bluuebunny/crossref_metadata_2025 huggingface dataset:
Bending Stress Reduction Through Mid-Plane Asymmetry in a Composite Sandwich Shell
Authors: Chen Zhaohui , Vinson Jack R.
Published: January 2022

For shell construction of complex shapes, loads such as a uniform internal pressure cause significant bending stresses which are added onto the membrane in-plane stresses that are produced. For these constructions, mid-plane asymmetry of the sandwich or laminate shell can be used effectively to minimize the bending stresses and deformations, due to the bending-stretching coupling effects of the asymmetric construction. As an example, a complex cylindrical shell is studied wherein flat sides are connected by circular comer 90° shell segments, a cross-section that can be effectively used for the fuselages of large transport aircraft.
Compressive Failure of Debonded Sandwich Beams
Authors: Avery John L. , Narayanan Manickam , Sankar Bhavani V.
Published: January 2022

Compression tests were performed on debonded sandwich beams made of graphite/epoxy face-sheets and aramid fiber honeycomb core. The sandwich beams were manufactured using a vacuum bagging process. The face-sheet and the sandwich beam were co-cured, thus the excess resin from the graphite/epoxy prepregs was used to bond the face-sheet and the core. Delamination between one of the face sheets and the core was introduced by using a Teflon® layer during the curing process. Axial compression tests were performed to determine the ultimate load carrying capacity of the debonded beams. Double Cantilever Beam tests were performed to determine the fracture toughness of the face-sheet/core interface. It was concluded that linear buckling analysis was inadequate for predicting the ultimate loads. A post-buckling analysis was carried out using a nonlinear plane finite element model of the sandwich beam. The ultimate loads predicted by the finite element model were reasonably good for specimens with long delaminations.
Hydrofoil Design and Optimization for Fast Ships
Authors: Besnard Eric , Schmitz Adeline , Kaups Kalle , Tzong George , Hefazi Hamid , Kural Orhan , Chen Hsun , Cebeci Tuncer
Published: January 2022

The paper presents a multi-disciplinary design/optimization method for the conceptual design of a hydrofoil based fast ship. The method is used to determine the maximum achievable lift-to-drag ratio (L/D) of an isolated foil-strut arrangement (hopefully greater than 50) at high transit speeds (greater than 75 knots) while lifting masses of 5,000 and 10,000 tons. First, the tools necessary for the study are presented. They comprise a panel method to compute three-dimensional flows around arbitrary configurations with a model for the free surface, a foil cross-section optimization tool, a strut cross-section design tool, and a structural analysis tool. The computational tools are then integrated into a multi-disciplinary design/optimization approach, which is applied to the design of single foil and biplane configurations. Results show that the goal of L/D = 50 is achievable for 75 knots (assuming that techniques can be developed for reducing the skin friction drag to a quarter of its nominal value) and, that for 90 knots, L/D ratios around 45 can be reached. The corresponding break horsepower requirements for 10,000 tons are around 130 khp and less than 200 khp, respectively.
Modeling of a Magnetorheological Fluid Damper Using Coaxial Cylinder Analysis
Authors: Falah Abdulazim H. , Clark William W. , Phule Pradeep P.
Published: January 2022

This paper presents the modeling and experimental testing of a magnetorheological (MR) fluid damper. The damper consists of a main cylinder and piston rod that pushes MR fluid through a very small clearance between the piston and the sidewalls of the cylinder. Magnetic coils are wrapped around the outside of the cylinder to create the magnetic field. The damper model is developed based on analysis of the fluid flow through the annulus between the coaxial piston and cylinder. Newtonian and Bingham shear flow mechanisms are used in the model, which is validated through experimental testing.
Parametric Analysis of Thermally Enhanced BGA Reliability Using a Finite-Volume-Weighted Averaging Technique
Authors: Cheng Hsien-Chie , Chiang Kuo-Ning , Chen Chao-Kuang
Published: January 2022

As the eager demand for high power-handling capability in smaller packages, thermally enhanced BGA (TEBGA) packages provide a very attractive solution in improving the poor thermal performance problems of conventional over molded plastic BGA packages. In this study, with solder joint reliability in concern during the initial package design stage, an engineering empirical approach using a finite-volume-weighted averaging technique is applied for characterizing the strain concentration field around the corners of solder joints due to a dramatic geometry/material change. Furthermore, a parametric finite element analysis is performed over number of geometry/material design parameters to investigate the dependence on the fatigue lives of the thermally loaded solder joint in a typical TEBGA assembly. Through the parametric design together with a rational characterization of the fatigue lives of the solder joints, the reliability characteristics of the thermally enhanced BGA package can then be effectively identified.
Analysis of Process Yield in Low Cost Flip Chip on Board Assembly Processes
Authors: Thorpe Ryan , McGovern Lawrence P. , Baldwin Daniel F.
Published: January 2022

