bluuebunny/crossref_metadata_2025 huggingface dataset:
Model-Based Estimation of Turbocharger Requirements for Boosting an HCCI Engine
Authors: Mamalis Sotirios , Babajimopoulos Aristotelis
Published: January 2011

Turbocharged Homogeneous Charge Compression Ignition (HCCI) has been modeled and has demonstrated the potential to extend the engine’s upper load limit. A commercially available engine simulation software (GT-Power®) coupled to the University of Michigan HCCI combustion and heat transfer correlations was used to model a single cylinder boosted HCCI engine including a phenomenological turbocharger model. The scope of this study is to explore the upper load limits of boosted HCCI operation and to identify turbocharger requirements for boosting the HCCI. The results of this study are consistent with the literature: Boosting helps increase the HCCI upper load limit, but matching of turbochargers is a problem. In addition, the low exhaust gas enthalpy resulting from HCCI combustion leads to high pressures in the exhaust manifold and increased pumping work. It is shown that loads as high as 17 bar NMEP can be reached at low engine speeds, when the intake pressure is 3 bar.
Closed-Loop Control Framework for Fuel-Flexible Combustion of Biodiesel Blends
Authors: Snyder David B. , Adi Gayatri H. , Hall Carrie M. , Bunce Michael P. , Shaver Gregory M.
Published: January 2011

This paper presents a closed-loop control framework for fuel-flexible combustion control of biodiesel blends. This framework consists of two parts: blend detection and blend accommodation. Blend detection can be accomplished by an experimentally-validated dynamic estimator using exhaust oxygen and air-fuel ratio information. Blend accommodation can be accomplished by changing the control variables that the engine control module uses, namely, replacing exhaust gas recirculation fraction with combustible oxygen mass fraction, replacing total injected fuel mass with total injected fuel energy, and replacing start of main injection timing with end of main injection timing. With the conventional control structure it is experimentally shown that pure biodiesel (B100) produced 38% more brake specific nitrogen oxides (BSNOx) than pure conventional diesel (B0). With the new proposed structure, B100 produced not only lower BSNOx than B0, but also higher torque, higher brake thermal efficiency, lower particulate matter, and lower combustion noise than B0. Comparable experimental results are also presented for B5 and B20 blends.
An Optical Study of Spark Ignition and Flame Kernel Development Near the Lean Limit at Elevated Pressure
Authors: Nesbitt Jaclyn E. , Lee Seong-Young , Naber Jeffrey D. , Arora Rajat
Published: January 2011

Spark ignition of lean and dilute fuel-air mixtures provides emission reductions of NOx. Furthermore, operation at the lean-dilute limit increases engine efficiency through reduced pumping loses and reduced heat transfer. However, ignition near the lean flammability limit becomes more stochastic and exhibits substantially decreased flame propagation rates. In this work, spark ignition and the subsequent flame kernel development and propagation are studied in a constant volume optical combustion vessel. The vessel provides full field orthogonal and line-of-site optical access via sapphire windows. Additionally, an automated process controller with a versatile gas system enables the creation of a wide range of fuel-air mixtures, including lean and dilute mixtures of hydrocarbons, oxygen, nitrogen, carbon dioxide, and other gases. Ambient conditions including in-chamber temperature and pressure levels, along with dilution conditions, can be set independently. Ignition is provided by an automotive spark plug in the chamber. Optical diagnostics including simultaneous CH* chemiluminescence and shadowgraph imaging are utilized to characterize initial kernel growth and flame development under elevated pressure conditions, from atmospheric to 17.3 bar. Chemiluminescence images are quantified to determine flame intensity and kernel radius to understand the success of initial flame kernel development and propagation. Increasing the pressure yields a slower rate of flame kernel development and propagation, with a thickening flame front, which in turn increases the effects of buoyancy and heat loss. Leaning the mixture can yield unsuccessful kernel development due to heat loss to the large electrode which may cause a failed sustaining of combustion. This knowledge on kernel development near the lean limit benefits the engine community by characterizing the importance of ambient conditions including pressure and mixture properties in sustaining flame growth and propagation.
Development of a Spark Discharge PM Sensor for Measurement of Engine-Out Soot Emissions
Authors: Gardiner David P. , Pucher Greg R. , Allan William D. , LaViolette Marc
Published: January 2011

Filter paper methods are well recognized as an effective means of measuring soot emissions from diesel engines. However, these methods provide an average soot value over a relatively long time period, rather than a real-time signal. Real-time measurements of engine-out soot emissions that could track changes in soot levels during transient operating conditions would be useful for the optimization of engine control strategies such as exhaust gas recirculation. This paper presents experimental results obtained using a real-time PM sensor based upon a spark discharge measuring principle. Like traditional filter paper devices, it is sensitive to the carbon or soot component of the particulate matter emitted by diesel engines. The sensor was tested on a turbocharged diesel engine, and compared with reference measurements of Filter Smoke Number (FSN) from an AVL 415s smokemeter. Improvements to the sensor made it possible to measure soot levels at FSN values over 3.5, while retaining good sensitivity below FSN values of 0.1. The sensor signal showed a high correlation with the reference FSN measurements. This correlation was used to develop a signal processing technique so the sensor provided a real-time signal for predicted FSN. Conversion of the FSN values to mass concentration values (using published techniques for the reference instrument) indicated that the output of the spark discharge soot sensor was nearly linear with mass concentration over a substantial portion of the measuring range. The sensor showed a response time of under 2 seconds to step changes in FSN levels.
A General Rezoning Technique for KIVA3V Internal Combustion Engines CFD Simulations
Authors: Hessel Randy P. , Musu Ettore , Aceves Salvador M. , Flowers Daniel L.
Published: January 2011

