Showing papers by "Beihang University published in 2003"

The Use of Kalman Filter and Neural Network Methodologies in Gas Turbine Performance Diagnostics: A Comparative Study

Abstract: The goal of gas turbine performance diagnositcs is to accurately detect, isolate, and assess the changes in engine module performance, engine system malfunctions and instrumentation problems from knowledge of measured parameters taken along the engine’s gas path. The method has been applied to a wide variety of commercial and military engines in the three decades since its inception as a diagnostic tool and has enjoyed a reasonable degree of success. During that time many methodologies and implementations of the basic concept have been investigated ranging from the statistically based methods to those employing elements from the field of artificial intelligence. The two most publicized methods involve the use of either Kalman filters or artificial neural networks (ANN) as the primary vehicle for the fault isolation process. The present paper makes a comparison of these two techniques. @DOI: 10.1115/1.1419016#

Effect of Ni excess on phase transformation temperatures of NiMnGa alloys

Abstract: A systematic substitution of Ni for Mn, Ga, or both Mn and Ga in the non-stoichiometric NiMnGa alloys is performed. The relationship among the composition, structure and martensitic transformation temperatures was studied in detail for the Ni excessive NiMnGa alloys. The martensitic transformation temperatures almost linearly increase with increasing Ni content in all the three series from lower than 0 °C up to 300 °C. The increases in rate of the martensitic transformation temperatures are different for the three cases. It is large for Ga substituted by Ni, slow for Mn and intermediate for both Mn and Ga. The size factor and electronic concentrations are thought to influence the martensitic transformation temperature in the NiMnGa alloys. The determined relationship will be significant for designing a suitable NiMnGa alloy with a required martensitic transformation temperature for application at a specific temperature.

Lift and power requirements of hovering insect flight

Abstract: Lift and power requirements for hovering flight of eight species of insects are studied by solving the Navier-Stokes equation numerically. The solution provides velocity and pressure fields, from which unsteady aerodynamic forces and moments are obtained. The inertial torque of wing mass are computed analytically. The wing length of the insects ranges from 2 mm (fruit fly) to 52mm (hawkmoth); Reynolds numbersRe (based on mean flapping speed and mean chord length) ranges from 75 to 3 850. The primary findings are shown in the following: (1) Either small (R=2mm,Re=75), medium (R≈10mm,Re≈500) or large (R≈50 mm,Re≈4000) insects mainly employ the same high-lift mechanism, delayed stall, to produce lift in hovering flight. The midstroke angle of attack needed to produce a mean lift equal to the insect weight is approximately in the range of 25° to 45°, which is approximately in agreement with observation. (2) For the small insect (fruit fly) and for the medium and large insects with relatively small wingbeat frequency (cranefly, ladybird and hawkmoth), the specific power ranges from 18 to 39 W·kg−1, the major part of the power is due to aerodynamic force, and the elastic storage of negatige work does not change the specific power greatly. However for medium and large insects with relatively large wingbeat frequency (hoverfly, dronefly, honey bee and bumble bee), the specific power ranges from 39 to 61 W·kg−1, the major part of the power is due to wing inertia, and the elastic storage of negative work can decrease the specific power by approximately 33%. (3) For the case of power being mainly contributed by aerodynamic force (fruit fly, cranefly, ladybird and hawkmoth), the specific power is proportional to the product of the wingbeat frequency, the stroke amplitude, the wing length and the drag-to-lift ratio. For the case of power being mainly contributed by wing inertia (hoverfly, dronefly, honey bee and bumble bee), the specific power (without elastic storage) is proportional to the product of the cubic of wingbeat frequency, the square of the stroke amplitude, the square of the wing length and the ratio of wing mass to insect mass.

Aerodynamic force generation and power requirements in forward flight in a fruit fly with modeled wing motion.

