bluuebunny/crossref_metadata_2025 huggingface dataset:
Design with Nonhomogeneous Materials—Part I: Pure Bending of Prismatic Bars
Authors: Stokes V. K.
Published: December 2011

Because material properties vary from point to point in nonhomogeneous materials, there is some question as to what “properties” are measured in tests such as the tensile test, and how such “properties” can be used in the mechanical design process. In this paper, the mechanical response of nonhomogeneous prismatic bars in pure bending has been shown to depend on parameters that are strongly coupled combinations of geometry and material properties. The purely geometry based inertia tensor in homogeneous beam theory is replaced in the nonhomogeneous case by the rigidity tensor, which combines geometry and material properties. Interpretations for the average elastic moduli, which would be determined by tests on nonhomogeneous materials, have been explored. Also discussed is the usefulness of such average moduli for predicting the mechanical response of nonhomogeneous bars.
Design with Nonhomogeneous Materials—Part III: Shear Effects in the Bending of Thin-Walled Prismatic Beams
Authors: Stokes V. K.
Published: December 2011

A simple theory, in which longitudinal and shear strains are not coupled, has been developed to account for shear effects in the bending of thin-walled nonhomogeneous prismatic beams. This extends the analysis for the pure bending of nonhomogeneous beams, for which the results are known to depend on average “elastic moduli” that are strongly coupled combinations of geometry and material properties. It is shown that shear effects can be analyzed without defining additional average moduli. This theory has been used for determining the shear centers of thin-walled sections.
Measurement of Hydrodynamic Interaction Matrices of Boiler Feed Pump Impellers
Authors: Bolleter Ulrich , Wyss Adolfo , Welte Ivon , Stu¨rchler Rudolf
Published: December 2011

For rotordynamic calculations on multistage pumps, one must know–among other things–the hydrodynamic forces generated by a vibrating impeller. In linearized form these forces may be described by stiffness, damping, and mass matrices. Such matrices were measured with the help of a test apparatus using the “rocking arm” principle for an impeller of 0.35 m (13.8 in.) dia at various speeds. It is shown that the hydrodynamic forces generated by the vibrating impeller can be described reasonably well by the standard rotordynamic stiffness, damping, and mass matrices, except for the direct damping term which had to be supplemented by a damping term whose magnitude is proportional to displacement rather than velocity. It is further shown how the test results can directly be compared with results from tests using circular orbits.
Two-Plane Balancing of a Rotor System Without Phase Response Measurements
Authors: Everett Louis J.
Published: December 2011

This paper presents, and experimentally verifies, a two-plane balancing technique for rigid rotors and possibly flexible rotors operating at a constant speed. The technique, based upon influence coefficients, extends the single-plane four-run balancing procedure to two planes. Like the four-run method, this technique is most easily performed graphically and does not require response phase measurement. Despite the additional runs required to obtain data, its simplicity and applicability to a wide range of equipment renders it more useful, in some cases, than the standard two-plane influence coefficient method.
An Approximate Explicit Solution for Polar Strain of Hydraulically Bulged Circular Diaphragms
Authors: Atkinson M.
Published: December 2011

Requirements for practical bulging tests of sheet metals favor small die aperture and surface extensometry with relatively large gage length. The practice of equating the meridional strain at the pole with the hoop strain indicated by the extensometer introduces significant error into the evaluation of representative strain under these conditions. Exact solutions, based on the measured chord and the embraced segment height, are implicit functions of the diaphragm thickness and require prior knowledge of the material’s properties: they are, therefore, unsuitable for materials testing purposes. An approximate explicit expression for representative polar strain is developed and shown to have good accuracy.
Fatigue Damage of Gear Teeth in Speed Reducers Moving Heavy Rotors
Authors: Michalopoulos D. , Aspragathos N. , Dimarogonas A. D.
Published: December 2011

An analytical investigation was undertaken of the dynamic loading and fatigue of the gear teeth of turbine generator turning gear mechanisms during engagement, using a nonlinear function of speed and load for the coefficient of friction, which was determined experimentally under stick-slip conditions and considering backlash. When heavy rotors are rotating on fluid bearings at low speeds, they are sometimes subject to stick-slip. The fatigue damage resulting in such systems due to the stick-slip self-excited vibrations developed on the bearings, and the backlash of the gear teeth can be predicted by a simulation procedure described in this paper. The effects of some design parameters on the fatigue life reduction and tooth loading are also investigated so that they may be used in design.
A Mathematical Model for Internal Friction and Local Fatigue Damage Based on Populations of Yielding Microelements
Authors: Whaley P. W.
Published: December 2011

A mathematical model for internal friction and fatigue damage based on populations of yielding microelements is described. Using two parameters, the model accounts for amplitude dependence of material damping. For low excitation levels the Zener theory of thermoelasticity is reproduced. The significance of this new damping model is that fatigue damage due to local accumulations of microplastic deformation is quantified. The entropy production is defined by expressing the second law of thermodynamics for irreversible processes as an equality, and quantifying local accumulations of microplastic strain energy as the source of irreversibility. A critical entropy threshold is defined in terms of the local microplastic strain energy density of local failure. The hypothesis is offered that local fatigue damage leading to crack nucleation occurs by exceeding the critical entropy threshold.
In Situ Determination of Rolling Bearing Stiffness and Damping by Modal Analysis
Authors: Kraus J. , Blech J. J. , Braun S. G.
Published: December 2011

