bluuebunny/crossref_metadata_2025 huggingface dataset:
Crack Linkup at Multiple Site Damage
Authors: Ma L. , Kobayashi A. S. , Atluri S. N. , Tan P. W.
Published: January 2022

A commonly used design criterion for predicting the onset of crack link up at a multiple site damage (MSD) is when the sum of the plastic zones of two adjacent cracks is equal to the remaining ligament (Swift 1985, Broek et al 1994). The collapse load predicted by this criterion, however, will differ with the analytical plastic zone and in general, will yield a nonconservative load. Recently, Pyo et al (1997) have shown that the T* integral, which was designed for elastic-plastic fracture mechanics, can predict the extent of stable crack growth and the subsequent collapse load of wide-panel MSD experiments (deWit et al, 1994). The purpose of this paper is to present experimental/numerical results on stable crack growth and linkup of idealized MSD based on the T* integral.

Moiré interferometry was used to determine the orthogonal displacement fields surrounding stably growing cracks in 0.8 mm thick 2024-T3 aluminum specimens with two or three cracks. Fatigue precracked cracks extended toward each other from two circular holes, which were 25.4 mm apart to simulate fastener holes in airplane fuselage, close to the outside edges of the specimens. A longer center crack from a center hole in the wider, three-crack specimens with three holes spaced 25.4 mm apart, provided information on the lead crack effect. T*ε integral, where ε is the distance of an elongating integration contour from the stably growing crack, was evaluated from the Moiré data using the procedure established by Okada et al (1996). ε in all studies was equated to the specimen thickness. An elastic-plastic finite element (FE) model of the fracture specimens were executed in its generation mode (Kobayashi, 1979) by inputting the measured Moiré displacement data along the width, 20 mm away from the crackline, of the specimen. T*ε integral was evaluated using an equivalent domain integral (Nikishkov et al, 1987).

The experimentally and the FE determined T*ε’s were in excellent agreement with each other. Moreover, the T*ε variation with stable crack growth closely followed the stable crack growth results generated previously using standard fracture specimens (Omori et al, 1998). Thus stable crack growth data generated by standard fracture specimens can be used to predict crack growth of MSD cracks. Collapsed load was reached when the remaining ligament exceeded the tensile strength of the 2024-T3 sheet and the two cracks rapidly propagated toward each other in the two-crack specimens. For the three-crack specimen, the lead crack propagated toward the smaller two MSD cracks.
Energy Released by Interfacial Decohesion in a Two-Phase Composite System
Authors: Srinivas Mullahalli V. , Dvorak George J.
Published: January 2022

Under service loads or during fabrication and processing, certain fibrous composite plies may experience extensive decohesion, such as debonding and sliding at fiber-matrix interfaces. The effect of some of these damage processes on overall stiffness and on internal stress redistribution is analyzed here with the Transformation Field Analysis method (Dvorak and Benveniste, 1992, Proc. R. Soc., London, Vol. A437, p. 291), which simulates creation of new internal surfaces by equivalent eigenstrains applied to an undamaged elastic system. Simple expressions for change in potential energy of the damaged ply are also obtained using the Colonetti’s theorem. The analytical results are shown to be in good agreement with selected finite element solutions for unit cells. Applications indicate that the energy released by fiber debonding depends linearly on fiber radius.
Comparison of Stress Concentrations in Plain and 8-Harness Satin Weave Composites
Authors: Whitcomb John , Tang Xiaodong , Chapman Clinton
Published: January 2022

Stress distributions in plain and satin weave composites were calculated using three-dimensional finite element analysis. Comparisons of the distributions showed that some of the satin weave behavior is predictable from the far simpler plain weave model. However, some aspects of the behavior require more geometric information than is provided by a plain weave model.
Micromechanics-Based Modeling of Uniaxially and Biaxially Compressed Graphite/Epoxy Laminates
Authors: Hauert Serge , Potter Daniel S. , Gupta Vijay
Published: January 2022

Uniaxial and in-plane biaxial testing were conducted on cross-ply graphite/epoxy laminates with different orientations. Results from these investigations are presented here only for the [±45]12s samples under different stress states. The stress-strain behavior is related to microscopic events through micromechanics-based modeling. It is shown that crack nucleation starts in the matrix when the local shear stress exceeds the shear strength of the epoxy. Depending on the stress state in the plies, two types of cracks form: (i) transverse cracks and (ii) angled out-of-plane cracks. While transverse cracks slide and allow the sample to accommodate large strains, angled cracks lead to massive delamination and an overall brittle behavior.
A Local/Global Sandwich Homogenization Procedure for Finite Element Simulation
Authors: Tabiei Ala , Tanov Romil R.
Published: January 2022