Abstract: Aerodynamic force generation and power requirements in forward flight in a fruit fly with modeled wing motion were studied using the method of computational fluid dynamics. The Navier-Stokes equations were solved numerically. The solution provided the flow velocity and pressure fields, from which the vorticity wake structure and the unsteady aerodynamic forces and torques were obtained (the inertial torques due to the acceleration of the wing-mass were computed analytically). From the flow-structure and force information, insights were gained into the unsteady aerodynamic force generation. On the basis of the aerodynamic and inertial torques, the mechanical power was obtained, and its properties were investigated. The unsteady force mechanisms revealed previously for hovering (i.e. delayed stall, rapid acceleration at the beginning of the strokes and fast pitching-up rotation at the end of the strokes) apply to forward flight. Even at high advance ratios, e.g. J=0.53-0.66 (J is the advance ratio), the leading edge vortex does not shed (at such advance ratios, the wing travels approximately 6.5 chord lengths during the downstroke). At low speeds (J approximately equal to 0.13), the lift (vertical force) for weight support is produced during both the down- and upstrokes (the downstroke producing approximately 80% and the upstroke producing approximately 20% of the mean lift), and the lift is contributed mainly by the wing lift; the thrust that overcomes the body drag is produced during the upstroke, and it is contributed mainly by the wing drag. At medium speeds (J approximately equal to 0.27), the lift is mainly produced during the downstroke and the thrust mainly during the upstroke; both of them are contributed almost equally by the wing lift and wing drag. At high speeds (J approximately equal to 0.53), the lift is mainly produced during the downstroke and is mainly contributed by the wing drag; the thrust is produced during both the down- and upstrokes, and in the downstroke, is contributed by the wing lift and in the upstroke, by the wing drag. In forward flight, especially at medium and high flight speeds, the work done during the downstroke is significantly greater than during the upstroke. At advance ratios J approximately equal to 0.13, 0.27 and 0.53, the work done during the downstroke is approximately 1.6, 2.8 and 4.2 times as much as that during the upstroke, respectively. At J=0 (hovering), the body-mass-specific power is approximately 29 W kg(-1); at J=0.13 and 0.27, the power is approximately 10% less than that of hovering; at J=0.40, the power is approximately the same as that of hovering; when J is further increased, the power increases sharply. The graph of power against flying speeds is approximately J-shaped. From the graph of power against flying speeds, it is predicted that the insect usually flies at advance ratios between zero and 0.4, and for fast flight, it would fly at an advance ratio between 0.4 and 0.53.

Mean-variance-skewness model for portfolio selection with transaction costs

Abstract: The mean-variance methodology originally proposed by Markowitz (1952) plays a crucial role in the theory of portfolio selection and gains widespread acceptance as a practical tool for portfolio optimization. Since the seminal works of Markowitz, numerous studies on portfolio selection and performance measures have been made based on only the first two moments of return distributions. However, there is a controversy over the issue of whether higher moments should be accounted for in portfolio selection. Many authors (e.g., [Arditti (1967,1971), Samuelson (1958), Rubinstein (1973), Konno et al. (1995)]) argued that the higher moments can not be neglected unless there is a reason to believe that the asset returns are normally distributed and the utility function is quadratic, or that the higher moments are irrelevant to the investor’s decision.

Self-organized Synthesis of Silver Chainlike and Dendritic Nanostructures via a Solvothermal Method

Abstract: Well-defined silver chainlike and dendritic nanostructures with fractal features were self-organized via a simple solvothermal method using poly(vinyl pyrrolidone) (PVP) as an adsorption agent and architecture soft template. The branching fractal morphology was reasonably explained by using the Cayley tree model. There is no obvious boundary observed at necks between continuous Ag particles. With prolonging reaction duration, the necks disappear, and the growth of the chainlike silver leads to the formation of the Ag dendritic nanostructure and nanowires. The formation of the Ag dendritic nanostructure can be explained as a process of initial reduction−nucleation−adsorption−growth−branching−growth.

Comparison of static response of structures using convex models and interval analysis method

Abstract: In this paper, by combining the finite element analysis and non-probabilistic convex models, we present the numerical algorithm of non-probabilistic convex models and interval analysis method for the static displacement of structures with uncertain-but-bounded parameters. Under the condition of the box or interval vector determined from the ellipsoid of the uncertain-but-bounded structural parameter vector, by comparing the numerical algorithm of non-probabilistic convex models and the interval analysis method in the mathematical proof and the numerical example, we can see that the width of the maximum or upper and minimum or lower bounds on the static displacement yielded by the numerical algorithm of non-probabilistic convex models is tighter than those produced by the interval analysis method. Copyright © 2003 John Wiley & Sons, Ltd.

