bluuebunny/crossref_metadata_2025 huggingface dataset:
Resonant Vibrations of Riser Guide Tubes Due to Wave Impact
Authors: Nestega˚rd Arne , Kalleklev Arve Johan , Hagatun Kjell , Wu Yu Lin , Haver Sverre , Lehn Erik
Published: January 2009

The Kristin platform is a catenary moored semi-submersible production vessel (SSPV) intended for production of gas at the Kristin field at Haltenbanken. Kristin has 24 riser guide tubes for tie in of flexible risers, umbilicals and electric cables to the riser balcony. The riser guide tubes (RGT) provide the necessary guiding, support and protection for risers and cables. The guide tubes run vertically from the deck and through the extended east pontoon. The guide tubes are welded to the pontoon and horizontally supported at the underside of the balcony deck. During model tests of the Kristin platform performed in the Ocean Basin laboratory at Marintek, high frequency in-line vibrations of the RGTs were observed during passage of steep waves. The resonance period for the individual RGTs is 0.3 sec. To mitigate the vibration problem, a vibration suppression arrangement of stiff rods was introduced between the guide tubes. Model tests were performed with respect to extreme- and fatigue loads in regular and irregular waves, with and without the suppression arrangement. The model included the floating framework representing the hull and the 24 RGTs with correct diameter and resonance period. The model was suspended in a horizontal mooring system, giving resonance periods in surge and sway close to the prototype platform. A load-response model for the interaction between large steep waves and vertical flexible cylinders has been developed. A slender body load model derived from Morison’s equation is shown to be able to excite the resonant vibrations. The dominant part of the loading comes from the rapid change of added mass momentum, giving rise to an additional slamming term in the load formulation. The structural response is calculated from a recognized non-linear slender body response program. Numerical simulations have been carried out and compared with model tests for both regular and irregular waves. The numerical predictions confirm the effect observed in the model tests; i.e. connecting the tubes generally leads to a reduction of the high frequency response amplitudes.
Development of a Stepped Line Tensioning Solution for Mitigating VIM Effects in Loop Eddy Currents for the Genesis Spar
Authors: Kokkinis T. , Sandstro¨m R. E. , Jones H. T. , Thompson H. M. , Greiner W. L.
Published: January 2009

A number of spars are being installed in deepwater areas in the Gulf of Mexico (GoM), which are subject to loop / eddy current conditions and must be designed for Vortex-Induced Motion (VIM). This paper shows how recent advances in VIM prediction enabled an efficient and effective mooring design solution for the existing Genesis classic spar, which is installed in Green Canyon Block 205 in the GOM. The solution may also be applicable to new spar designs. During the Gulf of Mexico Millennium Eddy Current event in April 2001, the Genesis spar platform underwent vortex induced motions (VIM) which were greater than anticipated during the design of the mooring & riser systems. Analysis showed that if such large motions were to occur in higher currents in the range of the 100-year event, they could cause significant fatigue damage, and could lead to peak tensions in excess of design allowables. After a comprehensive evaluation of potential solutions, Stepped Line Tensioning (SLT) was determined to be the best approach for restoring the platform’s original mooring capacity on technical, cost and schedule grounds. SLT did not require extensive redesign of the existing mooring system of the spar. Furthermore, SLT provided a means to improve mooring integrity on an interim basis, while completing details for permanent implementation. Under SLT, the pretensions of the mooring lines are adjusted based on forecast currents in order to keep the platform below the VIM lock-in threshold at all times and for all eddy/loop current conditions up to and including the 100-year condition. High Reynolds number model tests conducted with a new test methodology were used to get a reliable prediction of the spar’s VIM response for this evaluation.
Analysis of Icing Event Occurrences in the Northern Caspian Sea Based on Meteorological Satellite Data
Authors: van Gelder Pieter H. A. J. M. , Molenaar Wilfred F. , Bolgov Mikhail V. , Krasnozhon G. F.
Published: January 2009

This is a short descriptive paper. It is meant to familiarize the reader with some of the ice environment in the Caspian Sea and it presents data not fully used in western countries. The paper describes results of ice studies of the Northern part of the Caspian Sea based on the processing of space survey data. It is shown that medium-scale space surveys may be used to study icing events, but also river networks, and irrigated and unirrigated lands of the Northern Caspian Sea region. These studies are necessary for the optimal design of flood defences, offshore platforms and for other engineering purposes. Data from Meteor satellites is used to study the ice regime. The advantages of using meteo-satellite data to study the dynamics of ice cover and to identify various types of ice, are shown in comparison with aerial surveys.
Wave Induced VIV of Tubes in the Splash Zone
Authors: Moe Geir , Hagatun Kjell
Published: January 2009

