Local Approach Methods Research Articles

Optimization of automotive diesel engine calibration using genetic algorithm techniques

Although the advancements in automotive diesel engines in the last two decades have resulted in the possibility of achieving better performance with lower pollutant emissions and fuel consumption, the increased complexity of the system and the high number of control parameters require the solution of optimization problems of high dimensionality. It is of crucial importance to identify suitable methodologies, which allow achieving the full exploitation of the potential of these powertrains. In this paper, an original methodology for optimizing the latest generation of common rail automotive diesel engines has been presented.Random optimization methods along with surrogate models were firstly used to generate a population of engine calibrations, which then served as an initial population to a specifically conceived Genetic Algorithm (GA) based optimizer, which was finally applied on a real data set for a particular engine operating point. The results were compared with a calibration optimized using a traditional local approach method. A simultaneous reduction of about 20% in NOX and 1% in Brake Specific Fuel Consumption was achieved, with no significant increase in other emissions. The methodology described in the paper has the potential to reduce the calibration time and effort by half, while obtaining better calibrations.

A postprocessing method in the HMC framework for predicting gene function based on biological instrumental data.

Predicting gene function based on biological instrumental data is a complicated and challenging hierarchical multi-label classification (HMC) problem. When using local approach methods to solve this problem, a preliminary results processing method is usually needed. This paper proposed a novel preliminary results processing method called the nodes interaction method. The nodes interaction method revises the preliminary results and guarantees that the predictions are consistent with the hierarchy constraint. This method exploits the label dependency and considers the hierarchical interaction between nodes when making decisions based on the Bayesian network in its first phase. In the second phase, this method further adjusts the results according to the hierarchy constraint. Implementing the nodes interaction method in the HMC framework also enhances the HMC performance for solving the gene function prediction problem based on the Gene Ontology (GO), the hierarchy of which is a directed acyclic graph that is more difficult to tackle. The experimental results validate the promising performance of the proposed method compared to state-of-the-art methods on eight benchmark yeast data sets annotated by the GO.

Applicability of local approaches to assessment of cleavage fracture in complex constraint and load history cases

The paper presents results and analysis from an on-going investigation to better understand and quantify the effects of constraint on cleavage fracture under various initial stress and plastic strain conditions. Specifically, new fracture toughness data obtained with three-point bend specimens with crack-to-width ratios 0.4, 0.2 and 0.05 is shown for as-received material and material with 5% initial uniaxial plastic strain. Firstly, analysis with the J-Q approach is used to argue that while pre-strain initial conditions change the fracture toughness, the shape of the failure locus in the J-Q space might remain unaffected. The implication is significant reduction of tests required for assessments taking constraint into account. The potential to use current local approach methods to allow a fracture prediction, which is independent of initial conditions, is then investigated by application of modified Beremin models. It is demonstrated that the local approaches can predict changes in the apparent toughness across the three constraint levels for the as-received material. It is further shown that accommodation of load history effects, such as the initial plastic strain, requires an advancement of the classical approach, a subject of on-going work.

Combining discourse analyses to enrich theory: The case of local land-use policies in South Eastern France

Local land-use policies are determined by a wide range of considerations that do not always favor open-space preservation. To identify them, a field study was undertaken in South Eastern France via semi-directive interviews with people responsible for municipal land-use policies. We use it to compare a qualitative (i.e. manual) discourse analysis with two quantitative (i.e. computer-assisted) analyses and combine them to identify the drivers of land-use policies, especially with regard to urban sprawl. Performing all three analyses allows us to switch back and forth between a local empirical approach and large-scale modeling and methods. This should enrich micro-economic models by clarifying more complex local features, like unbalanced relationships with neighboring municipalities or why “agriculture” should be considered as an independent interest group.

The effect of welding residual stresses on brittle fracture in an internal surface cracked pipe

The change in brittle fracture properties due to the presence of welding residual stresses (RS) is studied in a pipe. Welding RS are simulated by using a 3-D finite element (FE) model and experimentally verified. An internal circumferential thumbnail crack is introduced at the weld line. The modified Beremin model is used as local approach method to predict toughness distributions in the presence of welding RS. The model is calibrated using experimental fracture tests at −150 °C consisting of low and high constraint specimens. The results indicate that, in the welded pipe, the fracture toughness will decrease dramatically in comparison with the as-received pipe. For the same fracture probability of 90%, fracture toughness will decrease from 65 to 40 MPa √m. This is due to the influence of tensile welding RS on the crack tip stress state, which result in a decrease in the opening mode stresses at the near crack tip up to 40%.

