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Employing incomplete complex modes for model updating and damage detection of damped structures

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Science China(Technological Sciences) 2008年第12期51卷 2244-2258页

作者： HU Sau-Lon james Department of Ocean Engineering University of Rhode Island

In the study of finite element model updating or damage detection,most papers are devoted to undamped ***,their objective has been exclusively restricted to the correction of the mass and stiffness *** contrast,this paper performs the model updating and damage detection for damped structures.A theoretical contribution of this paper is to extend the cross-model cross-mode(CMCM) method to simultaneously update the mass,damping and stiffness matrices of a finite element model when only few spatially incomplete,complex-valued modes are *** studies are conducted for a 30-DOF(degree-of-freedom) cantilever beam with multiple damaged elements,as the measured modes are synthesized from finite element *** numerical results reveal that applying the CMCM method,together with an iterative Guyan reduction scheme,can yield good damage detection in *** the measured modes utilized in the CMCM method are corrupted with irregular errors,assessing damage at the location that possesses larger modal strain energy is less sensitive to the corrupted modes.

关键词： incomplete complex modes model updating damage detection CMCM damped structures

WEAKLY COMPRESSIBLE TWO-PRESSURE TWO-PHASE FLOW

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Acta Mathematica Scientia 2009年第6期29卷 1497-1540页

作者： Hyeonseong Jin james Glimm Department of Mathematics Jeju National University Jeju 690-756 Republic of Korea Department of Applied Mathematics and Statistics Stony Brook University Stony Brook NY 11794-3600 Computational Science Center Brookhaven National Laboratory Upton NY 11793-6000 USA

We analyze the limiting behavior of a compressible two-pressure two-phase flow model as the Mach number tends to zero. Formal asymptotic expansions are derived for the solutions of compressible two-phase equations. Expansion coefficients through sec- ond order are evaluated in closed form. Underdetermination of incompressible pressures is resolved by information supplied from the weakly compressible theory. The incompressible pressures are uniquely specified by certain details of the compressible fluids from which they are derived as a limit. This aspect of two phase flow in the incompressible limit appears to be new, and results basically from closures which satisfy single phase boundary conditions at the edges of the mixing zone.

关键词： multiphase flow asymptotic analysis turbulence perturbation

Gas sorption and non-Darcy flow in shale reservoirs

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Petroleum Science 2017年第4期14卷 746-754页

作者： Xiukun Wang james Sheng Department of Petroleum Engineering Texas Tech UniversityPO Box 43111LubbockTX 79409USA

Gas sorption and non-Darcy flow are two important issues for shale gas reservoirs. The sorption consists of dissolution and adsorption. Dissolved gas and adsorbed gas are different. The former is dissolved in the shale matrix, while the latter is concentrated near the solid walls of pores. In this paper, the Langmuir equation is used to describe adsorption and Henry’s law is used to describe dissolution. The K coefficient in Henry’s law of 0.052 mmol/(MPa g TOC) is obtained by matching experimental data. The amount of dissolved gas increases linearly when pressure increases. Using only the Langmuir equation without considering dissolution can lead to a significant underestimation of the amount of sorbed gas in shales. For non-Darcy gas flow, the apparent permeability model for free gas is established by combining slip flow and Knudsen flow. For adsorbed gas, the surface diffusion effect is also considered in this model. The surface diffu- sion coefficient is suggested to be of the same scale as the gas self-diffusion coefficient, and the corresponding effective permeability is derived. When 1/ increases,k/ kincreases, but the relationship is not linear as the Klinkenberg effect suggests. The effect of adsorption on the gas flow is significant in nanopores (r≤2 nm). Adsorption increases apparent permeability in shales at low pressures and decreases it at high pressures.