On semisubmersible production platforms often a number of Riser Guide Tubes (RGT) are used to protect the risers through the wave splash zone from the floater pontoon and up to a balcony at deck level. Then the question comes up as to whether Vortex Induced Vibrations (VIV) of the RGT’s may be a problem. The present paper reports on part of the effort to investigate that matter. Here a computer programme was developed to analyse the situation and since model tests were made to clarify the behaviour of the RGT’s, also data were available against which the computational predictions could be compared. Unfortunately verification of the computational model turned out to be problematic. Most important it turned out that water entry forces dominated the force picture, and since flow in the region between the platform legs was quite complicated it was hard to know whether vibrations were due to VIV or water entry. VIV response is strongly dependent on the time histories of the relative particle velocity, which were not measured in the experiment, and could not be accurately estimated due to pronounced flow nonlinearities, refraction effects and platform motions. Also the experimental database on which the computer code relied for the force coefficients appeared to be too summaric at low VIV amplitudes for our purpose. This is understandable, since for VIV in steady currents only large motions have been of importance.
Hydrodynamic Analysis and Motions of the Octoplus Platform
Authors: Pascoal R. , Guedes Soares C. , Facon G. , Pe´trie´ F. , Vache´ M.
Published: January 2009

The hydrodynamic behavior of the OCTOPLUS, a new concept of FPSO is studied. The OCTOPLUS, stands for Optimum Concept TO Produce and Load with Underwater Storage and consists of surface piercing parallelepipedic columns and underwater storage caisson. It is designed for float over deck installation of its two main decks: production and utility deck. This enables fabrication of the decks to proceed in parallel with fabrication of the hull and therefore provides improvements in the construction schedule. The hydrodynamics are studied by physical testing and through numerical computations using a 3D radiation-diffraction code, comparison between both is provided. The experimental program encompasses 1, 10 and 100 year return period seas and the 6 DOF motions are measured. In addition to the comparison of motion transfer function modulus further calculations were performed in order to determine local pressure, having been found that there is a hydrodynamic effect peculiar to the interactions between waves scattered by the columns that is of some importance in design. The structure is shown to have exceptionally good hydrodynamic behavior in the sense that wave induced motions are small. Both the experimental and numerical results are in good agreement.
A Knowledge Based Approach Towards Design of Mechanical Systems and Components for Deep Sea Mining
Authors: Raphael Deepak C. , Kumaraswamy Sivasailam , Rao Medisetti M. , Ravindran Muthukamatchi
Published: January 2009

Development of systems, machinery and components for deep sea mining from 2000–6000 meters depth in the ocean is a major technological challenge. The existing engineering system concepts have been demonstrated for short duration and have to be well evaluated for long term mining operations. The need for conceptualization of new systems has often been emphasized. A Knowledge Based Design Support System has been developed which can be used as a tool to aid a system designer in evaluating existing systems as well as conceive new systems and components. The architecture for evaluating available products and development of evolvable products, hybrid products and genetically modified products are presented. System synthesis using far and near vision fused with conventional methods are described. System variants can be evaluated using a fusion of Analytical Hierarchy Processes (AHP) and Altschullerian approaches.
Non-Destructive Evaluation of Composite Pipes and Tanks: Development of Inspection Strategies
Authors: Thon Harald , Melve Bjo̸rn
Published: January 2009

The document describes practical experience gained from several research programmes and the use of GRP products both offshore and onshore. An OLF document was compiled during 1990’s and the visual inspection part of the document was used in the ISO 14692, part 4 [12] with requirements and defect criteria. Additional parts on ultrasonic and radiographic examination have been included in the Norwegian standard Norsok M-622 [1]. However, we would like to publish the full version of this document and make it available in the public domain. Some of the methods described is well developed, while others still would require research efforts to make the techniques practical useful. For practical use, the visual examination with failure description, acceptance criteria and corrective actions are most developed. Further, radiography has been useful in several projects in assessing the quality of adhesive joints. The ultrasonic testing is expected to become better to use as the equipments and methods are developing. Every reasonable effort has been made to ensure that this publication is based on the author’s best knowledge. However, no responsibility of any kind for any injury, delay, loss or damage can be accepted for parties using information given herein.
A Study on the Use of Ocean Fertilizer for Culture of Seaweed
Authors: Hotta Kenji , Guerrero Rafael D. , Guerrero Luzviminda A. , Okamoto Kyoichi
Published: January 2009

The use of ocean fertilizer containing 20% ferrous sulfate, for the culture of the red alga, K. appaphycus alvarezii, in 50 m2 floating raft was evaluated. Two levels of fertilizer application, 1 and 2 kg.wk−1, for a culture period of 60 days were tested. The efficiency of the fertilizer application using perforated plastic bags attached to the rafts was determined. The cost-effectiveness of the use of the fertilizer was also analyzed. Results showed that the application of ocean fertilizer at 2 kg.wk−1 gave the highest net yield of the seaweed that was 30% more than that of the control. The method of fertilizer application was found to be efficient. Considering the net yield of the seaweed and carrageean content, and the cost of the fertilizer, analysis showed that use of the fertilizer is highly cost-effective. Finally, author discusses a new possibility of ocean space use as a culture ground.
Full Scale Data Comparison for the Horn Mountain Spar
Authors: Halkyard John , Liagre Pierre , Tahar Arcandra
Published: January 2009

