Rotor blade is one of the most significant components of helicopters. But due to its highspeed rotation characteristics, it is difficult to collect the vibration signals during the flight stage.Moreover, sensors are h...Rotor blade is one of the most significant components of helicopters. But due to its highspeed rotation characteristics, it is difficult to collect the vibration signals during the flight stage.Moreover, sensors are highly susceptible to damage resulting in the failure of the measurement.In order to make signal predictions for the damaged sensors, an operational modal analysis(OMA) together with the virtual sensing(VS) technology is proposed in this paper. This paper discusses two situations, i.e., mode shapes measured by all sensors(both normal and damaged) can be obtained using OMA, and mode shapes measured by some sensors(only including normal) can be obtained using OMA. For the second situation, it is necessary to use finite element(FE) analysis to supplement the missing mode shapes of damaged sensor. In order to improve the correlation between the FE model and the real structure, the FE mode shapes are corrected using the local correspondence(LC) principle and mode shapes measured by some sensors(only including normal).Then, based on the VS technology, the vibration signals of the damaged sensors during the flight stage can be accurately predicted using the identified mode shapes(obtained based on OMA and FE analysis) and the normal sensors signals. Given the high degrees of freedom(DOFs) in the FE mode shapes, this approach can also be used to predict vibration data at locations without sensors. The effectiveness and robustness of the proposed method is verified through finite element simulation, experiment as well as the actual flight test. The present work can be further used in the fault diagnosis and damage identification for rotor blade of helicopters.展开更多
An output-only modal identification method by a combination use of the peak-picking method and the cross spectrum methods are presented. Meanwhile, a novel mode shape optimum method of the deck is proposed. The method...An output-only modal identification method by a combination use of the peak-picking method and the cross spectrum methods are presented. Meanwhile, a novel mode shape optimum method of the deck is proposed. The methods are applied to the operational modal identification system of the Runyang Suspension Bridge, which can be used to obtain the modal parameters of the bridge from out-only data sets collected by its structural health monitoring system （SHMS）. As an example, the vibration response data of the deck, cable and tower recorded during typhoon Matsa excitation are used to illustrate the program application. Some of the modal frequencies observed from deck vibration responses are also found in the vibration responses of the cable and the tower. The results show that some modal shapes of the deck are strongly coupled with the cable and the tower. By comparing the identification results from the operational modal system with those from field measurements, a good agreement between them is achieved, but some modal frequencies identified from the operational modal identification system （OMIS）, such as L1 and L2, obviously decrease compared with those from the field measurements.展开更多
To develop modal macro-strain （ MMS ） identification techniques and improve their applicability in a continuous health monitoring system for civil infrastructures, the concept of operational macro-strain shape （OMS...To develop modal macro-strain （ MMS ） identification techniques and improve their applicability in a continuous health monitoring system for civil infrastructures, the concept of operational macro-strain shape （OMSS） and the corresponding identification method are proposed under unknown ever-changing loading conditions, and the MMS is then obtained. The core of the proposed technique is mainly based on the specific property that the macro-strain transmissibility tends to be independent of external excitations at the poles of the system and converges to a unique value. The proposed method is verified using the experimental data from a three-span continuous beam excited by an impact hammer at different locations. The identified results are also compared with the commonly used methods, such as the peak- picking （PP） method, the stochastic subspace identification （SSI） method, and numerical results, in the case of unknown input forces. Results show that the proposed technique has unique merits in accuracy and robustness due to its combining multiple tests under changing loading conditions, which also reveal the promising application of the distributed strain sensing system in identifying MMS of operational structures, as well as in the structural health monitoring （SHM） field.展开更多
The tenth BRICS Summit was held in Johannesburg,South Africa in 2018,which attracted attention from the whole world.Especially,it is of great importance to the BRICS nations,for it is the first ten years of BRICS,whic...The tenth BRICS Summit was held in Johannesburg,South Africa in 2018,which attracted attention from the whole world.Especially,it is of great importance to the BRICS nations,for it is the first ten years of BRICS,which marks its growth.Meanwhile,this year the Trump administration imposed more strict policies on protectionism.Particularly,the trade war between China and the United States is so intensive.China,as the core member of BRICS has great clout on BRICS,so the trade war between China and US also arouse a heat discussion among the BRICS nations.During the Summit,CGTN invited experts from the five BRICS nations to discuss related topics.Systemic Functional Linguistics,as one of the most influential branches of Linguistics,was firstly established by M.A.K.Halliday,and it has been greatly developed over the past decades.Interpersonal meaning is one of the three meta-functions,which focuses on how addressers use language to communicate,establish and maintain relationships with addressees,and express their opinions.Mood and modality are two basic resources to the realization of interpersonal meaning.Mood is used to represent the interaction of the language users,while modality reflects the utterers’attitudes and judgments.The paper discusses the three aspects of modality:modal operators,modal adjuncts and metaphors of modality.The paper applies the modality system to the analysis of the transcript of BRICS TALK.The author selects the experts’speeches on the trade war between China and US as the data.The research questions are as followed:(1)the characteristics of the modality resources appeared in their talks;(2)the BRICS nations attitudes and stance on trade war and America’s protectionism.展开更多
