bluuebunny/crossref_metadata_2025 huggingface dataset:
Damping Measurements Using Operational Data
Authors: James G. H. , Carne T. G. , Veers P. S.
Published: February 2008

We have measured modal damping using strain-gauge data from an operating wind turbine. This new technique for measuring modal damping is easier and less expensive than previously used methods. Auto-correlation and cross-correlation functions of the strain-gauge data have been shown to consist of decaying sinusoids which correspond to the modal frequencies and damping ratios of the wind turbine. We have verified the method by extracting damping values from an analytically generated data set. Actual operating response data from the DOE/Sandia 34-m Test Bed has been used to calculate modal damping ratios as a function of rotor rotation rate. This capability will allow more accurate fatigue life prediction and control.
An Evaluation of Several Wind Turbine Trailing-Edge Aerodynamic Brakes
Authors: Miller S. , Migliore P. G. , Quandt G. A.
Published: February 2008

An investigation was undertaken to identify the aerodynamic performance of five separate trailing-edge control devices and to evaluate their potential for wind turbine overspeed control applications. A modular two-dimensional wind tunnel model was constructed and aerodynamic performance data were acquired. To further interpret their potential, the controls were evaluated using a performance analysis computer program and a generic wind turbine geometry. On the basis of the investigation results, the Spoiler-Flap control configuration was deemed best suited for turbine braking applications. This particular control exhibited a good suction coefficient behavior over a broad angle-of-attack range and good turbine braking capabilities, especially at low tip-speed ratios.
Fatigue Reliability of Wind Turbine Fleets: The Effect of Uncertainty on Projected Costs
Authors: Veers P. S.
Published: February 2008

The cost of repairing or replacing failed components depends on the number and timing of failures. Although the total probability of individual component failure is sometimes interpreted as the percentage of components likely to fail, this perception is often far from correct. Different amounts of common versus independent uncertainty can cause different numbers of components to be at risk of failure. The FAROW tool for fatigue and reliability analysis of wind turbines makes it possible for the first time to conduct a detailed economic analysis of the effects of uncertainty on fleet costs. By dividing the uncertainty into common and independent parts, the percentage of components expected to fail in each year of operation is estimated. Costs are assigned to the failures and the yearly costs and present values are computed. If replacement cost is simply a constant multiple of the number of failures, the average, or expected cost is the same as would be calculated by multiplying by the probability of individual component failure. However, more complicated cost models require a breakdown of how many components are likely to fail. This breakdown enables the calculation of costs associated with various probability of occurrence levels, illustrating the variability in projected costs. Estimating how the numbers of components expected to fail evolves over time is also useful in calculating the present value of projected costs and in understanding the nature of the financial risk.
The Effect of Cyclic Operation of a Horizontal Ground Loop on Ground Coupled Heat Pump Performance
Authors: Wibbels M. , Den Braven K.
Published: February 2008

When the required load for single-speed heat pump is a fraction of its capacity, the heat pump must cycle. Multispeed heat pumps are able to vary their speed, and so cycle much less than single-speed heat pumps. The effect of cyclic operation on the heat pump ground loop and the consequent effect on heat pump performance have been examined. To analyze the effect of cyclic operation on heat transfer within the ground, separate finite element models were written for the ground loop and the surrounding soil. The models were used to compare the operation of the ground loop for single-speed and multispeed systems. Results were used to explore the effects of the pipe length, and to examine parameters which alter the effects of cycling. Parameters included pipe size and percent capacity. Results show that cyclic operation will decrease the performance of the heat pump, based solely on the performance of the ground loop (i.e., the total load remains fixed). It is also shown that as the pipe radius is increased, the effect of cyclic operation decreases, again due to the fluid capacity, and that as percent capacity decreases the cycling penalty increases.
Transverse Impact of a Damped Plate near a Straight Edge
Authors: Danial A. N. , Doyle J. F.
Published: February 2008

The effects of boundaries on flexural wave propagation in plates with viscous damping are studied through spectral and finite element analyses of incident and reflected waves. The incident wave is generated by point impact and therefore has the complication of being circularly crested. Results show excellent agreement between finite element and spectral solutions for waves—with high and low damping—reflected from simply supported, clamped and free edges. In addition, the possibility of Rayleigh-type free edge waves are investigated.
Passive and Active Control of a Complex Flexible Structure Using Reaction Mass Actuators
Authors: Garcia E. , Webb Captain S. , Duke Major J.
Published: February 2008

Passive and active control have been performed on a flexible structure possessing complex modal behavior. Specifically, the structure has closely spaced modes which created a “beat phenomena” in the structure’s vibrations. Reaction mass actuators (RMAs) were used to suppress the structural vibrations with both passive and active control schemes. The results of using both types of control systems were compared both analytically and experimentally. It was determined that, although passive tuning of the RMAs did suppress the structure’s vibrations, additionally applying active control to the optimally tuned RMAs did not significantly increase the system’s vibration suppression performance. However, by choosing the actuator’s characteristics from active control considerations, an active strategy utilizing a local velocity feedback controller suppressed structural vibrations and reduced the active system’s settling time to 20 percent of the settling time with passive damping. Both the passive and the active control were found to be a significant improvement over the structure’s open-loop response.
Bifurcation and Modal Interaction in a Simplified Model of Bending-Torsion Vibrations of the Thin Elastica
Authors: Cusumano J. P. , Lin D.-C.
Published: February 2008

