Influence Of Geometrical Properties Research Articles

Numerical modeling of air ejectors covering supersonic, subsonic and closed-port operations

The physics and modeling of air ejectors in on- and off-design conditions have been extensively addressed in the past, reaching a good level of maturity. However, to achieve a robust model at system scale integrating an ejector, there is a need for developing 0D models suitable to tackle abnormal functioning modes, such as cases where the ejector works in subsonic conditions, reverse flows, or closed ports. Based on state-of-the-art models, a new 0D model has been built in the current work, where proper subroutine implementations allow covering normal and abnormal operations of convergent nozzle ejectors. The current research also focuses on understanding the physical behavior of air ejectors for aeronautical applications. In this regard, CFD-RANS simulations are used to perform model verification and calibration as well as to gain knowledge of the whole operational envelope. The regimes reproduced by the 0D model, and validated by CFD, cover the normal operating mode with different choking regimes, the occurrence of a subsonic primary flow, and the closed secondary port case. Additional cases are run to assess other features of the ejector behavior, such as the influence of geometrical properties on the choking mechanism and the impact of thermal effects.

An optimised and novel capacitance-based sensor design for measuring void fraction in gas–oil two-phase flow systems

ABSTRACT This study explores a new electrode configuration for measuring the void fraction of two-phase flows using capacitance-based sensors. The proposed method is considered ‘skewed’ because of its unique geometric shape, and the performance of the proposed sensor was evaluated and improved via multiple simulations using the COMSOL Multiphysics software. The simulations encompass three different flow patterns, stratified, annular and homogeneous, whose performance themselves were verified in a previous study. The influences of geometric properties and parameters on the sensitivity of the proposed sensor were evaluated to determine an optimal configuration. Furthermore, the sensitivity distribution on different void fractions of the sensor was analysed for various void fractions in different flow patterns. Additionally, the proposed configuration was also compared alongside double-ring and concave sensors to determine the overall sensitivity. At 2.11 pF, the overall sensitivity of the proposed sensor was significantly higher than that of the other sensors. It is worth mentioning that the measurement precision of multiphase flow meters is of high importance, particularly in petroleum industry because of the oil price and also the high amount of transported products.

In-plane modal studies of arbitrary laminated triangular plates with elastic boundary constraints by the Chebyshev-Ritz approach

Firstly, the Chebyshev-Ritz method is applied to the free in-plane vibration of arbitrary shaped laminated triangular plates with elastic boundary conditions. In order to facilitate the calculation of energy, the arbitrary shaped triangular laminated plate is mapped into a square plate by the coordinate transformation. The constitutive equation of laminated materials is constructed by the equivalent monolayer theory. The displacement functions of the square plate after transformation are generally expressed as two-dimensional Chebyshev polynomials multiplied by coefficients. By means of artificial virtual spring technology, the arbitrary elastic boundary conditions of the plate can be obtained by changing the stiffness values of each spring. The in-plane free vibration characteristics of the triangular laminated plate under different boundary conditions are calculated and the accuracy of this method is verified by comparing with finite element results and experimental results. In this paper, modal experiments of three different triangular plates with free boundary and cantilever support boundary are carried out. The comparison results show that the present method has good convergence, high efficiency and satisfactory actuarial accuracy. Finally, novelty numerical analysis is carried out, the influence of geometrical properties, material parameters and boundary conditions on in-plane modal characteristics of laminated triangular plates are studied in detail.

The Influence of the Geometrical Properties of Bulk Superconductors on Limiting Fault Current in an Electrical Network

The behavior of the superconducting fault current limiters SFCL used in Electrical Network is largely determined by the geometry properties and the type of the bulk superconductors used. In this work we present a numerical analysis of the electromagnetic and the thermal behavior of the SFCL and the influence of geometrical properties of the bulk superconductors of rectangular shape used in an electrical network The results are obtained from a three-dimensional computation code, developed and implemented under MATLAB environment where the formulation in magnetic vector potentials A and electrical scalar potential V are adopted to solve the electromagnetic problem and the heat diffusion formulation is also adopted to solve the thermal problem. The coupling is ensured by an alternating algorithm and the numerical resolution of the problem is ensured by the method of the finite volumes in its three-dimensional version in order to avoid certain problems of numerical convergence linked to the strongly nonlinear character of the problem to be solved.

