Cylindrical Structures Research Articles

A disposable cup inspired smart floor for trajectory recognition and human-interactive sensing

Smart floor is an indispensable component of future smart buildings, it is urgent to develop a low-cost, self-powered, and high reliability smart floor. Herein, we propose a disposable cups inspired self-powered smart floor (DCIS-floor) for trajectory recognition and human-interactive sensing. The conical surface of the cup-shaped triboelectric nanogenerator (TENG) is greater than the projected area, resulting in an increased working area of functional materials on a limited floor. This enables more power generation units to be arranged on the limited floor while ensuring that each unit can generate sufficient electricity. Both pressure and shear force are applied as two conical surfaces contact, increasing the degree of contact between functional materials while avoiding excessive frictional force and wear during working process. Compared to cylindrical structures, conical structures offer greater flexibility in contact-separation without intricate machining and assembly, which is ideal for efficient large-area manufacturing. In the experiments, DCIS-floor achieves object motion trajectory recognition, visual recognition based trajectory wireless sensing, and pressure distribution sensing functions. Utilizing a convolutional neural network for data analysis, DCIS-floor realizes personnel identification. This work provides an effective method for smart floors in the safety monitoring, intelligent identification, and emergency rescue of future smart buildings.

Quasistatic component generation of group velocity mismatched guided waves in tubular structures for microdamage localization

Quasistatic component (QSC) of guided wave (GW) has relatively low attenuation due to low frequency and high sensitivity to microdamage. The group velocity matching between primary GW and its QSC or higher harmonics usually facilitates the measurement of nonlinear signals due to cumulative effect of amplitude, but it restricts the determination of microdamage location. While group velocity mismatch is general for most of the wave mode pairs in nonlinear GW testing, this study presents a novel method for identifying the location of early stage microdamage using QSC generation of ultrasonic GW propagation in tubular structures under group velocity mismatching condition. A three-dimensional finite element (FE) model is developed to provide insights into the generation and propagation characteristics of the QSC induced by both global material weak nonlinearity and simulated local microdamage in metallic pipes. The FE analysis verifies the L(0,1) mode of the QSC generated from propagations of different fundamental wave modes. The generation efficiency and cumulation feature of the QSC pulse are obtained and discussed. By exploiting the group velocity mismatching condition, a microdamage localization method is proposed based on the L(0,1)-QSC mode pair, which requires one-way excitation of only one primary wave. Experiments are conducted using early corrosion aluminum specimens to investigate the QSC pulse signals and verify the proposed method. The FE and experimental results demonstrate the fundamental properties of QSC generation by GWs in isotropic metallic hollow cylindrical structures. The feasibility of the proposed microdamage localization method is validated experimentally for promising industrial applications.

The low frequency multi-linear spectrum vibration control study of cylindrical shell through a semi-analytical method

Dynamic vibration absorber is efficient in controlling low frequency vibration of cylindrical shell, which is meaningful for engineering practice. However, the efficiency of designing dynamic vibration absorber using traditional method is low. This paper demonstrates a semi-analytical method for designing dynamic vibration absorber of cylindrical shell. The convergence analysis presented in the research proves the accuracy of the current method when handling different edge constraints through limited truncation numbers. Additionaly, forced vibration and control of multi-line spectrum vibration of cylindrical shell have also been studied. The comparison between FEM and current method shows a significant improvement when handling equivalent mass, which is a key process when designing dynamic vibration absorbers. Finally, an intriguing relationship is discovered when controlling multiple resonance peaks through a single dynamic vibration absorber. The semi-analytical method described in this paper may be beneficial when controlling the vibration of cylindrical shell structures in the further research.

Cervical Cancer Screening Barriers Among Citizens of Jeddah.

The cervix, a cylindrical structure made of stroma and epithelium, is the lowest point of the uterus. A tissue-proven biopsy of the cervix with histological confirmation is necessary for aberrant cytologic results of Papanicolaou (Pap) smears to rule out cervical cancer. This study investigates barriers to cervical cancer screening among women. A cross-sectional study including 665 Saudi Arabian women residing in Jeddah between the ages of 21 and 65 years was carried out from May to November 2023. A four-part online survey was used to gather the data, which included questions about demographics, cervical cancer screening status, screening barriers, and predictors of cervical cancer screening. The most common barrierto Pap test screening was "have not been to a doctor/no regular provider"(39.7%, N = 251), followed by "lack of provider recommendation/or limited or no information in the community" (30.4%, N = 192) and "low priority/did not perceive need/being healthy" (27.7%, N = 175). The study provides valuable insights into the factors influencing cervical cancer screening in Jeddah, Saudi Arabia. The low prevalence of screening indicates a need for increased awareness and targeted interventions to improve uptake.