A frequency and spatial domain decomposition method （FSDD） for operational modal analysis （OMA） is presented in this paper, which is an extension of the complex mode indicator function （CMIF） method for experime...A frequency and spatial domain decomposition method （FSDD） for operational modal analysis （OMA） is presented in this paper, which is an extension of the complex mode indicator function （CMIF） method for experimental modal analysis （EMA）. The theoretical background of the FSDD method is clarified, Singular value decomposition is adopted to separate the signal space from the noise space. Finally, an enhanced power spectrum density （PSD） is proposed to obtain more accurate modal parameters by curve fitting in the frequency domain. Moreover, a simulation case and an application case are used to validate this method.展开更多
Sea-crossing bridges have attracted considerable attention in recent years as an increasing number of projects have been constructed worldwide.Situated in the coastal area,sea-crossing bridges are subjected to a harsh...Sea-crossing bridges have attracted considerable attention in recent years as an increasing number of projects have been constructed worldwide.Situated in the coastal area,sea-crossing bridges are subjected to a harsh environment(e.g.strong winds,possible ship collisions,and tidal waves)and their performance can deteriorate quickly and severely.To enhance safety and serviceability,it is a routine process to conduct vibration tests to identify modal properties(e.g.natural frequencies,damping ratios,and mode shapes)and to monitor their long-term variation for the purpose of early-damage alert.Operational modal analysis(OMA)provides a feasible way to investigate the modal properties even when the cross-sea bridges are in their operation condition.In this study,we focus on the OMA of cable-stayed bridges,because they are usually long-span and flexible to have extremely low natural frequencies.It challenges experimental capability(e.g.instrumentation and budgeting)and modal identification techniques(e.g.low frequency and closely spaced modes).This paper presents a modal survey of a cable-stayed sea-crossing bridge spanning 218 m+620 m+218 m.The bridge is located in the typhoon-prone area of the northwestern Pacific Ocean.Ambient vibration data was collected for 24 h.A Bayesian fast Fourier transform modal identification method incorporating an expectation-maximization algorithm is applied for modal analysis,in which the modal parameters and associated identification uncertainties are both addressed.Nineteen modes,including 15 translational modes and four torsional modes,are identified within the frequency range of[0,2.5 Hz].展开更多
Operational Modal Analysis(OMA) refers to the modal analysis of a structure in its operating state. The advantage of OMA is that only the output vibration signal of a system is used in the analysis process. Classic OM...Operational Modal Analysis(OMA) refers to the modal analysis of a structure in its operating state. The advantage of OMA is that only the output vibration signal of a system is used in the analysis process. Classic OMA is based on the white noise excitation assumption and many identification methods have been developed in both time domain and frequency domain. But in reality, many environmental excitations are not compliance with the white noise assumption. In this paper, a method of half power bandwidth analysis is applied to power spectrum analysis to deal with the colored noise and trapezoidal spectral excitation. The modal frequencies and modal damping ratios are derived and the error caused by trapezoidal spectral and colored noise excitation are analyzed. It is proved that the OMA algorithm based on the white noise assumption can be extended to the colored noise environments under certain conditions. Finally, a simulation example with a cantilever beam and a vibration test with four kinds of colored noise and trapezoidal spectrum base excitation are carried out and the results support the proposed method.展开更多
The experimental modal analysis of the selected self-propelled gun was completed to obtain its modal frequency distribution and modes by using an operational modal analysis experimental technique.The result obtained b...The experimental modal analysis of the selected self-propelled gun was completed to obtain its modal frequency distribution and modes by using an operational modal analysis experimental technique.The result obtained by the method was compared with that obtained by the traditional method.It indicates that the two results are in good agreement.展开更多
Output-only structural identification is developed by a refined Frequency Domain Decomposition（rFDD） approach, towards assessing current modal properties of heavy-damped buildings（in terms of identification challe...Output-only structural identification is developed by a refined Frequency Domain Decomposition（rFDD） approach, towards assessing current modal properties of heavy-damped buildings（in terms of identification challenge）, under strong ground motions. Structural responses from earthquake excitations are taken as input signals for the identification algorithm. A new dedicated computational procedure, based on coupled Chebyshev Type Ⅱ bandpass filters, is outlined for the effective estimation of natural frequencies, mode shapes and modal damping ratios. The identification technique is also coupled with a Gabor Wavelet Transform, resulting in an effective and self-contained time-frequency analysis framework. Simulated response signals generated by shear-type frames（with variable structural features） are used as a necessary validation condition. In this context use is made of a complete set of seismic records taken from the FEMA P695 database, i.e. all 44 ＂Far-Field＂（22 NS, 22 WE） earthquake signals. The modal estimates are statistically compared to their target values, proving the accuracy of the developed algorithm in providing prompt and accurate estimates of all current strong ground motion modal parameters. At this stage, such analysis tool may be employed for convenient application in the realm of Earthquake Engineering, towards potential Structural Health Monitoring and damage detection purposes.展开更多
A case study of excessive vibration on a motor-compressor system is presented in this paper.After barely two months of operation,the reciprocating compressor motor’s routine monitoring revealed excessive axial vibrat...A case study of excessive vibration on a motor-compressor system is presented in this paper.After barely two months of operation,the reciprocating compressor motor’s routine monitoring revealed excessive axial vibration amplitude.For this reason,the Operational Modal Analysis(OMA)was carried out in order to identify the pri-mary cause.According to the investigation,one of the harmonic components which was 18 times the motor’s running speed matched with a resonance frequency of 112 Hz.According to OMA study,the motor was vibrating in torsional motion because the compressor’s load had stimulated the entire motor-compressor unit at this reso-nance frequency.The analysis also demonstrates the bulging effect of the motor shaft’s axial vibration on the motor’s endplate.展开更多