Many Hard Examples in Exact Phase Transitions

Abstract: This paper first analyzes the resolution complexity of two random CSP models (i.e. Model RB/RD) for which we can establish the existence of phase transitions and identify the threshold points exactly. By encoding CSPs into CNF formulas, it is proved that almost all instances of Model RB/RD have no tree-like resolution proofs of less than exponential size. Thus, we not only introduce new families of CNF formulas hard for resolution, which is a central task of Proof-Complexity theory, but also propose models with both many hard instances and exact phase transitions. Then, the implications of such models are addressed. It is shown both theoretically and experimentally that an application of Model RB/RD might be in the generation of hard satisfiable instances, which is not only of practical importance but also related to some open problems in cryptography such as generating one-way functions. Subsequently, a further theoretical support for the generation method is shown by establishing exponential lower bounds on the complexity of solving random satisfiable and forced satisfiable instances of RB/RD near the threshold. Finally, conclusions are presented, as well as a detailed comparison of Model RB/RD with the Hamiltonian cycle problem and random 3-SAT, which, respectively, exhibit three different kinds of phase transition behavior in NP-complete problems.

Influences of Mounting Angles and Locations on the Effects of Gurney Flaps

Abstract: Experimental investigations were conducted on a NACA0012 airfoil to determine the influences of mounting angles and mounting locations on the lift-enhancing effects of Gurney flaps at a Reynolds number of 2.1 x 10 6 . The results revealed that all flaps of different mounting angles increased the lift coefficient, and an increment of maximum lift coefficient of 12.3, 15.1, and 17.4% was obtained by 45-, 60-, and 90-deg Gurney flap, respectively. There was a drag penalty associated with the lift enhancement. The best performance was obtained by the 45-deg Gurney flap for all flap deflections tested. When shifted forward from the trailing edge of the airfoil, the Gurney flap led to a decrease in lift, and an increment in drag, and thus a reduction in lift-to-drag ratio

Cured Shape of Cross-Ply Composite Thin Shells

Abstract: For a composite laminated plate, it has been found that classical laminate theory (CLT) can not always predict the final cured shape correctly and geometric nonlinearity must be considered. For com...

A study of aluminide coatings on TiAl alloys by the pack cementation method

Abstract: The lower case halide-activated pack cementation method was utilized to deposit aluminide coatings on TiAl alloys Emphasis was placed on the effect of alloying elements on the aluminizing behavior of TiAl alloy The addition of a small amount of Nb or Cr in the TiAl improved significantly the aluminizing kinetics of TiAl alloys by increasing the solid-state diffusion of Al through the formation of stable TiAl 3 layer The TiAl 3 layer formed on the TiAl alloyed with Nb or Cr had better toughness than the TiAl 3 formed on the non-alloyed TiAl The reason for better toughness of the coating formed on TiAl was that partial TiAl 3 with tetragonal structure was changed to high symmetry cubic L1 2 structure since Nb or Cr was dissolved into TiAl 3 The TiAl 3 layer formed on the TiAl alloyed with Nb or Cr had much better oxidation resistance than the TiAl 3 layer formed on the non-alloyed TiAl It was attributed to change in the crystal structure of TiAl 3 from the brittle tetragonal DO 22 to the ductile cubic L1 2 by addition of small amount of Nb or Cr

Intelligent selective disassembly using the ant colony algorithm

Abstract: Selective disassembly is an important issue in industrial and mechanical engineering for environmentally conscious manufacturing. This paper presents an intelligent selective disassembly approach based on ant colony algorithms, which take inspiration from the behavior of real ant colonies and are used to solve combinatorial optimization problems. For diverse assemblies, the algorithm generates different amounts of ants cooperating to find disassembly sequences for selected components, minimizing the reorientation of assemblies and removal of components. A candidate list that is composed of feasible disassembly operations, which are derived from a disassembly matrix of products, guides sequence construction in the implicit solution space and ensures the geometric feasibility of sequences. Preliminary implementation results show the effectiveness of the proposed method.

Empirical studies of design ideation: alignment of design experiments with lab experiments

Abstract: Although various Idea Generation (IG) methods exist for conceptual design, the ideation process is still hardly understood. There is a need for a Design Ideation Model that explains the variables and processes occurring during IG. Cognitive Science provides models and theories, but these are usually derived from simple tasks or problems. On the other hand, Design Research simulates real world design better, but experimentation at the design level is time consuming and is difficult to isolate due to interactions of the variables involved. This paper introduces an approach for the alignment of experiments at the design level with lab experiments in cognitive psychology. Two key concepts that make this alignment possible are: ideation components (mechanisms believed to promote IG) recognized in Design Research and Cognitive Science, and uniform measures. The long-term objective of this research is the creation of a Design Ideation Model; this will require the testing and modeling of several of these ideation components. This paper presents results from Design and Lab Experiments for a selected component: incubation. Results are discussed and their significance explained in the context of the Design Ideation Model. This study found that, based on the correlation at both the Lab and Design Experiments, incubation had a positive impact on Design Ideation. Further, the alignment approach followed proved to be appropriate for the individual modeling of ideation components.Copyright © 2003 by ASME