A new finite element approach to sandwich shells is proposed. It uses existing shell finite elements formulated for homogeneous shells. The “sandwich” nature of the problem is hidden from the main finite element program. Based on several assumptions the proposed homogenization procedure calculates stress increments in a homogeneous fictitious material, called “equivalent”, which correspond to the strain increments in the equivalent material points. The stresses in the equivalent material are calculated based on the stress and strain fields in the sandwich layers, which are determined from the incoming strain field for the equivalent material. This procedure is most suitable for including strain softening and other material nonlinear behavior. The approach can be combined with shell elements formulated for homogeneous materials, based on Reissner-Mindlin shell theory or with elements based on a higher order shell theory. It avoids the necessity of formulating special shell elements for sandwich constructions, which in most cases, due to their large number of degrees of freedom, significantly decrease the computational efficiency of the finite element analysis. The sandwich homogenization procedure is combined with a composite micromechanics-based model for woven composites to analyze sandwich shells with woven fabric faces.
Advanced Composite Turbine Engine Experience
Authors: Fecke Theodore G.
Published: January 2022

The United States has a coordinated government/ industry turbine engine technology program in place to double propulsion capability by the year 2003. The Integrated High Performance Turbine Engine Technology (IHPTET) program is slightly more than half complete, with specific goals identified for engine thrust to weight, compressor exit temperature, acquisition and maintenance cost. The IHPTET program represents a significant improvement in turbine engine technology. The program plan is to achieve the goals in three steps Phases I-III each resulting in 30% improvement. The achievement of these goals is project through the use of advance aerodynamics, materials and design concepts. The successful demonstration of the IHPTET goals depends on the technical success of composite structures. All types of composites: OMC (Organic Matrix Composite), MMC (Metal Matrix Composites), CMC (Ceramic Matrix Composite) as well as C/C (Carbon-Carbon), have been aggressively works since the program began in 1988. The composite experiences before the IHPTET program will be included in the form of lesson learn.

The IHPTET program has worked all aspects of composite development design, failure mode behavior and fabrication. The thrust in OMC’s has been primarily focus on Life prediction, low cost fabrication techniques and High temperature (>700F). The thrust in MMC’s has been mainly focus on fiber-reinforced titanium for high performance rotating engine hardware. The technology development includes design; failure mode behavior and testing of multiply engine components as well as Life prediction and low cost fabrication techniques, have been investigated. The thrust in high temperature composites CMC and C/C has been mainly focus on CMC’s. The technology development span both man-rate and non man-rate engine (cruise missile) applications, in the areas of design, failure mode behavior and testing of both rotating and nonrotating applications.

The payoffs to the aircraft derived from the IHPTET are enormous. Many radical new mission capabilities are made viable through the IHPTET program. The high Mach multi-role fighters as an example are only possible with a variable cycle design, which requires extensive use of composite structures. These new capabilities will provide truly affordable ways to carry out the military’s mission by allowing aircraft resources to effectively operate from fewer worldwide locations as well as more affordable and environmentally friendly.
First-Excursion Probability and Response Peak Distribution of a Nonlinear Structure Under Non-Gaussian Non-Stationary Loadings
Authors: Lua James , Mover E. Thomas
Published: January 2022

Probabilistic methods have been used recently for the reliability assessment and design of ship structures because of the presence of various uncertainties in structural configuration, material properties, and environmental and operating conditions. Among these uncertainties, random dynamic loads induced by either sea waves or slamming play a significant role in reliability-based ship structural design. The present state-of-the-art probabilistic method for ship design is based on a linear structural response model subjected to stationary Gaussian random processes. However, under extreme operating conditions, the ship structural response may not be linear due to the initiation and evolution of multiple local damage, such as local plastic deformation, stiffener tripping, panel buckling, or fracture. In addition, the complexity of fluid-structure interaction phenomena may render the assumptions on the loading process (stationary and Gaussian) invalid.

Under this study, we developed a simulation based probabilistic analysis framework for a nonlinear dynamic structural system under non-Gaussian non-stationary loadings. The general simulation based probabilistic analysis framework (SIMLAB) is formulated by integrating 1) random variable generating modules; 2) random process generation modules; and 3) user selected deterministic solver and limit state function. The developed random process simulation module is able to generate a Gaussian, non-Gaussian, stationary, or non-stationary process. To demonstrate the applicability of the developed tool for a structural dynamic system with random variables and random processes, a free-free beam subjected to a sea wave induced random process is solved by integrating a structural dynamics code, DYNA3D, with the developed probabilistic analysis framework. The limit state function is formulated based on the first crossing of a beam Von Mises stress at an integration point above a safe threshold.