Guided wave interaction with hole damage using the local interaction simulation approach

This paper considers the effects of hole damage on guided wave propagation in isotropic and composite plates using both the local interaction simulation approach (LISA) and experimental methods. Guided wave generation from piezoceramic wafers is modeled using the recently developed LISA hybrid approach. First, holes in isotropic plates are simulated to establish LISAʼs ability to capture the guided wave scattering effects of various hole sizes. Experimental results are compared with the simulations to aid in evaluating the LISA model. Next, hole damage in cross-ply composite laminates is modeled and compared with experimental results. Various hole sizes and azimuthal locations are simulated to determine the effects of varying those parameters. Results from both the isotropic and composite damage studies clearly display the ability of LISA to model hole damage. Both the simulation and experimental results illustrate the advantages and disadvantages of various sensor locations relative to the actuator and damage locations. Finally, the study shows the ability of the LISA model to capture mode conversions resulting from partial thickness holes.

Radiative damping of surface plasmon resonance in spheroidal metallic nanoparticle embedded in a dielectric medium

The local field approach and kinetic equation method is applied to calculate the surface plasmon radiative damping in a spheroidal metal nanoparticle embedded in any dielectric media. The radiative damping of the surface plasmon resonance as a function of the particle radius, shape, dielectric constant of the surrounding medium and the light frequency is studied in detail. It is found that the radiative damping grows quadratically with the particle radius and oscillates with altering both the particle size and the dielectric constant of a surrounding medium. Much attention is paid to the electron surface-scattering contribution to the plasmon decay. All calculations of the radiative damping are illustrated by examples on the Au and Na nanoparticles.

Constructing a Canonical form of a Matrix in Several Problems about Combinatorial Designs

The author developed computer programs needed for the classification of designs with certain automorphisms by the local approach method. All these programs use canonicity test or/and construction of canonical form of an integer matrix. Their efficiency substantially influences the speed of the whole computation. The present paper deals with the implemented canonicity algorithm. It is based on ideas used by McKay, Meringer, Kaski and Bouyukliev, but while their algorithms are for the equivalence test, the canonicity test or finding canonical representative of only one type of combinatorial object (graph, code, design, binary matrix, etc.), the algorithm presented in this paper is meant to work fast on all types of integer matrices used for the classification of designs with predefined automorphisms. This is achieved through the suitable spectrum invariant, and the way it is used to cut off some branches of the search tree.

Fatigue behaviour of tubular AlMgSi welded specimens subjected to bending–torsion loading

ABSTRACTThis paper is concerned with an experimental and numerical study of the fatigue behaviour of tubular AlMgSi welded specimens subjected to biaxial loading. In‐phase torsion–bending fatigue tests under constant amplitude loading were performed in a standard servo‐hydraulic machine with a suitable gripping system. Some tests in pure rotating bending with and without steady torsion were also performed. The influence of stress ratio R and bending–torsion stress ratio were analysed. Correlation of the fatigue lives was done using the distortion energy hypothesis (DEH), based on the local stresses and strains. The applicability of the local strain approach method to the prediction of the fatigue life of the welded tubular specimens was also investigated. Static torsion has only a slight detrimental influence on fatigue strength. The DEH (von Mises criterion) based on local stresses in the weld toes was shown to satisfactorily correlate fatigue lives for in‐phase multiaxial stress–strain states. The stress–strain field intensity predictions were shown to have less scatter and are in better agreement with the experimental results than the equivalent strain energy density approach.

A Local Approach Methodology for the Analysis of Ultimate Strength of Uncracked Tubular Joints

The local approach methodology in contrast to classical fracture mechanics can be used to predict the onset of tearing fracture, and the effects of geometry in tubular joints. Finite element analysis of T-joints plate geometries, and tubular joints has been done. The parameters of constraint, equivalent stress, plastic strain and maximum principal strain have been used. Sub-modelling using the finite element package ABAQUS, was necessitated in order to obtain the high state of stress at the weld toe. The load at which onset of tearing occurs has been well predicted by the local approach method. Local weld toe grinding can be used to increase substantially the load at which tearing starts. Tubular joints with thicker chords will commence ductile tearing at a lower load than those with thinner chords. Journal of Civil Engineering Research and Practice Vol.1(2) 2004: 91-106

Comparative analysis of fatigue life predictions in central notched specimens of Al–Mg–Si alloys