A ship is operated under an extremely complex environment, and waves and winds are assumed to be the stochastic excitations. Moreover, the propeller, host and mechanical equipment can also induce the harmonic response...A ship is operated under an extremely complex environment, and waves and winds are assumed to be the stochastic excitations. Moreover, the propeller, host and mechanical equipment can also induce the harmonic responses. In order to reduce structural vibration, it is important to obtain the modal parameters information of a ship. However, the traditional modal parameter identification methods are not suitable since the excitation information is difficult to obtain. Natural excitation technique-eigensystem realization algorithm （NExT-ERA） is an operational modal identification method which abstracts modal parameters only from the response signals, and it is based on the assumption that the input to the structure is pure white noise. Hence, it is necessary to study the influence of harmonic excitations while applying the NExT-ERA method to a ship structure. The results of this research paper indicate the practical experiences under ambient excitation, ship model experiments were successfully done in the modal parameters identification only when the harmonic frequencies were not too close to the modal frequencies.展开更多
Reinforced concrete buildings may experience partial damage after earthquakes or some human-induced actions.A decision about the future of those buildings requires detailed analyses,while determining the dynamic chara...Reinforced concrete buildings may experience partial damage after earthquakes or some human-induced actions.A decision about the future of those buildings requires detailed analyses,while determining the dynamic characteristics of a real building in its pre-and post-event situations can guide the analysis.Hence,this study was planned to monitor the dynamic response of an existing six-story,reinforced concrete building with regard to structural damage.The modal characteristics of the original building were initially determined by the use of operational modal analysis.Next,three steps of progressive structural damage were applied to the building.The first damage level peeled off the clear cover of a beam and three columns on a corner of the building’s ground floor.whereas the second and third levels completely razed the damaged columns.Operational modal analysis was repeated at each damage stage to extract the frequencies and detailed mode shapes.Moreover,numerical models based on the finite element method were constructed to confirm the obtained experimental findings.The well-agreed experimental and numerical findings revealed the damage sensitivity of the building’s dynamic response.The quantified amount of frequency change favored a retrofit of the partially damaged buildings rather than their replacement.展开更多
This research focuses on the seismic responses of the historic masonry minarets,conducted through the creation of a digital twin model using finite element methods.The study initiated the development of a comprehensiv...This research focuses on the seismic responses of the historic masonry minarets,conducted through the creation of a digital twin model using finite element methods.The study initiated the development of a comprehensive model in the ANSYS Workbench,supplemented by operational modal analysis(OMA),to ascertain the dynamic characteristics of the minaret.The alignment of numerical and experimental frequency data was achieved using the response surface method(RSM)within ANSYS Workbench DesignXplorer.This process resulted in the establishment of a digital twin,accurately representing the physical minaret in a virtual environment.Blender^(■)software was then used to simulate the effects of two consecutive earthquakes in Türkiye that occurred on February 6,2023.The simulations highlighted the heightened susceptibility of the minaret,especially in its upper sections,to consecutive seismic activities,culminating in significant damage and collapse.This innovative approach,merging traditional engineering methods with a cutting-edge digital simulation,provides a profound insight into the seismic behavior of historical structures.The research underscores the importance of advanced seismic modeling for the effective preservation and resilience of architectural heritage sites against earthquake risks.展开更多
Modal analysis,which provides modal parameters including frequencies,damping ratios,and mode shapes,is essential for assessing structural safety in structural health monitoring.Automated operational modal analysis(AOM...Modal analysis,which provides modal parameters including frequencies,damping ratios,and mode shapes,is essential for assessing structural safety in structural health monitoring.Automated operational modal analysis(AOMA)offers a promising alternative to traditional methods that depend heavily on human intervention and engineering judgment.However,estimating structural dynamic properties and managing spurious modes remain challenging due to uncertainties in practical application conditions.To address this issue,we propose an automated modal identification approach comprising three key aspects:(1)identification of modal parameters using covariance-driven stochastic subspace identification;(2)automated interpretation of the stabilization diagram;(3)an improved self-adaptive algorithm for grouping physical modes based on ordering points to identify the clustering structure(OPTICS)combined with k-nearest neighbors(KNN).The proposed approach can play a crucial role in enabling real-time structural health monitoring without human intervention.A simulated 10-story shear frame was used to verify the methodology.Identification results from a cable-stayed bridge demonstrate the practicality of the proposed method for conducting AOMA in engineering practice.The proposed approach can automatically identify modal parameters with high accuracy,making it suitable for a real-time structural health monitoring framework.展开更多
This research focuses on identifying the damping ratio of bridges using nonstationary ambient vibration data. The damping ratios of bridges in service have generally been identified using operational modal analysis （...This research focuses on identifying the damping ratio of bridges using nonstationary ambient vibration data. The damping ratios of bridges in service have generally been identified using operational modal analysis （OMA） based on a stationary white noise assumption for input signals. However, most bridges are generally subjected to nonstationary excitations while in service, and this violation of the basic assumption can lead to uncertainties in damping identification. To deal with nonstationarity, an amplitude-modulating function was calculated from measured responses to eliminate global trends caused by nonstationary input. A natural excitation technique （NExT）-eigensystem realization algorithm （ERA） was applied to estimate the damping ratio for a stationarized process. To improve the accuracy of OMA-based damping estimates, a comparative analysis was performed between an extracted stationary process and nonstationary data to assess the effect of eliminating nonstationarity. The mean value and standard deviation of the damping ratio for the first vertical mode decreased after signal stationarization.展开更多