A computational mesh is required when performing CFD-combustion modeling of internal combustion engines. For combustion chambers with moving pistons and valves, like those in typical cars and trucks, the combustion chamber shape changes continually in response to piston and valve motion. The combustion chamber mesh must then also change at each time step to reflect that change in geometry. The method of changing the mesh from one computational time step to the next is called rezoning. This paper introduces a new method of mesh rezoning for the KIVA3V CFD-combustion program. The standard KIVA3V code from Los Alamos National Laboratory comes with standard rezoners that very nicely handle mesh motion for combustion chambers whose mesh does not include valves and for those with flat heads employing vertical valves. For pent-roof and wedge-roof designs KIVA3V offers three rezoners to choose from, the choice depending on how similar a combustion chamber is to the sample combustion chambers that come with KIVA3V. Often, the rezoners must be modified for meshes of new combustion chamber geometries to allow the mesh to successfully capture change in geometry during the full engine cycle without errors. There is no formal way to approach these modifications; typically this requires a long trial and error process to get a mesh to work for a full engine cycle. The benefit of the new rezoner is that it replaces the three existing rezoners for canted valve configurations with a single rezoner and has much greater stability, so the need for ad hoc modifications of the rezoner is greatly reduced. This paper explains how the new rezoner works and gives examples of its use.
In-Cylinder Velocity Measurements and Analysis in a Briggs and Stratton Engine
Authors: O¨lc¸men Semih , Ashford Marcus
Published: January 2011

Unsteady velocity measurements made near the spark-plug location of an IC engine using a single-component fiber-optic LDV probe are reported. Measurements were made within a motored Briggs and Stratton single-cylinder air-cooled engine at ∼780 RPM. Data obtained was analyzed using Ensemble averaging, High-pass filtering, Wavelet Decomposition (WD), Proper-Orthogonal Decomposition (POD), and Wavelet-decomposition together with Principal Component Analysis (WD/PCA) techniques to determine the unsteady mean velocity and unsteady turbulence variations in such an engine. The results of the analysis are compared to each other. WD/PCA technique recommended for future engine unsteady flow studies was used to determine the cycle-to-cycle variations. Results indicate to large cycle-to-cycle variations in such an engine.
Flame Propagation in Natural Gas Fueled Direct Injection Engines
Authors: Fabbroni Mark , Wallace James S.
Published: January 2011

Injected natural gas requires some form of ignition assist in order to ignite in the time available in a diesel engine combustion chamber. A glow plug — a heated surface — is one form of ignition assist. Ignition by glow plug results in a single site of ignition from which the flame must propagate to other jets in the injection pattern. The goal of this work was to determine what factors affect how the flame propagates from this initial ignition site to the remaining unburned mixture site. The combustion of natural gas jets under diesel engine conditions was studied over a range to temperatures, pressures with and without a glow plug shield using a CFR engine as a rapid compression device. The results showed that of all the factors considered it is the geometry of the injection pattern, combustion chamber and glow plug shield that are most dominant in controlling combustion rates and fuel utilization.
Review of Proposed Methodology for Risk-Informed Relaxation to ASME Section XI: Appendix G
Authors: Dickson Terry , Focht Eric , Kirk Mark
Published: January 2011

The current regulations, as set forth by the United States Nuclear Regulatory Commission (NRC), to insure that light-water nuclear reactor pressure vessels (RPVs) maintain their structural integrity when subjected to planned normal reactor startup (heat-up) and shut-down (cool-down) transients are specified in Appendix G to 10 CFR Part 50, which incorporates by reference Appendix G to Section XI of the American Society of Mechanical Engineers (ASME) Code. The technical basis for these regulations are now recognized by the technical community as being conservative and some plants are finding it increasingly difficult to comply with the current regulations. Consequently, the nuclear industry has developed, and submitted to the ASME Code for approval, an alternative risk-informed methodology that reduces the conservatism and is consistent with the methods previously used to develop a risk-informed revision to the regulations for accidental transients such as pressurized thermal shock (PTS). The objective of the alternative methodology is to provide a relaxation to the current regulations which will provide more operational flexibility, particularly for reactor pressure vessels with relatively high irradiation levels and radiation sensitive materials, while continuing to provide reasonable assurance of adequate protection to public health and safety. The NRC and its contractor at Oak Ridge National Laboratory (ORNL) have recently performed an independent review of the industry proposed methodology. The NRC / ORNL review consisted of performing probabilistic fracture mechanics (PFM) analyses for a matrix of cool-down and heat-up rates, permutated over various reactor geometries and characteristics, each at multiple levels of embrittlement, including 60 effective full power years (EFPY) and beyond, for various postulated flaw characterizations. The objective of this review is to quantify the risk of a reactor vessel experiencing non-ductile fracture, and possible subsequent failure, over a wide range of normal transient conditions, when the maximum allowable thermal-hydraulic boundary conditions, derived from both the current ASME code and the industry proposed methodology, are imposed on the inner surface of the reactor vessel. This paper discusses the results of the NRC/ORNL review of the industry proposal including the matrices of PFM analyses, results, insights, and conclusions derived from these analyses.
Thermal Performance of Radioactive Material (RAM) Packages in Transport Configuration
Authors: Gupta Narendra K.
Published: January 2011

