bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Time Dependent Stress-Strain Simulation of Clay
Authors: Ou C.-Y. , Liu C.-C. , Chin C.-K.
Published: May 2011

The objective of this study is to derive a time dependent effective based constitutive law on the basis of framework of the Modified Cam-Clay model. This model takes into account the anisotropic characteristics and creep behavior, based on the theory of viscoplasticity. The model sets the initial yield surface symmetric to theKoline for modeling the initialKocondition. A method is then developed to compute the gyration and expansion of the loading surface to simulate the anisotropic behavior due to the principal stress gyration after shear. The creep or time dependent behavior is considered in the model by adopting Kutter and Sathialingam's model, which was derived from Taylor's secondary consolidation theory and Bjerrum's delayed compression model. Compared with the Modified Cam-Clay model, the model requires five additional parameters to describe the soil behavior. All of the additional parameters can be obtained through conventional soil tests or parametric studies. The model is evaluated through a series of simulation of undrained shear tests and undrained creep tests.
Anticipation of Stability Limits for Two Degree-of-Freedom Interrupted Milling
Authors: Imani B. M. , Sadeghi M. H. , Kazemi M.
Published: May 2011

Milling is becoming an increasingly universal machining operation for producing parts used in aerospace, automotive, and life science engineering industries. The characteristics common to such parts are a high level of complexity and structural flexibility, both of which usually necessitate using low radial immersion milling operations. Low radial immersion milling operations involve interrupted cutting which induces chatter vibration under certain cutting conditions. The stability behavior of low immersion helical end milling processes is investigated in this paper. Time Finite Element Analysis (TFEA) is suggested for an approximate solution for delayed differential equations encountered during interrupted milling. An improved TFEA is proposed which includes the effects of helix angle variations on cutting force, cutting time and specific cutting force coefficients for a 2 DOF vibratory system. To verify the proposed method, experimental tests have been conducted which prove that the improved TFEA method accurately predicts the stability behavior of low immersion milling.
Stability and Chaotic Vibrations of a Fluid-Conveying Pipe with Additional Combined Constraints
Authors: Wang L. , Ni Q. , Huang Y. Y.
Published: May 2011

The stability and possible chaotic vibrations of a fluid-conveying pipe with additional combined constraints are investigated. The pipe, restrained by motion constraints somewhere along the length of the pipe, is modeled by a beam clamped at the left end and supported by a special device (a rotational elastic constraint plus a Q-apparatus) at the right end. The motion constraints are modeled by both cubic and trilinear models. Based on the Differential Quadrature Method (DQM), the nonlinear dynamical equations of motion for the system are formulated, and then solved via a numerical iterative technique. Calculations of bifurcation diagrams, phase portraits, time responses and Poincare maps of the oscillations establish the existence of chaotic vibrations. The route to chaos is shown to be via period-doubling bifurcations. It is found that the effect of spring constant of the rotational elastic constraint on the dynamics is significant. Moreover, the critical fluid velocity at the Hopf bifurcation point for the cubic model is higher than that for the trilinear model.
Characteristics of Hydraulic Shock Waves in an Inclined Chute Contraction - Experiments
Authors: Jan C.-D. , Chang C.-J. , Lai J.-S. , Guo W.-D.
Published: May 2011

This paper presents the experimental results of the characteristics of hydraulic shock waves in an inclined chute contraction with consideration of the effects of sidewall deflection angle φ, bottom inclination angle θ and approach Froude number Fr0. Seventeen runs of laboratory experiments were conducted in the range of 27.45° ≤φ ≤ 40.17°, 6.22° ≤ θ ≤ 25.38° and 1.04 ≤ Fr0 ≤ 3.51. Based on the experimental data, three empirical dimensionless relations for the shock angle, maximum shockwave height, and corresponding position of maximum shockwave were obtained by regression analyses, respectively. These empirical relations would be useful for hydraulic engineers in designing chute contraction structures.
Semi-Active Fuzzy Control of MR Damper on Structures by Genetic Algorithm
Authors: Huang Z.-S. , Wu C. , Hsu D.-S.
Published: May 2011

The magnetorheological (MR) damper is a new device proposed for structural protection. It is filled with MR fluid that can be changed, when exposed to a magnetic field, regularly from free flowing liquid, linear viscous one to semi-solid. A phenomenological model based on the Bouc-Wen hysteresis model is adopted to predict both the force-displacement behavior and the complex nonlinear force-velocity response. The theory of fuzzy control is adopted here to determine the command voltage of MR dampers, but the applying of fuzzy control rules has always to deal with the classic problem of optimization. And due to the structural responses of analysis results, it can be confirmed that the reducing effects have an obviously improvement after an optimization by genetic algorithm.
Numerical Calculation of Turbulent Channel Flow with Porous Ribs
Authors: Chan H. C. , Zhang Yaoxin , Leu J. M. , Chen Y.-S.
Published: May 2011