In this review article,the past investigations carried out on heritage structures using Ambient Vibration Test(AVT)and Operational Modal Analysis(OMA)for system identification(determination of dynamic properties like ...In this review article,the past investigations carried out on heritage structures using Ambient Vibration Test(AVT)and Operational Modal Analysis(OMA)for system identification(determination of dynamic properties like frequency,mode shape and damping ratios)and associated applications are summarized.A total of 68 major research studies on heritage structures around the world that are available in literature are surveyed for this purpose.At first,field investigations carried out on heritage structures prior to conducting AVT are explained in detail.Next,specifications of accelerometers,location of accelerometers and optimization of accelerometer networks have been elaborated with respect to the geometry of the heritage structures.In addition to this,ambient vibration loads and data acquisition procedures are also discussed.Further,the state of art of performing OMA techniques for heritage structures is explained briefly.Furthermore,various applications of system identification for heritage structures are documented.Finally,conclusions are made towards errorless system identification of heritage structures through AVT and OMA.展开更多
A model based damage identification was proposed by facilitating parameter sensitivity analysis and applied to a general overhead travelling crane.As updating reference data,experimental modal frequency was obtained b...A model based damage identification was proposed by facilitating parameter sensitivity analysis and applied to a general overhead travelling crane.As updating reference data,experimental modal frequency was obtained by operational modal analysis(OMA)under ambient excitation.One dimensional damage function was defined to identify the damage by bending stiffness.The results showed that the model updating method could locate the damage and quantitatively describe the structure.The average error of eigenvalues between updated model analysis and the experimental results was less than 4% which proved the accuracy reliable.The comparison of finite element analysis and the test results of the deflection under the capacity load further verified the feasibility of this method.展开更多
Based on experiment modal analysis(EMA) and operation modal analysis(OMA), the dynamic characteristics of cylindrical grinding machine were measured and provided a basis for further failure analysis.The influences of ...Based on experiment modal analysis(EMA) and operation modal analysis(OMA), the dynamic characteristics of cylindrical grinding machine were measured and provided a basis for further failure analysis.The influences of grinding parameters on dynamic characteristics were studied by analyzing the diagnostic signals extracted from racing and grinding experiments.The significant frequency of 38 Hz related to grinding wheel spindle speed of 2 307 r/min showed that the wheel spindle system was in a state of imbalan...展开更多
Methods for scaling mode shapes determined by operational modal analysis(OMA)have been extensively investigated in the last years.A recent addition to the range of methods for scaling OMA mode shapes is the so-called ...Methods for scaling mode shapes determined by operational modal analysis(OMA)have been extensively investigated in the last years.A recent addition to the range of methods for scaling OMA mode shapes is the so-called OMAH technique,which is based on exciting the structure by harmonic forces applied by an actuator.By applying harmonic forces in at least one degree-of-freedom(DOF),and measuring the response in at least one response DOF,while using at least as many frequencies as the number of mode shapes to be scaled,the mode shape scaling(modal mass)of all modes of interest may be determined.In previous publications on the method the authors have proven that the technique is easy and robust to apply to both small scale and large scale structures.Also,it has been shown that the technique is capable of scaling highly coupled modes by using an extended multiple reference formulation.The present paper summarizes the theory of the OMAH method and gives recommendations of how to implement the method for best results.It is pointed out,as has been shown in previous papers,that the accuracy of the mode scaling is increased by using more than one response DOF,and by selecting DOFs with high mode shape coefficients.To determine the harmonic force and responses,it is recommended to use the three-parameter sine fit method.It is shown that by using this method,the measurement time can be kept short by using high sampling frequency and bandpass filtering whereas spectrum based methods require long measurement times.This means that even for structures with low natural frequencies,the extra measurement time for scaling the mode shapes can be kept relatively short.展开更多
Operational modal analysis(OMA)is vital for identifying modal parameters under real-world conditions,yet existing methods often face challenges with noise sensitivity and stability.This study introduces NExT-LF,a nove...Operational modal analysis(OMA)is vital for identifying modal parameters under real-world conditions,yet existing methods often face challenges with noise sensitivity and stability.This study introduces NExT-LF,a novel method that combines the well-known Natural Excitation Technique(NExT)with the Loewner Framework(LF).NExT enables the extraction of Impulse Response Functions from output-only vibration data,which are then converted into the frequency domain and used by LF to estimate modal parameters.The proposed method is validated through numerical and experimental case studies.In the numerical study of a two-dimensional Euler–Bernoulli cantilever beam,NExT-LF provides results consistent with analytical solutions and those from standard methods,NExT with Eigensystem Realization Algorithm(NExT-ERA)and stochastic subspace identification with canonical variate analysis.Additionally,NExT-LF demonstrates superior noise robustness,reliably identifying stable modes across various noise levels where NExT-ERA fails.Experimental validation on the Sheraton Universal Hotel is the first OMA application to this structure,confirming NExT-LF as a robust and efficient method for output-only modal parameter identification.展开更多
基金supported by grants from the High-Level Oversea Talent Introduction Plan,Chinathe Special Fund for Basic Scientific Research in Central Universities of China-Doctoral Research and Innovation Fund Project,China(No.3072023CFJ0206).