Drum type packages are routinely used to transport radioactive material (RAM) in the U.S. Department of Energy (DOE) complex. These packages are designed to meet the federal regulations described in 10 CFR Part 71. The packages are transported in specially designed vehicles for safety and security. In the transport vehicles, the packages are placed close to each other to maximize the number of units in the vehicle. Since the RAM contents in the packagings produce decay heat, it is important that they are spaced sufficiently apart to prevent overheating of the containment vessel (CV) seals and the impact limiter to ensure the structural integrity of the package. This paper presents a simple methodology to assess thermal performance of a typical 9975 packaging in a transport configuration.
Impact of Intensity of Residual Stress Field Upon Re-Yielding and Re-Autofrettage of an Autofrettaged Thick Cylinder
Authors: Parker Anthony P. , Underwood John H. , Troiano Edward
Published: January 2011

Re-autofrettage has been identified as a significant, cost-effective method to achieve higher re-yield pressure (RYP) and/or weight reduction in large caliber gun tubes. For a given overstrain, residual stress profiles for hydraulic and for swage autofrettage may differ significantly in their intensity. The simplest representation of this ‘intensity’ effect is the magnitude of the bending moment ‘locked in’ via the residual hoop stress. Hill’s analytical, plane strain, Von Mises, analysis predicts a larger ‘locked-in’ moment than does the equivalent open-end condition. By assuming a range of stress-field intensities (f) scaleing from 1.0 to 1.4 times that produced by open-end hydraulic autofrettage, it was possible to assess re-yield behavior following initial autofrettage via a generic numerical study. In cases where Bauschinger effect is absent, re-yield initiates at the original elastic plastic interface. This includes the ideal Hill distribution. When Bauschinger effect is present, re-yield for f ≤ 1.1 initiates at the bore and after further pressurization at the original elastic plastic interface within two zones. For f ≥ 1.2 the reverse is the case, with initial yield at the original elastic plastic interface and subsequently at the bore. RYP increases with increasing f up to f = 1.175 and then decreases significantly. This loss of RYP may be mitigated by hydraulic re-autofrettage. At f = 1.0 re-autofrettage increases RYP by 4%. At f = 1.4 RYP is increased by 19%. There are modest increases in safe maximum pressure as a result of re-autofrettage. RYP closely approaching re-autofrettage pressure is achievable for f ≥ 1.3. Within this range, re-autofrettage offers a significant benefit. Re-autofrettage also produces beneficial effects via increased bore hoop compressive stress, this increase varying from 20% for f = 1 to zero for f = 1.4. Such increased compression will benefit fatigue lifetime for fatigue cracks initiating at the bore. Conversely, tensile OD hoop stress increases, with increasing f, by a maximum of 6%.
New Design Basis for the Design of High Pressure Polyethylene Reactor Bay Using an Explosion Risk Analysis and Non Linear Finite Analysis
Authors: Catala Christophe , Allemand Cedric , Moine Michel , Paris Laurent , Salau¨n Nicolas , Iddir Olivier
Published: January 2011

High pressure technology used for the production of Low Density Polyethylene (LDPE) requires a particularly high degree of safety to protect both reactor and surroundings from an accidental event. For this reason, historically, such tubular reactors have been enclosed in roofless bunkers designed on empirical data. Recent improvement in production capacities, scientific knowledge and calculation tools now allows historic designs of these concrete structures to be challenged. The study we have conducted has offered a better understanding of the mechanisms involved in case of an accidental release of ethylene (ventilation and atmospheric dispersion conditions, gas detection efficiency) and subsequent explosion inside the reactor bay (maximum overpressure, impulsion duration, etc…). The methodology, using a combination of an explosion risk analysis (with help of 3D CFD tool) and a non linear finite element analysis (NLFEA) calculation tool has made it possible to define a clear and new basis of design for the enclosure walls to explosion overpressure loads. This in turn also offers new possibilities for an optimisation of the concrete wall thickness and design.
Measurements of Residual Stresses in 316 Stainless Steel Weldments
Authors: Davies C. M. , Hughes D. , Wimpory R. C. , Dean David W. , Nikbin K. M.
Published: January 2011

