bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving Vegetable Oil Fueled CI Engine Characteristics Through Diethyl Ether Blending
Authors: Vedharaj S. , Vallinayagam R. , Sarathy S. Mani , Dibble Robert W.
Published: December 2016

In this research, the flow and ignition properties of vegetable oil (VO) are improved by blending it with diethyl ether (DEE). DEE, synthesized from ethanol, has lower viscosity than diesel and VO. When DEE is blended with VO, the resultant DEEVO mixtures have favorable properties for compression ignition (CI) engine operation. As such, DEEVO20 (20% DEE + 80% VO) and DEEVO40 (40% DEE + 60% VO) were initially considered in the current study. The viscosity of VO is 32.4*10−6 m2/s; the viscosity is reduced with the increase of DEE in VO. In this study, our blends were limited to a maximum of 40% DEE in VO. The viscosity of DEEVO40 is 2.1*10−6 m2/s, which is comparable to that of diesel (2.3*10−6 m2/s). The lower boiling point and flash point of DEE improves the fuel spray and evaporation for DEEVO mixtures. In addition to the improvement in physical properties, the ignition quality of DEEVO mixtures is also improved, as DEE is a high cetane fuel (DCN = 139). The ignition characteristics of DEEVO mixtures were studied in an ignition quality tester (IQT). There is an evident reduction in ignition delay time (IDT) for DEEVO mixtures compared to VO. The IDT of VO (4.5 ms), DEEVO20 (3.2 ms) and DEEVO40 (2.7 ms) was measured in IQT. Accordingly, the derived cetane number (DCN) of DEEVO mixtures increased with the increase in proportion of DEE.

The reported mixtures were also tested in a single cylinder CI engine. The start of combustion (SOC) was advanced for DEEVO20 and DEEVO40 compared to diesel, which is attributed to the high DCN of DEEVO mixtures. On the other hand, the peak heat release rate decreased for DEEVO mixtures compared to diesel. Gaseous emissions such as nitrogen oxide (NOX), total hydrocarbon (THC) and smoke were reduced for DEEVO mixtures compared to diesel. The physical and ignition properties of VO are improved by the addition of DEE, and thus, the need for the trans-esterification process is averted. Furthermore, this blending strategy is simpler and enables operation of straight run oils and fats in CI engine, replacing diesel completely.
Control Oriented Modelling of Engine IMEP Variation
Authors: Zhu Qilun , Prucka Robert , Wang Shu , Prucka Michael , Dourra Hussein
Published: December 2016

Engine cycle-by-cycle combustion variation is a potential source of emissions and drivability issues in automobiles, and has become an important concern for engine control engineers. The nature of turbulent combustion in IC engines means that combustion variations cannot be eliminated completely. Furthermore, it is inevitable for the engine to run at conditions with high combustion variations in most vehicle applications. For example, during gear shifts spark timing can be changed dramatically to help track the fast transitions of torque demand, often resulting in high Coefficient of Variation in Indicated Mean Effective Pressure (COV of IMEP). Under these circumstances, the control engineers have to weigh between combustion variation and other performance demands (i.e. fast torque tracking). An accurate online estimation of COV of IMEP can be beneficial to this process. A calibrated map of COV of IMEP versus engine operating conditions can be an option for engines with few control actuators. As the number of control actuators increases, combustion variation modelling using inputs with physical representations becomes favorable due to the potential for reduced calibration effort. However, since COV of IMEP is a stochastic variable describing the distribution of IMEP output, it can only be modelled empirically. This research proposes a control-oriented real-time COV of IMEP model based on an Artificial Neural Network (ANN) and inputs from turbulent combustion research. The effects of premixed turbulent combustion variation are analyzed with flame regime analysis in this research after a brief introduction of the experimental setup and engine information. In-cylinder thermodynamics are then evaluated to reveal how the changes of heat release transform into the variation of cylinder pressure, producing COV of IMEP. A range of model input parameters are assessed to determine the set that produces the most accurate prediction of IMEP variation with minimal computational requirements. An Artificial Neural Network (ANN) is applied to capture the nonlinear coupled correlations between COV of IMEP and model inputs. The ANN is combined with a regression pretreatment to reduce network size and improve extrapolation stability. This computationally efficient single-layer three-neuron ANN COV of IMEP model achieved 0.29% normalized Root Mean Square Error (RMSE). Dynamometer tests show that the model performs well outside the training region.
Variable Intake Valve Train to Optimize the Performance of a Large Bore Gas Engine
Authors: Zelenka Jan , Hoff Claudio , Wimmer Andreas , Berger Roland , Thalhauser Josef
Published: December 2016

The present paper describes the investigations made using the electro-hydraulic intake valve timing system VCM® on a large bore gas engine. The first section explains what challenges have to be faced when developing concepts for present and future applications of large bore gas engines. Following an introduction to the VCM® system, an outline is presented of expected opportunities for using variable intake valve timing in combination with modern turbocharging concepts.