This paper presents a numerical study of bifurcation and modal interaction in a system of partial differential equations first proposed as a simplified model for bending-torsion vibrations of a thin elastic beam. A system of seven ordinary differential equations obtained using the first six bending and first torsional normal modes is studied, and Floquet theory is used to locate regions in the forcing frequency, forcing amplitude parameter plane where “planar” (i.e., zero torsion) motions are unstable. Numerical branch following and symmetry considerations show that the initial instability arises from a subcritical pitchfork bifurcation. The subsequent nonplanar chaotic attractor is part of a branch of 2-frequency quasiperiodic orbits which undergoes torus-doubling bifurcations. A new statistical technique which identifies interacting modes and the average stability properties of the associated subspaces is presented. The technique employs the Lyapunov vectors used in the calculation of the Lyapunov exponents. We show how this method can be used to split the modes into active and passive sets: active modes interact to contain the attractor, whereas passive modes behave like isolated driven oscillators. In particular, large amplitude modes may simply serve as conduits through which energy is supplied to the active modes.
Probe Reversal and Pressure Based Bias Error Correction Procedures Applied to Intensity Measurements in Planar Standing Waves
Authors: Guy R. W. , Luchian H.
Published: February 2008

An analytical application of probe reversal and pressure correction strategies to minimize channel phase errors in P-P intensity measurements within discrete frequency standing waves is made. Two potential error sources, error of position upon reversal and error of pressure correction, are examined and found negligible at low frequencies but likely to be problematic at high frequencies. It is predicted that pressure correction or probe reversal can lead to superior performance when compared with measures without correction at modest and higher standing wave ratios in true intensity assessment; the frequency range for a given probe spacing is also extended. The correction procedures are then applied to low frequency measurements (63 Hz and 125 Hz) for a range of standing wave ratios. It is found that correction procedures generally lead to better results than uncorrected measures, but beyond a standing wave ratio of about 30 dB at 63 Hz additional error source arises which renders inaccurate the result of correction procedures, particularly for smaller probe spacing measures.
Optimal Active Vibration Absorber: Design and Experimental Results
Authors: Lee-Glauser G. , Juang Jer-Nan , Sulla J. L.
Published: February 2008

An optimal active vibration absorber can provide guaranteed closed-loop stability and control for large flexible space structures with collocated sensors/actuators. The active vibration absorber is a second-order dynamic system which is designed to suppress any unwanted structural vibration. This can be designed with minimum knowledge of the controlled system. Two methods for optimizing the active vibration absorber parameters are illustrated: minimum resonant amplitude and frequency matched active controllers. The Controls-Structures Interaction Phase-1 Evolutionary Model at the NASA Langley Research Center is used to demonstrate the effectiveness of the active vibration absorber for vibration suppression. Performance is compared numerically and experimentally using acceleration feedback.
Improved Inverse Eigensensitivity Method for Structural Analytical Model Updating
Authors: Lin R. M. , Lim M. K. , Du H.
Published: February 2008

In order to update analytical models of practical engineering structures, inverse eigensensitivity method (IEM) has been developed. Though it has nowadays been widely accepted, the classical inverse eigensensitivity method does have some drawbacks such as the assumption of small error magnitudes and slow speed of convergence due to the fact that the sensitivity coefficients are calculated purely based on modal data of analytical model. In the present paper, an improved inverse eigensensitivity method, which avoids the existing problems of classical inverse eigensensitivity method, has been developed. The improved method employs both analytical and experimental modal data to calculate the required eigensensitivity coefficients which are very close to their true values. The method has been further extended to the case where measured coordinates are incomplete. Practical applicability of the method has been assessed by its application to the updating of the finite element model of a plane truss structure.
A State-Space Modeling of One-Dimensional Active Noise Control Systems
Authors: Wu Zhen , Varadan V. K. , Varadan V. V. , Lee K. Y.
Published: February 2008

A state-space representation of a dynamic system for one-dimensional sound reflection and transmission is developed. The state-space modeling is the first step for future development of an active noise control system using modern control synthesis tools. In contrast to a classical frequency-domain description, the state model allows direct computation of the system’s time response and provides a forum for modern control synthesis, which leads to an optimal control algorithm. Based on the governing wave equation, the state model is derived using a finite difference technique combined with analytical expressions. Numerical simulation of the dynamic system model is presented, which shows a good agreement with the frequency-domain solutions. Discretization errors are investigated and improved by using nonuniform grids.
Active Control of a Circular Membrane to Reduce Transient Noise Transmission
Authors: van Niekerk J. L. , Tongue B. H.
Published: February 2008

