bluuebunny/crossref_metadata_2025_split huggingface dataset:
Application of Composites in Helicopter Design at Sikorsky Aircraft
Authors: Dobyns Alan L. 
Published: January 2022

Abstract
The history of advanced composites usage at Sikorsky will be discussed, starting with small components in the 1970s up to the present where the structure of the RAH-66 Comanche helicopter is constructed almost entirely of composites. One of the initial composite components developed in the 1970’s was a reinforcing Boron strap for the tail of the UH-54 Skycrane. In the 1980’s the UH-60 Blackhawk and the S-76 production aircraft employed a graphite/epoxy tail rotor flexbeam. In addition a composite rear fuselage was developed for the UH-60 Blackhawk, and an all composite research helicopter was built under Army contract to develop composites technology (the S-75 ACAP). Also, graphite/epoxy composite fuel sponsons were put into production for the MH-53E Super Stallion. In the 1990’s the RAH-66 Comanche attack helicopter was developed, utilizing a graphite/epoxy-honeycomb primary structure. The S-92 Helibus commercial helicopter uses graphite/epoxy fuel sponsons, tail rotor flexbeams, and numerous fairings.
Cumulative Lifetime Loadings for Naval Ships
Authors: Sikora Jerome P. 
Published: January 2022

Abstract
The seaway loadings upon ships are inherently random in nature and can best be described by probabilistic methods. The primary loadings are those that cause a response of the overall hull girder and consist of vertical bending moments, lateral bending moments, and torsional moments. Since it is highly probable that these loads can be severe, it is important to predict the maximum lifetime or extreme values. Of equal concern is the cumulative effect of all of the waves upon the fatigue life of the ship. This paper presents a probabilistic method for predicting both the extreme and fatigue loadings in a unified and consistent manner.
The first part of the seaway loading is the low frequency, wave buoyancy contribution. This loading distribution is obtained by dividing the lifetime of the ship into two thousand stochastic cells defined by operability (probabilities of ship heading and speed) and sea conditions (wave height probabilities and spectral parameters). The ship response in the frequency domain (Response Amplitude Operators, RAO’s) for each operability condition is multiplied by the ocean spectrum for each wave height and spectral shape. The resulting response spectra produce the probability distributions for determining extreme and cumulative wave buoyancy loadings. This paper presents unique algorithms for the bending and torsional RAO’s based upon extensive model test and sea trial data, as well as data validating the probability distributions.
The second part of the seaway loading is the dynamic (high frequency) contribution from slam-induced whip-ping. The probability distributions for the filtered, high frequency responses were determined from model tests and sea trials. Algorithms for predicting the dynamic contributions to vertical and lateral bending are developed as functions of ship geometry, operability, and sea parameters. The whipping distributions are then combined with the wave distributions to form distributions for the total primary load for each cell. The method of combination accounts for the phasing of the slam event with the wave buoyancy cycle and includes algorithms for the hydrodynamic damping. A cumulative lifetime load distribution is then formed from the summation of all of the wave events in all of the cells. The cumulative exceedance load distribution is used for predicting both extreme events and fatigue lives.
Variable Structure Adaptive Force Tracking Control of a Cantilever Beam Using Piezoelectric Actuator
Authors: Yim Woosoon , Singh Sahjendra N. 
Published: January 2022

Abstract
This paper presents a robust force tracking control of a flexible beam using piezoceramic actuator. Based on the variable structure model reference adaptive control theory, a new force tracking control system using only force measurement is designed. For the derivation of the control law, it is assumed that parameters of the beam and contact surface stiffness are unknown. It is shown that in the closed-loop system designed using bounds on uncertain functions, the contact force tracks a given reference trajectory and beam vibration is suppressed. Digital simulations results show that the closed-loop system has a good transient behavior and robustness to uncertainties of beam’s dynamic parameters and unmodeled dynamics as well as contact surface property, which is modeled by a spring.
Stability and Robustness of Time Periodic Systems Under Random Parametric Perturbation
Authors: Sinha S. C. , Liu Jianhui 
Published: January 2022