The second section describes 0D/1D engine cycle simulations that were carried out to assess the influence of variable valve timing on the intake side compared to a fixed intake valve profile, which is the current standard for large bore gas engines. As a result, first predictions can be made about the gain in engine efficiency achieved with different operating strategies.

In order to assess the performance potentials of the variable valve train, extensive experimental investigations were carried out on a single cylinder research engine based on GE’s Type 6 gas engine. The investigations consisted of varying engine parameters including varying the geometric compression ratio as well as the engine boundary conditions. It will be shown how intake valve timing can be used to optimize engine efficiency by improving gas exchange. Furthermore, variable intake valve timing affects the overall system behavior, e.g. distances to the engine’s operating limits. Special attention was paid to analyzing combustion itself, which is necessary due to the strong influence that intake valve timing has on the thermodynamic states of the cylinder charge.
Effects of Gas Composition on Combustion, Emission and Knocking Characteristics of Marine Lean Burn Gas Engine
Authors: Ichikawa Yasuhisa , Sekiguchi Hidenori , Oleksiy Bondarenko , Yoo Dong-Hoon , Hirata Koichi
Published: December 2016

The present study has experimentally investigated the effect of fuel gas composition on the combustion, emission and knocking characteristics of a marine lean burn gas engine. The experiments was carried out using the lean burn gas engine, which has the rated power output of 400 kW with spark ignition pre-chamber system. The various compositions of the base fuel gas (Japanese city gas) changed by supplying propane-based LPG (liquefied petroleum gas), butane-based LPG and hydrogen.

This paper reports in detail the experimental results on the combustion and emission characteristics of the lean burn gas engine affected by the fuel gas composition.

The experimental results showed that the composition of fuel gas mixed with P-LPG and B-LPG has a small effect on the combustion characteristics, and the operation of the engine is hardly affected. However, the addition of hydrogen causes the rise of the maximum combustion pressure and the attention should be paid on the ratio of hydrogen in the fuel gas.

With regard to the emission characteristics, the NOx emission increased with increasing the ratio of P-LPG, B-LPG and hydrogen in the base fuel gas. The CO emission increased with increasing the ratio of P-LPG and B-LPG and decreased with increasing the ratio of hydrogen in the base fuel gas. It is expected that such the tendencies depended on the carbon quantity in the fuel gas. In addition, it was found that the knocking characteristics are associated with the methane number of fuel gas.
A Comparative Study of Alternative and Conventional Diesel Combustion Modes in a Single Cylinder Engine With a Single Injection Event
Authors: Cowart Jim , Hamilton Len , Luning Prak Dianne
Published: December 2016

A broadly ranging single injection event was used in a Waukesha diesel CFR engine in order to explore various conventional and alternative combustion modes at light load (2 bar GMEP) using n-heptane fuel. Start of injection (SOI) was varied from the start of the intake valve open (IVO) event all the way past TDC at the end of the compression stroke. Emissions, including detailed particulate, were collected at all of the operating points. Additionally, further experiments were performed with port fuel injection in order to create a homogeneous charge compression ignition (HCCI) combustion mode as well as partially premixed combustion (PPC) using both port and direct fuel injection.

HCCI and PPC combustion modes were achieved with the characteristic rise in carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions with however, a corresponding decrease in NOx emissions as compared to conventional direct (into cylinder) injection combustion modes. For conventional diesel operation with progressive advancement of SOI it was seen that start of combustion (SOC) advanced and then retarded slightly before stabilizing. This was associated with a general lengthening of ignition delay (IGD) with progressive SOI advancement. Even with very early intake valve open (IVO) injection events, the emissions behavior did not approach HCCI or PPC, suggesting that the charge mixture homogeneity of companion port injection could not be achieved in this engine using direct injection alone.

High speed optical natural light filming of the combustion events through a large quartz window showed conventional diesel combustion with strong diffusion flames, reducing in intensity with PPC operation, and then no visible combustion with HCCI.
The Effect of Grid Resolution on Predicted Spray Variability Using Multiple Large-Eddy Spray Simulations
Authors: Van Dam Noah , Som Sibendu , Swantek Andrew B. , Powell Christopher F.
Published: December 2016

Shot-to-shot spray variability is recognized as an important contributor to cycle-to-cycle variations in direct-injection engines. Large-eddy Simulations (LES) have been used to resolve more of the gas-phase turbulent fluctuations in Computational Fluid Dynamics (CFD) simulations, but the sources of shot-to-shot spray variability are not directly modeled in the Lagrangian parcel approach used most often for engine fuel spray simulations. Instead, the variability comes from variations in the spray boundary conditions. Currently, the most common way to introduce shot-to-shot variability in Lagrangian spray simulations is to vary the random seed used in the spray models for each spray realization. This approach was used to compare against recent near-nozzle (up to ≈9 mm downstream) projected mass density (PMD) measurements of a single-hole diesel injector. The injector has a nominal nozzle diameter of 110 μm, though analysis of experimental data indicates the actual diameter is approximately 118 μm. The measurements were acquired under non-vaporizing conditions using fast radiography with high-intensity X-rays available at the Advanced Photon Source at Argonne National Laboratory.

