bluuebunny/crossref_metadata_2025 huggingface dataset:
One-Dimensional Analysis Method for Cavitation Instabilities of a Rotating Machinery
Authors: Kawasaki Satoshi , Shimura Takashi , Uchiumi Masaharu , Iga Yuka
Published: October 2017

Rotating cavitation is an important problem, which makes it difficult to design reliable rotating machines. In this study, a simple analysis method that tried to evaluate the cavitation instabilities of a rotating machinery by using one-dimensional (1D) system analysis software was attempted. In this method, cavitation compliance and mass flow gain factor are distributed in each flow path of the inducer. Analysis results show that cavitation instabilities, including rotating phenomena, exist. With the evolved analysis model, effects of various parameters on the eigenvalues of the system were investigated. Analysis results agreed with inducer test results qualitatively. Furthermore, by the analysis considered whirl motion of the rotor, effects of it on cavitation instabilities were investigated.
An Experimental Analysis of the Structural Response of Flexible Lightweight Hydrofoils in Cavitating Flow
Authors: Lelong Alexandra , Guiffant Pierre , André Astolfi Jacques
Published: October 2017

This paper presents an original experimental study concerning the structural response of a flexible lightweight hydrofoil undergoing various flow conditions including partial cavitating flow. It is based on the analysis of the static deformation, the vibrations, the strains, and the stresses of a polyacetal NACA0015 cantilevered hydrofoil in a hydrodynamic tunnel, at Reynolds numbers ranging from 3 × 105 to 6 × 105. A specific distance measurement laser device was developed to measure the static deformation of the hydrofoil. The vibration response was measured by means of two laser vibrometers in order to identify the structural modal response. The strains and stresses were obtained from integrated strain gauges embedded in the foil close to the root section. A high-speed camera was used in order to analyze unsteady features of the cavitating flow. This paper presents the experimental setup and several results in both noncavitating and cavitating flow that should be very useful for numerical developments of fluid structure interaction (FSI) in heavy fluid. Several observations are reported in the paper showing the strong coupling between the fluid and the structure. Particularly, a frequency lock-in of the cavity frequency to the first bending mode is clearly observed for a narrow band of cavitation numbers.
Dynamic Response of an Unbalanced Rigid Rotor Bearing System With a Nonlinear Hydrodynamic Force
Authors: Kumar Chandan , Sarangi Somnath
Published: October 2017

Planar dynamics of a rotor supported by long hydrodynamic journal bearing is investigated theoretically. An analytical model of the long journal bearing system is numerically integrated for analysis of fixed point and periodic oscillations. The nonlinearities in the system arise due to a nonlinear fluid film force acting on the journal. The influences of three dimensionless parameters, viz. bearing parameter, unbalance, and rotor speed, on the dynamic behavior of the rotor bearing system is studied and compared with the short journal bearing. For the same bearing parameter, short bearing has large operating speed compared to a long bearing. The results are presented in the form of a bifurcation diagram and Poincaré map of the oscillations based on numerical computation. The considered unbalanced system shows periodic, multiperiodic, and quasi-periodic motion in different speed range. Jumping phenomenon is also observed for a high value of bearing parameter with unbalance.
Decreased Thermal Conductivity of Polyethylene Chain Influenced by Short Chain Branching
Authors: Luo Danchen , Huang Congliang , Huang Zun
Published: October 2017

In this paper, we have studied the effect of short branches (side chains) on the thermal conductivity (TC) of a polyethylene (PE) chain. With a reverse nonequilibrium molecular dynamics (RNEMD) method, TCs of the pristine PE chain and the PE-ethyl chain are simulated and compared. It shows that the branch has a positive effect to decrease the TC of a PE chain. The TC of the PE-ethyl chain decreases with the number density increase of branches, until the density becomes larger than about eight ethyl per 200 segments, where the TC saturates to be only about 40% that of a pristine PE chain. Because of different weights, different branches will cause a different decrease of TCs, and a heavy branch will lead to a lower TC than a light one. This study is expected to provide some fundamental guidance to obtain a polymer with a low TC.
Design Procedure for a Fast and Accurate Parallel Manipulator
Authors: Briot Sébastien , Caro Stéphane , Germain Coralie
Published: October 2017

This paper presents a design procedure for a two degree-of-freedom (DOF) translational parallel manipulator, named IRSBot-2. This design procedure aims at determining the optimal design parameters of the IRSBot-2 such that the robot can reach a velocity equal to 6 m/s, an acceleration up to 20 G, and a multidirectional repeatability up to 20 μm throughout its operational workspace. Besides, contrary to its counterparts, the stiffness of the IRSBot-2 should be very high along the normal to the plane of motion of its moving platform. A semi-industrial prototype of the IRSBot-2 has been realized based on the obtained optimum design parameters. This prototype and its main components are described in the paper. Its accuracy, repeatability, elasto-static performance, dynamic performance, and elasto-dynamic performance have been measured and analyzed as well. It turns out that the IRSBot-2 has globally reached the prescribed specifications and is a good candidate to perform very fast and accurate pick-and-place operations.
Low Load Operation Range Extension by Autothermal On-Board Syngas Generation
Authors: Baumgärtner Max H. , Sattelmayer Thomas
Published: October 2017

