Cross Section Of Cavity Research Articles

Investigation of free surface effect on the cavity expansion and contraction in high-speed water entry

The evolution of the water-entry cavity affects the impact load and the motion of the body. This paper adopts the Eulerian finite element method for multiphase flow for simulations of the high-speed water-entry process. The accuracy and convergence of the numerical method are verified by comparing it with the experimental data and the results of the transient cavity dynamics theory. Based on the results, the representative characteristics of the cavity are discussed from the perspective of the cavity cross-section. It is found that the asymmetry of the cavity expansion and contraction durations is related to the motion of the free surface and the closure of the cavity. The uplift of the free surface suppresses cavity expansion, while the jet generated from free surface closure accelerates cavity contraction. The duration of the contraction of the cavity near the free surface is shorter than the expansion duration due to the change in the velocity distribution caused by the free surface motion. The necking phenomenon during deep closure leads to an increase in the internal pressure of the cavity, prolonging cavity contraction near the deep closure area. This work provides new insights into the cavity dynamics in high-speed water entry.

United composite strength calculation method for special-shaped CFST columns with multiple cavities

The present study investigates the method of calculating the composite strength of special-shaped concrete-filled steel tube (CFST) members with multiple cavities. Based on the research findings of CFST unified theory and some tests, a quantitative method to evaluate the concrete constraint effect is proposed for cross-sectional shapes ranging from regular triangles, squares…regular octagons to circles. The cross-sectional composite strength of regular polygonal CFST members is determined by the way dividing the concrete into effective and ineffective constraint regions, discounting constraint coefficients, and applying unified formulas. Additionally, a regression analysis is conducted to establish the relationship between interior angles and constraint effects. Subsequently, using quadrangle CFSTs as an example, this study investigates the relationship between cross-sectional regularity and constraint effect, and proposes a composite strength calculation method related to it. Finally, the special-shaped multi cavity cross section is separated into several simple polygonal cross sections, taking into account shape efficiency and regularity, to calculate the composite strength of each cavity CFST member and summarize them for determining the total axial compressive bearing capacity. The research findings indicate that a linear relationship exists between the interior angle of the cross section and the initial tangent line angle of the second-degree curve, which serves as the boundary between effective and ineffective constraint regions in regular polygonal steel tube confined concrete. The proposed unified composite strength calculation method, specifically designed for special-shaped CFST columns with multiple cavities, can accurately predict their actual strength.

Broadband low-frequency sound-absorbing metastructure based on an impedance-matching coiled-up cavity with continuously variable cross section

Proposed here is a metastructure based on a micro-perforated panel and an impedance-matching coiled-up cavity with continuously variable cross section, which achieves perfect absorption with a resonant frequency of 496 Hz and an absolute bandwidth (α ≥ 0.5) of 468 Hz. The structure thickness is ca. 1/13 of the operating wavelength λ in the deep subwavelength range. A relative bandwidth of 84.04%–111.67% is achieved through parametric studies. Physically, the continuous variation of the cavity cross section through which sound waves enter weakens the acoustic reflections generated by cross-sectional abruptness and enhances the impedance matching with the air. Furthermore, particle swarm optimization is coupled with a theoretical model to tailor the metastructure to realize the maximum absorption coefficient in the defined frequency range. It is shown theoretically that coherent coupling “weak resonance”—in which each unit individually exhibits imperfect absorption peaks—significantly improves the absorption performance in a broad frequency band through the coherent coupling effect. Finally, a hybrid metastructure using a parallel coupling sample is fabricated, and its acoustic properties are measured in an impedance tube. The average absorption coefficient of this metastructure is 0.934 in the quasi-perfect band (α > 0.9) from 400 to 650 Hz, and the thickness is only ca. λ/15. The unique innovation of a cavity with continuously variable cross section provides new ideas for designing broadband low-frequency sound-absorbing metastructures.

