3D Cavity Research Articles

Experimental study on influence of wall acoustic materials of 3D cavity for targeted energy transfer of a nonlinear membrane absorber

In view of applying the membrane nonlinear energy sink (NES) to reduce the low-frequency noise inside vehicle interior with acoustic absorption materials, a simplified acoustic cavity is used to model vehicle interior cavity. The system of one acoustic mode of the parallelepiped cavity and one membrane is established and the experimental set-up is built. The forced vibration responses in frequency-domain and time-domain are analyzed by using the set-up with and without the acoustic materials. Under certain excitation amplitude and frequency range, the strongly modulated responses (SMR) occurs and the plateau of suppressed resonance peaks appears. Meanwhile, the energy of the system is studied when the SMR exists. The targeted energy transfer (TET) phenomenon and the theoretical model of the system is verified by the experimental method. The wall acoustic materials of 3D cavity could affect the TET of the system, where the excitation amplitude for the beginning threshold of the desired working zone becomes larger and the excitation amplitude interval of TET becomes larger simultaneously. The ending threshold of the desired working zone of the NES is redefined. The numerical results are in good agreement with the experimental results. The application of membrane NES in 3D acoustic cavity proposed in this paper provides a new technical idea for vehicle interior low-frequency noise reduction in the future.

GeoChemFoam: Direct Modelling of Multiphase Reactive Transport in Real Pore Geometries with Equilibrium Reactions

GeoChemFoam is an open-source OpenFOAM-based toolbox that includes a range of additional packages that solve various flow processes from multiphase transport with interface transfer, to single-phase flow in multiscale porous media, to reactive transport with mineral dissolution. In this paper, we present a novel multiphase reactive transport solver for simulations on complex pore geometries, including microfluidic devices and micro-CT images, and its implementation in GeoChemFoam. The geochemical model includes bulk and surface equilibrium reactions. Multiphase flow is solved using the Volume-Of-Fluid method, and the transport of species is solved using the continuous species transfer method. The reactive transport equations are solved using a sequential operator splitting method, with the transport step solved using GeoChemFoam, and the reaction step solved using Phreeqc, the US geological survey’s geochemical software. The model and its implementation are validated by comparison with analytical solutions in 1D and 2D geometries. We then simulate multiphase reactive transport in two test pore geometries: a 3D pore cavity and a 3D micro-CT image of Bentheimer sandstone. In each case, we show the pore-scale simulation results can be used to develop upscaled models that are significantly more accurate than standard macro-scale equilibrium models.

Kinematics-Based Five-Axis Trochoidal Milling Process Planning for Deep and Curved Three-Dimensional Slots

Abstract Trochoidal (TR) milling is a popular means for slotting operation. Attributing to its unique circular-shaped path pattern, TR milling avoids the full tool–workpiece engagement, which helps reduce the cutting heat accumulation and hence slow down the tool wear. While traditionally TR milling is only used for machining 2.5D cavities, it has now been extended to machining genuine 3D curved cavities under the realm of five-axis machining. However, since for a typical five-axis machine tool the rotary axes have a much larger moment of inertia than the three linear axes, to reduce both the total machining time and the consumed electric energy (for driving the machine tool), it is desirable to minimize the use of the two rotary axes (particularly the one with the larger moment of inertia) when planning a TR tool path for a given 3D cavity. Nevertheless, due to the newness of five-axis TR machining, there has no published reports on this subject. In this paper, we present a five-axis TR tool path planning algorithm for machining an arbitrary 3D curved cavity, which will consider the kinematical characteristics of the five-axis machine tool and try to minimize the use of the rotary axis with the largest moment of inertia, while tending to all the required constraints such as the threshold on the cutting force. Both computer simulation and physical cutting experiments of the proposed method have been conducted, and the results give a preliminary confirmation on the feasibility and advantages of the proposed method.