The increasing amount of volatile renewable energy sources drives the necessity of flexible conventional power plants to compensate for fluctuations of the power supply. Gas turbines in a combined cycle power plant (CCPP) adjust the power output quickly but a sudden increase of CO and unburned hydrocarbons emissions limits their turn-down ratio. To extend the turn-down ratio, part of the fuel can be processed to syngas, which exerts a higher reactivity. An autothermal on-board syngas generator in combination with two different burner concepts for natural gas (NG) and syngas mixtures is presented in this study. A mixture of NG, water vapor, and air reacts catalytically in an autothermal reactor test rig to form syngas. At atmospheric pressure, the fuel processor generates syngas with a hydrogen content of −30 vol % and a temperature of 800 K within a residence time of 200 ms. One concept for the combustion of NG and syngas mixtures comprises a generic swirl stage with a central lance injector for the syngas. The second concept includes a central swirl stage with an outer ring of jets. The combustion is analyzed for both concepts by OH*-chemiluminescence, lean blow out (LBO) limit, and gaseous emissions. The central lance concept with syngas injection exhibits an LBO adiabatic flame temperature that is 150 K lower than in premixed NG operation. For the second concept, an extension of almost 200 K with low CO emission levels can be reached. This study shows that autothermal on-board syngas generation is feasible and efficient in terms of turn-down ratio extension and CO burn-out.
Cooling Time (t8/5) Model for Submerged Arc Welded Pressure Vessel Steel Using Dimensional Analysis
Authors: Kumar Arya Harish , Singh Kulwant , Saxena R. K.
Published: October 2017

Most of the microstructural changes in weldment takes place during weld cooling from 800 ° C to 500 ° C (t8/5) specially in the heat-affected zone (HAZ). Weld strength and cracking tendency can also relate to t8/5. A generalized model using dimensional analysis has been proposed for estimation of the weld cooling time (t8/5) for variable plate thicknesses. The proposed model is based on rotatable central composite designed submerged arc welding (SAW) experiments. The model considers material properties, weld parameters, and environmental conditions for submerged arc welding. The model is validated with experimental data and cooling time observed by other researchers. The adequacy of the model was found to be 97% and able to predict cooling time for a plate thickness ranging from 8 to 41.5 mm thickness.
Redesign of a Compressor Stage for a High-Performance Electric Supercharger in a Heavily Downsized Engine
Authors: Wang Peng , Zangeneh Mehrdad , Richards Bryn , Gray Kevin , Tran James , Andah Asuquo
Published: October 2017

Engine downsizing is a modern solution for the reduction of CO2 emissions from internal combustion engines. This technology has been gaining increasing attention from industry. In order to enable a downsized engine to operate properly at low speed conditions, it is essential to have a compressor stage with very good surge margin. The ported shroud, also known as the casing treatment, is a conventional way used in turbochargers to widen the working range. However, the ported shroud works effectively only at pressure ratios higher than 3:1. At lower pressure ratio, its advantages for surge margin enhancements are very limited. The variable inlet guide vanes are also a solution to this problem. By adjusting the setting angles of variable inlet guide vanes, it is possible to shift the compressor map toward the smaller flow rates. However, this would also undermine the stage efficiency, require extra space for installing the inlet guide vanes, and add costs. The best solution is therefore to improve the design of impeller blade itself to attain high aerodynamic performances and wide operating ranges. This paper reports a recent study of using inverse design method for the redesign of a centrifugal compressor stage used in an electric supercharger, including the impeller blade and volute. The main requirements were to substantially increase the stable operating range of the compressor in order to meet the demands of the downsized engine. The three-dimensional (3D) inverse design method was used to optimize the impeller geometry and achieve higher efficiency and stable operating range. The predicted performance map shows great advantages when compared with the existing design. To validate the computational fluid dynamics (CFD) results, this new compressor stage has also been prototyped and tested. It will be shown that the CFD predictions have very good agreement with experiments and the redesigned compressor stage has improved the pressure ratio, aerodynamic efficiency, choke, and surge margins considerably.
The Increasing Complexity of Hot Corrosion
Authors: Shifler David A.
Published: October 2017

It has been conjectured that if sulfur in fuel is removed, engine materials will cease to experience attack from hot corrosion, since this sulfur has been viewed as the primary cause of hot corrosion and sulfidation. Historically, hot corrosion has been defined as an accelerated degradation process that generally involves deposition of corrosive species (e.g., sulfates) from the surrounding environment (e.g., combustion gas) onto the surface of hot components, resulting in destruction of the protective oxide scale. Most papers in the literature, since the 1970s, consider sodium sulfate salt as the single specie contributing to hot corrosion. Recent Navy standards for Navy F-76 and similar fuels have dropped the sulfur content down to 15 parts per million (ppm). Most observers believe that the removal of sulfur will end hot corrosion events in the Fleet. However, the deposit chemistry influencing hot corrosion is known to be much more complex consisting of multiple sulfates and silicates. Sulfur species may still enter the combustion chamber via ship's air intake, which may include seawater entrained in the air. In addition to sodium sulfate, seawater contains magnesium, calcium and potassium salts, and atmospheric contaminants that may contribute to hot corrosion. This paper will cover some of the revised understanding of hot corrosion and consider other possible contaminants that could further complicate a full understanding of hot corrosion.
Performance Evaluation of a Molten Carbonate Fuel Cell/Micro Gas Turbine Hybrid System With Oxy-Combustion Carbon Capture
Authors: Ahn Ji Ho , Seop Kim Tong
Published: October 2017