文摘Rotor blade is one of the most significant components of helicopters. But due to its highspeed rotation characteristics, it is difficult to collect the vibration signals during the flight stage.Moreover, sensors are highly susceptible to damage resulting in the failure of the measurement.In order to make signal predictions for the damaged sensors, an operational modal analysis(OMA) together with the virtual sensing(VS) technology is proposed in this paper. This paper discusses two situations, i.e., mode shapes measured by all sensors(both normal and damaged) can be obtained using OMA, and mode shapes measured by some sensors(only including normal) can be obtained using OMA. For the second situation, it is necessary to use finite element(FE) analysis to supplement the missing mode shapes of damaged sensor. In order to improve the correlation between the FE model and the real structure, the FE mode shapes are corrected using the local correspondence(LC) principle and mode shapes measured by some sensors(only including normal).Then, based on the VS technology, the vibration signals of the damaged sensors during the flight stage can be accurately predicted using the identified mode shapes(obtained based on OMA and FE analysis) and the normal sensors signals. Given the high degrees of freedom(DOFs) in the FE mode shapes, this approach can also be used to predict vibration data at locations without sensors. The effectiveness and robustness of the proposed method is verified through finite element simulation, experiment as well as the actual flight test. The present work can be further used in the fault diagnosis and damage identification for rotor blade of helicopters.
基金The National High Technology Research and Development Program of China(863Program)(No.2006AA04Z416)
文摘An output-only modal identification method by a combination use of the peak-picking method and the cross spectrum methods are presented. Meanwhile, a novel mode shape optimum method of the deck is proposed. The methods are applied to the operational modal identification system of the Runyang Suspension Bridge, which can be used to obtain the modal parameters of the bridge from out-only data sets collected by its structural health monitoring system （SHMS）. As an example, the vibration response data of the deck, cable and tower recorded during typhoon Matsa excitation are used to illustrate the program application. Some of the modal frequencies observed from deck vibration responses are also found in the vibration responses of the cable and the tower. The results show that some modal shapes of the deck are strongly coupled with the cable and the tower. By comparing the identification results from the operational modal system with those from field measurements, a good agreement between them is achieved, but some modal frequencies identified from the operational modal identification system （OMIS）, such as L1 and L2, obviously decrease compared with those from the field measurements.
基金The National Natural Science Foudation of China(No.51578140)the Natural Science Foundation of Jiangsu Province(No.BK20151092)Scientific Innovation Research of College Graduates in Jiangsu Province(No.CXZZ12_0108)
文摘To develop modal macro-strain （ MMS ） identification techniques and improve their applicability in a continuous health monitoring system for civil infrastructures, the concept of operational macro-strain shape （OMSS） and the corresponding identification method are proposed under unknown ever-changing loading conditions, and the MMS is then obtained. The core of the proposed technique is mainly based on the specific property that the macro-strain transmissibility tends to be independent of external excitations at the poles of the system and converges to a unique value. The proposed method is verified using the experimental data from a three-span continuous beam excited by an impact hammer at different locations. The identified results are also compared with the commonly used methods, such as the peak- picking （PP） method, the stochastic subspace identification （SSI） method, and numerical results, in the case of unknown input forces. Results show that the proposed technique has unique merits in accuracy and robustness due to its combining multiple tests under changing loading conditions, which also reveal the promising application of the distributed strain sensing system in identifying MMS of operational structures, as well as in the structural health monitoring （SHM） field.
文摘The tenth BRICS Summit was held in Johannesburg,South Africa in 2018,which attracted attention from the whole world.Especially,it is of great importance to the BRICS nations,for it is the first ten years of BRICS,which marks its growth.Meanwhile,this year the Trump administration imposed more strict policies on protectionism.Particularly,the trade war between China and the United States is so intensive.China,as the core member of BRICS has great clout on BRICS,so the trade war between China and US also arouse a heat discussion among the BRICS nations.During the Summit,CGTN invited experts from the five BRICS nations to discuss related topics.Systemic Functional Linguistics,as one of the most influential branches of Linguistics,was firstly established by M.A.K.Halliday,and it has been greatly developed over the past decades.Interpersonal meaning is one of the three meta-functions,which focuses on how addressers use language to communicate,establish and maintain relationships with addressees,and express their opinions.Mood and modality are two basic resources to the realization of interpersonal meaning.Mood is used to represent the interaction of the language users,while modality reflects the utterers’attitudes and judgments.The paper discusses the three aspects of modality:modal operators,modal adjuncts and metaphors of modality.The paper applies the modality system to the analysis of the transcript of BRICS TALK.The author selects the experts’speeches on the trade war between China and US as the data.The research questions are as followed:(1)the characteristics of the modality resources appeared in their talks;(2)the BRICS nations attitudes and stance on trade war and America’s protectionism.