As a concept to achieve high throughput low cost flip chip on board (FCOB) assembly, a process development activity has been undertaken implementing next generation flip chip processing based on large area underfill printing, integrated chip placement and underfill flow, and simultaneous solder interconnect reflow and underfill cure. The goals are to demonstrate feasibility of no flow underfill materials and the high throughput flip chip process, identify the critical process variables affecting yield, and analyze the effects of the process on different underfill materials. Reported in this work is the assembly of a series of test vehicles to assess process yield and process defects. The test vehicles were assembled by dispensing a controlled mass of underfill material on the chip site, followed by alignment and placement of the chip onto the substrate pads, inducing a compression type underfill flow. Next, the assemblies were reflowed in a commercial reflow oven in an air atmosphere to simultaneously form the solder interconnects and cure the underfill. A series of designed experiments identified the critical process variables to be underfill mass, reflow profile, placement velocity, and underfill type. Of particular interest was the fact that different underfill materials exhibited an affinity for unique reflow profiles to minimize process defects.
Automatic Warpage Measurement of Advanced Packages by Optical Method
Authors: He Xiaoyuan , Dai Jiabin , Liu Sheng
Published: January 2022

Optical techniques provide non-contact, full field measurement for the shape and deformation induced thermally mechanically. In this paper, a new portable projected grating moiré system, recently designed and built for component level warpage measurement, is presented and demonstrated. The system is coupled with an environmental chamber for real time measurement during thermal loading. Within a 50 mm square range, a few microns shape and out of plane deformation can be resolved with a standard CCD camera. An imaging analysis software is developed for automatic deformation measurement. Results on a plastic BGA (ball grid array) are reported. This new technique allows precision measurement of warpage, providing valuable information on packaging reliability, manufacturing process, and modeling validation.
Die Stress Measurements Using High Temperature Die-Attachment Materials
Authors: Zou Yida , Suhling Jeffrey C. , Jaeger Richard C. , Lin Shun-Tien , Benoit Jeffrey T. , Grzybowski Richard R.
Published: January 2022

In this work, special (111) silicon stress test chips containing an array of piezoresistive sensor rosettes have been applied within 281-pin ceramic Pin Grid Array (PGA) packages. The test chips contained optimized eight element dual polarity rosettes, which are uniquely capable of evaluating the complete stress state at points on the surface of the die. Calibrated and characterized test chips were attached to the PGA packages using five high temperature die attachment adhesives designed for avionic applications. The adhesive systems included silver filled glasses, polyimide pastes, and thermoplastic films. The resistances of the sensors were recorded at room temperature before and after die attachment. The induced thermal stresses at sites on the die surface have been calculated using the measured resistance changes and piezoresistive theory. A comparison of the room temperature die stresses caused by the different die-attachment materials has been made. The stresses on the die surface after packaging were also characterized as a function of temperature. In addition, thermal aging and thermal cycling tests were conducted on the packages. The various die attachment materials were further evaluated by observing the changes in stress that occurred during these reliability tests. Finally, three-dimensional finite element simulations of the PGA packages were performed, and the stress predictions were correlated with the experimental test chip data.
A Heuristic Model for the Shear and Bulk Viscosity of Concentrated Quiescent Suspensions
Authors: Buyevich Yuri A.
Published: January 2022

A simple model is presented to describe both first (shear) and second (bulk) viscosity coefficients for quiescent suspensions of fine spherical particles flow-induced fluctuations of which may be ignored. Components of the shear viscosity coefficient are distinguished that must be associated with mean flow of the continuous and dispersed phase. In dilute, and also moderately concentrated suspensions, the shear viscosity component attributed to the continuous phase is by far larger than that related to the dispersed phase. In dense suspensions whose concentration approaches that for the state of close packing, it is the shear viscosity of the dispersed phase that plays a dominant role. This viscosity characterizes shear stresses that are transmitted through a transient fluctuating network of occasional interparticle contacts. It is essentially dependent on the particle Peclet number, that is, on relative intensity of Brownian motion of the suspended particles. This dependence is ultimately responsible for the shear-thinning of suspensions, and it is can be described with the help of a reasonable semi-empirical approach. In accordance with the developed model, the bulk suspension viscosity must be wholly attributed to the dispersed phase, and it should not depend on the Peclet number.
Elastic Property of the So Called Newtonian Fluids
Authors: Hasegawa Tomiichi
Published: January 2022

It has been believed that water and silicon oil are Newtonian fluids. But recently it was found that both the fluids do not always fit the result of numerical calculation obtained using Navier-Stokes equation for the pressure drop in the flow through very small orifices. In the present study, the author measures the reaction force and the diameter of jets of water and silicon oil issuing from small orifices and examines the possibility of elasticity in these fluids. The measured values are compared with the numerical values calculated using N-S equation. The result shows that silicon oil of 30 centistokes of kinematic viscosity gives the data consistent with the numerically obtained data but water gives the characteristic of viscoelastic fluids; the reaction force is smaller than the numerically calculated value and the measured diameter of jet is larger than the value predicted with N-S equation. Then water is regarded as viscoelastic fluids and the elastic stress is estimated.
Electrorheological Fluids Applied to Impulsive Loads
Authors: El Wahed Ali K. , Sproston John L. , Schleyer Graham K.
Published: January 2022

This paper is concerned with an experimental determination of the dynamic performance of a prototype device employing an Electrorheological fluid for the rapid modification of the structural characteristics of fixing elements for use in offshore members subject to sudden explosive forces.