Spray simulations used the Dynamic Structure LES turbulence model along with a Lagrangian parcel approach with the blob injection model and modified KH-RT break-up model. 10 spray realizations were simulated each at three different minimum cell sizes, 62.5 μm, 93.75 μm and 125 μm. This is much finer mesh resolution than is typically performed for Lagrangian spray calculations and allows the simulations to capture more of the gas-phase turbulent fluctuations that develop from the different random seeds. The effect of the grid resolution on the predicted shot-to-shot variability was investigated. Larger minimum cell sizes increased the predicted variability in projected mass density slightly. This difference in predicted variability was less apparent in global spray quantities such as penetration length.

Initial turbulence kinetic energy (TKE) variations have also been proposed as a method to introduce shot-to-shot variations in spray simulations. 10 further simulations were run where the initial turbulence intensity was varied randomly between 0.1 and 1 m2/s2. The resulting spray variability was similar, but slightly lower than that introduced by varying the random seed.
Syngas Laminar Flame Speed Computation and its Application to Gaseous Fueled Spark Ignited Engines Performance Prediction
Authors: Xu Hui , LaPointe Leon A. , Bremmer Robin J.
Published: December 2016

Gaseous fueled spark ignited (SI) engines are often developed using pipeline quality natural gas as the fuel. However, natural gas engines are occasionally expected by customers to accommodate different fuel compositions when deployed in the field. Depending on the source or production processing of the fuel and the ambient conditions, gaseous fuels can have different levels of heavy hydrocarbons and/or significant levels of diluents when compared to natural gas. In recent years, there are increasing interests in using synthesis gas (syngas) from renewable sources in gaseous fueled spark ignition engines. This work investigated syngas compositions from different production processes and describes a methodology to predict engine performance using syngas. Syngas composition variations can provide different laminar flame speeds (LFS), which can result in changes in combustion burn rate, heat release rate and knock likelihood, if the engine combustion process is not optimized appropriately. It is challenging to obtain LFS data at the high pressure and temperature conditions that are characteristic of the piston engine combustion process. It has proven to be effective to employ a chemical kinetics solver using an appropriate chemical kinetics mechanism to obtain LFS values under piston engine combustion conditions. Alternative chemical kinetics mechanisms were investigated to identify one which best characterized combustion performance relative to detailed rig and engine measurements. With this appropriate chemical kinetics mechanism, LFS results are now used to guide natural gas engine combustion tuning when using syngas as a fuel. Engine performance is predicted in terms of NOx emissions and knock likelihood using the in-house developed methodology.
Numerical Investigation of Two-Stage Turbocharging Systems Performance
Authors: Avola Calogero , Copeland Colin , Burke Richard , Brace Chris
Published: December 2016

In regulated two-stage sequential turbocharging systems, a smaller, high pressure (HP), and a larger, low pressure (LP), turbocharger are sequentially positioned to recover the energy available in the exhaust gases and deliver acceptable level of boost to the intake of an internal combustion engine. Due to the different sizes of the turbochargers, by-pass valves are placed in the system to control operations.

Due to the turbocharging system layout, it is clear that the air pressurized by the LP compressor enters non-uniformly the HP compressor. This is caused by the rotating radial compressor and the interconnecting bends which cause swirl and velocity to scatter, respectively. Furthermore, the heat transfer in the two turbochargers may have an effect on the apparent efficiencies. For these reasons, the standard mapping approach for turbochargers is not able to take into account the effect of non-uniform flow and heat transfer.

In this paper, a novel approach for mapping the two-stage turbocharging system is proposed and performed into a mono-dimensional simulation code. Although, flow non-uniformity and turbochargers heat transfer effects on the performance of the turbocharging system are not considered, at this present time, the study centralizes on the investigation and the validation of the mapping approach. In fact, a two-stage sequential turbocharging system has been considered for the study and a simulation code to investigate the mapping technique has been implemented.
Tailoring Charge Reactivity Using In-Cylinder Generated Reformate for Gasoline Compression Ignition Strategies
Authors: Ekoto Isaac W. , Wolk Benjamin M. , Northrop William F. , Hansen Nils , Moshammer Kai
Published: December 2016

In-cylinder reforming of injected fuel during an auxiliary negative valve overlap (NVO) period can be used to optimize main-cycle combustion phasing for low-load Low-Temperature Gasoline Combustion, where highly dilute mixtures can lead to poor combustion stability. The objective of this work is to examine the effects of reformate composition on main-cycle engine performance for a research gasoline. A custom alternate-fire sequence with nine pre-conditioning cycles was used to generate a common exhaust temperature and composition boundary condition for a cycle-of-interest. Performance metrics such as main-period combustion stability and total cycle efficiency were collected for these custom cycles. The NVO-produced reformate stream was also separately collected using a dump valve apparatus and characterized in detail using both gas chromatography and photoionization mass spectroscopy. To facilitate gas sample analysis, sampling experiments were conducted using a five-component gasoline surrogate (iso-octane, n-heptane, ethanol, 1-hexene, and toluene) that matched the molecular composition, 50% boiling point, and ignition characteristics of the research gasoline.

