An integrated MEMS piezoresistive tri-axis accelerometer

An integrated MEMS accelerometer has been designed and fabricated. The device, which is based on the piezoresistive effect, accomplishes the detection of three components of acceleration by using piezoresistors to compose three Wheatstone bridges that are sensitive to the only given orientation. The fabrication of the accelerometer is described, and the theory behind its operation developed. Experimental results on sensitivity, crossaxis-coupling degree, and linearity are presented. The sensitivity of X, Y and Z were 5.49 mV/g, 5.12 mV/g and 4.82 mV/g, respectively; the nonlinearity of X, Y and Z were 0.01%, 0.04% and 0.01%, respectively; the crossaxis-coupling factor of X axis to Y axis and Z axis are 0.119% and 2.26%; the cross-axis-coupling factor of Y axis to X axis and Z axis are 0.157% and 4.12%; the cross-axis-coupling factor of Z axis to X axis and Y axis are 0.511% and 0.938%. The measured performance indexes attain accurate vector-detection in practical applications, and even at a navigation level. In conclusion, the accelerometer is a highly integrated sensor.

Quantitative investigation of multi-fracture morphology during TPDF through true tri-axial fracturing experiments and CT scanning

Due to the reservoir heterogeneity and the stress shadow effect, multiple hydraulic fractures within one fracturing segment cannot be initiated simultaneously and propagate evenly, which will cause a low effectiveness of reservoir stimulation. Temporary plugging and diverting fracturing(TPDF) is considered to be a potential uniform-stimulation method for creating multiple fractures simultaneously in the oilfield. However, the multi-fracture propagation morphology during TPDF is not clear now. The purpose of this study is to quantitatively investigate the multi-fracture propagation morphology during TPDF through true tri-axial fracturing experiments and CT scanning. Critical parameters such as fracture spacing, number of perforation clusters, the viscosity of fracturing fluid, and the in-situ stress have been investigated. The fracture geometry before and after diversion have been quantitively analyzed based on the two-dimensional CT slices and three-dimensional reconstruction method. The main conclusions are as follows:(1) When injecting the high viscosity fluid or perforating at the location with low in-situ stress, multiple hydraulic fractures would simultaneously propagate. Otherwise, only one hydraulic fracture was created during the initial fracturing stage(IFS) for most tests.(2) The perforation cluster effectiveness(PCE) has increased from 26.62% during the IFS to 88.86% after using diverters.(3) The diverted fracture volume has no apparent correlation with the pressure peak and peak frequency during the diversion fracturing stage(DFS) but is positively correlated with water-work.(4) Four types of plugging behavior in shale could be controlled by adjusting the diverter recipe and diverter injection time, and the plugging behavior includes plugging the natural fracture in the wellbore, plugging the previous hydraulic fractures, plugging the fracture tip and plugging the bedding.

Hydrologically induced orientation variations of a tri-axial Earth's principal axes based on satellite-gravimetric and hydrological models

The Earth is a tri-axial body, with unequal principal inertia moments, A, B and C. The corresponding principal axes a, b and c are determined by the mass distribution of the Earth, and their orientations vary with the mass redistribution. In this study, the hydrologically induced variations are estimated on the basis of satellite gravimetric data, including those from satellite laser ranging （SLR） and gravity recovery and climate experiment （GRACE）, and hydrological models from global land data assimilation system （GLDAS）. The longitude variations of a and b are mainly related to the variations of the spherical harmonic coefficients C 22 and S 22, which have been estimated to be consisting annual variations of about 1.6 arc seconds and 1.8 arc seconds, respectively, from gravity data. This result is confirmed by land surface water storage provided by the GLDAS model. If the atmospheric and oceanic signals are removed from the spherical harmonic coefficients C 21 and S 21, the agreement of the orientation series for c becomes poor, possibly due to the inaccurate background models used in pre-processing of the satellite gravimetric data. Determination of the orientation variations may provide a better understanding of various phenomena in the study of the rotation of a tri-axial Earth.

Determination of Direction of Arrival of Seismic Wave by a Single Tri-axial Fiber Optic Geophone

A fiber Bragg grating (FBG) geophone and a surface seismic wave-based algorithm for detecting the direction of arrival (DOA) are described. The operational principle of FBG geophone is introduced and illustrated with systematic experimental data, demonstrating an improved FBG geophone with many advantages over the conventional geophones. An innovative, robust, and simple algorithm is developed for obtaining the bearing information on the seismic events, such as people walking, or vehicles moving. Such DOA estimate is based on the interactions and projections of surface-propagating seismic waves generated by the moving personnel or vehicles with a single tri-axial seismic sensor based on FBGs. Of particular interest is the case when the distance between the source of the seismic wave and the detector is less than or comparable to one wavelength (less than 100 m), corresponding to near-field detection, where an effective method of DOA finding lacks.