The squeeze device has been built to incorporate an ER fluid sandwiched between two electrodes and which, upon sudden impact, is capable of absorbing the impulsive forces.

The transient characteristics of the device were assessed under various mechanical force levels for DC excitation of the fluid in conjunction with a digital controller to provide a constant applied electrical field.

Input and output force levels were monitored using a dedicated data acquisition system in conjunction with a PC enabling the dynamic response of the device to be determined using a combination of displacement, force, velocity and acceleration measurements.
Granular Modeling for Powder-Binder Compound Characterization in Powder Injection Molding
Authors: Aizawa Tatsuhiko , Iwai Takashi
Published: January 2022

New granular modeling is proposed to deal with the powder morphology. The simple shear viscosity testing is utilized to computationally measure the variation of relative viscosity with increasing shear strain or solid loading ratio of particles. Abrupt increase of non-newtonian viscosity with increasing the loading ratio has close relationship with the forced orientation of irregularly-shaped particles. This interparticle interaction reveals on the effect of powder morphology on the actual viscous behavior of the powder-binder compound in the powder injection molding.
Comprehensive Compensation for the Disturbance Torque of Electro-Hydraulic Load Simulator
Authors: Donghai Su , Qinghe Liu , Shenglin Wu
Published: January 2022

Electro-hydraulic load simulator is testing equipment used to simulate the actual torque exerted by air on the steering axle of flying object flying over through air. It belongs to the typical passive loading system, in which, in dynamic loading process, the disturbance torque generated by the rotation of steering axle will decrease loading accuracy and influence control performances of loading system. Because the highest rotation frequency of the steering axle may reach 20Hz, the loading system can not work normally with simple compensation. According to the characteristics of electro-hydraulic simulator, this paper presents a comprehensive compensation method to eliminate the disturbance torque and improve the control performances. Based on the synchro-compensation, this comprehensive compensation feeds the velocity difference between loading motor and synchronous motor forwards to realize the second discharge of disturbance torque coupling to the loading system. After founding mathematics model, the performances of the compensated system is analyzed through computer simulation. The correctness and effectiveness of the comprehensive compensation for eliminating disturbance torque are proved by experimental results.
Numerical Analysis of the Lateral Forces Acting on Spools of Hydraulic Components
Authors: Borghi M. , Cantore G. , Milani M. , Paoluzzi R.
Published: January 2022

This paper deals with the analysis of pressure distribution within the fluid film in the clearance between spool and sleeve of hydraulic components, in order to predict the value of the locking force induced by unbalanced pressure acting on tapered geometries.

Particular care is devoted to the investigation of the lateral force dependency on clearance and eccentricity of the spool.

Some theoretical results are presented, obtained solving (by the finite difference method) the two dimensional Reynolds equation for the fluid film. These results are then compared to those deriving from a generally adopted predictive formula. Results show remarkable differences, up to 70%, in presence of high values of eccentricity.

Moreover, an analogous Reynolds’ based solution is performed for a tapered geometry of the spool with one balancing groove, with particular attention to the influence of its length and position on resulting locking force and leakage flow.

Also the locking force reducing effect of a balancing groove is characterized, and a saturated behavior when the groove is placed very close to the high pressure spool side has been found.
The Generalized Pulse Code Modulation Pneumatic Servo System and its Control
Authors: Wang Xuanyin , Tao Guoliang , Ding Fang
Published: January 2022

Being aimed at the asymmetric pneumatic cylinder, a new type of pneumatic drive circuit is designed. The generalized pulse code modulation (GPCM) pneumatic control system is used for improving performances of the system. In addition, in stead of establishing a nonlinear mathematical model of pneumatic GPCM servo system, system identification by the recursive least square method is applied to find its mathematical model, then a self-tuning controller with the pole-placement approach is designed. In the end, experiments are run in detail. The results show that the GPCM pneumatic servo system is better than the PCM, the self-tuning controller is better than the conventional PID and they are effective in achieving a desired positioning and following accuracy.
Broadband Stator Noise From Distorting Turbulence
Authors: Martinez R. , Rudzinsky J. , Milewski W. M.
Published: January 2022