An electromagnetic vibration energy harvester with compact flexure guide for low frequency applications

This paper presents the design, modeling, fabrication, and characterization of a novel electromagnetic vibration energy harvester (EVEH) using a compact flexure guide structure and opposing permanent magnets. The flexure guide is a unique cylindrical structure, and can transfer force and motion by the deformation of elastic beams. It allows the single-degree-of-freedom motion characteristic, and eliminates the friction between the permanent magnets and the housing structure, which exists in mostly reported magnet-spring based vibration energy harvesters. The structure also greatly reduces the spacing between the coil and the permanent magnets, which considerably increases the magnetic flux linkage through the coil. Experimental results show that the EVEH prototype can generate an output voltage of 6.08 V and output power of 4.02 mW from 0.1 g acceleration at resonant (19.5 Hz), achieving a normalized power density of 3.28 mW cm − 3g − 2. In addition, the flexure guide can be directly fabricated by 3D printing, which greatly simplifies the harvester assembly compared to other EVEHs reported. In terms of the proposed EVEH, a self-powered sensor network is implemented to transfer the GPS data to some appointed terminals.

Effect of Internal Structure of Circular Dimples on Hydrodynamic Lubrication Characteristics of Thrust Bearings

In this study, the effects of three types of dimples with different internal structures on the fluid lubrication characteristics of seal-like thrust bearings were experimentally and numerically investigated. In the experiments, the load-carrying capacity and the frictional torque were measured. The measurements were performed with a fixed constant film thickness. The behaviors of cavitation bubbles occurred within the dimples were observed through the rotating glass plate. Three types of internal structures of dimples were tested: cylindrical, spherical and conical. The measurement results were simulated by using the Reynolds equation. In addition, applying the periodic condition, a single dimple was analyzed. As the results, in three types of dimples, the load-carrying capacity increased as the rotational speed increased. The cylindrical internal structure built up the largest pressure at the trailing edge of dimples, and consequently the largest load-carrying capacity. The frictional torque also increased with increasing the rotational speed in the dimpled bearings. However, the effect of the internal structure on the frictional torque was not significant. Analytical results showed that the pressure reached the maximum value at the trailing edge of the cylindrical internal structure. The conical and sphere internal structure had the maximum value slightly inside the trailing edge.

Preparation, Structure, and Properties of Chitosan Microtubes

Procedures were developed for forming hollow cylindrical structures with the wall thickness in the micrometer range (microtubes) from chitosan solutions in citric, lactic, and glycolic acids. The procedures are based on the phase-transfer neutralization induced by the transport of ions (hereinafter, ion-induced reaction), occurring at the liquid–liquid or solid–liquid interface, namely, on the polymer-analogous conversion of the salt form of the polymer to the base form in a NaOH or triethanolamine medium or formation of a water-insoluble polyelectrolyte complex with sodium dodecylbenzenesulfonate. Comparative analysis of the dependences of the morphological, structural, elastoplastic, physicomechanical, and biological properties of the structures on the reaction conditions and kind of the organic acid and neutralizing agent was made. The microtubes prepared from a chitosan solution in glycolic acid by ion-induced neutralization at the solid–liquid interface in a NaOH or triethanolamine medium exhibit the optimum levels of strength and elasticity, comparable with those of a fragment of human carotid artery and xenopericardial patch. The hemo- and biocompatibility and controlled biodegradation of these materials make them promising as analogs of biodegradable blood vessel implants.

Numerical Investigation of Phase Change Material-Based Hybrid Battery Thermal Management System for Mass Optimization

In this work, a hybrid battery thermal management system using active cooling and Phase Change Material (PCM) has been studied. The additional weight of PCM poses design challenges, and hence its optimization is required. In this regard, a PCM enclosure of a cylindrical structure with six cylindrical cells is considered in 6-row and 1-column arrangement in the present work. The thermal performance of the proposed system is numerically investigated with different thicknesses of PCM layers at constant heat generation and coolant (air) flow rates. It is found that the battery thermal management with only PCM shows unsatisfactory performance under extended severe operating conditions. However, the addition low-flow convectional cooling improved the performance and the system’s reliability. It is found that for the proposed system, PCM thickness of 1 mm for the first battery cell and 2 mm for the subsequent battery cells help in better heat dissipation showing minimal thermal non–uniformity (1.1 °C) and reduced maximum temperature (39.6 °C) within the battery pack. Consequently, the optimized system shows 68.3% reduction in PCM mass as compared to the case of uniform thickness of the PCM.