The turbulent flow in a channel with periodic porous ribs on one wall is numerically studied. The numerical model utilizes the Reynolds averaged Navier-Stokes (RANS) equations with a k−ε turbulent model for turbulence closure. Computational results show good agreements with experimental data in flows over a porous rib. The parameter effects, including the pitch ratio PR (1 ∼ 9) and porosity γ (0.4 ∼ 0.6), on flow fields are further examined in detail. Systematic variations of streamline, streamwise and vertical velocities, and turbulent kinetic energy are clearly identified. As to the PR effect, the interaction between outer flow and flow within the cavity is promoted by arranging ribs due to the penetration of the outer flow. Increasing porosity can reduce the downward outer flow by strong flows passing through the porous ribs. The numerical calculations suggest that the flow characteristics for porous ribs are not only a function of the rib geometry, i.e. pitch ratio, but also the porous property, i.e. porosity.
A New Analytical Model of a Centrifugal Compressor and Validation by Experiments
Authors: Pourfarzaneh H. , Hajilouy-Benisi A. , Farshchi M.
Published: May 2011

In the conceptual design phase of a turbocharger, where emphasis is mainly on parametric studies, before manufacturing and tests, a generalized and robust model that implies over a wide range properly, is unavoidable. The critical inputs such as compressor maps are not available during the conceptual design phase. Hence, generalized compressor models use alternate methods that work without any supplementary tests and can operate on wide range. One of the common and applicable modeling methods in design process is the ‘Dimensionless Modeling’ using the constant coefficient scaling (CCS). This method almost can predict the compressor characteristics at design point. However, at off design conditions, error goes up as mass flow and speed parameters increase. Therefore, the results are not reliable at these points. In this paper, a variable coefficient scaling (VCS) method is described. Then, a centrifugal compressor is modeled using the VCS method. To evaluate the model and compare it with the experimental results, some supplementary experiments are performed. Experimental studies are carried out on the compressor of a S2B model of the Schwitzer turbocharger in the turbocharger Lab., at Sharif University of Technology. The comparison between the experimental results and those obtained by the VCS method indicates a good agreement. It also suggests that the present model can be used as an effective design tool for all operating conditions.
Free Vibration of Rectangular Plate with Delamination
Authors: Shiau L.-C. , Zeng J.-Y.
Published: May 2011

In this paper, the effect of delamination on free vibration of a simply supported rectangular homogeneous plate with through-width delamination was investigated by the finite strip method. A constrained model was used and a finite strip with bending and in-plane stiffness was derived for the free vibration analysis. The effects of delamination length, delamination location in the thickness-wise and spanwise directions, and aspect ratio of the plate on the natural frequencies of the plate were presented. Results show that the delamination has considerable effect on the natural frequencies of the plate. The aspect ratio of the plate is also having significant effect on the natural frequency of the plate, especially on the mode 2 frequency of the plate.
Effect of Vapor Superheating on Mixed-Convection Film Condensation Along an Isothermal Vertical Cylinder
Authors: Chang T.-B.
Published: May 2011

This paper presents an analytical investigation into the effect of vapor superheating on the mixed-convection of a condensate layer flowing along the outside surface of an isothermal vertical cylinder. The governing system of partial differential equations is transformed into a dimensionless form using the nonsimilar transformation method. In investigating the heat transfer characteristics within the condensate layer and vapor phase, the analysis takes account of both the inertia effects and the convection effects within the condensate layer and the shear resistance at the liquid-vapor interface. The numerical results reveal that vapor superheating has a negligible effect on the temperature profile and local Nusselt number within the condensate layer. Moreover, it is found that a higher forced-flow intensity increases the temperature gradient in the vapor phase, but has a marginal effect on the temperature profile in the condensate layer. Finally, it is shown that the velocity at the liquid-vapor interface increases as the intensity of the forced-flow increases or as the ratio of the condensate layer viscosity to the vapor phase viscosity reduces.
The Effect of Kinematic Oscillations on Harmonic Wheel Flange Wear of Rail Vehicles
Authors: Ali Rezvani Mohammad , Asadi Lari Ali
Published: May 2011

A number of factors affect rail vehicle steel wheels. Kinematic oscillations uncovered by Klingel, is amongst the parameters affecting dynamic behaviour of the wheelset. Normal and tangential forces are also included within the wheel/rail interface. Geometry and material properties of the contacting bodies are within these parameters. Altogether, these inputs to the rail/wheel system can result in plastic deformation and wear. The authors of this paper make their attempts to introduce a noble study including a harmonic wear pattern in circumference of the flange region when contacting the rail gauge corner. Theoretical aspects of this harmonic pattern are then developed and presented.
Analysis of a Pot-Like Ultrasonic Sensor with an Anisotropic Beam Pattern
Authors: Cheng C.-C. , Lin C.-Y. , Ho J.-H. , Chen C.-S. , Shieh J. , Wu W.-J. , Wu K.-C. , Lee C.-K.
Published: May 2011