This paper describes new calculations of broadband stator noise from the ingestion of rapidly distorting turbulence. The stator blades may be thick, cambered, and at an arbitrary angle of attack relative to upstream infinity. The new numerical tool applies Notre Dame’s Euler code “CASGUST” to compute the basic influence function for gust ingestion by a cascade in freefield. i.e., in the absence of a finite-length diffraction duct, or cowl. The theory accounts fror spanwise variations in the building-block input gusts, on the resulting blade loading patterns, and so also on the computed nearfield and farfield pressures, the predictions of broadband radiated stator noise address observer positions both in the aircraft and ground reference frames. They are in the form of frequency spectra for any prescribed ray direction, and of directivity patterns for any chosen frequency.
Flow-Induced Lift Forces on a Towed Sphere
Authors: Lauchle Gerald C. , Jones Andrew R. , Dreyer James J. , Wang Jack
Published: January 2022

An experimental and computational effort to characterize the broadband flow-induced forces on a spherical body that is towed underwater is described. The body itself is the transducer which is comprised of a small geophone encased in a near-neutrally-buoyant sphere, 7.62 cm in diameter. The research described in this paper quantifies the flow-induced unsteady lift force signal as a function of the sphere diameter Reynolds number (215 < Re < 34,290) and the Strouhal number (1.5 < St < 30). It is found that the broadband flow-induced force spectral levels may be separated into two regimes characterized by: 1) unsteady laminar flow in which the forces are proportional to the product of viscosity, mean shear, and area; and 2) turbulent flow in which the unsteady lift forces are proportional to the product of an area and the dynamic pressure of the flow. The low-Reynolds number data were acquired by towing the sphere in various mixtures of glycerine and water. The high Reynolds number lift force spectra, obtained in pure water, are compared to similar data measured previously on a finite-length, right-circular cylinder in cross flow. This comparison indicates that the cylindrical body creates more unsteady side force than does the spherical one, particularly at the lower end of the Strouhal number range. This is also the range of Reynolds number (Re < 3,000) where a simulation of the unsteady laminar flow-induced forces, based on a numerical solution of the Reynolds-averaged Navier-Stokes equations, could be performed. The sphere was held fixed in these simulations, and the resulting forces are thus due to the unsteady flow of fluid around the body itself, with no influence due to free-stream turbulence or tow cable. The computational spectra are found to agree remarkably well with those measured.
Loudspeaker Vibro-Acoustic Computational Analysis Methods and Experimental Validation
Authors: Miccoli Giuseppe , Nizzoli Tommaso , Bie David
Published: January 2022

In this paper the results are reported of a computational analysis aimed at evaluating the sound field emitted by a loudspeaker as a production line commercial product and optimizing its working as a prototype. The elasto-aeoustic characteristics of the loudspeaker have been simulated by means of a commercial computational code. The system fluid/structural model as input to the acoustic analysis has been developed by the finite element code. The results on the emitted sound field have been computed as frequency response functions at the loudspeaker horn groove and acoustic pressure distributions on different planes. Such results achieved by means of 2D/3D finite element (FEM) and boundary element (BEM) coupled analysis methods have been compared and validated by experimental measurement procedures.
Prediction of Engine Cooling Fan Noise Radiation
Authors: Wu Sean F. , Su Shigong , Shah Hemant
Published: January 2022

A semi-empirical formulation is developed for predicting noise radiation from an engine cooling fan. This formulation is based on the mathematical model previously derived by the authors (Wu et al., 1997) for predicting noise spectra of axial flow fans running in a free field. The effects of shroud, radiator/condenser, and engine block on the ingested and discharged flow fields around the fan blades are taken into account by using certain shape functions. The computer model thus developed is used to predict the noise spectra from different fan assemblies under various working conditions, and the results thus obtained are compared with the measured data. Also, this model is used to calculate the overall sound pressure levels from dimensionally similar fans running under different working conditions, and the results are compared with those predicted by the fan laws currently used by engineers in the automotive industry.
Locating Damage in Beams Using Experimental Broadband Vibration Data
Authors: Ratcliffe Colin P.
Published: January 2022

This paper develops a method for locating structural damage using experimental broadband data. The method uses measured frequency response functions to obtain displacement as a function of frequency. The displacement functions are processed to yield a damage index, displayed on a plot of position versus frequency. The method can be applied when there is no a priori knowledge about the undamaged structure. The method can be automated. This paper details the theory of the broadband method, and the results of an experimental demonstration in which a steel beam was damaged with a narrow slot. It is shown that this method is highly sensitive, and can locate a very small amount of damage. For example, the slot was correctly located when there was only a 0.8% reduction in thickness. Traditionally, damage causes a change in natural frequencies, but at this small level of damage the frequency changes were within experimental error.
Improved Accurate Identification of the Modal Damping of Composite Structures Using Multi-Degree-of-Freedom Singular Value Decomposition in the Time Domain
Authors: Gibson Ronald F. , Liu Zhengyu
Published: January 2022

