Showing papers on "Vertical displacement published in 2014"

Experimental Study on Influence of Pitch Motion on the Wake of a Floating Wind Turbine Model

Abstract: Wind tunnel experiments were performed, where the development of the wake of a model wind turbine was measured using stereo Particle Image Velocimetry to observe the influence of platform pitch motion. The wakes of a classical bottom fixed turbine and a streamwise oscillating turbine are compared. Results indicate that platform pitch creates an upward shift in all components of the flow and their fluctuations. The vertical flow created by the pitch motion as well as the reduced entrainment of kinetic energy from undisturbed flows above the turbine result in potentially higher loads and less available kinetic energy for a downwind turbine. Experimental results are compared with four wake models. The wake models employed are consistent with experimental results in describing the shapes and magnitudes of the streamwise velocity component of the wake for a fixed turbine. Inconsistencies between the model predictions and experimental results arise in the floating case particularly regarding the vertical displacement of the velocity components of the flow. Furthermore, it is found that the additional degrees of freedom of a floating wind turbine add to the complexity of the wake aerodynamics and improved wake models are needed, considering vertical flows and displacements due to pitch motion.

Experimental and numerical analyses of circular footing on geogrid-reinforced granular fill underlain by soft clay

Abstract: Experimental and numerical investigations into the bearing capacity of circular footing on geogrid-reinforced compacted granular fill layer overlying on natural clay deposit have been conducted in this study. A total of 8 field tests were carried out using circular model rigid footing with a diameter of 0.30 m. 3D numerical analyses were performed to simulate soil behavior using finite element program Plaxis 3D Foundation. The results from the FE analysis are in very good agreement with the experimental observations. It is shown that the degree of improvement depends on thickness of granular fill layer and properties and configuration of geogrid layers. Parameters of the experimental and numerical analyses include depth of first reinforcement, vertical spacing of reinforcement layers. The results indicate that the use of geogrid-reinforced granular fill layers over natural clay soils has considerable effects on the bearing capacity and significantly reduces the lateral displacement and vertical displacement of the footing.

Thermal Borehole Shear Device

Abstract: This paper presents the details of a new modified borehole shear device that has the capability of measuring the impact of temperature on the in situ shear stress–displacement curves for soil–concrete interfaces. The thermal borehole shear device incorporates concrete shoes with embedded heaters, a pneumatic loading device for application of horizontal normal stresses, and an automated loading system with local vertical displacement and load measurement systems that permits either displacement–control or load–control testing. A methodology for measurement of the soil–concrete shear stress–displacement curves and for evaluation of the drained interface shear strength failure envelopes at different temperatures is presented in this study. Typical results from proof-of-concept tests performed in a clay layer compacted in a laboratory tank in a borehole in a silty sand deposit in the field are presented in this paper. The results are synthesized to show how the impacts of temperature and normal stress on the normalized shear stress–displacement curves can be evaluated. These normalized curves can be measured on a site-specific basis for the calibration of thermo-mechanical load transfer analyses or finite element analyses, which are often used to design and evaluate soil–structure interaction in drilled shaft foundations with geothermal heat exchangers (energy foundations).

A DQEM for transverse vibration analysis of multiple cracked non-uniform Timoshenko beams with general boundary conditions

Abstract: In this paper, a differential quadrature element method (DQEM) for free transverse vibration analysis of multiple cracked non-uniform Timoshenko beams with general boundary conditions is proposed. Governing equations, the compatibility conditions at the damaged cross-sections and implementation of the external boundary conditions are derived and formulated by the differential quadrature analogue. The accuracy, convergence, and versatility of the proposed method are confirmed by the exact solution of the uniform beam which has been presented by other authors, and 2D finite element method (FEM) numerical results for non-uniform beam. After the validation of the presented method, the effect of quantity, depth and location of the cracks on the frequency values of vibrations are investigated. The achieved results show that the existence of the crack leads to a decrease in the frequencies of the vibrations through decrease in the stiffness of the beam. Meanwhile, the compatibility conditions at the damaged section is considered as a discontinuity in slope and vertical displacement where the effect of the discontinuity in the slope is more considerable as many authors have neglected the discontinuity in the vertical displacement. As it will be shown, consideration of the discontinuity in the vertical displacement causes more decrease in the frequencies.

