bluuebunny/crossref_metadata_2025 huggingface dataset:
Vaporization of LNG Using Fired Heaters With Waste Heat Recovery
Authors: Rosetta M. J. , Martens D. H.
Published: July 2009

Liquefied Natural Gas (LNG) is an important component in meeting the future energy needs of the United States and other industrialized countries. The ability to locate (produce), process, liquefy, transport, and re-gasify stranded natural gas is vital to maintaining a stable long-term natural gas supply necessary for sustained economic growth [1]. Two of the key components in this supply chain are the vaporization of the LNG at the import terminal and the peak shaver trains that liquefy pipe line natural gas, store it and then vaporize the liquid to feed the gas to the pipe line when additional flow is required. This paper outlines a novel approach incorporating a traditional fired heater with waste heat recovery to vaporize LNG at an import terminal or peak shaver train while maintaining a high thermal efficiency. A comparison is made between the new technology and more conventional methods, with emphasis on emissions. Some of the advantages and disadvantages associated with the design and implementation of these systems are explored in this presentation. As a fundamental cannon of ethics, engineers are obligated to address the most efficient and responsible use of resources. The environmental impact of supplying the necessary natural gas energy to industry and consumers is significant. This paper addresses these aspects as considered during the development of the alternative LNG vaporization technology.
An Analysis of Residual Stress Improvement for a Dissimilar Metal Nozzle-to-Pipe Weld by Using the Heat Sink Method
Authors: Park J.-S. , Kim J.-M. , Sohn G.-H. , Kim Y.-H.
Published: July 2009

This study is concerned with the mechanics analysis of residual stress improvement by the heat sink method applied to a dissimilar metal weld (DMW) for the use in nuclear power plants. The DMW joint considered here is composed of ferritic low-alloy steel nozzle, austenitic stainless steel safe-end, and nickel-base alloy A52 weld metal. To prepare the DMW joint with a narrow-gap, the gas tungsten arc welding (GTAW) process is utilized, and the heat sink method is employed to control thermal gradients developed in the critical region of work pieces during welding. Weld residual stresses are computed by the non-linear thermal elasto-plastic analysis using the axisymmetric finite element (FE) model, for which temperature-dependent thermal and mechanical properties of the materials are considered. A full-scale mock-up test is conducted to validate analytical solution for the DMW joint, and residual stresses are measured by using the hole-drilling method. Results of the FE modeling and mock-up test for the DMW joint are compared and effects of the heat sink method are discussed. It is found that a significant amount of residual compressive stresses can be developed on the inner surface of the DMW joint by using the heat sink method, which can effectively reduce the susceptibility of the welded materials to stress corrosion or fatigue cracking.
Methodology for Reactor Vessel Head Drop Accident Analysis
Authors: Remic Joseph M. , Johnston Neal D. , Demetri George J. , Roarty David H.
Published: July 2009

Nuclear power plants are required to evaluate the risks associated with a potential accident in which the reactor vessel closure head is dropped onto a reactor with fuel installed. This is done as part of an overall effort to safely control the movement of heavy loads in a nuclear facility per NUREG-0612 [1]. In some cases, this requires that an analysis be done of the potential accident to confirm no damage to fuel would occur. This paper provides a methodology for such analysis, along with the basis for the methodology, for a typical pressurized water reactor design. The methodology uses nonlinear, dynamic transient finite element analysis to analyze the event. An example of typical results and acceptance criteria is provided.
ASME B31.3 Appendices P and S: Compensating for Shortcomings
Authors: Edwards Don R.
Published: July 2009

The 2004 edition of ASME B31.3 Process Piping Code [1] introduced both Appendix P and Appendix S Example 1; Examples 2 and 3 were included in the 2006 edition. Appendix P is to illustrate a nearly computer stress analysis basis by defining alternative rules for displacement stress range evaluation, and Appendix S contains examples describing how to satisfy the requirements of B31.3 when performing computer based stress analysis. As is possible with any extensive addition to any code, these first offerings contained shortcomings either explicitly or by lack of clarity. This paper discusses some of these issues, provides workarounds when using today’s commercially available piping stress analysis software, and proposes revisions to both Appendices for the 2010 edition of the B31.3 Process Piping Code.
Long-Term Stress Analysis of Plastic Pipe Reinforced by Cross-Winding Steel Wire
Authors: Li Xiang , Zheng Jinyang , Li Yaxian , Xu Ping , Zheng Chunying , Shao Taiqing , Shao Hangzeng , Chen Defu , Li Guangzhong , He Xiaolian
Published: July 2009