An improved approach for determination of modal vibration parameters of composite structures has been developed on the basis of the Least Squares Complex Exponential (LSCE) method and Singular Value Decomposition (SVD). When the SVD is applied to the Impulse Response Function (IRF) matrix of the system, the order of the system can be easily determined according to the rank of the system matrix. Furthermore, recalculation of the IRF matrix filters the IRF matrix of the system. The signal-to-noise ratio of the IRF is enhanced and, hence, more accurate damping parameters can be identified. MDOF SVD results from both simulations and experiments with E-glass fiber-reinforced composite beams and automotive composite components are presented and compared with results from the SDOF half-power bandwidth method.
Damping of Cantilever Beams With Constrained Viscoelastic Layers Using a Prony Series Representation
Authors: Slanik Marta L. , Nemes James A. , Potvin Marie-Josée , Piedboeuf Jean-Claude
Published: January 2022

The response of cantilevered steel beams treated with various configurations of constrained viscoelastic layers is considered experimentally and analytically. Modal analyses and spike input tests are performed. Analysis of the response of the beams to spike input loading is performed in the time domain using a Prony series representation of viscoelastic behavior. The number of terms required in the series to adequately simulate damping is addressed. Comparison of both natural frequencies and damping factors show good agreement.
Prediction of the Dynamic Response of Compliant Layers on Elastic Plates
Authors: Keltie Richard F.
Published: January 2022

An analytical model of an elastic coating attached to a submerged thin plate has been developed. A plane acoustic wave is incident from the water on to the elastic coating. The normal and tangential velocity components induced in the coating by the acoustic wave are calculated. The effects of incidence angle, frequency, location throughout the coating, and coating properties on the response velocity components are evaluated and examined. Many details of the dynamic response are explained based on simple uncoupled waveguide characteristics of the elastic coating. Typically, the normal velocity components in the coating are several tens of decibels higher in amplitude than the tangential velocity components. Results showed, however, that the tangential velocity component could be increased by an average amount of about 20 dB, without serious degradation of the normal component, by altering the coating elastic properties. In particular, combinations of high longitudinal wavespeed and low shear wavespeed were found to be advantageous. The effects of an outer plate on the compliant coating velocity response components are also presented.
Investigation of Centrifugal Blower Noise
Authors: Banks Christopher L. , Wu Sean F.
Published: January 2022

This paper presents the results of an investigation of centrifugal blower noise. Experiments on three different types of blowers were conducted to determine the major noise generation mechanisms. The information thus gained has led to an innovative noise reduction method utilizing a stationary, non-contacting transition mesh. Experiments showed that an overall noise reduction of up to 4 dB(A) was achieved for the blowers running at impeller tip speeds of 10 to 30 (m/s). In addition, a semi-analytical model was developed to predict the noise spectra from dimensionally similar blowers. This model yielded an acoustic power proportional to the fourth power of the blower speeds. Comparisons of the calculated and measured noise spectra from different blowers running under various speeds were demonstrated. Good agreements were obtained in all cases.
Estimating the Probability Distribution of von Mises Stress for Structures Undergoing Random Excitation: Part 1 — Derivation
Authors: Segalman Dan , Reese Garth
Published: January 2022

The von Mises stress is often used as the metric for evaluating design margins, particularly for structures made of ductile materials. For deterministic loads, both static and dynamic, the calculation of von Mises stress is straightforward, as is the resulting calculation of reliability. For loads modeled as random processes, the task is different; the response to such loads is itself a random process and its properties must be determined in terms of those of both the loads and the system. This has been done in the past by Monte Carlo sampling of numerical realizations that reproduce the second order statistics of the problem. Here, we present a method that provides analytic expressions for the probability distributions of von Mises stress which can be evaluated efficiently and with good precision numerically. Further, this new approach has the important advantage of providing the asymptotic properties of the probability distribution.
A Time-Domain Study of the Use of Moving Weights to Reduce Roll Motions
Authors: Treakle Thomas W. , Mook Dean T. , Liapis Stergios I. , Nayfeh Ali H.
Published: January 2022

The use of actively controlled moving weights on board ships to reduce roll motion is investigated. The weights simulate in principle anti-roll-tank systems and can also be considered a possible anti-roll device in their own right. The investigation is based on time-domain simulations. The full seven-degree-of-freedom set of governing equations for the complete system is derived. And a two-degree-of-freedom non-linear approximation for the roll motion only is derived from these seven equations. The reduced set of equations is used to determine the influence of various parameters and to evaluate control strategies. A PID controller is developed to command the position of the weight and a servomechanism model is used to predict its actual position. Then, the moving-weight system is incorporated into LAMP (Large-Amplitude-Motion Program), a computer code developed by SAIC that integrates the governing equations of the sea and the equations of motion of the ship interactively and predicts the motion of the ship in the time domain. Comparison of the results from the two simulations shows that there is fairly good correlation between the simple and complex models, but the simple model is a little optimistic in predicting the effectiveness of the moving-weight system. The results predict that the moving-weight system can be an excellent roll-suppressing device when (1) the moving weight is as small as 1% of the displacement of the ship, (2) the weight is located below the center of gravity, and (3) the maximum distance the weight moves is as small as 15% of the half-beam.
Simulation and Optimization of a Piezoelectric Micropump
Authors: Mu Y. H. , Hung N. P. , Ngoi B. K. A.
Published: January 2022

