Viscous Losses Research Articles

Phononic crystal as a homogeneous viscous metamaterial

At low frequencies, a phononic crystal behaves like a homogeneous medium. Different variants of homogenization technique have been recently proposed to calculate the effective elastic parameters of periodic medium. Here, we develop a homogenization theory for a phononic crystal of solid rods in a viscous fluid. Using the plane wave expansion method, we derive analytical formula for the decay coefficient of low frequency sound propagating in a 2D Bravais lattice with arbitrary unit cell. It is shown that due to the formation of a viscous boundary layer around each cylinder, the losses are enhanced by two to four orders of magnitude as compared to the losses in the free fluid. This enhancement depends on the filling fraction of solid rod and it becomes very strong for almost touching scatterers when sound propagates through narrow slits between the neighbouring rods. Also, the decay coefficient in a phononic crystal scales with frequency as ω2, unlike scaling √ω known for free viscous fluid. The enhanced viscous losses are associated with high effective viscosity of phononic crystal. Like other effective parameters the effective viscosity exhibits strong anisotropy, if the unit cell is asymmetric. The proposed theory can be used for evaluation of efficiency of acoustic devices based on phononic crystals. [This study is supported by NSF Grant No. 1741677.]

Evaluation of Computational Methodologies for Accurate Prediction of Wall Shear Stress and Turbulence Parameters in a Patient-Specific Aorta.

Background: Recent studies suggest that blood flow in main arteries is intrinsically disturbed, even under healthy conditions. Despite this, many computational fluid dynamics (CFD) analyses of aortic haemodynamics make the assumption of laminar flow, and best practices surrounding appropriate modelling choices are lacking. This study aims to address this gap by evaluating different modelling and post-processing approaches in simulations of a patient-specific aorta. Methods: Magnetic resonance imaging (MRI) and 4D flow MRI from a patient with aortic valve stenosis were used to reconstruct the aortic geometry and derive patient-specific inlet and outlet boundary conditions. Three different computational approaches were considered based on assumed laminar or assumed disturbed flow states including low-resolution laminar (LR-Laminar), high-resolution laminar (HR-Laminar) and large-eddy simulation (LES). Each simulation was ran for 30 cardiac cycles and post-processing was conducted on either the final cardiac cycle, or using a phase-averaged approach which utilised all 30 simulated cycles. Model capabilities were evaluated in terms of mean and turbulence-based parameters. Results: All simulation types, regardless of post-processing approach could correctly predict velocity values and flow patterns throughout the aorta. Lower resolution simulations could not accurately predict gradient-derived parameters including wall shear stress and viscous energy loss (largest differences up to 44.6% and 130.3%, respectively), although phase-averaging these parameters improved predictions. The HR-Laminar simulation produced more comparable results to LES with largest differences in wall shear stress and viscous energy loss parameters up to 5.1% and 11.6%, respectively. Laminar-based parameters were better estimated than turbulence-based parameters. Conclusion: Our findings suggest that well-resolved laminar simulations can accurately predict many laminar-based parameters in disturbed flows, but there is no clear benefit to running a HR-Laminar simulation over an LES simulation based on their comparable computational cost. Additionally, post-processing “typical” laminar simulation results with a phase-averaged approach is a simple and cost-effective way to improve accuracy of lower-resolution simulation results.

Kiel Probes for Stagnation Pressure Measurement in Rotating Detonation Combustors

Kiel probes have the potential to be a versatile tool for determining stagnation pressure gain in rotating detonation combustors (RDCs), accompanying the commonly used equivalent available pressure method. Although average pressure gain values determined with Kiel probes are comparable to those from thrust stand experiments, one can expect several sources of measurement error from the unsteady trans- and supersonic environment. This work investigates the response of a Kiel probe in highly unsteady flow, similar to what would be encountered in an RDC. The probe is subjected to an underexpanded starting jet behind an incident shock with Mach numbers of 1.6–2.7, emanating from a shock tube with a reservoir ratio of about 394. The incidence angle of the probe is varied between 0 and 90 deg, as is the probe’s axial location with respect to the tube’s exit plane. High-speed schlieren images reveal the Mach number of the moving shock wave and the structure of the detached bow shock at the Kiel head, which is similar to that of a bluff body. It is shown that the measured stagnation pressure signal is independent of inflow angle over a range of , and that signal attenuation is caused by gas processing through the bow shock and viscous losses in the probe’s capillary. The frequency response of the Kiel probe to sinusoidal, small-amplitude pressure fluctuations is determined in an acoustic calibration facility up to 5500 Hz, confirming linear behavior and that no unwanted resonance is present in the probe. A Berg–Tijdeman representation delivers amplitude ratio and phase lag of comparable magnitude. An assessment of representative boundary conditions reveals that the average stagnation pressure measurement error is of the order of 1%.