Plastic pipe reinforced by cross helically wound steel wires (PSP) is a new type of metal-plastics composite pipe developed in China. Time-dependent properties of PSP are investigated theoretically and experimentally in this paper. Although the steel wire can carry most of the loading in a liner elastic way, the time dependent behavior shown in the PSP should be further analyzed and described. Based on the structural features of PSP and the viscoelastic behaviors of HDPE in matrix, a three layer viscoelastic model is proposed to calculate time-dependent elastic stresses and strains in the PSP subjected to internal pressure. The experimental results show that the hoop strain decreases slowly, while the axial strain increases by 0.16% in 14000 minutes at constant internal pressure. Good agreement between theoretical results and experimental data shows that the three layer viscoelastic model is able to predict the time-dependent relationship of stress and strain in PSP. The effects of volume fraction and winding angle of the steel wires on the creep behaviour of the PSP subjected to an internal pressure are discussed in the end.
A Model for Predicting Temperature of Electrofusion Joints for Polyethylene Pipes
Authors: Shi Jianfeng , Zheng Jinyang , Guo Weican
Published: July 2009

Polyethylene (PE) pipe with electrofusion (EF) joints is widely used in the areas of gas distribution. Understanding and predicting the temperature during welding is crucial for ensuring the joint quality. The EF joining is generally conducted by applying a constant voltage to the heating wire. As the welding process develops, both the temperature and the resistance of the heating wire increase, which leads to a decrease in the rate of power input with increasing fusion time. However, the existing models for temperature prediction have not taken the change in the rate of power input into account. By comprehensively considering the variation in the rate of power input, the phase transition of PE and the thermal contact conductance between the heating wire and PE, the authors established an analytical model for predicting the temperature. Experiments are designed and the power inputs measured are shown to be in good agreement with the analytical results, in contrast to the interrogative measured temperature. In order to verify the temperature fields, the authors employ a new “Eigen-line” method based on ultrasonic tests which overcomes the difficulties found in the measuring methods by thermocouples. The experimental results also show good agreements. The developed model is then used to investigate the influence of the decline in the power input, physical properties of PE and the thermal contact conductance between heating wire and surrounding PE. It is found that the average power input is in proportion to the input voltage, and the temperature profile is greatly affected by the power decline and specific heat capacity. The proposed model can be used to optimize the welding specification.
Nondestructive Testing Technique for Atmospheric Storage Tanks
Authors: Ding Shoubao , Liu Fujun , Xu Yanting , Guo Xiaolian
Published: July 2009

In china, atmospheric storage tanks are not included in the management of special equipment, and therefore they are not required to be inspected compulsorily. There is larger difference between China and developed countries on atmospheric storage tank inspection technique than the other techniques on the inspection of pressure vessels. It is widely believed that the strength worsening and perforation of the tank is mainly caused by the serious corrosion at the bottom surface of tank floor. The present development of nondestructive testing on atmospheric storage tank was analyzed systematically in this paper, in which the principle, standard present status, the usage of inspection equipments and the application of the acoustic emission testing and magnetic flux leakage testing techniques on atmospheric storage tanks were mainly introduced. The problems existing in the inspection equipments usage were discussed. A practice for inspecting and evaluating atmosphere storage tanks using these testing methods was proposed.
Use of Elastic Follow-Up in Integrity Assessment of Structures
Authors: Hadidi-Moud Saeid , Smith David J.
Published: July 2009

This paper reviews the concepts and definitions related to elastic follow-up, Z, together with its potential use in stress classification. Based on the principles governing benchmark multiple bar structures elastic follow-up (EFU) is quantified. Local nonlinearities arising within a structure influence elastic follow-up. These include variations in the geometry of structure, its material properties, effects of plasticity and creep, structural discontinuities and boundary conditions. Elastic follow-up is shown to be simple to evaluate, is physically meaningful (as it relates strain accumulation in the structure to its cause) and is useful in design practice. In this generalised definition Z = 1 indicates no follow-up and represents a fully displacement controlled situation. In contrast Z = ∞ represents the extreme case of fully load controlled situation. Presence of mixed boundary conditions is interpreted as 1 < Z < ∞. A methodology that overcomes the singularity problem of cracked structure to determine Z is then proposed. The distinctive characteristic of the proposed approach is that it takes account of situations where the structure contains defects.
An Evaluation of Post-LOCA Debris on Multi-Stage Safety-Related Pumps in PWR ECCS in Support of Generic Safety Issue 191 Closure
Authors: Ezekoye L. Ike , Hundal Rolv , Pyle Paul V.
Published: July 2009

The U.S. Nuclear Regulatory Commission (NRC) issued Generic Safety Issue (GSI) 191 covering the ability of nuclear reactor containment building (RCB) sumps to support long-term core cooling post-accident for Pressurized Water Reactors (PWRs). The issue is that a postulated Loss-of-Coolant Accident (LOCA) for a PWR would result in the initial escape of high-pressure, high-temperature subcooled coolant from the pipe break location in the form of a two-phase jet. The impingement of the jet may damage materials used inside the RCB, resulting in the generation of debris. The debris transported to and through the sump screen when the Emergency Core Cooling (ECC) and the Containment Spray (CS) Systems are realigned to draw suction from the containment sump will be ingested by pumps in the flow path. Since wear affects the dynamics of the pump and hence vibration, the extent to which any pump can survive the abrasive nature of the ingested debris depends on how well one can predict the wear of pump critical dimensions using the debris mix and pump design parameters. This paper describes the issues to be considered in pump assessment and presents wear models that can be used to assess pump operability and performance. It shows that depending on assumptions made relative to the wear pattern, different results can be reached using the wear models. The question of what makes sense is discussed.
Hydrogen Effects on the Burst Properties of Type 304L Stainless Steel Flawed Vessels
Authors: Morgan Michael J. , Hall Monica C. , Lam Poh-Sang , Thompson W. Dean
Published: July 2009