ABSTRACTThe fatigue behaviour of an Al–Mg–Si alloy was studied using notched specimens. Fatigue tests were conducted at two stress ratios R= 0 and R= 0.4 on thin plates with a central hole. Constant and block variable loading amplitudes were applied to the specimens using a servo‐hydraulic machine. The applicability of the local strain approach method to the prediction of the fatigue life was investigated for this type of discontinuity. Two methods, the equivalent strain energy density approach and a modified stress–strain intensity field approach, were used to predict the fatigue strength. For the second one an elastic–plastic finite element analysis was carried out in order to obtain the local strain and stress distributions near the notch root. Based on Miner's rule an equivalent stress was used to correlate the fatigue lives for the variable amplitude histories. The experimental results were compared with the predicted results obtained by the two methods investigated and better agreement was found with the stress–strain field intensity approach, while the strain energy approach gave more conservative results. Miner's rule gives a good correlation between the variable amplitude and constant amplitude results.

The effect of long term exposure to elevated temperature on steam line steel properties

Premature failure of pipes presents serious problem in the service of steam lines, produced of steel 14MoV63, developed for steam high temperature (540 °C) for at least 100,000 service hours. Experimental research with specimens, taken from virgin and used material (117,000 service hours), is performed for better understanding of the effect of long-term exposure to high temperature and high stresses on this steel properties. In addition to classical testing method (tensile test, impact toughness test), local approach to fracture is applied, offering detail analysis of changes caused in service. New designed extensometer is applied for measurement of contraction in the specimen root radius at elevated temperature. The differences between virgin and used steel properties, noticed in tensile test results, are described in better way by local approach method. The premature failure can not be attributed completely to revealed reduction in 14MoV63 steel properties after use and further research is necessary for complete explanation of premature in-service failure of pipes, produced of 14MoV63 steel.

An analysis of the state of stress and of its effect on the fatigue strength of welded joints using the local approach method

An analysis of the state of stress and of its effect on the fatigue strength of welded joints using the local approach method

Influence of dynamic strain aging on the ductile tearing of C–Mn steels: modelling by a local approach method

C–Mn steels and associated welds can be susceptible to dynamic strain aging (DSA). In this case, fracture toughness passes through a minimum when the temperature increases from 20 to 300 °C. Since Charpy V-Notch data are not affected by the DSA phenomenon, the method for predicting the evolution of J 0.2 and d J/d a in the temperature domain where DSA occurs is still an open question. The purpose of the present study is the assessment of this decrease in fracture toughness using a local approach method. The results of J– R tearing resistance tests, characterized by crack initiation resistance J 0.2 and tearing modulus d J/d a relative to a base metal (A48 French standard steel) and manual metal arc deposited metals are presented and discussed. The local approach determination of J 0.2 was performed using the Rice and Tracey model. Comparisons between experimental results and the results of local approach modelling indicate that both J 0.2 and d J/d a decreases with DSA can be correctly predicted.

Developments in Local Approach methodology with application to the analysis/re-analysis of the NESC-1 PTS benchmark experiment

Local Approach methods have received considerable attention in recent years as a complementary approach to structural integrity assessment. These approaches are based on the application of micro-mechanistic models of failure in which the stress, strain and ‘damage’ local to the crack-tip are related to the critical conditions required to initiate/propagate fracture. The models are calibrated in terms of material parameters that are deemed fully transferable and derived using a combination of reference test data and supporting stress analysis. Once calibrated, using small-scale test data, the models are assumed independent on geometry and loading configuration. For a given failure mechanism, the model parameters may be used in the assessment of a structure fabricated from the same material (for appropriate temperatures, loading rates, etc). The paper describes the work initially undertaken in relation to the NESC-1 (Network for Evaluating Steel Components) spinning cylinder test, in order to validate the application of Local Approach methods for the case of PTS loading. The predicted amount of pre-cleavage ductile tearing and the timing of the subsequent cleavage event are compared with the observed fracture behaviour of the defect. The paper then highlights several areas in which Local Approach methodology has been developed since the initial work on PTS. These include: • Calibration of the cleavage model across a range of temperatures and constraint states. • Treatment of 3D defects. • Reference to hydrostatic stress in cleavage fracture predictions. • Simplification and standardisation of analytical techniques for more routine use in integrity assessments. The paper concludes that results from large-scale structural experiments, such as the NESC-1 spinning cylinder test, will be of lasting value in validating developments in Local Approach methodology and other advanced methods of fracture assessment. This is particularly true in the authors’ current work that seeks to achieve an overall simplification in methodology, without sacrificing predictive accuracy.

