3D Cavity Research Articles

A 3D thermal LB model on non-orthogonal grid and its application for natural convection in irregular domains

In this paper, a 3D thermal LB model on non-orthogonal grid is derived, as well as the corresponding boundary treatment method for irregular boundary. Numerical validation is then performed by modeling natural convection in a 3D annulus. It is proved that the thermal flow structure in the annulus is accurately predicted with less grids. After that, present method is applied to study natural convection in a 3D cavity with inclined side walls. Two opposite inclined walls on the left and right sides are kept at different constant temperatures, while the remained four walls of the cavity are either adiabatic (Type 1) or own linear temperature variations (Type 2). It is found out that natural convection in the inclined cavity exhibits distinct 3D features under Type 2 thermal boundary setting, yet it can be viewed as a 2D process under Type 1 condition. Moreover, a large Prandtl number (Pr = 10.0) can generally suppress the 3D effect stemmed from thermal boundary setting. The aforementioned results indicate that present model and boundary treatment method are reliable to deal with 3D natural convection in irregular domains.

A Three-Dimensional Linear-to-Circular Polarization Converter Tailored by the Gravity Field

In this paper, a three-dimensional (3D) linear-to-circular polarization converter (LCPC), innovatively tailored by the gravity field through the fluidity of liquid metal mercury (Hg), is designed and studied. The proposed LCPC is composed of a 3D glass cavity filled with Hg, a copper reflector, a trenched dielectric layer, and a copper patch. Due to the specially designed 3D glass cavity, Hg will flow in different parts of the glass cavity to form different resonant structures by means of rotation under the action of the gravity field. When the proposed LCPC is not rotated (is placed parallel to the xoy plane), the axial ratio band which is less than 3 dB (3-dB AR band) is obtained in the band of 32.42–42.82 GHz (the relative bandwidth is 27.64%). And when such a LCPC is rotated (is placed perpendicular to the xoy plane), the 3-dB AR band shifts to 18.88–32.86 GHz (the relative bandwidth is 54.04%). Besides, the surface current diagrams are investigated to explain the physics mechanism of the proposed LCPC, and relevant parameters are also discussed. In our design, the proposed LCPC has the advantages of wideband, tunable characteristics, and easy adjustment. In addition, it provides an innovative design idea of LCPC to promote potential applications of tunable devices.

High-Temperature Upconverted Single-Mode Lasing in 3D Fully Inorganic Perovskite Microcubic Cavity

Perovskite is an excellent gain medium with tightly confined sub-micrometer cavity structure, but the stability is a great challenge for perovskite microcavity lasers. At present, almost all perovskite microcavity lasers are operated at room or low temperature. Achieving high-temperature lasing emission, especially single-mode lasing, is quite difficult. In this paper, on the basis of the 3D CsPbBr3 microcubic cavity with high crystal quality, low threshold, and great light confinement, we first improve the operational temperature to 440 K in a perovskite material system. Upconverted single-mode lasing with stable output and high quality can be obtained. The improved operational temperature tolerance of the CsPbBr3 microcubic cavity makes a step toward integrated high power density optoelectronic devices and further electrically driven lasers. In addition, by the finite element method, the mode distributions of such a 3D CsPbBr3 microcubic cavity are analyzed systematically and clearly physical diagrams o...

MHD mixed convection of nanofluid in a three-dimensional vented cavity with surface corrugation and inner rotating cylinder