A method is presented for the extraction of rolling bearings characteristics (stiffness and damping) under operating conditions. The method is based on experimental modal analysis combined with a mathematical model of the rotor-bearings-support system. The method has been applied for the investigation of the effect of speed, preload, and free outer race bearings on system stiffness and damping. The method proves to be very accurate for stiffness determination and reasonably so for damping.
Nonlinear Steady-State Response of a Rotor-Support System
Authors: Choi Yeon-Sun , Noah Sherif T.
Published: December 2011

A numerical method is presented to determine the steady-state nonlinear response of a rotor-support system due to deadband and rubbing using discrete Fourier transformation and inverse discrete Fourier transformation. Damaging subharmonic and superharmonic responses are found to occur in presence of a side force. The calculated results agree with the general trends which have been observed experimentally by other investigators. The effects of selected nondimensionalized parameters on rotor response are studied.
Stress Analysis of a Spinning Annular Disk to a Stationary Distributed, In-Plane Edge Load
Authors: Chonan S. , Hayase T.
Published: December 2011

In-plane stress distribution in a spinning annular disk is studied analytically. The disk is clamped at the inner boundary and subjected to a stationary distributed load along the outer boundary. The solution is determined through a Galilean transformation by using the Lame´ potential functions and the two-dimensional elasticity theory. Numerical results are presented for WA vitrified grinding wheels with outer radii of 50 mm and inner radii of 25 mm rotating at 3000 rpm and 15000 rpm.
Flexibility Effects—Estimation of the Stiffness Matrix in the Dynamics of a Large Structure
Authors: Amirouche F. M. L.
Published: December 2011

In this paper, an estimation of the stiffness matrix for a mechanical tree-like structure is presented. The coefficients of the stiffness matrix are evaluated based on Kane’s equations together with the finite segment modeling technique and matrix structure analysis. The procedure developed is used to evaluate the stiffness coefficients in the case where the flexibility effects are modeled by uniform beam elements with springs and dampers at the connecting joints. The method presented in this paper is very useful in the study of the dynamics, vibration, and control of a large tree-like structure undergoing large motions. An illustration of how the method is used in extracting the natural frequencies and their corresponding mode shapes is presented. The set of equations developed in this paper are the complement equations used to monitor the transient response of the structure undergoing a rigid-body motion.
Analysis of Lined Ducts With Mean Flow, With Application to Dissipative Mufflers
Authors: Munjal M. L. , Shirahatti U. S.
Published: December 2011

Mufflers with at least one acoustically absorptive duct are generally called dissipative mufflers. Generally, for want of systems approach, these mufflers are characterized by transmission loss of the lined duct with overriding corrections for the terminations, mean flow, etc. In this article, it is proposed that dissipative duct should be integrated with other muffler elements, source impedance and radiation impedance, by means of transfer matrix approach. Towards this end, the transfer matrix for rectangular duct with mean flow has been derived here, for the least attenuated mode. Mean flow introduces a coupling between transverse wave numbers and axial wave number, the evaluation of which therefore calls for simultaneous solution of two or three transcendental equations. This is done by means of a Newton-Raphson iteration scheme, which is illustrated here for square ducts lined with porous ceramic tiles.
Free Vibrations of a Flexible Arm Attached to a Compliant Finite Hub
Authors: Mitchell T. P. , Bruch J. C.
Published: December 2011

A single-joint flexible robot arm consisting of one link and carrying an end effector is modeled by a continuous, uniform, clamped-free beam having a concentrated mass at the free end and being clamped at the other end to a compliant finite hub. The first six natural frequencies are given for various ratios of physical parameters. The modal shapes are also presented along with their orthogonality relationship. The limiting cases of some of the physical parameters are discussed.
Active Vibration Control in Microgravity Environment
Authors: Gerhold C. H. , Rocha R.
Published: December 2011