The Horn Mountain Production Spar was installed in 5,400 feet of water in June 2002. This was the deepest floating production unit at that time. A comprehensive instrumentation program was initiated to measure spar and riser responses (Edwards et al, DOT 2003). The present paper discusses the results of these measurements and comparison with analytical predictions of spar behavior during two selected events, hurricane Isidore in September 2002 and a summer storm in August 2003. Particular attention has been placed on the slowly varying surge and pitch motions and the importance of coupling with risers and mooring on hull motions. Our conclusion is that uncoupled analytical models for spar behavior predict accurately the wave frequency responses, however riser coupling has an influence on the slowly varying responses. This conclusion is consistent with earlier measurements of classic spar behavior (Gupta et al, OTC 2000, Prislin et al, OTC 1999).
Methods for Fatigue Assessment of Critical Ship Details
Authors: Wang Xiaozhi , Sun Haihong , Cheng Zhan
Published: January 2009

Fatigue assessment, as part of ship design, was not required until about 10 years ago, due to the increasing use of high strength steel and demand for minimizing structure weight. As early as 1993, ABS (American Bureau of Shipping) published Guidance on fatigue strength assessment of tankers (the latest version of the Guide can be found in [1]). Since then, ship design has been developed with more optimization involved, as a balance of cost, steel weight and safety. Consequently, fatigue assessment has become a more and more important factor in ship design. There are various methods, design codes and recommended practices on fatigue design and assessment of welded structures. Industries have tried to organize Joint Industry Projects (JIPs) to further develop the method or see the possibility of harmonizing the codes or practices. Individuals have also made their efforts to provide information from view points of designers, operators or regulators. This paper addresses some of the available methods applicable for critical ship details through the case studies of bilge knuckle joint of an oil tanker and a side longitudinal/frame connection of an FPSO. Various methods of hot spot stress calculation including mesh size schemes and element type selection will be evaluated and comparison of fatigue lives from the hot spot stress methods with associated S-N curves will be made with the experimental data.
Fully Coupled EDS/Drift-Off Analysis for a Harsh Environment, Deepwater Site
Authors: O’Sullivan Enda , Soles Julian , Dib Michel
Published: January 2009

In support of a well drilled in the Great Australian Bight (GAB) by the Glomar Jack Ryan dynamically-positioned (DP) drillship in 4308 feet of water in early 2003, drift-off riser analysis was carried out to establish “alert” offsets for the emergency disconnect sequence (EDS). Drift-off analysis of the vessel/riser system is a key element to the successful management of the riser on a DP drillship, as it deals with protecting the equipment in case of the potential loss of vessel power. At this well site, high seastates combined with wind and current conditions dictate that drilling should be carried out in accordance with “well-specific operating criteria” (WSOC). These criteria assist the crew by identifying the metocean conditions that limit various operations. Analysis of the drilling riser was carried out for drift-off, hang-off and recoil scenarios to establish certain criteria to avoid exceedence of allowable limits in the riser and conductor pipe. The novel aspect of this drift-off analysis is the use of a fully-coupled, time-domain, finite element solution. The fully-coupled aspect of this solution models the vessel / tensioner system / riser / LMRP / BOP / wellhead / conductor / soil interaction process more accurately and thus allows for less conservativism when compared to uncoupled solution methods. This enables the rig to work in areas that might otherwise be considered marginal due to the anticipated time spent waiting on weather.
Determining Profile and Alignment Using an Optical Technique With Extrapolations
Authors: Carr Gary A. , Diaz Christian , Martin Gary A.
Published: January 2009

In the field of railway inspection, track alignment and profile are measured as the mid-chord offset (MCO) of a specified chord length at a known contact point on the rail. Generally, a 31-foot chord length is used. In recent years, due to developments of high-speed rail standards, measuring longer wavelength MCO’s, such as 62 and 124 feet are required. This is currently done using inertial means, however verification under static conditions using mechanical means is difficult. Currently the MCO is measured by stretching a string of the desired chord length between two points and manually measuring the offset from the center of the string to the rail. This is labor intensive, and the accuracy is limited, as external effects such as wind can make the string sway back and forth. While measuring a short chord length, and then extrapolating to the longer wavelengths can eliminate the sway problem, the extrapolation process magnifies any error in measurement. This paper presents the application of an optical technique, consisting of cameras and targets to measure a 31-foot mid-chord offset with very high precision, and the extrapolation technique used to obtain long chord measurements with a high degree of accuracy.
Investigation of Hybrid Fuel Cell (HFC) Technology Applications on the Future Passenger Railroad Transportation
Authors: Moghbelli H. , Gao Y. , Langari R. , Ehsani M.
Published: January 2009