An active control approach that reduces transient noise transmission through a membrane in a circular duct is presented. Discrete sections of piezo-electrical film, PVDF, are used as actuators to adjust the tension of the membrane. Different control strategies, such as optimal, sliding mode and velocity feedback control, are investigated analytically and then implemented experimentally. It is shown that velocity feedback control is the more effective, stable controller for this application.
Characteristics of Dimension Functions Associated With Cutting Measurements
Authors: Rokni M. , Berger B. S. , Minis I.
Published: February 2008

The information dimension, D(0), of attractors associated with orthogonal turning is determined from experimental tool-workpiece relative acceleration data. Let E≡dimension of a delay coordinate space, n≡number of generic data points and m≡ number of reference points on the attractor. It is shown that properties of D(0) as a function of E, denoted by D(0):E, are unchanging, invariant, over large intervals of n and m. The qualitative properties of D(0):E discriminate between various cutting cases. This discrimination can be based on relatively small data sets. The computation of D(0) is shown to be robust in the sense that estimated values of D(0) are invariant or slowly varying over intervals of n and m.
Beam Element Structural Dynamics Modification Using Experimental Modal Rotational Data
Authors: Cafeo John A. , Trethewey Martin W. , Sommer H. Joseph
Published: February 2008

Structural dynamic modification (SDM) of a fixed-free (cantilever) beam to convert it into a fixed-fixed beam with experimental modal data is presented. The SDM focuses on incorporating experimental rotational degrees-of-freedom (DOF) measured with a novel laser measurement technique. A cantilever beam is tested to develop the experimental modal database including rotational degrees of freedom. A modal database from a finite-element model also is developed for comparison. A structural dynamic modification, with both databases, is performed using a Bernoulli-Euler beam to ground the free end of the cantilever beam. The hardware is then modified and a second experimental modal analysis of the resulting fixed-fixed beam performed. A finite-element model of the fixed-fixed beam also was created. Comparison of results from these four tests are used to assess the effectiveness of SDM using experimental modal rotational data. The evaluation shows that provided high quality experimental rotational modal data can be acquired, SDM work with beam elements can be effective in yielding accurate results.
Modelling and Performance of an Experimental Active Vibration Isolator
Authors: Miller L. R. , Ahmadian M. , Nobles C. M. , Swanson D. A.
Published: February 2008

The performance of an active vibration isolator consisting of a fluid mount and an electromagnetic actuator is discussed. The electromagnetic actuator augments the inertia effects of the fluid mount to reduce the dynamic stiffness of the mount at the vibrational disturbance frequencies of the engine. The active isolator is modeled using bond graphs. Dynamic stiffness, blocked force, and free displacement transfer functions are developed from the bond graph model to gain insight into the active mount’s performance. A mount effectiveness analysis shows that reducing the mount’s dynamic stiffness results in better dynamic isolation. Numerical simulations along with laboratory testing of the active isolator are used to evaluate the performance of the mount. A simple laboratory experiment shows that an active mount can be controlled to have a dynamic stiffness that is 100 times (40 dB) lower than a passive mount, without sacrificing static stiffness.
Combined Piezoelectric-Hydraulic Actuator Based Active Vibration Control for Rotordynamic System
Authors: Tang P. , Palazzolo A. , Kascak A. , Montague G. , Li W.
Published: February 2008

Previous research by the authors concentrated on using piezoelectric actuators for active vibration control (AVC) of rotating machinery. The current work extends this by positioning the piezo-actuator remotely from the controlled structure and transmitting the control force via a hydraulic line and two pistons. Liquid plastic (LP) is employed as a transmission “fluid” to obtain a high bulk modulus and low leakage. The paper presents results for bulk moduli measurement, and bench and rig tests for the entire actuator system. These results show the high effectiveness of the hybrid actuator for controlling vibrations on a laboratory rotor test rig.
The Use of Optimally Shaped Piezo-electric Film Sensors in the Active Control of Free Field Structural Radiation, Part 1: Feedforward Control
Authors: Snyder S. D. , Tanaka N. , Kikushima Y.
Published: February 2008

Feedforward active control of free field structural radiation using vibration control sources and piezo-electric polymer film error sensors is considered. The problem of what should be measured by the sensors is first examined, where it is shown that orthonormal decomposition of the equation governing the acoustic power output of the structure will define the optimal quantities, which are described using the in vacuo structural modes as a basis function. Computer simulations show that by using only a few of these quantities as error signals, practically the maximum levels of acoustic power attenuation can be obtained at low frequencies. Tonal and broadband experimental results are presented using the shaped piezo-electric polymer film sensors which demonstrate the effectiveness of the described approach.
Methods of Preserving Symmetry in Model Updating
Authors: Lam M. J. , Inman D. J.
Published: February 2008