Abstract
In this study, the stability and robustness of a linear time-periodic system subjected to a random parametric perturbation is investigated. Using the Lyapunov-Floquet (L-F) transformation and Lyapunov’s direct method, the stability/robustness bounds are obtained in terms of the Floquet exponents of the system. Two examples are included to demonstrate the applicability of the method to real engineering problems. The first example consists of a commutative system for which the L-F transformation can be computed in a closed form. In the second example, the stability and robustness of a Mathieu equation under arbitrary parametric perturbation is considered. Limiting mean square values of disturbance are computed to guarantee the almost sure asymptotic stability of the system.
Investigation of Perturbations in the Angle of Incidence for Constant Radius Acoustic Transducers
Authors: Bailo Kelly C. , Brei Diann E. , Grosh Karl 
Published: January 2022

Abstract
Curved piezoelectric polyvinylidene flouride (PVdF) acoustic transducers have shown promise for use in active noise cancellation and sound generation applications. Much of the past research has concentrated on straight or semi-circular transducer configurations. This work investigates a constant radius PVdF acoustic transducer with angle of incidences varying from 0° (straight) to greater than 90° (semi-circular). Acoustic performance models were developed and experimentally validated. Computer simulations based upon both the models and experiments were used to determine the device sensitivity to variations in the angle of incidence with respect to the fixed constraints. Acoustic sound intensities were found to dramatically increase as the angle of incidence was decreased from semi-circular to a shallow angle. In addition, sound levels increased significantly when the transducer was varied from straight to a shallow curved configuration. By varying the angle, the curved PVdF transducer has the capability to generate high sound intensities (over 100 dB) at distances greater than one meter in the frequency range below 2000 Hz. The optimal angle was observed to vary with transducer geometry and operating frequency.
Optimal Design of a Sensorless Magnetic Suspension System Using a Tuned LC Circuit
Authors: Krause Robert M. , Sinha Alok 
Published: January 2022

Abstract
In the existing literature, a sensorless AC magnetic suspension system which does not require direct damping of the suspended object for stability has been proposed. This is accomplished by suspending the electromagnet with a spring and damper. First, using a linearized transfer function model for the overall suspension system developed by Jin and Higuchi (1994), a study of the system’s stability is presented in this paper. A root locus is then used in order to see how the damping applied to the electromagnet affects stability. Next, optimization methods and results are proposed to determine values for indirect spring stiffness and damping to most effectively stabilize the system. Lastly, results from linearized analyses are compared to those from numerical integration of the nonlinear system of differential equations.
A Comparison of Placement Choice for Piezoelectric Actuator and Generalized Point Actuator in Active Vibration Control
Authors: Zhu Xuegeng , Alberts Thomas E. 
Published: January 2022

Abstract
A cantilevered beam is used to demonstrate the difference in placement index between piezoelectric actuator and generalized point force actuator. Since the effectiveness of the piezoelectric actuator is dependent upon the curvature of the mode shape, the results proposed for generalized actuator placement do not guarantee good performance for the piezoelectric actuator.
Effect of Manufacturing Induced Defects on the Reliability of Flip-Chip Packages
Authors: Wang Jianjun , Zou Daqing , Qian Zhengfang , Ren Wei , Liu Sheng 
Published: January 2022

