Fatigue life prediction of pressure vessels using an energy based approach

Pressure vessels are subjected to pulsed loading, resulting in the occurrence of stress concentration zones, initiation and propagation of fatigue cracks, and subsequent failure. Conventional approaches to fatigue life prediction are based on nominal stresses and strains. Methods of prediction involving an energy criteria give the best results. This paper presents the fatigue life prediction process of a pressure vessel designed by Neftohim — Bulgaria. The energy dissipated over a cycle and equal to the hysteresis loop area was used as the fatigue damage parameter. The stress values necessary for calculations were found analytically on the basis of shell theories. For an analysis of material inelastic behavior, some tension/compression fatigue tests were conducted at a frequency of 15 Hz. The experimental stress and strain values were used to determine the energy dissipation. The prediction has shown that the designed pressure vessel cannot serve 10 years without fatigue crack initiation. Such neglected factors as temperature, corrosion environment, welded joints, and a spread of material characteristics result in additional service life reduction. For the solution of the problem it is necessary to replace the steel and also to change the geometry of the vessel.Published inProblemy Prochnosti, Nos. 1–2, pp. 109–117, January–February, 1995.     

使用“分裂-合并"策略改进文本聚类集成算法的研究

探讨了"分裂-合并"(DM)策略对文本聚类集成算法改进的效果。首先在聚类成员生成阶段运行使用DM策略的超球K均值(SKM)算法r次,每次生成较多的文本子簇,并根据子簇的相似性使用凝聚层次聚类方法合并这些子簇,得到r个聚类成员,随后在聚类集成阶段采用两个快速的谱聚类算法进行集成。在6组真实文本集上进行了实验,使用DM策略的两个聚类集成算法获得的平均标准化互信息(NMI)分别比改进前的算法提高了4.6和7.9个百分点,证明了DM策略可以有效提高文本聚类集成算法的聚类质量。     

Quantitative prediction of microbial behaviour during food processing using an integrated modelling approach: a review

Microbiological safety of food relies on microbial examination of raw materials and final products, coupled with monitoring process parameters and hygiene standards. The concept of predictive microbiology was developed to evaluate the effect of processing, distribution and storage operations on food safety. The objective of this paper is to review the approaches proposed by researchers to quantify the effect of competitiveness or fluctuating conditions on bacterial behaviour. The main microbial models that quantify the effects of various hurdles on microbial kinetics are presented. To provide complementary information for microbial models, three areas have to be considered: process engineering that characterises and models mass and heat transfer; microbiology that characterises and models bacterial behaviour and metabolite production, and; applied thermodynamics that characterises and models the physico-chemical properties of a food product. Global modelling approaches, developed by integrating the previous models, are illustrated with recent results.     

Fatigue behavior prediction of welded joints by using an integrated fracture mechanics approach

Current fracture mechanics methods for fatigue assessment of welded joints are based on long crack behavior. The present work introduces a method to predict the fatigue strength of welded joints by means of an integrated fracture mechanics approach (IFMA) that takes into account the fatigue behavior of short cracks. This methodology estimates the fatigue crack propagation rate as a function of the difference between the applied driving force and the material threshold for crack propagation, function of crack length. Firstly, the proposed fracture mechanic method is introduced and compared with the traditional fracture mechanic approach, used mainly for fitness for purpose assessment of welded joints with cracks or other crack-like defects. Then, the method is used for several theoretical and parametric applications to show its ability to predict the influence of different mechanical, geometrical and microstructural parameters in the definition of the fatigue resistance of welded joints. The influence of plate thickness, initial crack length and reinforcement angle on fatigue strength of butt-welded joints has been analysed and results show good agreement with experimental trends. Finally, the method is applied to predict and analyze the fatigue behavior of butt welded and non-load-carrying transverse fillet welded joints, and estimated and experimental results are analysed and compared.     

