The Experts below are selected from a list of 237 Experts worldwide ranked by ideXlab platform

Nan Zhang - One of the best experts on this subject based on the ideXlab platform.

  • formation of mantle lone plumes in the global downwelling zone a multiscale modelling of subduction controlled plume generation beneath the south china sea
    Tectonophysics, 2018
    Co-Authors: Nan Zhang
    Abstract:

    Abstract It has been established that almost all known mantle plumes since the Mesozoic formed above the two lower mantle large low shear velocity provinces (LLSVPs). The Hainan plume is one of the rare exceptions in that instead of rising above the LLSVPs, it is located within the broad global mantle downwelling zone, therefore classified as a “lone plume”. Here, we use the Hainan plume example to investigate the feasibility of such lone plumes being generated by subducting slabs in the mantle downwelling zone using 3D geodynamic modelling. Our geodynamic model has a high-resolution regional domain embedded in a relatively low resolution global domain, which is set up in an adaptive-mesh-refined, 3D mantle convection code ASPECT (Advanced Solver for Problems in Earth's ConvecTion). We use a recently published plate motion model to define the top Mechanical Boundary Condition. Our modelling results suggest that cold slabs under the present-day Eurasia, formed from the Mesozoic subduction and closure of the Tethys oceans, have prevented deep mantle hot materials from moving to the South China Sea from regions north or west of the South China Sea. From the east side, the Western Pacific subduction systems started to promote the formation of a lower-mantle thermal-chemical pile in the vicinity of the future South China Sea region since 70 Ma ago. As the top of this lower-mantle thermal-chemical pile rises, it first moved to the west, and finally rested beneath the South China Sea. The presence of a thermochemical layer (possible the D″ layer) in the model helps stabilizing the plume root. Our modelling is the first implementation of multi-scale mesh in the regional model. It has been proved to be an effective way of modelling regional dynamics within a global plate motion and mantle dynamics background.

  • Formation of mantle “lone plumes” in the global downwelling zone — A multiscale modelling of subduction-controlled plume generation beneath the South China Sea
    Tectonophysics, 2018
    Co-Authors: Nan Zhang
    Abstract:

    Abstract It has been established that almost all known mantle plumes since the Mesozoic formed above the two lower mantle large low shear velocity provinces (LLSVPs). The Hainan plume is one of the rare exceptions in that instead of rising above the LLSVPs, it is located within the broad global mantle downwelling zone, therefore classified as a “lone plume”. Here, we use the Hainan plume example to investigate the feasibility of such lone plumes being generated by subducting slabs in the mantle downwelling zone using 3D geodynamic modelling. Our geodynamic model has a high-resolution regional domain embedded in a relatively low resolution global domain, which is set up in an adaptive-mesh-refined, 3D mantle convection code ASPECT (Advanced Solver for Problems in Earth's ConvecTion). We use a recently published plate motion model to define the top Mechanical Boundary Condition. Our modelling results suggest that cold slabs under the present-day Eurasia, formed from the Mesozoic subduction and closure of the Tethys oceans, have prevented deep mantle hot materials from moving to the South China Sea from regions north or west of the South China Sea. From the east side, the Western Pacific subduction systems started to promote the formation of a lower-mantle thermal-chemical pile in the vicinity of the future South China Sea region since 70 Ma ago. As the top of this lower-mantle thermal-chemical pile rises, it first moved to the west, and finally rested beneath the South China Sea. The presence of a thermochemical layer (possible the D″ layer) in the model helps stabilizing the plume root. Our modelling is the first implementation of multi-scale mesh in the regional model. It has been proved to be an effective way of modelling regional dynamics within a global plate motion and mantle dynamics background.

Raj N. Singh - One of the best experts on this subject based on the ideXlab platform.

  • Effect of the Mechanical Boundary Condition at the crack surfaces on the stress distribution at the crack tip in piezoelectric materials
    Materials Science and Engineering: A, 1998
    Co-Authors: Susmit Kumar, Raj N. Singh
    Abstract:

    Abstract A finite element technique is used to study the stress distributions at the crack tip of a piezoelectric ceramic because of the combined Mechanical and electrical loads. For high electrical to Mechanical load ratios, the assumption of crack surfaces to be free of surface traction as the Mechanical Boundary Condition is not valid for two cases of combined electrical and Mechanical loadings—(i) applied stress and negative applied electric field (electric field opposite to the direction of poling) and (ii) applied strain and positive applied electric field. The stress distributions at the crack tip for these loading Conditions under the assumption of closed crack Mechanical Boundary Condition are found to be different from those under the assumption of crack surfaces to be free of surface traction.