Due to the consideration of fragile security, and longer check-in times and inconveniences due to increased air travel security examination since September 11th 2001, more and more people have turn to ground transportation. Unfortunately, the inefficient, environment-unfriendly and unsafe passenger cars and buses are the only choices available for middle distance trips. Development of high efficiency, clean and high speed railroad passenger transportation system has become more necessary to overcome this weak link. In this paper, the applicability of hybrid drive train technologies for middle-distance passenger train locomotives will be investigated. A systematic design of the diesel based hybrid locomotive helps to increase efficiency, improve fuel economy, reduce emissions and also reduce mass production costs. Furthermore, professional management and maintenance of railroad train locomotives make such new technologies more practical than for road vehicles. The success of such transportation system will have a great positive impact on our social activities, quality of life, energy supply, environment and economy. A diesel based hybrid electric locomotive (HEL) with batteries or an ultracapacitor is an option to reduce fuel consumption and emissions and provide better performance and fuel economy. The reduced fuel consumption helps reduce the amount of pollutants released. Engineering estimation indicate that emissions will be reduced by 70% and fuel efficiency will be increased by at least 30% in hybrid locomotives.
The Influence of Suspension System Design on Vertical Loads Imposed on the Track
Authors: Strong Philip M.
Published: January 2009

The relative significance of vehicle dynamics on the dynamic component of wheel-rail interface vertical forces caused by relatively short wavelength track perturbations is estimated, based on a simple dynamic model, for a range of suspension design types. The results indicate the relative importance of suspension design on track damage. This study is analytical. However, it provides a basis for testing to ensure that the influence of suspension design on track-induced vertical loads is better documented and understood.
A Novel Combined Power and Cooling Thermodynamic Cycle for Low Temperature Heat Sources: Part I — Theoretical Investigation
Authors: Tamm Gunmar , Goswami D. Yogi , Lu Shaoguang , Hasan Afif A.
Published: January 2009

A combined thermal power and cooling cycle proposed by Goswami is under intensive investigation, both theoretically and experimentally. The proposed cycle combines the Rankine and absorption refrigeration cycles, producing refrigeration while power is the primary goal. A binary ammonia-water mixture is used as the working fluid. This cycle can be used as a bottoming cycle using waste heat from a conventional power cycle or an independent cycle using low temperature sources such as geothermal and solar energy. Initial parametric studies of the cycle showed the potential for the cycle to be optimized for first or second law efficiency, as well as work or cooling output. For a solar heat source, optimization of the second law efficiency is most appropriate, since the spent heat source fluid is recycled through the solar collectors. The optimization results verified that the cycle could be optimized using the Generalized Reduced Gradient method. Theoretical results were extended to include realistic irreversibilities in the cycle, in preparation for the experimental study.
A Numerical and Experimental Investigation of Low-Conductivity Unglazed, Transpired Solar Air Heaters
Authors: Gawlik Keith M. , Kutscher Charles F.
Published: January 2009

The performance of low-conductivity unglazed, transpired solar collectors was determined numerically and experimentally. The numerical work consisted of modelling flow conditions and plate geometries with the FLUENT computational fluid dynamics software and the experimental work utilized laboratory apparatus at the National Renewable Energy Laboratory. Good agreement was found between the numerical and experimental results. The results showed that for practical low-conductivity materials, performance differed little from the equivalent geometry in high-conductivity material.
Adaptive Optimal Control of a Grid-Independent Photovoltaic System
Authors: Henze Gregor P. , Dodier Robert H.
Published: January 2009

This paper investigates adaptive optimal control of a grid-independent photovoltaic system consisting of a collector, storage, and a load. The algorithm is based on Q-Learning, a model-free reinforcement learning algorithm, which optimizes control performance through exploration. Q-Learning is used in a simulation study to find a policy which performs better than a conventional control strategy with respect to a cost function which places more weight on meeting a critical base load than on those non-critical loads exceeding the base load.
Measured Versus Predicted Performance of Building Integrated Photovoltaics
Authors: Davis Mark W. , Fanney A. Hunter , Dougherty Brian P.
Published: January 2009

The lack of predictive performance tools creates a barrier to the widespread use of building integrated photovoltaic panels. The National Institute of Standards and Technology (NIST) has created a building integrated photovoltaic (BIPV) “test bed” to capture experimental data that can be used to improve and validate previously developed computer simulation tools. Twelve months of performance data have been collected for building integrated photovoltaic panels using four different cell technologies – crystalline, polycrystalline, silicon film, and triple-junction amorphous. Two panels using each cell technology were present, one without any insulation attached to its rear surface and one with insulation having a nominal thermal resistance value of 3.5 m2·K/W attached to its rear surface. The performance data associated with these eight panels, along with meteorological data, were compared to the predictions of a photovoltaic model developed jointly by Maui Solar Software and Sandia National Laboratories (SNL), which is implemented in their IV Curve Tracer software [1]. The evaluation of the predictive performance tools was done in the interest of refining the tools to provide BIPV system designers with a reliable source for economic evaluation and system sizing.
Investigation of a Solar-Thermal Bio-Mimetic Metal Hydride Actuator
Authors: Lloyd George , Kim Kwang J. , Razani A. , Shahinpoor Mohsen
Published: January 2009

