Li J.,Beihang University |
Fang J.,Beihang University |
Du M.,Institute of Disaster Prevention
IEEE Transactions on Instrumentation and Measurement | Year: 2012
The Position and Orientation System is integrated measurement equipment for airborne remote sensing system. The calibration of gyro biases is an effective way to reduce azimuth misalignment and navigation error of strapdown inertial navigation system (SINS). According to the analytic-coarse-alignment principle, the sensitivities of Euler angles with respect to inertial sensor biases are analyzed uniquely. The errors of Earth rotation rate in body frame caused by initial misalignment are obtained. Based on the transformation model of gyro biases, a novel analytic calibration of gyro biases with arbitrary double position is proposed. The simulation and experiment results show that the method can accurately calibrate the gyro biases, improve the precision of initial alignment and inertial navigation for SINS, and verify the efficiency of the proposed method. © 2012 IEEE.
Li J.,Beihang University |
Du M.,Institute of Disaster prevention
Proceedings - 2010 International Conference on Digital Manufacturing and Automation, ICDMA 2010 | Year: 2010
For MEMS gyroscope, The error of scale factor is severe and therefore vital to analyze and compensate the error to improve the performance of gyroscope. Based on the operational principle of Dual Gimbaled MEMS gyroscope, it is analyzed that the physical origin of offset, nonlinear and asymmetry errors of scale factor. The error model of scale factor is proposed. The fuzzy logic, a method to compensate scale factor, is presented. The experimental results show that the dynamic raw error of gyroscope is 4053.2°/h (1σ), and error compensated by the fuzzy logic is improved to79.0°/h (1σ). Compared with the conventional methods of 1th order curve fitting and segmented methods, the precision of gyroscope compensated by fuzzy logic is improved 15.4 and 7.5 times respectively. It verifies the accuracy of the fuzzy model and compensation, and improves of gyroscope in dynamic maneuvering. © 2010 IEEE.
Wang Y.,Beijing Institute of Technology |
Qiu L.,Beijing Institute of Technology |
Song Y.,Institute of Disaster Prevention |
Zhao W.,Beijing Institute of Technology
Measurement Science and Technology | Year: 2012
Based on the property that the absolute zero of an axial intensity curve exactly corresponds to the focus of the objective in a differential confocal system (DCS), a new laser differential confocal lens thickness measurement is proposed to achieve the high-precision non-contact measurement of lens thickness. The proposed approach uses the absolute zero of DCS axial response curve to precisely identify the vertexes of the test lens, obtains the central optical thickness of the test lens, and then uses the radius of curvature and refractive index of the test lens and the ray tracing facet iterative calculation to obtain the central geometrical thickness of the test lens. The theoretical analyses and preliminary experiments indicate that the measurement accuracy is better than 0.03%. © 2012 IOP Publishing Ltd.
Yanqin L.,Tianjin University |
Yanqin L.,Institute of Disaster Prevention |
Guoshan Z.,Tianjin University
Journal of Applied Geophysics | Year: 2014
Blind seismic deconvolution, which comprises seismic wavelet and reflectivity sequence, is a strongly ill-posed problem. The reflectivity sequence is modeled as a Bernoulli-Gaussian (BG) process, depending on four parameters (noise variance, high and low reflector variances, and reflector density). These parameters need to be estimated from the seismic record, which is the convolution of the reflectivity sequence and the seismic wavelet. In this paper, we propose a variational Bayesian method for blind seismic deconvolution which can determine the reflectivity sequence and the seismic wavelet. The connection between variational Bayesian blind deconvolution and the minimization of the Kullback-Leibler divergence of two probability distributions is also established. The gamma, beta distributions are used for the unknown parameters (hyperparameters) as prior distribution and also we give how these distributions can be inferred in actual situations. The proposed algorithms are tested by simulation and compared to existing blind deconvolution methods. The results show that variational Bayesian method has better agreement with the actual value. © 2014 Elsevier B.V.
Zhang W.,Tianjin University |
Liu H.,Tianjin University |
Zhou H.,Tianjin University |
Sheng Z.,Institute of Disaster Prevention
Geotechnical Testing Journal | Year: 2011
Drag anchors, including the vertically loaded plate anchors, play a very important role in deepwater mooring systems. However, the behavior of the anchor has never been clearly known, especially the trajectory of the anchor in soils when pulled into the seabed. Positioning in seabed soils is especially important for drag anchors because the working performance of the anchor is closely related to the embedment depth and orientation of the anchor and the properties of the surrounding soils. Hence, studying the trajectory by analytical and experimental methods is critical for the further application of drag anchors in offshore engineering. An overview of the present trajectory measurements demonstrates that there has not been an acceptable measurement technique for laboratory model flume experiments. In this paper, a contact measurement technique, which is based on the knowledge of the motion characteristic of the drag anchor in soils, is developed and applied in measuring the trajectory of the anchor models. This technique is easier to perform and has little effect on the behavior of drag anchors in soils. The measurement precision and applicability of the technique are verified through specially-designed experiments. Being an important application, the measurement technique can be adopted to detect the movement direction of the anchor with an arbitrary fluke section. The present work has demonstrated that through model tests and employing the developed technique, the movement direction of any type of drag anchor can be effectively and easily determined. Copyright © by ASTM Int'l (all rights reserved).