We investigated the design parameters of a compact pot-like ultrasonic sensor which possesses a highly anisotropic beam pattern. As the sensor size is small due to its application constraint, the parameters are thus highly coupled to one another. We analyzed the respective effects of the parameters in the case where there is a vertical beam width reduction. The parameters investigated include resonant frequency, vibrating plate width-expanded angle, and ratio of thickness discontinuity of the vibrating plate. Numerical models developed by combining finite-element analysis and spatial Fourier transforms were adopted to predict the far-field radiating beam pattern of the various design configurations. The displacement distribution of the vibrating plate was measured using a microscopic laser Doppler vibrometer and the far-field pressure beam patterns were measured using a standard microphone in a semianechoic environment. The three configurations we used to validate the simulation model resulted in an H-V ratio of 2.67, 2.68 and 3.13, respectively which all agreed well with the numerical calculations. We found that by increasing the operating resonant frequency from 40kHz to 58kHz, the vertical far-field beam width of an ultrasonic sensor can be reduced by 31.62%. We found that the vertical beam width can be significantly reduced when the ratio of the thickness discontinuity of the vibrating plate decreases from 1 to 0.4 and is incorporated with its optimal width-expanded angle of the vibrating plate. It appears that an ultrasonic sensor with this type of anisotropic beam pattern can be ideally adopted for today's automotive applications.
Micro-Droplets Atomizer Using PZT Ring Actuator
Authors: Huang Y.-L. , Chang S.-H.
Published: May 2011

This paper presents the ultrasonic atomizer composed of the lead zirconate titanate (PZT) ring actuator and the Ni nozzle plate with numerous minute nozzles. The atomizer operates at its resonant frequency in out-of-plane vibration. De-ionized (DI) water is fed by the open trough to the porous sponge that is in contact with one face of the nozzle plate and it is ejected through nozzles. Micro-droplets are formed at the opposite face of the nozzle plate. The resonance frequencies of the PZT ring are investigated and compared in theoretical analysis, three-dimensional (3-D) finite-element models (FEM) numerical simulation, and experimental measurement. The performance of the atomizer is examined. This ring shape design of ultrasonic atomizer demonstrates advantage of high atomization rate (64.3ml/min) and high atomization efficiency (l,007ml/h/W) at low power consumption (8.244W).
Rectangular-Plate Turbulator Effects on Heat Transfer and Near-Wall Flow Characteristics in Fan Flows
Authors: Chen T.Y. , Chen Y.H.
Published: May 2011

Heat transfer and near-wall flow characteristics in an inherently swirling fan flow, containing rectangular-plate turbulators with 45° and 90° angles of attack, were experimentally investigated. The heat transfer characteristics for uniform flows with the turbulators were also investigated for comparison. Eight heated aluminum plates, installed along a bottom duct-wall, were used as the heat transfer surfaces, which allows the studies of heat transfer variations along the duct and the studies of the relations between the local fluid flows and heat transfer variations. Three-component mean and fluctuating velocities were measured using a laser Doppler velocimetry to obtain the near-wall flow parameters, including the axial mean velocity, axial vorticity and turbulent kinetic energy. The temperatures on the eight heat transfer surfaces were measured using thermocouples to obtain the Stanton number distributions. Results suggest that the rectangular-plate turbulators in fan flows may cause the increases in the near-wall flow parameters and, consequently, augment the heat transfer, especially around the flow reattachment regions. Also, the rectangular-plate turbulator effect on heat transfer augmentation in fan flows may be as attractive as that in uniform flows at the investigated X/H ranges.
Development and Characterization of Jet-Injected Vee-Gutter
Authors: Chang Kuo T. , Huang Rong F.
Published: May 2011

The vee-gutter, which was conventionally used in a combustor for flame holding, was re-designed by employing the unsteady Coanda effect to inject fluids periodically into near wake of the vee-gutter. Fluidic targets were developed to induce self-sustained transverse oscillation of slit-jet. The self-sustained oscillating jet was conducted through passages and injected into the near wake of the vee-gutter. The behaviors and frequency characteristics of the slit-jet in the oscillation cavity and the turbulence properties in the wake were studied experimentally in a wind-tunnel by using the smoke-wire flow visualization technique and the hot-wire anemometer. The oscillation frequencies of the presently developed jet-injection vee-gutter were about 25 to 40 times higher than that of the conventionally used fluidic flowmeter. By estimating the Lagrangian integral time scale and employing the Taylor's frozen flow hypothesis, the integral length scales of turbulence fluctuations were calculated. The results showed that the integral length scales of turbulences of the jet-injected vee-gutter were significantly smaller than their counter parts of the conventional vee-gutter, which indicated the effects of vortex stretching induced by the periodic jet injection. The modifications of turbulence properties were presented and discussed.
Robust Frequency-Shaping Optimal Active Vibration Control of Uncertain Flexible Mechanical Systems with Persistent Excitation
Authors: Zheng Liang-An , Chen Shinn-Horng , Chou Jyh-Horng
Published: May 2011

Based on the frequency-shaping optimal control method, this paper proposes a time-domain robust disturbance rejection design approach for a class of uncertain flexible mechanical systems subject to persistent disturbances and time-varying parameter perturbations. In the approach, a frequency-shaping output filter is first employed to combine with the mechanical system and a Kalman filter to form an augmented system. Some eigenvalues of the frequency-shaping output filter coincide with the unstable poles of the disturbance dynamics to perform disturbance rejection. Then, for the designed closed-loop system to have asymptotic stability, a new robust stability condition is proposed. It is shown that, using the proposed stability condition, the resulting controller can suppress the persistent disturbance and keep the flexible mechanical system from the possibility of instability caused by spillover and time-varying parameter perturbations. Finally, two examples are given to demonstrate the use of the design approach.
A Spherical Inclusion with Inhomogeneous Interface in Conduction
Authors: Chen T. , Hsieh C. H. , Chuang P. C.
Published: May 2011