For the gasoline, it was found that the most advanced NVO start-of-injection (SOI) led to the most advanced main-cycle 10% burn angle. The effect was more pronounced as the fraction of total fuel injected in the NVO period increased. With the most retarded NVO SOI, shorter residence times and piston spray impingement limited the opportunity for injected fuel decomposition. For the gasoline surrogate, the most advanced NVO SOI had reduced reactivity relative to more intermediate NVO SOI, which was attributed to rapid in-cylinder mixing that led to a large amount of fuel quench in the piston crevice. For all NVO periods, combustion phasing advanced as the main-period fueling decreased. Slower kinetics for leaner mixtures were offset by a combination of increased bulk-gas temperature from higher charge specific heat ratios and increased fuel reactivity due to higher charge reformate fractions.
Insulated Catalyst With Heat Storage for Real World Vehicle Emissions Reduction
Authors: Daya Rohil , Singh Maneet Raj , Hoard John , Chanda Sreedhar
Published: December 2016

In previous publications, the model development and simulation of a vacuum-insulated catalytic converter was presented. GT-Suite model simulations demonstrated the heat retention capacity of the converter, and corresponding emissions reductions. This paper provides an update of the converter model development and analysis of real-world benefits of the converter.

The vehicle-aftertreatment model of the vacuum-insulated converter (VICC) was improved significantly, and detailed explanations of all theoretical modeling considerations are presented. In absence of experimental data, a flow-test experiment was conducted to measure the flow rate in exhaust tailpipe during vehicle soak due to thermosiphon. These results were used as inputs in the GT-Suite model simulations of conventional and hybrid electric vehicles (HEVs). New model simulations demonstrated the ability of the VICC to achieve significant emissions reductions following vehicle soaks of up to 18 hours.

To examine the real-world benefits of the converter, driving data was obtained from the National Renewable Energy Laboratory (NREL), and a MATLAB code was developed to statistically analyze 23,156 drive cycles. The VICC was simulated on standard drive cycles to develop a correlation between melt time of the phase-change material (PCM) and average drive cycle speed and acceleration. This correlation was used to predict the probability that the PCM will melt in a given real-world driving cycle. The MATLAB code was also used to calculate soak time and re-solidification time probability. Finally, FTP emission results were weighted with the soak time probabilities. This analysis showed that in real-world driving conditions, the VICC is expected reduce cold-start CO and HC emissions by 26% and 48% respectively.
Determination of Service Life for Undamaged and Damaged Delayed Coker Drums
Authors: Aumuller John J. , Carucci Vincent A.
Published: December 2016

A stated goal of governments in addressing climate warming and to transition to a low carbon future by the end of this century is to increase the proportion of energy supplied by alternative sources. For the hydrocarbon processing industry, the question of stranded assets will become significant as these alternative energy sources become more prevalent. Existing equipment will need to operate to the end of its useful life and new equipment may need to be avoided. In particular, coker drums are very expensive investments due to their size, materials and number required in the delayed coker unit of a processing facility. Because of the severe service environment in which coke drums operate, the service life of a drum is not well established.

Long term reliability of coker drums is impacted by thermo-mechanical damage mechanisms associated with self constraint of the drum shell and skirt during the formation of hot and cold temperature spots and patches. By assessing the imposed thermomechanical strains, a more precise determination of drum fatigue may be made, allowing better estimation of service life. This service life may be estimated for newly fabricated drums and those drums with shell damage, such as bulging.

Service life determination is of practical importance for operators since it provides a more realistic estimate of operational life as compared to the normally referenced Code design life. An accurate estimation of drum service life has not been available in the industry to date due to a number of deficiencies and conservatisms in the current calculation practices. Insight into the causal damage mechanism provides opportunities in identifying alternatives in design, material selection, fabrication, inspection, and maintenance for operating this equipment to a practical and optimal target service life.
Effects of Additional Gases Resulting From Residual Water Inside ILW Packages
Authors: Nehrig Marko , Wille Frank , Rolle Annette , Linnemann Konrad
Published: December 2016

Packages for intermediate level waste (ILW) often contain residual water besides the actual waste. The water either exists as obvious free water or it may be bound physically or chemically, e.g. as pore water. A water driven gas generation could occur by vaporisation and by radiolysis. Steam as the result of vaporisation causes an increasing pressure inside a package and can affect corrosion. Vaporisation and condensation processes itself change the thermal behavior of the content especially during strongly unsteady thermal situations like accident fire situations. Radiolysis changes the chemical composition of the content which could cause an unexpected interaction, e.g. hydrogen embrittlement. Besides the pressure build-up the radiolysis of water generates hydrogen and oxygen, which can be highly flammable respectively explosive. The gas generation caused by vaporisation and radiolysis must be taken into account during the design and the safety assessment of a package. Pressure build-up, a changed thermal behavior and content chemistry, and especially the risk of accumulation of combustible gases exceeding the limiting concentration for flammability has to be considered in the safety assessment. Approaches to ensure the transportability of stored packages due to radiolysis will be discussed.
Thermal Gradient Within DOE 3013 Containers During Storage
Authors: Hensel Steve J. , Lee Si
Published: December 2016

