bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regularization Techniques Applied to Nearfield Acoustical Holography
Authors: Williams Earl G. 
Published: November 2021

Abstract
Nearfield Acoustical Holography (NAH) is an inverse problem in wave propagation which has found applications to both interior and exterior noise control problems. We can view the fundamental equation of NAH in the spatial frequency domain as a linear equation, p=Gv, where p is the measured pressure, v is the unknown normal velocity (usually on the surface of a vibrator), and G is the known transfer function. NAH inverts this equation solving for the velocity. However, this equation is ill-posed since small changes in p usually lead to large changes in v. Thus the need for regularization of the inversion. We will discuss regularization techniques applied to NAH, and will compare the errors associated with several regularization schemes; Tikhonov, conjugate gradient, Landweber iteration and a simple exponential filter approach (which appears to provide the best results). Furthermore, in an effort to illuminate the physical propagation mechanisms of NAH, we will discuss these approaches in the light of k-space.
Correcting a Significant Bias Error in the Modal Damping Determined Using Transient Vibration Data
Authors: Ratcliffe Colin P. 
Published: November 2021

Abstract
This paper investigates the experimental vibration technique of impact excitation when used to determine modal damping. Current practices introduce a consistent bias error in the derived modal damping estimates. The error can be significant, with levels of damping being wrongly predicted by a factor of three or more. This paper identifies the source of the error, and derives a simple correction to be applied to the observed modal damping estimates. The procedure is demonstrated by experiment and the results of a round robin exercise.
Vibration Response of Multi-Functional Z-Pin Space Core Sandwich Composites
Authors: Vaidya Uday K. , Nelson Scott P. , Ulven Chad , Mathew Biju 
Published: November 2021

Abstract
Sandwich composite constructions that possess several multi-functional benefits in addition to providing structural strength and stiffness have been investigated in the current work. In comparison to traditional foam and honeycomb cores, the Z-pin reinforced space core provides multi-functionality to route wires and rods, embed electronic assemblies, store fuel and fire-retardant foam and provide tailored damping in structures among other conceivable benefits. The present study deals with vibration characterization of Z-pin sandwich plates with hollow and foam-filled core. A finite element study has been conducted on hollow Z-pin core sandwich panels to investigate the stiffness reduction associated with Z-pin buckling.
The Use of Multifunctional Composite Materials in Large Scale Naval Applications
Authors: Crane Roger M. 
Published: November 2021

Abstract
The U. S. Navy has a long-standing history of ship design using metals. With the improvements in weapon systems, it is becoming increasingly critical to design ship structures not only to satisfy the structural loading but also to exhibit additional multifunctional properties. This is becoming evident with structures such as the Advanced Enclosed Mast Sensor System, AEM/S, which was installed on the USS Radford. This structure was designed to house radar systems and allow the passage of certain radar frequencies through the structure while simultaneously not allowing the penetration of radar at other frequencies. In addition, the structure was designed to reduce the ship’s detectability.
This paper will present a summary of the large-scale composite manufacturing that is being considered for Naval Structures. These structures are being manufactured using low-cost manufacturing techniques and are incorporating multifunctional characteristics in addition to meeting the structural requirement of the application. This paper will provide a historical discussion on the use of composite applications in the surface fleet.
Sudden Drop Phenomena in Natural Frequencies of Composite Plates or Panels With a Non-Central (or Eccentric) Stiffening Plate Strip
Authors: Yuceoglu U. , Özerciyes V. 
Published: November 2021