The effects of hydrogen and burst media on the burst properties of Type 304L stainless steel vessels were investigated. The purpose of the study was to compare the burst properties of hydrogen-charged stainless steel vessels burst with different media: water, helium gas, and deuterium gas. A second purpose was to provide data to improve an existing finite-element model for predicting burst behavior. Burst tests were conducted on hydrogen-charged and uncharged axially-flawed cylindrical vessels. The results indicate that samples burst pneumatically had lower volume ductility than those tested hydraulically. For pneumatic burst tests, samples burst with deuterium gas had slightly lower ductility than helium gas tests. For uncharged samples, burst pressure was not affected by burst media. For samples pre-charged with hydrogen, deuterium burst pressures were about 80% of the hydraulic or helium burst pressures. Hydrogen-charged samples had lower volume ductility and slightly higher burst pressures than uncharged samples. The results of the tests were used to verify and improve a previously developed predictive finite-element model. The existing finite-element model can qualitatively predict the expected changes in burst properties with hydrogen or tritium service, but a better material property database is required for quantitative predictions.
API 579-1/ASME FFS-1 2007: A Joint API/ASME Fitness-for-Service Standard for Pressurized Equipment
Authors: Osage David A. , Janelle Jeremy L.
Published: July 2009

The first edition of API 579 Recommended Practice for Fitness-For-Service was published in 2000. Work on the second edition of API 579 was initiated the same year with many planned technical improvements. In addition to technical improvements, API and ASME agreed to form a joint committee to produce a joint API/ASME FFS Standard that can be used for pressure-containing equipment. This new standard designated as API 579-1/ASME FFS-1 2007 Fitness-For-Service is based on the first edition of API 579, incorporates all planned technical enhancements originally slated for the second edition, and also includes modifications to address the special needs of other industries such as the fossil electric power industry, and the pulp and paper industry. Insights into the driving force to create API 579 and an overview of the technical enhancements that will be incorporated into API 579-1/ASME FFS-1 are presented in this paper. The use of the API 579-1/ASME FFS-1 fitness-for-service assessment procedure models to establish a probability of failure for use with the API Risk Based Inspection Planning Technology is also provided.
The Present and the Future of the Korea Electric Power Industry Code
Authors: Byun Hoonseok , Yoon Seogchan , Kim Jonghae , Lee Samchul
Published: July 2009

Korea Electric Power Industry Code (KEPIC), a set of integrated standards applicable to the design, construction and operation of electric power facilities including nuclear power plants, has been developed on the basis of referring to the prevailing U.S. codes and standards which had been applied to the electric power facilities in Korea. Being the developing and managing organization of KEPIC, Korea Electric Association (KEA) published its first edition in 1995, the second in 2000 and the latest in 2005. KEPIC has been applied to the construction of nuclear power plants since 1997 in Korea. Along with the effectuation of the Agreement on Technical Barriers to Trade (TBT) in 1995, the international trend related to codes and standards is changing rapidly. KEA is, therefore, making its utmost efforts so as for KEPIC to keep abreast with the changing environment in international arena. KEA notified ISO/IEC Information Centre of its acceptance of the Code of Good Practice in the Agreement on TBT. Also the 2005 edition of KEPIC was published to be retrofitted according to the ISO/IEC Guide 21-Adoption of International Standards as regional or national standards. On the other hand, KEA is continuously performing to study on the improvement of KEPIC requirements. Such KEA’s efforts will help KEPIC correspond with international standards such as ISO/IEC standards, and internationally recognized standards such as ASME codes and standards. Furthermore KEA will expedite the publication of the bilingual edition of KEPIC at 2010 as per the globalization plan and KEA hopes that KEPIC can assist Korea Electric Power Corporation (KEPCO) and Korea Hydro & Nuclear Power Co., Ltd. (KHNP) in exportation of Korea Standard Nuclear Power Plant (KSNP) such as OPR-1000 and APR-1400 by the bilingual edition.
Propose of Simplified Stress Intensity Factor Equation for SCC Extension of the Pipe Welds
Authors: Ochi Mayumi , Hojo Kiminobu , Muroya Itaru , Ogawa Kazuo
Published: July 2009

