Web Layout Design of Large Cavity Structures Based on Topology Optimization

Large cavity structures are widely employed in aerospace engineering, such as thin-walled cylinders, blades andwings. Enhancing performance of aerial vehicles while reducing manufacturing costs and fuel consumptionhas become a focal point for contemporary researchers. Therefore, this paper aims to investigate the topologyoptimization of large cavity structures as a means to enhance their performance, safety, and efficiency. By usingthe variable density method, lightweight design is achieved without compromising structural strength. Theoptimization model considers both concentrated and distributed loads, and utilizes techniques like sensitivityfiltering and projection to obtain a robust optimized configuration. The mechanical properties are checked bycomparing the stress distribution and displacement of the unoptimized and optimized structures under the sameload. The results confirm that the optimized structures exhibit improved mechanical properties, thus offering keyinsights for engineering lightweight, high-strength large cavity structures.

Broadband acoustic focusing by symmetric Airy beams with phased arrays comprised of different numbers of cavity structures

We realize broadband acoustic focusing effect by employing two symmetric Airy beams generated from phased arrays,in which the units of the phased arrays consist of different numbers of cavity structures, each of which is composed of a square cavity and two inclined channels in air. The exotic phenomenon arises from the energy overlapping of the two symmetric Airy beams. Besides, we demonstrate the focusing performance with high self-healing property, and discuss the effects of structure parameters on focusing performance, and present the characteristics of the cavity structure with straight channels. Compared with other acoustic lenses, the proposed acoustic lens has advantages of broad bandwidth（about 1.4 kHz）, high self-healing property of focusing performance, and free adjustment of focal length. Our finding should have great potential applications in ultrasound imaging and medical diagnosis.

Correlation of adsorbent cavity structure with adsorption behavior and interaction of long-chainα-olefin/paraffin on microporous adsorbents

Long-chainα-olefins have a high added value as important raw materials for many highly marketable products.Fishcher-Tropsch synthesis products contain ultrahigh-contentα-olefins,which are of great value if the challenging separation ofα-olefin/paraffin is achieved through energy-saving ways,for which adsorption separation is an attractive technology.One of the most significant differences between the adsorption separation of long-chain and light hydrocarbons is the steric hindrance of the molecular chain.Herein,we propose a combination of window size,metal node spacing,and bending degree to quantitatively describe the adsorption cavity structure for the separation of long-chainα-olefin/paraffin.The general cavity structural characteristics of microporous materials with good separation performance for long-chainα-olefin/paraffin are revealed.The selective adsorption of liquid C6 and C_(8)α-olefin/paraffin mixtures on CuBTC(BTC=benzene-1,3,5-tricarboxylate)was studied in detail to reveal the influence of the cavity structure on the adsorption and interaction using a combination of batch adsorption experiments and molecular simulation techniques.CuBTC exhibited 360 and 366 mg/g olefin adsorption capacities for C6 and C8 linearα-olefins,respectively.The adsorption energies were−0.540 and−0.338 eV for C8 linearα-olefin and paraffin,respectively.The contributions of different types of interactions to the overall adsorption energy were quantified to illustrate the adsorption energy difference betweenα-olefin/paraffin and CuBTC.This work provides a new understanding of the long-chain hydrocarbon adsorption behavior different from ethylene/ethane and propylene/propane,which guides the design of adsorbents forα-olefin/paraffin separation.

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures （CCSs） in two-dimensional （2D） photonic crystals （PCs） are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain （FDTD） method, and the results show that within a very short coupling distance of about 3λ, where ）, is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.

Physical model for acoustic resonance in annular cavity structure

A physical model for acoustic resonance in the annular cavity structure is developed to represent the typical characteristic when acoustic resonance occurs.Firstly,the measurement of sound pressure in the casing and rotor blades vibration is operated in a multistage high pressure compressor.The sharp peak frequency and discrete multi-tone occur in the frequency spectrum of sound pressure in the compressor,and the vibration of the first stage of rotor blades synchronously presents the high amplitude.The frequencies associated with rotor blades vibration can be calculated with rotating sound source theory.It is also confirmed that acoustic resonance occurs in the multistage compressor.With acoustic similarity principle,an annular cavity model is established to simulate the typical characteristics of acoustic resonance in the compressor based on Large Eddy Simulation(LES)and Lighthill acoustic analogy.The coupling relationship between cavity acoustic mode and disc vibration mode shape is expounded when acoustic resonance occurs in the model.And acoustic resonance will be locked in the certain flow rate range.All these characteristics match well with those occur in the multistage high pressure compressor.