Compression-bending behavior of irregular pentagonal CFT columns with different cavity structures: Experimental study

This paper reported the test results of six irregular pentagonal concrete filled steel tube (CFT) columns with different cavity structures. The columns were tested under a constant axial compression and lateral low cyclic load. The test parameters are the lateral loading direction, cross-sectional cavity quantities, and with or without embedded reinforcements. The influence of these parameters on failure mode, strength, elastic-plastic deformability, energy dissipation ability was investigated. It was found that, irregular pentagonal CFT columns exhibit favorable ductility and energy dissipation ability. The multi-cavity structure significantly increases strength, while the reinforcements effectively improve ductility. Also, the bottom cross section strain distribution nephogram was mathematic fitted according to the measured gauge values. And it was founded that the bottom cross-sectional deformation obeys the plane cross section assumption before and at peak load point. And then, a calculation model using fiber model method was established considering difference among the cavity structures. The lateral load versus displacement curves, and axial load versus ultimate moment correlation curves are all predicted. Analysis shows that the constitutive relationship of confined concrete suggested by the author is better than available Han's in the prediction accuracy.

Study on the Influence of Rock Clip Production and Empty Hole Volume Effect of Upward Blind Shaft Blasting

Cutting blasting is the principal construction method for roadway and shaft excavation, but the studies on the damage mechanism of cutting blasting affected by the volume effect of empty holes under high ground stress are not insufficient. During cutting blasting, different damage zones are formed. In this paper, combined with the rock damage criterion and RHT constitutive function, the ranges of these damage zones are determined. The smooth particle hydrodynamics method is used to study the influence of high in-situ stress on rock blasting damage from the perspective of the number of empty holes and the production coefficient of rock clamp. The accuracy of the determined damage zone range is verified by supplemented field tests. The research results show that in the process of rock clamp production, the propagation of blasting stress wave is inhibited, especially the tensile stress wave which is more obviously inhibited. The empty holes reduce the inhibitory effect of rock clamp production. With the increase in the production coefficient of rock clip, the blasting damage radius is reduced by 39.7%, 35.1%, 30.5%, 26.7%, and 22.9% compared with the theoretical value, respectively, while its influence on the radius of crushing zone is small. The three-dimensional scanning results were used to inverse calculate the production coefficient of the rock clip. The fitting degree between the numerical simulation and the field test scanning results is about 94.5%, which proves the accuracy of the RHT constitutive parameters and the reliability of the determination range. The mathematical relationship between the production coefficient Kr for rock clip and the relative height H of the wellhead and the area Sc of the cross-section cavity is fitted based on the data of several upward cutting blasting field tests.

Modeling Horizontal Salt Cavern Leaching in Bedded Salt Formations

Summary The leaching of a salt cavern will trigger a series of rock-fluid interactions, including salt rock dissolution, cavity expansion, and brine transport caused by convection, turbulence, and diffusion effects. These interactions have influences on one another. The primary objectives of this study include developing a 3D multiphysical coupled model for horizontal salt cavern leaching and quantifying these interactions. The species transport equation and standard κ-ε equation were combined to describe the brine transport dynamics within the cavity. Based on the velocity and concentration distribution characteristics predicted, the interface movement equation implemented with mesh deformation techniques was applied to describe the cavity expansion. Next, the Volgograd cavern monitored data were collected for model validation. The predicted results are consistent with the field data. The average relative errors are 11.0% for brine displacing concentration and 4.5% for cavity volume. The results suggest that the cavity can be divided into three regions, including the main flow region, circulation region, and reflux region. The results also suggest that the brine concentration distribution is relatively uniform. With the dissolution threshold angle and anisotropic dissolution rates considered, the resultant cavity cross section is crown top and cone bottom. The results also show that the cavity can be divided into dissolution and erosion sections according to its position relative to the injection point.