PurposeThis study aims to numerically examine mixed convection of CuO-water nanofluid in a three-dimensional (3D) vented cavity with inlet and outlet ports under the influence of an inner rotating circular cylinder, homogeneous magnetic field and surface corrugation effects. In practical applications, it is possible to encounter some of the considered configurations in a vented cavity such as magnetic field, rotating cylinder and it is also possible to specially add some of the active and passive control means to control the convection inside the cavity such as adding nanoparticles, corrugating the surfaces. The complicated physics with nanofluid under the effects of magnetic field and inclusion of complex 3D geometry make it possible to use the results of this numerical investigation for the design, control and optimization of many thermal engineering systems as mentioned above.Design/methodology/approachThe bottom surface is corrugated with a rectangular wave shape, and the rotating cylinder surface and cavity bottom surface were kept at constant hot temperatures while the cold fluid enters the inlet port with uniform velocity. The complicated interaction between the forced convection and buoyancy-driven convection coupled with corrugated and rotating surfaces in 3D configuration with magnetic field, which covers a wide range of thermal engineering applications, are numerically simulated with finite element method. Effects of various pertinent parameters such as Richardson number (between 0.01 and 100), Hartmann number (between 0 and 1,000), angular rotational speed of the cylinder (between −30 and 30), solid nanoparticle volume fraction (between 0 and 0.04), corrugation height (between 0 and 0.18H) and number (between 1 and 20) on the convective heat transfer performance are numerically analyzed.FindingsIt was observed that the magnetic field suppresses the recirculation zone obtained in the lower part of the inlet port and enhances the average heat transfer rate, which is 10.77 per cent for water and 6.86 per cent for nanofluid at the highest strength. Due to the thermal and electrical conductivity enhancement of nanofluid, there is 5 per cent discrepancy in the Nusselt number augmentation with the nanoadditive inclusion in the absence and presence of magnetic field. The average heat transfer rate of the corrugated surface enhances by about 9.5 per cent for counter-clockwise rotation at angular rotational speed of 30 rad/s as compared to motionless cylinder case. Convective heat transfer characteristics are influenced by introducing the corrugation waves. As compared to number of waves, the height of the corrugation has a slight effect on the heat transfer variation. When the number of rectangular waves increases from N = 1 to N = 20, approximately 59 per cent of the average heat transfer reduction is achieved.Originality/valueIn this study, mixed convection of CuO-water nanofluid in a 3D vented cavity with inlet and outlet ports is numerically examined under the influence of an inner rotating circular cylinder, homogeneous magnetic field and surface corrugation effects. To the best of authors knowledge such a study has never been performed. In practical applications, it is possible to encounter some of the considered configurations in a vented cavity such as magnetic field, rotating cylinder and it is also possible to specially add some of the active and passive control means to control the convection inside the cavity such as adding nanoparticles, corrugating the surfaces. The complicated physics with nanofluid under the effects of magnetic field and inclusion of complex 3D geometry make it possible to use the results of this numerical investigation for the design, control and optimization of many thermal engineering systems as mentioned above.

Experimental studies in finite element model updating of vibro-acoustic cavities using coupled modal data and FRFs

The NVH design of cavities in aircraft, cars and other transportation equipment are mainly based on use of vibro-acoustic FE models to analyze low frequency structural vibration and interior noise. In order to improve the accuracy and reliability of these vibro-acoustic models, uncertainties associated with modeling of boundary conditions, joints, damping and acoustic absorption properties of cavity surfaces in acoustic domain, must be taken into account. Finite element (FE) model updating is now recognized as an effective approach to reduce modeling inaccuracies present in an FE model. This paper presents experimental studies in updating of FE model of vibro-acoustic cavity. Two experimental studies are presented. The first experimental study is about updating of structural FE model of the cavity incorporating acoustic loading using modal data based on an inverse eigen-sensitivity approach. The second study involves updating of structural and acoustic parameters of the vibro-acoustic model using frequency response functions based on a constrained optimization based approach. Thus, FE model and experimental coupled modal data and FRF data are integrated to obtain a more accurate vibro-acoustic model. Experimental example of a 3D rectangular-box cavity with a flexible plate is presented. The studies demonstrate that the improvement of the vibro-acoustic FE models through FE model updating can be an effective approach to obtain more accurate vibro-acoustic predictions.

Prediction and parametric analysis of cavity growth for the underground coal gasification project Thar

Underground coal gasification (UCG) is a promising clean coal technology to convert unmineable and deep coal reserves into syngas, which can be used in many industrial applications. In UCG field, real time monitoring of hydrological and geological conditions such as water influx rate, cavity growth and its interaction with overburden is a formidable task. UCG project Thar (UPT) lacks real time data acquisition system to monitor these parameters. In this work, a 3D axisymmetric cavity simulation model (CAVSIM) is parameterized with operating conditions of UPT and properties of Lignite B coal of Thar coal fields. For model validation, a comparison has been made between simulated and the UPT field data for the composition and heating value of syngas. The results of CAVSIM are also compared with our previous ID packed bed model, which show the superiority of CAVSIM model. Moreover, a comprehensive simulation study has been carried out to predict the cavity growth and its interaction with overburden. The effect of operating parameters of UPT on volumetric cavity growth and heating value of syngas are also investigated.