Probabilistic Analysis of Strip Footings Resting on Spatially Varying Soils and Subjected to Vertical or Inclined Loads

Abstract: A probabilistic analysis of vertically and obliquely loaded strip footings resting on a spatially varying soil is presented. The system responses are the footing vertical and horizontal displacements. The deterministic computation of these system responses is based on numerical simulations using the software FLAC3D. Both cases of isotropic and anisotropic random fields are considered for the soil elastic properties. The uncertainty propagation methodology employed makes use of a nonintrusive approach to build up analytical equations for the two system responses. Thus, a Monte Carlo simulation approach is applied directly on these analytical equations (not on the original deterministic model), which significantly reduces the computation time. In the case of the footing vertical load, a global sensitivity analysis has shown that the soil Young's modulus E mostly contributes to the variability of the footing vertical displacement, the Poisson ratio being of negligible weight. The decrease in the autocorrelation distances of E has led to a smaller variability of the footing displacement. On the other hand, the increase in the coefficient of variation of E was found to increase both the probabilistic mean and the variability of the footing displacement. Finally, in the inclined loading case, the results of the probability of failure against exceedance of a vertical and/or a horizontal footing displacement are presented and discussed.

Detection and Quantification of Slip Along Non-Uniform Frictional Discontinuities Using Digital Image Correlation

Abstract: A deformation measurement system based on the principles of digital image correlation (DIC) has been developed to evaluate the process of slip along frictional discontinuities. A biaxial compression apparatus is used to impose shear failure on perfectly mated gypsum specimens with nonhomogeneous contact surfaces. The contact surfaces are made by casting gypsum against flat surfaces with different frictional characteristics and consisted of a smooth surface with low frictional strength on the upper half and a rough surface with high frictional strength on the lower half. Design, implementation, and verification of the DIC measurement system are presented in this paper. DIC successfully identified slip as a jump in the displacement field across the discontinuity. Slip is observed to initiate from the smooth surface with minimum frictional resistance and as the shear load is increased, propagates to the rough surface that has higher frictional resistance. DIC clearly exhibits a reduction in fracture’s shear stiffness based on an increase in the rate of relative vertical displacement across the discontinuity, which initiates from the smooth surface and propagates to the rough surface.

Dynamic response of road pavement resting on a layered poroelastic half‐space to a moving traffic load

Abstract: SUMMARY This paper is dedicated to study the dynamic response of a thin-plate resting on a layered poroelastic half-space under a moving traffic load. Based on the dynamic poroelastic theory of Biot, the general solutions of the homogeneous poroelastic foundation are obtained by Fourier translation. By using the transmission and reflection matrices method in the frequency domain, the equivalent stiffness of the layered poroelastic half-space is presented. Kirchhoff's hypotheses are applied to obtain the vertical displacement of the thin plate. By using the inverse Fourier transform, the time domain solution is obtained. As an example of three layers, the influences of the load velocity, the material properties of poroelastic layers, and the flexural rigidity of the plate on the response of the pavement system are examined. Analyses show that a soft intermediate layer results in the significant increase of vertical displacement of road pavement. Comparison with the existing work validates the present model. Copyright © 2013 John Wiley & Sons, Ltd.

Vertical Dynamic Deflection Measurement in Concrete Beams with the Microsoft Kinect

Abstract: The Microsoft Kinect is arguably the most popular RGB-D camera currently on the market, partially due to its low cost. It offers many advantages for the measurement of dynamic phenomena since it can directly measure three-dimensional coordinates of objects at video frame rate using a single sensor. This paper presents the results of an investigation into the development of a Microsoft Kinect-based system for measuring the deflection of reinforced concrete beams subjected to cyclic loads. New segmentation methods for object extraction from the Kinect's depth imagery and vertical displacement reconstruction algorithms have been developed and implemented to reconstruct the time-dependent displacement of concrete beams tested in laboratory conditions. The results demonstrate that the amplitude and frequency of the vertical displacements can be reconstructed with submillimetre and milliHz-level precision and accuracy, respectively.