基金China Postdoctoral Science Foundation Under Grant No. 2004035215 Jiangsu Planned Projects for Postdoctoral Research Funds 2004 Aeronautical Science Research Foundation Under Grant No. 04152065
文摘A frequency and spatial domain decomposition method （FSDD） for operational modal analysis （OMA） is presented in this paper, which is an extension of the complex mode indicator function （CMIF） method for experimental modal analysis （EMA）. The theoretical background of the FSDD method is clarified, Singular value decomposition is adopted to separate the signal space from the noise space. Finally, an enhanced power spectrum density （PSD） is proposed to obtain more accurate modal parameters by curve fitting in the frequency domain. Moreover, a simulation case and an application case are used to validate this method.
基金supported by the Start-up Fund from Zhejiang University(No.130000-171207704/018)the National Natural Science Foundation of China(Nos.U1709207,51578506 and 51908494)。
文摘Sea-crossing bridges have attracted considerable attention in recent years as an increasing number of projects have been constructed worldwide.Situated in the coastal area,sea-crossing bridges are subjected to a harsh environment(e.g.strong winds,possible ship collisions,and tidal waves)and their performance can deteriorate quickly and severely.To enhance safety and serviceability,it is a routine process to conduct vibration tests to identify modal properties(e.g.natural frequencies,damping ratios,and mode shapes)and to monitor their long-term variation for the purpose of early-damage alert.Operational modal analysis(OMA)provides a feasible way to investigate the modal properties even when the cross-sea bridges are in their operation condition.In this study,we focus on the OMA of cable-stayed bridges,because they are usually long-span and flexible to have extremely low natural frequencies.It challenges experimental capability(e.g.instrumentation and budgeting)and modal identification techniques(e.g.low frequency and closely spaced modes).This paper presents a modal survey of a cable-stayed sea-crossing bridge spanning 218 m+620 m+218 m.The bridge is located in the typhoon-prone area of the northwestern Pacific Ocean.Ambient vibration data was collected for 24 h.A Bayesian fast Fourier transform modal identification method incorporating an expectation-maximization algorithm is applied for modal analysis,in which the modal parameters and associated identification uncertainties are both addressed.Nineteen modes,including 15 translational modes and four torsional modes,are identified within the frequency range of[0,2.5 Hz].
文摘Operational Modal Analysis(OMA) refers to the modal analysis of a structure in its operating state. The advantage of OMA is that only the output vibration signal of a system is used in the analysis process. Classic OMA is based on the white noise excitation assumption and many identification methods have been developed in both time domain and frequency domain. But in reality, many environmental excitations are not compliance with the white noise assumption. In this paper, a method of half power bandwidth analysis is applied to power spectrum analysis to deal with the colored noise and trapezoidal spectral excitation. The modal frequencies and modal damping ratios are derived and the error caused by trapezoidal spectral and colored noise excitation are analyzed. It is proved that the OMA algorithm based on the white noise assumption can be extended to the colored noise environments under certain conditions. Finally, a simulation example with a cantilever beam and a vibration test with four kinds of colored noise and trapezoidal spectrum base excitation are carried out and the results support the proposed method.
文摘The experimental modal analysis of the selected self-propelled gun was completed to obtain its modal frequency distribution and modes by using an operational modal analysis experimental technique.The result obtained by the method was compared with that obtained by the traditional method.It indicates that the two results are in good agreement.
基金Public research funding from“Fondi di Ricerca d’Ateneo ex 60%” and a ministerial doctoral grantfunds at the ISA Doctoral School,University of Bergamo,Department of Engineering and Applied Sciences (Dalmine)
文摘Output-only structural identification is developed by a refined Frequency Domain Decomposition（rFDD） approach, towards assessing current modal properties of heavy-damped buildings（in terms of identification challenge）, under strong ground motions. Structural responses from earthquake excitations are taken as input signals for the identification algorithm. A new dedicated computational procedure, based on coupled Chebyshev Type Ⅱ bandpass filters, is outlined for the effective estimation of natural frequencies, mode shapes and modal damping ratios. The identification technique is also coupled with a Gabor Wavelet Transform, resulting in an effective and self-contained time-frequency analysis framework. Simulated response signals generated by shear-type frames（with variable structural features） are used as a necessary validation condition. In this context use is made of a complete set of seismic records taken from the FEMA P695 database, i.e. all 44 ＂Far-Field＂（22 NS, 22 WE） earthquake signals. The modal estimates are statistically compared to their target values, proving the accuracy of the developed algorithm in providing prompt and accurate estimates of all current strong ground motion modal parameters. At this stage, such analysis tool may be employed for convenient application in the realm of Earthquake Engineering, towards potential Structural Health Monitoring and damage detection purposes.
文摘A case study of excessive vibration on a motor-compressor system is presented in this paper.After barely two months of operation,the reciprocating compressor motor’s routine monitoring revealed excessive axial vibration amplitude.For this reason,the Operational Modal Analysis(OMA)was carried out in order to identify the pri-mary cause.According to the investigation,one of the harmonic components which was 18 times the motor’s running speed matched with a resonance frequency of 112 Hz.According to OMA study,the motor was vibrating in torsional motion because the compressor’s load had stimulated the entire motor-compressor unit at this reso-nance frequency.The analysis also demonstrates the bulging effect of the motor shaft’s axial vibration on the motor’s endplate.