Investigation of pulp flow helicity in rotating and non-rotating grooves

Numerical simulation of pulp flow in rotating and non-rotating grooves is carried out to investigate the effect of pulp rheological properties and groove geometry on the rotational motion of the pulp flow. The eucalyptus pulp suspension is considered as a working fluid in the present study whose apparent viscosity correlation is available from the experimental measurements reported in the literature. The simulations are carried out with OpenFoam for different values of pulp material, fiber concentrations, and groove cross-section. Helicity is introduced to measure the turnover rate of pulp flow in the groove due to the importance of such motion on the final properties of the pulp flow. A measurement of helicity magnitude and its distribution along the groove revealed that a change in the pulp material would significantly affect the flow structures within the groove. Further investigation on the effects of fiber concentration, c, showed that this parameter does not have a significant effect on the averaged helicity magnitude for c = 2.0 and 2.5, whereas the helicity distribution over the groove cross-section changes clearly for c = 1.5. The results showed that the helicity level is negligible for almost half of the cavity cross-section in the non-rotating groove simulations, which can be considered as a shortcoming of the original geometry of the groove. Therefore, a smaller cross-section for the groove is considered through which an enhancement in the helicity magnitude is observed.

Sound-Absorption Mechanism of Structures with Periodic Cavities

A simplified finite element method (FEM) simulation method has been established and validated for analyzing the sound absorption mechanism of structures with periodic axisymmetric cavities. Combined with genetic algorithm, the simplified FEM method is used to optimize the sound absorption coefficient of the structure containing periodic cylindrical cavities and variable cross section cavities. The result of variable section cavities is much better than the case of cylindrical cavities. The effect of cavity shape on sound absorption mechanism is discussed through energy dissipation, structure deformation and modal analysis of the absorption structures. It is found that the cavity structure resonances include bending vibration of the surface layer and radial motion of particles near the cavities. The radial motion also changes along the axial direction. Adding geometric design parameters of the cavity cross section are conducive to moving the radial mode to low frequency. The radial vibration has a great influence on absorption performance, which is more conducive to promoting the conversion of longitudinal waves into transverse waves with more energy dissipation. Finally, a better sound absorption performance is obtained by introducing the material parameter of Young's modulus into the optimization model, indicating that comprehensive consideration of geometry and material parameters for optimization is expected to obtain the desired sound absorption structure in engineering practice.

Low-Profile Metasurface-Based Diaphragm for Compartment Shielding of Microwave Cavities

This article proposes several low-profile metasurface-based compartment shielding diaphragms for the high-speed and highly integrated circuits located in the space-limited cavities. It was demonstrated that the capacitive metasurface (CMS) and inductive metasurface (IMS) partially filled in the cross section of cavities can generate new transverse electric and magnetic resonance modes, which are orthogonal to the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode of the cavity. Benefitting from the mode-mismatch between the transverse electric/magnetic resonance modes and the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode, a large shielding effectiveness (SE) can be obtained. It is found that, even when the metasurfaces are designed with a low profile (the ratio between the metasurfaces' profile and the cavity's height h/h <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> <; 0.5), they can introduce a large SE at a desired frequency band, which is deemed difficult to achieve by utilizing conventional waveguide diaphragms with such a profile. Moreover, the CMS and IMS can be aligned as a complementary metasurface (CPMS) to enhance the working bandwidth significantly, by elaborately designing their surface impedances. The CMS, IMS, and CPMS samples with a thickness less than 0.1λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and a profile less than 0.15λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , i.e., less than one-third of the cavity's height, were fabricated and tested in a compartment scenario, respectively. The developed technique is validated by the good agreement between the simulation and measurement results. The low-profile shielding diaphragms reported in this work can provide the effective solutions in many compartment shielding scenarios, such as integrated radio frequency (RF) modules and system-on-chip (SoC) packages.