Neutron diffraction measurements have been performed to quantify the residual stresses distributions in austenitic type 316 stainless steel Manual Metal Arc (MMA) weldment sections, which are similar to those used in creep crack growth testing. Measurements have been taken along the expected crack path in these samples to determine the influence of residual stresses on high temperature crack growth. The influence of EB welding extension pieces onto the weldments sections, in order to increase specimen size, and sample cutting for compact tension specimen manufacture are also examined. Similar stress distributions have been measured in nominally identical MMA weldments sections, where peak stresses of up to 120 MPa have been shown. The effects of the EB weld used to attach extension pieces to the weldments sections dominate over the MMA weldments residual stress distributions in these samples, and increases the peak stresses by up to a factor of three. Significant stress relaxation takes place during compact tension specimen manufacture, and in addition creep strain accumulation will further relax these residual stresses. Residual stress effects are therefore considered to only influence the creep crack initiation period in short-term creep crack growth tests. However, in long-term creep crack growth tests, the residual stresses may also influence subsequent creep crack growth behaviour.
Considerations on Design, Operation and Performance of Hypercompressors
Authors: Giacomelli Enzo , Shi Jun-Xia , Manfrone Fabio
Published: January 2011

The production of LDPE may require huge power, heavy-duty reciprocating compressors, provided with opposite cylinders and special frames to withstand the loads, deriving from the operating pressures. In many new projects larger capacities and higher performance requirements, renew the challenge of engineers to handle the mechanical, thermodynamic, chemical-physical, process and operational aspects. Safety, performance, operation and reliability are usual expectations needing a thorough evaluation of the service and the machine selection is based on positive results in similar applications. Valve, packing and cylinder performance is noticeably influenced by the design, operation and maintenance activities. The cylinders are compound pressure vessels, excluded by design codes, but their design and construction have to consider the extreme internal pressures and the nature of the process gas. The ability to withstand the high fatigue stresses and the need to avoid any leakage of gas around the compressor area implies solutions to minimize such occurrences including abnormal operations and emergencies. The design must foresee all possible failure modes of each component, to have safe and smooth operation. Innovative methods of simulation and modeling, like FEA, CFD, and others, are very important tools for the design of cylinder components. Valves are simulated by mathematical models optimizing performance and ensuring reliable operation, to reach a correct mechanical behavior with minimum energy consumption. The available technological improvements are taken as a base, resulting from the R&D of manufacturers and long experience of End Users. Also the pulsation and related vibration of the piping have to be investigated to keep the plant in operation without hazard. The operation is the stage where all the parameters have to be kept under control and incipient problems have to be identified to minimize shut down and arrange various maintenance works. Automation systems, together with new monitoring and diagnostic systems, allow very high safety levels, availability and optimized maintenance interventions.
Compressive Pre-Strain Effects on the Creep and Crack Growth Behaviour of 316H Stainless Steel
Authors: Davies C. M. , Dean David W. , Mehmanparast A. N. , Nikbin K. M.
Published: January 2011

The effects of compressive plastic pre-strain on the creep deformation and crack growth behaviour of Type 316H stainless steel have been examined. Creep crack growth (CCG) tests have been performed on compact tension specimens of material which had been uniformly pre-strained by 4% and 8% in compression at room temperature. The CCG behaviour of the pre-compressed material has been interpreted in terms of the creep fracture mechanics parameter C* and compared with that of a significant data set of as-received (un-compressed) specimens and with CCG models. All creep testing has been performed at a temperature of 550 °C. High CCG rates, for a given value of C* have been observed for the pre-compressed material, compared with those of as-received material and these data follow the same trends as the long-term CCG data for as-received material. These observations are explained in terms of specimen constraint effects and variations in creep ductility.
Dynamic Structural Analysis of the 9516 Transport Package
Authors: Han Zenghu , Shah Vikram N. , Abou-Hanna Jeries , Liu Yung Y.
Published: January 2011

This paper presents the structural dynamic analysis of the 9516 package subjected to two hypothetical accidents in sequence: (1) the 30-ft drop test and (2) the puncture test. The analysis is performed with the general-purpose finite element analysis computer code, ABAQUS, using explicit integration. The 9516 package consists of a containment vessel placed inside a cask mounted inside a steel cage, which acts as the impact limiter and the personnel shield. The cask has a bolted closure that provides the confinement to the containment vessel. The closure bolts initially were modeled with one-dimensional elastic connector elements bearing only the axial loads, which was adequate for the analysis of the drop test. However, the closure lid experienced significant bending during the puncture test, implying bending load acting on the closure bolts. Therefore, the closure bolts were modeled by using solid elements in a refined model so that the response to the bending load during the puncture test can be simulated. The results of the analysis showed that the closure bolts experience significant bending during the puncture test. For model validation, a comparison between the analysis results and the test results for rigid body accelerations of the package is presented. The results of the analysis based on the refined model show that the maximum stress intensities in the closure bolts, containment vessel, and cask are lower than the corresponding allowable stresses specified in the American Society of Mechanical Engineering Boiler and Pressure Vessel Code.
Safety Assessment of Reactor Pressure Vessel Integrity for Loss of Coolant Accident Conditions
Authors: Beukelmann D. , Guo W. , Holzer W. , Kauer R. , Mu¨nch W. , Reichel C. , Scho¨ner P.
Published: January 2011