3D-printable hydrophobic silicone inks for antiadhesion tough objects via molecular engineering

3D printable hydrophobic ink is highly desirable to simply print hydrophobic objects for various applications, such as oil/water separation. However, printable hydrophobic monomers/inks are limited which seriously restricts the fabrication and application of 3D printing hydrophobic objects. Herein, simulating the crown, trunk, and roots of trees from the molecular levels, coatings/objects were designed and prepared using a 6-functional hyperbranching polyurethane acrylate (PUA) monomer as the “trunk”, mono-acrylate terminated polydimethylsiloxane (Vi-PDMS) as the “leaf”, and tripropylene glycol diacrylate (TPGDA) as the “root”. The printed objects with excellent mechanical properties and stable hydrophobicity with CAs and SAs in the range of 80°–110° and 10°–30°, respectively, and could be used in a variety of environments (e.g., acid-based solution, seawater) for a month. Cylindrical, ladder, and mushroom-shaped micro-nano structures could be prepared to improve the hydrophobicity of the printed objects to achieve CAs up to ∼170°. The antiadhesion tough teeth and microchannels could be prepared facilely with the hydrophobic inks. This work demonstrates a simple and rapid method to manufacture various complex and sophisticated hydrophobic coatings/objects and a broader strategy for 3D printing technology.

Solvent-Tailored Reversible Self-Assembly: Unveiling Ionic Transport Nanochannels in Block Copolymer Composite Electrolytes.

Block copolymer composite electrolytes have gained extensive attention for their promising performance in ionic conductivity and mechanical properties, making them valuable for future technologies. The control of the ionic conductivity through the self-assembly of block copolymers, however, remains a great challenge, especially in confined environments. In this study, we prepare block copolymer composite electrolytes using polystyrene-block-poly(ethylene oxide) (PS-b-PEO, SEO) as the polymer matrix and anodic aluminum oxide (AAO) templates as the ceramic skeleton. The self-assembly of SEO creates nanoscale ion transport pathways in the PEO regions through ionic interactions with lithium salts. The nanopores of the AAO templates provide a confined environment for complex phase separation of SEO controlled by selective solvent vapor annealing. Our findings demonstrate that transforming self-assembled SEO structures allows for precise control of ion transport pathways with cylindrical structures exhibiting 20 times higher ionic conductivities than those of helical structures. For AAO templates with pore diameters of 20 nm (SEO-LiTFSI@AAO-20), the ionic conductivities are approximately 410 times higher than those with pore diameters of 200 nm (SEO-LiTFSI@AAO-200), owing to the larger specific surface areas within the smaller nanopores. Utilizing the self-assembly of SEO not only enables the construction of vertically aligned ion transport channels on various scales but also offers a fascinating approach to tailor the conductive capabilities of composite electrolytes, enhancing the ion transport efficiency and allowing for the flexible design of block copolymer composite electrolytes.

Seismic evaluation of isolation performance on single layer cylindrical reticulated shells supported along four sides

This study investigated the dynamic characteristics and seismic isolation performance of a single-layer cylindrical grid shell structure with lower support structures and different seismic isolation schemes, which encompass the installation of layered rubber bearings and new three-dimensional isolation bearings. Seven reduced-scale models of the structure were tested on a shaking table, with acceleration, strain, and displacement sensors positioned in typical locations. The results showed that the seismic response of the upper cylindrical grid shell structure was amplified by the lower support structure, which indicates that separate seismic designs for both the upper structure and lower support structure are unsafe. The use of layered rubber bearings at the foundation effectively reduced horizontal seismic response but amplified vertical seismic response. To address this issue, the new three-dimensional isolation bearing was proposed, which showed better overall seismic isolation performance compared to the rubber bearings. Additionally, a new seismic isolation scheme was proposed, using a combination of three-dimensional isolation bearings at both the foundation and column tops. This scheme showed superior seismic isolation efficiency compared to other schemes and can reduce the volume and installation difficulty of the three-dimensional isolation bearing. Considering the functional requirements, cost, and technical difficulty is crucial when selecting suitable seismic isolation measures since different schemes have their advantages and disadvantages and perform differently under various seismic conditions.