A series solution is presented for a spherical inclusion embedded in an infinite matrix under a remotely applied uniform intensity. Particularly, the interface between the inclusion and the matrix is considered to be inhomegeneously bonded. We examine the axisymmetric case in which the interface parameter varies with the cone angle θ. Two kinds of imperfect interfaces are considered: an imperfect interface which models a thin interphase of low conductivity and an imperfect interface which models a thin interphase of high conductivity. We show that, by expanding the solutions of terms of Legendre polynomials, the field solution is governed by a linear set of algebraic equations with an infinite number of unknowns. The key step of the formulation relies on algebraic identities between coefficients of products of Legendre series. Some numerical illustrations are presented to show the correctness of the presented procedures. Further, solutions of the boundary-value problem are employed to estimate the effective conductivity tensor of a composite consisting of dispersions of spherical inclusions with equal size. The effective conductivity solely depends on one particular constant among an infinite number of unknowns.
Thermal Stress in a Finitely Deformed Incompressible Elastic Medium Containing a Penny-Shaped Crack
Authors: Tsai Y. M.
Published: May 2011

The thermal stress for a penny-shaped crack contained in an infinite isotropic elastic solid initially subjected to an axisymmetrical tension of any amount at infinity is investigated using the techniques of Hankel transforms and multiplying factors. The effect that the lateral normal stress has on the thermal stresses is studied on the basis of the theory of small deformations superposed on finite deformation. Symmetrical thermal loadings are applied over the crack surfaces. For the case of constant temperature over the crack surfaces, expressions for the crack shape and thermal stresses in the crack plane are obtained in closed forms. The stress intensity factor is also obtained and shown to be dependent on the lateral stress.
Singular Stress Fields of Anisotropic Bimaterial Wedges with Imperfect Interfaces
Authors: Wijeyewickrema Anil C. , Leungvichcharoen Somsak , Poonsawat Piya
Published: May 2011

The effect of an imperfect interface on the stress singularity of anisotropic bimaterial wedges subjected to traction free boundary conditions are investigated. The interfacial tractions are assumed to be continuous, directly proportional to the displacement jumps and inversely proportional to the radial coordinate. The characteristic equation for the order of singularity is obtained and numerical results are given for the angle-ply bimaterial composite wedge.
Analysis of Surface Acoustic Waves in Layered Piezoelectric Media and its Applications to the Design of Saw Devices
Authors: Wu T.-T. , Chen Y.-Y.
Published: May 2011

In this paper, we utilized a Stroh based formulation for solving problems of surface waves in layered piezoelectric media, and then, applied it to analyze surface acoustic wave (SAW) devices. The determination of the optimal cut of a piezoelectric crystal and the choice of the best propagation of SAW devices were given. The dispersion induced by a thin metal layer on SAW propagation in a SAW device was analyzed and discussed. Finally, we applied the formulation to calculate the effective permittivity and phase velocity dispersion of a LiNbO3/Diamond layered SAW device. Both of the null frequency bandwidth and the insertion loss of the dispersive SAW device were obtained.
Measurement and Modelling for the Dispersion Relations of Acoustic Waves Propagating in a Free Piezoelectric Plate
Authors: Yang C. H. , Huang M. F.
Published: May 2011

This research is focused in the measurement and modelling of the dispersion relations of Lamb waves propagating in a piezoelectric plate. A theoretical model based on a partial wave analysis is used to provide numerical calculations for the dispersion relations of Lamb waves propagating in an LiNbO3 plate with different propagating directions. The dispersion relations are presented in an innovative image format. A non-contact laser ultrasound technique operated in B-scan mode with the aid of double Fast Fourier transform signal-processing scheme is used to measured multi-mode dispersion realtions. Among all the propagation angles, the measured dispersion curves show good agreement with the theoretical calculations. The Rayleigh wave speeds are extracted from the measured and calculated dispersion curves, showing favorable comparison with classical theory by Campbell.
EndoFEM Intergrated Methodology of Fatique Crack Propagation With Overloaded Delay Retardation
Authors: Lee C. F.
Published: May 2011

In this paper, EndoFEM integrated methodology developed for fatigue crack growth under constant amplitude load, was extended successfully to investigate the Kumar's experimental observations, especially in the increasing severity of delayed retardation due to increasing overload ratio. This phenomenon was accompanied with an increasing max. crack closure load (Pcl) within 0.5mm crack extension after overload, and then followed by a longer recovery stage with lower fatigue crack propagation (FCP) rate.

In the methodology, the EndoFEM with rc controlled node-released strategy was employed to produce a 2mm fatigue crack length from 6% prestrained SEN specimen. To simulate the delayed retardation of overload with/without instant crack extension, five strategies of nodal release were proposed, and then the CMOD method was employed to determine Pcl. The resulting variations of Pcl during crack extension had the same tendency as those of experimental findings. These results allowed one to propose a quadratic relationship between Pcl and Kmax under a fixed overload ratio. As a consequence, a conventional formula of crack closure model could be preserved with a modified coefficient, i.e., da/dN = C(UΔK)m. The formula proposed could predict both the a vs. N crack growth data and the da/dN vs. ΔK data under fixed overload ratios quite well.
A Pdf Description of Momentum Fluctuation Correlations of a Rarefied Free Shear Layer
Authors: Hong Z.-C. , Zhen C.-E. , Yang C.-Y.
Published: May 2011

