Mathematical Modeling and Analysis of Flutter in Bending-Torsion Coupled Beams, Rotating Blades, and Hard Disk Drives

In this study I present a review of several research directions in the area of mathematical analysis of flutter phenomenon. Flutter is known as a structural dynamical instability that occurs in a solid elastic structure interacting with a flow of gas or fluid, and consists of violent vibrations of the structure with rapidly increasing amplitudes. The focus of this review is a collection of models of fluid-structure interaction, for which precise mathematical formulations are available. The main objects of interest are analytical results on such models, which can be used for flutter explanation, its qualitative and even quantitative treatments. This paper does not pretend to be a comprehensive review of the enormous amount of engineering literature on analytical, computational, and experimental aspects of the flutter problem. I present a brief exposition of the results obtained in several selected papers or groups of papers on the following topics: (1) bending-torsion vibrations of coupled beams; (2) flutter in transmission lines; (3) flutter in rotating blades; (4) flutter in hard disk drives; (5) flutter in suspension bridges; and (6) flutter of blood vessel walls. Finally, I concentrate on the most well-known case of flutter, i.e., flutter in aeroelasticity. The last two sections of this review are devoted to the precise analytical results obtained in my several recent papers on a specific aircraft wing model in a subsonic, inviscid, incompressible airflow.     

Mathematical Modeling and Analysis of Flutter in Long-Span Suspension Bridges and in Blood Vessel Walls

A review of several research directions in the area of mathematical analysis of the flutter phenomenon is presented in the present study. Flutter is known as a structural dynamical instability, which occurs in a solid elastic structure interacting with a flow of gas or fluid and consists of violent vibrations of the structure with rapidly increasing amplitudes. The focus of this review is a collection of models of fluid-structure interactions, for which precise mathematical formulations are available. The main objects of interest are analytical results on such models, which can be used for flutter explanation, qualitative, and even quantitative treatments of the models. This study does not pretend to be a comprehensive review of the enormous engineering literature on analytical, computational, and experimental aspects of the flutter problem. The entire survey provides a brief exposition of the results obtained in several selected papers or groups of papers on the following topics: (1) Bending-torsion vibrations of coupled beams; (2) flutter in transmission lines; (3) flutter in rotating blades; (4) flutter in hard disk drives; (5) flutter in suspension bridges; and (6) flutter of blood vessel walls. The last topic of the review is devoted to the most well-known cases of flutter, i.e., flutter in aeroelasticity. Namely, the precise analytical results obtained in the author’s several recent papers on a specific aircraft wing model in a subsonic, inviscid, incompressible airflow are discussed.     

Improved Method for Creating Time-Domain Unsteady Aerodynamic Models

Multidisciplinary aeroservoelastic interactions are studied by the combination of knowledge acquired in two main disciplines: aeroelasticity and servocontrols. In aeroelasticity, the doublet lattice method is used to calculate the unsteady aerodynamic forces for a range of reduced frequencies and Mach numbers on a business aircraft in the subsonic flight regime by use of NASTRAN software. For aeroservoelasticity studies, there is the need to conceive methods for these unsteady aerodynamic forces conversions from frequency into Laplace domain. A new method different from classical methods is presented, in which Chebyshev polynomials theories and their orthogonality properties are applied. In this paper, a comparison between flutter results expressed in terms of flutter speeds and frequencies obtained with our method with flutter results obtained with classical Padé and least squares methods is presented for a business aircraft at one Mach number and a range of reduced frequencies. It has been found that results obtained with our method are better in terms of average error than results obtained with the two classical methods here presented.     

Autopilot for Reconfigurable Flight Control System

The main factor in design and operation of aircraft is safety of an airplane. The “safety culture” developed in aeronautics results in detailed regulations and certification procedures in all phases of aircraft design and operation. But despite that, aircraft safety depends on several unpredictable factors, such as the hostile actions both inside and outside of the aircraft. When failures occur during the flight, the most important actions are aimed at maintaining the aircraft controllability. The aircraft control system should be fault tolerant and ensure aircraft controllability in the event of the failure of a part of the flight control system. In this paper the influence of control surface failures on autopilot operation has been investigated. The autopilot is designed for business jet airplanes and fulfills the main functions of the real autopilot system in longitudinal and lateral directions. The autopilot structure allows implementation of various methods of reconfiguration for aircraft protection.     

Transverse Cracking of Concrete Bridge Decks: State-of-the-Art

This state-of-the-art paper presents the results of a comprehensive literature review of the cause of transverse deck cracking. It includes compilation of experimental and analytical research results as well as survey studies on the effects of different factors on concrete deck cracking. Consistent with the past work on the subject, causes of transverse deck cracking are classified under three categories, namely: (1) material and mix design, (2) construction practices and ambient condition factors, and (3) structural design factors. The literature review revealed that the first two items have been studied extensively over the past several decades, while literature is limited on the effect of structural design factors on deck cracking. This paper evaluates the existing work in depth and presents recommendations on mix design and construction procedures to reduce the potential for transverse deck cracking. Furthermore, areas for additional research are identified.     