This work examines the model updating technique for both conservative and nonproportionally damped systems. In model updating, also referred to as model correction, the analytical model is updated until it agrees with the experimental data available. In this paper it is assumed that the measured modal data, i.e., natural frequencies and in some instances mode shapes, disagrees in part with the modal parameter predicted by the analytical model. Many model updating schemes tend to produce nonsymmetric updated stiffness (and damping) matrices. The methods presented here focus on retaining the desired symmetry in the updated model
The Modelling of the Opening and Closure of a Crack
Authors: Abraham O. N. L. , Brandon J. A.
Published: February 2008

The paper presents a method which utilizes substructure normal modes to predict the vibration properties of a cantilever beam with a breathing transverse crack. The two segments of the cantilever beam, separated by the crack, are related to one another by time varying connection matrices representing the interaction forces. The connection matrices are expanded in a Fourier series leading to a classical eigenvalue problem. Subsequently, the initial formulation is extended to avoid interference of the crack interfaces with a time domain formulation. The Lagrange multipliers, used to enforce the exact continuity constraints when the crack is closed, produce the interfaces forces needed for the modelling of interface dry friction.
Fundamental Noise Limits for Miniature Acoustic and Vibration Sensors
Authors: Gabrielson T. B.
Published: February 2008

Recent technological advances in microfabrication and fiber optics have made practical the construction of very small, sensitive sensors for acoustic or vibration measurements. As the sensitivity is increased or the size is decreased, a sensor becomes more susceptible to mechanical noise resulting from molecular agitation. Traditional noise analysis is often focused exclusively on electrical or optical noise; consequently, mechanical-thermal noise may not be considered in new types of sensors until the prototype testing reveals an unexpectedly high noise floor. Fortunately, mechanical-thermal noise is relatively easy to estimate early in the design process because the equivalent noise force is only a function of the temperature and the mechanical losses in the sensor There are a number of specific techniques that are applicable for evaluating either the total mechanical-thermal noise or the spectral distribution of that noise for simple or complex sensors. These techniques are presented and, in addition, a summary of other noise components is given in the context of design guidelines for high-sensitivity sensors.
Self-sensing Active Vibration Control using the Moving-Coil-Type Actuator
Authors: Okada Y. , Matsuda K. , Hashitani H.
Published: February 2008

Active vibration control requires a velocity signal which is fed back to the force actuator to produce the damping force to the structure. Usually a gap sensor is used to detect the displacement and a differentiator is needed to produce the velocity signal. Moreover, it is very difficult to install the sensor at the same position of the actuator. Setting the gap sensor close to the magnetic actuator may cause an undesirable interaction between them. Sometimes there is no space for installing the sensor. This paper introduces a method of using a moving-coil-type actuator as a two-port sensing and driving device. Four types of velocity identification algorithms are tested and their capability of reducing structural vibrations is compared.
Forced Harmonic Response of a Continuous System Displaying Eigenvalue Veering Phenomena
Authors: Ginsberg J. H. , Pham Hoang
Published: February 2008

Prior studies of self-adjoint linear vibratory systems have extensively explored the free vibration phenomena associated with veering of eigenvalue loci that depict the dependence of natural frequencies on a system parameter. The present work is an exploration of the effect of such phenomena on the response of a nearly-periodic continuum to harmonic excitation. The focus of the analysis is the prototypical system of a two-span beam with a strong torsional spring at the intermediate pin support. The results of an exact eigenvalue analysis, not previously disclosed, are used to perform a modal analysis of the steady-state response to a harmonic concentrated force applied to the middle of one span. The modal equations are used to identify situations in which the force response is localized to one span, as well as the degree to which the location and magnitude of the peak displacement display parameter sensitivity. The effect of hysteretic loss on forced localization is discussed.
Dynamic Surface Solutions in Linear Elasticity and Viscoelasticity With Frictional Boundary Conditions
Authors: Martins J. A. C. , Guimara˜es J. , Faria L. O.
Published: February 2008

This paper presents a study on the dynamic stability of the steady frictional sliding of a linear elastic or viscoelastic half-space compressed against a rigid plane which moves with a prescribed nonvanishing tangential speed. The system of differential equations and boundary conditions that govern the small plane oscillations of the body about the steady-sliding state of deformation is established. It is shown that for large coefficient of friction and large Poisson’s ratio the steady-sliding of the elastic body is dynamically unstable. This instability manifests itself by growing surface oscillations which necessarily propagate from front to rear and which in a short time lead to situations of loss of contact or stick. Similarly to what has been found with various finite dimensional frictional systems, these flutter type surface instabilities result from the intrinsic nonsymmetry of dry friction contact laws. The effect of viscous dissipation within the deformable body is also assessed: when viscous dissipation is present larger coefficients of friction are required for the occurrence of surface solutions propagating and growing from front to rear.
On the Geometric Stiffness Matrices in Flexible Multibody Dynamics
Authors: Tadikonda S. S. K. , Chang H. T.
Published: February 2008