In order to validate the accuracy of SIMLAB, a linear beam structure subjected to a stationary Gaussian process is considered first and the simulated statistical distributions of peak and extreme response variables are compared with analytical predictions. The effect of material nonlinearity on probability of failure and peak statistics is explored by using an elastoplastic beam model subjected to a random excitation. Results on probability of failure and peak statistics are compared with the corresponding statistical models for a linear structure. The great versatility of the simulation based probabilistic analysis framework provides us a solid foundation for the development of more advanced probabilistic analysis tools for reliability-based ship design.
Active Control of Vibration in a Flexible Structure With Uncertain Parameters via Sliding Mode and H∞/μ Techniques
Authors: Pai M. C. , Sinha A.
Published: January 2022

This paper presents a new approach for the robust control of vibration in flexible structures with uncertain parameters. The algorithm is based on sliding mode control and H∞ / μ techniques. First, the sliding mode control algorithm is developed using state feedback and the chattering behavior is eliminated using boundary layers around sliding hyperplanes. The LQ control method and H∞ control method for designing sliding hyperplanes are presented. The switching control is chosen to satisfy the so-called reaching condition. Then, the small gain theorem / μ analysis is applied to analyze the asymptotic behavior of the closed-loop system with parametric uncertainties inside boundary layers. Using a flexible tetrahedral truss structure, numerical examples are presented to verify the theoretical analysis. Results from H∞ full state feedback control method, sliding mode with H∞ full state feedback control method, LQ control method and sliding mode with LQ control method are presented and compared.
Modeling and Robust Control of Vibrations in a Flexible Four-Bar Mechanism
Authors: Karkoub Mansour , Yigit Ahmet S.
Published: January 2022

Dynamic modeling and controller design for a flexible four-bar mechanism is studied. The fully coupled nonlinear equations of motion are obtained through a constrained Lagrangian approach. Resulting differential-algebraic equations are solved numerically to obtain the system response. A linearized dynamic model is developed which facilitates design of various controllers. The fully coupled nature of the governing equations facilitates control of elastic motion through the input link alone. A simple PD and a robust μ-synthesis controller are shown to be efficient in suppressing the vibrations of the flexible link as well as controlling the rigid body motion.
Global Sensor Systems for Vibration and Noise Control Applications
Authors: Sun J. Q. , Hirsch S. M. , Jayachandran V.
Published: January 2022

A sensor system is defined as being global if the reduction of a performance measure based on the sensor measurements guarantees a decrease in a global response measure of the system. In this paper, the mathematical condition for such a sensor system is derived and this concept is then applied to structural and acoustic control problems. It is shown that the nodal placement of sensors always leads to a global sensor system, and that in this case, the sensor based performance measure differs from the global performance measure by only a scaling constant. In tonal and narrow band problems, a global sensor system may be redundant. A criterion is developed to determine the number of sensors needed in such applications. Some simple examples are used to demonstrate the theory.
Passive Control of Systems Subjected to Repetitive Impulse
Authors: Minas Constantinos
Published: January 2022

A model describing a dynamic system subjected to repetitive impulse was developed. The methodology presented addressed the specific case where the impulse repetition occurred at equal time intervals. The methodology was illustrated through an example, where a cryocooler induced repetitive impulse to a cryocooler cooled device. The analysis considered both a rigidly and a flexibly mounted cryocooler. Passive control was implemented by varying the coupling stiffness between the cryocooler and the cryocooler cooled system, the stiffness to ground and the mass of the cryocooler.
Flow Modeling and Validation of the Encapsulation of Plastic Packages
Authors: Nguyen L. , Quentin C. , Lee W. , Bayyuk S. , Bidstrup-Allen S. A. , Wang S.-T.
Published: January 2022

A major manufacturing defect encountered in plastic encapsulation of IC components by transfer molding is wire sweep, the permanent deformation of wirebonds under the hydrodynamic loads imposed by the viscous flow front. Optimization of design geometries and processing conditions to minimize defects still cannot be achieved without time-consuming and expensive experiments that frequently involve hardware modifications. Thus, a need for simulation and defect-prediction techniques to replace the costly experiments is much needed for true design-for-manufacturability and faster cycle time.

This paper will present the results of a DARPA-funded program to develop a self-contained methodology and software suite (called PLICE-CAD) for modeling the entire packaging process. Simulation of the reactive flow in the molding of a thin quad flat package (TQFP) will be presented and validated with operating parameters (e.g., pressure, temperature, flow front advancement, ...) measured with in-process sensors.
A Testing Method and Device for Intrinsic Stress Measurement in Wafer Bumping Process
Authors: Guo Yifan , Mitchell Dianne , Sarihan Vijay , Zheng Dawei
Published: January 2022

A novel concept and the related testing methodology for a sensing device is presented. This device is used to determine the distributions of local residual stresses induced in wafer processes such as metalization and bumping. The sensing device is essentially a pressure sensor structure with a specified membrane thickness. Either a whole pressure sensor wafer or a single die sensor can be used for this purpose. This sensing device is put into the processes which are under investigation or being monitored. After each processing step, the membrane is deformed due to the process induced residual stress. The membrane deformation is either monitored continuously by the electrical signals from the pressure sensor during the process or measured by an optical method after each process step. Residual stresses are calculated from the measured membrane deformations.
Rheology of Suspensions in Reduced Gravity
Authors: Bakhtiyarov Sayavur I. , Overfelt Ruel A.
Published: January 2022

Viscosity of settling suspensions was studied experimentally in a series of reduced gravity parabolic flights aboard NASA’s KC - 135 aircraft. Slurries were made using silica sand (0.150 mm < dp < 0.212 mm) and Glycerol solution. The experimental set up incorporated instrumentation to measure the apparent viscosity of the sand suspensions at the wide range of the shear rates. The container had transparent walls to allow visualization of the structure changes involved in Couette flow in reduced gravity. Experiments were performed over a broad range of gravitational accelerations including microgravity and double gravity conditions.