Alloy 600 weld joints have potential for primary water stress corrosion cracks (PWSCC). At the present time it has been understood that PWSCC generates and propagates in the Alloy 600 base metal and the Alloy 600 weld metal and there has been no observation of cracking the stainless and the low alloy steel. For the life time evaluation of the pipes or components the crack extension analysis is required. To perform the axial crack extension analysis the stress intensity database or estimation equation corresponding to the extension crack shape is needed. From the PWSCC extension nature mentioned above, stress intensity factors of the conventional handbooks are not suitable because most of them assume a semi-elliptical crack and the maximum aspect ratio crack depth/crack half length is one (The evaluation in this paper had been performed before API 579-1/ASME FFS was published). Normally, with the advance of crack extension in the thickness direction at the weld joint, the crack aspect ratio exceeds one and the K-value of the conventional handbook can not be applied. Even if those equations are applied, the result would be overestimated. In this paper, considering characteristics of PWSCC’s extension behavior in the welding material, the axial crack was modeled in the FE model as a rectangular shape and the stress intensity factors at the deepest point were calculated with change of crack depth. From the database of the stress intensity factors, the simplified equation of stress intensity factor with parameter of radius/thickness and thickness/weld width was proposed.
Deformation Process of Metal Pipe by Underwater Shock Loading
Authors: Iyama Hirofumi , Watanabe Toshiaki , Itoh Shigeru
Published: July 2009

We have investigated on underwater explosive forming and explosive welding. Until now, many experiments and numerical simulation have investigated. As our new target, study on a deformation of pipe made of metal material by underwater shock loading has been done. This phenomenon is often occurred. For example, metal pipe forming by underwater shock wave. This method is a forming method that pipe make forms to desired shape. An metal pipe set inside the metal die and the underwater shock wave is generated by explosive from one side the pipe. The underwater shock wave is propagated to another side and the pip is expanded to outer side. Finally, the metal pipe becomes the shape along the metal die. We are researching these mechanisms. This method can be applied to various metal pipe forming. It is necessary to investigate the behavior of the underwater shockwave that through the inside pipe.
Interaction Integrals for Fracture Analysis of Functionally Graded Piezoelectric Materials
Authors: Rao B. N.
Published: July 2009

This paper presents domain form of interaction integrals based on three independent formulations for computation of stress intensity factors and electric displacement intensity factor for cracks in functionally graded piezoelectric materials. Conservation integrals of J–type are derived based on the governing equations for piezoelectric media and the crack tip asymptotic fields of homogeneous piezoelectric medium as auxiliary fields. Each of the formulation differs in the way auxiliary fields are imposed in the evaluation of interaction integral and each of them results in a consistent form of interaction integral in the sense that extra terms naturally appears in their derivation to compensate for the difference in the chosen crack tip asymptotic fields of homogeneous and functionally graded piezoelectric medium. The additional terms play an important role of ensuring domain independence of the presented interaction integrals. Comparison of numerically evaluated intensity factors through the three consistent formulations with those obtained using displacement extrapolation method is presented by means of an example.
Modeling of the Large Deformation and Rupture of a Metallic Plate Subjected to Explosive Loading
Authors: Daudonnet Benjamin , Mercier Fre´de´ric , Woznica Krzysztof
Published: July 2009

Thin walled metal pressure vessels or pipes commonly used in industry can burst under certain circumstances: as a result, the pressure envelope may undergo large deformations, which may eventually lead to a rupture. The response of these vessels to static and quasi-static loads is relatively well-understood but their response to highly dynamic pressure loading conditions is not. This paper describes a numerical study of the response of circular metal plates to the dynamic loads produced by hydrogen-oxygen explosions. In this study, a range of dynamic responses and rupture criteria models are considered and compared with the results of experiments. The ability of MSC MARC software to model the rupture phase and, in some cases, the post-rupture phase (i.e., fragment production) is also discussed.
Optimizing the Strength of a Condenser Tube
Authors: Huang Michael
Published: July 2009

Extruded multi-port aluminum tubes are widely used in current condenser applications. The cross-section of the tube has multiple rectangular ports (openings) that allow refrigerant to flow through. Since the tube is working with pressurized refrigerant, the burst pressure becomes an important specification of the tube. The objective of this study is to seek the optimized cross-section configuration for a given maximum burst capability. The first part of this study utilizes a linear elastic 2-D model which shows that octagonal shaped ports perform the best up to the yield point. The second part of the study utilizes a Finite Element Method (FEM) model with more detailed dimensions and material nonlinear elastic/plastic properties. A case study shows that an octagon-port tube could outperform the commonly used rectangular-port tube in burst resistance by 27 percent.
Bending Fatigue of Pipe and Piping Components Fabricated From High Density Polyethylene Materials
Authors: Adams Timothy M. , Scavuzzo Rudolph J. , Hall Siegrid , Munson Douglas , Andrasik Jeffrey W. , Findlan Shane
Published: July 2009