3D-FEM simulation model of the Earth-ionosphere cavity

ABSTRACTRadio waves of extremely low frequencies (5–40 Hz) propagate in a special way. Since their wavelengths correspond to the Earth's radius, global resonances are found inside the cavity bounded by the Earth’s surface and the lower ionosphere. These so-called Schumann resonances form a system of standing waves around the planet. They can be a powerful tool for investigating the electrical processes occurring in the lower ionosphere. This paper describes finite element method (FEM) simulations in the frequency domain of Schumann eigenmodes in 3D inhomogeneous Earth-ionosphere cavity. Such an approach provides result independence from source configuration and allows to separate ionosphere configuration influence on Schumann resonances. Also the approach visually reproduces line splitting in the global resonances. The ionosphere was modeled by a simple conventional vertical conductivity profile and by means of a complex 22-species plasmachemical model. Obtained simulation results are compared with the experiment and discussed.

Escape of a Driven Quantum Josephson Circuit into Unconfined States

Josephson circuits have been ideal systems to study complex non-linear dynamics which can lead to chaotic behavior and instabilities. More recently, Josephson circuits in the quantum regime, particularly in the presence of microwave drives, have demonstrated their ability to emulate a variety of Hamiltonians that are useful for the processing of quantum information. In this paper we show that these drives lead to an instability which results in the escape of the circuit mode into states that are not confined by the Josephson cosine potential. We observe this escape in a ubiquitous circuit: a transmon embedded in a 3D cavity. When the transmon occupies these free-particle-like states, the circuit behaves as though the junction had been removed, and all non-linearities are lost. This work deepens our understanding of strongly driven Josephson circuits, which is important for fundamental and application perspectives, such as the engineering of Hamiltonians by parametric pumping.

MHD mixed convection of nanofluid due to an inner rotating cylinder in a 3D enclosure with a phase change material

PurposeThe purpose of this study is to numerically examine the mixed convection of CuO-water nanofluid due to a rotating inner hot circular cylinder in a 3D cubic enclosure with phase change material (PCM) attached to its vertical surface. Heat transfer and fluid flow characteristics were examined for various values of pertinent parameters.Design/methodology/approachFinite element method was used in the numerical simulation. Influence of various pertinent parameters such as Rayleigh number (between 10$^5$ and 10$^6$), Hartmann number (between 0 and 100), angular rotational speed of the cylinder (between −50 and 50), solid nanoparticle volume fraction (between 0 and 0.04) and PCM parameters (height-between 0.2H and 0.8H, thermal conductivity ratio- between 0.1 and 10) on the convective heat transfer characteristics are numerically studied.FindingsIt was observed that local heat transfer variations along the hot surface differ significantly for the cases with and without magnetic field where three distinct hot spots of peak Nusselt number are established when magnetic field is imposed. The average Nusselt number enhancement with the nanofluid at the highest particle volume fraction is 52.85 per cent at Hartmann number of 100, whereas its value is 39.76 per cent for the case in the absence of magnetic field. When the inner cylinder rotates, flow and thermal fields are affected within the cavity. The local heat transfer variations spread over the hot surface with cylinder rotation and 16.43 per cent of reduction in the average heat transfer is obtained with counter-clockwise rotation at 100 rad/sec. An enhancement in the PCM height and a reduction in the thermal conductivity of the PCM result in average heat transfer deterioration for the 3D cavity. The amount of the reduction is 43 per cent when the PCM height is increased from 0.2H to 0.8H, whereas 19.10 per cent enhancement in the heat transfer is achieved when thermal conductivity ratio (PCM) to the base fluid is increased from 0.1 to 10.Originality/valueSuch configurations can be designed for convection control, and in our case, various methods are available. Some of the investigated methods can be used in applications where magnetic field already exists. Convection control study in 3D cavity gives more realistic results as compared to 2D configurations, and results of the current investigation may be used for the design, optimization and flow control of many thermal applications involving magnetic field effects.