A new aluminum based valveless fluid micropump is designed by micromachining method. The pump consists of two fluid diffuser/nozzle elements on each side of a chamber with an oscillating diaphragm which is actuated with a piezoelectric disc. The two simultaneously vibrating diaphragms produce a large oscillating chamber volume. To obtain the optimal structural parameters at the design stage of the pump, the ANSYS finite element software is used for the simulation. The pump prototype with two aluminum diaphragms of ϕ10mm × 0.1mm has been simulated. The chamber oscillating volume can reach as high as 800μl for water pumping.
Analysis on the Stability of Steady-State Responses of an Over-Hung Rotor With Two Disks Supported on Squeeze Film Damper
Authors: Nan Xia , Guang Meng , Tong Fang
Published: January 2022

The stability characteristics of steady-state circular responses of an over-hung rotor with two disks supported on centralized squeeze film damper (SFD) are analyzed in this paper by means of Lyapunov approximation criterion. The eigen-values of the characteristic matrix of variational equations for perturbed motion are solved and the four steps Runge-Kutta integration method is used to evaluate the rotor orbit. It is shown that the unstable response region is greatly influenced by system parameters. With appropriate parameters, die system will have totally stable response and small vibration amplitude. It is also found that the unstable response often appears before the response peak and the system may have three steady-state circular responses. The middle solution is usually unstable and the large solution may also unstable in some cases. There exist other kinds of stable steady-state responses, like non-synchronous responses. Only in very few special cases, the system response is numerically divergent.
Progress in the Analytical Modeling of Stochastic Layers
Authors: Luo Albert C. J. , Han Ray P. S.
Published: January 2022

The exponentially small splitting of separatrix, standard and whisker map approaches. Chirikov overlap criterion, renormalization group technique, incremental energy method are surveyed herein for the analytic modeling of stochastic layers caused by the interaction of nonlinear resonance in nonlinear dynamics. For verification of the analytic modeling, the numerical method to predict the onset of resonance in the stochastic layer through its minimum and maximum energy spectra is also presented. Illustrations of stochastic layers are given by the Poincare mapping section of the Duffing oscillator and periodically-driven pendulum.
Limit Cycles in Ballooning Strings
Authors: Zhu Fang , Rahn Christopher D.
Published: January 2022

This paper uses the Hopf bifurcation theorem to predict the limit cycles of ballooning strings observed in many textile manufacturing processes. The steady state and linearized solutions of the nonlinear governing equations are reviewed. The nonlinear dynamic equations are discretized and projected to a finite dimensional linear normal mode space, resulting in a set of nonlinearly coupled but linearly uncoupled ordinary differential equations. The first two equations, corresponding to the lowest normal mode, are analyzed using the Hopf bifurcation theorem. The first Lyapunov coefficient is calculated to prove the existence of stable limit cycles for double loop balloons with small string length. The bifurcation theorem, however, fails to apply to the large string length Hopf bifurcation point because the first Lyapunov coefficient is indeterminable. Numerical simulation of the nonlinear two-dimensional equations agrees with experimental results quantitatively for small string length and qualitatively for large string length.
Boiling-Induced Two-Phase Natural Convection in an Annular Channel Heated on the Downward Facing Side
Authors: Liu Y. C. , Cheung F. B.
Published: January 2022

The process of two-phase natural convection in an annular channel formed between a heated hemispherical vessel and a surrounding thermal insulation structure is studied theoretically and experimentally. The flow, being driven by buoyancy, is induced entirely by the boiling process taking place on the downward-facing side of the channel, i.e., on the outer surface of the heated vessel. Results of the flow analysis and the experimental observations indicate that there is a strong interaction between the induced two-phase motion and the boiling process. While the mass flow rate of the induced flow is a strong function of the wall heat flux, the rate of boiling is significant affected by the resulting flow. Relative to the case without thermal insulation, a higher boiling heat transfer is obtained in the present case, evidently due to an enhanced mass flow rate induced by the boiling process with the presence of a thermal insulation structure.
Natural Convection From Vertically Stacked Inclined Cylinders
Authors: Clark M. C. , Stewart J. C. , Gir S.
Published: January 2022

While there are published correlations dealing with average natural convection coefficients from a single horizontal, vertical, or inclined cylinder, there do not appear to be any for vertically stacked inclined cylinders. This study investigates natural convection from parallel inclined cylinders spaced two diameters apart in a low Rayleigh number range and Nusselt-Rayleigh number correlations are presented for this case. Convection coefficients generally decreased for both rods as the angle of inclination increased (from horizontal to vertical) and were consistently higher for the bottom rod in all configurations except vertical. Convection from the top cylinder appears to be impaired at this close spacing. Comparisons of the data to modified versions of various horizontal and one inclined cylinder formulation show that while predicted Nusselt numbers have similar trends, no single equation is a good predictor for both rods in this Rayleigh number range.
The Influence of Sun Patches on Buoyancy-Driven Air Movement and Heat Transfer Within a Passive Solar Test Cell
Authors: Arnold’ Peter D. , Hammond Geoffrey P. , Irving Andrew D. , Martin Christopher J.
Published: January 2022