Metal hydrides have been investigated for use in a number of solar thermal energy applications, such as heat regenerators or hydrogen storage technology, but rarely for thermal actuators. Preliminary experimental results from a prototype solar thermal metal hydride actuator, using copper-encapsulated porous metal hydride compacts of LaNi5, indicate that this thermal-mechanical system can produce high specific forces (over 100 (N/g)), with response times on the order of seconds. These operational characteristics, along with features such as being bio-mimetic, compact, operationally safe, lubricationless, noiseless, soft actuating, and environmentally benign, result in an actuator that is ideal for many industrial, space, defense, and biomedical applications. In this paper, we report recent work directed toward predicting and characterizing the performance bounds of the actuator, specically concentrating on elements which might comprise an actuator driven by concentrated solar radiation. A complete solution of the 1D governing heat and mass transfer equations with an ideally selective reactor surface are used to predict bounds on performance in terms of volume flow rates and realistic actuation times. The advantages and disadvantages of the design are discussed from this perspective. The preliminary data show a great potential for these metal hydride actuators to be used for solar thermo-mechanical applications.
Experimental Rotordynamic Coefficient Results for a Load-on-Pad Flexible-Pivot Tilting-Pad Bearing With Comparisons to Predictions From Bulk-Flow and Reynolds Equation Models
Authors: Rodriguez L. E. , Childs D. W.
Published: January 2009

Experimental dynamic-stiffness-coefficient results are presented for a high-speed, lightly loaded, load-on-pad, flexible-pivot tilting-pad bearing. Results show that the real part of the direct dynamic-stiffness coefficients are quadratic functions of the excitation frequency. This frequency dependency is modeled well by an added-mass coefficient, and the resultant [M], [K], and [C] matrix model is frequency-independent versus a conventional [K] and [C] model that is frequency dependent. The dynamics introduced by the additional pad degrees of freedom (including pad inertia and web moment stiffness) and the effects of fluid inertia in the lubricant film account for part of this frequency dependency. Experimental results are compared to numerical predictions from models based on: (i) the Reynolds equation, and (ii) a Navier-Stokes (NS) equations bulk-flow model that retains the temporal and convective fluid inertia terms. The NS bulk-flow model results correlate better with experimental dynamic stiffness results, including added-mass terms. Both models underestimate the measured added-mass coefficients for the full excitation range; however, they do an adequate job for excitation frequencies up to synchronous frequency. The frequency dependency predicted by using a [K] and [C] model can be removed by adding a mass matrix to the reaction-force model with either a Reynolds equation or a bulk-flow NS model, with a very considerable speed up in calculation of damped eigenvalues for rotor-bearing systems.
Probabilistic Main Bearing Performance for an Internal Combustion Engine
Authors: Mourelatos Zissimos P. , Vlahopoulos Nickolas , Ebrat Omidreza , Liang Jinghong , Wang Jin
Published: January 2009

A probabilistic analysis is presented for studying the variation effects on the main bearing performance of an I.C. engine system, under structural dynamic conditions. For computational efficiency, the probabilistic analysis is based on surrogate models (metamodels), which are developed using the kriging method. An Optimum Symmetric Latin Hypercube (OSLH) algorithm is used for efficient “space-filling” sampling of the design space. The metamodels provide an efficient and accurate substitute to the actual engine bearing simulation models. The bearing performance is based on a comprehensive engine system dynamic analysis which couples the flexible crankshaft and block dynamics with a detailed main bearing elastohydrodynamic analysis. The clearance of all main bearings and the oil viscosity comprise the random variables in the probabilistic analysis. The maximum oil pressure and the percentage of time within each cycle that a bearing operates with oil film thickness below a threshold value of 0.27 μm at each main bearing constitute the system performance measures. Probabilistic analyses are first performed to calculate the mean, standard deviation and probability density function of the bearing performance measures. Subsequently, a probabilistic sensitivity analysis is described for identifying the important random variables. Finally, a Reliability-Based Design Optimization (RBDO) study is conducted for optimizing the main bearing performance under uncertainty. Results from a V6 engine are presented.
A New Implicit Algorithm for the Simulations of Slider Dynamics Based on the Unstructured Triangular Mesh
Authors: Hua Wei , Li Jianhua , Liu Bo , Ma Yansheng
Published: January 2009

The unstructured triangular mesh is successfully applied to the steady simulations of the slider due to its flexibility, accuracy and mesh efficiency in capturing various complex ABS rails and recess wall regions. This paper introduces a new implicit algorithm with second order time accuracy for the time-dependent simulations of the slider dynamics based on the unstructured triangular mesh. The new algorithm is specially developed for the unstructured triangular mesh and the finite volume method. It is applied to simulate the load/unload details based on the 9-D model, such as the influences of the limiter position on the flying height during the unload process, and the development and the 3-D profiles of the air bearing pressure during the load process. Because of the mesh efficiency of the unstructured triangular mesh and the flexibility of applying greater time steps, the simulation times are significantly shorter than those of the structured rectangular mesh. The simulation results based on the algorithm are in good correlation with the experimental results.
A General Solution for Optimized Circular Contacts
Authors: Glovnea Marilena , Diaconescu Emanuel
Published: January 2009