The Department of Energy (DOE) Model 9975 Package is used to store plutonium bearing materials at the Savannah River Site (SRS). The plutonium is packaged in a 3013 container which consists of a convenience container, an inner welded container, and an outer welded container [1]. All containers are made of stainless steel. A portion of the population of 3013 containers have plutonium oxide with alkaline earth chloride salts. Temperatures and temperature gradients within the 3013 container are useful to evaluate the transport of water vapor and potential corrosion in the inner container, particularly near the weld region. Thermal analyses of plutonium oxide packaged in 3013 containers which are stored in 9975 shipping packages were performed with emphasis on the temperatures and temperature gradients between the plutonium oxide and the inner container weld region. Thermal analyses investigated various plutonium oxide fill levels, heat generation, plutonium oxide thermal conductivity and 9975 package boundary conditions.

Not surprisingly, the results suggest the source heat is mostly dissipated radially outward as opposed to the vertical direction, and the 9975 package is insensitive to an adiabatic top and bottom surface boundary condition versus an adiabatic bottom surface assumption. The temperatures at locations of interest, such as the inner container weld region and the plutonium oxide centerline temperature may be correlated as a linear function of thermal loading and ambient temperature.
A Basic Procedure for the Integrity Assessment of Structural Steels Containing Notches
Authors: Cicero Sergio , Madrazo Virginia , García Tiberio
Published: December 2016

This paper presents a basic procedure for the integrity assessment of structural steels containing notches. It is based on the work developed by the authors in the last five years analyzing the notch effect in structural steels, with the Theory of Critical Distances as the main theoretical framework. The procedure combines the notch effect corrections provided by this theory with a basic Failure Assessment Diagram, and has been successfully validated through its application to 394 fracture tests performed on 4 different steels working at different temperatures.
Dissimilar Metal Welds: Impact of the Residual Stresses on the Risk of Failure
Authors: Blouin A. , Chapuliot S. , Marie S.
Published: December 2016

One important part of the integrity demonstration of large ferritic components is based on the demonstration that they could never undergo brittle fracture. Connections between a ferritic component and an austenitic piping (Dissimilar Metal Weld - DMW) have to respect these rules, in particular the Heat Affected Zone (HAZ) created by the welding process and which encounters a brittle-to-ductile transition.

Within that frame, the case considered in this article is a Ni base alloy narrow gap weld joint between a ferritic pipe (A533 steel) and an austenitic pipe (316L stainless steel). The aim of the present study is to show that in the same loading conditions, the weld joint is less sensitive to the brittle fracture than the surrounding ferritic part of the component. That is to say that the demonstration should be focused on the ferritic base metal which is the weakest material. In addition, residual stresses are also considered and their impact on the fracture resistance is evaluated.

The bases of this study rely on a stress-based criterion developed by Chapuliot et al, using a threshold stress (σth) below which the cleavage cannot occur. This threshold stress can be used to define the brittle crack occurrence probability, which means it is possible to determine the highest loading conditions without any brittle fracture risk.
Deterministic Analysis Results Supporting xLPR Version 2 Code Development
Authors: Shim Do Jun , Rudland David
Published: December 2016

The External Review Board (ERB) for xLPR (eXtremely Low Probability of Rupture) has raised questions regarding the possibility of non-LBB (Leak-Before-Break) conditions for several scenarios of crack growth. There are essentially two areas of concern that need to be addressed regarding this issue. The first is with regard to the effect of weld residual stresses (WRS) on through-wall crack growth where the axial WRS field has high values of compression near the mid thickness region. In this case, the crack growth in the depth direction will slow down when the crack reaches the compressive WRS field especially if the service bending loads are relatively small. However, the crack growth near the inner diameter (ID) surface may continue and possibly become very large and even possibly a 360-degree crack prior to leakage. This may lead to a non-LBB situation which the xLPR code needs to address. The second area of suggested study recommended by the ERB is related to the effect of WRS fields on through-wall crack (TWC) growth and its effect on crack opening displacement (COD) and therefore leak rate. This paper summarizes the efforts taken to address the ERB comments.
Experimental and Numerical Analysis of Structures With Bolted Joints Subjected to High Impact Load: Part 2
Authors: Karpanan Kumarswamy , O’Toole Brendan
Published: December 2016

Military vehicles sustain damaging high impacts and shock loadings due to mine blasts, projectile impacts, and frontal or rear crashes. In all these cases, the vehicle structure and the bolts used in the structure may experience high impact loads. These loads may yield or damage the structure and the bolts. Only a limited amount of published literature describes the proper method for measuring and analyzing transient shock propagation across bolted connections for high-impact loading. Understanding, modeling, and simulating the vehicle response to these impact loadings is critical to designing better vehicle components. This will also help isolate critical components such as electronics and personnel from the shock.