Model complexity versus ensemble size: allocating resources for climate prediction

A perennial question in modern weather forecasting and climate prediction is whether to invest resources in more complex numerical models or in larger ensembles of simulations. If this question is to be addressed quantitatively, then information is needed about how changes in model complexity and ensemble size will affect predictive performance. Information about the effects of ensemble size is often available, but information about the effects of model complexity is much rarer. An illustration is provided of the sort of analysis that might be conducted for the simplified case in which model complexity is judged in terms of grid resolution and ensemble members are constructed only by perturbing their initial conditions. The effects of resolution and ensemble size on the performance of climate simulations are described with a simple mathematical model, which is then used to define an optimal allocation of computational resources for a range of hypothetical prediction problems. The optimal resolution and ensemble size both increase with available resources, but their respective rates of increase depend on the values of two parameters that can be determined from a small number of simulations. The potential for such analyses to guide future investment decisions in climate prediction is discussed.     

Determination of the scattered fields of an SH-wave by an eccentric coating-fiber ensemble using DEIM

To date, the existing theories pertinent to the determination of the scattered fields of an inhomogeneity have been limited to certain topological symmetries for which the method of wave-function expansion is widely used. In the literature the wave-function expansion method has also been employed to the case involving concentric coated fiber. An alternative approach is the dynamic equivalent inclusion method (DEIM) proposed by Fu and Mura [L.S. Fu, T. Mura, The determination of elastodynamic fields of an ellipsoidal inhomogeneity. ASME J. Appl. Mech. 50 (1983) 390-396.] who found the scattered field of a single spheroidal inhomogeneity. The pioneering work of Eshelby [J.D. Eshelby, The determination of the elastic field of an ellipsoidal inclusion, and related problems, Proc. R. Soc. London, Ser. A A241 (1957) 376-396.] on elastostatic EIM is based on polynomial form of eigenstrains which holds certain useful properties and subsequently its application is only effective for certain relevant situations and not necessarily efficient for other problems. Nevertheless, Fu and Mura’s analysis is also based on polynomial eigenstrains. It will be shown that taking the dynamic homogenizing eigenstrains in the form of the series expansion whose general term is products of functions of r and trigonometric functions of θ, is more rigorous and attractive for the problem under consideration. This natural form of solution gives very accurate result with just the first few terms of the series. Moreover, this work aims to extend the DEIM to the case of coated fiber obstacle with the rather complex topology where the coating-fiber phases are not concentric. The effect of variableness of the coating thickness on the elastodynamic fields is examined. Comparison with other analytical solutions, whenever available, establishes the remarkable accuracy and robustness of the proposed theory.     

Volumetric medical image compression using inter-slice correlation switched prediction approach

With the advancement in medical data acquisition and telemedicine systems, image compression has become an important tool for image handling, as the tremendous amount of data generated in medical field needs to be stored and transmitted effectively. Volumetric MRI and CT images comprise a set of image slices that are correlated to each other. The prediction of the pixels in a slice depends not only upon the spatial information of the slice, but also the inter-slice information to achieve compression. This article proposes an inter-slice correlation switched predictor (ICSP) with block adaptive arithmetic encoding (BAAE) technique for 3D medical image data. The proposed ICSP exploits both inter-slice and intra-slice redundancies from the volumetric images efficiently. Novelty of the proposed technique is in selecting the correlation coefficient threshold (T_ϒ) for switching of ICSP. Resolution independent gradient edge detector (RIGED) at optimal prediction threshold value is proposed for intra-slice prediction. Use of RIGED, which is modality and resolution independent, brings the novelty and improved performance for 3D prediction of volumetric images. BAAE is employed for encoding of prediction error image to resulting in higher compression efficiency. The proposed technique is also extended for higher bit depth volumetric medical images (16-bit depth) presenting significant compression gain of 3D images. The performance of the proposed technique is compared with the state-of-the art techniques in terms of bits per pixel (BPP) for 8-bit depth and was found to be 31.21%, 27.55%, 21.89%, and 2.39% better than the JPEG-2000, CALIC, JPEG-LS, M-CALIC, and 3D-CALIC respectively. The proposed technique is 11.86%, 8.56%, 7.97%, 6.80%, and 4.86% better than the M-CALIC, 3D CALIC, JPEG-2000, JPEG-LS and CALIC respectively for 16-bit depth image datasets. The average value of compression ratio for 8-bit and 16-bit image dataset is obtained as 3.70 and 3.11 respectively by the proposed technique.     