The results of the flight and ground experiments reveal significant differences in the apparent viscosity of sand suspensions and overall void factor in microgravity as compared to one-g conditions.
Rheology of Drag-Reducing Surfactant Solutions
Authors: Pal Rajinder
Published: January 2022

The rheology of drag reducing cationic surfactant solutions was investigated using a controlled-stress rheometer. Both steady and oscillatory shear measurements were carried out at 25°C with the help of the cylindrical double-gap measuring geometry. The cationic surfactant investigated was Ethoquad T/13-27W, a commercial product manufactured by Akzo Nobel Chemicals Inc., U.S.A. Sodium salicylate (NaSal) was used as counterion. The effects of the surfactant and counterion concentrations on the rheological behaviour were also determined.

The surfactant solutions in the presence of counterion exhibit non-Newtonian rheological behaviour. At shear rates below some critical value, the surfactant solutions behave as either shear-thinning or Newtonian depending upon the counterion concentration; at low NaSal concentrations, shear-thinning is observed whereas at high NaSal concentrations, Newtonian behaviour is observed. When the shear rate is increased above the critical value, a rise in viscosity is observed indicating shear-thickening or dilatant behaviour. Oscillatory shear measurements indicate that the surfactant solutions are significantly viscoelastic. At a given surfactant concentration, the rheological parameters such as zero shear viscosity, critical shear rate, storage and loss moduli, etc. first increase, reach a maximum value, and then decrease with the increase in NaSal concentration. With the increase in surfactant concentration at a fixed NaSal/surfactant weight ratio, the rheological parameters show a significant increase.
A Rheological Characterization of High Percent Solids Kraft Black Liquor
Authors: Sanders Christian L. , Bakhtiyarov Sayavur I. , Siginer Dennis A.
Published: January 2022

Tube flow elastic recovery is employed to measure the normal stresses of an experimental liquid, polyacrylamide, and an industrial liquid, kraft black liquor. It is shown that the elastic recovery provides a reasonable method to measure normal stresses where the conditions of interest are difficult to reproduce in standard measurement techniques. Tube flow elastic recovery assumptions are tested for the liquids under study. New normal stress measurement data is presented for the kraft black liquor and it is shown to be a function of shear rate and temperature.
Shear Stress of ER Suspensions
Authors: Tsukiji Tetsuhiro , Saito Shigeaki , Asako Yoshinobu , Kawakami Toshihiro
Published: January 2022

The shear stresses of ER (Electro-rheological) suspensions are measured by changing a shear rate, amplitude and frequency of electric fields using rotational viscometer whose gap between electrodes can be changed. We use two ER suspensions which are called ERFC and ERFP. ERFC consist of cellulose suspended in silicone oil. The size of cellulose particles is typically about 10∼20 μm and a viscosity of silicone oil is 10mm2/s. Cellulose concentration is 20wt.% and the percentage of moisture content is 0.6%. ERFP contains highly sulfonated poly (styrene-co-divinylbenzene) particles. An average particle diameter of ERFP is 9 microns and the water content is 2.0 wt.%. Unipolar sine-wave electric fields which is AC with DC bias and bipolar sine-wave electric fields without DC bias are used. The shear rates of 400 s−1 are employed. Amplitudes of the electric fields are 0.4 and 0.8 kV/mm and DC component is 1.0 kV/mm for unipolar sine-wave electric fields. Amplitudes are between 1.0 and 2.5 kV/mm for bipolar sine-wave electric fields. The frequency of the electric fields is changed from 0.1 to 100 Hz. Dependence of the shear stress on electrical excitation frequency is investigared.
Recent Developments in Network Theory
Authors: De Kee D. , Chan Man Fong C. F.
Published: January 2022

An understanding of the flow properties of non-Newtonian fluids is important in many areas of application. To solve flow problems, it is required to introduce a constitutive equation that relates the stress tensor to various kinematic tensors. The determination of a constitutive equation which describes adequately the rheological properties of a fluid under all flow conditions is one of the central problems in rheology. Constitutive equations have been developed based on either continuum mechanics or on the molecular structure of the fluids.
Preform-Particle-Flow Interactions in Impregnation of Fibrous Preforms With Particle-Filled Resin
Authors: Erdal Merve , Güçeri Selçuk
Published: January 2022