The low gravity environment of the Space Station is suitable for experiments or manufacturing processes which require near zero-g. Such experiments are packaged to fit into rack-mounted modules approximately 106.7 cm (42 in.) wide × 190.5 cm (75 in.) high × 76.2 cm (30 in.) deep. The mean acceleration level of the Space Station is expected to be on the order of 10−6 g (9.81 × 10−6 m/s2). This steady state acceleration is a superposition of aerodynamic drag, centripetal forces, and the gravitational attraction of the earth and of the moon. Excitations such as crew activity or rotating unbalance of nearby equipment can cause momentary disturbances to the vibration-sensitive payload which degrade the microgravity environment and compromise the validity of the experiment or process. Isolation of the vibration-sensitive payload from structure-borne excitation is achieved by allowing the payload to float freely within an enclosed space. Displacement-sensitive transducers indicate relative drift between the payload and the surrounding structure. Small air jets fixed to the structure direct air flow to impinge on the payload. This thrust force keeps the payload centered within the enclosed space. The mass flow rate of the air jets is controlled such that the resultant acceleration of the payload is less than a criterion of 10−5 g. It is expected that any power or fluid lines that connect the experiment to the Space Station structure can be designed such that their transmitted vibration levels are within the criterion. An experiment has been fabricated to test the validity of the active control process and to verify the flow and control parameters identified in a theoretical model. Zero-g is approximated in the horizontal plane using a low-friction air-bearing table. An analog control system has been designed to activate calibrated air jets when displacement of the test mass is sensed. The experiment demonstrates that the air jet control system introduces an effective damping factor to control oscillatory response. The amount of damping as well as the flow parameters, such as pressure drop across the valve and flow rate of air, are verified by the analytical model.
Identification of a Positive Definite Mass Matrix
Authors: Mottershead John E. , Tee T. K. , Lees A. W.
Published: December 2011

In system identification it is important that any a priori information about the system is utilized in the processing of measured data. Structural vibration problems can be modelled in terms of mass, stiffness, and damping and it is usually the case that the mass matrix is positive definite. In this paper the authors demonstrate how the property of positive definiteness of the mass matrix can be included in the formulation of a continuous frequency domain filter. Results are compared with those obtained from a linear, frequency domain filter which does not impose the condition of positive definiteness on the mass matrix.
The Two-Microphone Sound Intensity Probe
Authors: Pope J.
Published: December 2011

A probe consisting of a pair of pressure-sensing microphones is an integral part of most commonly used sound intensity measurement systems. Sound intensity is a vector that describes the average rate and direction of energy flow in an acoustic field. Recently the measurement of sound intensity has been of increasing theoretical and practical interest. The theory and technology of two-microphone probes are reviewed, with particular attention to the factors that impact the accuracy of intensity measurements. Proper measurement techniques and validation of results are discussed.
Crack Depth Analysis of a Rotating Shaft by Vibration Measurement
Authors: Dirr B. O. , Schmalhorst B. K.
Published: December 2011

The increasing development of measurement techniques for monitoring rotor plants requires improved possibilities for the interpretation of vibration response. Therefore, computer programs that have been used will have to be constantly updated. This especially concerns the modelling of a rotor for calculation purposes. This paper deals with a propagating crack that causes the slender uniform round shaft to vibrate about its main axis. Experiments using a stationary shaft are also performed. Beach marks are used to measure the crack depth and the actual shape of the cracked cross section. These results are compared with those obtained using the dc-potential method, applied to the same cracked cross-section. A finite element model for the cracked region of the rotor is then deduced from the experimental results. Three-dimensional 20-node elements are applied, so a single edge crack of the rotor can be described and varying forms of the cross section—as shown by the beach marks—can be modelled. The additional installation of nonlinear truss elements to the finite element structure permits the breathing of the cracked rotor to be calculated.
Evaluation of Pivot Stiffness for Typical Tilting-Pad Journal Bearing Designs
Authors: Kirk R. G. , Reedy S. W.
Published: December 2011

The manufacturers of high speed turbomachinery are concerned with the accurate prediction of rotor response and stability. One major factor in the placement of system critical speeds and amplification factors is the stiffness and damping of both the fluid-film bearing and support structure. Typical calculated results for tilting-pad fluid-film bearings have neglected the influence of the point or line contact of the pivot support for the individual pads. This paper will review the equations developed considering the Hertzian contact stress and deformation theory and present the equations for pivot stiffness necessary for inclusion in tilting pad bearing computer programs. In addition, the influence of various standard pivot designs will be compared for typical fluid-film bearing stiffness and damping characteristics.
Evaluation of Aerodynamic Instability Mechanisms for Centrifugal Compressors—Part II: Advanced Analysis
Authors: Kirk R. G.
Published: December 2011

The results of advanced analysis for labyrinth seal dynamic characteristics are compared to current methods of calculating aerodynamic excitation and to test rig data published in the literature to date. The results of a shop full load test are presented and compared to predicted stability parameters. Results of the labyrinth analysis of the full-load test compressor are presented. Conclusions and recommendations are given for high pressure compressor rotor dynamics analysis with design guidelines for evaluation of new or proposed compressor designs.
Fuselage Structural-Acoustic Modeling for Structure-Borne Interior Noise Transmission
Authors: Unruh J. F. , Dobosz S. A.
Published: December 2011

Detailed finite element models of a fuselage structure and acoustic cabin volume of a laboratory based prototypical aircraft fuselage were generated for the purpose of studying the predictive capabilities of deterministic modeling procedures for structure-borne noise transmission. Comparative predictions are made to measured wing-to-fuselage attach point inertances and interior noise to force responses. Several structural models with increased structural definition were evaluated. It was found that to accurately predict wing-to-fuselage attach point inertances required increased local area structural definition, while interior noise can be reasonably well predicted without paying additional attention to local area structural details.
Theory Versus Experiment for the Rotordynamic Coefficient of Labyrinth Gas Seals: Part II—A Comparison to Experiment
Authors: Childs D. W. , Scharrer J. K.
Published: December 2011