Doc2vec-based link prediction approach using SAO structures: application to patent network

Scientometrics - As the amount of documents has exploded in the Internet era, many researchers have tried to understand the relationships between documents and predict the links between similar but...     

Constraint-based design using an operational approach

Constraint-based design, which explicitly represents and operates upon constraints, has been recognized as a promising tool for achieving intelligent support of design, particularly the design of mechanical parts or assemblies. It is essential for a constraint-based system to realize the constraint-solving capability. This paper presents an operational approach to constraint solving using incremental feature operations. The approach is based on an operational interpretation of constraints, i.e. the constraint satisfaction is carried out in terms of operations incrementally. A grammatic formalism is used for operational modeling of constraints. Each graph production within a graph grammar corresponds to an operation or a sequence of operations designated for constraint satisfaction that is related to a rule or a procedure. Therefore, a constraint satisfaction process can be represented by a graph grammar parsing process. The operation sequence is planned by graph grammar parsing and invocation of the related rules or procedures. Constraints are then evaluated by invoking the sequenced operations. Features are introduced as higher-level abstractions into the geometric constraints network. This enables reasoning about design validation from topological and manufacturing views.     

Data-based stochastic subgrid-scale parametrization: an approach using cluster-weighted modelling

A new approach for data-based stochastic parametrization of unresolved scales and processes in numerical weather and climate prediction models is introduced. The subgrid-scale model is conditional on the state of the resolved scales, consisting of a collection of local models. A clustering algorithm in the space of the resolved variables is combined with statistical modelling of the impact of the unresolved variables. The clusters and the parameters of the associated subgrid models are estimated simultaneously from data. The method is implemented and explored in the framework of the Lorenz '96 model using discrete Markov processes as local statistical models. Performance of the cluster-weighted Markov chain scheme is investigated for long-term simulations as well as ensemble prediction. It clearly outperforms simple parametrization schemes and compares favourably with another recently proposed subgrid modelling scheme also based on conditional Markov chains.     

Synthesis of gold nanoparticles: an ecofriendly approach using Hansenula anomala

This work describes a bioassisted approach for the preparation of metal nanoparticles using yeast species Hansenula anomala. Gold nanoparticles were prepared using gold salt as the precursor, amine-terminated polyamidoamine dendrimer as the stabilizer, and the extracellular material from H. anomala as the bioreductant. It could also be demonstrated that, using our approach, small molecules such as cysteine can act as stabilizers as well. This synthetic approach offers a greener alternative route to the preparation of gold sols that are devoid of cellular and toxic chemical components. The ability of as-synthesized gold sol to function as biological ink for producing patterns for the analysis of fingerprints and to act as an antimicrobial reagent is evaluated. The generality of this toxin-free synthetic approach to other metals was assessed using palladium and silver.     

Positive-operator-valued-measure view of the ensemble approach to polarization optics

The statistical ensemble formalism of Kim et al [J. Opt. Soc. Am. A4, 433 (1987)] offers a realistic model for characterizing the effect of stochastic nonimage-forming optical media on the state of polarization of transmitted light. With suitable choice of the Jones ensemble, various Mueller transformations-some of which are hitherto unknown-are deduced. It is observed that the ensemble approach is formally identical to the positive-operator-valued measures (POVMs) on the quantum density matrix. This observation, in combination with the recent suggestion by Ahnert and Payne [Phys. Rev. A71, 012330-1 (2005)]-in the context of generalized quantum measurement on single photon polarization states-that linear optics elements can be employed in setting up all possible POVMs enables us to propose a way of realizing different types of Mueller devices.     