Abstract
A combined experimental and numerical studies are conducted to investigate whether the reliability of flip-chip solder interconnects are affected by the manufacturing induced defects (non-cleaning situations), in which underfill cannot be completely filled in the corners of the solder balls because contamination like flux residues subsist on those parts after solder reflow. The real-time moiré interferometry technique is used to measure the warpage for the selected “cleaning” and “non-cleaning” flip-chip package specimens during the test. A nonlinear finite element technique, in which the viscoplastic material properties (strain rate-dependent) of solder balls and underfill are considered, is adapted to simulate the corresponding “cleaning” and “non-cleaning” samples to assess the impact on solder interconnect reliability. The non-cleaning test and simulation results are contrast to the cleaning test and simulation results considered by many researchers. The results indicate that there is no obvious difference for the warpage obtained by either the test data or the numerical analyses between the cleaning samples and the non-cleaning samples. However, the simulation results of the stresses (strains) reveal that the non-cleaning situation decreases the mechanical stability and shortens the life time of those flip-chip packages to a level well below the predictions of the cleaning simulations. The fatigue life in some points of the outmost solder joint predicted by using the cleaning FE models is much higher than that predicted by using the non-cleaning FE models. Since it is hard to find perfect filled layers for any real world samples, the cleaning model yield overly conservative results. In addition, the predicted deformation values of the flip-chip package obtained from the finite element analysis are also compared with the test data obtained from the laser moiré interferometry technique. Good agreement is obtained. In particular, the displacement contours of the flip-chip package samples both in the x and y directions obtained from the test show similar distribution patterns compared with those modeled by the finite element method.
Thermal Deformation Analysis of a Plastic Quad Flat Package by Hybrid Moiré and Finite Element Method
Authors: Liu D. S. , Hsu S. C. , Tung Y. C. 
Published: January 2022

Abstract
This paper presented a hybrid computational models that can be use as design tools to study the thermal deformation of a PQFP. A whole field optical testing method moiré interferometry were applied first to detect thermal strain within the packages cut plane with high sensitivity 2400 lines/mm and the effects of temperature change in the range from 80 up to 120 degree °C. Full field strain maps were measured and the effective CTE properties of the materials used in PQFP can also be obtained from the thermal deformations. Next, a three-dimension finite element model of PQFP was built and analyzed with the material constitutive law and the CTE values found by Moiré. The thermal deformation predict by this hybrid FE model was re-compared with Moiré testing data to validate the accuracy of the FE model. Once the FE Model that compare well with Moiré testing data then it can be used for further structural modification studies.
Thermal Characterization of Anisotropic Polymer Films for Electronic Systems
Authors: Kurabayashi K. , Asheghi M. , Touzelbaev M. N. , Goodson K. E. 
Published: January 2022

Abstract
Polymer films are playing an important role in the development of fast integrated circuits, novel micromachined sensors and actuators, organic optoelectronic devices, and advanced packaging and underfill structures. The low thermal conductivities of polymer layers yield large temperature rises and temperature gradient magnitudes that strongly influence performance and reliability. This work develops three experimental techniques for measuring both the in-plane and out-of-plane thermal conductivities of spin-coated polyimide films of thicknesses between 0.5 and 2.5 μm and at temperatures between 260 and 360 K. Two of the techniques use transient electrical heating and thermometry in micromachined structrures to isolate the in-plane and out-of-plane components. These techniques are used to establish confidence in a third, simpler technique, which is fully IC compatible micromachining and measures both components independently. The data illustrate anisotropy in the thermal conductivity of the polymide films investigated here, with the in-plane conductivity larger by a factor between 4 and 8 depending on thickness and temperature.
Secondary Flows of a Viscoelastic Fluid in Pipes of Complex Cross-Section Shapes
Authors: Siginer Dennis A. , Letelier Mario F. 
Published: January 2022

Abstract
The transversal flow field in pipes of non-circular cross-section shapes is determined for a Green-Rivlin fluid. An analytical approach is presented, which is applicable to unsteady flows driven by small amplitude pressure gradients. Both the longitudinal flow velocity and secondary velocity components are found by prescribing a pipe contour through a shape factor conveniently defined. Secondary flow patterns are computed for several pipe shapes. Results are presented herein for the specific cases where the shape factor prescribes tube cross-section of approximately triangular, square and pentagonal shapes.
Drag Reduction in Turbulent Flow of Gas-Solid Mixtures
Authors: Buyevich Yuri A. , Kapbasov Shakir K. 
Published: January 2022