关键词： Apparent gas permeability Shale Adsorbed gas Dissolved gas Surface diffusion

Enhancing PIV image and fractal descriptor for velocity and shear stresses propagation around a circular pier

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Geoscience Frontiers 2017年第4期8卷 869-883页

作者： Alireza Keshavarzi james Ball Water Department Shiraz University School of Civil and Environmental Engineering University of Technology Sydney

In this study,the fractal dimensions of velocity fluctuations and the Reynolds shear stresses propagation for flow around a circular bridge pier are *** the study reported herein,the fractal dimension of velocity fluctuations（u′,v′,w′） and the Reynolds shear stresses（u′v′ and u′w′） of flow around a bridge pier were computed using a Fractal Interpolation Function（FIF） *** velocity fluctuations of flow along a horizontal plane above the bed were measured using Acoustic Doppler Velocity meter（ADV）and Particle Image Velocimetry（P1V）.The PIV is a powerful technique which enables us to attain high resolution spatial and temporal information of turbulent flow using instantaneous time *** this study,PIV was used for detection of high resolution fractal scaling around a bridge *** results showed that the fractal dimension of flow fluctuated significantly in the longitudinal and transverse directions in the vicinity of the *** was also found that the fractal dimension of velocity fluctuations and shear stresses increased rapidly at vicinity of pier at downstream whereas it remained approximately unchanged far downstream of the *** higher value of fractal dimension was found at a distance equal to one times of the pier diameter in the back of the ***,the average fractal dimension for the streamwise and transverse velocity fluctuations decreased from the centreline to the side wall of the ***,the results from ADV measurement were consistent with the result from PIV,therefore,the ADV enables to detect turbulent characteristics of flow around a circular bridge pier.

关键词： Fractal dimension Fractal interpolation function Fractal scaling Bridge pier Turbulent flow

The Mysterious Mid-Carnian “Wet Intermezzo” Global Event

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Journal of Earth Science 2015年第2期26卷 181-191页

作者： james G.Ogg Department of Earth Atmospheric and Planetary Sciences Purdue University Key Laboratory of Biogeology and Environmental Geology of Ministry of Education China University of Geosciences

Approximately 230 million years ago in the middle of the Carnian stage of the Upper Triassic, the sedimentary records in different regional basins display dramatic changes. Tropical carbonate platforms abruptly ended, and engorged river systems left widespread sand-rich layers across inland basins and coastal regions. This pulse lasted less than a million years in some basins, but constituted a permanent shift in others. Following this event, the Late Carnian has the earliest record of significant dinosaurs on land and the emergence of the calcareous nannoplankton in the oceans that now govern Earth＇s carbon cycle. This ＂most distinctive climate change within the Tri- assic＂ has been interpreted by some geoscientists as a global disruption of the Earth＇s land-ocean-biological system. The eruption of the Wrangellia large igneous province may have been the trigger for a sudden carbon-dioxide-induced warming and associated increased rainfall in some of these regions. Indeed, some workers have proposed that this ＂wet intermezzo＂ warming event is a useful analog to aid in predicting the effects of our future greenhouse on land ecosystems and ocean chemistry. However, the understanding of the onset, duration, global impacts and relatively rapid termination of this postulated warming pulse has been hindered by lack of a global dataset with inter-calibrated terrestrial and marine biostratigraphy, precise radio-isotopic ages, stable isotope records of temperature and the carbon system, and cycle-calibrated rates of regional and global change.

关键词： Triassic Carnian climate pluvial Wrangellia carbon isotope excursion dolomite China LIP Yangtze Platform Wet Intermezzo large igneous province.

Defining laboratory reference values and decision limits＇ populations, intervals, and interpretations

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Asian Journal of Andrology 2010年第1期12卷 83-90页

作者： james C. Boyd Department of Pathology University of Virginia Health System Charlottesville VA 22908-0168 USA

This article provides a brief overview of various approaches that may be utilized for the analysis of human semen test results. Reference intervals are the most widely used tool for the interpretation of clinical laboratory results. Reference interval development has classically relied on concepts elaborated by the International Federation of Clinical Chemistry Expert Panel on Reference Values during the 1980s. These guidelines involve obtaining and classifying samples from a healthy population of at least 120 individuals and then identifying the outermost 5% of observations to use in defining limits for two-sided or one-sided reference intervals. More recently, decision limits based on epidemiological outcome analysis have also been introduced to aid in test interpretation. The reference population must be carefully defined on the basis of the intended clinical use of the underlying test. To determine appropriate reference intervals for use in male fertility assessment, a reference population of men with documented time to pregnancy of 〈 12 months would be most suitable. However, for epidemiological assessment of semen testing results, a reference population made up ofunselected healthy men would be preferred. Although reference and decision limits derived for individual semen analysis test results will undoubtedly be the interpretational tools of choice in the near future, in the long term, multivariate methods for the interpretation of semen analysis alone or in combination with information from the female partner seem to represent better means for assessing the likelihood of achieving a successful pregnancy in a subfertile couple.