Dynamic Aeroelastic Instabilities of an Aircraft Wing with Underwing Store in Transonic Regime

The research used the transonic small disturbance theory to better understand the dynamic aeroelastic phenomena and factors that affect the onset of flutter and store induced limit-cycle oscillations (LCO) in the transonic regime. Several parametric studies of the flutter and LCO of an aircraft wing with underwing store in the transonic regime were conducted, as well as an investigation of the effect of inclusion of store aerodynamics on the onset of flutter. The flutter sensitivity was analyzed for the following store parameters: (1) location of underwing store center of gravity with respect to aerodynamic root chord; (2) location of underwing store along the span of the wing; and (3) underwing clearance (pylon length). The parametric studies indicated that as the store center of gravity is moved fore of the elastic axis, the flutter velocity of the wing increased. Also, as the store is moved towards the aerodynamic tip chord, the flutter velocity of the wing decreased. The research work also concluded that as the underwing clearance is increased, the flutter velocity of the wing decreased. In addition to these results, it also helped in understanding that addition of store aerodynamics had no significant influence on the flutter velocity of the wing. Also, studies were conducted to identify the onset of LCO for different configurations of underwing store and flight regimes (unmatched analysis), thereby identifying the parameters that induce LCO. The sensitive parameters that affect flutter and LCO are identified.     

Adaptive Control of Aircraft Wing Flutter by Stress-Induced Stiffness Modification

Lightweight unoccupied air vehicles (UAVs) with wide wingspans are especially vulnerable to dynamic instability. Such instability can be contained by using mass and stiffness balancing and the shape and attitude of the aircraft in flight. Passive methods and pilot-operated devices such as dampers, ailerons, flaps, and other actuators, are currently used. Also, ongoing attempts exist to develop self-adaptive controls by using piezoelectric and other devices. The present work is concerned with controlling aerodynamic flutter by using stress-induced elements in selected structural components of the aircraft wing. A scheme has been developed to determine the “optimal” locations for such elements to be activated, in real time, to contain the dynamic instability or flutter condition. Various stress-induced stiffening schemes have been developed to modify the frequency response of aircraft wings by shifting the critical flutter speed to safe levels. Results and conclusions include the identification of the optimal location and type of the stress-induced elements and the magnitude and distribution of induced stress for best results with the least expense of energy during actuation.     

X射线荧光光谱在地球化学调查中的应用评介

中国的勘查地球化学在过去40年间走到了国际最前端,极大地带动了中国地质分析技术的发展,尤其是X射线荧光光谱(XRF)分析技术的应用水平得到了迅速发展和提高。作者记述了XRF分析技术在全国地球化学勘查(“化探扫面”)39个元素、多目标地球化学调查54个元素(指标)和国际地球化学填图76个元素分析3个配套方案中所发挥的重要作用、成果及其意义。在中国30多年的各类地球化学调查样品分析中,XRF提交的数以亿计的高质量数据是几代一线XRF工作者做出的令地球化学和分析化学家都惊叹的历史性贡献。文章收集和评介了1984—2018年间XRF在地球化学调查样品主、次、痕量多元素分析方面文献47篇,以列表方式统计了所用仪器、制样方法、校准与基体校正方法、测定组分及代表性元素的检出限等要点,其中测定组分超过30种的有15篇文献。对28篇方法研究及少数痕量分析文献也做了简述,最后评介了地球化学调查分析成果在地质分析技术发展中的意义,特别强调分析方法的整合与集成、标准与质量监控方法的统一和全国地质实验室的协调运作等措施为以后解决地质工作中的重大地质分析问题提供了宝贵经验。全篇引文129篇。     

X射线荧光光谱在地球化学调查中的应用评介

中国的勘查地球化学在过去40年间走到了国际最前端,极大地带动了中国地质分析技术的发展,尤其是X射线荧光光谱(XRF)分析技术的应用水平得到了迅速发展和提高。作者记述了XRF分析技术在全国地球化学勘查(“化探扫面”)39个元素、多目标地球化学调查54个元素(指标)和国际地球化学填图76个元素分析3个配套方案中所发挥的重要作用、成果及其意义。在中国30多年的各类地球化学调查样品分析中,XRF提交的数以亿计的高质量数据是几代一线XRF工作者做出的令地球化学和分析化学家都惊叹的历史性贡献。文章收集和评介了1984—2018年间XRF在地球化学调查样品主、次、痕量多元素分析方面文献47篇,以列表方式统计了所用仪器、制样方法、校准与基体校正方法、测定组分及代表性元素的检出限等要点,其中测定组分超过30种的有15篇文献。对28篇方法研究及少数痕量分析文献也做了简述,最后评介了地球化学调查分析成果在地质分析技术发展中的意义,特别强调分析方法的整合与集成、标准与质量监控方法的统一和全国地质实验室的协调运作等措施为以后解决地质工作中的重大地质分析问题提供了宝贵经验。全篇引文129篇。     

I can''t believe you asked that!