Abstract
Well-developed one-dimensional steady turbulent flow of a dilute gas-solid mixture in a vertical pipe is considered on the basis of a closure model that accounts for the Reynolds stresses in both mixture phases and specific pseudoturbulent stresses that arise in the dispersed phase. The model is proven to be in an excellent agreement with experimental data as regards usually observed cross-sectional profiles of mixture concentration and mean velocities of the phases. This model is applied to evaluate a systematic variation in total gas flow rate caused by the insertion of fine particles into pure gas flow under the condition of the overall pressure drop being kept invariable. For this purpose, the ratio of gas flow rate in the pure gas flow to that in a mixture flow was studied as a function of the mixture concentration and other relevant parameters. All other things being equal, this ratio first decreases below unity as the amount of the inserted particles increases, reaches a minimum, and then begins to grow with concentration, eventually assuming values well above unity. This means that a drag reduction effect occurs if the concentration varies within a certain interval of relatively low concentrations, but if gives way to a drag enhancement effect as concentration further increases beyond the said interval.
Periodic Motion in Multiparticle Settling
Authors: Zhu Qinsheng , Clark Peter E. 
Published: January 2022

Abstract
Particle settling in quiescent fluids is important in many industrial processes. Single particle settling in Newtonian fluids has been studied extensively. Less work has been done in non-Newtonian fluids using both single and multiple particles. Two or more particles settling in non-Newtonian fluids exhibit unusual behavior that includes simple interactions to form a coupled pair and periodic motion in which the particles preform a complex “dance” as they move through the fluid. This paper describes some preliminary work on the periodic motion observed in three and four particle systems.
Heat Transfer and Fluid Mechanics of Herschel-Bulkley Fluids
Authors: Vradis George C. 
Published: January 2022

Abstract
A comprehensive review of the heat transfer phenomena related to the flow of purely viscous non-Newtonian fluids exhibiting a yield stress in some simple and complex geometries is presented. Both attached and separated flows of Bingham and Herschel-Bulkley fluids are discussed. The presence of a yield-stress is shown to significantly impact the heat transfer and flow characteristics, as compared to those in the case of a Newtonian fluid, in particular in the cases where separation of the flow would be expected.
Electrorheology of Chitin and Chitosan Suspensions: Conductivity vs Molecular Structure
Authors: Choi Ung-su , Conrad Hans 
Published: January 2022

Abstract
The electrical and rheological properties pertaining to the electrorheological (ER) behavior of chitin and chitosan suspensions in silicone oil were investigated. Chitosan suspension showed a typical ER response (Bingham flow behavior) upon application of an electric field, while chitin suspension acted as a Newtonian fluid. The difference in behavior results from the difference in the conductivity of the chitin and chitosan particles, even though they have a similar chemical structure. The shear stress for the chitosan suspension exhibited a linear dependence on the volume fraction of particles and a 1.18 power of the electric field. The experimental results for the chitosan suspension correlated with the conduction model for ER response.
Secondary Control Technology and Applications
Authors: Wüsthof Peter 
Published: January 2022

Abstract
Secondary control is the definition for a variable displacement rotary hydrostatic drive working with constant pressure. The controlling element of the system is the swivel angle of the hydraulic drive, normally an axial piston unit. If a load change occurs, the secondary control reacts immediately by accelerating or decelerating the process, thus maintaining a constant speed. Compared to conventional hydrostatic drives the secondary control is a dynamic drive.
A Comparison of a PID Controller to a Neural Net Controller in a Hydraulic System With Nonlinear Friction
Authors: Qian W. , Burton R. , Schoenau G. , Ukrainetz P. 
Published: January 2022