An experimental test facility is used to measure the leakage and rotordynamic coefficients of teeth-on-rotor and teeth-on-stator labyrinth gas seals. The test results are presented along with the theoretically predicted values for the two seal configurations at three different radial clearances and shaft speeds to 16,000 cpm. The test results show that the theory accurately predicts the cross-coupled stiffness for both seal configurations and shows improvement in the prediction of the direct damping for the teeth-on-rotor seal. The theory fails to predict a decrease in the direct damping coefficient for an increase in the radial clearance for the teeth-on-stator seal.
Damping Matrix Identification Using the Spectral Basis Technique
Authors: Fabunmi J. , Chang P. , Vorwald J.
Published: December 2011

This paper presents a method for estimating the damping matrix of a structural system when the stiffness matrix, mass matrix, and frequency response data are given. The method is based on the fact that the forced responses of a structure can be decomposed into linear combinations of sets of frequency-dependent function. A set of orthonormal basis vectors of the frequency response is first determined. The forced responses are then expressed as linear combinations of these basis vectors. The coefficients of the damping matrix are then solved using the pseudo inverse of these basis vectors. Because the vectors that span the space of the frequency response are required to be linearly independent, an orthogonalization process is used to identify the number of significant basis vectors. Several examples are presented to illustrate the use and advantages of the proposed method.
Dimensional Analysis in Design
Authors: Schnittger J. R.
Published: December 2011

New guidelines for dimensional analysis remove traditional road-blocks to its widespread use in mechanical design. Cases, with or without prior formula given, are exposed as well as those with a governing differential equation. The examples include bevel gear, helical spring, centrifugal pump, journal bearing, vibration of turbine blades, and a disk brake. A matrix method to determine nondimensional groups is reviewed.
Investigation of Fixed-Free Annular Plate Resonant Frequency Predictions
Authors: Flatau Alison , Flandro G. A. , Van Moorhem W. K.
Published: December 2011

Nondimensional frequency parameters for predicting the resonant frequencies of annular plates with fixed-free boundary conditions as the plate inner to outer radius ratio approaches unity have been investigated experimentally. Frequency parameters have been determined by using modal analysis to measure resonant frequencies for annular plates of varied materials, thicknesses, and with radius ratios of 0.5 to 0.9. The data are compared to two different analytical frequency predictions which have been presented as solutions for resonance of fixed-free annular plates based on classical elastic plate theory.
On Free Vibrations of a Thin Spinning Disk Stiffened With an Outer Reinforcing Ring
Authors: Sinha S. K.
Published: December 2011

Thin spinning annular disks, which have widely varying applications ranging from inertial wheels in spacecraft to computer data storage devices, experience some inherent vibration problems during operation. One of the techniques to control the vibrations of the disk, being analyzed in this paper, is to stiffen it by attaching a reinforcing ring at its outer edge. The present work considers the effect of adding such a ring and discusses the changes in the natural frequencies for a large range of design parameters. The classical plate bending equation based upon small deflection theory which includes the contribution of rotational membrane stresses has been used in the eigenvalue formulation. Numerical results presented in a nondimensional form should be useful in predicting the dynamic response of such a disk stiffened with a circular ring under the spinning conditions.
Power Flow Finite Element Analysis of Dynamic Systems: Basic Theory and Application to Beams
Authors: Nefske D. J. , Sung S. H.
Published: December 2011

A power flow analysis has been developed for predicting the vibration response of dynamic systems to high frequencies at which the traditional finite element method is no longer practical. As compared to Statistical Energy Analysis, which predicts an overall vibration response of each dynamic subsystem, the power flow analysis enables one to predict the spatial variation of the vibration response within each subsystem, as well as the power flow and vibration response throughout the entire system. The formulation of the power flow analysis is based on a differential, control-volume approach and is shown to result in a partial differential equation of the heat conduction type which can be solved by applying the finite element method. Example applications to (1) an uncoupled beam and (2) two coupled beams are presented to illustrate the analysis.
The Residual Shaft Bow Effect on Dynamic Response of a Simply Supported Rotor With Disk Skew and Mass Unbalances
Authors: Shiau Ting Nung , Lee En Kuan
Published: December 2011

The effect of residual shaft bow on the dynamic response of a simply supported single disk rotor with disk skew and mass unbalances is studied. The influence of disk-positioning between bearings also is investigated. Under the combined influences, the zero amplitude speed for a thin disk and the first zero amplitude speed for a thick disk are shown to be smaller than or equal to the square root of the ratio of residual bow amplitude to unbalance eccentricity. Moreover, when the rotor passes through the critical speed associated with disk pitch, the rotational amplitudes are greater than when it passes through the first translational critical mode. The results, shown in this study, can significantly assist in the determination of rotor unbalances.
Uniaxial and Equibiaxial Strength of a Vitreous-Bonded Abrasive
Authors: Service T. H. , Ritter J. E.
Published: December 2011