Effects of crystalline anisotropy on resonant acoustic loss of torsional quartz viscometers.

Vibrational modes of unrestrained elastic cylinders of trigonal crystals are studied using Ritz-based polynomial approximations for displacements formulated in rectangular Cartesian coordinates. The selected orientation of the threefold trigonal axis is perpendicular to the cylinder axis, corresponding to the configuration employed in torsional quartz viscometry (TQV) for characterizing Newtonian fluids. A revised working equation for TQV is derived, incorporating effects of crystalline anisotropy, and Ritz results are used to numerically quantify effects of acoustic radiation from surface-normal displacements and viscous loss from nontorsional surface-parallel displacements of resonant modes corresponding to the purely torsional modes of isotropic cylinders traditionally employed as an approximation in TQV analysis. For a cylinder typical of TQV, with 3 mm diameter and 50 mm length, the anisotropy-related correction to the extracted fluid viscosity is a positive shift of 36 ppm relative to the isotropic approximation, if radiative losses are neglected. This contribution is independent of fluid properties. Radiative losses depend on the properties of the fluid and reduce the extracted viscosity. The total magnitude of corrections varies between several tens of parts per million for low density gases to values on the order of 0.01% for normal liquids near atmospheric pressure and 0.06% for superfluid helium.

A DMA-Based Approach to Quality Evaluation of Digitally Manufactured Continuous Fiber-Reinforced Composites from Thermoplastic Commingled Tow

Direct digital manufacturing of continuous fiber-reinforced thermoplastics exhibits the potential to relieve many of the constraints placed on the current design and manufacture of composite structures. At present, the additive manufacturing of continuous fiber-reinforced thermoplastics is demonstrated to varying extents; however, a comprehensive investigation of manufacturing defects and the quality of additively manufactured high fiber volume fraction continuous fiber-reinforced thermoplastic composites is limited. Considering the preliminary nature of the additive manufacturing of continuous fiber-reinforced thermoplastics, composites processed in this manner are typically subject to various manufacturing defects, including excessive void content in the thermoplastic matrix. Generally, quality evaluation of processed composites in the literature is limited to test methods that are largely influenced by the properties of the continuous fiber reinforcement, and as such, defects in the thermoplastic matrix are usually less impactful on the results and are often overlooked. Hardware to facilitate the direct digital manufacturing of continuous fiber-reinforced thermoplastic matrix composites was developed, and specimens were successfully processed with intentionally varied void content. The quality of the additively manufactured specimens was then evaluated in terms of the measured maximum storage modulus, maximum loss modulus, damping factor and the glass transition temperature by means of dynamic mechanical analysis (DMA). DMA allows for thermomechanical (i.e., highly matrix sensitive) evaluation of the composite specimens, specifically in terms of the measured elastic storage modulus, viscous loss modulus, damping factor and the glass transition temperature. Within the tested range of void contents from roughly 4–10%, evaluation by DMA resulted in a distinct reduction in the maximum measured storage modulus, maximum loss modulus and glass transition temperature with increasing void content, while the damping factor increased. Thus, the results of this work, which focused on the effect of void content on DMA measured properties, have demonstrated that DMA exhibits multi-faceted sensitivity to the presence of voids in the additively manufactured continuous fiber-reinforced thermoplastic specimens.