Abstract
In this study the free bending vibrations of compsite base plates or panels reinforced by a non-central (or eccentric) stiffening plate strip are considered. The base plate and the stiffening plate strip are dissimilar orthotropic plates. They are connected by a very thin and flexible adhesive layer. The dynamic equations of the entire composite plate system are obtained from the “Mindlin Plate Theory” for orthotropic plates. The set of the governing partial differential equations of the composite plate or panel system are reduced to a set of first order ordinary differential equations by the elimination of the time variable and one of the space variables. This final system of the first order differential equations in one space variable is integrated by the “Modified Version of the Transfer Matrix Method”. It was shown that the natural frequencies, at any mode, of the plate or panel system gradually increase at first with the increasing “Bending Cross Stiffness Ratio”. After then, for certain values of this “Ratio”, the natural frequencies for each mode, suddenly drop to a lower value and subsequently start to go up, although slowly, regardless of the support conditions. This unusual “Sudden Drop Phenomena” is explained in detail and, also, the mode shapes corresponding to the sudden drop are presented. The effect of the “hard” and the “soft” adhesive layer on the “Phenomena” are also shown.
Effects of Cure State on the Ultrasonic Nonlinear Parameter in Adhesive Joints
Authors: Liu Guoli , Qu Jianmin , Jacobs Laurence J. 
Published: November 2021

Abstract
The objective of this paper is to characterize the cure state of polymer adhesive joints using nonlinear ultrasonic techniques. To this end, through transmission tests were carried out on joint samples that had been subjected to various curing conditions. In these tests, a 40-cycle harmonic signal was generated by a 2MHz narrow-band PZT transducer as the incident wave. The wave transmitted through the adhesive joint was received with a 4MHz narrow-band PZT transducer. The magnitude of the second order harmonics in the transmitted signal was measured and the corresponding nonlinear parameter β was calculated. A fairly good correlation was observed between the nonlinear parameter and the cure state. It was found that under-curing (lower curing temperature or short curing time) tends to increase the nonlinear parameter.
Parametric Studies of Gas Turbine Combustion NOx Emissions Using KIVA With a Reduced Mechanism
Authors: Su K. , Zhou C. Q. 
Published: November 2021

Abstract
A numerical study was conducted to determine the effects of combustion condition parameters, including inlet temperature and pressure, fuel spray characteristics on NOx emissions in gas turbine combustion using the KIVA-3V code. Log-normal spray distribution was assumed for the simulation of real fuel spray distributions at injection. A simplified mechanism with 17-species and 26-step was employed for chemical reactions of Jet A in a formula of C12H23. A sector model of a typical annular combustor was used in calculations. Flow fields and temperature distributions were analyzed. A wide range of operating condition was varied with the inlet pressure from 0.1 to 2.0 MPa, inlet temperature from 400 to 900 K, and overall fuel/air ratio from 0.012 to 0.08. The results reasonably agreed with those from experimental data and Chemkin modeling, which demonstrates the applicability of KIVA-3V and the chemical mechanism to the predictions of NOx emissions. With respect to the inlet temperature, NOx productions show a trend of monotone increasing. As the inlet pressure increases, NOx emissions increase at the beginning and then decrease. The droplet mean diameter as well as injection velocity and angle were independently varied to distinguish the separate effects of variables involved. It is found that the NOx emissions decrease with the Sauter mean diameter, but increase with the injection velocity and angle of fuel sprays. It appears that KIVA-3V code can be a valuable tool for the development of low emission combustors.
Numerical Prediction of the Transient Operation of a Gas-Fired Reheating Furnace
Authors: Correia Sara A. C. , Ward John , Sousa João L. V. A. 
Published: November 2021

Abstract
The well-known “zone method”, treats thermal radiation in an enclosure in a global manner so that reliable estimates of this mode of heat transfer can be obtained in systems such as gas-fired furnaces. Consequently the paper employs a two-dimensional thermal radiation model in which both the height and length of the furnace was divided into surface and volume zones. An isothermal computational fluid dynamics simulation was used to estimate the relative mass flow rates, and hence enthalpy flows, into or out of each volume zone. This simplified approach was considered to provide a reasonable estimate of the appropriate inter-zone mass flows since the use of small-scale experimental, near ambient temperature models has been shown in the past to give useful data on flow related behaviour of combustion systems. The computing times resulting from the coupling of a multi-zone model with a single isothermal computation of the flows are relatively short so that the transient performance of the reheating furnace can be analysed. The mathematical model was thus used to predict the fuel consumptions and load temperatures in a gas-fired furnace heating steel bars to a nominal discharge temperature of 1250°C over a typical transient operating period of 8 hours including the start-up from cold. The influences of burner geometry as well as the effects of changes to the value of the roof set point temperature which was used to control the thermal input to the burners were studied. The effects of varying the position of the roof temperature control sensor relative to the burners and of changes in the roof construction were also investigated.
On the Effectiveness of Aerodynamic Design and Analysis for Centrifugal Compressors
Authors: Aungier Ronald H. 
Published: November 2021