Owing to the increasing consumption of fossil fuels and emission of greenhouse gases, interests in highly efficient and low carbon emitting power systems are growing fast. Several research groups have been suggesting advanced systems based on fuel cells and have also been applying carbon capture and storage technology to satisfy the demand for clean energy. In this study, the performance of a hybrid system, which is a combination of a molten carbonate fuel cell (MCFC) with oxy-combustion carbon capture and an indirectly fired micro gas turbine (MGT), was predicted. A 2.5 MW MCFC system that is used in commercial applications was used as the reference system so that the results of the study could be applied to practical situations. The ambient pressure type hybrid system was modeled by referring to the design parameters of an MGT that is currently being developed. A semi-closed type design characterized by flow recirculation was adopted for this hybrid system. A part of the recirculating gas is converted into liquefied carbon dioxide and captured for storage at the carbon separation unit (CSU). Almost 100% carbon dioxide capture is possible with this system. In these systems, the output power of the fuel cell is larger than in the normal hybrid system without carbon capture because the partial pressure of carbon dioxide increases. The increased cell power partially compensates for the power loss due to the carbon capture and MGT power reduction. The dependence of net system efficiency of the oxy-hybrid on compressor pressure ratio is marginal, especially beyond an optimal value.
Numerical Analysis of the Impact of Manufacturing Errors on the Structural Stiffness of Foil Bearings
Authors: Fatu Aurelian , Arghir Mihai
Published: October 2017

The dynamic characteristics of foil bearings operating at high rotation speeds depend very much on the mechanical characteristics of the foil structure. For this reason, the stiffness and damping of the structure of foil bearings are problems that are the focus of many analyses. The mechanical characteristics of the foil structure (top and bump foil) are analyzed either by using a simple approach obtained for an isolated bump modeled as a beam or with more elaborate ones taking into account the three-dimensional nature of the bumps and their mutual interactions. These two kinds of models give different foil structure stiffness, with lower values for the simplified model. However, the published experimental results of the foil bearing structure tend to validate the simplified model. The present paper explains the differences between the simplified and the elaborate models by taking into account the manufacturing errors of the foil structure. A three-dimensional model based on the nonlinear theory of elasticity is developed. The model offers a unique insight into the way the bearing structure deforms when the rotor is incrementally pushed into the foil structure. Three realistic manufacturing errors, bump height, bump length, and radius of the bump foil, are analyzed. Bump height and length vary following a normal distribution with a given standard deviation while the radius of the bump foil is given a waviness form with an imposed peak-to-peak amplitude. Three to five cases were calculated for each kind of error. Results show that only the manufacturing errors of the bump height affect the stiffness of the foil structure by diminishing its values. Height errors of 20 μm standard deviation (4% of the average bump height and 60% of the radial clearance) may induce a 40–50% reduction of the stiffness of the foil structure, i.e., in the range of the predictions of the simplified model.
Correcting Inflow Performance Relationship Curves for Explicitly Coupling Reservoir Simulations and Production Systems Simulations
Authors: von Hohendorff Filho João Carlos , Schiozer Denis José
Published: October 2017

There are many ways to integrate reservoir and production system simulations to forecast production, in a single model (implicit) or in coupled models (explicit). Explicit coupling, a simple and flexible coupling method, has the advantage of using commonly available commercial software to integrate reservoir and production systems simulations. However, explicit coupling may produce large deviations as the inflow performance relationship (IPR) curve, which combines well pressure and production and injection rates, can only be evaluated or amended at the beginning of a time-step. As the IPR curve changes during a time-step, it may be necessary to correct unstable results for well pressure and rates. Using a previously proposed IPR correction method, numerical stability was improved, reducing deviations during advancing the time step. A formula was created to support the correction of IPR curve. The methodology was tested using cases with known responses for pressures and flow rates, for a predetermined production strategy from the benchmark case UNISIM-I-D. Deviations were reduced to near zero when compared with uncoupled and decoupled methodologies to integrate reservoir with production system simulations.
Solar Heat Underground Storage Based Air Conditioning Vis-à-Vis Conventional HVAC Experimental Validation
Authors: de Nardin Carlos R. , Fernandes Felipe T. , Longo Adriano J. , Lima Luciano P. , Farret Felix A. , Simões Marcelo G.
Published: October 2017

