Papers by Keyword: Inversion

Abstract: The exciting source of ground vibration from urban rail generally consists two parts, a quasi-static load moving through the railway, and a dynamic interaction between wheel and rail. The latter is caused mainly from the wheel-rail unevenness, and usually described by a power spectral density function, PSD in brief. From the three dimensional point of view, this kind of exciting source can hardly be measured directly. A procedure is proposed to invert the source function from the ground vibrations observed at array. A dynamic coupled train-track-3D ground model is adopted to calculate the vibrations from given PSD. The Micro-Genetic Algorithm including the operators of the tournament selection, the uniform crossover and the re-initialization together with an elitist strategy is schemed to the inversion. The object function is designed as minimum of the sum of residua between calculated and observed ground vibration acceleration levels of 18 center frequencies, at 4 ground points and twice trains. The result shows that the ground vibration acceleration levels calculated from the obtained excitation source function agree with those from the observed data quite well, even for an additional point where the observed data have never been adopted in the inversion process.

Abstract: It is essential to investigate influence factors of inversion for improving inversion quality. Firstly to classify the influencing factors, then to make numerical experiment for each influence factor using the forward and inversion simulation technology. The results show that the collection parameters and quality of echoes have the great influence on the inversion quality, and the assigned parameters of T2 spectrum inversion have little influence. Hence, optimizing the parameter of echo collection can improve the T2 spectrum inversion quality and application effect of NMR. As for the assigned parameters, they could be selected flexibly according to the concrete conditions.

Abstract: Strong earthquake ground motion leads to residual displacements of gravity retaining walls. Since large deformation occurs in foundation soil, nonlinear mechanical behavior should not be neglected in numerical modeling. The inversion methodology in geophysics is borrowed here to study the nonlinearity, i.e. the variation of shear modulus and damping ratio with the increase of shear strain of soil. A simplified model for the seismic displacement of retaining walls is combined with a genetic algorithm for the inversion. The dynamic shear modulus and damping ratio curves, representing the nonlinear property of foundation soil in a centrifuge test for gravity retaining walls, is obtained by the use of an inversion scheme. The result indicates that, for low level of shear strain, the shear modulus is larger than that used in the literature, implying that the model ground may be stiffer than expectation. For high level of shear strain, the inverted damping ratio is larger than the conventional one, which has efficiently suppressed an overestimation of seismic displacements. It is also displayed that the inversion method is an effective way to obtain quantitatively the dynamic nonlinearity of foundation soil of gravity retaining walls.

Abstract: In order to improve the application effect of the NMR in Petroleum exploration and development, the quality of T2 spectrum inversion need to be controlled. Echo resolution matrix,T2 spectrum resolution matrix are deduced, the quality control index of T2 spectrum inversion is provided: the stretch coefficient, maximum, minimum, average and range of principal diagonal elements of resolution matrix. Calculating the inversion quality control index under different observation modes and choosing the observation mode of resolution matrix approximate to unit matrix for data acquisition can improve T2 spectrum inversion quality. Numerical experimentation indicate there is very good consistency between inversion quality and control index. Hence, it may direct the design before NMR data acquisition, control inversion quality of T2 spectrum

Abstract: Through the measured simply supported bridge's dynamic parameters, we can establish the finite element model of the structure.As the flexibility matrix can reflect the actual state of the bridge, making the actual measured flexibility matrix as a basis to inverse the bridge’s finite element model .Combined with the engineering practice static load test, we can assess the bearing capacity of the bridge according to inversion model bridge.

Abstract: he application of artificial neural network and genetic algorithm is made into the Shuibuya concrete face rock-fill dam project. At the beginning of design phase, genetic algorithm was used to predict the deformation of the dam; One year after the completion of construction, the rheological constitutive model parameters of Shuibuya concrete face rock-fill dam (CFRD) was inverted based on the monitoring data. And the permanent deformation of the dam was computed with the help of artificial neural network and genetic algorithm. The study result not only can accurately grasp the characteristic of Shuibuya CFRD, but also is propitious for the advancement of the computation theory about superhigh project.

Abstract: To compare the different effects under different excitation methods during the measurement on the particle size of silicon carbide (SiC), an experimental system has been established to get different signal excitations of burst wave, continuous wave and pulsed wave. Variable sound path method is adopted during the measurement to obtain the ultrasonic attenuation spectrum of SiC suspensions with two immersion transducers at four different mass concentrations under the same experimental condition. It is found that the ultrasonic attenuation coefficients excited by three different waves increase with increasing frequency and the tendency is approaching the same. The result calculated by a normalized spectrum of the optimal regularization methods shows that SiC particle size distribution under the three excitation methods is similar, which indicate that the different excitation methods on particle size characterization have almost no influence to result.

Abstract: In light extinction particle sizing, a classification inversion algorithm is proposed for the non-spherical particles. The measured spheroidal particle system is inversed with different particle distribution functions and classified according to the inversion errors in the dependent model. Simulation experiments illustrate that it is feasible to use the inversion errors to inverse the spheroidal particle size distribution in the light extinction particle sizing technique and the inversion results are steady and reliable, which avoid the defects that the type of the size distribution must be assumed beforehand for the light extinction method.

Abstract: For regions without adequate strong ground motion records, a method is developed to establish strong ground motion attenuation relationships, based on the stochastic method. Sendai area of Japan is selected as the target, since there are enough data from seismographic observation for calculation, and those from strong ground motion observation and some empirical relationships for result testing. Three parameters related to regional source and crustal medium are inversed by the micro-Genetic Algorithm. Total of 240 records from 77 small events, recorded by F-net, are adopted for the inversion. Fourier spectra are adopted as the objective function. These parameters are then taken into the stochastic method to estimate PGA. The regional ground motion attenuation relationships are compared with some strong ground motion records from K-NET and some empirical relationships to illustrate the reliability of this method.

Abstract: With the increase of the difficulty and intensity on competitive movement, the rate of sport injury will happen in training and competing frequently. The metatarsal is one of the most prone to injury part in the human body. The incidence of metatarsal injuries is rising in recently years. In this study, Pedar-X plantar pressure measure system and Novel emed pressure distribution measure plate were used in order to get the dynamics data in normal landing and inverted landing. The research concluded that: metatarsal peak stress had been transferred from the first metatarsal to the fifth metatarsal with increasing of varus angle. When the foot was in inverted state, stress distribution of metatarsal changed significantly. Lateral metatarsal played a major role in supporting function. Also, forefoot pressure distribution changed a lot in different functional sports shoes. The purpose is to provide the reliable correlative theoretical basis for improving sport equipments and security protection recommendations for people to engage in sports.