The dynamic (time-varying) behaviour of buoyancy-driven air movement and heat transfer has been examined for a thermally lightweight, low energy test cell subject to external climatic variations. Measurements include heat transfer from a sun patch induced by solar gain through a south-facing, glazed façade This data was analysed by two different methods; simple single-sample thermo-fluid experiments and time-series analysis techniques. These were in turn compared with computational fluid dynamics simulations and recent correlating equations. The results provide insights into the physics of buoyancy-driven convective flows within, and the thermal design requirements for, passive solar buildings.
Turbulent Heat Transfer to Near-Critical Water in a Heated Curved Pipe Under the Conditions of Mixed Convection
Authors: Li L. J. , Lin C. X. , Ebadian M. A.
Published: January 2022

Numerical modeling was performed to investigate the developing turbulent flow and heat transfer characteristics of water near the critical point in a curved pipe. The renormalization group κ-ε model was used to account for the turbulent flow and heat transfer in the curved pipe at a constant wall temperature with or without buoyancy force effect. A control volume finite element method was used to numerically solve the three-dimensional fully elliptic governing equations for the problem. Due to the great variations in physical properties of water near the critical point, the turbulent structure can be significantly altered compared with the pure forced convection in the curved pipe. This study explored the influence of the near-critical pressure and wall temperature on the development of fluid and heat transfer along the pipe.
On Computations of Complex Turbulent Flow by Using Non-Linear K-ω Model
Authors: Song B. , Liu G. R. , Lam K. Y. , Amano R. S.
Published: January 2022

This paper presents the performance of a new non-linear k-ω model for computations of turbulent flows and heat transfer in several different flow types. This model is developed by incorporating cubic terms that take into account the anisotropy of the Reynolds stresses, and the effects of extra strain rates due to a streamline curvature and the rotation of the flow passages. Five cases of turbulent flows are numerically simulated: fully developed turbulent flows in a channel without rotation, in a curved channel, in a rotating channel, and the flow over a two-dimensional blunt rectangular section. Both flow and heat transfer characteristics were examined for the above mentioned flow passages. The governing equations are discretized using a non-staggered finite-volume formulation employing a bounded higher-order differencing scheme. The comparisons are made among the experimental data and the results obtained by DNS, linear and nonlinear k-ω models. It is shown that the non-linear k-ω model generally gives superior results over the existing linear k-ω model by demonstrating better agreement with the data for both flow and heat transfer computations.
Evaluation of Several Typical Correlations for Upward Flow Boiling Heat Transfer of Kerosene in Smooth Tube
Authors: Cheng Lixin , Chen Tingkuan
Published: January 2022

Experiment of upward flow boiling heal transfer with kerosene in vertical smooth tube was conducted. The length of the test section is 2.5m and the size of the tube is Φ19 × 2mm. The test is performed at an absolute pressure of 3 bar. The heat flux ranges from 28.5 to 93.75kW/m2 and the mass flux ranges from 410 to 810kg/m2s. The experimental results are used to evaluate six typical correlations. The selected correlations include Chen correlation, Shah correlation, the correlation of Gungor and Winterton, the correlation of Liu and Winterton, Klimenko correlation and Kandilar correlation. By comparison, the most suitable correlations are recommended for the calculation of flow boiling heal transfer coefficient of kerosene in smooth tube.
Effect of Surface Finish on Flow Boiling Heat Transfer
Authors: Kandlikar Satish G. , Spiesman Paul H.
Published: January 2022

It is well known that the surface structure affects the pool boiling heat transfer from a heater surface. The number and size distribution of cavities present on a heater surface affect the nucleation characteristics. This fact is utilized in developing structured and sintered surfaces for enhanced boiling performance. The nucleate boiling component in flow boiling is also expected to exhibit a somewhat similar dependence.

The present study investigates the flow boiling heat transfer of subcooled water over heater surfaces prepared with different roughness characteristics. The setup consists of a 9.5 mm diameter circular heater placed on the lower wall of a 3 mm × 40 mm horizontal channel. Four different surface finishes are tested on the same heater unit. Each surface is observed under a microscope, and analyzed with an image processing software to obtain the cavity size distribution. Relationships between the cavity size distribution and the heat transfer are then compared for the four surfaces.