GPGPU를 활용한 OpenFOAM 기반 해석자 성능 분석

Two benchmark tests were carried out to analyze the performance of OpenFOAM-based CFD solvers using General-Purpose computing on Graphics Processing Units(GPGPU). In the present study, RapidCFD, which is an implementation of OpenFOAM capable of running most of the functions of OpenFOAM on GPUs, was used to apply GPGPU to OpenFOAM. The numerical simulations of 1) 3D lid-driven cavity incompressible flows and 2) steady flows around a motorbike were conducted on two kinds of CPU, single-GPU, and multi-GPU systems, and the computational times were analyzed. For the test of cavity flows, as the number of cells increased, the performance and the scalability of GPGPU were improved. When the number of cells was 2503, a system with 8-GPUs showed the highest performance with 42 times of speedup over a CPU system. For the test of flows around a motorbike, a system with 8-GPUs showed the highest performance with 20 times of speedup over a CPU system. For both single precision and double precision calculations, the performance improvements using GPGPU were efficient. The results demonstrate that GPGPU would be more efficient than computing on CPUs when computing large-scale flows and practical problems that require massive parallelism.

Halide-modulated self-assembly of metal-free perovskite single crystals for bio-friendly X-ray detection

Halide-modulated self-assembly of metal-free perovskite single crystals for bio-friendly X-ray detection

Acoustic cavities in 2D heterostructures

Two-dimensional (2D) materials offer unique opportunities in engineering the ultrafast spatiotemporal response of composite nanomechanical structures. In this work, we report on high frequency, high quality factor (Q) 2D acoustic cavities operating in the 50–600 GHz frequency (f) range with f × Q up to 1 × 1014. Monolayer steps and material interfaces expand cavity functionality, as demonstrated by building adjacent cavities that are isolated or strongly-coupled, as well as a frequency comb generator in MoS2/h-BN systems. Energy dissipation measurements in 2D cavities are compared with attenuation derived from phonon-phonon scattering rates calculated using a fully microscopic ab initio approach. Phonon lifetime calculations extended to low frequencies (<1 THz) and combined with sound propagation analysis in ultrathin plates provide a framework for designing acoustic cavities that approach their fundamental performance limit. These results provide a pathway for developing platforms employing phonon-based signal processing and for exploring the quantum nature of phonons.

Heterojunction photocatalyst of cavity shaped Bi2S3/g-C3N4 for bisphenol a degradation: Regulation of internal electric field via assistance of interfacial functional groups

The p-n heterojunction with internal electric field (IEF) is flourishingly developed in photocatalysis. Enlarging the space charge region width can effectively improve the migration/separation of charge carriers. Here, adequate functional groups (–COOH, -N-(C)3, -C-N–H) were generated from graphitic carbon nitride (GCN) decomposition, worked as the dispersant and electric charge contributor in the heterojunction. Bi ions were adsorbed on –COOH to achieve localized nucleation, formed Bi2S3 can be uniformly dispersed on GCN surface to form FGBS/GCN. Additionally, the incorporation of functional groups not only ameliorated the 3D cavity structure and optimized the band structure of functional groups modified Bi2S3 (FGBS) but also widened the space charge region of IEF in FGBS/GCN and resulted in efficient carriers separation. Benefit from functional groups, the initial rate of bisphenol A (BPA) degradation over 2FGBS/GCN was 0.0280 mmol⋅gcat-1⋅h−1. This work provides new insight into the regulation of the space charge region in the p-n heterojunction.

Acoustic fluid–structure study of 2D cavity with composite curved flexible walls using graphene platelets reinforcement by higher-order finite element approach

In the present study, acousto-vibration analysis of 2D fluid-filled cavities/tanks having flat and curved flexible walls is made using a trigonometric function based shear deformable theory andthe Helmholtz wave model for fluid domain. The governing equation formed here is solved through higher-order finite element approach. The walls are modeled by C1 continuous 3-noded beam element and the fluid is idealized using an eight-noded quadrilateral element. Structural and coupled frequencies are evaluated for fluid-filled cavities with rigid/flexible vertical walls along with flat/curved beam on top.The sound pressure level is also predicted in the fluid domain due to a steady-state mechanical harmonic load on the top of the cavity. This investigation is conducted for metallic cavities and then extended to graphene platelets reinforced cavity. The effect of degree of fluid–structure coupling is examined assuming different fluid domains. Considering a wide range of cavity geometry and material parameters such asthickness ratio, curved beamangle, graded porosity and graphene platelets, porosity coefficient, loading of GPL, fluid medium, a comprehensive investigation is depicted to highlight their impacts on vibro-acoustic nature of fluid-filled cavities. It is observed that the dynamic characteristics of rigid and flexible wall cavities are significantly different from each other.