The mixing properties of various orders of fluctuation correlations are investigated in the present paper for a rarefied gas free shear layer at hypersonic speed. The molecular kinetic theory and the direct simulation Monte Carlo (DSMC) method are employed for the present calculations. The Reynolds average process is assumed in obtaining the correlation functions. The results show that flow field structure was very similar to that of continuum flow ones at high Reynolds numbers. The probability density functions (pdf) in velocity spacef(u′),f(v′), andf(u′,v′) are also calculated to counter explain the distributions of the correlation functions in the mixing layer. From the calculated distributions of the fluctuation correlation functions, , , and , one can find that the distributions behave similar to the turbulent transport phenomena in that of a continuum flow one. The distributions of the fluctuation correlation functions,  is described via the joint probability density function,f(u′,v′). The behavior of the higher-order fluctuation correlation functions, ,  and , are also explained via the probability density function.
Nonlinear Stability Analysis of Thin Film Flow from a Liquid Jet Impinging on a Circular Concentric Disk
Authors: Cheng P.-J. , Lai H.-Y.
Published: May 2011

The paper investigates the stability of thin film flow from a liquid jet impinging on a circular concentric disk using a long-wave perturbation method to solve for the generalized nonlinear kinematic equations of free film interface. To begin with a normal mode approach is employed to obtain the linear stability solution for the film flow. In the linear stability solutions only subcritical region can be resolved. In other words, no solution of supercritical region can be obtained in linear domain. Furthermore, the role that the forces of gravitation and surface tension play in the flow is nothing but to stabilize the system. To further investigate the realistic impinging jet flow stability conditions, the weak nonlinear dynamics of a film flow is studied by using the method of multiple scales. Various subcritical nonlinear behaviors expressed in terms of absolute stability, conditional stability and explosive instability can be characterized by solving the Ginzburg-Landau equation. It is found that the jet flow will become relatively unstable for an increasing Reynolds number, a relative smaller distance from the center of the impinging jet on the disk and a smaller diameter of the exit jet. It is also concluded that the flow will always stay in a subcritical instability region if the characteristic diameter of the potential core at nozzle exit is less than 0.01mm for the numerical conditions given in this paper. In such a case when the amplitude of external flow disturbance is smaller than the threshold amplitude a stable jet flow can be ensured.
Experimental and Computational Analysis of Periodic Flow Structure in Oscillatory Gas Flow Meters
Authors: Chen C.-K. , Wang L. , Yang J.-T. , Chen L.-T.
Published: May 2011

The oscillatory characteristics and dynamic structure of periodic flow in an oscillatory gas flow meter were studied experimentally and numerically. The flow oscillations were triggered by the Coanda effect and an universal correlation between Strouhal number and Reynolds number, Str = 1.09 × 10−3 for ReHD >800, was deduced based on spectral analysis of the pressure fluctuations in the flow channel. Numerical simulation indicated that the evolution of the flow patterns was classified into stages of induction and sustainable periodic oscillation. The transformation between the two stages was noticeably affected by the design of the feedback channels. The results further revealed that the development of the main vortex in the oscillating chamber and the small vortices at the entrance of the feedback channels concurrently modulate the mechanism of oscillation. The small vortices located at both entrances of the feedback channels play the role of a pair of modulating valves, which alternatively switch on and off the bypass flow through each feedback channel, thus reinforcing the periodic oscillation.
Numerical study of Transient Flow in a Full-Size Reflected Shock Tunnel
Authors: Tai Chang-Hsien , Miao Jr-Ming , Li Chun-Chi
Published: May 2011

The aim of this paper is to develop a CFD solver that used to simulate the transient flow phenomena in a reflected shock tunnel. The transient flow phenomena in a shock tunnel include the reflected shock/boundary layer interaction and the starting process of nozzle flow that can affect the duration of test flow in actual conditions. To numerically simulate these transient flow features, a full-size, axisymmetric reflected shock tunnel model is used. The governing equations are a full Navier-Stokes equation, a species equation and a simplified polynomial correlation to simulate the real gas effects. The numerical code is developed based on the finite volume method coupled with the upwind Roe's scheme and the total variation diminishing (TVD) method. To increase the calculation efficiency, a multi-block and multi-mesh grid generation technique is employed in a huge computational domain. The present computational results have not only confirmed the theoretical characteristics of a shock tube, but have also qualitatively presented the phenomena of reflected shock/boundary layer interaction and the starting process of nozzle flow. This numerical code is a useful tool to demonstrate the actual flow phenomena and to assist the design of experiments.
Exact Solutions for Electroelastic Analysis of Generalized Plane Strain and Torsion of Piezoelectric Cylinders
Authors: Tarn Jiann-Quo
Published: May 2011

Exact electroelastic analysis of hollow and solid circular cylinders subjected to a uniform temperature change and electromechanical loads that do not vary axially are presented. Generalized plane strain and torsion of a piezoelectric cylindrical body is formulated in a state space framework. Uniformly valid exact solutions are obtained for hollow and solid circular cylinders subjected to extension, torsion, pressuring, shearing, electric loadings and a uniform temperature change.
Simulation of Hydraulic Shock Waves by Hybrid Flux-Splitting Schemes in Finite Volume Method
Authors: Lai J.-S. , Lin G.-F. , Guo W.-D.
Published: May 2011