The results indicate that the wall superheats for the four surfaces tested were within 0–30 percent of each other for a given heat flux. Although the roughest surface generally performed the best, no definite trend could be observed. It is also noted that the cavity size distribution of a surface is not significantly affected by simple polishing techniques. A commercially prepared sintered surface is also tested. Its performance was markedly above the four roughened surfaces. However, the sintered surface exhibited a large hysteresis effect, while the four roughened surfaces showed little hysteresis under the test conditions.
CHF Enhancement by Modulated Porous-Layer Coating
Authors: Liter Scott G. , Kaviany Massoud
Published: January 2022

The effect of structural modulation of porous-layer coating on the qCHF for horizontal surfaces is examined experimentally. The surface consists of a copper substrate coated with spherical copper particles which are diffusion sintered into modulated structures inside graphite molds. Results are reported for pentane boiling on four different surfaces; a plain uncoated surface, a surface with a porous-layer coating of uniform thickness, and two surfaces with different modulated porous-layer coatings. A two-fold increase in the critical heat flux (qCHF) is found for one of the modulated porous-layer coatings. A brief explanation of the hydrodynamic theory for the qCHF is then given in which it is postulated that the qCHF occurs when columnar, vapor-escape passages through the liquid become unstable and collapse. It is then hypothesized that the enhancement of the modulated coating results from surface-induced changes in the characteristic interfacial wavelengths that stabilize the liquid-vapor interfaces, delaying the collapse of these vapor escape paths, and ultimately increasing qCHF.
Turbulent Heat Transfer in Single Phase Jet Impingement Flow Over a Flat Circular Disk
Authors: Siba Erick A. , Ganesa-Pillai M. , Harris Kendall T. , Haji-Sheikh A.
Published: January 2022

The flow and heat transfer characteristics of a turbulent submerged air jet impinging on a horizontal flat surface is studied. The primary aerodynamics that influence the heat transfer are shown to be the turbulent fluctuations of the free stream velocity. Two regions with distinct flow characteristics are observed, the impingement or stagnation region, and the wall-jet region. Heat transfer relations are derived for each region, based on the assumption that the sum of the laminar and turbulent component of heat flux approximates the total wall heat flux. The laminar component, hlam, of the heat transfer coefficient agrees well with published data. The turbulent component, htur, in the stagnation and wall-jet region are shown to vary linearly with the root mean square value of the fluctuating component of velocity, u’. Unlike the stagnation region, htur in the wall-jet region shows dependence on the Nozzle Reynolds Number, ReD.
The Effect of Geometrical Arrangement on the Transient Temperature Computation of Contacting Spheres
Authors: Siu W. W. M. , Lee S. H.-K.
Published: January 2022

Among engineering systems requiring heat transfer analyses, spheres in a packing structure is one of the more common configuration. A porous medium approach is often used to solve such a complicated system. In fact, it is a useful tool for solving a system involving a large number of spheres, such as in a geothermal system. However for systems containing less spheres, such as in a sintering application, this approach may not be accurate. Recently, a method was developed to solve the mean temperature of contacting spheres in 180 degree orientation. This method used thermal constriction resistances and was able to provide much finer resolution, but contact angles of 180 degree are not a realistic arrangement for spheres in a packing. The present study seeks to extend the earlier formulation to accommodate spheres with varying contact angles. A finite volume formulation was developed using non-uniform grids. Since the grid size must necessarily be small at the contact surfaces, the computation time was significant. To alleviate this, a Multi-Spatial-Temporal Grid Scheme was utilized. A new governing equation has been formulated and verified for packed spheres with varying contact angles. In addition, correlations for the corresponding constriction resistance and the characteristic time parameter have also been developed.
Mixed Convection in Flow Past a Porous Cavity: Application of the UNIFAES Discretization Scheme
Authors: Llagostera Jorge , Figueiredo José R.
Published: January 2022

Combined natural and forced convection occurring in saturated porous media is an important subject in several engineering fields, including design of high performance thermal insulation systems, packed beds, contaminants flow, and the development of geothermal resources.

The paper presents numerical simulation results on mixed convection flow past a porous cavity located in a porous layer. The steady-state regime is studied for several intensities of the buoyancy effects due to temperature variations. The influences of Péclet and Rayleigh numbers on flow pattern and temperature distributions are examined. Local and global Nusselt numbers are reported for the heated wall.

The differential equations were approximated numerically, being discretized by integration over finite volumes. The fluxes at the volume boundaries were represented using the UNIFAES discretization scheme. The UNIFAES, unified finite approaches exponential scheme for convective-diffusive fluid transport equations, has shown excellent accuracy and stability with irregular grids.
Experimental Study of Solids Conveying in Single-Screw Food Extrusion
Authors: Zhang Shibo , Sernas Valentinas
Published: January 2022

Up to now, all the theories on solids conveying in single-screw extruders (Darnell and Mol, 1956; Broyer and Tadmor, 1972; Campbell and Dontula, 1995; Hyun and Spalding, 1997) considered the solids to move as a plug flow (i.e., there is no relative movement in the granular solid, the velocity of the granules is constant in time and uniform in space). Therefore, the solids were treated as a rigid body which never experienced any deformation. But our experiments have shown that in corn meal extrusion, the solids move as a plug only in the loose powder region. After the start of compaction, there is a helical flow in the extruder channel. The flow in this region is not a plug flow at all, and the convective heat transfer is not negligible. Based on our experiments, the whole extrusion process can be divided into four zones, each one having different characteristics. Each zone should be treated with different motion models.