On‐Demand Coherent Perfect Absorption in Complex Scattering Systems: Time Delay Divergence and Enhanced Sensitivity to Perturbations

AbstractNon‐Hermitian photonic systems capable of perfectly absorbing incident radiation recently attracted much attention both because fundamentally they correspond to an exotic scattering phenomenon (real‐valued scattering matrix zero) and because their extreme sensitivity holds great technological promise. The sharp reflection dip is a hallmark feature underlying many envisioned applications in precision sensing, secure communication, and wave filtering. However, a rigorous link between the underlying scattering anomaly and the system's sensitivity to a perturbation is still missing. Here, a theoretical description in complex scattering systems is developed which quantitatively explains the reflection dip's shape. It is furthermore demonstrated that coherent perfect absorption (CPA) is associated with a phase singularity and that the sign of the diverging time delay is related to the mismatch between excitation rate and intrinsic decay rate. The theoretical predictions are confirmed in experiments based on a 3D chaotic cavity excited by eight channels. Rather than relying on operation frequency and attenuation inside the system to be two free parameters, “on‐demand” CPA is achieved at an arbitrary frequency by tweaking the chaotic cavity's scattering properties with programmable meta‐atom inclusions. Finally, the optimal sensitivity of the CPA condition to minute perturbations of the system is proven theoretically and verified experimentally.

Oral-3D: Reconstructing the 3D Structure of Oral Cavity from Panoramic X-ray

Panoramic X-ray (PX) provides a 2D picture of the patient's mouth in a panoramic view to help dentists observe the invisible disease inside the gum. However, it provides limited 2D information compared with cone-beam computed tomography (CBCT), another dental imaging method that generates a 3D picture of the oral cavity but with more radiation dose and a higher price. Consequently, it is of great interest to reconstruct the 3D structure from a 2D X-ray image, which can greatly explore the application of X-ray imaging in dental surgeries. In this paper, we propose a framework, named Oral-3D, to reconstruct the 3D oral cavity from a single PX image and prior information of the dental arch. Specifically, we first train a generative model to learn the cross-dimension transformation from 2D to 3D. Then we restore the shape of the oral cavity with a deformation module with the dental arch curve, which can be obtained simply by taking a photo of the patient's mouth. To be noted, Oral-3D can restore both the density of bony tissues and the curved mandible surface. Experimental results show that Oral-3D can efficiently and effectively reconstruct the 3D oral structure and show critical information in clinical applications, e.g., tooth pulling and dental implants. To the best of our knowledge, we are the first to explore this domain transformation problem between these two imaging methods.

Collaborative optimization of conical cutter sequence for efficient multi-axis machining of deep curved cavities

As an essential part of the composite fan blade, the leading edge protection cap (LPC) has a very narrow and deep cavity which, in order to avoid the interference, requires the conical ball-end cutter to be long and thin. It calls to improve the cutter’s stiffness so to increase the roughing efficiency of the whole cavity. Targeting this important problem, this paper proposes a novel method to collaboratively optimize a conical cutter sequence, the machining ranges, and the cutting parameters for achieving the highest material removal efficiency. The main difficulty is that all the relevant entities – i.e., the LPC cavity geometry, tool size, tool axis, machining ranges, minimum tool length, tool stiffness, and cutting performance – collaboratively affect the total cutting efficiency. To facilitate decoupling them, the 3D LPC cavity is characterized by its medial surface. To identify all the geometrically accessible conical tools of each medial point, an efficient algorithm is proposed, which is featured by searching characteristic points on the cavity surface. By considering both the geometric and physical accessibilities, the tool sequence domain is constructed. To obtain the appropriate cutting parameters, the best cutting performance of a weak conical cutter is modeled under the constraint of deflection due to the cutting force. Finally, the complicated collaborative optimization model aiming for the minimum cutting time is established and solved by a PSO-based algorithm. The experimental results confirm that the proposed model and algorithm are practicable for improving the roughing efficiency of LPC cavity.

Effects of composite material fin conductivity on natural convection heat transfer and entropy generation inside 3D cavity filled with hybrid nanofluid

The current paper offers a numerical investigation of the combined effects of an inserted composite material fin conductivity ratio and hybrid nanofluid volume fraction on natural convection heat transfer and entropy production inside 3D cubic cavity. In this investigation, a fin is embedded at the left heated wall and is horizontally oriented toward the right cold wall, while the other surfaces are insulated from the surrounding. A broad range of parameters such as composite material conductivity ratio (1 ≤ RC ≤ 103), volumetric fraction of hybrid nanofluid (0 ≤ φ ≤ 0.05) and Rayleigh number (103 ≤ Ra ≤ 105) were considered. Obtained results reveal that the flow structure, the temperature distribution and the entropy generation rate are sensitive to nanoparticles volume fraction and composite material fin conductivity. Moreover, regardless of the latter parameter, the heat transfer is found to be enhanced with adding hybrid nanoparticles. However, the effect of increasing the conductivity on the average Nusselt number and the total generated entropy is significant only for RC > 100. The maximum Nusselt number and entropy production rate are achieved for Ra = 105, φ = 0.05 and RC = 1000.