One of the critical issues for Reactor Pressure Vessel (RPV) structural integrity is related to the Pressurized Thermal Shock (PTS) event. Therefore, within the framework of safety assessments special emphasis is given to the effect of PTS-loadings caused by the non-uniform azimuthal temperature distribution due to cold water plumes or stripes during emergency coolant injection. The paper describes the method used to predict the thermal mechanic boundary conditions (system pressure, wall temperature). Using a system code the pressure and global temperature distributions were calculated, systematically varying the leak size and the location of the coolant water injection. Local and temporal temperature distributions in the main circulation pipes and at the RPV wall were predicted by mixing analyses with a Computational Fluid Dynamics (CFD) code. The model used for these calculations was validated by post-test calculations of a UPTF (Upper Plenum Test Facility) experiment simulating cold leg injection during a small break Loss of Coolant Accident (LOCA). Comparison with measured temperatures showed that the modelling used is suitable to obtain bounding results. Fracture mechanics analyses were carried out for circumferential flaw sizes in the weld joint near the core region and between the RPV shell and the flange, as well as for axial flaws in the nozzle corner. Stress intensity factors KI were calculated numerically using the finite element program ANSYS and analytically on the basis of weight and polynomial influence functions using stresses obtained from elastic finite element analyses. Benchmark tests revealed good agreement between the results from numerical and analytical calculations. In order to determine the worst case loading conditions a wide spectrum of thermal-hydraulic transients was considered. Since the resulting load paths decrease with lower temperatures after a maximum, the warm prestress (WPS) effect was employed. The fracture toughness curve determined by deeply notched specimens with high constraint is not representative of the nozzle corner due to the considerable loss of constraint at LOCA conditions. Hence the influence of constraint on fracture toughness was accounted applying the constraint modified master curve concept and the relationship between the T-stress and the reference temperature T0. According to ASME Code Cases N-629 and N-631 the reference temperatures RTNDT and RTT0 can be used alternatively for the adjustment of the KIC-curve. Therefore both the RTNDT- and the RTT0-concept were considered. For all regions of the RPV investigated and the most severe transients it was demonstrated that a large safety margin against crack initiation exists and brittle fracture of the RPV can be excluded.
Probabilistic Fatigue Assessment of a Notched Detail Taking Into Account Mean Stress Effects
Authors: De Jesus Abi´lio M. P. , Ruiz Ripoll M. Luisa , Gonc¸alves Norberto J. , Pereira He´lder F. S. G.
Published: January 2011

Probabilistic fatigue models are required to account conveniently for the several sources of uncertainty arising in the prediction procedures, such as the scatter in material behavior. In this paper, a recently proposed stress-based probabilistic model is assessed using fatigue data available for the P355NL1 steel (a pressure vessel steel). The referred probabilistic model is a log-Gumbel regression model, able to predict the probabilistic Wo¨hler field (P-S-N field), taking into account the mean stress (or stress R-ratio) effects. The parameters of the probabilistic model are identified using stress-life data derived for the P355NL1 steel, from smooth specimens, for three distinct stress R-ratios, namely R = −1, R = −0.5 and R = 0. The model requires a minimum of two test series with distinct stress R-ratios. Since data from three test series is available, extrapolations are performed to test the adequacy of the model to make extrapolations for stress R-ratios other than those used in the model parameters assessment. Finally, the probabilistic model is used to model the fatigue behavior of a notched plate made of P355NL1 steel. In particular, the P-S-N field of the plate is modeled and compared with available experimental data. Cyclic elastoplastic analysis of the plate is performed since plasticity at the notch root is developed.
Seismic Response of Floating Roof Liquid Storage Tanks: Part II—Contact Pressure Approach
Authors: Kozak Alexander L. , Cacciatore Philip J. , Gustafsson L. Magnus
Published: January 2011

Seismic response of liquid storage tank floating roofs involve phenomena that require dynamic analysis of nonlinear geometric and material behavior as well as surface to surface contact. Good engineering practice requires a practical analytical approach that captures the essential ingredients of structural behavior under earthquake excitation by making reasonable, conservative, and manageable approximations to the actual conditions. This paper discusses an approach to approximating the stresses and deformations of a liquid storage tank floating roof under seismic loading. The method is validated by a fully coupled fluid-structure interaction (FSI) finite element analysis using actual earthquake ground accelerations. The method is supported by both the American Petroleum Institute (API) and the Petroleum Association of Japan (PAJ).
Machining of Aircraft Titanium With Abrasive-Waterjets for Fatigue Critical Applications
Authors: Liu H.-T. , Hovanski Y. , Dahl M. E.
Published: January 2011