The inert strength of a vitreous-bonded abrasive material was measured using bars in four-point bending and disks in ring-on-ring flexure. It was found that the strength of the bend bars could be described by a unimodal flaw population while the strength of the disks was controlled by an exclusive bimodal mixture of flaw populations. The results show that the Weibull multiaxial statistical theory accurately predicts from bend-bar strength the ring-on-ring strength of this material, provided that the strength-controlling flaw population is properly characterized.
Analytical Results for Optimum Actively Damped Suspensions Under Random Excitation
Authors: Karnopp D.
Published: December 2011

A single degree-of-freedom system under white noise base velocity excitation is optimized using analytical expressions for mean square response quantities. In addition to a parallel spring and passive damper combination, a force generator is assumed to provide an active damping force proportional to the isolated mass absolute velocity. Several optimal and sub-optimal boundary curves are found and the corresponding optimal parameters are also presented. The results show trends which may be useful in designing variable parameter and semiactive vehicle suspensions.
Bending Flexibility of Bolted Flanges and Its Effect on Dynamical Behavior of Structures
Authors: Lifson A. , Smalley A. J.
Published: December 2011

This paper presents a basis for determining the bending flexibility of flanged joints in complex piping systems for use in predicting natural frequencies, mode shapes, and response to excitation forces. Data was developed by a combination of laboratory testing and analysis. Highly instrumented testing initially identified and isolated the contributing deformations in a flanged joint and later provided overall flexibilities of flanged assemblies for verification of the analytical model. The analysis, its results, and model verification are presented in the paper. Further results are provided which compare predicted dynamic characteristics of reciprocating compressor manifold piping systems with measured data obtained in the field for vibration modes which are sensitive to flange flexibility. Consistent good agreement has been achieved of the techniques utilized in some 50 design and field analyses conducted at the Center for Applied Machinery and Piping Technology (CAMPT) at Southwest Research Institute.
Review of Linear Stochastic Optimal Control Systems and Applications
Authors: Panossian H. V.
Published: December 2011

Many complex control systems can be modeled by linear ordinary differential/difference equations with multiplicative and additive noise. The characteristics and behavior of such systems are different from a regular linear quadratic Gaussian system, the basic difference being the inapplicability of the separation or the certainty equivalence principle. Control systems with multiplicative and additive noise are reviewed herein and the fundamental results, in continuous and discrete-time setting, are presented. Furthermore, the advantages and disadvantages are underlined and the need for further research is pointed out.
On the Nature of Natural Control
Authors: Silverberg L. , Morton M.
Published: December 2011

This paper examines families of structural control systems and reveals inherent properties that provide the essential motivation behind the theory of Natural Control. It is determined that the associated fuel consumed by the controls is near minimal when the natural frequencies are identical to the controlled modal frequencies, and when the natural modes of vibration are identical to the controlled modes of vibration. Also, by casting the objective to suppress vibration in the form of an exponential stability condition, it is found that vibration is most efficiently suppressed when the modal damping rates are identical to a designer chosen decay rate. The use of a limited number of control forces over distributed control is characterized by a change in fuel consumed by the controls and by a deterioration in the dynamic performance reflected by changes in the modal damping rates. The Natural Control of a space truss demonstrates the results.
Fatigue Reliability Functions
Authors: Avakov V. A. , Shomperlen R. G.
Published: December 2011

There are many fatigue test and statistical procedures to establish the life distribution function Q = Q(N) at constant stress (S) level. But the stress distribution function, Q = Q(S), at specified life (N) is more important to the designer, and it remains less developed. Generally, if the fatigue life distribution Q(N) and fatigue curve S(N) equations are defined, the fatigue strength distribution Q(S) is implied. However, it has been shown [4, 6, 7, 9] that any life distribution model Q(N) may be transformed into the complicated strength distribution function Q(S). In this study orthogonal relations have been developed in order to predict complications and to resolve the problem under certain conditions. With the aid of the orthogonal relations strength distributions Q(S) have been deduced using (1) lognormal, (2) two-parameter Weibull, and (3) three-parameter logweibull life models Q(N).
Sound Intensity Distribution and Energy Flow in the Nearfield of a Clamped Circular Plate
Authors: Krishnappa G. , McDougall J. M.
Published: December 2011

Sound intensity distribution and energy flow in the nearfield of a clamped circular plate vibrating at its resonant frequencies were investigated. Theoretical calculation of the sound intensity vector was based on Rayleigh’s integral formula and the finite difference approximation of pressures to determine the particle velocity of sound in the fluid medium. The theoretically determined nearfield sound intensity distributions agreed well with the experimental measurements carried out using the two microphone method. Energy lines plotted on radial planes using the method suggested by Waterhouse et al. [3] for the axisymmetric modes of vibration showed the presence of vortex lines close to the nodal lines. The recirculating energy zones appeared to increase with the number of nodal circles, with the farfield radiation predominantly emanating from the center and outer edges of the plate. The theoretical results also revealed the existence of recirculating energy zones for the nonaxisymmetric modes of vibration.
Transfer Matrix Eigensolutions for Damped Torsional Systems
Authors: Doughty S. , Vafaee G.
Published: December 2011