A flexible branch body in a multibody chain undergoing large overall motions experiences geometric stiffening effects due to its own motions and interbody forces arising from bodies outboard of it. The self-motion effects are modelled through the use of 21 geometric stiffness matrices, in the literature, for an arbitrarily shaped flexible body. In this paper, the effect of interbody forces on the flexible body dynamics is modelled using up to 6 additional geometric stiffness matrices per outboard joint. Simulation results presented indicate that for a flexible body consisting of outboard bodies one may consider only the interbody force effects, without loss of accuracy, and thus significantly reduce the computational burden. This approach is especially suitable for multibody systems such as the Shuttle Remote Manipulator System, where the long boom masses are of similar magnitude, or when the payloads are several orders of magnitude larger than the link masses.
Modeling Fluid Inertia Forces of Short Journal Bearings for Rotordynamic Applications
Authors: El-Shafei A.
Published: February 2008

It has been recently suggested that fluid inertia may play an important role in the dynamic behavior of rotors supported on journal bearings. This paper presents a model for fluid inertia forces in short cylindrical journal bearings based on an energy approximation. The inertialess velocity profiles predicted by the solution of Reynolds’ equation are inserted in the axial momentum equation multiplied by the axial velocity profile and integrated across the film thickness, to obtain the pressure in short journal bearings including the fluid inertia effect. The pressure is then integrated to obtain the fluid inertia forces. It is shown that the inertia forces thus obtained are proportional to the usual radial, centripetal, tangential and coriolis accelerations of the journal, in addition to a nonlinear radial acceleration. Moreover, it is shown that the inertia forces contribute to the stiffness and damping characteristics of the journal bearings. The inertia coefficients of the bearings are obtained in cartesian and cylindrical coordinates, for both uncavitated and cavitated bearings, and are plotted versus the eccentricity ratio. The model thus obtained is an approximate analytical closed form model for fluid inertia forces in short journal bearings. Such a model is the most suitable for rotordynamic applications, particularly for time transient rotordynamic simulations.
Vibrations of Composite Noncircular Cylindrical Shells
Authors: Kumar V. , Singh A. V.
Published: February 2008

The free vibrational characteristics of composite noncircular cylindrical shells are investigated in this paper. The shells are composed of layered media of different material properties. The thickness of each layer is considered to be constant. First order composite shell theory, which includes the effects of shear deformation and rotary inertia, is used in the formulation. A combination of Bezier functions and beam functions is used to describe the displacement fields along the circumference and longitudinal directions, respectively, of the shell surface. The shell is modelled using a number of curved cylindrical panels. Displacement (C0), slope (C1) and curvature (C2) continuities between the panels are enforced by proper blending of the Bezier curves. Numerical results are included for a circular sandwich shell and a two-layer cross-ply oval cylinder that provide excellent agreement with those from the literature. The natural frequencies of clamped oval sandwich cylinders made of stiff outer layers and light middle layer are also presented.
A Simple Estimating Method for Reduction of Welding Residual Stresses in Thick Welded Joint From Stress-Relief Annealing—Part II: The Characteristics of Reduction of Welding Residual Stresses in Very Thick Joints During SR Treatment
Authors: Nakacho K. , Ueda Y.
Published: February 2008

Stress-relief annealing (SR treatment) is often applied to relieve welding residual stresses in the fabrication process of pressure vessels, etc. This study aims at development of an efficient method as simple as hand calculation to estimate reduction of residual stresses of very thick welded joint by SR treatment. In the first report, an estimating method was developed for relaxation tests, in uniaxial stress state, at changing and constant temperatures because the stress relaxation phenomenon is considerably similar to that observed in the SR treatment of a joint. In this report, the stresses relaxed by SR treatment in a very thick welded joint are analyzed accurately by the finite element method based on thermal elastic-plastic-creep theory. The characteristics of the changes of the welding residual stresses in multiaxial stress state are studied in detail for further development of the estimating method to SR treatment of a very thick welded joint, of which the stress state and boundary condition are very complex.
Applications of Iterative Elastic Techniques for Elastic-Plastic Analysis of Pressure Vessels
Authors: Mohamed A. I. , Megahed M. M. , Bayoumi L. S. , Younan M. Y. A.
Published: February 2008

The paper presents an application of iterative elastic techniques for the determination of elasto-plastic stress-strain fields, limit and shakedown loads. The iterative elastic method relies on iterative modification of elastic modulus in regions at which elastically calculated effective stress exceeds material yield strength. The technique is applied first to thick spherical and cylindrical shells under combined pressure and thermal gradient. Results showed good correlation with analytical elasto-plastic solutions. The elastic compensation technique is then applied to predict elasto-plastic stresses and shakedown loads of thin spherical shell with cylindrical nozzle subjected to internal pressure or end-thrust loading. Predicted shakedown loads were found to be in good agreement with the well-known Leckie and Penny results adopted in pressure vessel codes.
Overview of Fatigue Crack Initiation in Carbon and Low-Alloy Steels in Light Water Reactor Environments
Authors: Chopra O. K. , Shack W. J.
Published: February 2008