基金Supported by the National Natural Science Foundation of China（51079027）
文摘A ship is operated under an extremely complex environment, and waves and winds are assumed to be the stochastic excitations. Moreover, the propeller, host and mechanical equipment can also induce the harmonic responses. In order to reduce structural vibration, it is important to obtain the modal parameters information of a ship. However, the traditional modal parameter identification methods are not suitable since the excitation information is difficult to obtain. Natural excitation technique-eigensystem realization algorithm （NExT-ERA） is an operational modal identification method which abstracts modal parameters only from the response signals, and it is based on the assumption that the input to the structure is pure white noise. Hence, it is necessary to study the influence of harmonic excitations while applying the NExT-ERA method to a ship structure. The results of this research paper indicate the practical experiences under ambient excitation, ship model experiments were successfully done in the modal parameters identification only when the harmonic frequencies were not too close to the modal frequencies.
基金supported by the Scientific and Technological Research Council of Türkiye(TUBITAK)under Research Grant 116M254.
文摘Reinforced concrete buildings may experience partial damage after earthquakes or some human-induced actions.A decision about the future of those buildings requires detailed analyses,while determining the dynamic characteristics of a real building in its pre-and post-event situations can guide the analysis.Hence,this study was planned to monitor the dynamic response of an existing six-story,reinforced concrete building with regard to structural damage.The modal characteristics of the original building were initially determined by the use of operational modal analysis.Next,three steps of progressive structural damage were applied to the building.The first damage level peeled off the clear cover of a beam and three columns on a corner of the building’s ground floor.whereas the second and third levels completely razed the damaged columns.Operational modal analysis was repeated at each damage stage to extract the frequencies and detailed mode shapes.Moreover,numerical models based on the finite element method were constructed to confirm the obtained experimental findings.The well-agreed experimental and numerical findings revealed the damage sensitivity of the building’s dynamic response.The quantified amount of frequency change favored a retrofit of the partially damaged buildings rather than their replacement.
基金product of the research project titled,Video Camera Based Structural Health Monitoring of Historic Masonry Minarets and Development of a Long-Term Decision-Making Model Based on Deep Learning Method(Project No.222M140)supported by TÜBİTAK 1001-Scientific and the Technological Research Projects Support Program.
文摘This research focuses on the seismic responses of the historic masonry minarets,conducted through the creation of a digital twin model using finite element methods.The study initiated the development of a comprehensive model in the ANSYS Workbench,supplemented by operational modal analysis(OMA),to ascertain the dynamic characteristics of the minaret.The alignment of numerical and experimental frequency data was achieved using the response surface method(RSM)within ANSYS Workbench DesignXplorer.This process resulted in the establishment of a digital twin,accurately representing the physical minaret in a virtual environment.Blender^(■)software was then used to simulate the effects of two consecutive earthquakes in Türkiye that occurred on February 6,2023.The simulations highlighted the heightened susceptibility of the minaret,especially in its upper sections,to consecutive seismic activities,culminating in significant damage and collapse.This innovative approach,merging traditional engineering methods with a cutting-edge digital simulation,provides a profound insight into the seismic behavior of historical structures.The research underscores the importance of advanced seismic modeling for the effective preservation and resilience of architectural heritage sites against earthquake risks.
基金supported by the National Natural Science Foundation of China(No.52408200)the Natural Science Foundation of Jiangsu Province(No.BK20240996)+1 种基金China,the Suzhou Science and Technology Plan(Basic Research)Project(No.SJC2023002)China,and the Natural Science Research Projects of Colleges and Universities in Jiangsu Province(No.24KJB560022),China.
文摘Modal analysis,which provides modal parameters including frequencies,damping ratios,and mode shapes,is essential for assessing structural safety in structural health monitoring.Automated operational modal analysis(AOMA)offers a promising alternative to traditional methods that depend heavily on human intervention and engineering judgment.However,estimating structural dynamic properties and managing spurious modes remain challenging due to uncertainties in practical application conditions.To address this issue,we propose an automated modal identification approach comprising three key aspects:(1)identification of modal parameters using covariance-driven stochastic subspace identification;(2)automated interpretation of the stabilization diagram;(3)an improved self-adaptive algorithm for grouping physical modes based on ordering points to identify the clustering structure(OPTICS)combined with k-nearest neighbors(KNN).The proposed approach can play a crucial role in enabling real-time structural health monitoring without human intervention.A simulated 10-story shear frame was used to verify the methodology.Identification results from a cable-stayed bridge demonstrate the practicality of the proposed method for conducting AOMA in engineering practice.The proposed approach can automatically identify modal parameters with high accuracy,making it suitable for a real-time structural health monitoring framework.
基金supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (2017R1A2B4008973)supported by grants (17SCIPB119960-02) from the Ministry of Land+2 种基金 Infrastructure and Transport of the Korean Governmentpartially supported by the BK21 PLUS research program of the National Research Foundation of Koreathe New Technology Research Center for Bridges through the Institute of Engineering Research at Seoul National University
文摘This research focuses on identifying the damping ratio of bridges using nonstationary ambient vibration data. The damping ratios of bridges in service have generally been identified using operational modal analysis （OMA） based on a stationary white noise assumption for input signals. However, most bridges are generally subjected to nonstationary excitations while in service, and this violation of the basic assumption can lead to uncertainties in damping identification. To deal with nonstationarity, an amplitude-modulating function was calculated from measured responses to eliminate global trends caused by nonstationary input. A natural excitation technique （NExT）-eigensystem realization algorithm （ERA） was applied to estimate the damping ratio for a stationarized process. To improve the accuracy of OMA-based damping estimates, a comparative analysis was performed between an extracted stationary process and nonstationary data to assess the effect of eliminating nonstationarity. The mean value and standard deviation of the damping ratio for the first vertical mode decreased after signal stationarization.