NUMERICAL SIMULATION OF NATURAL CONVECTION MELTING IN 2D AND 3D ENCLOSURES

Natural convection melting in 2D and 3D enclosures with a local heater is studied numerically. The present research is related to a development of effective cooling system for the electronic devices using the phase change material that is essentially important nowadays. The domain of interest includes vertical cold walls, adiabatic horizontal walls and a discrete heater of constant high temperature located on the bottom adiabatic wall. The cavity is filled with a phase change material (PCM) in solid state at the beginning of the process. During the heating from the heat source PCM is melting. Numerical solution of the present problem has been conducted using the dimensionless transformed variables such as stream function and vorticity for 2D cavity and vector potential functions and vorticity vector for 3D cavity with appropriate initial and boundary conditions. The developed numerical technique has been verified comprehensively. Obtained results have shown a potential of the used methods for 2D and 3D problems. It has been found that, melting process is more intensive in 3D case and the heat transfer rate at the heater is greater for 2D in comparison with 3D data.

Oscillatory rarefied gas flow inside a three dimensional rectangular cavity

The oscillatory rarefied gas flow in a three-dimensional (3D) rectangular cavity, which is frequently encountered in micro-electro-mechanical systems, is investigated on the basis of the gas kinetic theory. The effects of the cavity aspect ratio, the cavity depth ratio, and the oscillation frequency of the driving lid on flow characteristics and damping force are systematically studied using the discrete unified gas-kinetic scheme over a broad range of gas rarefactions. For the highly rarefied flow, when the lid oscillates at a low frequency, as a consequence of the strong rarefaction effect, the damping force on the lid in a 3D cavity could even be smaller than that of a corresponding 2D one (i.e., the depth in the lateral direction approaching infinity). This finding contradicts our intuitive understanding that the damping force is expected to be amplified due to the presence of the lateral walls. Meanwhile, when the lid oscillation frequency becomes sufficiently high, due to the effect of gas anti-resonance, the damping force on the oscillating lid will increase again as the depth reduces for the highly rarefied flow. In addition, the gas resonance and anti-resonance found inside the 2D cavity also appear in 3D ones, and the anti-resonance and resonance frequencies as a function of the cavity aspect ratio are nearly the same. However, the presence of the lateral walls will suppress their formation: the smaller the depth, the weaker the intensity of the (anti-)resonance. These findings can help to design the structure of the micro-electro-mechanical devices.

Superconducting circuit quantum computing with nanomechanical resonators as storage

We analyze the quantum information processing capability of a superconducting transmon circuit used to mediate interactions between quantum information stored in a collection of phononic crystal cavity resonators. Having only a single processing element to be controlled externally makes this approach significantly less hardware-intensive than traditional architectures with individual control of each qubit. Moreover, when compared with the commonly considered alternative approach using coplanar waveguide or 3d cavity microwave resonators for storage, the nanomechanical resonators offer both very long lifetime and small size—two conflicting requirements for microwave resonators. A detailed gate error analysis leads to an optimal value for the qubit-resonator coupling rate as a function of the number of mechanical resonators in the system. For a given set of system parameters, a specific amount of coupling and number of resonators is found to optimize the quantum volume, an approximate measure for the computational capacity of a system. We see this volume is higher in the proposed hybrid nanomechanical architecture than in the competing on-chip electromagnetic approach.

Low-Cost and Lightweight 3D-Printed Split-Ring Resonator for Chemical Sensing Applications.

In this paper, a microwave cavity resonator is presented for chemical sensing applications. The proposed resonator is comprised of a three dimensional (3D) split-ring resonator (SRR) residing in an external cavity and capacitively coupled by a pair of coaxial probes. 3D-printing technology with polylactic acid (PLA) filament is used to build the 3D SRR and cavity. Then, the surfaces of the SRR and the inside walls of cavity are silver-coated. The novelty of our proposed structure is its light weight and inexpensive design, owing to the utilization of low density and low-cost PLA. A Teflon tube is passed through the split-gap of the SRR so that it is parallel to the applied electric field. With an empty tube, the resonance frequency of the structure is measured at 2.56 GHz with an insertion loss of 13.6 dB and quality factor (Q) of 75. A frequency shift of 205 MHz with respect to the empty channel was measured when deionized water (DIW) was injected into the tube. Using volume occupied by the structure, the weight of the proposed microwave resonator is estimated as 22.8 g which is significantly lighter than any metallic structure of comparable size.