Recent test data illustrate potentially significant effects of light water reactor (LWR) coolant environments on the fatigue resistance of carbon and low-alloy steels. The crack initiation and crack growth characteristics of carbon and low-alloy steels in LWR environments are presented. Decreases in fatigue lives of these steels in high-dissolved-oxygen water are caused primarily by the effect of environment on growth of short cracks <100 μm in depth. The material and loading parameters that influence fatigue life in LWR environments are defined. Statistical models have been developed to estimate the fatigue lives of these steels in LWR environments, and design fatigue curves have been developed for carbon and low-alloy steel components in LWR environments. The significance of environmental effect on the current Code design curve is evaluated.
Acoustic Emission Waveform Analysis From Weld Defects in Steel Ring Samples
Authors: Shiwa M. , Yamaguchi A. , Sato M. , Murao S. , Nagai M.
Published: February 2008

Acoustic emission (AE) signals from weld defects, incomplete penetration (IP), slag inclusion (SI), and porosity (PR), in longitudinal seam welding of UOE steel pipes were evaluated by using an envelope analysis system and waveform analysis system. In test results, the location accuracy of the envelope and the waveform systems during the loading tests were a few 10 mm and a few mm, respectively. AE activity and intensity and waveform type could identify the welding defect types. Three types of AE spherical radiation patterns (AERPs), a monopole mode, a tensile fracture of dipole mode, and a tensile and shear mixed of dipole mode, were observed during the test. Information from cross section observation of the IP by SEM and AERP suggested that activity and intensity of AE signals from welding defects could depend on both stress concentration of the defect and brittleness of the microstructure around the defect.
Analysis of Thermal Stresses in a Boiler Drum During Start-Up
Authors: Taler J. , We˛glowski B. , Zima W. , Gra˛dziel S. , Zborowski M.
Published: February 2008

The paper presents an analytical way of calculating thermal stress distributions in cylindrical vessels, nonuniformly heated on their circumference. In thick-walled vessel elements, simplified analytical formulas do not give satisfactory results. A new method for determining thermal stresses has been developed. On the basis of temperature history measurements at several points on the drum outer surface, a time-space temperature distribution in the component cross section is determined, and next, thermal stresses are calculated using the finite element method (FEM). The new method, proposed for the solution of the inverse heat conduction problem, is sufficiently accurate. Knowledge of the boundary conditions on the inner surface of the drum, i.e., fluid temperature and heat transfer coefficient, is not necessary because the transient temperature distribution in the component is obtained from the solution of the inverse heat conduction problem. Comparison of the thermal distributions from FEM versus the new method demonstrate the accuracy of the new method. An example application of the new method demonstrates its benefits over the solution of the boundary-initial problem obtained by FEM.
Effective Stress Factor Correlation Equations for Piping Branch Junctions Under Internal Pressure Loading
Authors: Moffat D. G. , Mistry J. , Moore S. E.
Published: February 2008

The results from a previous finite element parametric study by the authors on the effective stress factors (ESFs) occurring in piping branch junctions under internal pressure loading are used to produce an ESF correlation equation for use in design. This is compared with some experimental data and also with other finite element data. Results suggest that ESFs can be predicted with some confidence using the correlation equation.
Elastic-Plastic Failure Analysis of Pressure Burst Tests of Thin Toroidal Shells
Authors: Jones D. P. , Holliday J. E. , Larson L. D.
Published: February 2008

This paper provides a comparison between test and analysis results for bursting of thin toroidal shells. Testing was done by pressurizing two toroidal shells until failure by bursting. An analytical criterion for bursting is developed based on good agreement between structural instability predicted by large strain-large displacement elastic-plastic finite element analysis and observed burst pressure obtained from test. The failures were characterized by loss of local stability of the membrane section of the shells consistent with the predictions from the finite element analysis. Good agreement between measured and predicted burst pressure suggests that incipient structural instability as calculated by an elastic-plastic finite element analysis is a reasonable way to calculate the bursting pressure of thin membrane structures.
Estimation of the η Factors for Mixed-Mode Cracks in Compact Tension Specimens
Authors: Wang Y. , Pan J.
Published: February 2008

The η factors for mixed-mode cracks in compact tension specimens are investigated for estimation of the J-resistance curve under mixed-mode loading conditions. The derivation of the η factor is first generalized for mixed-mode cracks. Based on a lower-bound approach for rigid-perfectly plastic materials, the η factors are then derived under mixed-mode I and III and mixed-mode I and II loading conditions. The results indicate that the η factor is only a function of the normalized crack length under mixed-mode I and III loading conditions. However, under mixed-mode I and II loading conditions, the η factor is not only a function of the normalized crack length, but also influenced by the fixture design due to the moment induced by the mode II load.
An Investigation of Cladding Effects on Shallow-Flaw Fracture Toughness of Reactor Pressure Vessel Steel Under Prototypic Biaxial Loading
Authors: Bass B. R. , McAfee W. J. , Bryson J. W. , Pennell W. E.
Published: February 2008