This paper is an introduction to this issue of review papers on the biological role of nitric oxide. The history, modern state, and promising directions for research in this field are briefly considered.     

Psychologist as ethics educator: Successes, failures, and unanswered questions.

Critically analyzes the literature documenting ethics education over the last 35 yrs, discussing changes in instructional methodology, current course content, and the empirical literature relevant to the outcomes of ethics education. This analysis reveals several gaps in the ethics competencies of students. The article next describes the results of a national survey of the views of 101 internship directors on the ethical capabilities of predoctoral interns in psychology. In contrast to ethics researchers, internship directors rate the ethics knowledge of psychology interns highly. It ends with a discussion of strengths and weaknesses of current knowledge and directions for future research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

In all directions.

Directions are normally given to help guide a person's behavior. However, at times, they can be misleading. Recently, I surveyed the directions published with some of the more popular standardized tests of the last fifteen years. I was particularly interested in the test makers' instructions to the examinee about "guessing." I found that, when viewed together, the directions from these various tests presented a rather confusing picture. Roughly 40% of the tests surveyed were to be scored with a subtraction for wrong answers. Presumably this was done to discourage guessing and to promote the habit of critical thinking by the examinee. The other tests employed a right-only score. For the tests which used a subtraction formula, the directions could be classified in three categories: (a) no directions, (b) a rather strong statement not to guess, and (c) a definite statement to guess. The tests which gave no directions about guessing also did not mention that a subtraction would be made for wrong answers. Another test advised the examinee not to guess, but gave as a reason that it wasted time, and did not mention the penalty. Directions for tests which used a rights-only score could also be grouped into three categories: (a) no directions, (b) a cautious suggestion to guess, and (c) a definite statement to guess. It is likely that the test makers have given considerable thought to their directions and have written them with a purpose. Despite this, the survey shows that they have ridden off in all directions. To present a more professional image to the public, in the area of testing, I would suggest that the test makers get together and try to agree upon some standardized instructions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Liquefaction Resistance of Soils: Summary Report from the 1996 NCEER and 1998 NCEER∕NSF Workshops on Evaluation of Liquefaction Resistance of Soils

Following disastrous earthquakes in Alaska and in Niigata, Japan in 1964, Professors H. B. Seed and I. M. Idriss developed and published a methodology termed the “simplified procedure” for evaluating liquefaction resistance of soils. This procedure has become a standard of practice throughout North America and much of the world. The methodology which is largely empirical, has evolved over years, primarily through summary papers by H. B. Seed and his colleagues. No general review or update of the procedure has occurred, however, since 1985, the time of the last major paper by Professor Seed and a report from a National Research Council workshop on liquefaction of soils. In 1996 a workshop sponsored by the National Center for Earthquake Engineering Research (NCEER) was convened by Professors T. L. Youd and I. M. Idriss with 20 experts to review developments over the previous 10 years. The purpose was to gain consensus on updates and augmentations to the simplified procedure. The following topics were reviewed and recommendations developed: (1) criteria based on standard penetration tests; (2) criteria based on cone penetration tests; (3) criteria based on shear-wave velocity measurements; (4) use of the Becker penetration test for gravelly soil; (4) magnitude scaling factors; (5) correction factors for overburden pressures and sloping ground; and (6) input values for earthquake magnitude and peak acceleration. Probabilistic and seismic energy analyses were reviewed but no recommendations were formulated.     

Liquefaction Resistance of Soils: Summary Report from the 1996 NCEER and 1998 NCEER∕NSF Workshops on Evaluation of Liquefaction Resistance of Soils

Following disastrous earthquakes in Alaska and in Niigata, Japan in 1964, Professors H. B. Seed and I. M. Idriss developed and published a methodology termed the “simplified procedure” for evaluating liquefaction resistance of soils. This procedure has become a standard of practice throughout North America and much of the world. The methodology which is largely empirical, has evolved over years, primarily through summary papers by H. B. Seed and his colleagues. No general review or update of the procedure has occurred, however, since 1985, the time of the last major paper by Professor Seed and a report from a National Research Council workshop on liquefaction of soils. In 1996 a workshop sponsored by the National Center for Earthquake Engineering Research (NCEER) was convened by Professors T. L. Youd and I. M. Idriss with 20 experts to review developments over the previous 10 years. The purpose was to gain consensus on updates and augmentations to the simplified procedure. The following topics were reviewed and recommendations developed: (1) criteria based on standard penetration tests; (2) criteria based on cone penetration tests; (3) criteria based on shear-wave velocity measurements; (4) use of the Becker penetration test for gravelly soil; (4) magnitude scaling factors; (5) correction factors for overburden pressures and sloping ground; and (6) input values for earthquake magnitude and peak acceleration. Probabilistic and seismic energy analyses were reviewed but no recommendations were formulated.     