Flow of transversely isotropic fluid in curved pipes

We study a fully developed creeping flow of nematic liquid crystals in a curved pipe with a circular cross-section. A special limit of zero Deborah number and an infinite Ericksen number limit is considered, so the flow and orientation of the director are described by the transversely isotropic fluid (TIF) model. Analytical solutions are obtained by expanding the governing equation in the limit of small pipe curvature δ, defined as the ratio of the pipe radius to the radius of the bend. We show that the presence of bend curvature alters the orientation of the microstructure and axial velocity profile. The additional non-Newtonian stress generates a secondary flow, which consists of two counter-rotating vortices. Two mechanisms responsible for the secondary motion are identified (1) combination of normal stresses with pipe curvature (2) asymmetry of the stress distribution. The relative strength and direction of those mechanisms in the framework of the transversely isotropic fluid model is quantified through a parameter q. For all liquid crystals considered in this paper, the stress asymmetry dominates, thus controlling the direction of the secondary flow, which is opposite to the secondary flow induced by inertia. Finally, we quantify the contribution of the secondary motion to the viscous dissipation and show that additional shearing increases viscous losses and power consumption without contributing to the throughput.

Comparison of Four-Dimensional Magnetic Resonance Imaging Analysis of Left Ventricular Fluid Dynamics and Energetics in Ischemic and Restrictive Cardiomyopathies.

BackgroundTime‐resolved three‐directional velocity‐encoded (4D flow) magnetic resonance imaging (MRI) enables the quantification of left ventricular (LV) intracavitary fluid dynamics and energetics, providing mechanistic insight into LV dysfunctions. Before becoming a support to diagnosis and patient stratification, this analysis should prove capable of discriminating between clearly different LV derangements.PurposeTo investigate the potential of 4D flow in identifying fluid dynamic and energetics derangements in ischemic and restrictive LV cardiomyopathies.Study TypeProspective observational study.PopulationTen patients with post‐ischemic cardiomyopathy (ICM), 10 patients with cardiac light‐chain cardiac amyloidosis (AL‐CA), and 10 healthy controls were included.Field Strength/Sequence1.5 T/balanced steady‐state free precession cine and 4D flow sequences.AssessmentFlow was divided into four components: direct flow (DF), retained inflow, delayed ejection flow, and residual volume (RV). Demographics, LV morphology, flow components, global and regional energetics (volume‐normalized kinetic energy [KEV] and viscous energy loss [ELV]), and pressure‐derived hemodynamic force (HDF) were compared between the three groups.Statistical TestsIntergroup differences in flow components were tested by one‐way analysis of variance (ANOVA); differences in energetic variables and peak HDF were tested by two‐way ANOVA. A P‐value of <0.05 was considered significant.ResultsICM patients exhibited the following statistically significant alterations vs. controls: reduced KEV, mostly in the basal region, in systole (−44%) and in diastole (−37%); altered flow components, with reduced DF (−33%) and increased RV (+26%); and reduced basal–apical HDF component on average by 63% at peak systole. AL‐CA patients exhibited the following alterations vs. controls: significantly reduced KEV at the E‐wave peak in the basal segment (−34%); albeit nonstatistically significant, increased peaks and altered time‐course of the HDF basal–apical component in diastole and slightly reduced HDF components in systole.Data ConclusionThe analysis of multiple 4D flow‐derived parameters highlighted fluid dynamic alterations associated with systolic and diastolic dysfunctions in ICM and AL‐CA patients, respectively.Level of Evidence2Technical Efficacy Stage3

Experimental Characterization of Losses in Bladeless Turbine Prototype

Abstract Multidisk bladeless turbines, also known as Tesla turbines, are promising in the field of small-scale power generation and energy harvesting due to their low sensitivity to down-scaling effects, retaining high rotor efficiency. However, low (less than 40%) overall isentropic efficiency has been recorded in the experimental literature. This article aims for the first time to a systematic experimental characterization of loss mechanisms in a 3 kW Tesla expander using compressed air as working fluid and producing electrical power through a high-speed generator (40 krpm). The sources of losses discussed are stator losses, stator–rotor peripheral viscous losses, end-wall ventilation losses, and leakage losses. After description of experimental prototype, methodology, and assessment of measurement accuracy, the article discusses such losses aiming at separating the effects that each loss has on the overall performance. Once effects are separated, their individual impact on the overall efficiency curves is presented. This experimental investigation, for the first time, gives the insight into the actual reasons of low performance of Tesla turbines, highlighting critical areas of improvement, and paving the way to next-generation Tesla turbines, competitive with state-of-the-art bladed expanders.

