waves. Once the wavelength is near the length of the ship model, the responses of the resistance and ship motions become strongly influenced by nonlinear factors, as a result difficulties within simulations occur. In the paper, a comparison of the experimental results and the nonlinear strip theory was reviewed and based on the findings, the RANS simulations by the solver naoe-FOAM-SJTU were considered competent with the prediction of added resistance and vertical ship motions in a wide range of wave lengths.
基金Supported by the National Natural Science Foundation of China(10874090,50775109)the Jiangsu Provincial High-Tech Project of China(BG2006005)~~
文摘The forming of elliptic motions on the modal conversion ultrasonic motors （MCUMs） is discussed. The principles of the modal conversion are investigated based on the coupling with the stator and the rotor, and using an independent coupler. The elliptical locus observed on the longitudinal-torslonal vibration converter with oblique slits is analyzed by using vibration theory. A method for the modal conversion is proposed by using the local mode of a substructure On a main structure. The method can be used to design the modal conversion type ultrasonic motors.
基金The National Natural Science Foundation of China under contract Nos 41276006,40976013 and 41121091the China Scholarship Councilthe UK Natural Environment Research Council Programme FASTNEt under contract No.NE/I030259/1
文摘Features of near-inertial motions on the shelf （60 m deep） of the northern South China Sea were observed under the passage of two typhoons during the summer of 2009. There are two peaks in spectra at both sub-inertial and super-inertial frequencies. The super-inertial energy maximizes near the surface, while the sub-inertial energy maximizes at a deeper layer of 15 m. The sub-inertial shift of frequency is induced by the negative background vorticity. The super-inertial shift is probably attributed to the near-inertial wave propagating from higher latitudes. The near-inertial currents exhibit a two-layer pattern being separated at mid-depth （25-30 m）, with the phase in the upper layer being nearly opposite to that in the lower layer. The vertical propagation of phase implies that the near-inertial energy is not dominantly downward. The upward flux of the near-inertial energy is more evident at the surface layer （〈17 m）. There exist two boundaries at 17 and 40 rn, where the near-inertial energy is reflected upward and downward. The near-inertial motion is intermittent and can reach a peak of as much as 30 cm/s. The passage of Typhoon Nangka generates an intensive near-inertial event, but Typhoon Linfa does not. This difference is attributed to the relative moor- ing locations, which is on the right hand side of Nangka＇s path （leading to a wind pattern rotating clockwise with time） and is on the left hand side of Linfa＇s path （leading to a wind pattern rotating anti-clockwise with time）.
基金supported by the National Natural Science Foundation of China(Grant Nos.51475246 and 51075215)the Natural Science Foundation of Jiangsu Province of China(Grant No.Bk20131402)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry of China(Grand No.[2012]1707)
文摘With the increase of system scale, time delays have become unavoidable in nonlinear power systems, which add the complexity of system dynamics and induce chaotic oscillation and even voltage collapse events. In this paper, coexisting phenomenon in a fourth-order time-delayed power system is investigated for the first time with different initial conditions.With the mechanical power, generator damping factor, exciter gain, and time delay varying, the specific characteristic of the time-delayed system, including a discontinuous ＂jump＂ bifurcation behavior is analyzed by bifurcation diagrams, phase portraits, Poincar′e maps, and power spectrums. Moreover, the coexistence of two different periodic orbits and chaotic attractors with periodic orbits are observed in the power system, respectively. The production condition and existent domain of the coexistence phenomenon are helpful to avoid undesirable behavior in time-delayed power systems.
基金The National Key Research and Development Program of China(No.2018YFC1504703)the Basic Research Project of Institute of Geology,China Earthquake Administration(No.IGCEA1909)the Active Fault Survey Project for Aba Prefecture,Sichuan,China(No.IGCEA-X1906G)。
文摘In this work,the correlations between spatial distributions of landslide point density(LPD)and strong ground motions of the three strong earthquakes are qualitatively investigated.Meanwhile the qualitative relationship between the distribution of LPD and the fault rupture process is also characterized.Three strong events are the Lushan,Wenchuan,and Jiuzhaigou earthquakes.In order to reconstruct the near filed strong ground motions and the fault processes of these earthquakes,the broadband ground simulation method of University of California Santa Barbara(UCSB)and the simplified crustal layer structures are applied.To show the rationality of the UCSB method,the fault slip distributions of the three earthquakes reconstructed by the kinematic rupture generator model in the UCSB method are compared with those by inversed.Furthermore,the validation of the UCSB method for the three earthquakes is also carried according to the validation exercise of the Southern California Earthquake Center(SCEC)Broadband Platform(BBP).Lastly,the fields of peak ground acceleration(PGA)and peak ground velocity(PGV)in three mutually perpendicular directions of the three earthquakes are achieved.Generally,the landslide distribution length of large LPD values along the fault strike is less than the fault strike length.Therefore,the slip modes of earthquake faults affect the distributions of landslides.For the strike slip earthquakes,the distributions of large LPD values relate well to PGA and PGV components of the parallel and normal to the fault strike.For the reverse slip earthquakes,distributions of LPD relate to ground motion components in all directions.Moreover,distributions of landslides in near fields of earthquakes are significantly affected by the focus parameters and fault scales.
基金financially supported by the National Basic Research Program of China(973 Program,Grant No.2014CB046203)
文摘A domain decomposition and matching method in the time-domain is outlined for simulating the motions of ships advancing in waves. The flow field is decomposed into inner and outer domains by an imaginary control surface, and the Rankine source method is applied to the inner domain while the transient Green function method is used in the outer domain. Two initial boundary value problems are matched on the control surface. The corresponding numerical codes are developed, and the added masses, wave exciting forces and ship motions advancing in head sea for Series 60 ship and S175 containership, are presented and verified. A good agreement has been obtained when the numerical results are compared with the experimental data and other references. It shows that the present method is more efficient because of the panel discretization only in the inner domain during the numerical calculation, and good numerical stability is proved to avoid divergence problem regarding ships with flare.