Abstract
Effectiveness is promoted as an essential feature of a centrifugal compressor aerodynamic design and analysis system. Effectiveness measures the system’s ability to apply sound technology to the wide range of functions the centrifugal compressor engineer needs to perform to develop, apply and maintain these complex machines. Effectiveness compliments efficiency (or productivity) in the overall evaluation of a design and analysis system. This paper discusses several features that an effective aerodynamic design and analysis system should have to support the design and application of industrial process centrifugal compressors. These features are known to be occasionally (if not often) neglected. Yet they all can be incorporated using technology available from the open literature.
Aerodynamic Analysis of Return Channels of Multi-Stage Centrifugal Compressors
Authors: Lenke L. J. , Simon H. 
Published: November 2021

Abstract
From the wide range of applications in which centrifugal compressors are used, two different return channels will be investigated, to demonstrate the influence of flow coefficients onto the flow structure. The investigated return channels are typical to join the exit from one stage of a centrifugal machine to the inlet of the next stage and cover the range of very small and large flow coefficients.
Starting with a comparison between measurements and numerical results to demonstrate the performance of the calculations, the comparison of both return channels show that three-dimensional phenomena and viscous effects such as secondary flow and wakes have appreciable effect on the fluid dynamics and performance of centrifugal compressors. Especially the deceleration of the flow introduces large separations and recirculations which will decrease the efficiency.
Furthermore, a variation of the 180°-bend demonstrates the influence of streamline curvature onto the separation behaviour within the whole return channel.
Due to the strongly three-dimensional flow structure with high streamline curvature and secondary flows on hub and shroud of the return channel vanes, a modified explicit algebraic Reynolds stress model will be used for all calculations.
Fabrication of Porous NiTi Shape Memory Alloy by Elemental Powder Sintering
Authors: Thangaraj K. , Chen Y. C. , Salama K. 
Published: November 2021

Abstract
Porous equi-atomic NiTi Shape Memory Samples were fabricated using the Elemental Powder Sintering technique for varying starting powder sizes of Ni and Ti. The porosity was primarily dependent on the starting powder sizes, and less dependent on the sintering parameters and compaction loads. Sintering at higher temperatures of 1120°C and 48 hrs resulted in a completion of reaction to equilibrium NiTi. The average pore size was found to be in proportion to the starting powder size. The martensitic-austenitic transformations as determined from the electrical measurements had a broad transformation behavior. Compressive tests performed on the sample showed a recoverable strain of up to 2.5 %.
Transient Thermal Stress Analysis of an Interior Crack in Functionally Graded Materials
Authors: Jin Zhi-He , Paulino Glaucio H. 
Published: November 2021

Abstract
An internal crack in a strip of a functionally graded material (FGM) is studied under transient thermal loading conditions. The FGM is assumed having constant Young’s modulus and Poisson’s ratio, but the thermal properties of the material vary along the thickness direction of the strip. Thus the material is elastically homogeneous but thermally nonhomogeneous. This kind of FGMs include some ceramic/ceramic FGMs such as TiC/SiC and MoSi2/Al2O3, and also some ceramic/metal FGMs such as zirconia/nickel and zirconia/steel. Thermal stress intensity factors (TSIFs) are calculated for a TiC/SiC FGM with various volume fraction profiles of the constituent materials. It is found that the TSIF could be reduced if the thermally shocked cracked edge of the FGM strip is pure TiC.
Large Deformation Thermal-Plasticity in a Shape Active Aluminum Metal Matrix Composite
Authors: Armstrong William D. , Lorentzen Torben 
Published: November 2021