Shape optimisation for faster washout in recirculating flows

Abstract

Scaled Boundary Finite Element Method for Mid-Frequency Acoustics of Cavities

In this paper, a semi-analytical framework, based on the scaled boundary finite element method (SBFEM), is proposed, to study interior acoustic problems in the mid-frequency range in two and three dimensions. The SBFEM shares the advantages of both the finite element method (FEM) and the boundary element method (BEM). Like the FEM, it does not require the fundamental solution (Green’s function) and similar to the BEM only the boundary is discretized, thus reducing the spatial dimensionality by one. The solution within the domain is represented analytically, while on the boundary, it is represented by finite elements. Although different boundary representations are possible, only the Lagrangian description is investigated in this paper. The proposed framework is validated using closed-form solutions, and direct comparisons are made with the conventional FEM based on Lagrangian description; this will be demonstrated using two 2D cavities from literature as well as one 3D cavity. The improved accuracy and reduced computational time can be attributed to the semi-analytical formulation combined with the boundary discretization.

Effects of the boundary-layer thickness at the cavity entrance on rarefied hypersonic flows over a rectangular cavity

A comprehensive numerical study is performed to investigate rarefied hypersonic flows past a flat plate with a two- (2D) or three-dimensional (3D) rectangular cavity using the direct simulation Monte Carlo method. In this work, we obtain different boundary-layer thicknesses at the cavity entrance by varying the length of upstream flat plate. Then, the effects of boundary-layer thickness at the cavity entrance on flow characteristics and aerodynamic surface quantities are analyzed in depth. The concept of total-enthalpy boundary layer successfully identifies the boundary-layer edge while the traditional boundary layer based on velocity fails to captures the shock-wave front due to the presence of the weak shock wave in the rarefied hypersonic flow past a flat plate. The boundary-layer thickness at the cavity entrance has strong effects on the flow past the 2D cavity. As the boundary layer at the cavity entrance becomes thicker, the external stream can penetrate deeper into the cavity and transfer more momentum and energy to the cavity, so the cavity flow develops gradually from an open flow to a transitional one and ultimately to a closed one. In addition, the 3D effect plays an important role for the cases of extremely thick boundary layers at the cavity entrance, while it can almost be neglected when boundary layers at the cavity entrance are exceedingly thin.

Application of modal expansion method for sound prediction in enclosed spaces subjected to boundary excitation

In this paper, the steady-state and transient sound fields inside 3D enclosed spaces were examined theoretically using the modal expansion method. An analytic formula for the Green’s function was derived allowing to predict the interior sound field for both the harmonic and impulse boundary excitations. A theoretical model was tested numerically for a 3D car-like cavity with a sound absorbing material placed on walls. For a harmonic excitation, calculation results revealed high impact of a frequency and a sound damping on a distribution of the steady-state pressure amplitude. They also indicated irregularly located energy vortices in the active intensity vector field. Simulations of a transient sound field were carried out for a boundary excitation producing a sine wave pulse. Temporal changes in this field were studied using the pressure amplitude determined via the discrete Hilbert transform. A large temporal variability of a distribution of this amplitude was noted due to a strong dependence of a transient sound on a position of the observation point. Simulation results also shown that for a small sound damping on cavity walls, there was an intense sound reverberation inside the cavity.