Wear and corrosion resistance of laser clad Ni2Si/NiSi composite coatings

Abstract: Wear- and corrosion-resistant Ni2Si/NiSi composite coatings were fabricated on a substrate of 0.2% C carbon steel by laser-cladding using Ni–40 at.% Si elemental powder blends. Microstructure of the Ni2Si/NiSi composite coatings consists of plate-like Ni2Si primary phase and small amount of Ni2Si/NiSi eutectics in the inter-plate regions. Corrosion properties were evaluated using the anodic polarization and immersion corrosion methods in H2SO4 and NaCl water solutions. Wear resistance was tested under room-temperature block-on-wheel dry sliding wear test conditions. Because of the high hardness and abnormal temperature dependence and excellent corrosion-resisting properties inherent to the nickel silicides Ni2Si and NiSi, the laser clad/rapidly solidified Ni2Si/NiSi composite coatings have excellent chemical and electrochemical corrosion resistance and exhibit outstanding wear resistance and low friction coefficient under dry sliding wear test conditions.

Synthesis and evolution of rod-like nano-scaled ZnC2O4·2H2O whiskers to ZnO nanoparticles

Abstract: A new route has been developed to prepare rod-like nano-scaled ZnC2O4·2H2O whiskers using dodecylbenzenesulfonic acid sodium salt (DBS) as a template. Rod-like nano-scaled ZnC2O4·2H2O whiskers with diameters of 200–300 nm and lengths in the range of 5–20 µm were prepared successfully. The structure and morphology changes on heat treatment of the as-prepared product were investigated by means of scanning electron microscopy (SEM), X-ray powder diffractometry (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). By heating the rod-like nano-scaled ZnC2O4·2H2O whiskers below 280 °C, rod-like anhydrous nano-scaled β-ZnC2O4 whiskers with several small holes were obtained. On increasing the temperature to 500 °C, the rod-like nano-scaled whiskers broke into ZnO nanoparticles with diameters of 50–60 nm and display wurtzite crystal structure. On heating the products to 1280 °C, the particles gradually melted into each other to form blocks with smooth surfaces which keep the same phase structure. When we compare the products of this method with the crystalline octahedron ZnC2O4·2H2O prepared in aqueous solution, we can conclude that the surfactant DBS plays a pivotal role in the shape and structure formation. ZnC2O4·2H2O whiskers were formed in a microreactor formed by DBS, thus the size and shape of the microreactor determines and limits the product’s shape and diameter as well as the temperature.

The Microstructure and Character of the PVDF-g-PSSA Membrane Prepared by Solution Grafting

Abstract: A new method based on a solution-grafting technique was used to prepare poly(vinylidene fluoride) grafted polystyrene sulfonated acid (PVDF-g-PSSA) proton exchange membrane. Polystyrene is easily grafted into PVDF, which has been treated in KOH solution. There is a linear relationship between the degree of grafting and the treatment time in KOH solution. Fourier transform infrared spectroscopy and differential scanning calorimetry were used to characterize the changes of the membrane's microstructure after grafting and sulfonation. The conductivity of the solution-grafted PVDF-g-PSSA membranes was investigated by the four-probe dc technique and reached S cm−1 at 25°C. Gas chromatographic studies show that the methanol permeability of the PVDF-g-PSSA membrane is almost one order of magnitude lower than that of a Nafion-112 membrane. © 2003 The Electrochemical Society. All rights reserved.

Calibrating camera radial distortion with cross-ratio invariability

Abstract: The calibration of camera distortion plays an important role in the field of industrial machine vision application. In this paper, a novel approach for calibrating camera radial distortion is presented based on cross-ratio invariability for perspective projection. Assumed to be with one-order radial distortion, the image coordinates and the cross-ratio of only four collinear points in space are needed in this approach. The cross-ratio, easily known from a calibration target, is identical with that of the four corresponding image points. This is called the cross-ratio invariability for perspective projection. A monadic two-order equation is built based on the cross-ratio invariability, which gives an accurate solution to radial distortion coefficients. A digital simulation and a practical image correction prove this approach to be simple, accurate, efficient and time saving.