This paper presents a comparison of air conditioners using the conventional heating, ventilation, and air conditioning heat pumps and the one using solar heat stored underground, also known as shallow geothermal air conditioning. The proposed air conditioner with solar heat stored underground reunites practical data from an implementation of the heuristic perturb-and-observe (P&O) control and a heat management technique. The aim is to find out the best possible heat exchange between the room ambient and the underground soil heat to reduce its overall consumption without any heat pump. Comparative tests were conducted in two similar rooms, each one equipped with one of the two types of air conditioning. The room temperature with the conventional air conditioning was maintained as close as possible to the temperature of the test room with shallow geothermal conditioning to allow an acceptable data validation. The experiments made both in the winter of 2014 and in the summer of 2015 in Santa Maria, South Brazil, demonstrated that the conventional air conditioner consumed 19.08 kWh and the shallow geothermal conditioner (SGC) consumed only 4.65 kWh, therefore, representing a reduction of energy consumption of approximately 75%.
Effective Prediction and Management of a CO2 Flooding Process for Enhancing Oil Recovery Using Artificial Neural Networks
Authors: Van Si Le , Chon Bo Hyun
Published: October 2017

The injection of CO2 has been in global use for enhanced oil recovery (EOR) as it can improve oil production in mature fields. It also has environmental benefits for reducing greenhouse carbon by permanently sequestrating CO2 (carbon capture and storage (CCS)) in reservoirs. As a part of numerical studies, this work proposed a novel application of an artificial neural network (ANN) to forecast the performance of a water-alternating-CO2 process and effectively manage the injected CO2 in a combined CCS–EOR project. Three targets including oil recovery, net CO2 storage, and cumulative gaseous CO2 production were quantitatively simulated by three separate ANN models for a series of injection frames of 5, 15, 25, and 35 cycles. The concurrent estimations of a sequence of outputs have shown a relevant application in scheduling the injection process based on the progressive profile of the targets. For a specific surface design, an increment of 5.8% oil recovery and 4% net CO2 storage was achieved from 25 cycles to 35 cycles, suggesting ending the injection at 25 cycles. Using the models, distinct optimizations were also computed for oil recovery and net CO2 sequestration in various reservoir conditions. The results expressed a maximum oil recovery from 22% to 30% oil in place (OIP) and around 21,000–29,000 tons of CO2 trapped underground after 35 cycles if the injection began at 60% water saturation. The new approach presented in this study of applying an ANN is obviously effective in forecasting and managing the entire CO2 injection process instead of a single output as presented in previous studies.
Dose Rates From the Accidental Withdrawal of a Fuel Element From an Open Pool-Type Reactor
Authors: Abdelhady Amr
Published: October 2017

This paper studies the radiological consequences resulting from withdrawal of nuclear fuel element (FE) from a core of open pool type reactor during normal operation. The FE withdrawal accident may be occurred due to human error during routine transport of spent FE process or from failure of FE clamp during reactor normal operation. For both cases, the FE will move vertically upward toward pool water surface. In case of accidental failure of fuel clamp, a negative reactivity insertion in the core after FE withdrawal and the reactor will be shutdown. MCNP5 code was used in this study to calculate the radiation dose rate levels in the reactor hall and inside the control room during FE withdrawal. The results show that the operator in control room will receive dose rate lower than permissible dose rate limit when FE reaches at depths more than to 211 cm for vertical FE and at depths more than to 246 cm for horizontal FE.
Stand-Alone Containment Analysis of the Phébus Fission Products Test 1 With the ASTEC and the MELCOR Codes
Authors: Gonfiotti Bruno , Paci Sandro
Published: October 2017

The estimation of fission products (FPs) release from the containment system of a nuclear plant to the external environment during a severe accident (SA) is a quite complex task. In the last 30–40 yr, several efforts were made to understand and to investigate the different phenomena occurring in such a kind of accidents in the primary coolant system and in the containment. These researches moved along two tracks: understanding of involved phenomenologies through the execution of different experiments and creation of numerical codes capable to simulate such phenomena. These codes are continuously developed to reflect the actual SA state of the art, but it is necessary to continuously check that modifications and improvements are able to increase the quality of the obtained results. For this purpose, also a continuous verification and validation work should be carried out. Therefore, the aim of the present work is to re-analyze the Phébus fission products test 1 (FPT-1) test employing the accident source term evaluation code (ASTEC) and MELCOR codes (respectively, ASTEC v.2.0 revision 3 patch 3 and MELCOR V2.1.6840 version). The analysis focuses on the stand-alone containment aspects of the test, and three different modelizations of the containment vessel have been developed showing that at least 15/20 control volumes (CVs) are necessary for the spatial schematization to correctly predict the test thermal hydraulics and the aerosol behavior. Furthermore, the paper summarizes the main thermal-hydraulic results and presents different sensitivity analyses carried out on the aerosols and FPs behavior.
Full-Scale Measurement on the Aerodynamics of Nonplanar Rotor Pairs in a Hexacopter
Authors: Lei Yao , Ji Yuxia , Wang Changwei , Bai Yue , Xu Zhijun
Published: October 2017