Three-dimensional gravity tailored ultra-broadband absorber based on a high-impedance surface

In this paper, we present a novel, to the best of our knowledge, 3D ultra-broadband tunable metamaterial absorber (TMA), which is innovatively tuned by the gravity field with changing the position of the liquid metal (eutectic gallium-indium) in theory. The given TMA consists of a 3D glass cavity filled with the liquid metal, two-layer high-impedance surfaces, two dielectric layers, and a metallic plate on the bottom. The ultra-broadband absorption is achieved by the high-impedance surface and the liquid metal. Furthermore, it is noted that the liquid metal is poured into the different parts of the glass cavities via rotation under the action of the gravity field to obtain the tunable absorption. When such a TMA is not rotated, for the TE wave, the absorption rate exceeds 90% from 1.8 to 57.5 GHz with a wide relative absorption bandwidth (AB) of 187.8%. However, for the TM wave, the absorptivity goes beyond 90% at 5.6–56.4 GHz. The proposed TMA exhibits ultra-broadband absorption in the frequency regime of 1.6–45.3 GHz (the absorption rate is higher than 90%) with such a TMA rotated 180° in the x − y plane, while the absorption rate is near zero from 1.6 to 60 GHz when the proposed TMA is rotated 180° in the y − z plane. Moreover, the surface current distributions, the near-field amplitude | E z | , the phase φ z , and the magnetic field distributions are investigated to describe the operating mechanism of the designed TMA. Besides, the numerical results indicate that such a TMA can realize high absorption under a wider incident angle. Compared with traditional tunable devices, the gravity field regulation, which can change the operating frequencies of an absorber in a noncontact way, has the advantages of easy implementation and resource savings. The proposed absorber tuned by the gravity will have potential applications in frequency selection. With the change of liquid metal and structure design, this design can also be potentially applied in other microwave and terahertz devices. Taken together, this study suggests a role for such an absorber in promoting a novel application for tunable devices.

Slow light in rod type 2D photonic crystal waveguide comprising of cavity: Optimization and analysis

Structure comprising of 2D photonic crystal waveguide and cavity (PhCWC) is designed in this paper and propagation of slow light through it is investigated for its potential application as optical delay device. Rod type 2D photonic crystal structure has been considered here. Two-dimensional finite difference time domain (2DFDTD) method has been used in the present investigations. The proposed PhCWC structure is optimized in two steps. In the first step, Q factor is optimized by varying the number of rods of the cavity. In the second step, number of rods are kept fixed (as optimized for Q in the first step), and the delay is maximized by varying radius of the cavity rods. The resultant structure thus obtained is further investigated for (i) dispersion and group velocity, (ii) variation of optical delay with input pulse width, (iii) variation of optical delay with wavelength and (iv) variation of optical transmission with wavelength.The present paper proposes optical delay in the one cavity structure that could be manipulated by manipulating the number of cavity rods in the waveguide and radius of the central rod of the cavity. Further, the structure can be designed to operate at a desired wavelength.

Macroscopic axisymmetric lattice Boltzmann method (MacAxLAB)

The author has recently proposed a macroscopic lattice Boltzmann method (MacLAB) for the Navier–Stokes equations. The method is formulated for the first time to retain the streaming step by removing the collision step in the two integral steps of the standard lattice Boltzmann method. It relies on one fundamental parameter of lattice size δx in the model. This leads to a revolutionary and precise minimal “Lattice” Boltzmann method, which directly uses physical variables as boundary conditions with less required storage for more accurate and efficient simulations. In this paper, the MacLAB is further developed for solving incompressible axisymmetric flow equations (MacAxLAB). The model is validated through simulations of a 3D unsteady Womersley flow and two 3D steady cylindrical cavity flows. The numerical results have compared with other numerical ones and available analytical solutions; it shows that the MacAxLAB is applicable and accurate for modelling incompressible axisymmetric flow.

Highly uniform polycrystalline diamond coatings of three-dimensional structures

Diamond is highly desirable as a conformal thin-film coating for three-dimensional (3D) devices due to its extreme hardness, durability and biocompatibility, especially in the case of implantable medical devices and prosthetics. Recent advances in microwave plasma chemical vapour deposition (CVD) have enabled conformal coating of such 3D structures with nanodiamond films. However, these techniques have not been extended to micro-crystalline diamond, due to interactions between the 3D substrates and resonant microwave cavity. Here we demonstrate more uniform growth of CVD polycrystalline diamond (PCD) coatings on complex-shaped structures, with the use of in-cavity Faraday cages, to isolate the 3D sample from the microwave cavity. While this does disrupt the distribution of the microwave plasma, which surrounds the 3D structure, we show that growth of relatively uniform micro-crystalline and faceted PCD films is possible over the entirety of the exposed 3D sample surface. The resultant technique opens possibilities for the coating of complex 3D geometries with a wider range of diamond materials than has been possible to date.