关键词： decision limits fertility assessment human semen testing likelihood ratios reference values semen analysis

A comparison of the ballistic behaviour of conventionally sintered and additively manufactured alumina

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Defence Technology（防务技术） 2020年第2期16卷 275-282页

作者： Gareth james Appleby-Thomas Kevin Jaansalu Amer Hameed Jonathan Painter james Shackel Julie Rowley Centre for Defence Engineering Cranfield Defence and SecurityCranfield UniversityShrivenhamSwindonSN68LAUK Department of Chemistry and Chemical Engineering Royal Military College of CanadaPO Box 17000Station ForcesKingstonOntarioK7K 7B4Canada

Production of ceramic armour solutions on-demand/in-theatre would have significant logistical and military ***,even assuming that such technologies could be successfully deployed in the field,such near net-shape manufacturing technology is relatively immature compared to conventional sintering of *** this study,the ballistic performance of a series of additively manufactured(AM)/rapidly-prototyped(RP)alumina tiles of 97.2%of the density of Sintox FATM were investigated using both forward-and reverse-ballistic *** experiments,undertaken with compressed gasguns,employed the depth-of-penetration technique and flash X-ray as primary diagnostics to interrogate both efficiency of penetration and projectile-target interaction,*** RP alumina was found to exhibit useful ballistic properties,successfully defeating steel-cored(AP)7.62×39 mm BXN rounds at velocities of up-to c.a.850 m/s,while exhibiting comparable failure modes to conventionally sintered armour-grade Sintox ***,where a<1%by *** dopant was introduced into the RP material failure modes changed dramatically with performance dropping below that of conventionally sintered ***,the results from both sets of experiments were complimentary and clearly indicated the potential of such RP materials to play an active role in provision of real-world body armour solutions provided quality control of the RP material can be maintained.

关键词： Additive manufacture Rapidly prototyped Body armour Ballistics Ceramics

Robust control for electric vehicle powertrains

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Control Theory and Technology 2019年第4期17卷 382-392页

作者： Johannes BUERGER james ANDERSON BMW Group MunichGermany Department of Computing and Mathematical Sciences the California Institute of TechnologyPasadenaU.S.A.

This paper considers the application of robust control methods(μ-and H∞-synthesis)to the speed and acceleration control problem encountered in electric vehicle *** this end,we consider a two degree of freedom control structure with a reference *** underlying powertrain model is derived and combined into the corresponding interconnected system required forμ-and H∞-*** closed-loop performance of the resulting controllers are compared in a detailed simulation analysis that includes nonlinear *** is observed that theμ-controller offers performance advantages in particular for the acceleration control problem,but at the price of a high-order controller.

关键词： Automotive control electric vehicle powertrains robust control

Fundamental modeling issues on benchmark structure for structural health monitoring

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Science China(Technological Sciences) 2009年第7期52卷 1999-2008页

作者： HU Sau-Lon james Department of Ocean Engineering University of Rhode Island Narragansett RI 02882-1197 USA

The IASC-ASCE Structural Health Monitoring Task Group developed a series of benchmark problems, and participants of the benchmark study were charged with using a 12-degree-of-freedom (DOF) shear building as their identification model. The present article addresses improperness, including the parameter and modeling errors, of using this particular model for the intended purpose of damage detec- tion, while the measurements of damaged structures are synthesized from a full-order finite-element model. In addressing parameter errors, a model calibration procedure is utilized to tune the mass and stiffness matrices of the baseline identification model, and a 12-DOF shear building model that preserves the first three modes of the full-order model is obtained. Sequentially, this calibrated model is employed as the baseline model while performing the damage detection under various damage scenarios. Numerical results indicate that the 12-DOF shear building model is an over-simplified identification model, through which only idealized damage situations for the benchmark structure can be detected. It is suggested that a more sophisticated 3-dimensional frame structure model should be adopted as the identification model, if one intends to detect local member damages correctly.

关键词： benchmark structural health monitoring damage detection modeling error