NUMERICAL MODELLING OF WAVE SHAPES DURING SHPB MEASUREMENT

The paper aims at the numerical simulation of the wave propagation in compressive Split Hopkinson Pressure Bar (SHPB) experiment. The paper deals with principles of SHPB measurement, optimisation of a numerical model and techniques of pulse shaping. The parametric model of the typical SHPB configuration developed for LS-DYNA environment is introduced and optimised (in terms of element size and distribution) using the sensitivity study. Then, a parametric analysis of a geometric properties of the pulse shaper is carried out to reveal their influence on a shape of the incident pulse. The analysis is algorithmized including the pre- and post-processing routines to enable automated processing of numerical results and comparison with the experimental data. Results of the parametric analysis and the influence of geometric properties of the pulse shaper (diameter, length) on the incident wave are demonstrated.

Elastoplastic postbuckling analysis of moderately thick rectangular plates using the variational differential quadrature method

In this research, the elastoplastic postbuckling response of moderately thick rectangular plates subjected to in-plane loadings is analyzed by a novel numerical approach. The influence of transverse shear deformation is taken into account via the first-order shear deformation theory (FSDT). Also, the elastoplastic behavior is captured based on two theories of plasticity including the incremental theory (IT) (with the Prandtl-Reuss constitutive relations) and the deformation theory (DT) (with the Hencky constitutive relation). Moreover, it is assumed that the material of plate obeys the Ramberg-Osgood (RO) elastoplastic stress-strain relation. First, the matrix formulations of strain rates and constitutive relations are derived. In the next step, according to Hamilton's principle, the weak form of governing equations is derived which is then directly discretized using the variational differential quadrature (VDQ) technique. The discretization process is performed by accurate matrix derivative and integral operators of VDQ. Plates with various boundary conditions under uniaxial and equibiaxial compressions are considered. It is first indicated that the present results are in excellent agreement with the analytical solutions existing in the open literature. Thereafter, the influences of geometrical properties, boundary conditions, elastic modulus-to-nominal yield stress ratio and value of power c in the RO relation on the elastoplastic postbuckling paths of plates are studied. Furthermore, several comparisons are made between the predictions of IT and DT.

Effects of geometric parameters on the performance of solar chimney power plants

In this study, the influences of geometrical properties on a solar chimney were investigated numerically by applying the κ−ε turbulence model, continuity, momentum, and energy equations in the 3D finite volume approach inside a solar chimney power plant. The following variables should be involved: collector radius (Rcl), collector height (Hcl), chimney height (Hch), chimney radius (Rch), and heat flux (q″). The effects of changes in these variables on temperature, velocity, pressure distributions, efficiency, and output power were investigated. The results indicated that output power and solar chimney efficiency have positive relationships with chimney height and collector radius but a negative one with collector height. In addition, it was found that the parameter of chimney radius has an optimum range which has the maximum values for efficiency and output power.

Friction Coefficient and Mobility Radius of Fractal-Like Aggregates in the Transition Regime

The influence of geometric properties and particle size on mobility properties of fractal-like aggregates was studied in the mass and momentum-transfer transition regimes. Two methodologies were investigated. The Collision Rate Method (CRM) that determines the slip correction factor through the ratio of two fictitious Brownian particle-aggregate effective collision rates, and the Adjusted Sphere Method (ASM) that assumes the existence of a virtual, flow-independent adjusted sphere with the same slip correction factor as the aggregate over the entire transition regime. The simulated fractal-like aggregates were synthetic as they were generated via a cluster–cluster agglomeration algorithm. The CRM was used to calculate the adjusted-sphere radius of various aggregates: we found it to be weakly dependent on the monomer Knudsen number for Kn greater than 0.5. Numerical expressions for the aggregate orientationally-averaged projected area and the adjusted-sphere radius are proposed. Both expressions depend on ...