Degradation of service water systems is a major issue facing nuclear power plant owners, and many plants will require repair or replacement of existing carbon steel piping components. High Density Polyethylene pipe has been used in non-safety service water systems for over nine years and found to perform well, but it is not currently permitted in the ASME Section III Boiler and Pressure Vessel Code, Division 1 for use in nuclear safety-related systems. To assist in the implementation of High Density Polyethylene pipe in the ASME Boiler and Pressure Vessel Code, Section III, Division 1 for Safety Class 3 applications, EPRI initiated a testing program that includes tensile and fatigue testing of HDPE piping and components and the development of slow crack growth data. Straight cantilever bending fatigue tests on PE 4710 pipe with a minimum cell classification of 445474C were conducted. The tests were designed to comply with the requirements for fatigue testing given in Appendix II of the ASME Boiler and Pressure Vessel Code, Section III, Division 1. They were also designed to achieve failure at the fusion butt welds near the cantilever support. S-N curves developed from both sets of data were found to fit well to power formulas of the type S = C/Nb required by mandatory Appendix II. The tests were conducted at various temperatures from 50° F to 160° F and in addition the effects of cyclic rate and aging were evaluated. Based on the straight pipe tests, stress intensification factors were calculated for 5-segment miter bends in both the in-plane and out-of-plane directions. The test elbows were fabricated from PE 4710 material with cell classification 445474C. Two sizes of 5-segment miter bends were tested, 4” and 12” diameter. The fatigue testing results showed one of the unique characteristics of High Density Polyethylene pipe: a significant decrease in material stiffness from the first few test cycles to a lower value that remains almost constant until failure. Thus, S-N curves and SIFs were determined twice: first based on the initial cycle results and again at the midlife of the fatigue tests. This paper provides a description and overview of the test program, testing methods and materials tested. In addition, an overview and summary of the test program results are provided.
Status of French Fatigue Analysis Procedure
Authors: Faidy Claude
Published: July 2009

During the past 15 years many works has been done on stainless steel fatigue curves: • in many cases over 105 cycles the RCC-M mean curve has been found un-conservative, in a similar situation than ASME Section III curve [12]; • the fatigue data other 106 cycles can now be done under strain control in a reliable way (improvements in fatigue test machine); • a large test program has been done in Japan and partially in USA; • a limited program has been done in France. This paper presents a new proposal for fatigue stainless steel mean curve in air (the existing ASME curve C seems to cover environmental effect on real structures) and a comparison with the NRC Regulatory Guide 1.207 [14] proposal for new curves. In order to transfer these mean curve data to structures, different complementary tests have been developed, some under air conditions, some under environmental effects. The paper ends with proposed code improvements in fatigue analysis rules in the RCC-M French Code.
Nonlinear Plastic Modeling of Materials Based on the Generalized Strain Rate Tensor
Authors: Ghavam Kamyar , Naghdabadi Reza
Published: July 2009

In this paper, a method for modeling of elastic-plastic hardening materials under large deformations is proposed. In this model the generalized strain rate tensor is used. Such a tensor is obtained on the basis of the method which was introduced by the authors. Based on the generalized strain rate tensor, a flow rule, a Prager-type kinematic hardening equation and a kinematic decomposition is proposed and the governing equations for such materials are obtained. As an application, the governing equations for the simple shear problem are solved and some results are compared with those in the literature.
Structural Self-Diagnosis for Damage in Carbon-Fiber Reinforced Composites
Authors: Ngabonziza Yves , Ergun Hale , Kuznetsova Regina , Li Jackie , Liaw Benjamin , Delale Feridun
Published: July 2009

Composite structural self-diagnostic (CSSD) technology has been tested to detect the mechanical damages in carbon-fiber reinforced polymer-matrix composites. In order to characterize the self-sensing technique for damage detection, discrete electrodes were mounted on Double-Cantilever-Beam (DCB). Results on mechanical properties with corresponding electrical resistance changes of the CFRC specimens are presented in this paper. The lay-up configuration of the composite specimens is [06/Teflon/06]T. In addition, acoustic emission was also used to corroborate the CSSD results.
Structural Damage Detection Based on Natural Frequency Vector
Authors: Yang Zhichun , Wang Le
Published: July 2009

Based on the new conception of natural frequency vector (NFV) and natural frequency vector assurance criterion (NFVAC), a new damage detection method using the natural frequencies as damage character is described in detail. For a specific structure, a series of small damage states can be simulated and the NFVs of these damaged structures can be calculated and used to build the damage feature database of the structure. Then, the values of natural frequency vector assurance criterion (NFVAC) which are calculated between the damage states in the damage feature database and the actual structure are used as damage index. An 8-story shear frame model is adopted as an example to show the feasibility and validity of the proposed method. Both numerical simulations and model experiments for damage detection are performed, the results demonstrate that using NFVAC, the damage location can be identified correctly and the damage extents can be estimated as well.
Feedback Control of Biomolecular Systems Formed From Droplet-Interface Bilayers
Authors: Sarles Stephen A. , Leo Donald J.
Published: July 2009

Applying feedback control strategies to biological materials establishes a new paradigm for creating controlled biomolecular systems. Specifically, current tracking and feedback voltage amplification are demonstrated separately on bilayer lipid membranes (BLMs) formed via the droplet-interface bilayer (DIB) method. Ion channel induced degradation of the bilayer is studied in order to provide a convenient method for causing changes to the bilayer which can be monitored using proportional-integral (PI) feedback voltage control. Alpha-hemolysin (αHL) from Staphylococcus aureus was shown to cause large scale reductions (+90%) to the resistance of the lipid bilayers formed at the interface of connected water droplets within 90 minutes of bilayer formation. Feedback integral current control was demonstrated on pure 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) DIBs not containing αHL and provided accurate current tracking of a 100pA desired current signal driven at a rate of 10mHz and less. Voltage amplification monitoring was achieved on DPhPC DIBs containing αHL, providing a way to detect decreasing resistance and capacitance of the bilayer and nonlinear current-voltage relationship.
Fiber Optic Strain Sensor Vibration Separation for Detection of Seeded Faults in Rotorcraft Transmissions
Authors: Coker Joseph D. , Pines Darryll J. , Samuel Paul D. , Kiddy Jason
Published: July 2009