Particle-filled preceramic polymer injection into woven fiber preforms is currently under investigation as a means of processing dense, complex-shaped ceramic composites. The distribution of filler particles as a result of filtration during their impregnation into dense fiber preforms, has a crucial effect on the properties of the end product. In general, highly filtered particle distributions are not desirable since they lead to nonhomogeneous part microstructure and hence, mechanical properties of the composite. In order to understand how various process parameters (injection velocity, inlet particle concentration, fiber preform permeability, etc.) interact during impregnation and to ultimately control the amount of filtration, a process model is presented. A multi-dimensional, transient particle filtration formulation is coupled with isothermal, anisotropic Darcy’s flow to predict filler concentration profiles during molding of complex shapes. The permeability of the preform, porosity of the flow domain, viscosity of the impregnating resin and filtration coefficient are all affected by the particle deposition and they constitute the nonlinearity in the coupled flow and filtration equations. Results for 2-D impregnation into complex preforms are presented and methods for manipulating particle distribution are discussed.
Steering System of John Deere 8000 Series Track Tractors
Authors: Mistry Sanjay I. , Hou Yifei R.
Published: January 2022

The John Deere 8000 series track (8000T) tractors, introduced in June 1997 represent a significant change in steering system compared to previous John Deere tire tractor models. John Deere 8000 series track tractors are the first tractors in North America using “steer-by-wire” philosophy. The new steering system uses an electric signal to control the electro-hydraulic hydro-static system. The steering system provides performance improvements in several areas for unmatched operator convenience and control. This paper describes the steering system configuration, components, operation, characteristics and some of the engineering considerations dealt with in the development process. The overall steering system truly represents a mechatronic design.
An Investigation of a Roll Control Suspension Hydraulic Actuation System
Authors: Darling Jos , Hickson Luke R.
Published: January 2022

It is recognised that roll control suspensions offer a partial solution to the well known compromise between ride and handling. In this paper a simulation and experimental study of a vehicle with a roll control hydraulic actuation system is presented in which a variety of ways to reduce power consumption and cost are investigated. The introduction of dead-band into the control system can reduce power consumption while a proportional valve with a spool configuration which interconnects the load and tank ports when in the null position is shown to improve ride comfort and raise the system damping during conditions when the vehicle is subjected to aerodynamic lateral side loads. In the prototype vehicle it is argued that the system pressure could be reduced to levels similar to those of existing power steering systems, if the actuation system control gains are chosen appropriately.
A Self-Tuning Fuzzy Control of an Electro-Hydraulic Fin Position Servo System
Authors: Lee Sang Yeal , Park Young Jun , Cho Hyung Suck
Published: January 2022

Electro-hydraulic servo systems have been frequently used in the fin position servo system of a missile because of their high power and good positioning capability. The objective of this paper is to realize a self-tuning fuzzy controller for the position control of an electro-hydraulic fin servo system. In this paper, we propose a new self-tuning fuzzy controller, which can improve the overall performance of the electro-hydraulic fin position servo system. The uniqueness of this self-tuning fuzzy controller is that the performance evaluation of the fin position servo system is carried out in a phase plane mapped to a decision rule table. The effectiveness of this control scheme is verified by comparison with a fixed fuzzy control with initial rules through a series of simulation studies.
Continuous CMAC and its Application in Identification of Electrohydraulic Servo System
Authors: Wei Sun , Hong He , Shulian Wang
Published: January 2022

Based on finite element interpolation method a continuos CMAC (CCMAC) is proposed in this paper, the output of the network can change with its input continuously, the generalization of network is improved, the training speed and identification precision are also improved. The continuous CMAC is used in the system identification of electrohydraulic velocity servo control system, many simulation and experiment results are satisfactory.
Towards Autonomous Control of Hydraulic Actuator Systems
Authors: Hansen Poul E. , Conrad Finn
Published: January 2022

The proper adjustment of parameters in electro-hydraulic positioning controls demands a knowledge of the plant and the controller. Since this information is seldom available to the electrician, the result is often a crude tuned control system and even instability can occur. Different control algorithms are developed in this paper in order to increase the autonomy or intelligence of hydraulic controls. A refinement of the relay-tuning method is used to determine the controller parameters of a lag-lead and a pole placement controller. Furthermore, an integral action is included in the pole placement controller for eliminating steady state errors. A fail-safe function is developed to hinder surges and mechanical fractures. Experiments conducted on a hydraulic test robot demonstrate that the controllers considered perform well.
A Pneumatic Library for AMESim
Authors: Bideaux E. , Scavarda S.
Published: January 2022

The present development of the simulation and virtual prototyping actually has lead to the development of specialized software packages to industries using fluid power based components as the truck, railway or car industry. These specialized packages such as AMESim (Advanced Modeling Environment for performing Simulations), consist of a robust solver and multidisciplinary libraries of models, since the solving method is strongly linked to the simulation aim and the modeling step itself. AMESim has already proposed hydraulic and one-dimensional mechanical components and some useful tools for the study of fluid power systems. As strong links exist between hydraulic and pneumatic technology, we have implemented a library of pneumatic components that could be used in connection with the other existing libraries. The models arise directly from our pseudo bond graph knowledge and our experience of measuring existing pneumatic components. The first library (the Basic Elements Library) contains the basic elements : sources, modulated dissipative elements, modulated transformers, capacitive elements, sensors, which allow the simulation of any pneumatic based system. In the second library called the Elementary Component Library, we propose a selection of standard components such as relief valves, distributors, servo-valves and spools. The third and last library is the Advanced Component Library and it consists of models for specialists such as pipes, variable volume chambers, and more complex components.