Experimental study on mechanical properties of methane-hydrate-bearing sediments

Mechanical properties of methane hydrate- bearing-sediments （MHBS） are basic parameters for safety analysis of hydrate exploration and exploitation. Young＇s modulus, cohesion, and internal friction angle of hydrate- bearing sediments synthesized in laboratory, are investigated using tri-axial tests. Stress-strain curves and strength parameters are obtained and discussed for different compositions and different hydrate saturation, followed by empirical expressions related to the cohesion, internal friction angle, and modulus of MHBS. Almost all tested MHBS samples exhibit plastic failure. With the increase of total saturation of ice and methane hydrate （MH）, the specimens＇ internal friction angle decreases while the cohesion increases.

A generalized three-dimensional failure criterion for rock masses

The smooth convex generalized failure function, which represents 1/6 part of envelope in tile deviatoric plane, is proposed. The proposed function relies on four shape parameters （L, a, b and c）, in which two parameters （a and b） are dependent on the others. The parameter Ls is called extension ratio. The proposed failure function could be incorporated with any two-dimensional （2D） failure criteria to make it a three-dimensional （3D） version. In this paper, a mathematical formulation for incorporation of Hoek-Brown failure criterion with the proposed function is presented. The Hoek-Brown failure criterion is the most suited 2D failure criterion tbr geomaterials. Two types of analyses for best-fitting solution of published true tri-axial test data were made by considering （1） constant extension ratio and （2） variable extension ratio. The shape and strength parameters for different types of rocks have been determined by best-fitting the published true tri-axial test data for both the analyses. It is observed from the best-fitting solution by considering uniform extension ratio （L~） that shape constants have a correlation with Hoek-Brown strength parameters. Thus, only two parameters （c~. and m） are needed for representing the 3D failure criterion for intact rock. The statistical expression between shape and Hoek-Brown strength parameters is given. In the second analysis, when considering varying extension ratio, another parameterfis introduced. The modified extension ratio is related tofand extension ratio. The results at minimum mean misfit for all the nine rocks indicate that the range off varies from 0.7 to 1.0. It is found that mean misfit by considering varying extension ratio is lower than that in the first analysis. But it requires three parameters. A statistical expression betweenfand Hoek-Brown strength parameters has been established. Though coefficient of correlation is not reasonable, we may eliminate it as an extra parameter. At the end of the paper, a methodology has also been given for its application to isotropic jointed rock mass, so that it can be implemented in a numerical code for stability analysis of jointed rock mass structures.

Accurate estimation of soil shear strength parameters

The cost and safety of geotechnical engineering are highly depending on the accuracy of soil shear strength parameters.There are three methods often used to estimate soil shear strength parameters,i.e.,moment method,3-sigma rule and linear regression method.In this study,the accuracy of these three methods is compared.Traditional linear regression method(LRM)can only offer the mean of shear strength parameters.Some engineers misuse the standard error of shear strength indexes as the standard deviations.Such misuse may highly underestimate the uncertainty and induce high risk to the geotechnical design.A modified LRM is proposed to determine both the mean and variance of shear strength parameters.The moment method,three-sigma rule and LRM are used to analyze the tri-axial test data in Xiaolangdi Hydraulic Project and three numerical shear strength tests.The results demonstrate that:1)The modified LRM can offer the most accurate estimation to shear strength parameters;2)A dimensionless formula is much preferred in LRM rather than a dimensional formula.The stress ratio formula is much better than stress relation in the shear strength parameter analysis.The proposed method is applicable to shear strength parameter analysis for tri-axial test data,direct shear test and the un-drained shear strength test of stratified clay.

Smart projectile acceleration testing in harsh launch environment

In order to solve the problem of parametric test of smart projectile launch,the launch environment of smart projectile was analyzed.a reasonable and feasible storage testing method was proposed,and a multi-channel test system suitable for the environment was designed.The system was successfully applied to a certain range test,and dynamic parameters such as triaxial acceleration of smart projectile launch environment were acquired.The test results play an important role in the improvements of smart projectile design process.

Measurement of Forces and Torques during Non-Homogeneous Material Drilling Operation

The purpose of this study is to measure the forces and torques produced in the drilling process of a non-homogenous material （bone）. An automated 5 DoF CataLyst-5 robot is used during the drilling process and it is integrated to a 6 DoF force-torque sensor. A force-torque controller which is built in the Matlab Simulink environment is employed to control the drilling process of the bone. Different feed rate is used during the experimental process of the bone drilling operation. The sensor is calibrated to measure the tri-axial direction of the resultant forces and torques. The profiles of the forces and torques obtained are non-linear due to the diversity of the bone density. The profiles generated also indicated fluctuation in the interface layers of the bone.

Grain crushing and its effects on rheological behavior of weathered granular soil

To disclose the grain crushing effects on the weathered granular soil rheological behavior,a series of rheological tests (odometer compression and triaxial shearing) were carried out.At the same time,the sieving analysis tests of these specimens were also executed before and after tests,and the grain crushing degree,Br and n5,were collectively adopted to estimate the grain crushing.The grain crushing degree depends on the stress path,stress level,and load time,especially,the longer load time and more intensive gradient shearing path will increase the grain crushing quantity.The Hardin crushing degrees Br are 0.191,0.118 and 0.085 in the ordinary compression,rheological compression and triaxial rheological shearing,respectively;The grain crushing degrees n5 are 1.9,1.4 and 1.32,respectively.The strain softening phase indicates the grain crushing and diffusive collapse,and the strain hardening phase indicates the rearrangement of these crushed grains and formation of new bearing soil skeleton.The rheological deformation of granular soil can be attributed to the coarse grain crushing and the filling external porosity with crushed fragments.

