In order to investigate the behavior of buildings and engineering structures during earthquakes, based on the data of seismic observation devices mounted on constructions with typical characteristics, results of inves...In order to investigate the behavior of buildings and engineering structures during earthquakes, based on the data of seismic observation devices mounted on constructions with typical characteristics, results of investigating the change of mechanical properties of building structural system over time and the results of examination of structural rigidity and safety change over time, depending on the dynamic characteristics of the building, determined by experimental investigations made at intervals are mentioned in this article. In addition, evaluation of earthquake acceleration acting on structures due to earthquake-induced damage characteristics of buildings and engineering constructions which are made earthquake resistant is also included here.展开更多
Steam-cured concrete is widely used to manufacture prefabricated units of high-speed railway foundation structure such as girder and track slab.The dynamic mechanical property of steam-cured concrete is one of the key...Steam-cured concrete is widely used to manufacture prefabricated units of high-speed railway foundation structure such as girder and track slab.The dynamic mechanical property of steam-cured concrete is one of the key properties affecting service performance of high-speed railway foundation structure.In the present paper,serial macro/micro-experiments were carried out to investigate the dynamic elastic modulus,shear modulus,damping ratio,and microstructure of steam-cured concrete.The relationships between compositions,curing regime,microstructure,and dynamic properties of steam-cured concrete as well as the corresponding mechanisms were discussed.The results indicate that steam-cured concrete in early age has a larger dynamic elastic modulus and shear modulus as well as a smaller damping ratio compared with standard-cured concrete.On the contrary,at a later age a slightly smaller dynamic elastic modulus and a larger damping ratio of steam-cured concrete are observed.Addition of mineral admixture results in a bit lower dynamic elastic modulus and damping ratio of concrete than that of the control specimen without mineral admixtures.The achievements can provide some fundamental suggestions for materials parameters selection during structural design of steam-cured concrete precast element.展开更多
Regenerative cooling with fuel as the coolant is used in the scramjet engine. In order to grasp the dynamic cha- racteristics of engine fuel supply processes, this article studies the dynamic characteristics of hydroc...Regenerative cooling with fuel as the coolant is used in the scramjet engine. In order to grasp the dynamic cha- racteristics of engine fuel supply processes, this article studies the dynamic characteristics of hydrocarbon fuel within the channel. A one-dimensional dynamic model was proved, the thermal energy storage effect, fuel volume effect and chemical dynamic effect have been considered in the model, the ordinary differential equations were solved using a 4th order Rungc-Kutta method. The precision of the model was validated by three groups of expe- rimental data. The effects of input signal, working condition, tube size on the dynamic characteristics of pressure, flow rate, temperature have been simulated. It is found that cracking reaction increased the compressibility of the fuel pyrolysis mixture and lead to longer responding time of outlet flow. The responding time of outlet flow can reach 3s when tube is 5m long which will greatly influence the control performance of the engine thrust system. Meanwhile, when the inlet flow rate appears the step change, the inlet pressure leads to overshoot, the overshoot can reach as much as 100%, such highly transient impulse will result in detrimental effect on fucl pump.展开更多
Vibration signal is an important prerequisite for mechanical fault detection. However, early stage defect of rotating machiner- ies is difficult to identify because their incipient energy is interfered with background...Vibration signal is an important prerequisite for mechanical fault detection. However, early stage defect of rotating machiner- ies is difficult to identify because their incipient energy is interfered with background noises. Multiwavelet is a powerful tool used to conduct non-stationary fault feature extraction. However, the existing predetermined multiwavelet bases are independ- ent of the dynamic response signals. In this paper, a constructing technique of vibration data-driven maximal-overlap adaptive multiwavelet （MOAMW） is proposed for enhancing the extracting performance of fault symptom. It is able to derive an opti- mal multiwavelet basis that best matches the critical non-stationary and transient fault signatures via genetic algorithm. In this technique, two-scale similarity transform （TST） and symmetric lifting （SymLift） scheme are combined to gain high designing freedom for matching the critical faulty vibration contents in vibration signals based on the maximal fitness objective. TST and SymLift can add modifications to the initial multiwavelet by changing the approximation order and vanishing moment of mul- tiwavelet, respectively. Moreover, the beneficial feature of the MOAWM lies in that the maximal-overlap filterbank structure can enhance the periodic and transient characteristics of the sensor signals and preserve the time and frequency analyzing res- olution during the decomposition process. The effectiveness of the proposed technique is validated via a numerical simulation as well as a rolling element beating with an outer race scrape and a gearbox with rub fault.展开更多
文摘In order to investigate the behavior of buildings and engineering structures during earthquakes, based on the data of seismic observation devices mounted on constructions with typical characteristics, results of investigating the change of mechanical properties of building structural system over time and the results of examination of structural rigidity and safety change over time, depending on the dynamic characteristics of the building, determined by experimental investigations made at intervals are mentioned in this article. In addition, evaluation of earthquake acceleration acting on structures due to earthquake-induced damage characteristics of buildings and engineering constructions which are made earthquake resistant is also included here.