  • Influence of applied electric field and Mechanical Boundary Condition on the stress distribution at the crack tip in piezoelectric materials
    Materials Science and Engineering: A, 1997
    Co-Authors: Susmit Kumar, Raj N. Singh
    Abstract:

    A finite element technique is used to study the stress distributions at the crack tip of a piezoelectric ceramic subject to the applied electric fields. Under a negative applied electric field (electric field opposite to the direction of poling), the assumption of crack surfaces to be free of surface traction as the Mechanical Boundary Condition is found to be invalid. It is shown that the stress distributions at the crack tip under the negative applied electric field are different for the closed crack Mechanical Boundary Condition than those for the traction-free crack surface Mechanical Boundary Condition.

  • Crack propagation in piezoelectric materials under combined Mechanical and electrical loadings: A finite element study
    1995
    Co-Authors: Susmit Kumar, Raj N. Singh
    Abstract:

    A finite element technique is used to study the stress distributions at the crack tip of a piezoelectric ceramic because of the Mechanical and/or electrical loads. The stress distribution at the crack tip is found to be in conformity with those predicted theoretically by Sosa and Pak. For combined Mechanical and electrical loads, the stress intensity factor at the crack tip is observed to increase with an increase in the electrical to Mechanical load ratio for a negatively applied electric field (electric field opposite to the direction of poling) which is in agreement with the experimental findings of Wang and Singh. For the positively applied field, compressive stresses are found to develop around the crack tip for high electrical to Mechanical load ratios. The effect of the Mechanical Boundary Condition at the crack surfaces on the stress distributions at the crack tip will be also discussed.

Howard Brenner - One of the best experts on this subject based on the ideXlab platform.

  • phoresis in fluids
    Physical Review E, 2011
    Co-Authors: Howard Brenner
    Abstract:

    : This paper presents a unified theory of phoretic phenomena in single-component fluids. Simple formulas are given for the phoretic velocities of small inert force-free non-Brownian particles migrating through otherwise quiescent single-component gases and liquids and animated by a gradient in the fluid's temperature (thermophoresis), pressure (barophoresis), density (pycnophoresis), or any combination thereof. The ansatz builds upon a recent paper [Phys. Rev. E 84, 046309 (2011)] concerned with slip of the fluid's mass velocity at solid surfaces--that is, with phenomena arising from violations of the classical no-slip fluid-Mechanical Boundary Condition. Experimental and other data are cited in support of the phoretic model developed herein.

  • Beyond the no-slip Boundary Condition.
    Physical review. E Statistical nonlinear and soft matter physics, 2011
    Co-Authors: Howard Brenner
    Abstract:

    This paper offers a simple macroscopic approach to the question of the slip Boundary Condition to be imposed upon the tangential component of the fluid velocity at a solid Boundary. Plausible reasons are advanced for believing that it is the energy equation rather than the momentum equation that determines the correct fluid-Mechanical Boundary Condition. The scheme resulting therefrom furnishes the following general, near-equilibrium linear constitutive relation for the slip velocity of mass along a relatively flat wall bounding a single-component gas or liquid: (v(m))(slip)=-α∂lnρ/∂s|(wall), where α and ρ are, respectively, the fluid's thermometric diffusivity and mass density, while the length δs refers to distance measured along the wall in the direction in which the slip or creep occurs. This constitutive relation is shown to agree with experimental data for gases and liquids undergoing thermal creep or pressure-driven viscous creep at solid surfaces.

Susmit Kumar - One of the best experts on this subject based on the ideXlab platform.

  • Effect of the Mechanical Boundary Condition at the crack surfaces on the stress distribution at the crack tip in piezoelectric materials
    Materials Science and Engineering: A, 1998
    Co-Authors: Susmit Kumar, Raj N. Singh
    Abstract:

    Abstract A finite element technique is used to study the stress distributions at the crack tip of a piezoelectric ceramic because of the combined Mechanical and electrical loads. For high electrical to Mechanical load ratios, the assumption of crack surfaces to be free of surface traction as the Mechanical Boundary Condition is not valid for two cases of combined electrical and Mechanical loadings—(i) applied stress and negative applied electric field (electric field opposite to the direction of poling) and (ii) applied strain and positive applied electric field. The stress distributions at the crack tip for these loading Conditions under the assumption of closed crack Mechanical Boundary Condition are found to be different from those under the assumption of crack surfaces to be free of surface traction.