Equivalent Surface Impedance of an Infinite Periodic Array of Slot Impedance Loads Based on an Equilateral Triangle Cross-Section Cavity with a Dielectric Coating

In this paper, we consider a two-dimensional problem of determining the equivalent surface impedance of an infinite array of slot impedance loads with a dielectric layer. Each element of the array contains three regions: the first region occupies the entire half-space above the interface and the primary field is excited in this region by a plane wave; the second region does not contain excitation sources and is a dielectric layer; and the third region also does not contain exciting sources and is bounded by the walls of the cavity with a equilateral triangle cross section. The second and third regions are connected through one or several slots in a perfectly conducting screen located at their border. A strip conductor is located in the opening of each slot. The problem was solved by the method of integral equations, for the numerical implementation of which the Krylov–Bogolyubov method was used. Numerical results are presented as the dependences of the equivalent surface impedance on the geometric dimensions of the structure at fixed values ​​of the array period, the incidence angle of the electromagnetic wave, and the thickness of the dielectric layer. A comparative analysis of the obtained dependences with the characteristics of a similar array without a dielectric layer is performed.

Polaritonic Tamm states induced by cavity photons

Abstract We consider a periodic chain of oscillating dipoles, interacting via long-range dipole–dipole interactions, embedded inside a cuboid cavity waveguide. We show that the mixing between the dipolar excitations and cavity photons into polaritons can lead to the appearance of new states localized at the ends of the dipolar chain, which are reminiscent of Tamm surface states found in electronic systems. A crucial requirement for the formation of polaritonic Tamm states is that the cavity cross section is above a critical size. Above this threshold, the degree of localization of the Tamm states is highly dependent on the cavity size since their participation ratio scales linearly with the cavity cross-sectional area. Our findings may be important for quantum confinement effects in one-dimensional systems with strong light–matter coupling.

Simulation of Lid-Driven Cavity Flow with Internal Circular Obstacles

The Lattice Boltzmann method (LBM) has been applied for the simulation of lid-driven flows inside cavities with internal two-dimensional circular obstacles of various diameters under Reynolds numbers ranging from 100 to 5000. With the LBM, a simplified square cross-sectional cavity was used and a single relaxation time model was employed to simulate complex fluid flow around the obstacles inside the cavity. In order to made better convergence, well-posed boundary conditions should be defined in the domain, such as no-slip conditions on the side and bottom solid-wall surfaces as well as the surface of obstacles and uniform horizontal velocity at the top of the cavity. This study focused on the flow inside a square cavity with internal obstacles with the objective of observing the effect of the Reynolds number and size of the internal obstacles on the flow characteristics and primary/secondary vortex formation. The current LBM has been successfully used to precisely simulate and visualize the primary and secondary vortices inside the cavity. In order to validate the results of this study, the results were compared with existing data. In the case of a cavity without any obstacles, as the Reynolds number increases, the primary vortices move toward the center of the cavity, and the secondary vortices at the bottom corners increase in size. In the case of the cavity with internal obstacles, as the Reynolds number increases, the secondary vortices close to the internal obstacle become smaller owing to the strong primary vortices. In contrast, depending on the sizes of the obstacles ( R / L = 1/16, 1/6, 1/4, and 2/5), secondary vortices are induced at each corner of the cavity and remain stationary, but the secondary vortices close to the top of the obstacle become larger as the size of the obstacle increases.

The production of the splash phenomenon, as a way of dissipating the energy of a gravitational wave

Investigations are aimed at revealing the conditions for the generation of a Splash wave phenomenon by a submerged breakwater, as having a particularly effective form of wave energy dissipation. On the basis of a wide range of well-known theoretical studies of wave transformation over bottom inhomogeneities, the expediency of laboratory experiments on physical models is shown as a method that allows taking into account the peculiarities of the influence of targeted turbolization of the water flow. Numerous experiments on physical models have shown the possibility of the occurrence of such a phenomenon over a system of bottom inhomogeneities and the rationality of further scientific search. However, the effect is achieved when certain parameters of many independent variables (significant and represented in a wide range of factors) are combined. This circumstance makes a positive solution of the problem rare in nature.In view of the multifactority of the hydrodynamic process under investigation, an analysis of the theoretical premises was carried out, which allowed us to concentrate on a new variant of the solution of the problem posed – a single breakwater with a special crest design. The version of a "box" type breakwater was taken.as a basis But part of the wave energy quenched in it is directed to quenching another part of the energy of the wave flow passing over the top of the breakwater. The task was to find the location, shape and size of the opening in the top. Two versions were investigated: in the form of a perforation and in the form of a slit located along the breakwater. The last version showed its superiority and this result allowed to proceed to the solution of the next problem, the search for the most effective of the of the breakwater cavity cross-section.shape. The obvious direction of the search was the effect of a curvilinear wave-breaking wall of the embankment. Instead of the vertical face under the "visor" (that is, under the horizontal plane of the top surface) previously accepted in the studies, two schemes for calculating the surface curves, differing from each other in radius and length, are studied. The size of the slit in the "visor" varied. The conditions and prospects for the development of Recommendations for the design of the submerged breakwater of this type are described.The urgency of the solution of the problem lies in the broad perspective of the use of submerged breakwaters in recreational zones.