Performance Evaluation of LowThrust Rocket Nozzles of Various Geometries

Issues of viscous loss in rocket nozzle become increasingly more important as the thrust chamber is reduced in size. A properly designed nozzle is critical since small geometrical differences can result in dramatically modified performance. The present study analyzes the performance of conical converging-diverging nozzle for low-thrust rocket application. A total of five nozzles with different area ratio and divergence length were numerically tested; two optimum area ratio nozzles, one underexpanding nozzle and two overexpanding nozzles. The main aim is to analyze the flow phenomena of compressible gas flows within these nozzles and its relation to the rocket performance (i.e. thrust). The axisymmetric flow problems are numerically solved using a well-validated software with the Spalart-Allmaras turbulence model is employed to model the effect of turbulent on the flow. The results revealed technique of eliminating flow separation and obviously, knowledge of the point of separation is essential for performance enhancement. The elimination of flow separation inside the overexpanding nozzle by means of truncating it at a point of separation increases the thrust produced by 18% for a relatively low combustion pressure. It is anticipated that the thrust enhancement would be greater for a higher nozzle pressure ratio (NPR, i.e. the ratio of combustion chamber total pressure and atmospheric static pressure). With the demonstrated performance enhancement, this work serves as a driver for further nozzle enhancement using this technique.

Inhibition of Micro-pitting by Tribofilm-Forming ZrO2 Nanocrystal Lubricant Additives: A Micro-pitting Rig and Transmission Electron Microscope Study

The drive to reduce fuel consumption in transportation has encouraged the emergence of low viscosity lubricants to reduce viscous losses in the engine, drivetrain, and other components. However, viscosity reduction increases the risk of surface damage, thus motivating the development of new anti-wear (AW) additives. Capped ZrO2 nanocrystals (NCs) in base oils have been shown to form AW tribofilms within microscale sliding contacts. However, the potential of ZrO2 NCs to protect surfaces subjected to rolling-sliding contact from macroscale damage, such as micro-pitting, remains unexplored. Here, we explore the ability of ZrO2 NCs to form protective tribofilms under harsh conditions using a micro-pitting rig (MPR), consisting of a three ring-on-roller configuration. The experiments were conducted in polyalphaolephin (PAO) base oil, with and without 5 nm diameter ZrO2 NCs, at two levels of slide-to-roll ratio (SRR) (30% and 0%) and at variable test durations up to long durations (119 h). MPR results showed the use of ZrO2 NCs gives rise to the formation of a tribofilm covering the roller surfaces and decreases the initiation and propagation of micro-pits compared to tests in pure PAO base stock. Transmission electron microscopy (TEM) performed on focused ion beam (FIB) milled cross-sectional samples of the roller surfaces revealed the growth of dense and 50–100 nm thick ZrO2-based tribofilms independent of (SRR), indicating the potential for robust micro-pitting fatigue protection. Nevertheless, small cracks localized within the near surface region of the roller tested at the most severe conditions (30% SRR and 119 h) were observed. The initiation of these cracks was directly related to the presence of manganese sulphide (MnS) inclusions in the steel, revealed using TEM combined with energy dispersive spectroscopy (EDS). The results highlight the benefits of the protective tribofilms formed by ZrO2 NCs and suggest approaches for further optimizing their use.Graphical Abstract

Mathematical Analysis of an Atherosclerotic Artery in Presence of Externally Applied Magnetic Field