This paper presents an original Hexacopter with three nonplanar rotor pairs where the variable thrust is provided by fixed-pitch rotors with variable speed. The corresponding face-to-face rotor pair (F–F) and back-to-back rotor pair (B–B) are proposed as the research components to maximize the overall aerodynamic performance with different transverse spacings and disk plane angles. Together with the rotor interactions involved in low Reynolds number (Re) environments, experiments in the presence of the uncertainty analysis are performed to validate the aerodynamic interference and test the effectiveness of the proposed rotor pairs. Experimental results show that the performance of the rotor pair can be improved significantly by having an optimal combination with a larger angle and a moderate spacing. Indeed, the aerodynamic interactions between the two rotors decrease with a larger disk plane angle, and the aerodynamic interference of the rotor pairs is mainly involved in the face to face type. Furthermore, parametric studies were also performed to study the effects of low Re and to attempt to maximize the thrust and minimize the total power required in hover flight. Useful conclusions are provided for the further aerodynamic analysis and control strategy to meet design requirements.
Ranking Ideas for Diversity and Quality
Authors: Ahmed Faez , Fuge Mark
Published: October 2017

When selecting ideas or trying to find inspiration, designers often must sift through hundreds or thousands of ideas. This paper provides an algorithm to rank design ideas such that the ranked list simultaneously maximizes the quality and diversity of recommended designs. To do so, we first define and compare two diversity measures using determinantal point processes (DPP) and additive submodular functions. We show that DPPs are more suitable for items expressed as text and that a greedy algorithm diversifies rankings with both theoretical guarantees and empirical performance on what is otherwise an NP-Hard problem. To produce such rankings, this paper contributes a novel way to extend quality and diversity metrics from sets to permutations of ranked lists. These rank metrics open up the use of multi-objective optimization to describe trade-offs between diversity and quality in ranked lists. We use such trade-off fronts to help designers select rankings using indifference curves. However, we also show that rankings on trade-off front share a number of top-ranked items; this means reviewing items (for a given depth like the top ten) from across the entire diversity-to-quality front incurs only a marginal increase in the number of designs considered. While the proposed techniques are general purpose enough to be used across domains, we demonstrate concrete performance on selecting items in an online design community (OpenIDEO), where our approach reduces the time required to review diverse, high-quality ideas from around 25 h to 90 min. This makes evaluation of crowd-generated ideas tractable for a single designer. Our code is publicly accessible for further research.
A Detailed Comparison on the Influence of Flow Unsteadiness Between the Vaned and Vaneless Mixed-Flow Turbocharger Turbine
Authors: Padzillah M. H. , Rajoo S. , Martinez-Botas R. F.
Published: October 2017

A turbocharger is a key enabler for lowering CO2 emission of an internal combustion engine (ICE) through the reutilization of the exhaust gas energy that would otherwise have been released to the ambient. In its actual operating conditions, a turbocharger turbine operates under highly pulsating flow due to the reciprocating nature of the ICE. Despite this, the turbocharger turbines are still designed using the standard steady-state approach due to the lack of understanding of the complex unsteady pressure and mass propagation within the stage. The application of guide vanes in a turbocharger turbine stage has increased the complexity of flow interactions regardless of whether the vanes are fixed or variable. Although it is enticing to assume that the performance of the vaned turbine is better than the one without (vaneless), there are currently no tangible evidences to support this claim, particularly during the actual pulsating flow operations. Therefore, this research looks into comparing the differences between the two turbine arrangements in terms of their performance at flow field level. For this purpose, a three-dimensional (3D) “full-stage” unsteady turbine computational fluid dynamics (CFD) models for both volutes are constructed and validated against the experimental data. These models are subject to identical instantaneous inlet pressure profile of 60 Hz, which is equivalent to an actual three-cylinder four-stroke engine rotating at 2400 rpm. A similar 95.14 mm diameter mixed-flow turbine rotor rotating at 48,000 rpm is used for both models to enable direct comparison. The complete validation exercises for both steady and unsteady flow conditions are also presented. Results have indicated that neither vaned nor vaneless turbine is capable of maintaining constant efficiency throughout the pulse cycle. Despite that, the vaneless turbine indicated better performance during peak power instances. This work also showed that the pulsating pressure at the turbine inlet affected the vaned and vaneless turbines differently at the flow field level. Furthermore, results also indicated that both the turbines matched its optimum incidence angle for only a fraction of pulse cycle, which is unfavorable.
Characterization of Nonequilibrium Condensation of Supercritical Carbon Dioxide in a de Laval Nozzle
Authors: Lettieri Claudio , Paxson Derek , Spakovszky Zoltan , Bryanston-Cross Peter
Published: October 2017