In this paper, we propose an overview of this library of pneumatic components and we show its possibilities by simulating of an existing pneumatic systems.
On the Application of an Industrial Motion Controller to a Pneumatic Positioning System
Authors: Brook N. , Surgenor B. W.
Published: January 2022

This paper documents experience with the application of an industrial motion controller, originally intended for an electric servomotor positioning system, to a pneumatic positioning system. The pneumatic system consisted of a rodless cylinder connected to a proportional servovalve with a command signal generated by the motion controller. A linear analog potentiometer provided position feedback to the controller. The payload was 5 kg with a stroke of 0.6 m. Results demonstrate that respectable performance can be achieved, although the PID tuning technique normally implemented with the motion controller could not be used. An achievable motion trajectory is identified, and an appropriate PID tuning techniques is presented.
Influence of Viscosity on Aircraft Noise Diffracted by Edges
Authors: Pierce Allan D. , Zampolli Mario
Published: January 2022

The analysis of the influence of viscosity on diffraction of aircraft noise by edges is exemplified by the mathematical problem of diffraction of an acoustic plane wave by a thin rigid screen. The linearized equations of compressible fluid mechanics with viscosity included are considered with the overall disturbance field regarded as a sum of acoustic and vorticity fields. Each such field, for disturbances of fixed frequency, is governed by a separate Helmholtz equation, but they are coupled by the no-slip and nonpenetrability conditions at the screen’s surface. With viscosity taken into account, the perturbation-induced fluid velocity near the edge is not infinite, but is nevertheless very large when the viscosity is small, even though the velocity vanishes identically at the surface.
Structural Acoustics and Active Constrained Layer Damping of a Full Scale Fuselage Section: An Experimental Approach
Authors: Herdic Peter C. , Baz Amr M. , Houston Brian H.
Published: January 2022

The mechanisms and underlying structural acoustics associated with the response of a full scale aircraft fuselage section are examined in its uncontrolled state and with the application of Active Constrained Layer Damping (ACLD) treatment to the structure. In these experiments, active structural acoustic control is demonstrated, where both the surface vibration and interior acoustic pressure are attenuated. The uncontrolled response is first studied experimentally under three different physical forcing functions by use of high spatially sampled surface velocity and interior pressure measurements over a band from 0–1000 Hz. These results indicate rich modal excitation of the fuselage and interior by a point force applied at a frame/stringer intersection of the structure. Real time active control experiments using simple surface minimization control laws are performed under this excitation, yielding good performance.
The Response of Acoustic Sensor Arrays to Turbulent Boundary Layer Noise by Structural Modification
Authors: Madden Peter E.
Published: January 2022

The performance of high speed, underwater vehicles is limited by flow noise. Turbulent flow over the vehicle shell causes an output from an array which is mounted to it. Arrays which are located under the boundary layer are affected by high wave number components and must be separated from the turbulence by a coating. Arrays which are located in the laminar region are still affected by the turbulent flow but in this case the energy is transported through the structure. The paper discusses the mechanisms involved and shows techniques which can be used to mitigate the problem. Some results are shown indicating the amount of reduction that has been achieved with some of the approaches.
Design and Performance of the Acoustic Wind Tunnel at the Naval Undersea Warfare Center
Authors: Corriveau Pierre , Polhemus Stanley , Tingstad Gordon , Abbot Philip , Gedney Charles
Published: January 2022

The Naval Undersea Warfare Center (NUWC) Division Newport recently designed, built and commissioned a low-noise, low-turbulence acoustic wind tunnel for aerodynamic and aeroacoustic testing. Special features include an upstream centrifugal ventilation fan, integrated sting mounting system, unique downstream flow collector, low-speed return air plenums, an acoustically isolated fan room, and an anechoic test chamber. This paper describes the NUWC wind tunnel facility and its supporting design criteria. The wind tunnel has achieved its design requirements of: 60 m/s maximum flow speed in a 1.2 m diameter open jet with flow uniformity within 0.5% and free stream turbulence level of 0.3%. Background noise levels are below the design goal: at 60 m/s, the 1/3 octave band sound pressure levels, 1 m from the nozzle exit, are less than 60 dB re 20 μPa @ 100 Hz and 33 dB re 20 μPa @ 20 kHz. Examples are given of experiments conducted in the wind tunnel.
Inferring Blade Rate Propeller Forces From Wind Tunnel Sound Power Measurements
Authors: Gedney Charles J. , Abbot Philip A. , Corriveau Pierre J.
Published: January 2022