Growth differences of Capnocytophaga canimorsus strains and some other fastidious organisms on various Columbia-based blood agar media

It is a little-known fact that lightning casualties often involve travel or transportation. López and colleagues, in their studies on the epidemiology of lightning injuries, have reported that 10% of lightning injuries are categorized under transportation. In the majority of their cases, victims were struck while standing outside or near their vehicles during a thunderstorm. During my review of the neurologic complications of lightning injuries, I was impressed by the number of case reports in which the victim was struck while either in or near a vehicle, airplane or vessel. In this article, I shall put forth information on four aspects of lightning that relate to the danger to people traveling in vehicles, boats, and airplanes. First, I shall deal with lightning safety on ships and boats. People who enjoy recreational sailing, including the "weekend sailor" and those who enjoy fishing from a boat, should be fortified with knowledge about lightning protection. Second, I shall consider the matter of lightning strikes to aircraft. In the third section, I shall discuss the question of lightning safety in automobiles. Fourth, I shall review those cases found in my literature review in which the victim was struck while in or near a vehicle, boat, or airplane.     

Lateral–Torsional Buckling of Singly Symmetric Tapered Beams: Theory and Applications

A general variational formulation to analyze the elastic lateral–torsional buckling (LTB) behavior of singly symmetric thin-walled tapered beams is presented, numerically implemented, validated and illustrated. It (1) begins with a precise geometrical definition of a tapered beam; (2) extends the kinematical assumptions traditionally adopted to study the LTB of prismatic beams; (3) includes a careful derivation of the beam total potential energy; and (4) employs Trefftz’s criterion to ensure the beam adjacent equilibrium. In order to validate and illustrate the application and capabilities of the proposed formulation, several numerical results are presented, discussed and, when possible, also compared with values reported by other authors. These results (1) are obtained by means of the Rayleigh–Ritz method, using trigonometric functions to approximate the beam critical buckling mode, and (2) concern the critical moments of doubly and singly symmetric web-tapered I-section simply supported beams and cantilevers acted by point loads. In particular, one shows that modeling a tapered beam as an assembly of prismatic beam segments is conceptually inconsistent and may lead to rather inaccurate (safe or unsafe) results. Finally, it is worth mentioning that the paper includes a state-of-the-art review concerning one-dimensional analytical formulations for the LTB behavior of tapered beams.     

Flutter of a Swept Aircraft Wing with a Powered Engine

The flutter analysis of swept aircraft wings carrying a powered engine is presented. Because of the powered engine, both concentrated engine mass and the thrust force terms are combined in the governing equations which are obtained using Hamilton’s principle. Heaviside and Dirac delta functions are used to precisely consider the location and properties of the engine mass and the thrust force. The wing performs as a classical beam; and the structural model, which incorporates bending-torsion flexibility, is used. Also, Peter’s unsteady aerodynamic pressure loadings are considered and modified to take the sweep effects into account. The Galerkin method is subsequently applied to convert the partial differential equations into a set of ordinary differential equations. Moreover, the numerical results are compared with published results and excellent agreement is observed. Numerical simulations indicating the significant effects of the sweep angle, the thrust and the design parameters such as the mass ratio and the engine attached locations on the flutter boundaries are presented.     

Review of CPA review of annals of theoretical psychology, Volume 3.

Reviews the book, CPA review of annals of theoretical psychology, Volume 3 edited by K. B. Madsen and L. P. Mos (1985). This book deals with metatheory, or with: theory-laden facts, linked to theory-laden hypotheses, linked to theory-laden epistemology, linked to theory-laden ontology. Part of a five volume series which presents the work of international scholars, this third volume, a three hundred and fifty page treatise, includes: an introductory chapter on metatheory; five major papers; three commentaries per paper; and a reply from the author of each major paper. The reviewer recommends this book highly, and regret that limited space has made it impossible to enumerate the probing insights of its many contributors. In future volumes the reviewer would like to see authors discuss the implications for their work of Simon's concept of bounded rationality (1979, 1983), and discuss as well its implications for rational empiricism in general, and for Popperian revisions in particular. (PsycINFO Database Record (c) 2010 APA, all rights reserved)