Carbon capture and storage could significantly reduce carbon dioxide (CO2) emissions. One of the major limitations of this technology is the energy penalty for the compression of CO2 to supercritical conditions. To reduce the power requirements, supercritical carbon dioxide compressors must operate near saturation where phase change effects are important. Nonequilibrium condensation can occur at the leading edge of the compressor, causing performance and stability issues. The characterization of the fluid at these conditions is vital to enable advanced compressor designs at enhanced efficiency levels but the analysis is challenging due to the lack of data on metastable fluid properties. In this paper, we assess the behavior and nucleation characteristics of high-pressure subcooled CO2 during the expansion in a de Laval nozzle. The assessment is conducted with numerical calculations and corroborated by experimental measurements. The Wilson line is determined via optical measurements in the range of 41–82 bar. The state of the metastable fluid is characterized through pressure and density measurements, with the latter obtained in a first-of-its-kind laser interferometry setup. The inlet conditions of the nozzle are moved close to the critical point to allow for reduced margins to condensation. The analysis suggests that direct extrapolation using the Span and Wagner equation of state (S–W EOS) model yields results within 2% of the experimental data. The results are applied to define inlet conditions for a supercritical carbon dioxide compressor. Full-scale compressor experiments demonstrate that the reduced inlet temperature can decrease the shaft power input by 16%.
Pressure Measurements in a Wire-Wrapped 61-Pin Hexagonal Fuel Bundle
Authors: Vaghetto Rodolfo , Jones Philip , Goth Nolan , Childs Mason , Lee Saye , Thien Nguyen Duy , Hassan Yassin A.
Published: October 2017

To achieve longer-life liquid-metal fast reactor cores, designers are considering to increase the wall gap of the wire-wrapped hexagonal fuel bundles to account for volumetric void swelling and radiation creep. A new wire-wrapped hexagonal test bundle has been constructed, with a wall gap larger than prior experiments, and experimental pressure drop data have been generated under laminar, transition, and turbulent flow regimes (corresponding to Re of 250–19,000), to complement the existing database of small wall gap experimental bundles. The comparison of the experimental data set with the predictions of four existing correlations (Baxi and Dalle Donne, Cheng and Todreas detailed (CTD), Kirillov, and Rehme) showed general agreement between data and the selected correlations. However, the CTD correlation most accurately predicted the experimental trend and the transition between flow regimes. The analysis of the experimental data also revealed that the larger wall gap size caused a lower bundle pressure drop due to the increased bypass flow area.
Design of the Solenoid Valve of an Antilock Braking System With Reduced Flow Noise
Authors: Joong Kim Seung , Jin Sung Hyung
Published: October 2017

Large eddy simulations are carried out to predict the flow noise produced in the solenoid valve of an antilock braking system (ABS) using Lighthill’s acoustic analogy and the Ffowcs Williams and Hawkings (FW–H) surface integral method. The fluid inside the valve is assumed to be incompressible at a fixed temperature. The solenoid valve operation is realized by applying an overset grid methodology to the moving plunger, and the plunger has a linear motion in the axial direction. Several types of solenoid valves are numerically designed to maximally reduce the flow noise. The upstream flow is detached through a small opening between the plunger and the seat, which generates pressure fluctuation around the narrow gap, which is subject to high wall pressure fluctuations and shear stresses. Large eddy simulations are performed by varying the position of the flow separation. An optimal design of the valve is obtained, featuring a small radius of surface curvature, a smooth surface, and a large plunger tip area angle. Measurements are obtained from the optimal design to validate the design in a real vehicle performance test, and the predicted pressure frequency in the solenoid valve agreed well with the experimental results.
Effects of Steam Ingestion on Under Fuselage Inlet Performance During a Catapult-Assisted Takeoff Process
Authors: Fan Yuehua , Gao Zhenxun , Jiang Chongwen , Lee Chun-Hian
Published: October 2017

A naval aircraft has the potential to experience inlet performance decline when taking off from the carrier deck with the steam-driven catapult assistance. The steam ingested into inlet may cause time-dependent rise and spatial distortion of the total temperature on the inlet–exit, which would decrease the compressor stall margin and then lower the performance of the turbine engine. In this paper, these temporal and spatial temperature nonuniformities are numerically studied using the dual-time-step transient method with a real aircraft/inlet model taken into account. The flowfield characteristics of a designed baseline case are first analyzed, indicating that the engine’s suction effect and the wind velocity relative to the aircraft are two key factors affecting the steam ingestion. The former is dominant at the beginning of takeoff since the aircraft's velocity is low, while the latter is increasingly significant as the aircraft accelerates. Next, parametric studies show that the greater the wind speed is, the less significantly the flowfield of the inlet–exit would be influenced by the steam. The effects are also studied among various steam leakage profiles—two are constant in time histories of the steam leakage rate, whereas the other two are nonlinear with the maximum value at different instants. It is found that the temperature rise rate of the inlet–exit would increase apparently if the steam leakage rate reaches the maximum earlier.
A Novel Modeling Approach to Simulate Rolling Contact Fatigue and Three-Dimensional Spalls
Authors: Walvekar Aditya A. , Morris Dallin , Golmohammadi Zamzam , Sadeghi Farshid , Correns Martin
Published: October 2017