Abstract
The present work reports macroscopic thermal mechanical and in-situ neutron diffraction measurements from a 14.4 volume percent, 50.7 at% Ni-Ti fiber actuated 6082-T4 aluminum matrix composite and 6082-T4 homogeneous aluminum control material subjected to a room temperature 5% tensile elongation, and subsequent room temperature to 120 deg. C unconstrained heating process. During the unconstrained room temperature to 120 deg. C heating process, the composite exhibited a 2.2%, nonlinear thermal contraction, while the homogeneous control exhibited the expected linear thermal expansion. The composite thermal compression was clearly the result of a powerful shape memory response in the actuating NiTi fibers. During a subsequent temperature hold at 120 deg. C the composite exhibited an external stress free compressive creep response. The compressive creep behavior was the result of matrix creep under the large compressive stresses imposed by the shape memory active NiTi fibers. In summary, the experimental composite has demonstrated a new form of large deformation self thermal-plastic response which may be used in thermally controlled adaptive machine parts and structures.
Design and Testing of a Turbomachinery Dynamics Simulator
Authors: Duffield Colin J. , Agnes Gregory S. 
Published: November 2021

Abstract
A novel flywheel exitation system for examining the dynamics of bladed-disk assemblies is presented. The excitation is rotated allowing a stationary hub reducing the cost of the testing while maintaining the essential dynamics which lead to HCF failure in turbomachinery. The success of this measurement system offers a new experimental tool to further advance our understanding of bladed-disk dynamics.
The Effect of Mechanical Prestress on Dielectric and Piezoelectric Response of PZT-5H at High Electric Fields
Authors: Chaplya Pavel M. , Carman Gregory P. 
Published: November 2021

Abstract
The dielectric and piezoelectric response of PZT-5H ceramics at high electrical and mechanical loads is presented. The purpose of this study is to provide a detailed explanation of the effect of prestress on the induced polarization and strain. The material is electrically cycled (−2/+2 MV/m, 0/+2 MV/m, and −0.4/+2 MV/m) at constant mechanical prestress levels up to 175 MPa. A descriptive model is used to explain the results in terms of consecutive non-180° domain wall motion only. The response of the material depends on the non-180° domain wall motion produced by the balance between the applied electric field and prestress. The limitation of the model is that it neglects 0° and 180° domains contribution to the response of the actual material.
Dielectric Properties of 0.9PMNTa-0.1PT Relaxor
Authors: Tang Feng , Wang Jin T. 
Published: November 2021

Abstract
Ta-Modified lead magnesium niobate-lead titanate crystalline solutions 0.9PbMg1/3(Nb(1−x)Tax)2/3O3-0.1PbTiO3 (PMN-PT) were first synthesized. The dielectric constant and the dielectric loss of the ceramic for different compositions as a function of frequency and temperature were measured using a Hewlett Packard 4284A LCR precision meter, which can cover a frequency range from 20 to 106Hz in a Delta 9039 test chamber operated between −75°C to +330°C. Dramatic changes of the dielectric properties were observed in Ta-modified 0.9PMN-0.1PT. It was noticed that the samples with appropriate amount of Ta-doping (x = 0.1, 0.2, and 0.3) have smaller grain size, larger dielectric constant, and lower dielectric loss than those of the specimens without doping (x = 0.0) or over doping (x = 1.0) in the frequency band of 100 – 105Hz. Proper Ta-doping in PMN-PT also resulted in a weaker frequency dispersion. It was also found that with increasing of Ta addition x, the transition temperature shifts downward to the lower temperature and the peaks of the dielectric constant versus temperature are getting sharper. Ta-doped PMNTa-PT shows a typical relaxor behavior.
Continuous Sensors for Structural Health Monitoring
Authors: Ghoshal Anindya , Sundaresan Mannur J. , Schulz Mark J. , Pai P. Frank 
Published: November 2021