Many classical applications in machine design and recent ones in the field of electrical contacts or micro-contacts involve surface circular contacts which show important edge effects. To optimize these contacts, a uniform pressure distribution must be generated over an important part of contact area. This requires a specifically profiled front surface. Previously, these authors proposed a solution based on an optimum pressure distribution. This leads numerically to a punch profile which is approximated by a polynomial. The pressure generating this polynomial profile is found and compared to initial proposal. Recent investigations establish a correspondence between a polynomial punch surface and generated pressure. Starting from this correspondence, a new general approach is offered. The same optimum pressure as previously is accepted. Its profile is approximated by a function advanced in the paper. This function yields directly an even polynomial punch profile. Formulae for central pressure and normal approach are derived.
Effect of Silicon Nitride Balls and Rollers on Rolling Bearing Life
Authors: Zaretsky Erwin V. , Vlcek Brian L. , Hendricks Robert C.
Published: January 2009

Three decades have passed since the introduction of silicon nitride rollers and balls into conventional rolling-element bearings. For a given applied load, the contact (Hertz) stress in a hybrid bearing will be higher than an all-steel rolling-element bearing. The silicon nitride rolling-element life as well as the lives of the steel races were used to determine the resultant bearing life of both hybrid and all-steel bearings. Life factors were determined and reported for hybrid bearings. Under nominal operating speeds, the resultant calculated lives for deep-groove, angular-contact, and cylindrical-roller hybrid bearings are respectively, 3.8, 3.3, and 5.5 times that using the Lundberg-Palmgren equations. An all-steel bearing under the same load and nominal operating speeds will always have higher life than the equivalent hybrid bearing operating under the same conditions. Under these conditions, hybrid bearings are predicted to have a lower fatigue life than the all-steel bearings by 58 percent for deep-groove bearings, 41 percent for angular-contact bearings and 28 percent for cylindrical roller bearings.
Modeling and Parametric Study of Torque in Open Clutch Plates
Authors: Aphale Chinar R. , Cho Jinhyun , Schultz William W. , Ceccio Steven L. , Yoshioka Takao , Hiraki Henry
Published: January 2009

The relative motion of the friction and separator plates in wet clutches during the disengaged mode causes viscous shear stresses in the fluid passing through the 100 microns gap. This results in a drag torque on both the disks that wastes energy and decreases fuel economy. The objective of the study is to develop an accurate mathematical model for the above problem with verification using FLUENT and experiments. Initially we start with two flat disks. The mathematical model enables us to calculate the drag torque on the disks and 2D axisymmetric solver verifies the solution. The surface pressure distribution on the plates is also verified. Then 3D models of one grooved and one flat disk are tested using CFD, experiments and an approximated 3D mathematical model and three parameters namely number of grooves, depth of groove and clearance between the disks are studied to understand the effect they have on the drag torque. Conclusions are finally drawn and design implementations are suggested to reduce drag.
A Mechanics Approach to Static Friction of Elastic-Plastic Fractal Surfaces
Authors: Yang J. , Komvopoulos K.
Published: January 2009

A contact mechanics theory of static friction is presented for isotropic rough surfaces exhibiting fractal behavior. The analysis is based on a piece-wise power-law size distribution and a normal slope distribution of the asperity contacts and elastic-fully plastic deformation models. Numerical integration yields solutions for the normal and friction forces in terms of fractal parameters, elastic-plastic material properties, and interfacial shear strength. The variation of the static coefficient of friction with normal load is related to the effect of the surface topography on the dominant deformation mode at the asperity contacts. Plastic deformation of the smaller asperity contacts dominates at low loads and elastic deformation of the larger asperity contacts at high loads. The critical load signifying the transition from predominantly plastic to elastic deformation depends on the fractal parameters and material properties. In the low-load range, the static coefficient of friction decreases with the increase of the load, while in the high-load range it increases relatively faster with the load. Numerical results for copper fractal surfaces illustrate the effects of normal load, surface topography, and interfacial shear strength on the static coefficient of friction.
Transient Solution of the Inhomogeneous Thermoelastic Contact Problem Using Fast Speed Expansion
Authors: Li Jiayin , Barber James R.
Published: January 2009

Numerical integration has been widely used in commercial FEA software to solve transient problems. However, for the large-scale inhomogeneous thermoelastic contact problem (ITEC), this method is found to be extremely computation-intensive. This paper introduces a new approach to solve the ITEC transient problem with much lower computational complexity. The method is based on the transient modal analysis (TMA) method in conjunction with the fast speed expansion (FSE) method. The TMA method is used to obtain the inhomogeneous transient solution by expressing the solution in modal coordinates, corresponding to eigenfunctions of the homogeneous (unloaded) problem. If the sliding speed is constant, the eigenfunctions can be found by one run of the commercial software program ‘HotSpotter’. However, if the speed varies, the eigenfunctions change and numerous runs of HotSpotter are needed, making the method computationally inefficient. However, the FSE method employs an efficient algorithm to interpolate and expand the eigenfunctions and eigenvalues over a range of speeds. This reduces the number of eigenvalue solutions required and results in a significant reduction in computation time. The method is illustrated with application to an axisymmetric transmission clutch problem.
A Three-Dimensional Friction Model for Elastic-Plastic Contact With Tangential Loading: Application to Dented Surfaces
Authors: Antaluca Eduard , Ne´lias Daniel , Cretu Spiridon
Published: January 2009