This paper presents a refined methodology for performing helicopter transmission anomaly detection through the use of vibration separation techniques applied to the output of a fiber optic sensor array. Fiber Bragg grating (FBG) sensors—distributed about the exterior of a planetary gearbox annulus—record the local strain response of the annulus surface due to tooth-mesh interactions. These strain profiles are collected for a number of loading conditions both with and without seeded faults. The profiles are separated and synchronously averaged to illustrate the effect of damage to planetary gears on local strain variation. Results of experiments conducted on the University of Maryland Transmission Test Rig (UMTTR) are included. Additional processing and comparison to traditional vibration-based diagnostic methods indicate the potential for increased sensitivity to damage of such a system and the feasibility of fiber optic strain sensors for in situ health and usage monitoring.
Damage Monitoring in Woven Composites Using Fiber-Bragg Grating Sensors on Multiple Time Scales
Authors: Propst Adam , Parker Adam , Capps Zachary , Peters Kara , Zikry Mohammed A.
Published: July 2009

Low-velocity impact events occurring over the span of a few milliseconds cause changes in composite structures through relaxation and delamination propagation which manifest themselves over the span of several seconds. Changes in embedded fiber Bragg grating sensor response allow the damage in the composite structure to be measured in lieu of simply analyzing the impact event itself. By observing the damage progression and subsequent failure of the sample, the sensor signal response can thus be used to predict the lifetime of the structure. In this paper, we expand previous sensor interrogation and damage identification methodologies by using scanning instrumentation capable of operating over multiple time scales. 2D woven composite specimens are subjected to multiple low velocity impacts while the fiber Bragg grating (FBG) sensor response is monitored in time scales of one millisecond to tens of seconds. A high frequency scanning spectrometer is used to determine the peak Bragg wavelength while scanning the FBG sensor at approximately 1 kHz during and immediately after the impact. Also, a high fidelity slow-scan laser source measures the quasi-static sensor response several seconds to minutes following the impact events. Features of the two measurement sets are used to identify the structural integrity of the laminate specimen after each impact event.
Robust Control of Magnetostrictive Actuators With Uncertain System
Authors: Ekanayake Dinesh B. , Iyer Ram V.
Published: July 2009

In this paper, the problem of designing a state feedback controller over a wide frequency range (0 – 1kHz) for a magnetostrictive actuator connected to a mechanical system is discussed. Our model for the magnetostrictive actuator includes hysteresis, classical and excess eddy current losses. The hysteresis nonlinearity is modeled using a classical Preisach operator, and it is assumed that the density function is approximately known. The feedback controller achieves uniform ultimate boundedness — a property weaker than global asymptotic stability when the trajectory to be tracked is zero — in the presence of exogenous disturbances and uncertainty in the model. The main objective of the paper is to demonstrate that knowledge of the induced emf can be used to eliminate the need for hysteresis compensation in the control scheme. The novelty of this work is that we utilize the induced emf in the actuator coil as an observed variable, and also demonstrate how this quantity can be measured in real-time. Most controllers use inverse compensators to cancel out actuator hysteresis nonlinearity. We show that we can achieve uniform ultimate bounded control without an explicit inverse computation (using least squares minimization or otherwise).
Multi-Pulse Orbits With a Melnikov Method and Chaotic Dynamics in Motion of Composite Laminated Rectangular Thin Plate
Authors: Yao Ming-Hui , Zhang Wei , Guo Xiang-Ying , Cao Dong-Xing
Published: July 2009

This paper presents an analysis on the nonlinear dynamics and multi-pulse chaotic motions of a simply-supported symmetric cross-ply composite laminated rectangular thin plate with the parametric and forcing excitations. Firstly, based on the Reddy’s three-order shear deformation plate theory and the model of the von Karman type geometric nonlinearity, the nonlinear governing partial differential equations of motion for the composite laminated rectangular thin plate are derived by using the Hamilton’s principle. Then, using the second-order Galerkin discretization approach, the partial differential governing equations of motion are transformed to nonlinear ordinary differential equations. The case of the primary parametric resonance and 1:1 internal resonance is considered. Four-dimensional averaged equation is obtained by using the method of multiple scales. From the averaged equation obtained here, the theory of normal form is used to give the explicit expressions of normal form. Based on normal form, the extended Melnikov method is utilized to analyze the global bifurcations and multi-pulse chaotic dynamics of the composite laminated rectangular thin plate. The results obtained above illustrate the existence of the chaos for the Smale horseshoe sense in a parametrical and forcing excited composite laminated thin plate. The chaotic motions of the composite laminated rectangular thin plate are also found by using numerical simulation. The results of numerical simulation also indicate that there exist different shapes of the multi-pulse chaotic motions for the composite laminated rectangular thin plate.
Design of Mesostructured Materials Under Uncertainty
Authors: Patel Jiten , Choi Seung-Kyum
Published: July 2009