Hygrothermal effects in composites: Influence of geometry and determination of transverse coefficient of thermal expansion

This work evaluates the influence of geometric properties, the length-to-width ratio, named Aspect Ratio, on curvatures in [θ − 90/θ]T carbon/epoxy composite laminates at room temperature due to thermal residual stresses. A new method to determine experimentally thermal residual curvatures in composites laminates by defining small-length increments on the surface of deformed plate has been exposed. [–454/454]T was considered to obtain a simple analytical expression of twisting curvature. A new way to determine transverse coefficient of thermal expansion α2 is proposed in squared laminates based on experimental values of twisting curvatures of [–454/454]T laminates.

The influence of geometrical features on rewetting behaviour of cylindrical components

During immersion quenching the transition from film to nucleate boiling - the rewetting of the sample surface - is a complex process which leads to extreme local changes of the heat transfer coefficient. The start of the rewetting process depends on specific geometrical features like edges, boreholes, couplings, etc. From these starting points the rewetting front moves forward. The present paper investigates the influence of geometrical properties on the starting of rewetting and the movement of the rewetting front across the work piece. Cylinders made out of stainless steel with different edge shapes, lengths, and diameters will be considered. The edge configuration varies in a few steps from chamfered edges to spherical formed edges. The quenching was done with high speed oil (Isorapid 277®). The aim of the paper is the gathering of information of the local and time dependent HTC necessary for heat treatment simulations.

Free vibrations of rotating composite conical shells with stringer and ring stiffeners

In this paper, an analytical solution for the free vibration of rotating composite conical shells with axial stiffeners (stringers) and circumferential stiffener (rings), is presented using an energy-based approach. Ritz method is applied while stiffeners are treated as discrete elements. The conical shells are stiffened with uniform interval and it is assumed that the stiffeners have the same material and geometric properties. The study includes the effects of the coriolis and centrifugal accelerations, and the initial hoop tension. The results obtained include the relationship between frequency parameter and circumferential wave number as well as rotating speed at various angles. Influences of geometric properties on the frequency parameter are also discussed. In order to validate the present analysis, it is compared with other published works for a non-stiffened conical shell; other comparison is made in the special case where the angle of the stiffened conical shell goes to zero, i.e., stiffened cylindrical shell. Good agreement is observed and a new range of results is presented for rotating stiffened conical shells which can be used as a benchmark to approximate solutions.

The Maximum Levitation Force of High-T c Superconductors

In this paper we present the dependence of the maximum levitation force (F max ) of a high-T c superconductor (HTS) on the structural factors of high-T c superconducting systems based on the Bean critical state model and Ampere’s law. A transition point of the surface magnetic field (B s ) of a permanent magnet (PM) is found at which the relation between F max and B s changes: while the surface magnetic field is less than the transition value the dependence is subject to a nonlinear function, otherwise it is a linear one. The two different relations are estimated to correspond to partial penetration of the shielding currents inside the superconductor below the transition point and complete penetration above it respectively. The influence of geometric properties of superconductors on the dependence is also investigated. In addition, the relation between F max and the critical current density (J c ) of the HTS is discussed. The maximum levitation force saturates at high J c . An optimum function of the J c and the B s is presented in order to achieve large F max .

Influence of geometrical properties on light emission of ZnO nanowires

The present paper deals with the preparation and study of optical properties of ZnO nanowires. Nanoporous ion track polycarbonate foils were used as templates for ZnO nanowires growth by electrochemical deposition. The growth was performed using an aqueous electrochemical bath at a temperature of 70°C. SEM and TEM were employed to study the morphological properties of the nanowires. Electron diffraction was employed for structural characterization. Reflection and photoluminescence spectroscopy were used for optical characterization. A comparison between the properties of electrodeposited thin films and nanowires of ZnO was made from the point of view of photoluminescence properties.

Design and analysis of a double superimposed chamber valveless MEMS micropump

The newly designed micropump model proposed consists of a valveless double chamber pump completely simulated and optimized for drug delivery conditions. First, the inertia force and viscous loss in relation to actuation, pressure, and frequency is considered, and then a model of the nozzle/diffuser elements is introduced. The value of the flowrate obtained from the first model is then used to determine the loss coefficients starting from geometrical properties and flow velocity. From the developed model IT analysis is performed to predict the micropump performance based on the actuation parameters and no energy loss. A single-chamber pump with geometrical dimensions equal to each of the chambers of the double-chamber pump was also developed, and the results from both models are then compared for equally applied actuation pressure and frequency. Results show that the proposed design gives a maximum flow working frequency that is about 30 per cent lower than the single chamber design, with a maximum flowrate that is 140 per cent greater than that of the single chamber. Finally, the influences of geometrical properties on flowrate, maximum flow frequency, loss coefficients, and membrane strain are examined. The results show that the nozzle/ diffuser initial width and chamber side length are the most critical dimensions of the design.