Condition number analysis of flow fields arising from CFD simulations

Condition numbers of pressure and velocity matrices obtained from an unstructured finite volume discretization of the three dimensional Navier–Stokes equations are studied for two distinct flow configurations. The exact condition number is calculated based on singular values. The continuous estimation of condition number of the velocity matrices with respect to the time varying velocity field is achieved through the Gershgorin theoretical bounds for the eigenvalues. The focus of the present study is on the analysis of flow dynamics with respect to the degree of ill-conditioning of the linear systems. For the two benchmark problems, condition numbers of pressure and velocity matrices are presented. The pressure matrix is shown to be more ill-conditioned than velocity and requires strong preconditioning. For a 3D lid-driven cavity, the appearance and disappearance of corner vortices at higher Reynolds number is clearly reflected in the condition number variation with time. In a second application of flow past a circular cylinder, condition number variation with time during the initial phase clearly reveals the onset of vortex shedding. The condition number based on Gershgorin bounds is also used to switch the SGS and ILU preconditioners for velocity matrices when they are well conditioned. Consequently, an overall reduction in the simulation time is demonstrated.

Absorption Performance of an Anechoic Layer with a Steel Plate Backing at Oblique Incidence

The sound absorption of steel-plate-backed anechoic coatings at oblique incidence is investigated theoretically and numerically. An analytical expression for the absorption coefficient is derived using elasticity theory. A 2D numerical periodic model suitable for inhomogeneous coatings under oblique incidence is built using the finite-element method. To interpret the absorption mechanism, the dispersion curves for guided elastic waves in a uniform coating and a steel plate are calculated using the spectral method. The absorption coefficients are analyzed with respect to the incident angle and frequency using elastic plate resonance theory. The effects of the steel plate backing and the attenuation of the coating are investigated. For the Alberich anechoic coating with a steel plate backing, the absorption coefficients are calculated numerically, and the absorption mechanism is investigated by structural displacement vectors and deformations. The following absorption characteristics can be found. In the frequency-angle spectra for absorption coefficients, the bright areas resulting from low-order Lamb waves in the coating are recognizable at low frequencies. A broad, strong anechoic area appears at large incident angles and low frequencies; under these conditions, the displacements of the steel plate and the 2D cavity are the main components of structural vibration. The resonance moves to low frequency when the thickness of the steel plate is incorporated and the cavity height is increased. At relatively high frequencies, some new absorption areas result from the resonance of periodic cavities and cover the contribution from the high-order Lamb waves in the coating caused by attenuation. The corresponding absorption coefficients decrease with an increasing angle of incidence.

Experimental Research on Machining Localization and Surface Quality in Micro Electrochemical Milling of Nickel-Based Superalloy.

Micro electrochemical machining is becoming increasingly important in the microfabrication of metal parts. In this paper, the machining characteristics of micro electrochemical milling with nanosecond pulse were studied. Firstly, a mathematical model for the localization control of micro electrochemical milling with nanosecond pulse was established. Secondly, groups of experiments were conducted on nickel-based superalloy and the effects of parameters such as applied voltage, pulse on time, pulse period, electrolyte concentration and electrode diameter on machining localization and surface roughness were analyzed. Finally, by using the optimized machining parameters, some 2D complex shapes and 3D square cavity structures with good shape precision and good surface quality were successfully obtained. It was proved that the micro electrochemical milling with nanosecond pulse technique is an effective machining method to fabricate metal microstructures.

Room Temperature Coherently Coupled Exciton-Polaritons in Two-Dimensional Organic-Inorganic Perovskite.