Potential structural-integrity benefits or liabilities of the stainless steel cladding on the inner surface of a reactor pressure vessel (RPV) are important considerations in the effort to refine or improve safety assessment procedures applied to RPVs. Clad-beam tests were carried out to investigate and quantify effects of the clad structure on fracture initiation toughness of through-clad shallow surface flaws in RPV material. A cruciform beam specimen was developed at ORNL to introduce a prototypic, far-field, out-of-plane biaxial stress component that provides a linear approximation of the nonlinear stress distribution generated by thermo-mechanical loading transients in an RPV. The cruciform specimens (102-mm-thick test section) were fabricated from RPV shell segments available from a canceled pressurized-water reactor plant. The specimens were tested under biaxial load ratios ranging from 0.0 (uniaxial) to 1.0 (full biaxial), the ratio being defined as the total load applied to the transverse beam arms divided by that applied to the longitudinal arms. The test results imply that biaxial loading is effective in reducing the shallow-flaw fracture toughness of the clad/heat-affected zone/structural-weld region of the RPV shell below that determined from uniaxial loading conditions. The lowest toughness value from the clad cruciform specimens tested under biaxial loading is only slightly above the ASME Section XI KIc curve. For all biaxiality ratios, the test results imply that shallow-flaw fracture toughness data from the RPV structural weld material are significantly lower than that obtained from a high-yield strength plate material.
Analytical Model for Self-Excited Vibration of an Overflow Flexible Plate Weir
Authors: Kaneko S. , Nagakura H. , Nakano R.
Published: February 2008

An analytical model for the self-excited vibration of an overflow flexible weir as observed in the French demonstration fast breeder reactor, Super Phenix-1, is proposed. The instability condition was derived for the case in which the plate vibrates at the frequency of the downstream tank sloshing. In this analysis, the flexible plate weir is modeled as a simply supported-free-simply supported-clamped rectangular plate. Eigenfunction expansions were applied for analyzing both plate vibrations and the downstream tank sloshing. The effect of an overflow liquid is formulated based on the assumption that the momentum change due to the collision of an overflow liquid partly transmitted to the pressure rise on the free surface. As a result, the characteristic equation of the system yielding the theoretical stability boundary was obtained. The stability boundary thus derived agreed well with experimental results.
Steam Generator Fretting-Wear Damage: A Summary of Recent Findings
Authors: Gue´rout F. M. , Fisher N. J.
Published: February 2008

Flow-induced vibration of steam generator (SG) tubes may sometimes result in fretting-wear damage at the tube-to-support locations. Fretting-wear damage predictions are largely based on experimental data obtained at representative test conditions. Fretting-wear of SG materials has been studied at the Chalk River Laboratories for two decades. Tests are conducted in fretting-wear test machines that simulate SG environmental conditions and tube-to-support dynamic interactions. A new high-temperature force and displacement measuring system was developed to monitor tube-to-support interaction (i.e., work-rate) at operating conditions. This improvement in experimental fretting-wear technology was used to perform a comprehensive study of the effect of various environment and design parameters on SG tube wear damage. This paper summarizes the results of tests performed over the past 4 yr to study the effect of temperature, water chemistry, support geometry and tube material on fretting-wear. The results show a significant effect of temperature on tube wear damage. Therefore fretting-wear. The results show a significant effect of temperature or tube wear damage. Therefore, fretting-wear tests must be performed at operating temperatures in order to be relevant. No significant effect of the type of water treatment on tube wear damage was observed. For predominantly impacting motion, the wear of SG tubes in contact with 410 stainless steel is similar regardless of whether Alloy 690 or Alloy 800 is used as tubing material or whether lattice bars or broached hole supports are used. Based on results presented in this paper, an average wear coefficient value is recommended that is used for the prediction of SG tube wear depth versus time.
The Structural Response of Cylindrical Shells to Internal Shock Loading
Authors: Beltman W. M. , Burcsu E. N. , Shepherd J. E. , Zuhal L.
Published: February 2008

The internal shock loading of cylindrical shells can be represented as a step load advancing at constant speed. Several analytical models are available to calculate the structural response of shells to this type of loading. These models show that the speed of the shock wave is an important parameter. In fact, for a linear model of a shell of infinite length, the amplitude of the radial deflection becomes unbounded when the speed of the shock wave is equal to a critical velocity. It is evident that simple (static) design formulas are no longer accurate in this case. The present paper deals with a numerical and experimental study on the structural response of a thin aluminum cylindrical shell to shock loading. Transient finite element calculations were carried out for a range of shock speeds. The results were compared to experimental results obtained with the GALCIT 6-in. shock tube facility. Both the experimental and the numerical results show an increase in amplitude near the critical velocity, as predicted by simple steady-state models for shells of infinite length. However, the finite length of the shell results in some transient phenomena. These phenomena are related to the reflection of structural waves and the development of the deflection profile when the shock wave enters the shell.
Development of NiCrAlY Alloys for Corrosion-Resistant Coatings and Thermal Barrier Coatings of Gas Turbine Components
Authors: Nickel H. , Clemens D. , Quadakkers W. J. , Singheiser L.
Published: February 2008