A three-dimensional numerical model based on a semi-analytical method in the framework of small strains and small displacements with respect of Hertz’s hypotheses is presented for solving an elastic-plastic dented contact with friction. The calculation of surface deformations and pressure distribution, which is the most time consuming step during the elastic-plastic algorithm, is obtained using a method based on a variational principle with a Fast Fourier Transform (FFT) and a Conjugate Gradient Method (CGM). The method is fast enough to allow investigating the effect of a small size surface defect, here a debris denting, on the subsurface elastic-plastic stress state, requiring a fine mesh with around 106 surface grid points. Further, the FFT approach is also involved in the calculation of internal stress state. The plasticity model is based on an incremental load and Von Mises yield criterion. The effects of the contact pressure distribution and residual strain on the geometry of the contacting surfaces yield from the Betti’s reciprocal theorem with initial strain. The code is used to compute a few smooth and dented contacts, with several types of contact interfaces conditions, including frictionless and Coulomb friction. The effects of surface dents and friction on the contact pressure and subsurface stress field are presented and discussed.
Micro/Nanotribology of RF MEMS Switches
Authors: Patton Steven T. , Eapen Kalathil C. , Zabinski Jeffrey S.
Published: January 2009

Microelectromechanical systems (MEMS) radio frequency (RF) switches hold great promise in a myriad of commercial, aerospace, and military applications. MEMS switches offer important advantages over current electromechanical and solid state technologies including high linearity, low insertion loss, low power consumption, good isolation, and low cost [1–21]. However, there is little fundamental understanding of the factors determining the performance and reliability of these devices. Our previous work investigated fundamentals of hot-switched direct current (DC) gold (Au) contacts using a modified microadhesion apparatus as a switch simulator [1]. Those experiments were conducted under precisely controlled operating conditions in air at MEMS-scale forces with an emphasis on the role of surface forces and electric current on switch performance, reliability, and durability [1]. Electric current had a profound effect on deformation mechanisms, adhesion, contact resistance (R), and reliability/durability. At low current (1–10 μA), asperity creep and switching induced adhesion were the most important observations, whereas, at high current (1–10 mA), lack of adhesion and switch shorting by nanowire formation were prominent [1].
Pre-Sliding Tangential Deflections Can Govern the Friction of MEMS Devices
Authors: Corwin Alex D. , Street Mark D. , Carpick Robert W. , Ashurst William R. , de Boer Maarten P.
Published: January 2009

We have measured pre-sliding tangential deflections (PSTD) between micromachined surfaces of up to 200 nanometers in length before the static friction event using a polysilicon nanotractor actuator [1,2]. The detailed PSTD structure is resolved by a one-nanometer-resolution in-plane optical metrology we have developed, and may be a manifestation of discrete asperity-asperity interactions leading to an effective spatial distribution of friction coefficients. Results indicate a dependence on surface treatment, with a perfluorinated eight-carbon chain monolayer coating showing substantially different PSTD than an eighteen-carbon chain hydrocrabon monolayer. This behavior may qualitatively be related to variations in dynamic versus static friction. We present a simple phenomenological model that captures some of the behavior of PSTD, and suggest some possible microscopic interpretations.
Fast Speed Expansion Technique for the Transient Analysis of Automotive Clutches
Authors: Li Jiayin
Published: January 2009

The transient modal analysis method (TMA) has been used to solve the inhomogeneous (loaded) transient thermoelastic contact problem (ITTEC). In the TMA method, the solution of the inhomogeneous transient problem is expressed in modal coordinates, corresponding to eigenfunctions of the homogeneous (unloaded) problem. However, for the large-scale ITTEC problem, this method is found to be extremely time-consuming, because of the computation-intensive of the eigen-solutions. This paper describes a new approach to solve the large-scale ITTEC problem with a dramatic reduction in computational complexity. The method is referred to as fast speed expansion method (FSE). With the FSE method, full eigen-solutions are performed only at a limited number of sparsely located speeds. For speeds between these speeds, eigenvectors are solved by linear interpolation, while the eigenvalues are computed from Taylor series. The method is illustrated with application to an automotive clutches.
Surface Temperature in Oscillating Sliding Interfaces
Authors: Mansouri M. , Khonsari M. M.
Published: January 2009

A model is developed to predict the behavior of two sliding bodies undergoing oscillatory motion. A set of four dimensionless groups is introduced to characterize the transient dimensionless surface temperature rise. They are: the Peclet number Pe, the Biot number Bi, the amplitude of oscillation A, and the Hertzian semi-contact width α. Also considered in the analysis is the effect of the ratio β = A/α of the amplitude to the semi-contact width. The results of a series of simulations, covering a range of these independent parameters, are presented and examples are provided to illuminated the utility of the model.
Treatment with the Fusion Inhibitor Enfuvirtide Influences the Appearance of Mutations in the Human Immunodeficiency Virus Type 1 Regulatory Protein Rev
Authors: Svicher Valentina , Alteri Claudia , D'Arrigo Roberta , Laganà Alessandro , Trignetti Maria , Lo Caputo Sergio , Callegaro Anna Paola , Maggiolo Franco , Mazzotta Francesco , Ferro Alfredo , Dimonte Salvatore , Aquaro Stefano , di Perri Giovanni , Bonora Stefano , Tommasi Chiara , Trotta Maria Paola , Narciso Pasquale , Antinori Andrea , Perno Carlo Federico , Ceccherini-Silberstein Francesca
Published: January 2009