An extensive series of acoustic tests were conducted on an experimental propeller in the Naval Undersea Warfare Center Acoustic Wind Tunnel. The objective of the tests was to infer the fluctuating forces at blade rate frequency (BR) and its harmonics from sound power measurements, and validate an assumed radiation model. Ten microphones were used to spatially sample the acoustic field. Measurements were made at constant advance ratio for speeds of 6 to 52 m/s, in increments of 3 m/s. As expected, the BR sound power levels scaled as U6 and exhibited cos2θ (θ being the angle to the force) directivity, consistent with compact dipole theory. For (kD)2 > about 6.5 (k is the acoustic wavenumber, D the propeller diameter), the scaling shifted to U8, the mechanism being dominated by lateral quadrupole radiation (two dipoles separated by the diameter). At the second BR harmonic, sound power levels scaled significantly different than at BR. Possible mechanisms for this effect are discussed.
Noise and Flow Measurements in Automotive Blower Scroll
Authors: Humbad Niranjan G. , Foss John F. , Porada Robert A. , Morris Scott C. , Prevost Richard J. , Johnston David G.
Published: January 2022

The climate control air handling system is one of the major contributors to automobile interior noise. The most annoying features can be characterized as low frequency (20–400 Hz) “rumble”, and “blade passing frequency, BPF tone” noise. Time resolved flow velocity measurements in the blower scroll have been made to identify the noise source locations. The velocity power spectral density (psd) plots show areas within the blower scroll where the turbulence fluctuations are relatively high for the tone and rumble frequencies. The inference of origin of BPF tone near the scroll cut-off is not supported by the present data. The psd magnitudes show that the velocity psd values associated with the rumble noise were highest in the blower scroll expansion near the cut-off. Such findings are expected to be useful in the design development of the scroll geometry to reduce tonal and rumble noise.
Dynamic Performance Characterization of Hockey Sticks Using a Combined Vibrational Energy Level and Modal Analysis Approach
Authors: Barpanda Dev , Mantena P. Raju
Published: January 2022

Composite materials offer significant improvements in fatigue behavior, impact performance and damping coupled with high stiffness and strength. Due to these properties and an increasing demand for high performance cutting-edge sports equipment, more scientific and engineering research is now being focused in the field of recreation. The use of stiff, lightweight composite materials has created many novel features in golf clubs, baseball bats and skis; features generally not possible with conventional materials. The performance, user comfort, and fatigue life of these products are strongly related to their dynamic characteristics. Design decisions relevant to these issues should, therefore, be made based on an understanding of the dynamic characteristics through modal parametric studies.

This paper discusses the vibration response characteristics of some commercially available hockey sticks with wooden, aluminum and graphite shafts, when subjected to short duration impact loads. Using an instrumented impact hammer, a complete modal survey is initially conducted on these hockey sticks to study their dynamic behavior. A comparative study of the modal parameters (natural frequency, damping, and mode shapes) of the different hockey sticks provides valuable information for design optimization and to validate the accuracy of a finite element model. In addition, a refined two-accelerometer technique has been utilized to perform vibrational energy level tests (on the blade portion of the hockey sticks) to obtain the flexural and torsional vibration level distribution and to map out the sweet spot locations. Results indicate that this combined strategy of using both approaches provides a better understanding of the vibration performance characteristics of hockey sticks. Work is currently in progress to extend this technique for characterizing golf clubs.
Reconstruction of Radiated Acoustic Pressure Fields From a Complex Vibrating Structure
Authors: Wu Sean F. , Wu Yuhua
Published: January 2022

The Helmholtz Equation Least Squares (HELS) method previously derived by Wang and Wu (1997) and Wu and Wang (1998) is used to reconstruct the radiated acoustic pressure fields from a complex vibrating structure. The structure under consideration is of the form of a real, full-size four-cylinder engine designed for a passenger vehicle. To simulate sound radiation from a vibrating engine block, harmonic forces are assumed to exert on two arbitrarily selected sides. The resulting vibration responses are solved by using finite element method (FEM) through a commercial software package, I-DEAS Master Series 5®. Once the normal component of surface velocity distribution is determined, the surface acoustic pressures are calculated by the Helmholtz-Kirchhoff integral theory using the standard boundary element method (BEM) codes. The radiated acoustic pressure fields are then calculated by the Helmhollz-Kirchhoff integral formulation. The results thus obtained are taken as the input to the HELS formulation to reconstruct the surface and field acoustic pressures. Numerical results show that good agreement can be obtained with relatively few measurements in the field. Further, sound pressures over the entire surface of a complex structure can be reconstructed This method is shown to be very effective at low to mid frequency ranges. The effectiveness of the HELS method may deteriorate, however, as the frequency increases. This is because the HELS method is based on an expansion of spheroidal functions, which converges slowly at high frequencies. Nonetheless, in engineering practice noise diagnostics are often carried out in the low to mid frequency ranges. Under this circumstance, the present HELS method can become a robust and effective noise diagnostic tool.
Parallel Computation of Harmonic Waves Using Domain Decomposition: Part 1 — General Formulation
Authors: Atassi Hafiz M. , Susan-Resiga Romeo F.
Published: January 2022