Laboratory tests were conducted to determine the fatigue performance of AWJ-machined aircraft titanium. Dog-bone specimens machined with AWJs were prepared and tested with and without sanding and dry-grit blasting with Al2O3 as secondary processes. The secondary processes were applied to remove the visual appearance of AWJ-generated striations and to clean up the garnet embedment. The fatigue performance of AWJ-machined specimens was compared with baseline specimens machined with CNC milling. Fatigue test results of the titanium specimens not only confirmed our previous findings in aluminum dog-bone specimens but in comparison also further enhanced the fatigue performance of the titanium. In addition, titanium is known to be difficult to cut, particularly for thick parts, however AWJs cut the material 34% faster than stainless steel. AWJ cutting and dry-grit blasting are shown to be a preferred combination for processing aircraft titanium that is fatigue critical.
Leak Localization in Pipelines via Computational Pipeline Monitoring
Authors: Moustafa Kamal A. F. , Haik Yousef , Aldajah Saud , Omar Farag
Published: January 2011

Leaks in pipelines contribute to the environmental pollution, promote corrosion and equipment failures and produce instabilities in the pipeline operation and control. Leaks are inevitable as third party damage, equipment failures, and errors in pipeline design and operation do occur. Being able to accurately detect the location of leaks is imperative. One objective of this paper is to develop a mathematical model that accounts for the behavior of pressure and flow-rate profiles in leaky pipeline systems. Such a mathematical model is needed to better understand the dynamic behavior of the pipeline and its characteristics and for the detection the leak locations. The paper also involves computer simulation of pipeline conditions using the developed mathematical model and Kalman filtering technique. Leak localization is accomplished by a marching scheme that scans the pipeline from the inlet side to the outlet side to find the location at which the minimum residuals are obtained. Simulation results are reported to demonstrate the effectiveness of the proposed leak localization scheme.
Rational Design of Novel Materials From Polymer Microrheology
Authors: Teixeira Rodrigo E. , Graham Richard S.
Published: January 2011

The visco-elastic properties of entangled polymer liquids arise from molecular-scale topological interactions and stochastic fluctuations under flow. Here, the evolutions of individual entangled polymers were observed in rheologically relevant shear flow histories. We uncover a high degree of molecular individualism and broad conformational distributions resulting from incessant stretch-collapse cycles. The data and insights of the present study may lead to improved molecular-level models and constitutive equations. These tools, in turn, may enable the rational design of novel materials with properties tailored to accomplish specific tasks such as high-pressure vessels and piping with greater safety margins and cost-effectiveness.
The Effect of a Starter Notch on the Isothermal and Thermomechanical Fatigue Life of a Nickel-Based Superalloy
Authors: Hyde C. J. , Sun W. , Hyde T. H. , Becker A. A.
Published: January 2011

The effect that a starter notch has on the life of a Nickelbased superalloy which is used in the high temperature regions of aeroengines has been considered for this study under both isothermal fatigue (IF) and thermomechanical fatigue (TMF) conditions. The components made from this material in these regions are usually subjected to cyclic mechanical and thermal loading and hence it is necessary that this form of loading does not lead to cracking and hence crack growth leading to failure. It is therefore important to build up an understanding of the effect that these loading conditions have on the crack growth and therefore failure life of such materials. Such TMF conditions usually incorporate high temperatures which permit creep to play a significant role in the evolution of deformation and damage of the material with time. An experimental programme of TMF crack growth testing for a Nickel-based superalloy, has been carried out using an Instron TMF test machine with induction coil heating using uniaxial as well as initially corner notched (CN) specimens. A variation of conditions in terms of strain and temperature range(s) have been studied in order to build up life curves as a function of these conditions. TMF test results have also been compared to corresponding isothermal data, in order to investigate the effect that temperature cycling has on the material response. Details of the experimental set-up, as well as the experimental results are presented. Future application of the test data for component life prediction has been addressed.
On the Penetrator Nose Drag Measurements
Authors: Holland Joseph P. , Tanner Yesenia , Schinetsky Phillip A. , Olcmen Semih , Jones Stanley
Published: January 2011

In the current study, a rigid body penetrator nose shape that is optimized for minimum penetration drag [1] has been tested to determine the aerodynamic drag of such a penetrator in comparison to three additional nose shapes. Other nose shapes tested were an ogive cylinder, a 3/4 power series nose, and a standard cone. Fineness ratio for the studied nose geometries was chosen as l/d = 1 to maximize variation of the aerodynamic drag forces acting on the nose shapes. This paper discusses the measurements carried out in the University of Alabama’s 6″ × 6″ supersonic wind tunnel, using a 4 component force balance system. In separate experiments, drop tests were made in a viscous fluid to determine the skin-friction effects on these nose shapes. Supersonic wind-tunnel experiments were performed on each of the nose shapes at nine different Mach numbers ranging from 2 to 3.65. Results show that the nose shape optimized for penetration has the lowest drag coefficient of all the shapes at each Mach number within an uncertainty of 5.75%. In the viscous flow drop-test experiments, each nose shape was dropped from rest through water and then separately through viscous fluid (Nu-Calgon vacuum pump oil) under freefall conditions. Each drop was recorded via videotape, and the video was then analyzed to find the terminal velocity of each individual nose shape. Using classical dynamics equations, the weight, buoyant force, and experimentally determined terminal velocity are used to determine the drag force applied to each nose cone shape. Results indicate that while the optimal shape has a lesser drag coefficient than tangent ogive and the cone, the 3/4 power series shape is observed to have the least drag coefficient. In addition to the experiments performed, results on further investigation of the optimal nose shape for penetration are presented. The nose shape has been split into a series of line segments, and a program written has been utilized to search through numerical space for the combination of line segment slopes that produces the nose geometry with the lowest nose shape factor. The results of the numerical analysis in this study point to a different nose shape than the “optimal nose” shape tested in the current study.
Effects of Moisture in the 9975 Shipping Package Fiberboard Assembly
Authors: Daugherty W. L. , Dunn K. A. , Murphy J. L. , Hackney E. R.
Published: January 2011