In the framework of the finite volume method, a robust and easily implemented hybrid flux-splitting finite-volume (HFF) scheme is proposed for simulating hydraulic shock waves in shallow water flows. The hybrid flux-splitting algorithm without Jacobian matrix operation is established by applying the advection upstream splitting method to estimate the cell-interface fluxes. The scheme is extended to be second-order accurate in space and time using the predictor-corrector approach with monotonic upstream scheme for conservation laws. The proposed HFF scheme and its second-order extension are verified through simulations of the 1D idealized dam-break problem, the 2D oblique hydraulic shock-wave problem, and the 2D dam-break experiments with channel contraction as well as wet/dry beds. Comparisons of the HFF and several well-known first-order upwind schemes are made to evaluate numerical performances. It is demonstrated that the HFF scheme captures the discontinuities accurately and produces no entropy-violating solutions. The HFF scheme and its second-order extension are proven to achieve the numerical benefits combining the efficiency of flux-vector splitting scheme and the accuracy of flux-difference splitting scheme for the simulation of hydraulic shock waves.
The Torsional Dislocation Loop and Mode III Cylindrical Crack
Authors: Demir I. , Khraishi T.A.
Published: May 2011

The elastic fields of a torsional dislocation loop in a homogeneous material are first derived. The solution is based on torsional symmetry. The stress and displacement solutions are then extended to the case of a torsional loop in a bi-material. A main utility of basic dislocation solutions is in fracture mechanics. In particular, circular loop solutions can be used in the modeling of both cylindrical and penny-shaped cracks. In the present study we use them to model a Mode III cylindrical crack via the application of a “distributed-dislocation technique”. Stress intensity factors at the crack tips are presented. The influences of crack radius and material pair on the stress intensity factor of interfacial cracks are investigated.
CO2 mediation of adverse effects of seawater acidification in Calcidiscus leptoporus
Authors: Langer Gerald , Bode Maya
Published: May 2011

The coccolithophore Calcidiscus leptoporus (strain RCC1135) was grown in dilute batch culture at CO2 levels ranging from ∼200 to ∼1600 μatm. Increasing CO2 concentration led to an increased percentage of malformed coccoliths and eventually (at ∼1500 μatm CO2) to aggregation of cells. Carbonate chemistry of natural seawater was manipulated in three ways: first, addition of acid; second, addition of a HCO3−/CO32− solution; and third, addition of both acid and HCO3−/CO32− solution. The data set allowed the disentangling of putative effects of the different parameters of the carbonate system. It is concluded that CO2 is the parameter of the carbonate system which causes both aberrant coccolithogenesis and aggregation of cells.
A revisit of drawdown behavior during pumping in unconfined aquifers
Authors: Mao Deqiang , Wan Li , Yeh Tian‐Chyi J. , Lee Cheng‐Haw , Hsu Kuo‐Chin , Wen Jet‐Chau , Lu Wenxi
Published: May 2011

In this study, the S‐shaped log‐log drawdown‐time curve typical of pumping tests in unconfined aquifers is reinvestigated via numerical experiments. Like previous investigations, this study attributes the departure of the S shape from the drawdown‐time behavior of the confined aquifer to the presence of an “additional” source of water. Unlike previous studies, this source of water is reinvestigated by examining the temporal and spatial evolution of the rate of change in storage in an unconfined aquifer during pumping. This evolution is then related to the transition of water release mechanisms from the expansion of water and compaction of the porous medium to the drainage of water from the unsaturated zone above the initial water table and initially saturated pores as the water table falls during the pumping of the aquifer. Afterward, the 1‐D vertical drainage process in a soil column is simulated. Results of the simulation show that the transition of the water release mechanisms in the 1‐D vertical flow without an initial unsaturated zone can also yield the S‐shaped drawdown‐time curve as in an unconfined aquifer. We therefore conclude that the transition of the water release mechanisms and vertical flow in the aquifer are the cause of the S‐shaped drawdown‐time curve observed during pumping in an unconfined aquifer. We also find that the moisture retention characteristics of the aquifer material have greater impact than its relative permeability characteristics on the drawdown‐time curve. Furthermore, influences of the spatial variability of saturated hydraulic conductivity, specific storage, and saturated moisture content on the drawdown curve in the saturated zone are found to be more significant than those of other unsaturated properties. Finally, a cross‐correlation analysis reveals that the drawdown at a location in a heterogeneous unconfined aquifer is mainly affected by local heterogeneity near the pumping and observation wells. Applications of a model assuming homogeneity to the estimation of aquifer parameters as such may require a large number of observation wells to obtain representative parameter values. In conclusion, we advocate that the governing equation for variably saturated flow through heterogeneous media is a more appropriate and realistic model that explains the S‐shaped drawdown‐time curves observed in the field.
Coseismic slip distribution of the February 27, 2010 Mw 8.8 Maule, Chile earthquake
Authors: Pollitz Fred F. , Brooks Ben , Tong Xiaopeng , Bevis Michael G. , Foster James H. , Bürgmann Roland , Smalley Robert , Vigny Christophe , Socquet Anne , Ruegg Jean‐Claude , Campos Jaime , Barrientos Sergio , Parra Héctor , Soto Juan Carlos Baez , Cimbaro Sergio , Blanco Mauro
Published: May 2011