Abstract
Neural networks have been applied to a wide spectrum of applications in the last decade, including the fluid power area. The popularity of neural networks can be attributed, in part, to their ability to deal with nonlinear systems. Their use as a controller, however, poses many interesting problems, especially when trying to apply them to practical systems. In hydraulics, PID controllers have been used with some degree of success; however, when it comes to highly nonlinear systems, this established method encounters some difficulties.
This paper considers the applied problem of a hydraulic servovalve controlling a actuator with nonlinear friction characteristics. A neural net controller is pre-trained to the performance of a special PID controller which has been tuned to a specific waveform. The plant is a model of a hydraulic servovalve and a linear actuator with slip-stick friction characteristics. The neural net controller replaces the PID controller and shows superior performance for waveforms that it was not trained for. The addition of a “kicker” signal reduced the distortion of velocity (a consequence of nonlinear friction) when the velocity was near zero. It is concluded that in certain applications, a neural net controller does show potential for use in nonlinear systems, but many other issues such as stability, reliability, and adaptability must be addressed in the future.
Nonlinear Robust Control of an Electro-Hydraulic Positioning System
Authors: McLain Timothy W. , Beard Randal W. 
Published: January 2022

Abstract
In this paper, a novel approach for the formulation of nonlinear H∞ control laws is applied to the position control of an electro-hydraulic servo system. These robust controllers are obtained by numerically approximating the solution to the Hamilton-Jacobi-Isaacs (HJI) equation and result in nonlinear control laws in feedback form. The approximation is accomplished by a two-step successive Galerkin approximation strategy. The application of this approach to the control of a hydraulic positioning system with uncertain fluid bulk modulus and density is described.
Theoretical and Experimental Research on Sliding Mode Control for an Electrohydraulic Servosystem
Authors: Liu Y. , Handroos H. 
Published: January 2022

Abstract
The present paper discusses a sliding mode control method suitable for controlling a hydraulic position servo with a flexible load. Due to the requirements of the control system, the reference model is designed for case of a flexible load. The core of sliding mode control is switching surfaces which are specially defined for the system according to the mathematical model and control goal. A novel algorithm is developed, and the simulated and experimental results of the control system are shown. The results show the extremely good robustness of the proposed method.
Dual Electrohydraulic Servo Motors Synchrodrive System Using Adaptive Neural Control Strategy
Authors: Xingwu Fu , Keding Zhao , Qinghe Liu 
Published: January 2022

Abstract
The adaptive neural control strategy is employed for the characteristics and specifications of the middle gimbals synchrodriven by the dual electrohydraulic servo motors in the simulator with three axes, the decoupling is implemented. Simulation results show that this strategy, because of it’s self-learning and inherent nonlinear, etc.[1], makes the system present superior dynamic performance and adaptability, the superior synchromotion performance of the system has been obtained.
Transient Flow Force Estimation on the Pilot Stage of a Hydraulic Valve
Authors: Borghi M. , Milani M. , Paoluzzi R. 
Published: January 2022

Abstract
The effect of flow forces on the spool equilibrium of hydraulic components is well known, and a number of methods have been developed in order to estimate their effect. They span from analytical expression, to experimental evaluation, to CFD analysis. This last approach is usually considered too demanding to the purpose of hydraulic component design, however a careful approach to the problem statement can lead to the collection of a complete set of data, starting from a limited number of numerical runs. A further extension to transient flow is made possible by the acceptance of further approximations on the effect of fluid compressibility, leading to a computational technique able to extend the amount of information extracted from a single model.
Several Aerospace Applications of Computational Aeroacoustics
Authors: Long Lyle N. , Morris Philip J. , Ahuja Vineet , Hall Chris M. , Liu Jingmei , Scheidegger Thomas E. , Shieh Chingwei M. 
Published: January 2022

Abstract
This paper describes some recent Computational Aeroacoustics (CAA) simulations of problems of practical importance. Many previous CAA studies have emphasized the development of algorithms and their application to relatively simple model problems. Examples of computational aeroacoustic calculations are given for ducted fans, rotors, cavities, engine inlet liners, and jets. The need for three-dimensional, non-linear simulations and the feasibility of such solutions on high performance parallel computers is emphasized.