The gp41-encoding sequence of theenvgene contains in two separate regions the Rev-responsive elements (RRE) and the alternative open reading frame of the second exon of the regulatory protein Rev. The binding of Rev to the RRE allows the transport of unspliced/singly spliced viral mRNAs out of the nucleus, an essential step in the life cycle of human immunodeficiency virus type 1 (HIV-1). In this study, we have investigated whether the fusion-inhibitor enfuvirtide (ENF) can induce mutations in Rev and if these mutations correlate with the classical ENF resistance gp41 mutations and with viremia and CD4 cell count. Specific Rev mutations were positively associated with ENF treatment and significantly correlated with classical ENF resistance gp41 mutations. In particular, a cluster was observed for the Rev mutations E57A (E57Arev) and N86Srevwith the ENF resistance gp41 mutations Q40H (Q40Hgp41) and L45Mgp41. In addition, the presence at week 48 of the E57Arevcorrelates with a significant viremia increase from baseline to week 48 and with a CD4 cell count loss from baseline to week 48. By modeling the RRE structure, we found that the Q40gp41and L45gp41codons form complementary base pairs in a region of the RRE involved in Rev binding. The conformation of this Rev-binding site is disrupted when Q40Hgp41and L45Mgp41occur alone while it is restored when both mutations are present. In conclusion, our study shows that ENF pressure may also affect both Rev and RRE structures and can provide an excellent example of compensatory evolution. This highlights the multiple roles of ENF (and perhaps other entry inhibitors) in modulating the correct interplay between the different HIV-1 genes and proteins during the HIV-1 life cycle.
Postantibiotic Effects of Telavancin against 16 Gram-Positive Organisms
Authors: Pankuch G. A. , Appelbaum P. C.
Published: January 2009

The in vitro postantibiotic effects (PAEs), postantibiotic sub-MIC effects (PA-SMEs), and sub-MIC effects of telavancin were determined for 16 gram-positive organisms. Telavancin staphylococcal, streptococcal, and enterococcal PAE ranges were 0.9 to 3.9 h, 0.4 to 6.7 h, and 0.3 to 2.2 h, respectively. The PA-SME ranges (0.4 times the MIC) for staphylococci, streptococci, and enterococci were 6.7 to >10.7 h, >10.7 to >11.0 h, and >10 to >10.8 h, respectively. The extended PAE of telavancin, together with its long elimination half-life in humans, supports once-daily dosing for this investigational drug.
Distribution, Diversity, and Seasonality of Waterborne Salmonellae in a Rural Watershed
Authors: Haley Bradd J. , Cole Dana J. , Lipp Erin K.
Published: January 2009

Salmonella
outbreaks from contaminated water and nonanimal foods (e.g., produce) are increasingly reported. To address the environment as a potential source of pathogenic
Salmonella
, we investigated levels of salmonellae and the geographic and temporal variation of
Salmonella
serotypes from surface waters in a region of Georgia (United States) with a history of high salmonellosis case rates. Monthly water samples were collected from six stations in the Little River (Upper Suwannee Basin) for 12 months (April 2005 to April 2006). Salmonellae were enumerated using a three-step most-probable-number (MPN) assay. Salmonellae were detected in 57 of the 72 water samples collected (79.2%). Monthly
Salmonella
densities ranged from an MPN of 2.5 liter
−1
in April 2005 to 36.3 liter
−1
in August 2005; concentrations were significantly higher in the summer months compared to other seasons (
P
< 0.05). Concentrations were not significantly different between stations. Levels of salmonellae were correlated with average daily watershed rainfall for the 1 and 2 days preceding each sample collection (
r
= 0.77 and 0.68, respectively;
P
< 0.005). Additionally, water temperature was also positively associated with total
Salmonella
levels (
r
= 0.44;
P
< 0.05). In total, 13
S. enterica
serotypes were identified among 197
Salmonella
isolates. Eighty (40.6%) were identified as
S. enterica
subsp.
arizonae
. Muenchen and Rubislaw were the most frequently identified serotypes of the remaining 117 isolates (28 and 26 isolates, respectively). Serotype diversity peaked in the summer, with 9 serotypes observed in August compared to only one serotype (
S. enterica
subsp.
arizonae
) observed in April (2005 and 2006) (
P
< 0.05). Furthermore, all samples collected in August (6/6) contained multiple serotypes (two to five per sample). The results of this study suggest that
Salmonella
abundance and diversity in the environment vary temporally and are strongly influenced by seasonal precipitation and water temperature.