In this study, a new approach has been developed to simulate three-dimensional (3D) experimental rolling contact fatigue (RCF) spalls using a two-dimensional (2D) finite element (FE) model. The model introduces a novel concept of dividing the 3D Hertzian pressure profile into 2D sections and utilizing them in a 2D continuum damage mechanics (CDM) RCF model. The distance between the two sections was determined by the size of the grains in the material microstructure. The 2D RCF model simulates characteristics of case carburized steels by incorporating hardness gradient and residual stress (RS) distribution with depth. The model also accounts for the topological randomness in the material microstructure using Voronoi tessellation. In order to define the failure criterion for the current model, sub-surface stress analysis was conducted for the Hertzian elliptical contact. It was predicted that the high shear stress region near the end of the major axis of the contact is the cause of catastrophic damage and spall formation. This prediction was validated by analyzing the spalls observed during RCF experiments using a surface profilometer. The model was implemented to predict RCF lives for 33 random material domains for different contact geometry and maximum Hertzian pressures. The model results were then compared to the RCF experiments conducted on two different test rigs, a three-ball-on-rod and a thrust bearing test apparatus (TBTA). It was found that the RCF lives obtained from the model are in good agreement with the experimental results. The results also demonstrated that the spalls generated using the analytical results resemble the spalls observed in experiments.
Tribo-Investigations on Oils With Dispersants and Hexagonal Boron Nitride Particles
Authors: Gupta Manoj Kumar , Bijwe Jayashree , Kadiyala Ajay Kumar
Published: October 2017

A dispersant is almost an unavoidable additive in engine oils since it helps to keep the carbonaceous particles in a suspended form. Dispersants can be multifunctional and can therefore interfere with the functions of other additives either synergistically or antagonistically. The present work investigated the influence of four dispersants (with and without particles of hexagonal boron nitride (hBN) on selected lubrication-related properties of the oils using four ball tester. Particles of hBN, though known as effective anti-wear (AW) and anti-friction (AF) additives, did not prove effective in oil in the presence of dispersants. On the other hand, it proved to be a good extreme pressure (EP) additive by showing 27% improvement in weld load (WL). Worn surfaces were examined using scanning electron microscopy (SEM), energy dispersion X-ray analysis (EDAX), and Raman spectroscopy.
Shock Analysis of a Stern Ramp Using Dynamic Design Analysis Method
Authors: Ringsberg Jonas W. , Johnson Erland , Zhang Meng , Yu Yunbo
Published: October 2017

Shock load caused by underwater explosion in naval battles can lead to malfunction of the equipment on-board naval vessels. It makes the ships vulnerable and they can lose the ability to accomplish their missions. This study presents a shock analysis, using the dynamic design analysis method (DDAM), of a naval ship stern ramp subjected to a non-contact underwater explosion. The objective is to evaluate the performance of the ramp subjected to a shock load, identify areas for structural improvements and recommend design changes. The DDAM in the commercial software ANSYS is used in the evaluation of the ramp. The structural response to the shock load is estimated by combined modal and response spectrum analyses. The shock load is applied in three directions (vertical, fore and aft, athwart ships) and the results show that the vertical direction is the most severe loading direction and critical to the functionality of the ramp. A parametric study is presented which shows which parameters that influence the most the structural response. The results from this study are used to suggest improvements of the ramp structure to make it more resistant to shock loads.
Effect of Drainage on Upheaval Buckling Susceptibility of Buried Pipelines
Authors: Tom Joe G. , White David J.
Published: October 2017

This paper investigates the effect of soil drainage on the uplift resistance of buried pipelines, and their susceptibility to upheaval buckling. The uplift resistance of buried pipelines is considered through analytical and numerical predictions for both drained and undrained conditions. Combinations of soil strength parameters for typical soils are estimated based on common correlations. For certain ranges of typical normally consolidated soil conditions, particularly those with high critical state friction angles, the drained uplift resistance may be lower than the undrained resistance. This observation is important because in typical practice only drained or undrained behaviour is considered depending on the general type of soil backfill used. In this case, the critical or minimum uplift resistance may be overlooked. Further, the changing undrained uplift mechanism between shallow and deep conditions is investigated. It is found that the common approach of considering the minimum of either a local (flow around) or global (vertical slip plane) failure can overestimate the uplift resistance in normally consolidated soils.
Wellhead Monitoring: Measured Fatigue Damage Validation
Authors: Kebadze Elizbar B. , Killbourn Stuart , Henderson John , Chomczuk Gavin , Mosley Andrew , Bolger David , Maher Jim
Published: October 2017

A hydroacoustic monitoring system is deployed on a BOP-stack and riser during drilling of production wells to record fatigue accumulation in the subsea wellhead and conductor. Data is relayed to the vessel in real-time so that well operations can be planned to manage fatigue life. The monitoring assures the asset integrity is maintained throughout its lifecycle: construction, work-over operations and abandonment.

Motion measurements of the BOP-stack and riser are analysed in conjunction with a finite-element model of the wellhead-BOP-riser-vessel system to determine stresses at various welds and hotspots. The main drawback of such an approach is that “measured” fatigue still relies on the model accuracy, which cannot be guaranteed due to uncertainty associated with many parameters used in modelling.