Earthquake Response Characteristics of Contained Masonry Infilled Frames

The strength and stiffness contribution of infill masonry is generally ignored in the design, due to the uncertainty in the strength properties of masonry, separation of infill from frame, low tensile strength, brittle characteristics of masonry walls, less out of plane strength and stiffness, etc.. They are considered as nonstructural elements which is reasonable for the frames under gravity loads but it is not true for the frames under seismic loads. Contained masonry as infill in RC （reinforced concrete） frames provides better contact at the interface and a higher out of plane strength and stiffness. Considering the seismic action on the frames which are likely to be subjected to in-plane as well as out of plane shaking, a research work has been carried out by the authors to investigate the seismic performance of RC frames with and without contained masonry infill panels using FE （finite element） computer program （ANSYS-Ver. l 1） and experimentally using the tri-axial shake table to evaluate the methods proposed in IS-1893-2002 to calculate the fundamental natural frequency. The RC frames were designed and detailed as per IS （Indian Standard） specifications such as IS 456-2000, IS 1893-2002 and IS 13920-1993. Based on the experimental and analytical investigations, the contained masonry infill panels significantly affect the seismic load resisting characteristics of the RC frames. The IS 1893-2002 formulation does not predict the values and hence the recommendation needs to be validated with experimental results.

New CCD photometry of asteroid(1028)Lydina

New CCD photometric observations for asteroid（1028）Lydina,carried out with the 1-m and 2.4-m telescopes at Yunnan Observatory from 2011 December 19 to 2012 February 3,are presented.Using the new light curves,the rotation period of 11.680±0.001 hours is derived with the Phase Dispersion Minimization（PDM） method.In addition,using the Amplitude-Aspect method,the elementary results of the pole orientation of asteroid（1028）Lydina are obtained：λp=111°＋4°-4°,βp=31°＋4°-5°. Meanwhile,the axial ratios of the tri-axial ellipsoid are estimated：a/b=1.77＋0.10 -0.08 and b/c=1.17＋0.07 -0.09 .

Nonlinear Constitutive Equation for Green Sand Considering the Tri-axial Compression Behavior

The compression characteristics of green sand were investigated experimentally, including the squeezing and yielding during deformation. An expression was developed for the transient compression modulus of sand during compression. Based on the hypothesis put forward of the compression state, the differential equation for the nonlinear constitutive equation was deduced by introducing a move-yield poten- tial function. The state constitutive equation under the tri-axial experiment is further studied according to the sand attributes, considering the differential form of Hooke’s law and the Mohr-Coulomb condition. The re- lated experiment data are applied to verify the proposed constitutive model of sand.

Axiomatic design method to design a screw drive in-pipe robot passing through varied curved pipes

A screw drive in-pipe robot is promising inspection equipment for small pipes. However, most of the existing screw drive in-pipe robots have problems of motion interference and slipping inside curved or irregular pipes. These problems result from the coupled relations among the steering motion, the motion speed and the load ability of the robot. In order to deal with the problems, the axiomatic design （AD） theory is applied to evaluate and analyze the existing designs. Then an uncoupled con- cept design based on the AD theory is proposed and the complete AD decomposition process is presented. After that, the pro- posed robot based on a tri-axial differential angle modulation mechanism is designed to realize the uncoupled concept. Finally, the uncoupled property is verified in a dynamics simulation system. The simulation results indicate that the mc tion speed, load ability and steering motion of the proposed robot can be adjusted individually compared with the robots taat have inclin- ing-angle-fixed rollers. Owing to the uncoupled design, the proposed robot can mechanically adapt to straight pipes and curved pipes with less roller slipping.

Experimental Research on the Mechanical Properties of Gypsum Breccia with Different Water Content

This paper deals with the influence of water content on the mechanical properties of gypsum breccia with different initial water contents. The experimental research was taken on the GDS (geotechnical digital systems) tri-axial experiment system by strain rate control. The mechanical properties,including stress-strain curves,peak deviator stress,relative residual strength,elastic modulus,Poisson's ratio,angle of internal friction and cohesion of gypsum breccia,were studied by experiment. The results showed that the water content has obvious infiuence on the mechanical properties of gypsum breccia. With increasing of water content,the angle of internal friction and cohesion of gypsum breccia decrease linearly. Meanwhile,the stress-strain curves go through from the declining,hump curve to the strain hardening curve. At the same confining pressure,the peak deviator stress and elastic modulus decrease exponentially,while Poisson's ratio increases linearly with the increasing of the water content. At the same water content,with increasing of the confining pressure,the peak deviator stress,elastic modulus and the peak deviator stress increase trend but Poisson's ratio decreases at a lower water content. While at a high water contents,the Poisson's ratio doesn't change much. It shows that water content plays an important role in the process of changing from the brittleness to plastic for the mechanical properties of gypsum breccia.