The fiberboard assembly used in 9975 shipping packages as an impact-absorption and insulation component has the capacity to absorb moisture, with an accompanying change to its properties. While package fabrication requirements generally maintain the fiberboard moisture content within manufacturing range, there is the potential during use or storage for atypical handling or storage practices which result in the absorption of additional moisture. In addition to performing a transportation function, the 9975 shipping packages are used as a facility storage system for special nuclear materials at the Savannah River Site. A small number of packages after extended storage have been found to contain elevated moisture levels. Typically, this condition is accompanied by an axial compaction of the bottom fiberboard layers, and the growth of mold. In addition to potential atypical practices, fiberboard can exchange moisture with the surrounding air, depending on the ambient humidity. Laboratory data have been generated to correlate the equilibrium moisture content of cane fiberboard with the humidity of the surrounding air. These data are compared to measurements taken within shipping packages. With a reasonable measurement of the fiberboard moisture content, an estimate of the fiberboard properties can be made. Over time, elevated moisture levels will negatively impact performance properties, and promote fiberboard mold growth and resultant degradation.
Lower Bound Buckling Load of a Floating Roof Pontoon
Authors: Yoshida Shoichi
Published: January 2011

The 2003 Tokachi-Oki earthquake caused severe damage to oil storage tanks due to liquid sloshing. Seven single-deck floating roofs had experienced sinking failures in large diameter tanks at a refinery in Tomakomai, Japan. The pontoons of the floating roofs might be buckled due to bending load during the sloshing. The content in the tank was spilled on the floating roof from small failures which were caused in the welding joints of pontoon bottom plate by the buckling. Then the floating roof began to lose buoyancy and sank into the content slowly. The elastic buckling of the pontoon is important from the viewpoint of the single-deck floating roof sinking. The authors had reported the buckling strength of the pontoons subjected to bending and compressive loads in the published literatures. The axisymmetric shell finite element method for linear elastic bifurcation buckling was used in the analysis. The buckling characteristics of the pontoon both with and without ring stiffeners were investigated. The initial geometrical imperfection may diminish the buckling load. This paper presents the lower bound buckling load according to the reduced stiffness method proposed by Croll and Yamada. The lower bound buckling loads of the pontoon subjected to circumferential bending load are evaluated from the axisymmetric finite element analysis which includes the reduced stiffness method.
Seismic Response Analysis for Sloshing of a Single-Deck Floating Roof With Center Pontoon in Oil Storage Tank
Authors: Yoshida Shoichi , Sekine Kazuyoshi , Tsuchida Tomohiko , Iwata Katsuki
Published: January 2011

Floating roofs are widely used to prevent evaporation of contents of large cylindrical oil storage tanks. The 2003 Tokachi-Oki earthquake caused severe damage to floating roofs due to liquid sloshing. Seven single-deck floating roofs deformed to leak oil on them, and they lost buoyancy to sink. Two of them were the single-deck type with center pontoon in large diameter tanks. The present paper deals with an axisymmetric finite element analysis for the sloshing response of a floating roof with center pontoon. The hydrodynamic coupling of the fluid and the floating roof under seismic excitation is taken into consideration in the analysis. The fluid is assumed to be incompressible and inviscid, and the roof is assumed to be linear elastic. In addition, the sidewall and the bottom are assumed to be rigid. In the finite element analysis, the behavior of the fluid is formulated in terms of dynamic pressure using the Eulerian approach. The basic vibration characteristics of the single-deck floating roof with center pontoon, such as the natural periods and vibration modes, can be obtained from this analysis. These characteristics are shown comparing with those of the single-deck floating roof without center pontoon. The seismic response analysis for the input of an earthquake wave is also performed.
Prediction Method for Plastic Collapse of Pipes Subjected to Combined Bending and Torsion Moments
Authors: Li Yinsheng , Hasegawa Kunio , Hoang Phuong H. , Bezensek Bostjan
Published: January 2011