Uncertainties in material properties, geometry, manufacturing processes, and operational environments are clearly critical at all scales (nano-, micro-, meso-, and macro-scale). Specifically, reliabilty analysis in mesostructured materials can be driven by these uncertainties. The concept of mesostructured materials is motivated by the desire to put material only where it is needed for a specific application. This research develops a reliability-based synthesis method to design mesostructures under uncertainty, which have superior structural compliant performance per weight than parts with bulk material or foams. The efficiency of the proposed framework is achieved with the combination of topology optimization and stochastic approximation which utilizes stochastic local regression and Latin Hypercube Sampling. The effectiveness of the proposed framework was demonstrated using a ground structure topology optimization approach.
Optimal Control of a Nonlinear Magnetic Bearing System Using the Trigonometric Collocation Method
Authors: Nataraj C. , Marx Steven
Published: July 2009

Magnetic bearings are non-contacting, with the rotor being suspended between electromagnets, and therefore they can eliminate the need for lube oil and reduce machinery wear. The magnetic bearing is naturally unstable, and very nonlinear. This paper proposes a method designed to suppress the motion of a nonlinear magnetic bearing system rotor due to base excitation. The method combines PD feedback with feedforward optimal control, where a measured base motion is used to select a control signal designed to suppress the rotor response. The signal is generated from a combination of subharmonic frequencies and optimized coefficients stored in a lookup table. The trigonometric collocation method (TCM) is used to generate solutions for the four degree-of-freedom system made up of a shaft suspended at each end by a magnetic bearing. The TCM method uses a trigonometric series to simulate the multiharmonic behavior of each degree-of-freedom of strongly nonlinear systems. The method is easy to use and its advantage over numerical methods is that it demands less computation, particularly with higher numbers of degrees-of-freedom.
Drawing Insight From Nature: A Bat Wing for Morphing Aircraft
Authors: Manzo Justin E. , Leylek Emily A. , Garcia Ephrahim
Published: July 2009

Being the only flying mammal, bats have evolved unique flight devices affording them high maneuverability and efficiency despite their low flight speeds. By selecting bats of three different ecological niches — a highly efficient fishing bat, a nimble insectivorous forager, and a large soaring bat of the ‘flying fox’ family — passive wing shapes can be demonstrated as capable of attaining very different aerodynamic performance characteristics. The aerodynamics of man-made equivalents to these wing shapes, using thin airfoils rather than skeleton and membrane construction, are studied both computationally through a lifting-line approach and experimentally with quasistatic wind tunnel data of ‘morphed’ and ‘unmorphed’ wing shapes. Results confirm that shape inspired by the larger soaring bat has higher lift-to-drag ratios, while that of the foraging bat maintains lift at higher angles of attack than the other wings. The advantages are more pronounced by morphing, increasing both lift coefficient and lift-to-drag ratios by up to 50% for certain wings. This is validated both numerically and in the Cornell University 4′×4′ wind tunnel. Analysis of these shapes provides the first phase of wing design for use on a morphing aircraft vehicle. In order to take greater advantage of vehicle morphing, wing shapes with camber and twist distributions unique from those found in nature will evolve to suit a man-made structure. In this way, a wing shape intended for cruise may extend its practicality into highly maneuverable operations through the use of wing morphing. Starting from the bat planform shapes, a series of optimizations determines the best camber and twist distributions for effective morphing. Given a fixed degree of shape change at any point along an airfoil based on mechanism constraints, improved morphing performance can be found compared to initial assumptions of the natural shape change. Heuristic optimization employing simulated annealing determines the required morphing shapes for increased performance, broadening the abilities of each wing shape by increasing parameters such as lift, rolling moment, and endurance.
Ornithopter Trajectory Generation With Stabilization
Authors: Dietl John M. , Garcia Ephrahim
Published: July 2009

Ornithopter flight dynamics and a method for developing flight trajectories are described. These are used to study the unstable modes in hovering ornithopter flight. Stabilization is accomplished through three strategies: pitch-rate feedback control, linear quadratic regulator, and discrete-time periodic linear quadratic regulator. The discrete time controller is the only controller tested that was capable of stabilizing position of the vehicle in hover.
A Neural Network-Based Controller for a Piezoelectrically-Actuated Nano/Micromanipulator
Authors: Eslami Sohrab , Jalili Nader , Saeidpourazar Reza
Published: July 2009

