다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

This chapter introduces the finite element method (FEM) as a tool for solution of classical electromagnetic problems. Although we discuss the main points in the application of the finite element method to electromagnetic design, including formulation and implementation, those who seek deeper understanding of the finite element method should consult some of the works listed in the bibliography section.

Introduction to the Finite Element Method

PREFACE. ACKNOWLEDGMENTS. PROLOGUE. 1 INTRODUCTION. 1.1 Historical Perspective. 1.2 Diagnostic and Prognostic System Requirements. 1.3 Designing in Fault Diagnostic and Prognostic Systems. 1.4 Diagnostic and Prognostic Functional Layers. 1.5 Preface to Book Chapters. 1.6 References. 2 SYSTEMS APPROACH TO CBM/PHM. 2.1 Introduction. 2.2 Trade Studies. 2.3 Failure Modes and Effects Criticality Analysis (FMECA). 2.4 System CBM Test-Plan Design. 2.5 Performance Assessment. 2.6 CBM/PHM Impact on Maintenance and Operations: Case Studies. 2.7 CBM/PHM in Control and Contingency Management. 2.8 References. 3 SENSORS AND SENSING STRATEGIES. 3.1 Introduction. 3.2 Sensors. 3.3 Sensor Placement. 3.4 Wireless Sensor Networks. 3.5 Smart Sensors. 3.6 References. 4 SIGNAL PROCESSING AND DATABASE MANAGEMENT SYSTEMS. 4.1 Introduction. 4.2 Signal Processing in CBM/PHM. 4.3 Signal Preprocessing. 4.4 Signal Processing. 4.5 Vibration Monitoring and Data Analysis. 4.6 Real-Time Image Feature Extraction and Defect/Fault Classification. 4.7 The Virtual Sensor. 4.8 Fusion or Integration Technologies. 4.9 Usage-Pattern Tracking. 4.10 Database Management Methods. 4.11 References. 5 FAULT DIAGNOSIS. 5.1 Introduction. 5.2 The Diagnostic Framework. 5.3 Historical Data Diagnostic Methods. 5.4 Data-Driven Fault Classification and Decision Making. 5.5 Dynamic Systems Modeling. 5.6 Physical Model-Based Methods. 5.7 Model-Based Reasoning. 5.8 Case-Based Reasoning (CBR). 5.9 Other Methods for Fault Diagnosis. 5.10 A Diagnostic Framework for Electrical/Electronic Systems. 5.11 Case Study: Vibration-Based Fault Detection and Diagnosis for Engine Bearings. 5.12 References. 6 FAULT PROGNOSIS. 6.1 Introduction. 6.2 Model-Based Prognosis Techniques. 6.3 Probability-Based Prognosis Techniques. 6.4 Data-Driven Prediction Techniques. 6.5 Case Studies. 6.6 References. 7 FAULT DIAGNOSIS AND PROGNOSIS PERFORMANCE METRICS. 7.1 Introduction. 7.2 CBM/PHM Requirements Definition. 7.3 Feature-Evaluation Metrics. 7.4 Fault Diagnosis Performance Metrics. 7.5 Prognosis Performance Metrics. 7.6 Diagnosis and Prognosis Effectiveness Metrics. 7.7 Complexity/Cost-Benefit Analysis of CBM/PHM Systems. 7.8 References. 8 LOGISTICS: SUPPORT OF THE SYSTEM IN OPERATION. 8.1 Introduction. 8.2 Product-Support Architecture, Knowledge Base, and Methods for CBM. 8.3 Product Support without CBM. 8.4 Product Support with CBM. 8.5 Maintenance Scheduling Strategies. 8.6 A Simple Example. 8.7 References. APPENDIX. INDEX.

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Intelligent Fault Diagnosis and Prognosis for Engineering Systems

Boundary Value Problems in Physics and Engineering By Frank Chorlton. Pp. 250. (Van Nostrand: London, July 1969.) 70s

Boundary value problems

random data analysis and measurement procedures is available in our digital library an online access to it is set as public so you can get it instantly. Our book servers spans in multiple countries, allowing you to get the most less latency time to download any of our books like this one. Merely said, the random data analysis and measurement procedures is universally compatible with any devices to read.