The R6 procedure: recent developments and comparison with alternative approaches

The R6 defect assessment procedure has been continually developed since 1976. It is currently at Revision 3 and a major new release, Revision 4, is planned for 2000. Recent developments in R6 include the incorporation of new appendices on crack arrest methods, weld mismatch effects, local approach and finite element methods. These additions to R6 and other recent developments are briefly described in this paper. The overall aim has been to provide additional advice, which can reduce conservatism in the basic procedure, to increase validation, and to maintain R6 up-to-date with progress in fracture mechanics. R6 has had a major influence on the development of other codes and standards, including the new BS guide BS7910:1999 and the SINTAP procedure. The relationship between these other approaches and R6 is discussed. The paper concludes with a brief outline of the intended framework of R6 Revision 4.

Fracture toughness transition curve estimation from a notched round bar specimen using the local approach method

The local approach method for the brittle or transition region describes the fracture probability of specimens or structures using Weibull statistics. Many papers have discussed the characteristics of the Weibull parameter using notched tensile specimens and the applicability to fracture toughness scatter evaluation using CT specimens. However few papers have made clear whether the Weibull parameter of the Weibull stress is a material property or not. In this paper the distribution of Weibull stress in the brittle fracture region using notched round bar specimens and CT specimens were investigated and it was confirmed that both distributions agreed well. Furthermore the estimation method for the fracture toughness transition curve including its scatter from notched round bar tensile tests was proposed based on the relation between the Weibull stress and the Wallin's fracture toughness transition curve. As a result, the estimated fracture toughness curve in the brittle and lower transition region from the notched round bar specimens coincided with the measured fracture toughness curve from CT specimens. This method will be applicable to fracture toughness curve estimation under plane strain conditions even if there is no possibility of obtaining thick enough CT specimens from a structure because of geometry or some other restrictions.

Graded Compositional Design of FGM Compliant Pad for Thermoelectric Conversion Module Based on Residual Thermal Stress Analysis.

Thermoelectric power generation is an electric system used to directly translate a temperature difference to a potential difference based on the Seebeck effect. Although thermoelectric generation as a small power source in spacecraft has been developed mainly in the U.S., the generation system did not spread industrial power generation because of high manufacturing cost. We proposed a structural concept of a FGM (functionally gradient material) compliant pad to reduce the concentration of thermal stress between the thermoelectric cell and the wall of the heat exchanger for a SiGe thermoelectric conversion system as industrial power generation. This paper describes a graded compositional design of the compliant pad for reducing the residual stress caused by a sintering process. The graded compositional profile in Pd/Si3N4 and Si3N4/Cu graded interface was examined by a local approach method which was proposed in this study. As results, a concentration of residual thermal stress in the thermoelectric cell was reduced by an application of the compliant pad with Si3N4-rich FGM. Also, the application of FGM to compliant pad had no effect on temperature distribution in the module.

FATIGUE CRACK INITIATION LIFE PREDICTION IN HIGH STRENGTH STRUCTURAL STEEL WELDED JOINTS

AbstractThe local approach method is used to calculate the fatigue crack initiation/early crack growth lives (Ni) in high strength structural steel weldments. Weld‐toe geometries, welding residual stresses and HAZ (heat affected zone) cyclic mechanical properties are taken into account in the Ni estimation procedure. Fatigue crack initiation lives are calculated from either a Basquin type or a Manson‐Collin type equation. The local (HAZ) stress and strain amplitudes and the local mean stress are determined from an analysis based on the Neuber rule and the Molski‐Glinka energy approach. The accuracy of the different methods is evaluated and discussed. Finally the previous methods are used with HAZ cyclic mechanical properties estimated from hardness measurements.

Many-particle effects in the bond length alternation of alternant hydrocarbons

The local approach (LA) method has been employed to investigate the correlated ground state wavefunction in alternant monocyclic and linear hydrocarbon π systems as a function of the bond length alternation δ. The LA has been supplemented by a simple model-Hamiltonian developed in the ZDO (zero differential overlap) approximation. The integrals have been calculated ab initio in a Slater-type basis. To quantify many-particle effects in the studied systems we have determined the interatomic π correlation energy E corr and a π electron localization parameter Δi as a function of δ. Δi measures the reduction of the charge fluctuations due to electronic correlations and is thus a convenient measure for the atomic electron density localization. It is demonstrated that monocyclic 4n + 2 (n = 1,2,3, …) Huckel rings allow for a coincidence of increasing |E corr| numbers and increasing atomic electron density delocalization with enlarged δ values. The δ variation of Δi reflects in a transparent form that hydrocarbon...