In general Atherosclerosis is the narrowing of the arteries caused by formation of plaque (fat and calcium) in inner arterial wall. Hardening in inner wall of the arteries restricts the speed of flow in the arteries, which prevents the organs and tissues to get sufficient oxygenated blood for smooth functioning. The characteristics of blood and its flow can deliberate the fundamental understanding with respect to different rheological and haemodynamic properties of blood, which may help in detection and medication of several cardio-vascular, cerebro-vascular and arterial diseases. Many cardio-vascular diseases are caused due to abnormal flow of blood caused by stenosis (tapered segment in local lumen of the inner arterial wall). The arterial turbulence and flow variations are mainly caused by means of unpleasant arterial flow of blood and viscous head losses due to stenosis. The platelets of blood are generally activated by means of very high shear-stresses near stenosis-throat. The induced thrombosis may cause reduced flow velocity of blood flow to the brain and heart. The collective applications of analytical measures and numerical techniques may analyze the problem for more quantifiable investigation. It has been notified to different analytical study that the resistance of flow causes the increase of inner wall skin-friction with simultaneous increase of height of stenosis. Here the character of flow in artery is considered as axi-symmetric in nature. The measure of asymmetrical stenosis found from a mild stenosed artery in threedimensional structure, so that from physiological approach analysis would be more authentic under consideration with the different parameters of flow. According to the rheological parameters the flow model is considered to be Herschel-Bulkley fluid Model. The outcomes connected to Newtonian model of flow are represented as a distinct event of investigations by assuming the suitable values of fluid-index considered as “n”. Blood is characterized as a fluid having electrical conductance, the externally applied magneto hydrodynamic effects are also applied to reduce the flow acceleration of blood in arteries. The analysis is much efficient to explore the collective measures of data information related to phenomena of physiological problem in Atherosclerotic artery.

4D flow cardiovascular magnetic resonance derived energetics in the Fontan circulation correlate with exercise capacity and CMR-derived liver fibrosis/congestion

AimThis study explores the relationship between in vivo 4D flow cardiovascular magnetic resonance (CMR) derived blood flow energetics in the total cavopulmonary connection (TCPC), exercise capacity and CMR-derived liver fibrosis/congestion.BackgroundThe Fontan circulation, in which both caval veins are directly connected with the pulmonary arteries (i.e. the TCPC) is the palliative approach for single ventricle patients. Blood flow efficiency in the TCPC has been associated with exercise capacity and liver fibrosis using computational fluid dynamic modelling. 4D flow CMR allows for assessment of in vivo blood flow energetics, including kinetic energy (KE) and viscous energy loss rate (EL).MethodsFontan patients were prospectively evaluated between 2018 and 2021 using a comprehensive cardiovascular and liver CMR protocol, including 4D flow imaging of the TCPC. Peak oxygen consumption (VO2) was determined using cardiopulmonary exercise testing (CPET). Iron-corrected whole liver T1 (cT1) mapping was performed as a marker of liver fibrosis/congestion. KE and EL in the TCPC were computed from 4D flow CMR and normalized for inflow. Furthermore, blood flow energetics were compared between standardized segments of the TCPC.ResultsSixty-two Fontan patients were included (53% male, 17.3 ± 5.1 years). Maximal effort CPET was obtained in 50 patients (peak VO2 27.1 ± 6.2 ml/kg/min, 56 ± 12% of predicted). Both KE and EL in the entire TCPC (n = 28) were significantly correlated with cT1 (r = 0.50, p = 0.006 and r = 0.39, p = 0.04, respectively), peak VO2 (r = − 0.61, p = 0.003 and r = − 0.54, p = 0.009, respectively) and % predicted peak VO2 (r = − 0.44, p = 0.04 and r = − 0.46, p = 0.03, respectively). Segmental analysis indicated that the most adverse flow energetics were found in the Fontan tunnel and left pulmonary artery.ConclusionsAdverse 4D flow CMR derived KE and EL in the TCPC correlate with decreased exercise capacity and increased levels of liver fibrosis/congestion. 4D flow CMR is promising as a non-invasive screening tool for identification of patients with adverse TCPC flow efficiency.