Nonlinear Static Response and Free Vibration Analysis of Doubly Curved Cross-Ply Panels

In this paper, the nonlinear static and free vibration analyses of doubly curved cross-ply laminated panels subjected to thermomechanical loading are examined. The shell theory adopted in the present case is an extension of Reissner’s shallow shell simplifications that accounts for parabolic distribution of the transverse shear strains through thickness of the shell and tangential stress-free boundary conditions. A multiterm Galerkin’s method is adopted to solve the governing nonlinear partial differential equations. The static equilibrium paths are traced using the Newton-Raphson method in conjunction with the Riks approach to overcome the limit points. The free vibration frequencies about a static equilibrium state of a deformed panel are reported by solving the linear eigenvalue problem. Analytical results are presented for symmetric [0/90/0] and antisymmetric [0/90] cross-ply laminated doubly curved panels that illustrate the influence of geometric properties, in-plane edge boundary conditions, latera...

Additional Smoothness Phenomena for Analytic Functions

We study the influence of geometric properties of a domain on the smoothness of Holder class analytic functions defined on it. The case of the disk is covered by the classical results of Hardy and Littlewood. We consider a domain G with an inward cusp boundary point ξ)(this means that meas \(U_\xi \cap ({\mathbb{C}}\backslash G)\)/ meas \(U_\xi \to 0\) as meas\(U_\xi \to 0\), whereUξ is a neighborhood of ξ). Three zones are distinguished near such a point: the outer zone, where high smoothness occurs, the boundary zone, where the smoothness is “standard,” and the intermediate zone, where the smoothness decays steadily from high to standard one. A sharp geometric description of these zones is given. Bibliography: 7 titles.

Cracking analysis of fibre-reinforced polymer-reinforced concrete tension members

The paper is devoted to the analysis of crack evolution of fibre-reinforced polymers (FRP) reinforced concrete tension members and, as a consequence, their deformability in terms of load-elongation relationships. Such analysis permits the determination of tension stiffening effects. The stiffness of the reinforced tension members, in fact, can be evaluated and compared to rebars whilst the scatter gives a measure of the reduced deformability due to the contribution of the tensile concrete. Results of an experimental investigation, carried out on cylindrical concrete specimens in order to analyse the influence of geometrical properties on cracking and deformability of the members, are reported in the paper. Comparisons with results obtained from a theoretical analysis and from code relationships are also made, aiming to give useful information from a design point of view.

Magnetic Susceptibility in the Vertebral Column

A magnetic resonance method is described which provides good-quality field-mapping images of the spine, although the in vivo signals from red bone marrow of the vertebral bodies exhibit similar fractions of lipid and water protons with their chemical-shift difference of 3.4 ppm. The susceptibilities of bone marrow and intervertebral disks were examined in 20 cadaveric human spines, 9 healthy volunteers, and 9 patients with degenerative disk alterations. The influence of geometrical properties was studied in cylindrical spine phantoms of different size and contents with different susceptibility. The measurements reveal interindividual differences of the susceptibility of the intervertebral disks in healthy subjects. Three out of nine degenerated disks with low signal in T2-weighted spin-echo images showed irregularities of the field distribution within the nucleus pulposus.

Gruppen mit geometrischen Abschnitten im Untergruppenverband

Our aim is to analyse the influence of geometric properties which are valid in a section of the lattice of subgroups of an (abstract or topological) group on the structure of the group itself and to test thereby the applicability of genuine methods of synthetic geometry for algebraic purposes.

Influence of geometric properties of space on the convergence of Cauchy's method in the best-approximation problem

The reciprocity of certain geometrical properties of finite-dimensional Banach space is established. The role of these properties in the construction of best-approximation elements by Cauchy's method is investigated.