The demand for improved efficiency and power output of energy conversion systems has lead to an increase of gas inlet temperatures in modern land-based gas turbines. The resulting increase of component surface temperature leads to an enhanced oxidation attack of the blade coating, which, in stationary gas turbines, is usually of the MCrAlY (with M = Co and/or Ni) type. Considerable efforts have been made in the improvement of the high temperature properties of MCrAlY coatings by additions of minor alloying elements. In the present paper, the effect of systematic composition variations, especially yttrium, silicon, and titanium additions, on the protective properties of MCrAlY coatings are presented. The coatings were applied to a steel substrate by low-pressure plasma spraying. Then, free-standing MCrAlY-bodies were machined from the coating. Isothermal and cyclic oxidation tests were carried out in the temperature range 950°C–1100°C. The effect of systematic variation of titanium and silicon contents on oxidation and micro structural stability was studied by characterization of the coating and the corrosion products using light and electron optical microscopy and by secondary neutrals mass spectrometry (SNMS).
Experimental, Analytical, and Regulatory Evaluation of Seismic Behavior of Piping Systems
Authors: Touboul F. , Blay N. , Lacire M. H.
Published: February 2008

Based on an experimental program, including both individual components and piping system, CEA has evaluated the margins coming from present design procedures and has developed sound analytical methods that allow for a modelization, in the linear or nonlinear domain. For industrial purposes, simplified methods are proposed that are much less time-consuming than nonlinear time-history calculations, but much more accurate than linear methods. They are devoted to a better evaluation of the global behavior (internal moments in the piping system or reactions in supports, displacements, rotations).
Scanned Orbital Welding: Thermal Modeling and Lumped Adaptive Control
Authors: Sfetsos H. , Angelis J. , Doumanidis C.
Published: February 2008

Scan orbital welding of cylindrical vessel, flange, and piping parts is performed by their rapid revolution under a radially or axially translated heat source, with its power modulated so as to implement a specified thermal distribution. Thus, the plasma-arc welding torch sweeps the stainless steel surface to generate a desirable temperature field and the concomitant material features. A numerical simulation of the thermal field is developed for off-line analysis. On this basis, a lumped thermal regulator of the heat-affected zone, employing infrared temperature feedback at a single spot, as well as standard PI, gain scheduling, and self-tuning control algorithms is tested. The thermal model is also employed for real-time torch efficiency identification and compensation. The numerical reference model serves as the basis for an in-process adaptive thermal control system to regulate the temperature field, using thermal feedback from the infrared pyrometer. A distributed-parameter control strategy, with guidance of the torch motion and power by a new weighted attraction strategy to randomly sampled points, is tested on scan-welded flanges. The regulator is validated computationally and experimentally, and its applicability to other scanned processing of materials is considered.
Acoustically Induced Structural Fatigue of Piping Systems
Authors: Eisinger F. L. , Francis J. T.
Published: February 2008

Piping systems handling high-pressure and high-velocity steam and various process and hydrocarbon gases through a pressure-reducing device can produce severe acoustic vibration and metal fatigue in the system. It has been previously shown that the acoustic fatigue of the piping system is governed by the relationship between fluid pressure drop and downstream Mach number, and the dimensionless pipe diameter/wall thickness geometry parameter. In this paper, the devised relationship is extended to cover acoustic fatigue considerations of medium and smaller-diameter piping systems.
Eliminating Thermoacoustic Oscillations in Heat Exchanger and Steam Generator Systems
Authors: Eisinger F. L.
Published: February 2008

Systems comprised of hot and cold components containing gaseous fluids may be subject to thermoacoustic oscillations if the temperature gradient between the two components exceeds a critical value. An evaluation of the Sondhauss-type and the Rijke-type thermoacoustic oscillations in combined turbine/heat exchanger/duct systems and furnace/burner systems will be presented. Parameters which will reduce or eliminate the likelihood of thermoacoustic oscillations in such systems are identified and discussed in this paper.
A Review of Engineering Developments of Aqueous Phase Solar Photocatalytic Detoxification and Disinfection Processes
Authors: Goswami D. Y.
Published: February 2008

Scientific research on photocatalytic oxidation of hazardous chemicals has been conducted extensively over the last three decades. Use of solar radiation in photocatalytic detoxification and disinfection has only been explored in the last decade. Developments of engineering scale systems, design methodologies, and commercial and industrial applications have occurred even more recently. A number of reactor concepts and designs including concentrating and nonconcentrating types and methods of catalyst deployment have been developed. Some commercial and industrial field tests of solar detoxification systems have been conducted. This paper reviews the engineering developments of the solar photocatalytic detoxification and disinfection processes, including system design methodologies.