A transfer matrix method is presented for the determination of complex eigensolutions associated with the damped torsional vibrations of single shaft machine trains. The system is described and the natures of the eigenvalues are discussed. The general solution method is developed, and the method is applied to two example problems. One of the examples is quite simple, while the other is entirely realistic.
The Control of Frame Vibration by Friction Damping in Joints
Authors: Beards C. F. , Woowat A.
Published: December 2011

Some effects of friction damping occurring in joints on the frequency response of a portal frame are presented and discussed. The frame was designed so that the joint clamping forces could be varied, allowing some control of the friction damping caused by interfacial slip in the joints. It was found that a joint clamping force less than that required to tightly fasten a joint gave a minimum frame response: reducing the clamping force from 15 kN to 320 N caused a reduction in frame response of 21 dB. Some changes in resonance frequencies were also observed.
Concepts of a General Substructuring System for Structural Dynamics Analyses
Authors: Hale A. L. , Warren L. V.
Published: December 2011

Multilevel substructuring algorithms in structural dynamics are considered together with their software implementation. The paper emphasizes a consistent data structure for representing objects on hierarchical levels. The data structure permits recursive numerical procedures to be easily implemented. As an example, a recursive multi-subspace iteration algorithm is introduced. The paper also considers the definition and implementation of a problem specification language. The language is similar to and retains the expressive power of Lisp. Finally, a numerical example is given.
Reduction of Residual Vibrations in Positioning Control Mechanism
Authors: Yamada I. , Nakagawa M.
Published: December 2011

This paper clarifies numerically and experimentally the characteristics of residual vibrations caused by the natural frequency variation for a positioning mechanism, such that a load modeled as a one-degree-of-freedom vibratory system is driven by a servomotor. Moreover, a multi-design-point method is proposed, which can reduce residual vibrations over a comparatively wide range of parameter variations. It is also shown that this method enables high-speed and accurate positioning for a serial printer carriage.
The Radiation of Sound from Mass-Loaded and Stiffened Beams
Authors: Seybert A. F. , Bowles P. J.
Published: December 2011

This study examines the sound radiation efficiency of uniform, mass-loaded, and stiffened beams. The radiation efficiency of vibrating beams is determined using a finite element vibration model of the beam and a numerical approach to determine the radiated sound field. The radiation efficiency of mass-loaded and stiffened beams deviates from that of the uniform beam for frequencies near and below coincidence. The radiation efficiency of the nonuniform beams depends on the change in natural frequency and the distortion of the mode shape of the vibrating beam. Near coincidence, the radiation efficiency of nonuniform beams approaches that of the uniform beam. Above coincidence, all beams exhibit a radiation efficiency of unity.
Finite Element Modeling of Annular-Like Acoustic Cavities
Authors: Kung Chaw-Hua , Singh Rajendra
Published: December 2011

A finite element technique has been developed to find natural frequencies and modes of undamped three-dimensional acoustic cavities. This method utilizes the analogy between a special form of the discretized transient heat conduction equations and discretized equations of acoustic pressure oscillation. The proposed technique is verified by applying it to several cavities of known theoretical eigen-solutions. Computed results for an acoustic ring, an acoustic disk, and a pure annular cavity match extremely well with exact solutions. In addition, the condensation scheme is investigated and guidelines of selecting acoustic master nodes appropriately are also discussed in the paper. Using the validated finite element method along with suitable condensation, the eigenvalue problem of an annular-like cavity is solved. Since the exact solution for this case is not possible, finite element computations for natural frequencies and modes are compared with the measured results obtained using an acoustic modal analysis experimental technique; again very good agreement has been found.
Forced Vibration of Timoshenko Beams Made of Multimodular Materials
Authors: Bert C. W. , Gordaninejad F.
Published: December 2011

This paper presents a transfer-matrix analysis for determining the sinusoidal vibration response of thick, rectangular cross-section beams made of “multimodular materials” (i.e., materials which have different elastic behavior in tension and compression, with nonlinear stress-strain curves approximated as piecewise linear). An experimentally determined stress-strain curve for aramid-cord rubber is approximated by four straight-line segments (two segments in tension and two segments in compression). To validate the transfer-matrix results, a closed-form solution is also presented for the special case in which the neutral-surface location is uniform along the length of the beam. Also, comparisons are made among multimodular, bimodular (two line segments), and unimodular models. Numerical results for axial displacement, transverse deflection, bending slope, bending moment, transverse shear and axial forces, and the location of the neutral surface are presented for the multimodular model. Effects of translatory and rotatory inertia coefficients on axial force are investigated for a clamped-clamped beam. Moreover, natural frequencies associated with the first three modes of a clamped-free beam are presented. Transfer-matrix results agree very well with the closed-form results for the corresponding material model (one, two, or four segments).
Flow Boiling of Water on Nanocoated Surfaces in a Microchannel
Authors: Trieu Phan Hai , Caney Nadia , Marty Philippe , Colasson Stéphane , Gavillet Jérôme
Published: December 2011