This paper provides a detailed experimental setup and procedure for analyzing high-impact loading on structures with bolted joint connections. An air gun was used to fire an aluminum slug at high velocities on to a bolted structure to induce medium- and high-impact loading. Two structural configurations were evaluated: a hat section bolted to a flat plate, and two hat sections bolted together. Finite element models were created to simulate the damage and shock propagation phenomena during impact. Simulation predictions from detailed 3D solid element models and 2D shell element models were compared to experimental results, including shape deformation and accelerometer data at specific locations. A load cell recording impact force was also used for validation of the simulation. The simplified FE model developed for the bolted joint structure in this report reduced the computational time by one order and can be practically implemented in the full vehicle FE model for crash or blast analysis.
The Case for MACA: The Optimization of Corrosion Allowance
Authors: Taagepera Jaan
Published: December 2016

Engineers are taught to optimize. In the case of pressure vessel design, one means of optimizing the steel which is used is to increase the rated pressure capacity of the vessel beyond the design needs. This optimized pressure is formally known by the term MAWP or Maximum Allowable Working Pressure. Of historical interest, this concept has existed for over 100 years, with the MAWP formula for cylindrical shells being tracable back to the original edition of the Boiler Code.

However, other variables in vessel design can also be optimized. In addition to pressure, consideration can be given to temperature or corrosion allowance. Increasing the temperature has the effect of reducing the basic allowable tensile stress as well as the allowable compressive stress and flange ratings. In the case of some specialty vessels such as reactors with exothermic reactions adding a few degrees to the design temperature may be very beneficial.

But virtually all vessels degrade in some manner, most often corrosion but sometimes via erosion or other degradation mechanisms. Significant amounts of time and effort are spent with unnecessary shutdowns, repairs, and / or fitness for service (FFS) evaluations all of which might have been avoided or deferred for years had the vessel originally been optimized for corrosion allowance. The term Maximum Allowable Corrosion Allowance or MACA is used to describe this approach.

This paper presents some arguments in favor of optimizing the corrosion allowance of pressure vessels, using a MACA based optimization for the design of new vessels rather than a pressure optimization or MAWP philosophy.
Effects of Loading Mode on Brittle Fracture of X70 Pipe Girth Welds
Authors: Park Dong-Yeob , Gravel Jean-Philippe
Published: December 2016

A series of single-edge notched tension (SENT or SE(T)) and single-edge notched bend (SENB or SE(B)) testing was carried out at −15°C using BxB specimens machined from two API X70 large diameter pipeline girth welds. An initial notch was placed either on the heat-affected zone (HAZ) or the weld metal center from the outer diameter side of pipe to simulate a circumferential surface flaw. SE(T) and SE(B) tests were performed according to the CANMET procedure and ASTM E1820, respectively. For all HAZ SE(B) specimens machined from one pipe, ductile cracks initially propagated away from the fusion line and toward the base metal side due to asymmetric deformation, and then pop-in (i.e., the initiation and arrest of a brittle crack) occurred after ductile crack growth of approximately 1 mm where the crack reached around the inter-critical heat-affected zone. HAZ SE(T) specimens also showed that the ductile crack propagation deviated toward the base metal side, but an unstable brittle crack extension was not observed from any SE(T) specimens as opposed to SE(B) specimens. None of the weld metal SE(T) and SE(B) specimens showed pop-in or brittle fracture at −15°C or room temperature. The difference in test results, for the same material, is likely due to the different constraint levels in the two loading modes. While pop-ins were triggered in high-constraint SE(B) tests, it was not the case for the low-constraint SE(T) tests. This paper presents these observations and discussion.
Comparison of Various Damage Models in Modelling 3D Crack Propagation
Authors: Williams Bruce W. , Simha C. Hari M.
Published: December 2016

It is of interest to model crack propagation in irradiated Zr-2.5Nb nuclear pressure tubes and X70 pipeline steel. These materials can undergo a range of conditions leading to fracture with operating temperatures between room temperature and 300 °C for Zr-2.5Nb and strain-rates ranging from quasi-static to dynamic in the case of pipeline steel. In the case of the hexagonal closed-packed zirconium alloy, the influence of plastic anisotropy is also of interest. When trying to capture the fracture response under a wide variety of conditions, limitations of traditional Linear Elastic and Elastic Plastic Fracture Mechanics become apparent such as trying to capture effects of crack tunnelling, the transition from flat-to-slant fracture, and anisotropy. Various damage mechanics based approaches to model 3D crack propagation will be presented and discussed including the crack tip opening angle, a Gurson-Tvergaard-Needleman type damage model based on void nucleation, growth, and coalescence, and the Xue and Wierzbicki model based on the relationship between failure strain with stress triaxiliaty and lode angle dependence. A non-local damage scheme, which mitigates the mesh-dependence of results, will also be presented. For Zr-2.5Nb pressure tube, simulations were performed using Hill’48 and Cazacu-Barlat-Plunkett 2006 anisotropy yield functions. Experimental data from compact tension and rising pressure burst tests on irradiated Zr-2.5Nb pressure tube and both static and dynamic drop weight tear tests on X70 pipeline steel will be compared to predictions from finite element simulations. It is shown that simulations using the various damage models can capture the measured crack propagation behaviour, including crack tunnelling, to varying degrees of accuracy. The Xue and Wierzbicki fracture model was shown to capture the transition from a flat, tunnelling (ductile fracture) crack to a slanted (shear fracture) crack during propagation that was observed in both Zr-2.5Nb and pipeline steel.
Improvement of Tightening Accuracy of Torque Control Method by Taking Account Geometric Errors in Threaded Fasteners
Authors: Fukuoka Toshimichi , Nakano Keisuke
Published: December 2016