Effect of the Cross-Section of a Porous Burner on the Combustion Stability Limit of Premixed Oxy-Methane Flames.

This study presents the idea of using a porous media burner to improve the oxy-methane combustion reaction rate and broaden the stability limit. Numerical studies on the premixed combustion of CH4/O2/CO2 in a two-layer porous medium burner using a two-dimensional symmetrical volume-average model with the skeleton mechanism based on OpenFOAM. The combustion characteristics of burners with variable cross-sectional (VC) and straight cylindrical (SC) structures were compared, including stable range, temperature field, thermal cycle efficiency, and CO emissions. It is confirmed that the cross-sectional structure is effective for broadening the stable range, and the broadening rate is more than 4 times. As more heat is lost from the outlet due to the increased cross-section, the solid-phase temperature of VC is lower than that of SC. As a result, the flame temperature of VC will be about 200 K lower than that of SC under the condition of insulated walls. It also leads to a reduction of about 2% in thermal cycle efficiency compared with SC. Meanwhile, it is shown that the VC structure slightly increases CO emissions at low thermal power but is smaller than that of SC at high power. When the wall heat loss of the burner is considered, the VC structure is still effective for improving the stable range. In addition, the VC structure slightly affects flame tilt and temperature uniformity at the burner outlet when the thermal power is large. It is confirmed that the VC structure is effective for increasing the power adjustment range and reducing pollutant emissions at high power.

Multi-patch isogeometric Kirchhoff–Love shell analysis for post-buckling of functionally graded graphene platelets reinforced composite shells

This paper develops a multi-patch isogeometric Kirchhoff–Love shell method for post-buckling of functionally graded graphene platelets reinforced composite (FG-GPLRC) cylindrical, spherical, and conoidal shell structures, which are built with single or multiple NURBS patches. A penalty strategy is employed to weakly couple nonconforming interfaces between adjacent patches. The coupling work induced by enforcing displacement continuity and rotational continuity is added to the equilibrium equation, and the corresponding stiffness matrix is derived in detail. A simplified arc-length method is utilized to capture the complex equilibrium paths including snap-through and snap-back behaviors. Five distribution patterns of the shells including uniform (UD), V-type, A-type, O-type, and X-type are considered. The cylindrical and spherical shells are subjected to concentrated loadings at central points while for conoidal shells the concentrated loadings are enforced at the center points of an edge. The post-buckling of isotropic and laminated shell structures is first studied to validate the developed formulations by comparing the obtained results with those given in existing literature. Then a series of numerical examples considering nonlinear FG-GPLRC shell problems are conducted to explore the effect of various parameters like geometric dimensions, GPL distribution patterns, and shell thickness on the mechanical performance. Finally, the post-buckling of a cylindrical shell subjected to an offset concentrated load, with extremely complicated equilibrium paths, is modeled and analyzed by using the developed multi-patch isogeometric method. The numerical results reveal that the X-type GPL distribution pattern demonstrates better performance in load–deflection responses and provides the largest buckling critical load among the five patterns. Additionally, the increase in height ratio could deteriorate the stability performance of FG-GPLRC conoidal shells.

Axial Structure of Gas Discharge Sustained by the Eigen Dipolar Wave of The Metal Waveguide with Varying Radius Filled by Magnetized Nonuniform Plasma

The article presents the results of the theoretical study of the plasma density axial distribution in a stationary gas discharge sustained by the eigen dipolar wave that propagates in a long cylindrical plasma-metal structure. The discharge structure consists of a column of magnetized non-uniform plasma placed in the metal waveguide of variable radius. The study of the gas discharge is carried out within the framework of the electrodynamic model, in which the main attention is paid to the electrodynamic part of the model. To describe the processes that take place in plasma, the model equations are used. The influence of the metal waveguide inhomogeneity along the structure and the plasma density radial non-uniformity on the phase characteristics of the dipolar wave, its spatial attenuation, the field components radial distribution, the axial distribution of the plasma density sustained by this mode are determined. It is also analysed the condition for the discharge stability and find the regions, where dipolar mode can sustain the stable discharge. The obtained results can be useful for various technological applications.