Random Data Analysis And Measurement Procedures

The readers ought to be aware of some claims based on unfounded theories in the subject paper [1], which could possibly distort results and hinder future research and development. To start, Eq. (3) in the subject paper is stated to be taken from Ref. [70] (Johnson’s classical textbook). However, said Eq. (3) is imprecise because it uses a constant coefficient θy = 1.1, as claimed. That coefficient does not account for the variability in compressibility of the materials in contact, i.e., the Poisson’s ratios of the materials. The general range of Poisson’s ratios, ν, for crystalline and engineering materials is between -1 and 0.5. For example, ν = 0.2 for cast iron, ν = 0.18 for glass, or ν = 0.44 for gold. There are many materials and crystallines that have negative Poisson ratios (some are even time-dependent). Thus, limiting analyses and discussions to narrow subsets of Poisson ratios, say around 0.3, would likewise be narrow. That dependence upon Poisson’s ratio is addressed not only in Ref. [70], but also in other dated work, such as by the Chang et al. (CEB) model [2]. The CEB derivation, however, has other flaws—see discussions in Refs. [3] and [4].There is another, and even more significant problem in the subject paper in regards to what constitutes the “yield strength” when the half-space and the sphere in contact have dissimilar material properties. The authors base their Eq. (6) on references [40,71,72]. Starting with Ref. [40], in which no form of Eq. (6) is present, but the author there offers an “effective hardness,” or a “reduced hardness” for bodies having dissimilar material properties. In one case it is postulated that H = (1/H1+ 2/H2)−1, and then H = (2/H1+ 2/H2)−1. Not only that these two equations yield very different results, more importantly, there is no scientific or engineering foundation for such a “reduced hardness.” In Ref. [67], the same author in addition to the “reduced hardness” also offers the form of Eq. (6) used in the subject paper [1]. However, a review by Ghaednia et al. [5] states on these offerings: “Note that there appears to be no fundamental mechanics based derivation for [the said equations]… [it] is not possible for combining the plasticity properties of two contacting bodies [in that manner].” Then, Ref. [71] does not support anywhere the said Eq. (6). Reference [72] proposes an ad hoc equation (identical to Eq. (6)) but careful reading reveals that that postulation is particular to “Level III – plasticity,” i.e., full and complete plasticity of the surfaces with particular attention directed at the edges of contact and not at the onset of yielding taking place at a point under the contacting surface at the centerline. Those conditions in Ref. [72] have little to do with tribology. The bottom line is that the authors’ Eq. (6) cannot be fundamentally supported and should never be used. That equation affects the authors’ parameters at yielding onset in their Eqs. (3)–(5).The authors would have been served better had they reviewed the additional Ref. [6] given below, which was published nearly two decades ago. That reference derives analytically all of the relevant parameters at plasticity onset for hemispherical and cylindrical contacts and specifically addresses correctly how to handle contacting bodies having dissimilar material properties without the limitation of the Poisson ratio value over its entire range. That approach is used in Ref. [7] on a whole array of different cases of impacting spheres against flat plates where the bodies have vast material properties dissimilarities. Notably, contact unloading (the objective of the subject paper [1]) is implicitly incorporated in the restitution phase in Ref. [7]. The accuracies of the results in Ref. [7] vary from excellent to perfect when compared to finite element analysis and experimental results obtained independently by Higgs et al. [8–10]. To benefit the reader, the following recaps the underlying fundamentals. The discussion below signifies S as the strength, while σ signifies the stress.When two contacting bodies are ductile and have dissimilar material properties—suppose that the yield strengths, Sy1 ≠ Sy2, etc.—then it is imperative to use the procedure detailed by Green [6] to calculate the critical parameters (significant errors might ensue otherwise). Briefly, in normal elastic contacts, Green [6] defined C = po/σe-max to be the ratio between the maximum Hertzian contact pressure, po, and the maximum von Mises stress,1σe-max (which transpires in normal three-dimensional contact under the surface along the centerline). That ratio solely depends upon the Poisson ratio. A curve-fit is given in Ref. [3] to a numerical solution of a transcendental equation, rendering for hemispherical (3D) contacts, C(v) = 1.295exp(0.736ν), while in Ref. [6] a slightly higher fidelity expression is provided, C(v) = 1.30075 + 0.87825 ν+0.54373 ν2. In elastic Hertzian contacts, the two bodies share the same contact area and the same maximum pressure, po. Abiding by the von Mises criterion,2σe-max = Sy at yielding onset, the product C(ν)· Sy gives identically the corresponding critical contact pressure, poy ≡ C(ν)· Sy, that would initiate yielding for that body. For dissimilar materials, Green [6] instructs to pick the smallest between two maximum contact pressure possibilities to decide which of the contacting bodies yields first. Hence(1)(poy)min≡CSy=min[C(ν1)Sy1,C(ν2)Sy2]where(2)C(ν)=1.295exp(0.736ν)Equations (1) and (2) are now used to calculate the critical interference, load, and contact radius, which are also given in Ref. [6]. In the subject paper’s notation these are(3)δy=(π(poy)min2E*)2R=(π(CSy)2E*)2R(4)Fy=16(RE*)2[π(poy)min]3=16(RE*)2[π(CSy)]3(5)ay=π(poy)min2E*R=π(CSy)2E*Rwhere R is the composite radius calculated by 1/R = 1/R1+ 1/R2, and E* is the equivalent modulus of elasticity. Emphasizing, C and Sy always appear grouped in a product to signify the minimum value of the maximum contact pressure that brings upon yielding onset, (poy)min ≡ (CSy), occurring in either material 1 or material 2 according to Eq. (1). Hence, the current Eqs. (3)–(5) given here should replace the corresponding equations in Ref. [1], while current Eqs. (1) and (2) should be used instead of the unfounded Eq. (6) in Ref. [1] (and, of course, in other works as well). Note that all parameters in Eqs. (1)–(5) account accurately for the Poisson ratios regardless of their values or ranges.Another issue is the authors’ usage of ratios such as E*/Sy throughout the paper (see Table 1 and other locations in the paper). That reciprocal of that ratio denotes an equivalent strain at yielding onset. That aspect is again discussed in Refs. [3,7]. Following the same logic as in Eq. (1), we have(6)εy*={Sy1/E*↔C(ν1)Sy1≤C(ν2)Sy2Sy2/E*↔C(ν1)Sy1>C(ν2)Sy2The subject paper [1] uses its own critical parameter definitions to normalize and present results. Using the correct parameters given herein is bound to alter to some extent the presence of the outcomes. A considerable effort had been invested in the paper [1]. The subject of contact unloading rightfully deserves such an effort. The purpose of this discussion is to bring attention to the inaccuracies in the definitions used, as they are based on postulations and unfounded theories. There is the correct theory, and then there are all other “viewpoints.” In summary, based on sound analytical foundations in Ref. [6], this discussion explains and recasts the correct definitions of the critical parameters.There is no conflicts of interest.The data sets generated and supporting the findings of this article are obtainable from the corresponding author upon reasonable request. 