Study on the growth curve of the internal cavity of ‘Dwarf green’ coconut fruits

The aim of the work was to evaluate the adjustment of the logistic and gompertz model with structure of first-order autoregressive errors in the study on the ‘Dwarf green’ coconut fruit growth based on longitudinal and cross-sectional internal cavity diameter data (DLCI and DTCI). Model adjustments showed positive residual autocorrelation, according to the Durbin-Watson test and for both variables, DLCI and DTCI, the residue was modeled according to first-order autoregressive process (AR1). The analysis was performed using the least squares method in the PROC MODEL of the SAS software and results indicated that for both characteristics under study, the logistic model was the most appropriate in describing fruit growth and, according to the model, fully developed ‘Dwarf green’ coconut fruits have longitudinal and cross-sections internal cavity diameter of approximately 7.39 cm and 7.60 cm, respectively.

AGE-RELATED CHANGES IN THE CROSS-SECTIONAL AREA OF THE I AND II PHALANGES, THEIR BONE MARROW CAVITIES AND COMPACTS IN THE POSTNATAL ONTOGENESIS OF ROMANOV SHEEP

The article presents the results of morphological studies of cross-sectional area growth in the first and second phalanges, their bone-marrow cavities and compacted tissue in the postnatal ontogenesis of Ro-manov sheep. As the material for this work we used the I and II phalanges, taken from the left thoracic limb of opposite gender twins at birth, as well as at 3,6,9,12 months of age and in adults 3–4 years of age. To identify phalanges development patterns we used classical morphological methods of research: we determined the growth rate (“K”), age-related changes in the cross-sectional area of the first and second fingers, their bone-marrow cavities and compacts in the studied age periods (M ± m) and in relation to the same indicator in adult sheep in %.. The received digital material was subjected to static processing. It was established that, due to the periosteal growth of bone tissue, cross-sectional area of the I and II phalanges increases all the time, reaching the definitive value by 12 months at the I phalanx, and in the II phalanx it occurs somewhat later. More accelerated periosteal growth is observed in both phalanges in the first three months of lambs’ life. Due to the processes of bone resorption on the side of endosteum, the same thing happens with the cross section of bone marrow cavities, they only reach the definitive state a little earlier, that was noted in the cross section of the bones. In general, the intensity of periosteal growth and resorption processes occur more quickly in I phalanges compared with II.

Miniaturized suspended strip-line bandpass filter based on spoof surface plasmon polaritons

In this letter, we propose the design of miniaturized suspended strip-line (SSL) filters based on spoof surface plasmon polariton (SSPP), a sub-wavelength mode confined tightly around artificial structures. To avoid using high-density lossy dielectric fillings, we place a periodic corrugated metallic strips (PCMS) structure in a rectangular metallic cavity. Two probes are positioned near the two ends of PCMS structure. Since PCMS structure support SSPP with shorter wavelength, it can be treated as low-loss artificial dielectrics with high permittivity εr equivalently. The cut-off frequency f lower of waveguide modes in the cavity will be reduced, which, plus the cut-off frequency f upper of SSPP, will produce a pass band between f lower and f upper. Due to high εr, low insertion loss and light weight of the PCMS structure, miniaturized band-pass filters can be implemented using such a configuration. We demonstrated a prototype operating a bandpass filter in 2.7–4.6 GHz. The cross-section of cavity is reduced by more than 75%. The filter is with quite low insertion loss only 0.1–0.3 dB. Both simulation and measurement results verify this design. This work provides an alternative to miniaturized, light-weight, high-efficiency SSL filters.