Torque control method is commonly used when tightening bolted joints because of its easy operation. However, the method involves an essential problem of fairly large scatter in bolt preloads. It has been reported that even if the same torque is applied, bolt preloads show a considerable scatter, e.g., ranging from 25% to 35%. A scatter in coefficients of friction on nut bearing surface and thread pressure flank is a primary source of bolt preload scatter. Meanwhile, the effect of Equivalent Friction Diameter at the bearing surfaces of nut and bolt head cannot be ignored. The scatter in Equivalent Friction Diameter is caused by imperfect geometry, i.e., the flatness deviation at the bearing surfaces. In this paper, the magnitudes of Equivalent Friction Diameter are quantitatively evaluated by FEA, using the experimental data of flatness deviation measured for a number of commercial nuts and bolts. It is shown that the bolt preload is likely to be scattered by as much as plus minus 10% of the target value, owing to the flatness deviation. Based on the comprehensive calculations by considering the imperfect geometry, a strategy to effectively suppress the bolt preload scatter is proposed.
Developments in Structural Integrity Safety Cases for Highest Reliability Components in the UK
Authors: Jelfs T. , Hayashi M. , Toft A.
Published: December 2016

Gross failure of certain components in nuclear power plant has the potential to lead to intolerable radiological consequences. For these components, UK regulatory expectations require that the probability of gross failure must be shown to be so low that it can be discounted, i.e. that it is incredible. For prospective vendors of nuclear power plant in the UK, with established designs, the demonstration of “incredibility of failure” can be an onerous requirement carrying a high burden of proof. Requesting parties may need to commit to supplementary manufacturing inspection, augmented material testing requirements, enhanced defect tolerance assessment, enhanced material specifications or even changes to design and manufacturing processes.

A key part of this demonstration is the presentation of the structural integrity safety case argument. UK practice is to develop a safety case that incorporates the notion of ‘conceptual defence-in-depth’ to demonstrate the highest structural reliability. In support of recent Generic Design Assessment (GDA) submissions, significant experience has been gained in the development of so called “incredibility of failure” arguments. This paper presents an overview of some of the lessons learned relating to the identification of the highest reliability components, the development of the structural integrity safety arguments in the context of current GDA projects, and considers how the UK Technical Advisory Group on Structural Integrity (TAGSI) recommendations continue to be applied almost 15 years after their work was first published. The paper also reports the approach adopted by Horizon Nuclear Power and their partners to develop the structural integrity safety case in support of the GDA process to build the UK’s first commercial Boiling Water Reactor design.
Comparison Between Different Calculation Methods for Determining Bolting Up Moments
Authors: Mutz Alexander , Schaaf Manfred
Published: December 2016

There are several different standards for flange calculation used in the European and so in the Suisse context. The European Standard EN 1591-1 that is used for the calculation of bolted flanged joints and EN 13555 in which the determination of the required gasket characteristics are defined were reissued in 2013 and in 2014, respectively.

The ASME BPVC, Section III, Appendix 11 regulates the flange calculation for class 2 and 3 components in Suisse nuclear power plants it is also used for class 1 flange connections. A standard for the determination of the required gasket characteristics is not well established which leads to a lack of clarity. As a hint, different m and y values for different kind of gaskets are invented in ASME BPVC Section III. As cited in the Note of table XI-3221.1-1 the values m and y are not mandatory. In Switzerland, mainly the ASME BPVC should be used for the calculation of flange connections. The aim of the ASME Code is more or less not the tightness of the flanges but the integrity. Therefore, stresses are derived for dimensioning the flanges. Following loads are not considered neither for calculation of stresses nor for calculation of tightness. Considering the experience with flanges in general it could be asked, if it is more useful to look at the tightness than at the stresses.

The codes KTA 3201.2 and KTA 3211.2 regulate the calculation of flange connections in German nuclear power plants. Stresses in floating type and in metal-to-metal contact type of flange connections and the tightness are calculated for the different load cases.