The experiments were performed to study the effects of surface wettability on flow boiling of water at atmospheric pressure. The test channel is a single rectangular channel 0.5 mm high, 5 mm wide and 180 mm long. The mass flux was set at 100 kg/m2 s and the base heat flux varied from 30 to 80 kW/m2. Water enters the test channel under subcooled conditions. The samples are silicon oxide (SiOx), titanium (Ti), diamond-like carbon (DLC), and carbon-doped silicon oxide (SiOC) surfaces with static contact angles of 26 deg, 49 deg, 63 deg, and 104 deg, respectively. The results show significant impacts of surface wettability on heat transfer coefficient.
Theoretical and Experimental Study of a Flexible Wiretype Joule–Thomson Microrefrigerator for Use in Cryosurgery
Authors: Widyaparaga Adhika , Kuwamoto Masashi , Sakoda Naoya , Kohno Masamichi , Takata Yasuyuki
Published: December 2011

We have developed a model capable of predicting the performance characteristics of a wiretype Joule–Thomson microcooler intended for use within a cryosurgical probe. Our objective was to be able to predict cold tip temperature, temperature distribution, and cooling power using only inlet gas properties as input variables. To achieve this, the model incorporated gas equations of state to account for changing gas properties due to heat transfer within the heat exchanger and expansion within the capillary. In consideration of inefficiencies, heat in-leak from free convection and radiation was also considered and the use of a 2D axisymmetric finite difference code allowed simulation of axial conduction. To validate simulation results, we have constructed and conducted experiments with two types of microcoolers differing in inner tube material, poly-ether-ether-ketone (PEEK) and stainless steel. The parameters of the experiment were used in the calculations. CO2 was used as the coolant gas for inlet pressures from 0.5 MPa to 2.0 MPa. Heat load trials of up to 550 mW along with unloaded trials were conducted. The temperature measurements show that the model was successfully able to predict the cold tip temperature to a good degree of accuracy and well represent the temperature distribution. For the all PEEK microcooler in a vacuum using 2.0 MPa inlet pressure, the calculations predicted a temperature drop of 57 K and mass flow rate of 19.5 mg/s compared to measured values of 63 K and 19.4 mg/s, therefore, showing that conventional macroscale correlations can hold well for turbulent microscale flow and heat transfer as long as the validity of the assumptions is verified.
Large-Eddy
Simulation of Shallow Water Langmuir Turbulence Using Isogeometric Analysis and the Residual-Based
Variational Multiscale Method
Authors: Tejada-Martínez Andrés
E. , Akkerman Ido , Bazilevs Yuri
Published: December 2011

We develop a residual-based variational multiscale (RBVMS) method based on isogeometric analysis for large-eddy simulation (LES) of wind-driven shear flow with Langmuir circulation (LC). Isogeometric analysis refers to our use of NURBS (Non-Uniform Rational B-splines) basis functions which have been proven to be highly accurate in LES of turbulent flows (Bazilevs, Y., et al. 2007, Comput. Methods Appl. Mech. Eng., 197, pp. 173–201). LC consists of stream-wise vortices in the direction of the wind acting as a secondary flow structure to the primary, mean component of the flow driven by the wind. LC results from surface wave-current interaction and often occurs within the upper ocean mixed layer over deep water and in coastal shelf regions under wind speeds greater than 3 m s−1. Our LES of wind-driven shallow water flow with LC is representative of a coastal shelf flow where LC extends to the bottom and interacts with the sea bed boundary layer. The governing LES equations are the Craik-Leivobich equations (Tejada-Martínez, A. E., and Grosch, C. E., 2007, J. Fluid Mech., 576, pp. 63–108; Gargett, A. E., 2004, Science, 306, pp. 1925–1928), consisting of the time-filtered Navier-Stokes equations. These equations possess the same structure as the Navier-Stokes equations with an extra vortex force term accounting for wave-current interaction giving rise to LC. The RBVMS method with quadratic NURBS is shown to possess good convergence characteristics in wind-driven flow with LC. Furthermore, the method yields LC structures in good agreement with those computed with the spectral method in (Thorpe, S. A., 2004, Annu. Rev. Fluids Mech., 36, pp. 584 55–79) and measured during field observations in (D’Alessio, S. J., et al., 1998, J. Phys. Oceanogr., 28, pp. 1624–1641; Kantha, L., and Clayson, C. A., 2004, Ocean Modelling, 6, pp. 101–124).
A Comparative Study Based on Patient-Specific Fluid-Structure Interaction Modeling of Cerebral Aneurysms
Authors: Takizawa Kenji , Brummer Tyler , Tezduyar Tayfun E. , Chen Peng R.
Published: December 2011