Boundary Layer Updrafts Driven by Airflow over Heated Terrain

Abstract: This study presents linear and nonlinear scalings for boundary layer ascent forced by airflow over heated terrain and compares them to results from corresponding high-resolution numerical simulations. Close agreement between theory and simulation is found over most of the parameter space considered, including variations in background winds, boundary layer stability, mountain height, and diabatic heating rate. As expected, the linear and nonlinear scalings perform best for linear and nonlinear flows, respectively. For a convective boundary layer, the scalings accurately predict vertical motion for all flows considered, including those that extend well into the nonlinear regime. Thus, these scalings may ultimately help to improve the parameterization of subgrid orographic ascent in large-scale models. The vertical velocity scalings are less accurate for mechanically blocked flows in stable boundary layers, for which a simple vertical displacement scaling is superior. Although the scalings do not tre...

Vertical displacement rates in the Upper Rhine Graben area derived from precise leveling

Abstract: The recent vertical displacement field of the Upper Rhine Graben (URG) located in the tri-national region between Germany, France and Switzerland is investigated using repeatedly measured leveling data. We estimate vertical displacement rates at leveling benchmarks by applying a kinematic network adjustment on more than 40,000 height differences measured by German, French and Swiss surveying agencies. Focusing on an optimal solution for the adjusted rates in the URG area also historical data (measured before 1900) are used, significantly increasing the time span of available measurements and the number of transnational connections between the three countries. To account for inhomogeneities apparent in the database, we apply an iterative variance component estimation within the adjustment procedure, particularly revealing more realistic information on the accuracy of the estimated rates. A special focus within our analysis is put on the statistical testing of gross errors in the observations and model-related errors at benchmarks with non-linear movement. As some of the estimated vertical rates behave significantly different compared to the vertical rates of adjacent benchmarks, a filtering of outliers is applied after the adjustment procedure. The resulting map of linear height changes in an area of 280 km in N–S and 230 km in E–W direction provides detailed insight into the recent vertical displacements of the URG and neighboring regions. In the German part of the study area, it was possible for the first time to consistently constrain an average subsidence rate of 0.5 mm/a ( $$\pm $$ 0.2 mm/a) of the Graben interior w.r.t. the Black Forest. In addition to the tectonic displacements, some man-induced surface movements, e.g., caused by oil and groundwater extraction, are observed and discussed.

Far-Field Deformation Resulting from Rheologic Differences Interacting with Tectonic Stresses: An Example from the Pacific/Australian Plate Boundary in Southern New Zealand

Abstract: The Miocene in Southern New Zealand was dominated by strike-slip tectonics. Stratigraphic evidence from this time attests to two zones of subsidence in the south: (a) a middle Cenozoic pull-apart basin and (b) a regionally extensive subsiding lake complex, which developed east and distal to the developing plate boundary structure. The lake overlay a block of crust with a significantly weak mid-crustal section and we pose the question: can rheological transitions at an angle to a plate boundary produce distal subsidence and/or uplift? We use stratigraphic, structural and geophysical observations from Southern New Zealand to constrain three-dimensional numerical models for a variety of boundary conditions and rheological scenarios. We show that coincident subsidence and uplift can result from purely strike-slip boundary conditions interacting with a transition from strong to weak to strong mid-crustal rheology. The resulting pattern of vertical displacement is a function of the symmetry or asymmetry of the boundary conditions and the extent and orientation of the rheological transitions. For the Southern New Zealand case study, subsidence rates of ~0.1 mm/yr are predicted for a relative plate motion of 25 mm/yr, leading to ~500 m of subsidence over a 5 Ma time period, comparable to the thickness of preserved lacustrine sediments.

Experimental study on the performance of bowl-tray rice precision seeder

Abstract: In order to optimize the parameters of bowl-tray rice precision seeder and improve its performance, three major factors respectively at five levels, including shaped hole diameter, vertical displacement of rice seeds and rotating speed of cam, were tested, the quadratic orthogonal rotational regression experiments were conducted, and the effects on seeding rate, leakage sowing rate and the injury rate were investigated. The test results show that factors affecting rice seeding rate are in the order of shaped hole diameter, rotating speed of cam and vertical displacement of rice seeds. The factors affecting rice planting leakage rate are in the order of shaped hole diameter, vertical displacement of rice seeds and rotating speed of cam, and the factors affecting rice injury rate are in the order of rotating speed of cam, vertical displacement of rice seeds and shaped hole diameter. Optimal parameters (shaped hole diameter: 10 mm, vertical displacement of rice seeds: 27 mm, rotating speed of cam: 13 r/min) and performance index (seeding rate: 95.43%, leakage sowing rate: 0.37%, injury rate: 0.58%) provided the basis for design and performance improvement of the bowl-tray rice precision seeder.