DETERMINATION OF THE MAIN MECHANICAL CHARACTERISTICS OF CLASSIC GEOMETRIC CONTAINERS WITH HOMOGENEOUS FILLERS

An urgent issue in many branches of the modern economy is the possibility of various uses of large-volume containers of various manufacturing geometries for the purpose of storage, transportation and use of various types of technical liquids, water, etc. The most common geometry for the manufacture of such containers is cylindrical, hemispherical, parabolic tanks. In most cases, the spatial arrangement of such containers during their direct use has a vertical orientation. But as the review and trends of modern uses of such cylindrical structures show, there is a trend towards their horizontal or combined location methods during practical operation. The volume of the filler in the conditions of constant use of such containers is also constantly changing, and therefore the main energy characteristics of the filler materials themselves change accordingly, to which we can attribute the actual volume of the liquid, the set of static moments, as a result, the coordinates of the center of gravity, moments of inertia relative to certain coordinate axes, planes, etc. The issue of changing certain geometric characteristics when changing the location of such cylindrical containers from horizontal to vertical or vice versa can be interesting and relevant. A significant number of sectors of the economy show interest in plastic horizontal containers for water storage, and this is understandable, because the ease of use and variety of products attract an increasing number of consumers. Plastic types of cylindrical containers have been gaining popularity in various industries for a long time due to their useful features. Innovative technologies and materials have made it possible to create plastic products of various shapes, sizes and purposes, and this has many obvious advantages. The use of plastic materials in the manufacture of various containers allows to significantly reduce the initial weight of such a product in comparison with its metal counterparts or glass products, which means that when establishing the main energy characteristics, the weight of the container itself can be neglected. In addition, the use of this type of container is convenient for its transportation, installation, etc.

Wave diffraction and radiation studies of an array of coaxial double-layer porous cylindrical structures placed on a porous seabed

This article theoretically investigates the diffraction and radiation of an array of coaxial double-layer porous cylindrical structures placed on a porous seabed. The array of the structures is considered a bottom-mounted cylindrical structure with vanishing thickness. Under the assumption of a small amplitude wave theory, the hydrodynamic characteristics of an array of coaxial double-layer porous cylindrical structures are investigated. The diffraction and the radiation of the structure array are investigated using the eigenfunction expansion method, Bessel function addition theory, and Darcy's law. Analytical expressions for the velocity potentials and free-surface elevations for the diffraction and radiation of the structural array are derived. Finally, the unknown coefficients of the velocity potential are determined using the matching feature function method. After completing the validation, a detailed parameter study is conducted on the structural array, and the hydrodynamic characteristics of the structure array under the influence of different parameters are discussed and explained. Taking the horizontal layout as an example, the results show that in addition to the influence of structure parameters such as porosity, the radius ratio, and the cylinder distance on the hydrodynamic presence of the array of porous structures, the number of cylinders has a greater influence on the hydrodynamic characteristics of the array of porous structures. The calculation results of the diffraction and radiation of an array of porous structures placed on a porous seabed are closer to the actual situation, which can better understand the interaction between waves and porous structure and provide effective theoretical reference for engineers to design ocean structures.

Numerical Simulation of Hetero Dielectric Trench Gate JAM Gate-All-Around FET (HDTG-JAM-GAAFET) for Label Free Biosensing Applications

The label free detection of various biomolecules associated with different diseases has been proposed in this manuscript using a novel biosensor design named as the Hetero Dielectric Trench Gate Junctionless Accumulation Mode Gate-All-Around FET (HDTG-JAM-GAAFET). This biosensor employs a silicon cylindrical Gate All Around FET which operates in Junctionless Accumulation Mode (JAM) and has a hetero dielectric layer comprised of SiO2 and HfO2. The cylindrical gate structure’s metal gate is trenched into the Hafnium oxide dielectric layer, which provides the gate with enhanced control over the surface characteristics of the channel. A Trench Gate architecture in a hetero dielectric Gate All Around FET is emulated for the biosensing for the first time. The HDTG-JAM-GAAFET has been compared to Normal Gate JAM Gate-All-Around FET (NG-JAM-GAAFET) biosensors immobilizing a variety of neutral biomolecules and biomolecules having a range of positive and negative charges. The effect of biomolecules on HDTG-JAM-GAAFET biosensor’s output properties, including surface potential, electron concentration, threshold voltage drift (ΔVTH), subthreshold leakage current (IOFF), subthreshold slope (SS), switching ratio (ION/IOFF), ION current sensitivity, transconductance (gm), output conductance (gd), channel resistance (Rch) and intrinsic gain ( AVint ) has been studied. For instance, HDTG-JAM-GAAFET biosensor has drain ON-current sensitivity (SION) which is 67.68% greater for gelatin biomolecules, 69.4% higher for positive biomolecules, and 8% higher for negative biomolecules bound in the nanogap cavity than that of a Normal Gate JAM Gate-All-Around FET. The proposed device exhibits exceptional performance characteristics and it can effectively identify specific biomolecules to diagnose many diseases, such as breast cancer, lung cancer, and numerous viral infections, using their respective biomarkers.