We present an extensive comparative study based on patient-specific fluid-structure interaction (FSI) modeling of cerebral aneurysms. We consider a total of ten cases, at three different locations, half of which ruptured. We use the stabilized space-time FSI technique developed by the Team for Advanced Flow Simulation and Modeling (T⋆AFSM), together with a number of special techniques targeting arterial FSI modeling, which were also developed by the T⋆AFSM. What we look at in our comparisons includes the wall shear stress, oscillatory shear index and the arterial-wall stress and stretch. We also investigate how simpler approaches to computer modeling of cerebral aneurysms perform compared to FSI modeling.
A DEM-FEM
Coupling Approach for the Direct Numerical Simulation of 3D Particulate
Flows
Authors: Avci B. , Wriggers P.
Published: December 2011

A computational approach is presented in this paper for the direct numerical simulation of 3D particulate flows. The given approach is based on the fictitious domain method, whereby the Discrete Element Method (DEM) and the Finite Element Method (FEM) are explicitly coupled for the numerical treatment of particle-fluid interactions. The particle properties are constitutively described by an adhesive viscoelastic model. To compute the hydrodynamic forces, a direct integration method is employed, where the fluid stresses are integrated over the particles’ surfaces. For the purpose of verifying the presented approach, computational results are shown and compared with those of the literature. Finally, the method is applied for the simulation of an agglomeration example.
Predicted Response of the Die-Carrier Assembly in Flexible Electronics to the Combined Action of Tension and Bending Applied to the Carrier
Authors: Suhir E.
Published: December 2011

A die-carrier assembly, subjected to the external tensile forces and bending moments applied to the flexible carrier is considered. The objective of the analysis is to develop a simple, easy-to-use, and physically meaningful predictive analytical (“mathematical”) model aimed at understanding the physics of the combined action of tension and bending experienced by the carrier and transmitted to the die through the more-or-less compliant bond. The addressed stresses include the interfacial shearing and peeling stresses, as well as the normal stress acting in the cross sections of the die. The obtained formulae can be used in the analysis and design of assemblies of the type in question.
Predicted Thermal Stresses in a Circular Assembly With Identical Adherends and With Application to a Holographic Memory Package Design
Authors: Suhir E. , Gu C. , Cao L.
Published: December 2011

A simple, easy-to-apply and physically meaningful analytical (“mathematical”) stress model is developed for the prediction of the thermally induced stresses in a circular adhesively bonded assembly with identical adherends. The assembly is fabricated at an elevated temperature and is subsequently cooled down to a lower temperature. The developed model can be helpful for stress-strain analyses and physical design of electronic and photonic assemblies of the type in question, and particularly those employed in holographic memory systems.
Dynamics of an Eccentric Rotational Nonlinear Energy Sink
Authors: Gendelman O. V. , Sigalov G. , Manevitch L. I. , Mane M. , Vakakis A. F. , Bergman L. A.
Published: December 2011

The paper introduces a novel type of nonlinear energy sink, designed as a simple rotating eccentric mass, which can rotate with any frequency and; therefore, inertially couple and resonate with any mode of the primary system. We report on theoretical and experimental investigations of targeted energy transfer in this system.
Design and fabrication of GaN crystal ultra-small lateral comb-drive actuators
Authors: Tanae Takuma , Sameshima Hidehisa , Hane Kazuhiro
Published: December 2011

Ultra-small electromechanical comb-drive actuators made of GaN crystal were studied in order to apply them to optical micro-electromechanical systems. Using GaN crystals grown on Si substrates by metal-organic chemical vapor deposition, two kinds of electrostatic comb-drive actuators were designed and fabricated. In the fabrication, due to a residual stress of the grown crystal, the movable part of the actuator suffered considerable deformation depending on the growth conditions. The strain-stress issue of the grown crystal layer is discussed on the basis of lattice misfit and thermal expansion. To compensate for a convex deformation, crystallization tension of a thin HfO2 film deposited on a GaN layer was investigated. The displacement of the actuator having dimensions of 52.2 μm in width and 105.4 μm in length was 1.3 μm at 70 V. Several variable systems will be feasible by combining the actuators monolithically with GaN opt-electronic devices. Future applications are also briefly discussed.
Sounds of Indo-Pacific humpback dolphins (Sousa chinensis) in West Hong Kong: A preliminary description
Authors: Sims Paul Q. , Vaughn Robin , Hung Samuel K. , Würsig Bernd
Published: December 2011

Vocalizations of Indo-Pacific humpback dolphins (Sousa chinensis) in west Hong Kong waters were described from 12 recordings in 2010. A broadband hydrophone system recorded sounds. Vocalizations were characterized as broadband click trains, burst pulses, and narrowband frequency modulated sounds, including whistles generally similar to those of some other delphinid cetaceans. A comparison of results to previous humpback dolphin sound descriptions for Moreton Bay, Australia found broad similarities except for the apparent absence of “quacks” and “grunts” in the present study, which are of low frequency and thus were possibly masked by anthropogenic and other low frequency noise in the Hong Kong habitat.