Discussion “Contact Unloading Behaviors of Elastic-Power-Law Strain Hardening Material Considering Indenter Elasticity Effect” (Chuanqing C., Qiao W., Hui W., Huaiping D., Wei H., Wenhao X., Panpan W., Liang J., and Xiaochun Y., 2022, ASME

Discussion: “A Multi-Objective Optimization Approach on Spiral Grooves for Gas Mechanical Seals” (Wang, X., Shi, L., Huang, W., and Wang, X., 2018, ASME J. Tribol., 140(4), p. 041701)

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Discussion: “Operation of Foil Bearings Beyond the Bending Critical Mode” [ASME J. Tribol., 122, No. 1, pp. 192–198 (2000)]

Tribology research at Georgia Tech


 Mechanical face seals are wide-spread in many applications, such as centrifugal compressors, submersible pumps, drill-bits for oil and water, hydrocarbon processing equipment, and turbomachinery. Often vibration and noise are unavoidable because of changing environments which can be persistent and forceful. In critical applications when seals fail, they may have significant or even catastrophic consequences. To ensure the safety of such machinery and its associated mechanical components, the vibration and noise must be diagnosed and kept within certain limits. This work focuses on the dynamics of a flexibly mounted stator mechanical face seal that is subjected to combinations of axial broad-band noisy vibrations of the shaft and the housing. The current analysis builds upon the dynamic models that have been developed over the last four decades. In all that body of work, the positions of the housing and the shaft have been considered fixed. The current work relaxes that condition, augmenting the equations of motion to incorporate the said noisy vibrations. While the exact root-causes and sources of machinery vibration are very difficult to ascertain, the current analysis uses some general common causes of noisy seal operation, and provides markers to be observed for diagnosis. While the forcing noises are assumed to originate along the main axis of the seal, because of the strong coupling between the axial and angular modes, the seal is affected (even strongly) in all modes (axial and angular). A numerical simulation ensues, and the results are subject to spectral analyses. Results show that under some design conditions, the seal is largely insensitive to machine vibrations. However, under other design parameters, the seal response exhibits a rich spectral content that stems from various transient phenomena that include (among others) half frequency whirl, synchronous steady-state response, and the natural (eigen) response. Under aggravated noisy conditions the investigated seal exhibits large oscillations and leakage, along with face contact and rubbing. Prolonged rubbing causes faces to wear and leads ultimately to seal failure.

Itzhak Green

Papers

Discussion “Contact Unloading Behaviors of Elastic-Power-Law Strain Hardening Material Considering Indenter Elasticity Effect” (Chuanqing C., Qiao W., Hui W., Huaiping D., Wei H., Wenhao X., Panpan W., Liang J., and Xiaochun Y., 2022, ASME

Discussion: “A Multi-Objective Optimization Approach on Spiral Grooves for Gas Mechanical Seals” (Wang, X., Shi, L., Huang, W., and Wang, X., 2018, ASME J. Tribol., 140(4), p. 041701)

Discussion: “Operation of Foil Bearings Beyond the Bending Critical Mode” [ASME J. Tribol., 122, No. 1, pp. 192–198 (2000)]

Tribology research at Georgia Tech

Mechanical Face Seal Dynamics Subjected to Machine Vibration and Noise