Static offsets produced by the February 27, 2010 Mw = 8.8 Maule, Chile earthquake as measured by GPS and InSAR constrain coseismic slip along a section of the Andean megathrust of dimensions 650 km (in length) × 180 km (in width). GPS data have been collected from both campaign and continuous sites sampling both the near‐field and far field. ALOS/PALSAR data from several ascending and descending tracks constrain the near‐field crustal deformation. Inversions of the geodetic data for distributed slip on the megathrust reveal a pronounced slip maximum of order 15 m at ∼15–25 km depth on the megathrust offshore Lloca, indicating that seismic slip was greatest north of the epicenter of the bilaterally propagating rupture. A secondary slip maximum appears at depth ∼25 km on the megathrust just west of Concepción. Coseismic slip is negligible below 35 km depth. Estimates of the seismic moment based on different datasets and modeling approaches vary from 1.8 to 2.6 × 1022 N m. Our study is the first to model the static displacement field using a layered spherical Earth model, allowing us to incorporate both near‐field and far‐field static displacements in a consistent manner. The obtained seismic moment of 1.97 × 1022 N m, corresponding to a moment magnitude of 8.8, is similar to that obtained by previous seismic and geodetic inversions.
Crustal anisotropy structure related to lateral and down‐dip variations in interplate coupling beneath the Kii Peninsula, SW Japan
Authors: Saiga Atsushi , Kato Aitaro , Sakai Shin'ichi , Iwasaki Takaya , Hirata Naoshi
Published: May 2011

Anisotropy is an important feature of elastic wave propagation in the Earth, and can arise from a variety of ordered architectures such as fractures with preferential alignments or lattice‐preferred orientations. We studied regional variations in shear wave anisotropy beneath southern Kii Peninsula, which is located above the subducting Philippine Sea plate, using waveforms of local earthquakes observed with a dense seismic network. The fast directions of polarization are normal to the strike of the plate margin in the proximity of the locked portion of the underlying mega‐thrust fault, but they are subparallel to the strike of the margin along the fault's down‐dip extension. The distribution of the fast directions roughly coincides with that of the maximum horizontal compressive stress axis directions as inferred from earthquake focal mechanisms and borehole stress measurements. This indicates that the observed anisotropy is likely controlled by crustal stresses. Furthermore, the directions of the stress‐induced anisotropy correlate well with variations of the plate coupling ratio along the plate boundary as inferred from geodetic measurements. These results indicate the possibility that crustal anisotropy within an overlying plate can be used as an effective measure to monitor temporal variations of the plate coupling strength during the interseismic period.
Ultra-diffuse hydrothermal venting supports Fe-oxidizing bacteria and massive umber deposition at 5000 m off Hawaii
Authors: Edwards Katrina J , Glazer B T , Rouxel O J , Bach W , Emerson D , Davis R E , Toner B M , Chan C S , Tebo B M , Staudigel H , Moyer C L
Published: May 2011

A novel hydrothermal field has been discovered at the base of Lōihi Seamount, Hawaii, at 5000 mbsl. Geochemical analyses demonstrate that ‘FeMO Deep’, while only 0.2 °C above ambient seawater temperature, derives from a distal, ultra-diffuse hydrothermal source. FeMO Deep is expressed as regional seafloor seepage of gelatinous iron- and silica-rich deposits, pooling between and over basalt pillows, in places over a meter thick. The system is capped by mm to cm thick hydrothermally derived iron-oxyhydroxide- and manganese-oxide-layered crusts. We use molecular analyses (16S rDNA-based) of extant communities combined with fluorescent in situ hybridizations to demonstrate that FeMO Deep deposits contain living iron-oxidizing Zetaproteobacteria related to the recently isolated strain Mariprofundus ferroxydans. Bioenergetic calculations, based on in-situ electrochemical measurements and cell counts, indicate that reactions between iron and oxygen are important in supporting chemosynthesis in the mats, which we infer forms a trophic base of the mat ecosystem. We suggest that the biogenic FeMO Deep hydrothermal deposit represents a modern analog for one class of geological iron deposits known as ‘umbers’ (for example, Troodos ophilolites, Cyprus) because of striking similarities in size, setting and internal structures.
Linking phytoplankton community composition to seasonal changes in f-ratio
Authors: Ward Bess B , Rees Andrew P , Somerfield Paul J , Joint Ian
Published: May 2011

Seasonal changes in nitrogen assimilation have been studied in the western English Channel by sampling at approximately weekly intervals for 12 months. Nitrate concentrations showed strong seasonal variations. Available nitrogen in the winter was dominated by nitrate but this was close to limit of detection from May to September, after the spring phytoplankton bloom. The 15N uptake experiments showed that nitrate was the nitrogen source for the spring phytoplankton bloom but regenerated nitrogen supported phytoplankton productivity throughout the summer. The average annual f-ratio was 0.35, which demonstrated the importance of ammonia regeneration in this dynamic temperate region. Nitrogen uptake rate measurements were related to the phytoplankton responsible by assessing the relative abundance of nitrate reductase (NR) genes and the expression of NR among eukaryotic phytoplankton. Strong signals were detected from NR sequences that are not associated with known phylotypes or cultures. NR sequences from the diatom Phaeodactylum tricornutum were highly represented in gene abundance and expression, and were significantly correlated with f-ratio. The results demonstrate that analysis of functional genes provides additional information, and may be able to give better indications of which phytoplankton species are responsible for the observed seasonal changes in f-ratio than microscopic phytoplankton identification.
Analysis of bacterial and archaeal diversity in coastal microbial mats using massive parallel 16S rRNA gene tag sequencing
Authors: Bolhuis Henk , Stal Lucas J
Published: May 2011