Mathematical modeling of non-stationary deformation of cylindrical structures

The paper investigates the dynamic behavior of a hollow elastic cylinder of finite length, placed in a rigid cylindrical shell, under a sharp change in internal pressure. A numerical solution of a two-dimensional dynamic problem is obtained using the method of spatial characteristics. The stress-strain state of an elastic cylinder is described by a system of hyperbolic equations with two circular conical surfaces as characteristic surfaces. The outer cones correspond to longitudinal waves; the inner ones correspond to transverse waves. The calculations were carried out under various conditions at the ends and the outer (contact) surface of the cylinder and shell. An analysis of the results for a cylinder with load-free ends shows that the absence of gluing the outer surface of the cylinder with the shell leads to a significant increase in the velocities of the points of the cylinder. Under the action of internal pressure, the ends move apart, resulting in a significant increase in the radial velocities of the internal channel. Qualitative patterns of behavior of the structures under consideration, which are widely used in mechanical engineering, on impact-type impacts, can be used to improve and optimize them at the design stage.

Efficient NVH Analysis of Electric Motors by Means of 2D Spectral Decomposition of Airgap Forces

The growing popularity of hybrid and electric vehicles has created a need for quieter electric motors. This has led to a focus on designing electric machines with reduced audible noise. Estimating the emitted noise requires complex calculations, but analyzing electromagnetic forces alone can provide valuable insights. Electric motors’ simple cylindrical structure allows for decoupling excitation forces and mode shapes, which are closely related. By representing the internal forces in a complex-valued matrix and calculating its 2D Fast Fourier Transform (FFT), we can obtain a comprehensive 2D spectrum that reveals temporal and spatial frequencies. The method enables individual analysis of unique harmonic components. This paper discusses the mathematical representation of forces, their spectra, and the relationship between force harmonics and mode shapes. Industrial examples of electric power-assisted steering systems demonstrate the practical application of this approach.

Practical tutorial on cylindrical structure vibro-acoustics Part 2 - Acoustics

In part 1 of this tutorial (proceedings of Inter-noise 2022) I explained vibrations in cylindrical shell structures. In that paper I limited the mathematics and focused on the key behavior of shells based on critical parameters like the ring frequency, helical wavenumbers, and mean mobilities over different frequency ranges. I compared measured data to the simple theories. In part 2, I focus on the acoustics of cylindrical shells, including sound within shells and the sound radiated outside them. Exterior sound radiation depends strongly on the circumferential order of the shell modes. Breathing modes near the ring frequency radiate sound extremely well, but have very high impedances, so can be difficult to excite. Beam-like modes, where the entire shell cross-section vibrates transversely, radiate less efficiently, but can be easily driven. Higher order, or 'lobar' modes radiate even less efficiently, but nevertheless are commonly observed in radiated sound spectra due to their low impedances. I also review statistical estimates of radiation efficiency of groups of shell modes, which show clear peaks at both the ring frequency as well as at the critical frequency of bending waves. The mathematics of sound inside cylindrical shells is some of the most challenging in vibro-acoustics. At low frequencies, however, the interior sound is dominated by simple one-dimensional planar acoustic waves. At higher frequencies, the sound depends on how well a shell vibration field matches the interior acoustic field based on proximity of resonance frequencies and the similarity of mode shape orders, as well as the 'cut on' frequencies of higher order internal acoustic modes. Finally, I review the well-known phenomenon of how a low shell wall impedance can reduce the effective acoustic sound speed of one-dimensional waves inside cylindrical shells.