A Multi-Phase Closed Pipelines Simulation Approach for Transportation of Heavy Oil with Openfoam in HPC

Transportation of heavy crude oil through closed pipelines is a challenging issue both in offshore and in land oil transportation. The scope of the present paper deals with the computational modelling of two phase extra heavy crude oil &amp; water flow in OpenFOAM. In order to validate the flow model the pressure variation along the length of the channel are investigated, which shows the typical plot of two roughly constant pressure lines at different levels connected by a sharp change of pressure at the interface of two fluids. The validated flow model, aims at optimizing the kinematic viscosity of the multiphase flow, by regulating the flow velocity of the components, such that there is minimum viscous heat loss and hence minimum pump power consumption from the horizontal centrifugal pumping system. Using the OpenFOAM(Open Source Field Operation &amp; Manipulation) software, which is free opensource software, developed in 2004, under GNU general public license, paraview has been used here as post processing tool. Multiphase flow simulation is done using the k-ɛ turbulence model in HPC of kanchenjungha cluster, NIT Sikkim, India.

Inversion for Parameters of Mud as a Porous Medium

In this article, the seven input parameters of a porous medium model for mud are defined and inverted for the New England Mud Patch. One distinguishing feature is that the skeletal frame may contain adsorbed water, and the pore water may contain suspended solid material. This means that the effective properties of the skeletal frame and pore water are different from that of the pure solid and pure seawater, and the effective porosity is not the same as the bulk water fraction. The model contains two loss mechanisms: creep and viscous loss due to relative motion between skeletal frame and pore water. It is demonstrated that the input parameters could be inverted from the wave speeds, attenuations, and reflection. The inversion from reflection loss exclusively is more difficult due to the relative insensitivity to shear properties. A partial solution is obtained by using a regression relationship to constrain the shear speed. A connection between the assumed shear speed and the inverted compressional wave attenuation is consistent with a recent finding by Godin. Regarding reflection loss from a half-space, for frequencies less than about 10&#x00A0;kHz, a homogeneous medium model is indistinguishable from a porous medium model, and for shear speeds less than 50&#x00A0;m/s, a fluid model would be adequate. The porous medium model does not suffer from these restrictions.

Experimental study on a bottom corner of the floating WEC

The study is investigating the effects of various back bottom corner geometries of the Backward Bent Duct Buoy floating oscillating water column at different wave height conditions. Three BBDB with different geometries of the back bottom corner, namely curved, square, and inclined were used. The 3-dimensional wave basin was used to generate the regular wave spectrum with wave heights of 0.05 m–0.15 m and wave periods of 1 s–5 s. It demonstrated the characteristics inside the air column of each BBDB were significantly influenced by the back bottom corner geometry. The results showed that the curved bottom corner produced the highest water elevation, water column chamber pressure, and outlet air flow rate. This observation was due to the curved geometry that reduced the viscous energy loss from the body surface and water. Moreover, it was found that the curved bottom corner produced the higher primary conversion efficiency compared to the square and inclined bottom corner. Despite the characteristics inside air column, it was found that the resonance frequency contributed to the maximum value of the primary conversion efficiency regardless of the various geometries of the back bottom corner.

Low-Frequency, Open, Sound-Insulation Barrier by Two Oppositely Oriented Helmholtz Resonators.

In this work, a low-frequency, open, sound-insulation barrier, composed of a single layer of periodic subwavelength units (with a thickness of λ/28), is demonstrated both numerically and experimentally. Each unit was constructed using two identical, oppositely oriented Helmholtz resonators, which were composed of a central square cavity surrounded by a coiled channel. In the design of the open barrier, the distance between two adjacent units was twice the width of the unit, showing high-performance ventilation, and low-frequency sound insulation. A minimum transmittance of 0.06 could be observed around 121.5 Hz, which arose from both sound reflections and absorptions, created by the coupling of symmetric and asymmetric eigenmodes of the unit, and the absorbed sound energy propagating into the central cavity was greatly reduced by the viscous loss in the channel. Additionally, by introducing a multilayer open barrier, a broadband sound insulation was obtained, and the fractional bandwidth could reach approximately 0.19 with four layers. Finally, the application of the multilayer open barrier in designing a ventilated room was further discussed, and the results presented an omnidirectional, broadband, sound-insulation effect. The proposed open, sound-insulation barrier with the advantages of ultrathin thickness; omnidirectional, low-frequency sound insulation; broad bandwidth; and high-performance ventilation has great potential in architectural acoustics and noise control.