Fatigue life prediction of copper single crystals using a critical plane approach

A critical plane multiaxial fatigue criterion was employed to predict the fatigue life of copper single crystals. The detailed stress-strain response was obtained through the constitutive modeling using a newly developed crystal plasticity theory. The constitutive model was capable of capturing the major deformation features of copper single crystals under cyclic loading including the cyclic stress-strain curves, cyclic hardening behavior, and the evolution of the hysteresis loops with increasing number of loading cycles. Fatigue life prediction of the single crystal copper was conducted based upon the stress-strain response obtained from the cyclic plasticity model. The fatigue criterion takes into account the plastic strain localization within a single crystal. The critical plane (cracking plane) was identified as the material plane where the fatigue damage accumulation first reached a critical value. For copper single crystals with the crystal orientations being within the standard crystallographic triangle, the fatigue criterion can predict both fatigue life and cracking direction consistent with the experimental observations. More importantly, the constants used in the fatigue criterion were found to be identical to those used for the pure polycrystalline copper with different grain sizes and texture.     

Fabrication of vertically stacked single-crystalline Si nanowires using self-limiting oxidation

A simple method for fabricating vertically stacked single-crystal silicon nanowires on standard bulk silicon wafers is presented. The process uses inductively coupled plasma (ICP) etching to create silicon fins with uneven yet controllable vertical profiles. The fins are then thermally oxidized in a self-limiting process, and the narrow regions are completely consumed to create multiple nanowires vertically stacked on each other. It was found that the number of nanowires in the vertical stack depends on the number of ICP cycles. A mechanism for the formation of the nanowires is proposed and confirmed with numerical simulations.     

Equivalence-set genes partitioning using an evolutionary-DP approach

Computation of transitive-closure equivalence sets has recently emerged as an important step for building static and dynamic models of gene network from DNA sequences. We present an evolutionary-DP approach in which dynamic programming (DP) is embedded into a genetic algorithm (GA) for fitness function evaluation of small equivalence sets (with m genes) within a large-scale genetic network of n genes, where n/spl Gt/m. This approach reduces a computation-intensive optimal problem of high dimension into a heuristic search problem on /sub n/C/sub m/ candidates. The DP computation of transitive closure forms the basic fitness evaluation for selecting candidate chromosomes generated by GA operators. By introducing bounded mutation and conditioned crossover operators to constrain the feasible solution domain, small transitive-closure equivalence sets for large genetic networks can be found with much reduced computational effort. Empirical results have successfully demonstrated the feasibility of our GA-DP approach for offering highly efficient solutions to large scale equivalence gene-set partitioning problem. We also describe dedicated GA-DP hardware using field programmable gate arrays (FPGAs), in which significant speedup could be obtained over software implementation.     

Tracking multi-phase boundaries using an integration-based approach

An integration-based method to track multi-phase boundaries for multi-component alloys systems is proposed. The foundation of the method is considering the phase boundary tracking as an initial value problem. It starts with the utilization of Gibbs–Duhem relation to find the slope of a phase boundary (the partial derivatives of the solvus temperature with respect to the equilibrium phase composition) and the partial derivatives of partition coefficients with respect to the equilibrium phase composition. Then, with these derivatives and a pair of known initial points on a phase boundary, the rest of the phase boundary can be calculated using a numerical integration technique such as the Runge–Kutta or Predictor–Corrector method in a stepwise manner. The integration method has been applied to track various types of phase boundaries in binary, ternary and quaternary systems. The calculated ones are in good agreement with the ones obtained by the commercial CALPHAD software Thermo-Calc. It provides a different computational method for the tracking of multi-phase boundaries and might be useful in the calculation of phase diagram when combined with the overlapping of Zero Phase Fraction (ZPF) lines technique and global minimization technique.     

Tolerance optimization using the Lambert W function: an empirical approach

This paper explores the integration of the Lambert W function to a tolerance optimization problem with two unique features. First, the Taguchi loss function has been a popular tool for quantifying a quality loss incurred by the customer. This paper utilizes an empirical approach based on a well-established regression analysis, which may be more appealing to engineers and better capture the customer's perception of product performance. Second, by trading off manufacturing and rejection costs incurred by a manufacturer and quality loss incurred by the customer, this paper shows how the Lambert W function, widely used in physics, can be efficiently applied, which is perhaps the first attempt in the literature related to tolerance optimization and synthesis. Using the concept of the Lambert W function, this paper derives a closed-form solution, which may serve as a means for quality practitioners to make a quick decision on their optimal tolerances without resorting to rigorous optimization procedures using numerical methods. A numerical example is illustrated and a sensitivity analysis is performed.