When a crack is detected in a pipe during in-service inspection, the failure estimation method given in the codes such as ASME Boiler and Pressure Vessel Code Section XI non-mandatory Appendix C or JSME S NA-1-2008 Appendix E-8 can be applied to assess the integrity of the pipe. In the current editions of these codes, the failure estimation method is provided for bending moment and pressure. Torsion load is assumed to be relatively small and is not considered in the method. In this paper, finite element analyses are conducted for 24-inch stainless steel pipe with a circumferential surface crack subjected to the combined bending and torsion moments, focusing on large and pure torsion moments. Based on the analysis results, a prediction method for plastic collapse under the combined loading conditions of bending and torsion is proposed for the entire range of torsion moments.
Study on Numerical Analysis of Temperature Fluctuations in a Mixing Piping
Authors: Li Chao-Jen , Tsai Yao-Long , Tsai Tai-Ping , Wang Li-Hua
Published: January 2011

In reactor cooling systems of nuclear power plants, the fluctuating stresses on a piping system are potential causes of thermal fatigue failures. These stresses are generated by temperature fluctuations in regions where hot and cold flows are intensively mixed together. The present paper describes BSL Reynolds Stress (BSL-RSM) and Shear Stress Transport (SST) simulation data of thermal mixing in a mixing piping compared with results from experimental data carried out by the Laboratory for Nuclear Energy Systems, Institute for Energy Technology, ETHZ, Zu¨rich, Switzerland. The experimental measurements (concentration of de-ionized water) have been carried out by the use of the 16×16 electrode wire-mesh sensors (WMS) on the basis of difference in liquid electrical conductivities. To verify the analogy between electrical conductivity of de-ionized water and temperature of water, the inlet temperatures of the hot and cold water are set to 80°C and 15 °C respectively in the simulation process. The analytic results are calculated by the commercial CFD code ANSYS CFX 11.0. It is known from literatures, that the different mesh types (Tetrahedral, Tetrahedral/Wedge, Hexahedral), different turbulence models (BSL-RSM, SST), and turbulent Prandtl numbers (0.9, 0.2, 0.1) will affect the simulation results of temperature fluctuations. Since the coefficient of determination, R2, obtained by using Prt = 0.1 for SST turbulence model is between 0.999 and 0.915, which is higher than that by using Prt = 0.2 and Prt = 0.9, the perditions for smaller turbulent Prandtl number are in better agreement with measurements. Moreover, predicted results for Prt = 0.1 obtained by using BSL-RSM turbulence model are almost the same as those by using SST turbulence model. The computational results are in qualitative good agreement with experimental data that the mixing phenomenon of two different temperature water can be explained by de-ionized water with two different electrical conductivities. Additionally, the simulation results with Tetrahedral/Wedge and Hexahedral mesh types are better than those with Tetrahedral mesh type.
Thermal Analysis of Geologic High-Level Radioactive Waste Packages
Authors: Lee S. Y. , Hensel S. J. , De Bock C.
Published: January 2011

The engineering design of disposal of the high level waste (HLW) packages in a geologic repository requires a thermal analysis to provide the temperature history of the packages. Calculated temperatures are used to demonstrate compliance with criteria for waste acceptance into the geologic disposal gallery system and as input to assess the transient thermal characteristics of the vitrified HLW Package. The objective of the work was to evaluate the thermal performance of the supercontainer containing the vitrified HLW in a non-backfilled and unventilated underground disposal gallery. In order to achieve the objective, transient computational models for a geologic vitrified HLW package were developed by using a computational fluid dynamics method, and calculations for the HLW disposal gallery of the current Belgian geological repository reference design were performed. An initial two-dimensional model was used to conduct some parametric sensitivity studies to better understand the geologic system’s thermal response. The effect of heat decay, number of co-disposed supercontainers, domain size, humidity, thermal conductivity and thermal emissivity were studied. Later, a more accurate three-dimensional model was developed by considering the conduction-convection cooling mechanism coupled with radiation, and the effect of the number of supercontainers (3, 4 and 8) was studied in more detail, as well as a bounding case with zero heat flux at both ends. The modeling methodology and results of the sensitivity studies will be presented.
Variation of Plant Electrical Output Due to Main Steam Temperature and Thermal Power
Authors: Yoon D. W. , Park C. K. , Lee B. H. , Jeong K. C.
Published: January 2011

As a measure of power plant thermodynamic performance, heat rate (H.R.) is used. As heat rate is inversely proportional to thermal efficiency, the thermal efficiency of a power plant increases as the heat rate decreases. The major thermodynamic performance parameters in a plant thermal cycle affecting the electrical output include but are not limited to: the initial pressure of main steam at the turbine inlet, the initial moisture content or superheated condition of main steam at the turbine inlet, the effectiveness of the feedwater heating cycle, the effectiveness of the moisture separator, the effectiveness of the reheater, the condenser pressure, the level of cycle separation and the accuracy of electric output measurement. A review of thermodynamic principles involved in a thermal performance plan is needed to understand the changes in the parameters and recognize the thermal performance status and trends, which will lead us to propose corrective actions when appropriate. This paper focuses on the effects of main steam temperature and thermal power.