文摘In this review article,the past investigations carried out on heritage structures using Ambient Vibration Test(AVT)and Operational Modal Analysis(OMA)for system identification(determination of dynamic properties like frequency,mode shape and damping ratios)and associated applications are summarized.A total of 68 major research studies on heritage structures around the world that are available in literature are surveyed for this purpose.At first,field investigations carried out on heritage structures prior to conducting AVT are explained in detail.Next,specifications of accelerometers,location of accelerometers and optimization of accelerometer networks have been elaborated with respect to the geometry of the heritage structures.In addition to this,ambient vibration loads and data acquisition procedures are also discussed.Further,the state of art of performing OMA techniques for heritage structures is explained briefly.Furthermore,various applications of system identification for heritage structures are documented.Finally,conclusions are made towards errorless system identification of heritage structures through AVT and OMA.
基金supported by the Research Program of General Administration of Quality Supervision,Inspec-tion and Quarantine of the People's Republic of China(AQSIQ)(No.2014QK182)the Key Laboratory of Risk Identification and Structural Damage Detection Technology for Large Cranes of Jiangsu Province,Donghua Testing Technology Co.,Ltd
文摘A model based damage identification was proposed by facilitating parameter sensitivity analysis and applied to a general overhead travelling crane.As updating reference data,experimental modal frequency was obtained by operational modal analysis(OMA)under ambient excitation.One dimensional damage function was defined to identify the damage by bending stiffness.The results showed that the model updating method could locate the damage and quantitatively describe the structure.The average error of eigenvalues between updated model analysis and the experimental results was less than 4% which proved the accuracy reliable.The comparison of finite element analysis and the test results of the deflection under the capacity load further verified the feasibility of this method.
文摘Based on experiment modal analysis(EMA) and operation modal analysis(OMA), the dynamic characteristics of cylindrical grinding machine were measured and provided a basis for further failure analysis.The influences of grinding parameters on dynamic characteristics were studied by analyzing the diagnostic signals extracted from racing and grinding experiments.The significant frequency of 38 Hz related to grinding wheel spindle speed of 2 307 r/min showed that the wheel spindle system was in a state of imbalan...
文摘Methods for scaling mode shapes determined by operational modal analysis(OMA)have been extensively investigated in the last years.A recent addition to the range of methods for scaling OMA mode shapes is the so-called OMAH technique,which is based on exciting the structure by harmonic forces applied by an actuator.By applying harmonic forces in at least one degree-of-freedom(DOF),and measuring the response in at least one response DOF,while using at least as many frequencies as the number of mode shapes to be scaled,the mode shape scaling(modal mass)of all modes of interest may be determined.In previous publications on the method the authors have proven that the technique is easy and robust to apply to both small scale and large scale structures.Also,it has been shown that the technique is capable of scaling highly coupled modes by using an extended multiple reference formulation.The present paper summarizes the theory of the OMAH method and gives recommendations of how to implement the method for best results.It is pointed out,as has been shown in previous papers,that the accuracy of the mode scaling is increased by using more than one response DOF,and by selecting DOFs with high mode shape coefficients.To determine the harmonic force and responses,it is recommended to use the three-parameter sine fit method.It is shown that by using this method,the measurement time can be kept short by using high sampling frequency and bandpass filtering whereas spectrum based methods require long measurement times.This means that even for structures with low natural frequencies,the extra measurement time for scaling the mode shapes can be kept relatively short.
基金The first author has been supported by the Madrid Government(Comunidad de Madrid—Spain)under the Multiannual Agreement with the Universidad Carlos III de Madrid(UC3M)(IA_aCTRl-CM-UC3M)and by the Grants for research activity of young PhD holders,part of the UC3M Own Research Program(Ayudas para la Actividad Investigadora de los Jóvenes Doctores,del Programa Propio de Investigación de la UC3M)supported by the Centro Nazionale per la MobilitàSostenibile(MOST—Sustainable Mobility Center),Spoke 7(Cooperative Connected and Automated Mobility and Smart Infrastructures),Work Package 4(Resilience of Networks,Structural Health Monitoring and Asset Management).
文摘Operational modal analysis(OMA)is vital for identifying modal parameters under real-world conditions,yet existing methods often face challenges with noise sensitivity and stability.This study introduces NExT-LF,a novel method that combines the well-known Natural Excitation Technique(NExT)with the Loewner Framework(LF).NExT enables the extraction of Impulse Response Functions from output-only vibration data,which are then converted into the frequency domain and used by LF to estimate modal parameters.The proposed method is validated through numerical and experimental case studies.In the numerical study of a two-dimensional Euler–Bernoulli cantilever beam,NExT-LF provides results consistent with analytical solutions and those from standard methods,NExT with Eigensystem Realization Algorithm(NExT-ERA)and stochastic subspace identification with canonical variate analysis.Additionally,NExT-LF demonstrates superior noise robustness,reliably identifying stable modes across various noise levels where NExT-ERA fails.Experimental validation on the Sheraton Universal Hotel is the first OMA application to this structure,confirming NExT-LF as a robust and efficient method for output-only modal parameter identification.