Nano-scale displacement sensing based on Van der Waals interaction

Abstract: We propose the nano-scale displacement sensor with high resolution for weak-force systems could be realized based on vertical stacked two-dimensional (2D) atomic corrugated layer materials bound through Van der Waals (VdW) interaction. Using first-principles calculations, we found the electronic structure of bi-layer blue phosphorus (BLBP) varies appreciably to both the lateral and vertical interlayer displacement. The variation of electronic structure due to the lateral displacement is attributed to the changing of the interlayer distance dz led by atomic layer corrugation, which is in a uniform picture with vertical displacement. Despite different stacking configurations, the change of in-direct band gap is proportional to dz-2. This stacking configuration independent dz-2 law is found also works for other graphene-like corrugated bi-layer materials, for example MoS2. By measuring the tunable electronic structure using absorption spectroscopy, the nano-scale displacement could be detected. BLBP represents a large family of bi-layer 2D atomic corrugated materials for which the electronic structure is sensitive to the interlayer vertical and lateral displacement, thus could be used for nano-scale displacement sensor. Since this kind of sensor is established on atomic layers coupled through VdW interaction, it provides unique applications in measurements of nano-scale displacement induced by tiny external force.

Three-direction displacement measurement method based on laser speckle imaging technology

Abstract: The invention relates to a three-direction displacement measurement method based on a laser speckle imaging technology. The three-direction displacement measurement method based on the laser speckle imaging technology can achieve synchronous three-direction displacement measurement. According to the technical scheme, the method includes the following steps that firstly, two laser transmitter sets are installed on a reference point, and a laser speckle imaging system is installed on a position I; secondly, light beams are transmitted to an imaging target surface by the laser transmitters and are focused to form a speckle image by an imaging lens, the speckle image is received by an imaging photoelectric device, and the coordinate values of the center points of two speckles relative to the imaging system are found out by a signal processing unit through an image processing algorithm and serve as original values; thirdly, the laser speckle imaging system is moved to a position II, light beams are transmitted to the imaging target surface by the laser transmitters, and the coordinate values of the center points of two speckles relative to the imaging system are found out and serve as test values; fourthly, the test values are compared with the original values, and the horizontal displacement and the vertical displacement are worked out; fifthly, the three-direction displacement of the position II where test points are located relative to the position I is worked out.

Observed features of acoustic gravity waves in the heterosphere

Abstract: According to measurements on the Dynamic Explorer 2 satellite, features of the propagation of acoustic gravity waves (AGWs) in the multicomponent upper atmosphere have been investigated. In the altitude range 250–400 km in wave concentration variations of some atmospheric gases, amplitude and phase differences have been observed. Using the approach proposed in this paper, in different gases, AGW variations have been divided into components associated with elastic compression, adiabatic expansion, and the vertical background distribution. The amplitude and phase differences observed in different gases are explained on the basis of analyzing these components. It is shown how to use this effect in order to determine the wave propagation, the vertical displacement of the volume element, the wave frequency, and the spatial distribution of the wave energy density.

Numerical Simulation of Tire Reinforced Sand Behind Retaining Wall Under Earthquake Excitation

Abstract: This paper studies the numerical simulations of retaining walls supporting tire reinforced sand subjected to El Centro earthquake excitation using finite element analysis. For this, four cases are studied: cantilever retaining wall supporting sand under static and dynamical excitation, and cantilever retaining wall supporting waste tire reinforced sand under static and dynamical excitation. Analytical external stability analyses of the selected retaining wall show that, for all four cases, the factors of safety for base sliding and overturning are less than default minimum values. Numerical analyses show that there are no large differences between the case of wall supporting waste tire reinforced sand and the case of wall supporting sand for static loading. Under seismic excitation, the higher value of Von Mises stress for the case of retaining wall supporting waste tire reinforced sand is 3.46 times lower compared to the case of retaining wall supporting sand. The variation of horizontal displacement (U1) and vertical displacement (U2) near the retaining wall, with depth, are also presented.