Nowadays, nanorobots form the most important element of many precision manufacturing and industries such as medical instruments. Apparently, the most important property of these devices is their precision and durability. The more they have accuracy, the more delicate tasks may be performed. Hence, the design of an accurate model for achieving this objective is a challenging problem that has attracted the attention of many recent researchers in the nanotechnology field. In this paper, the kinematics and dynamics as well as development of appropriate controllers for a RRP (revolute-revolute-prismatic) nanomanipulator are presented. The specific task considered here for this manipulator is for the tip to track a predefined trajectory. For the real-time control implementation, a neural network (NN) is applied in order for the fast response of the system. A comparison between a standard PD controller and NN-based controller is presented through a numerical example.
Vibration Absorbers for Cyclic Rotating Flexible Structures: Linear and Nonlinear Tuning
Authors: Olson Brian J. , Shaw Steven W.
Published: July 2009

The nonlinear performance of centrifugally-driven, order-tuned absorbers is investigated for vibration reduction of a cyclic rotating flexible structure under traveling wave (TW) engine order excitation. A key finding from previous work by the authors using a linearized model is the existence of a no-resonance zone, that is, an entire range of absorber designs that avoid system resonance for any rotation speed. Linearization is generally valid for the rotating structure but absorber motions can become large for typical loading conditions. This work generalizes the linear results to account for large-amplitude, nonlinear absorber motions. Existence and stability of the steady-state TW response to TW excitation are investigated in terms of the absorber path design, which fixes its linear and nonlinear tuning characteristics. A TW response is unique for the linearized system and is shown to exist for the weakly nonlinear model. The nonlinear model exhibits the usual characteristics of a weakly nonlinear system, including bistability and the attendant hysteresis near resonance. More significantly, no additional instabilities associated with the symmetry could be identified. Hence the desired TW response is robust to nonlinear absorber effects and can be described by an equivalent model, which is obtained by reduction using the symmetry. It is shown that good performance can be obtained by linear absorber tuning in the no-resonance zone and the absorber paths should have a slightly softening nonlinear characteristic.
Experimental Study of the Mechanics of Motion of Flapping Insect Flight Under Weight Loading
Authors: Reissman Timothy , MacCurdy Robert B. , Garcia Ephrahim
Published: July 2009

The results of this study are an evaluation of the mechanics of motion of a weight loaded Manduca sexta Hawkmoth during flight using accelerations recorded with an onboard sensory system. Findings indicate that these ‘normal’ flapping insects maintain relatively fixed body frequencies in both free and weight loaded flight, which correspond with the driving frequency, or wing beat frequency. Within the analysis, a presence of a harmonic body frequency at twice the wing beat frequency was also discovered. The conclusions from this study indicate an average excess muscle power of over 40mW available in free, unloaded flight. Stability robustness of these flapping insects in flight using the results of a large payload disturbance, 856mg or nearly half to one-third the mass of insect, is demonstrated, and their usefulness as platform for cyborg MAV (CMAV) development is presented.
Accumulated sidewall damage in dry etched photonic crystals
Authors: Berrier A. , Shi Y. , Siegert J. , Marcinkevicius S. , He S. , Anand S.
Published: July 2009

Evidence for accumulated damage is provided by investigating the effect of etch duration on the carrier lifetime of an InGaAsP quantum well (QW) inside the InP-based photonic crystal (PhC) structures. It is found that once the quantum well is etched through, additional etching reduces the carrier lifetimes from 800to70ps. The surface recombination velocity (SRV) at the exposed hole sidewalls is determined from the measured carrier lifetimes of the PhC fields with different lattice parameters. The observed variation in the SRV with etch duration also confirms the presence of accumulated sidewall damage. It increases from 6×103to1.2×105cms−1 as the etching time increases from 3to50min. A geometric model based on sputtering theory and on the evolution of the hole shape is developed to explain the accumulation of sidewall damage. The model is used to estimate the number of impact events from sputtered species reaching the QW sidewalls, and the variation in the accumulated impact events with etch duration is shown to be qualitatively consistent with the experimental observations. Finally, the results suggest a new method for tailoring the carrier lifetimes in PhC membrane structures.
Bcl6 Mediates the Development of T Follicular Helper Cells
Authors: Nurieva Roza I. , Chung Yeonseok , Martinez Gustavo J. , Yang Xuexian O. , Tanaka Shinya , Matskevitch Tatyana D. , Wang Yi-Hong , Dong Chen
Published: July 2009

T Follicular Helper Cell Differentiation

When B cells respond to an infection, they often require help from CD4
+
T cells to mount a proper response. It is thought that a subset of CD4
+
effector T cells, called T follicular helper cells (T
FH
), performs this function. Several subsets of effector CD4
+
T cells arise, depending on the type of infection, which have distinct transcriptional programs driving their differentiation. Whether this is also the case for T
FH
cells has not been clear (see the Perspective by

Awasthi and Kuchroo

).

Nurieva
et al.

(p.
1001
, published online 23 July) and

Johnston
et al.

(p.
1006
; published online 16 July) now demonstrate that the transcription factor Bcl6 is both necessary and sufficient for T
FH
differentiation and subsequent B cell–mediated immunity, suggesting that it is a master regulator of this lineage. Johnston
et al.
also show that expression of Bcl6 and the transcription factor, Blimp-1, are reciprocally regulated in T
FH
cells and that, when ectopically expressed, Blimp-1 inhibits T
FH
development.