This paper describes validation of the modelled subsea stack and its foundation characteristics against measurements so that “measured” fatigue is as accurate as possible. This involves (1) determining the depth of BOP-stack centre of rotation; (2) identifying the BOP-stack characteristic frequency, and (3) matching stress responses derived from measurements taken at different heights on the stack. Model parameters (e.g. soil stiffness and added mass) are tailored to optimise agreement with measurements thereby improving the accuracy of “measured” fatigue estimations.
Hydroelastic Response of Very Large Floating Structures (VLFS) Connected With Wind Turbines
Authors: Muhamed Basheer Naseema Sibin , Saha Nilanjan
Published: October 2017

Very large floating structure (VLFS) technology is a novel idea being introduced in ports and harbors, fishing, land reclamation, petroleum product storage facilities and so on. The flexible nature of VLFS makes the response hydroelastic and it is important to have a reduced response of VLFS. The term hydroelasticity refers to the action of hydrodynamic excitation over elastic body limits. The present study tries to examine the combined effect of horizontal loads of wind turbine tower along with the vertical hydrodynamic loads which question the stability of the performance of VLFS. This would lead to better understanding of the hydroelastic response of integrated wind farm-VLFS configuration. To examine the effect of relevant parameters on the VLFS hydrodynamic responses, motion amplitude transfer functions (RAO) for a wide range of wave frequencies are computed.

Pontoon type VLFS are giant platforms resting on the sea surface, which are modeled by very large plates according to the Mindlin thick plate theory. The boundary integral element method (BIEM) is used to solve for the velocity potential using Laplace equation providing suitable boundary conditions. The fluid model is based on linear wave hypothesis. The effect of wind on wind turbines which are located at the edges and corner of the VLFS is investigated in the model. The Kaimal wind spectrum is used to generate time series of wind speed incident on the blades of the turbine and loads are computed using blade element momentum theory as in wind simulator FAST (Fatigue, Aerodynamics, Structures, and Turbulence).

The finite element framework is used to develop the model and to find the hydrodynamic loading. Mooring line connections are used to reduce structural instability. In order to reduce the hydroelastic response of VLFS, connection with hinges or semi rigid line connections are observed to be effective. The elastic and dynamic effects of the combined wind-wave loading over the integrated VLFS are being considered. The hydroelastic effects of mooring lines will not be accounted for.
Electric Impulse Drilling: Future-Orientated HT/HP Analysis of Drilling Fluids
Authors: Lehmann Franziska , Beier Katja , Schulz Anne , Anders Erik
Published: October 2017

Modern rheological analyses provide good possibilities to understand the deformation and flow of fluids under different conditions. These methods used so far in the food industry as well as in the paints and coatings industry should transferred to the oil and gas industry, especially to the drilling fluid sector, to understand the drilling fluid behavior under borehole conditions. Traditionally, the rheology of drilling fluids is based on measurements under atmospheric conditions. The present study describes a new HT/HP measuring system by Anton Paar GmbH consisting of a modern rheometer including a high-pressure cell. This new system allows rheological analyses under a pressure up to 1000 bar and a temperature up to 300 °C. In consequence it is possible to observe conventional challenges within the drilling fluid sector under new points of view. Within the present study different drilling fluid systems were analyzed under common as well as under new rheological aspects. The results of both measuring systems were compared to each other. Furthermore, drilling fluid properties such as density, filtration and settling behavior were determined under different temperature regimes. Regarding to the operating principle of the electric impulse drilling (EID) technique the electric conductivity plays an important role and has to be taken into account. The results of these tests are also presented shortly.
Integrated System to Evaluate Moored Ship Behavior
Authors: Peña E. , Figuero A. , Sande J. , Guerra A. , Perez J. D. , Maciñeira E.
Published: October 2017

The development of loading and unloading operations is an essential part of the logistical chain of maritime transportation. One of the determining factors in this process is the movement of moored ships, which has a notable influence over the efficiency of the operation. The implementation of systems to characterize their real behavior would provide an important tool for the management of these activities.

In this context the Water and Environmental Engineering Group (GEAMA) at the University of A Coruña, Spain (UDC), through different projects executed in collaboration with the Port Authority of A Coruña (Spain), has developed an integrated system for monitoring the dynamic behavior of moored vessels. This system includes different devices which allow to characterize their six degrees of freedom and tensions in certain mooring lines.

The analysis of motions is carried out using three combined technologies. Ship rotations (roll, pitch and yaw) are registered by means of an Inertial Measurement Unit (IMU) developed by the Research Group. The translations of heave and surge are analyzed with a visual tracking system using fixed cameras deployed near the location. Finally, the evaluation of sway motion and an additional measure of yaw are obtained using two laser-distance meters located over the dock.

All devices integrated in the system were calibrated in laboratory at the R+D Centre CITTEC-UDC with several series of tests. Once the methodology was validated, the system has been employed in different projects carried out in Inner and Outer Ports of the city of A Coruña, with more than 30 monitored ships.