A method is presented for parallel computation of time-harmonic waves using an iterative scheme based on domain decomposition. For exterior radiation and scattering problems, a finite computational domain is obtained by introducing a computational outer boundary on which a modified Dirichlet-to-Neumann map is used as a nonreflecting condition. The computational domain is then decomposed into subdomains and for each a boundary-value problem is defined using impedance-like transmission conditions on the subdomain interfaces. An iterative scheme updates the subdomain boundary conditions so that a global continuous solution is recovered.
Some Recent Advances in the Use of Kirchhoff’s Method in Computational Aeroacoustics
Authors: Lyrintzis Anastasios S.
Published: January 2022

A review of recent advances in the use of Kirchhoff’s method in Computational AeroAcoustics (CAA) is given. Kirchhoff’s integral formulation allows the radiating sound to be evaluated based on quantities on an arbitrary control surface if the wave equation is assumed outside. Thus only surface integrals are needed for the calculation of the far-field sound, instead of the volume integrals required by the traditional acoustic analogy method (i.e. Lighthill, Ffowcs Williams-Hawkings equation). A numerical CFD method is used for the evaluation of the flow-field solution in the near field and thus on the control surface. However, diffusion and dispersion errors associated with wave propagation in the far-field are avoided. The surface integrals and the first derivatives needed can be easily evaluated from the near-field numerical aerodynamic data. The equivalence of Kirchhoff’s method and Acoustic Analogy methods was recently proven rigorously. Kirchhoff’s integral formulation was also extended to include nonlinear source regions as well as refraction effects outside the Kirchhoff control surface. The method has been applied to helicopter noise, jet noise, propeller noise, ducted fan noise, etc. A simple set of portable Kirchhoff/Acoustic Analogy subroutines can be developed to calculate the far-field noise from inputs supplied by any aerodynamic near/mid-field code.
Closed-Form Transient Analysis of Delayed Mechanical Systems
Authors: Yang Bingen , Wu Xuqiang
Published: January 2022

Conventional modal analyses are not applicable to delayed mechanical systems because any possible orthogonality among system eigenvectors would be destroyed by time delays. Presented in this paper is a new approach which relates system eigensolutions to the residues of system transfer function. With this relation, closed-form transient response of mechanical systems can be practically estimated in eigenfunction series through inverse Laplace transform, without the need for orthogonal eigenvectors. The proposed method is illustrated on a delayed gyroscopic dynamic system.
A Study of Damping in a Fluid Loaded Micro-Sensor
Authors: Dohner Jeffrey L.
Published: January 2022

In the macro-domain, the mechanisms of energy loss in a fluid structure system are well understood. Damping can occur in the structure due to relaxation or in the fluid due to relaxation and radiation. For many fluids, such as air or water, fluid relaxation effects are small and are neglected. Moreover, structural relaxation effects are also often negligible. Therefore, for many systems, energy loss is assumed to be dominated by radiation effects alone. This macro-level assumption is a common one; however, as the size of the structure is reduced, the frequencies of excitation are increased, viscous losses are enhanced, and the applicability of this assumption becomes questionable. In this paper the acoustic losses in a micro-scale fluid structure system will be examined and the applicability of this assumption discussed.
A Novel Technique for Measurement of Vibration Using Acousto Optic Modulator (AOM)
Authors: Ngoi B. K. A. , Venkatakrishnan K.
Published: January 2022

A novel method for the measurement of vibration using an acousto optic modulator (AOM) is described. Previous methods generally rely on holographic (off-line measurement) and laser Doppler vibrometers (on line measurement). This method shows a new direction of vibration measurement using AOM rather than relying on laser Doppler vibrometer and laser Doppler displacement meter for on-line vibration measurement. A method of obtaining resolution in the range of sub-nanometer is proposed. The technique proposed not only projects a novel technique but also brings to light the possible application of AOM.
Study of Deformation Processes in Normal Slow Speed Impact
Authors: Lim Chwee Teck , Lim Chee Tiong
Published: January 2022

This paper models the normal slow speed impact of a deformable sphere against a rigid surface using elastic-plastic and fully-plastic compliance relationships derived from Johnson’s cavity model (Johnson, 1970) and Chang’s volume conservation model (Chang et al., 1987). These relationships describe the deformation processes occurring at the point of contact of the deformable sphere under slow speed inelastic impact. Comparison with results obtained from finite element program DYNA2D shows that the analytical model can accurately predict the deformation behavior at the point of impact.
Dynamic Numerical Simulation of the Motion of a Clamp Passing Over a Cable Supporting Roller Battery
Authors: Chen Nan , Meyer-Piening H.-R.
Published: January 2022

This paper presents a method to deal with the numerical simulation of a moving clamp that is ranning over a roller battery support of a cable transport system. It is a dynamic procedure involving time and form varying non-holonomic kinematics constraints as well as inter-excitation between parts of the system. The theoretical results are compared with laboratory test results.