In this paper, the differences in the calculations are shown between KTA 3211.2, ASME BPVC, Section III, Appendix 11, EN 1591-1 and Finite element calculations. In all load cases leakage shouldn’t occur. Therefore, internal pressure and temperature in test and operational conditions after bolting-up are also considered for the stress calculation if it is possible in the calculation algorithm.
Vulnerability-Based Design of Sliding Concave Bearings for the Seismic Isolation of Steel Storage Tanks
Authors: Phan Hoang Nam , Paolacci Fabrizio , Alessandri Silvia , Hoang Phuong Hoa
Published: December 2016

Liquid steel storage tanks are strategic structures for industrial facilities and have been widely used both in nuclear and non-nuclear power plants. Typical damage to tanks occurred during past earthquakes such as cracking at the bottom plate, elastic or elastoplastic buckling of the tank wall, failure of the ground anchorage system, and sloshing damage around the roof, etc. Due to their potential and substantial economic losses as well as environmental hazards, implementations of seismic isolation and energy dissipation systems have been recently extended to liquid storage tanks. Although the benefits of seismic isolation systems have been well known in reducing seismic demands of tanks; however, these benefits have been rarely investigated in literature in terms of reduction in the probability of failure. In this paper, A vulnerability-based design approach of a sliding concave bearing system for an existing elevated liquid steel storage tank is presented by evaluating the probability of exceeding specific limit states. Firstly, nonlinear time history analyses of a three-dimensional stick model for the examined case study are performed using a set of ground motion records. Fragility curves of different failure modes of the tank are then obtained by the well-known cloud method. In the following, a seismic isolation system based on concave sliding bearings is proposed. The effectiveness of the isolation system in mitigating the seismic response of the tank is investigated by means of fragility curves. Finally, an optimization of design parameters for sliding concave bearings is determined based on the reduction of the tank vulnerability or the probability of failure.
Review and Case Study of the Linear Matching Method Framework for Structure Integrity Assessment
Authors: Barbera Daniele , Chen Haofeng , Liu Yinghua
Published: December 2016

The Linear Matching Method Framework (LMMF) consists of a number of simplified direct methods for generating approximate inelastic solutions and answering specific design related issues in pressure vessel design codes using standard finite element codes. Currently, all the LMM procedures have been implemented in ABAQUS through user subroutines with powerful user-friendly plug-in tools. The LMM ABAQUS user subroutines and plug-in tools for structural integrity assessment are now in extensive use in industries for the design and routine assessment of power plant components. This paper presents a detailed review and case study of the current state-of-the art LMM direct methods applied to the structural integrity assessment. The focus is on the development and use of the LMMF on a wide range of crucial aspects for the power industry. The LMMF is reviewed to show a wide range of capabilities of the direct methods under this framework, and the basic theory background is also presented. Different structural integrity aspects are covered including the calculation of shakedown, ratchet and creep rupture limits. Furthermore, the crack initiation assessments of an un-cracked body by the LMM are shown for cases both with and without the presence of a creep dwell during the cyclic loading history. Finally an overview of the in house developed LMM plug-in is given. Its implementation in ABAQUS finite element solver through an intuitive Graphical User Interface is presented. The efficiency and robustness of these direct methods in calculating the aforementioned quantities are confirmed through a numerical case study, which is a semi-circular notched (Bridgman notch) bar. A 2D axisymmetric finite element model is adopted, and the notched bar is subjected to both cyclic and constant axial mechanical loads. For the crack initiation assessment, different cyclic loading conditions are evaluated to demonstrate the impact of the different load types on the structural response. The creep dwell impact is also investigated to show how this parameter is capable of causing in some cases a dangerous phenomenon known as creep ratcheting. All the results in the case study demonstrate the level of simplicity of the LMMs but at the same time accuracy, efficiency and robustness over the more complicated and inefficient incremental finite element analyses.
An Experimental Study on the Damping of a Steam Generator Tube With Gap Supports in Air and Water
Authors: Kang Heung Seok , Lee Kang Hee , Shin Chang Whan , Ha Chang Hoon , Park Tae Jeung
Published: December 2016

In this study, we present an analysis and experiment on the fluid damping of a Steam Generator (SG) tube with one and several plate-type supports that are submerged under water. For the damping measurement, a short tube of 2.2 meters in length with one gap support as well as a long tube of up to 10 meters with 11 and 13 supports are used. To see a fluid effect through an analytical approach, Mulcahy’s theory on a tube with finite-length gap support and Pettigrew’s empirical correlation for SG design were reviewed. The theoretical model is good at predicting the fluid damping at the first mode in a low frequency range which is an inactive mode at the support, while the practical model is much better at the higher modes, which are active modes, rocking modes, at the support(s). Experimental results from the short length tube with single support shows good agreement with a previous measurement by other researchers. A theoretical model and empirical correlation are in good agreement. Our measurements from a longer tube with several supports are reasonable compared with the others. There is, however, a wide discrepancy between predictions by the two models. As compared with the whole measurements, the theoretical model seems to be a good guideline in a low frequency range, while an empirical model is relatively good guideline in a high frequency range. Based on the whole collected data, a new correlation modified from Pettigrew’s correlation is suggested.