Abstract
An active fiber composite tape with segmented electrodes was modeled for use as a continuous sensor for structural health monitoring. The material has unidirectional piezoceramic fibers with interdigital electrodes on the top and bottom surfaces and is poled in the fiber direction. The elastic response of a plate with the modeled sensor was computed in closed form at small time steps, and the coupled piezoceramic constitutive equations and the electrical circuit equations were solved. Sensor voltages and wave propagation responses were computed in the simulations. The simulations indicate that such a sensor will be capable of detecting damage to the plate from the changes in the wave propagation response. Further, the sensor has adequate sensitivity to detect fiber breaks in the composite plate making it useful for both passive and active interrogation. A continuous sensor comprised of PZT patches was tested to measure simulated acoustic emissions on panel structures. The sensor was shown to reduce the number of channels of data acquisition required to detect simulated acoustic emissions in a fiberglass panel, but the source of the emission is not precisely determined.
Active Control of Periodic Structures
Authors: Baz A. 
Published: November 2021

Abstract
Conventional passive periodic structures exhibit unique dynamic characteristics that make them act as mechanical filters for wave propagation. As a result, waves can propagate along the periodic structures only within specific frequency bands called the “Pass Bands” and wave propagation is completely blocked within other frequency bands called the “Stop Bands”.
In this paper, the emphasis is placed on providing the passive structures with active control capabilities in order to tune the spectral width and location of the pass and stop bands in response to the structural vibration.
Apart from their unique filtering characteristics, the ability of periodic structures to transmit waves, from one location to another, within the pass bands can be greatly reduced when the ideal periodicity is disrupted resulting in the well-known phenomenon of “Localization”. In the case of passive structures, the aperiodicity (or the disorder) can result from unintentional material, geometric and manufacturing variability. However, in the case of active periodic structures the aperiodicity is intentionally introduced by proper tuning of the controllers of the individual substructure or cell.
The theory governing the operation of this class of Active Periodic structures is introduced and numerical examples are presented to illustrate their tunable filtering and localization characteristics. The examples considered include periodic/aperiodic spring-mass systems controlled by piezoelectric actuators.
The presented results emphasize the unique potential of the active periodic structures in controlling the wave propagation both in the spectral and spatial domains in an attempt to stop/confine the propagation of undesirable disturbances.
Simultaneous Structure-Control Optimization of a Steering Wheel for Vibration Suppression
Authors: Zhu Ye , Qiu Jinhao , Tani Junji 
Published: November 2021

Abstract
This paper presents both simulation and experimental investigation into the simultaneous design of a steering wheel and its control system for vibration suppression. The research can be divided into two stages. In the first stage, the simultaneous design is formulated as a nonlinear programming problem in which the H∞ norm of the closed-loop system is minimized with respect to the structural parameters and the control parameters. For the convenience and efficiency of using existing control design tools, the original formulation is replaced by a nested one in which only the structural parameters are used as explicit design variables in the main optimization and for a given structure, a sub-optimization is carried out to find the corresponding optimal control parameters. The design obtained by simultaneous optimization is compared with the original structure combined with the corresponding optimal controller and the effectiveness of the simultaneous optimization is verified by simulation. In the second stage, experiments are performed to evaluate the design of simultaneous optimization. For simplicity, standard H∞ control is used in the first stage and the effects of modeling error and system uncertainty are not considered. However, dealing with these factors is important issue in a real structure-control system. Since μ synthesis is a systematic robust control method to analyze and quantify the effects of uncertainty, it is adopted in the experimental evaluation. The experimental result shows that the optimized structure is still superior to the original one after the controllers are redesigned in the framework of μ synthesis.
Bifurcations in a Mathieu Equation With Cubic Nonlinearities
Authors: Ng Leslie , Rand Richard 
Published: November 2021

Abstract
We investigate the nonlinear dynamics of the classical Mathieu equation to which is added a nonlinearity which is a general cubic in x, ẋ. We use a perturbation method (averaging) which is valid in the neighborhood of 2:1 resonance, and in the limit of small forcing and small nonlinearity. By comparing the predictions of first order averaging with the results of numerical integration, we show that it is necessary to go to second order averaging in order to obtain the correct qualitative behavior. Analysis of the resulting slow flow equations is accomplished both analytically as well as by use of the software AUTO.