  • Influence of applied electric field and Mechanical Boundary Condition on the stress distribution at the crack tip in piezoelectric materials
    Materials Science and Engineering: A, 1997
    Co-Authors: Susmit Kumar, Raj N. Singh
    Abstract:

    A finite element technique is used to study the stress distributions at the crack tip of a piezoelectric ceramic subject to the applied electric fields. Under a negative applied electric field (electric field opposite to the direction of poling), the assumption of crack surfaces to be free of surface traction as the Mechanical Boundary Condition is found to be invalid. It is shown that the stress distributions at the crack tip under the negative applied electric field are different for the closed crack Mechanical Boundary Condition than those for the traction-free crack surface Mechanical Boundary Condition.

  • Crack propagation in piezoelectric materials under combined Mechanical and electrical loadings: A finite element study
    1995
    Co-Authors: Susmit Kumar, Raj N. Singh
    Abstract:

    A finite element technique is used to study the stress distributions at the crack tip of a piezoelectric ceramic because of the Mechanical and/or electrical loads. The stress distribution at the crack tip is found to be in conformity with those predicted theoretically by Sosa and Pak. For combined Mechanical and electrical loads, the stress intensity factor at the crack tip is observed to increase with an increase in the electrical to Mechanical load ratio for a negatively applied electric field (electric field opposite to the direction of poling) which is in agreement with the experimental findings of Wang and Singh. For the positively applied field, compressive stresses are found to develop around the crack tip for high electrical to Mechanical load ratios. The effect of the Mechanical Boundary Condition at the crack surfaces on the stress distributions at the crack tip will be also discussed.

Reza Kolahchi - One of the best experts on this subject based on the ideXlab platform.

  • Nonlinear vibration of a nanobeam elastically bonded with a piezoelectric nanobeam via strain gradient theory
    International Journal of Mechanical Sciences, 2015
    Co-Authors: A. Ghorbanpour Arani, M. Abdollahian, Reza Kolahchi
    Abstract:

    Abstract Nonlinear vibration of a nanobeam (NB) coupled with a piezoelectric nanobeam (PNB) is investigated in this article based on the strain gradient theory. The two nanobeams are coupled by an enclosing elastic medium which is simulated as Pasternak foundation. The PNB is subjected to an external electric voltage in thickness direction and a uniform temperature change. Considering the Von-Karman geometric nonlinearity and charge equation for coupling of electrical and Mechanical fields, the motion equations are derived using strain gradient theory and Hamilton׳s principle. The differential quadrature method (DQM) is applied to obtain the nonlinear frequency of NB for clamped–clamped Mechanical Boundary Condition. Research results reveal that the dimensionless frequency of NB reduction results from increasing the external electric voltage. Furthermore, at higher values of small scale parameters, the difference between the results obtained by modified couple stress and strain gradient theories become considerable.

  • The effect of time-dependent creep on electro-thermo-Mechanical behaviors of piezoelectric sphere using Mendelson's method
    European Journal of Mechanics - A Solids, 2013
    Co-Authors: A. Ghorbanpour Arani, Reza Kolahchi, A.a. Mosallaie Barzoki, Abbas Loghman
    Abstract:

    Abstract This paper describes a numerical model which is used for the computation of stresses, electric potential and displacement histories in a hollow piezoelectric sphere subjected to an internal pressure and a distributed temperature field. The mentioned model is on the basis of the Mendelson's method which predicts the variation of the stresses, electric potential and displacement with time through the thickness. The creep constitutive model for the effective strain is on the basis of the Bailey–Norton's law. Since, creep strains are time, temperature and stress dependent, the closed form solution cannot be represented for this constitutive differential equation. Therefore, a semi-analytical method in conjunction with the method of successive approximation has been proposed for this analysis. The results indicate that in Mechanical Boundary Condition which the sphere acts as an actuator, the effect of time-dependent creep causes to change radial stresses from compressive to tensile after 15 years. Hence, the actuator is not usable after 15 years. It has been found that in electrical Boundary Condition which the sphere acts as a sensor, the radial stresses are compressive during the life of the sphere. This state is suitable, because the sensor can be used for long time.