Qi W.-H.,Institute of Engineering Mechanics |
Bo J.-S.,Institute of Disaster Prevention |
Liu H.-S.,Institute of Engineering Mechanics
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2013
The current formula can not calculate the fundamental periods of the sites containing soft soil layers accurately. In order to solve the problem, a fundamental period formula for a horizontal layered site, on which the effect of soil layer construction is considered, is deduced based on the vibration theory. According to the rules of natural vibration periods being equal, a single layer site is simplified into a SDOF system by means of the lumped mass method, and the equivalent height coefficient between their heights is deduced. A horizontal multi-layer site can be simplified into a SDOF system based on any one soil layer, and the height of the SDOF system is equal to that of the soil layer multiplied by the equivalent height coefficient. The natural vibration period of the SDOF system is called contributing fundamental period of the soil layer here, and the fundamental period of the site should be equal to the square root of sum square (SRSS) of the contributing fundamental periods of all the soil layers in the site, and its formula is also deduced. The test results show that (a) the proposed formula can reflect the effect of soil layer construction on fundamental periods of sites very well, and (b) by comparing the calculated fundamental periods with the test ones of 5 engineering sites by use of the microtremor method, the proposed formula is of higher accuracy and reliability than the current formula. A conclusion is drawn that the deduced formula can be adopted to estimate the fundamental period of a layered horizontal site.
Deng X.,Institute of Disaster Prevention
Applied Mechanics and Materials | Year: 2013
Performance evaluation for agent construction manager is an important way to manage agent construction manager market. The author studied the SCP (Structure-Conduct-Performance) analysis paradigm. And on this basis, this paper establishes a three-dimensional performance evaluation model, which consists of three dimensions: agent organization, agent conduct and agent performance. Through the questionnaire survey, the author further refined evaluation dimension. Finally this paper sets up a comprehensive and practical performance evaluation index system. © (2013) Trans Tech Publications, Switzerland.
Zhao X.,Institute of Disaster Prevention
Journal of Dispersion Science and Technology | Year: 2015
The triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (L64, PEO13PPO30PEO13) in 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) can form lamellar liquid crystalline (Lα). The effect of apolar cyclohexane molecules on the Lα phase was investigated by using polarized optical microscopy (POM) and small-angle x-ray scattering (SAXS). The results of POM and SAXS show that a suitable amount of cyclohexane can contribute to the formation of lamellar liquid crystals, and the ordering of Lα phase is increased. For comparison, the effect of polar water on Lα phase was explored. After adding water, both EO groups and [BF4]– anion can form hydrogen bonds with water molecules, which weakens the electrostatic interactions between L64 and [Bmim][BF4] and therefore the ordering of lamellar structures is destroyed. © 2015, Taylor & Francis Group, LLC.
Wan Y.-G.,Institute of Disaster Prevention
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2015
Crustal stress field is fundamental information in studying earthquake dynamics and seismogenic environments. One of methods to determine stress tensors is to fit observed striation. But such data are seldemly measured in geological field investigations. The sense of fault slip (such as thrust fault or normal faulting, left lateral or right lateral strike-slip faulting) is also tightly associated with the stress tensor, which are abundantly obtained from geological field work. So in the case that striation data are too little to constrain the stress tensor, the data of fault slip can be used to attain this aim. This study attempted to combine the two kinds of data (striation data and fault slip data) to determine stress tensors in a certain area. We analyzed the stress tensor representation in the north-east-down coordinate system, which is composed of three principal stress axes. The stress tensor is represented by 4 parameters, 3 of which give stress directions of the stress tensor and the other one gives the stress shape ratio. We also gave the criteria of fitting the striation data and sense of fault slip with the determined stress tensors. By using a grid search strategy, we provided a method to invert the stress tensors by combination of striation and fault slip data. The confidence itervals of the inverted stress tensors under a certain confidence level were determined by the F-test. Assuming the certain stress tensors of thrust, normal and strike-slip stress regimes, we generated 3 sets of data including 7 striations and 80 fault slip “data”, the strike and dip of which were randomly generated, the rake (for striation) and nature (qualitative data) of which were determined by the corresponding stress tensors with a certain level of “noise”. By using the artifical “data”, we inverted the stress tensors by only striation “data” and the hybrid “data” composed of striation “data” and fault slip “data”, respectively. The results show that the principal stress directions determined by the hybrid “data” are closer to the assumed principal stress directions than that determined only by striation “data”, and the uncertainty of the stress parameters are greatly decreased. We applied this method to the striation and fault slip data in the Urumqi area obtained by geological field investigation, and determined the stress tensors. The results show that the compressive stress is nearly in NS direction, the extensional stress is nearly vertical, the stress shape ratio is 0.03. They mean the dominant thrust faults trending nearly EW in this area are caused by the north-south compressive stress and vertical extensional stress. The low stress shape ratio implies that the NS compressive stress, complemented by nearly east-west extrusion of the Borocco and Bogda Mountains, will result in the uplift of the Urumqi area. ©, 2015, Science Press. All right reserved.
Liu Q.,Institute of Disaster Prevention
Guangzi Xuebao/Acta Photonica Sinica | Year: 2013
A polarization-independent two-port wave-guided multi-wavelength tunable fiter is designed based on the electro-optic effect of birefringent Lithium Niobate (LiNbO3) crystal. Mode-coupled electrode and phase-shifted electrode periodically alternated cascaded are set on each arm of an asymmetric interferometer to realize mode conversion. Z-domain analysis of Jones matrix is utilized to get the values of driving voltages so that wavelengths can be selected simultaneous. Narrow-band multi-wavelength with arbitrary distribution is simulated successfully in Free Spectrum Range (FSR). 100% transmittance is obtained at each wavelength. Number of wavlengths has an influence on sidelobe of each wavelength. And sidelobe of 12 dB can be realized when three wavelengths are selected. Comb filter can also be obtained using this method, which has a flat passband and sidelobe of more than 15 dB.