Experimental and Numerical study of Mixed Convection in a Partially Opened Cavity with Tilted Baffle

In this study the mixed convection heat transfer process in a square cross section cavity with a bottom groove heated from three side walls (left, right, and bottom) with vertically unheated baffle is investigated numerically and experimentally. In the numerical part the in-house CFD commercial code of ANSYS-FLUENT-V.16.0 based on finite volume method has been used to solve the 2D governing equations. The results are represented in terms of wall temperature profiles and Nusselt numbers of the heated wall. For the experimental work, a test rig were built to determine the effect of heater position, baffle height ratio (h/H), the baffle angle for the range of 300 &lt;Re &lt;1000 and 1 &lt;Ri&lt; 700. The experimental results show a good enhancement about (35 %) in heat transfer can be obtained by using the baffle while the maximum values was by using right heater and with baffle angle 90o. The numerical flow visualization gives a good indication to temperature boundary layer and vortices location of flow. Good agreement was observed when comparing the experimental and numerical work and with other pervious work.

Расчет расщепления собственной частоты цилиндрического резонатора твердотельного волнового гироскопа на основе численного интегрирования высокой точности

Solid-state wave gyroscopes are widely used in various fields of technology. The principle of their operation is based on the phenomenon of precession of the elastic wave, which rotates at an angular velocity proportional to the angular velocity of device body rotation. The accuracy of the device is significantly affected by splitting the gyroscope resonator frequency. The article considers splitting caused by the distortion of the cylindrical resonator cross-section shape. Since the splitting is very small, the perturbation method is usually used to determine it. The article proposes a new method for calculating the splitting based on the numerical high accuracy integration of equations of dynamics of a cylindrical shell with a non-circular cross section. To search for two very close frequencies, through the difference of which the splitting was found, a linear boundary eigenvalue problem was solved with retention of a large number of decimal places. Examples of determining the natural frequency splitting are presented for various laws of the distribution of the radial deviation of the cavity cross-section shape along the circumferential coordinate. Verification of the results was performed by the finite element method. When using the method each of the two close frequencies was calculated with high accuracy

Double slapping effects on a supercavitation projectile

Based on the theory of rigid body kinematics, a double slapping theoretical model is established for supercavitation projectile. And a parabolic simplification model is used for replacing the supercavitation equation in the part region of the cavity. Meanwhile, a time interval of two slapping impacts formula is derived from the parabolic simplification model. Then, the Logvinovich bubble expansion equation is discretized by using the Compound Simpson Formula and the cavity cross-section area of the projectile tail is solved in the condition that the projectile decelerates movement underwater. And, the cavity radius value of the projectile tail is obtained from Logvinovich bubble expansion equation, and it is substituted into the time interval formula. Compared with the experimental results, it demonstrates the rationality of the parabola simplification model and time interval formula. The projectile slapping impact, which is the main mode of motion in the cavity, is closely related to the stability of the underwater trajectory. This conclusion has a specific significance for studying the instability of the underwater trajectory.

Light-Forbidden Transitions in Plasmon-Emitter Interactions beyond the Weak Coupling Regime

We investigate the impact of light-forbidden exciton transitions in plasmon-emitter interactions beyond the weak coupling regime. We consider a V-type quantum emitter, with dipolar and quadrupolar excited states, placed at the subnanometric gap of a particle-on-a-mirror metallic cavity. We present a fully analytical description of the near-field population dynamics and far-field scattering spectrum of the hybrid system. Our approach enables us to reveal two realistic system configurations in which the dipole-inactive exciton alters significantly and in completely opposite ways the Purcell enhancement and Rabi splitting phenomenology, effectively enlarging or reducing the emitter lifetime and generating or removing spectral features in the cavity cross section.