基金supported by the National Basic Research Program of China("973"Project)(Grant No.2013CB036201)the Program for New Century Excellent Talents in University(Grant No.NCET-10-0839)
文摘Steam-cured concrete is widely used to manufacture prefabricated units of high-speed railway foundation structure such as girder and track slab.The dynamic mechanical property of steam-cured concrete is one of the key properties affecting service performance of high-speed railway foundation structure.In the present paper,serial macro/micro-experiments were carried out to investigate the dynamic elastic modulus,shear modulus,damping ratio,and microstructure of steam-cured concrete.The relationships between compositions,curing regime,microstructure,and dynamic properties of steam-cured concrete as well as the corresponding mechanisms were discussed.The results indicate that steam-cured concrete in early age has a larger dynamic elastic modulus and shear modulus as well as a smaller damping ratio compared with standard-cured concrete.On the contrary,at a later age a slightly smaller dynamic elastic modulus and a larger damping ratio of steam-cured concrete are observed.Addition of mineral admixture results in a bit lower dynamic elastic modulus and damping ratio of concrete than that of the control specimen without mineral admixtures.The achievements can provide some fundamental suggestions for materials parameters selection during structural design of steam-cured concrete precast element.
文摘Regenerative cooling with fuel as the coolant is used in the scramjet engine. In order to grasp the dynamic cha- racteristics of engine fuel supply processes, this article studies the dynamic characteristics of hydrocarbon fuel within the channel. A one-dimensional dynamic model was proved, the thermal energy storage effect, fuel volume effect and chemical dynamic effect have been considered in the model, the ordinary differential equations were solved using a 4th order Rungc-Kutta method. The precision of the model was validated by three groups of expe- rimental data. The effects of input signal, working condition, tube size on the dynamic characteristics of pressure, flow rate, temperature have been simulated. It is found that cracking reaction increased the compressibility of the fuel pyrolysis mixture and lead to longer responding time of outlet flow. The responding time of outlet flow can reach 3s when tube is 5m long which will greatly influence the control performance of the engine thrust system. Meanwhile, when the inlet flow rate appears the step change, the inlet pressure leads to overshoot, the overshoot can reach as much as 100%, such highly transient impulse will result in detrimental effect on fucl pump.
基金supported by the National Natural Science Foundation of China(Grant No.51275384)the Key Project of National Natural Science Foundation of China(Grant No.51035007)+1 种基金the National Basic Research Program of China(Grant No.2009CB724405)the Specialized Research Fund for the Doctoral Program of Higher Education(Grant No.20110201130001)
文摘Vibration signal is an important prerequisite for mechanical fault detection. However, early stage defect of rotating machiner- ies is difficult to identify because their incipient energy is interfered with background noises. Multiwavelet is a powerful tool used to conduct non-stationary fault feature extraction. However, the existing predetermined multiwavelet bases are independ- ent of the dynamic response signals. In this paper, a constructing technique of vibration data-driven maximal-overlap adaptive multiwavelet （MOAMW） is proposed for enhancing the extracting performance of fault symptom. It is able to derive an opti- mal multiwavelet basis that best matches the critical non-stationary and transient fault signatures via genetic algorithm. In this technique, two-scale similarity transform （TST） and symmetric lifting （SymLift） scheme are combined to gain high designing freedom for matching the critical faulty vibration contents in vibration signals based on the maximal fitness objective. TST and SymLift can add modifications to the initial multiwavelet by changing the approximation order and vanishing moment of mul- tiwavelet, respectively. Moreover, the beneficial feature of the MOAWM lies in that the maximal-overlap filterbank structure can enhance the periodic and transient characteristics of the sensor signals and preserve the time and frequency analyzing res- olution during the decomposition process. The effectiveness of the proposed technique is validated via a numerical simulation as well as a rolling element beating with an outer race scrape and a gearbox with rub fault.