Linear theory of beam–wave interaction in double-slot coupled cavity travelling wave tube

A three-dimensional model of the double-slot coupled cavity slow-wave structure （CCSWS） with a solid round elec- tron beam for the beam-wave interaction is presented. Based on the ＂cold＂ dispersion, the ＂hot＂ dispersion equation is derived with the Maxwell equations by using the variable separation method and the field-matching method. Through numerical calculations, the effects of the electron beam parameters and the staggered angle between adjacent walls on the linear gain are analyzed.

Different optical properties in different periodic slot cavity geometrical morphologies

In this paper,optical properties of two-dimensional periodic annular slot cavity arrays in hexagonal close-packing on a silica substrate are theoretically characterized by finite difference time domain（FDTD） simulation method.By simulating reflectance spectra,electric field distribution,and charge distribution,we confirm that multiple cylindrical surface plasmon resonances can be excited in annular inclined slot cavities by linearly polarized light,in which the four reflectance dips are attributed to Fabry–Perot cavity resonances in the coaxial cavity.A coaxial waveguide mode TE11 will exist in these annular cavities,and the wavelengths of these reflectance dips are effectively tailored by changing the geometrical pattern of slot cavity and the dielectric materials filled in the cavities.These resonant wavelengths are localized in annular cavities with large electric field enhancement and dissipate gradually due to metal loss.The formation of an absorption peak can be explained from the aspect of phase matching conditions.We observed that the proposed structure can be tuned over the broad spectral range of 600–4000 nm by changing the outer and inner radii of the annular gaps,gap surface topography.Meanwhile,different lengths of the cavity may cause the shift of resonance dips.Also,we study the field enhancement at different vertical locations of the slit.In addition,dielectric materials filling in the annular gaps will result in a shift of the resonance wavelengths,which make the annular cavities good candidates for refractive index sensors.The refractive index sensitivity of annular cavities can also be tuned by the geometry size and the media around the cavity.Annular cavities with novel applications can be implied as surface enhanced Raman spectra substrates,refractive index sensors,nano-lasers,and optical trappers.

Propagation of polarized photons through a cavity withan anisotropic metamaterial

We present a theoretical study of the propagation properties of polarized photons passing through the cavity with an anisotropic metamaterial. We find that the resonant peaks of transmission appear for photons polarized in a certain direction corresponding to a negative element of the permittivity tensor. This indicates the potential for applying such cavity structures as filters for photons with certain polarizations. The resonant peak of transmission for photons having a given frequency can be achieved by adjusting the thicknesses of the air and metamaterial. If the frequency of the incident photons and the thickness of the metamaterial are fixed, the cavity structure can be used as a photon switch controlled by the thickness of the air. The effect of the absorption is considered, and the result shows that the transmission peak always appears, even for metamaterials with large absorption. Finally, the polarization manipulation of such structures is explored.

Hydroacoustic analysis of open cavity subsonic flow based on multiple parameter numerical models

The prediction of the flow-induced noise level is a key issue in the fluid–dynamic acoustics. In the hydroacoustics field, the complicated feedback induced by the flow past open cavities can amplify the convection instability in the shear layer which further leads to important noise radiations. The noise consists of intense narrowband and broadband components. In this paper, the level of the noise radiated by a subsonic cavity flow is calculated by using numerical flow computations based on the large eddy simulation（LES） and by solving the Ffowcs Williams-Hawkings equation. A series of three-dimensional open cavity models with overset grids and appropriate boundary conditions are developed for the hydroacoustic numerical computation. The self-sustained oscillation characteristics of the cavity flow are investigated, together with the mechanisms of the cavity noise generation. The distinguishing features of the flow-induced noise of the underwater structure cavities are studied with respect to the parameters of the cavity models, such as the free stream velocity, the dimensions of the cavity mouth, the angle of the cavity neck, the horizontal and vertical porous cavity models and the actual submarine open cavity model with an incoming flow attack angle. It is shown that it may be feasible to reduce the flow-induced noise by appropriate optimal parameters of the underwater structure cavities.