Two-dimensional (2D) organic-inorganic perovskite semiconductors with natural multiquantum well structures and confined 2D excitons are intriguing for the study of strong exciton-photon coupling, due to their large exciton binding energy and oscillation strength. This strong coupling leads to a formation of the half-light half-matter bosonic quasiparticle called exciton-polariton, consisting of a linear superposition state between photonic and excitonic states. Here, we demonstrate room temperature strong coupling in exfoliated wavelength-tunable 2D organic-inorganic perovskite semiconductors embedded into a planar microcavity, exhibiting large energetic splitting-to-line width ratios (>34.2). Angular-dependent spectroscopy measurements reveal that hybridized polariton states act as an ultrafast and reversible energy oscillation, involving 2D perovskite exciton, cavity modes (CM), and Bragg modes of the distributed Bragg reflector. Meanwhile, sizable hybrid particles dominantly couple to the measured optical field through the CMs. Our findings advocate a considerable promise of 2D organic-inorganic perovskite to explore fundamental quantum phenomena such as Bose-Einstein condensation, superfluidity, and exciton-polariton networks.

Flow and heat transfer characteristics of an open cubic cavity with different inclinations

Natural convection of air in an inclined differentially heated open cubic cavity is studied. From the literature, it can be seen that there is no definite relationship between the Nusselt numbers obtained for square and cubic cavities for different Rayleigh numbers (Ra) and cavity inclinations. For some combinations of Ra and cavity inclinations, the Nusselt numbers are significantly lower in the cubic cavity compared to that of the square cavity, while for other combinations, it is quite the opposite. To understand the cause of these variations, a detailed study of the flow patterns is carried out for different Ra and cavity inclination angles. It is seen that for a lower range of Ra, the finiteness of the cavity reduces the flow, resulting in lower heat transfer for the 3D cavity when compared to the 2D cavity. Similar results are seen for larger inclination angles of the cavity (hot wall close to the vertical) even for higher Ra. However, for the cases with higher Ra and small inclination angles (hot wall close to the horizontal), the flow becomes three-dimensional. The three-dimensionality in the flow is attributed to the weak convection currents that rise from the side adiabatic walls and go down from the center of the cavity. The combination of these convection currents with the predominantly strong convection currents, which are going up from the hot wall, results in the complex three dimensional flow patterns. Due to this phenomenon, the cubic cavity with such a configuration has significantly higher Nusselt number compared to that of the square cavity.

Construction of two-qubit logical gates by transmon qubits in a three-dimensional cavity**Project supported by the National Basic Research and Development Program of China (Grant No. 2011CBA00304), the National Natural Science Foundation of China (Grant Nos. 60836001 and 61174084), and the Tsinghua University Initiative Scientific Research Program, China (Grant No. 20131089314).

We report the implementation of qubit–qubit coupling in a three-dimensional (3D) cavity, using the exchange of virtual photons, to realize logical operations. We measure single photon and multi-photon transitions in this qubit–qubit coupling system and obtain its energy avoided-crossing spectrum. With ac-Stark effect, fast control of the qubits is achieved to tune the effective coupling on and off and the state-swap gate is successfully constructed. Moreover, using two-photon transition between the ground state and doubly excited states, a kind of two-photon Rabi-like oscillation is observed. A quarter period of this oscillation corresponds to the logical gate , which is used for generating Bell states. and are the foundations of future preparation of two-qubit Bell states and realization of CNOT gate.

Characteristics of fuel evaporation, mixture formation and combustion of 2D cavity impinging spray under high-pressure split injection

The objective of this study is to obtain an enhanced understanding of the effect of split injection on the mixture formation and combustion processes of diesel spray. The study focused on the evaporation, mixture, and combustion of diesel fuel under 2D piston cavity sprays with split injection strategies in a constant volume combustion chamber. Three injection strategies with injection pressures of 100 MPa and 160 MPa, respectively, and a single nozzle hole with a diameter of 0.111 mm were employed. The tracer Laser Absorption Scattering (LAS) technique was used to visualize the spray mixture formation process. High speed imaging of OH∗ chemiluminescence and the two-color method were used to visualize the instantaneous spray combustion process. The experimental results reveal that the vapor distribution of the split main injection with a high injection pressure was more homogeneous than that of a single main injection with low injection pressure at the end of injection (EOI). The split injection can decrease the soot mass. Ignition is more easily during the main injection as a result of the pre-injection. High soot concentration appeared near the cavity wall region under the three injection strategies. The results also indicate that the split injection accelerates the soot oxidation process during the post combustion period.