The curves of crack relative length lib and crack growth time t of granite were gained under compressive stresses state according to subcritical crack growth parameters and crack stability growth equation by double-to...The curves of crack relative length lib and crack growth time t of granite were gained under compressive stresses state according to subcritical crack growth parameters and crack stability growth equation by double-torsion constant displacement load relaxa- tion method. The relations between crack relative length and the crack growth time were discussed under different stresses and different crack lengths. The results show that there is a turning point on curve of crack relative length lib and crack growth time of granite. The slope of curve is small when crack relative length is less than the vertical coordinate of the point, and crack grows stably in this case. Cracks grow, encounter and integrate catastro- phically when crack relative length is more than the vertical coordinate of the point, and there is not a gradual stage from crack stability growth to crack instability growth, i.e. rock mass instability is sudden. The curves of crack relative length lib and crack growth time t of granite move to right with decrease of stress σl or crack length a, which implies that limit time increases consequently. The results correspond to practicality.展开更多
The seismic records of borehole-to-borehole me- asurements on frequency of 200 Hz in the mi-crostrain range have been analysed. Microplas-ticity manifestations caused by seismic wave are detected on seismic records. I...The seismic records of borehole-to-borehole me- asurements on frequency of 200 Hz in the mi-crostrain range have been analysed. Microplas-ticity manifestations caused by seismic wave are detected on seismic records. It is the lad-der-like stepwise change in amplitude course in some parts of the seismic trace. The step dura-tion (time plateau) presents the amplitude- dependent time delay that shifts the arrival time and protracts pulse front. The microplastic process occurs owing to the anomalous re-alignment of the internal stresses on the micro-structural defects in “elastic” domain. Result is the useful contribution for improvement of the theory of wave attenuation in the rocks. It can also be used in solving the applied problems in material science, seismic prospecting, diagnos-tics etc.展开更多
Robust H-infinity filtering for a class of uncertain discrete-time linear systems with time delays and missing measurements is studied in this paper. The uncertain parameters are supposed to reside in a convex polytop...Robust H-infinity filtering for a class of uncertain discrete-time linear systems with time delays and missing measurements is studied in this paper. The uncertain parameters are supposed to reside in a convex polytope and the missing measurements are described by a binary switching sequence satisfying a Bernoulli distribution. Our attention is focused on the analysis and design of robust H-infinity filters such that, for all admissible parameter uncertainties and all possible missing measurements, the filtering error system is exponentially mean-square stable with a prescribed H-infinity disturbance attenuation level. A parameter-dependent approach is proposed to derive a less conservative result. Sufficient conditions are established for the existence of the desired filter in terms of certain linear matrix inequalities （LMIs）. When these LMIs are feasible, an explicit expression of the desired filter is also provided. Finally, a numerical example is presented to illustrate the effectiveness and applicability of the proposed method.展开更多
For the structure system with epistemic and aleatory uncertainties,a new state dependent parameter(SDP)based method is presented for obtaining the importance measures of the epistemic uncertainties.By use of the margi...For the structure system with epistemic and aleatory uncertainties,a new state dependent parameter(SDP)based method is presented for obtaining the importance measures of the epistemic uncertainties.By use of the marginal probability density function(PDF)of the epistemic variable and the conditional PDF of the aleatory one at the fixed epistemic variable,the epistemic and aleatory uncertainties are propagated to the response of the structure firstly in the presented method.And the computational model for calculating the importance measures of the epistemic variables is established.For solving the computational model,the high efficient SDP method is applied to estimating the first order high dimensional model representation(HDMR)to obtain the importance measures.Compared with the direct Monte Carlo method,the presented method can considerably improve computational efficiency with acceptable precision.The presented method has wider applicability compared with the existing approximation method,because it is suitable not only for the linear response functions,but also for nonlinear response functions.Several examples are used to demonstrate the advantages of the presented method.展开更多
基金China Postdoctoral Science Foundation(20060400264)CSU Postdoctoral Science Foundationthe National Nature Science Foundation of China(50490274)
文摘The curves of crack relative length lib and crack growth time t of granite were gained under compressive stresses state according to subcritical crack growth parameters and crack stability growth equation by double-torsion constant displacement load relaxa- tion method. The relations between crack relative length and the crack growth time were discussed under different stresses and different crack lengths. The results show that there is a turning point on curve of crack relative length lib and crack growth time of granite. The slope of curve is small when crack relative length is less than the vertical coordinate of the point, and crack grows stably in this case. Cracks grow, encounter and integrate catastro- phically when crack relative length is more than the vertical coordinate of the point, and there is not a gradual stage from crack stability growth to crack instability growth, i.e. rock mass instability is sudden. The curves of crack relative length lib and crack growth time t of granite move to right with decrease of stress σl or crack length a, which implies that limit time increases consequently. The results correspond to practicality.
文摘The seismic records of borehole-to-borehole me- asurements on frequency of 200 Hz in the mi-crostrain range have been analysed. Microplas-ticity manifestations caused by seismic wave are detected on seismic records. It is the lad-der-like stepwise change in amplitude course in some parts of the seismic trace. The step dura-tion (time plateau) presents the amplitude- dependent time delay that shifts the arrival time and protracts pulse front. The microplastic process occurs owing to the anomalous re-alignment of the internal stresses on the micro-structural defects in “elastic” domain. Result is the useful contribution for improvement of the theory of wave attenuation in the rocks. It can also be used in solving the applied problems in material science, seismic prospecting, diagnos-tics etc.
基金This work was supported by the National Natural Science Foundation of China(No.60574084)the National 863 Project(No.2006AA04Z428)the National 973 Program of China(No.2002CB312200).
文摘Robust H-infinity filtering for a class of uncertain discrete-time linear systems with time delays and missing measurements is studied in this paper. The uncertain parameters are supposed to reside in a convex polytope and the missing measurements are described by a binary switching sequence satisfying a Bernoulli distribution. Our attention is focused on the analysis and design of robust H-infinity filters such that, for all admissible parameter uncertainties and all possible missing measurements, the filtering error system is exponentially mean-square stable with a prescribed H-infinity disturbance attenuation level. A parameter-dependent approach is proposed to derive a less conservative result. Sufficient conditions are established for the existence of the desired filter in terms of certain linear matrix inequalities （LMIs）. When these LMIs are feasible, an explicit expression of the desired filter is also provided. Finally, a numerical example is presented to illustrate the effectiveness and applicability of the proposed method.
基金supported by the National Natural Science Foundation of China(Grant No.51175425)the Aviation Science Foundation(Grant No.2011ZA53015)the Doctorate Foundation of Northwestern Polytechnical University(Grant No.CX201205)
文摘For the structure system with epistemic and aleatory uncertainties,a new state dependent parameter(SDP)based method is presented for obtaining the importance measures of the epistemic uncertainties.By use of the marginal probability density function(PDF)of the epistemic variable and the conditional PDF of the aleatory one at the fixed epistemic variable,the epistemic and aleatory uncertainties are propagated to the response of the structure firstly in the presented method.And the computational model for calculating the importance measures of the epistemic variables is established.For solving the computational model,the high efficient SDP method is applied to estimating the first order high dimensional model representation(HDMR)to obtain the importance measures.Compared with the direct Monte Carlo method,the presented method can considerably improve computational efficiency with acceptable precision.The presented method has wider applicability compared with the existing approximation method,because it is suitable not only for the linear response functions,but also for nonlinear response functions.Several examples are used to demonstrate the advantages of the presented method.