A new propulsion concept for high propulsive hydrodynamic efficiency

A novel marine propulsor concept is presented for high hydrodynamic efficiency. Optimum performance is sought by thrust-producing counter-flapping foils cyclically oscillating along a closed trajectory. The thrusting device exhibits low propulsion loading and low viscous losses. In particular, the concept incorporates.-lifting surfaces located at the ship stern with propulsive swept area larger than that of conventional propellers;-optimum spatial distribution of axial velocities induced by the propulsor in the wake.-elimination of transverse velocities induced by the propulsor in directions perpendicular to the ship motion;-minimization of unsteady viscous losses compared to conventional oscillating foil concepts for thrust production.The arrangement of lifting surfaces allows for optimum generation of a steady and uniform overall thrust over the propulsor swept area. In addition, no rudders are needed for directional motion control. Gains in efficiency relative to other propulsion concepts are estimated by potential flow theory. Significant efficiency improvements relative to other advanced propulsors like CRP, cycloidal propellers, etc. are foreseen. An URANS method is used to validate and quantify energy savings in open water conditions for a particular design case.

Higher-order Lamb waves with quasi-zero surface displacement components on a GaAs piezoelectric plate

Higher-order Lamb waves with quasi-zero surface displacement components are reported on (100)-cut GaAs propagating along the <110> direction where the total displacement at the surface of the plate is less than 10% of the maximum total displacement. The dispersion curves and the displacement component profiles show the reduction of total displacement at the surface of the plate starting when the phase velocities of the higher-order modes are crossing the shear bulk acoustic wave velocity to the value as low as 5%. Due to the concentration of acoustic energy inside the plate, the reported quasi-zero plate acoustic waves (QZ-PAW) further reduce the radiation of acoustic energy when the plate surface is in contact with liquid. The experimental results validate the occurrence of QZ-PAW with a reduction of viscous damping insertion loss compared to previously reported quasi-longitudinal Lamb waves. The results demonstrate the potential QZ-PAW mode for emerging applications such as dual-mode PAW sensors, PAW devices with integrated sensor and actuator, thin-film and ultra-high frequency PAW sensors in highly viscous liquid media.

Analytical, computational, and experimental study of thermoviscous acoustic damping in perforated micro-electro-mechanical systems with flexible diaphragm.

An analytical model for the damping and spring force coefficients of micro-electro-mechanical systems (MEMS) with a flexible diaphragm is developed. The model is based on the low reduced-frequency method, which includes thermal and viscous losses as well as inertial and compressibility effects. Specifically, the solutions are derived for circular MEMS with a clamped diaphragm with both open-edge and closed-edge boundaries. The deflection function of the circular clamped diaphragm is incorporated into the thermoviscous acoustic (TA) formulation to take into account the effect of the flexibility of the diaphragm. TA finite-element analysis (FEA) is also used to develop a computational model. The analytical results are in good agreement with the FEA results for a wide range of parameters and frequencies. The significance of the effect of the flexibility of the diaphragm on damping for actual MEMS is demonstrated. Measurements of the damping coefficient of circular MEMS are conducted for experimental validation of the presented model. The small difference between the experimental results and the results from the model (less than 6%) validates the accuracy of the presented model. The proposed analytical model can be applied to MEMS with various geometries and boundary conditions.

Calculation of the trumpet impedance with various mouthpieces

This project explored computationally how mouthpieces of various dimensions affect the acoustic input impedance for the entire trumpet. Theimpedance was calculated using a cone approximation. The trumpet was divided into cones shorter than the wavelengths considered. The measurements for the trumpet were taken from the literature. Each cone was further divided into 1 mm-long slices in order to get an accurate value for the thermal and viscous wall losses. The load impedance at the open bell was taken as zero. The input impedance of the trumpet with mouthpiece was calculated iteratively such that the input impedance of one cone was used as the load impedance for the next cone. Calculations were done for frequencies up to 2000 Hz and for a variety of mouthpiece geometries but with the same trumpet sections. The effect of the mouthpiece geometry on the instrument’s impedance spectrum will be discussed.