Coastal microbial mats are small-scale and largely closed ecosystems in which a plethora of different functional groups of microorganisms are responsible for the biogeochemical cycling of the elements. Coastal microbial mats play an important role in coastal protection and morphodynamics through stabilization of the sediments and by initiating the development of salt-marshes. Little is known about the bacterial and especially archaeal diversity and how it contributes to the ecological functioning of coastal microbial mats. Here, we analyzed three different types of coastal microbial mats that are located along a tidal gradient and can be characterized as marine (ST2), brackish (ST3) and freshwater (ST3) systems. The mats were sampled during three different seasons and subjected to massive parallel tag sequencing of the V6 region of the 16S rRNA genes of Bacteria and Archaea. Sequence analysis revealed that the mats are among the most diverse marine ecosystems studied so far and consist of several novel taxonomic levels ranging from classes to species. The diversity between the different mat types was far more pronounced than the changes between the different seasons at one location. The archaeal community for these mats have not been studied before and revealed a strong reaction on a short period of draught during summer resulting in a massive increase in halobacterial sequences, whereas the bacterial community was barely affected. We concluded that the community composition and the microbial diversity were intrinsic of the mat type and depend on the location along the tidal gradient indicating a relation with salinity.
Archaea in Yellowstone Lake
Authors: Kan Jinjun , Clingenpeel Scott , Macur Richard E , Inskeep William P , Lovalvo Dave , Varley John , Gorby Yuri , McDermott Timothy R , Nealson Kenneth
Published: May 2011

The Yellowstone geothermal complex has yielded foundational discoveries that have significantly enhanced our understanding of the Archaea. This study continues on this theme, examining Yellowstone Lake and its lake floor hydrothermal vents. Significant Archaea novelty and diversity were found associated with two near-surface photic zone environments and two vents that varied in their depth, temperature and geochemical profile. Phylogenetic diversity was assessed using 454-FLX sequencing (∼51 000 pyrosequencing reads; V1 and V2 regions) and Sanger sequencing of 200 near-full-length polymerase chain reaction (PCR) clones. Automated classifiers (Ribosomal Database Project (RDP) and Greengenes) were problematic for the 454-FLX reads (wrong domain or phylum), although BLAST analysis of the 454-FLX reads against the phylogenetically placed full-length Sanger sequenced PCR clones proved reliable. Most of the archaeal diversity was associated with vents, and as expected there were differences between the vents and the near-surface photic zone samples. Thaumarchaeota dominated all samples: vent-associated organisms corresponded to the largely uncharacterized Marine Group I, and in surface waters, ∼69–84% of the 454-FLX reads matched archaeal clones representing organisms that are Nitrosopumilus maritimus-like (96–97% identity). Importance of the lake nitrogen cycling was also suggested by >5% of the alkaline vent phylotypes being closely related to the nitrifier Candidatus Nitrosocaldus yellowstonii. The Euryarchaeota were primarily related to the uncharacterized environmental clones that make up the Deep Sea Euryarchaeal Group or Deep Sea Hydrothermal Vent Group-6. The phylogenetic parallels of Yellowstone Lake archaea to marine microorganisms provide opportunities to examine interesting evolutionary tracks between freshwater and marine lineages.
Comparison of Measures of Adiposity in Identifying Cardiovascular Disease Risk Among Ethiopian Adults
Authors: Wai Wint S. , Dhami Ranjodh S. , Gelaye Bizu , Girma Belaineh , Lemma Seblewengel , Berhane Yemane , Bekele Tamrat , Khali Atsede , Williams Michelle A.
Published: May 2011

We sought to determine which measures of adiposity can predict cardiovascular disease (CVD) risk and to evaluate the extent to which overall and abdominal adiposity are associated with cardiometabolic risk factors among working adults in Ethiopia. This was a cross‐sectional study of 1,853 individuals (1,125 men, 728 women) in Addis Ababa, Ethiopia. The World Health Organization STEPwise approach was used to collect sociodemographic data, anthropometric measurements, and blood samples among study subjects. Fasting blood glucose (FBG) and lipid concentrations were measured using standard approaches. Spearman's rank correlation, receiver operating characteristic (ROC) curves, and logistic regression were employed to determine the association and predictive ability (with respect to CVD risk factors) of four measures of adiposity: BMI, waist circumference (WC), waist‐to‐hip ratio (WHR), and waist‐to‐height ratio (WHtR). Overall, FBG is best associated with WHtR in men and WC in women. Systolic blood pressure (SBP) is most strongly associated with BMI in men, but with WC in women. Compared to those with low BMI and low WC, the risk of having CVD is the highest for those with high BMI and high WC and those with high WC and low BMI. Review of ROC curves indicated that WC is the best predictor of CVD risk among study subjects. Findings from our study underscore the feasibility and face validity of using simple measures of central and overall adiposity in identifying CVD risk in resource‐poor settings.