Computation of unsteady viscous flow and aeroacoustic noise of cross flow fans

Time-accurate viscous flow solutions are sought for the prediction of unsteady flow characteristics and associated aeroacoustic blade tonal noise of a cross flow fan. The two-dimensional incompressible Navier-Stokes equations in a moving coordinate are time-accurately solved by an unstructured finite-volume method on triangular meshes, and a sliding mesh technique is utilized at the interface between the domain rotating with blades and the stationary one for allowing the unsteady interactions. An accuracy assessment of the present method is made by comparing the fan performances with experimental data for a rotational speed at 1000 rpm and the Reynolds number 5300 based on blade tip speed and chord length. With the computed unsteady viscous flow solutions, sound pressure is predicted using Curle’s equation and narrow-band noise characteristics of three impellers with a uniform and two random pitch (type-A and -B) blades are compared by their sound pressure level spectra. Also, the frequency modulations of the blade passing frequency noise by random pitch fans are discussed.     

Performance of traveling-wave electroabsorption modulators depending on microwave properties of waveguides calculated using the FDTD method

We present a method to analyze electrical and optical characteristics of traveling-wave electroabsorption modulators (TW-EAMs) using the finite-difference time-domain method. We consider the interaction between electromagnetic fields and optical powers in waveguides in time domain to model electrical and optical behaviors of TW-EAMs. The effects of microwave properties of waveguides on modulation response and output optical power of TW-EAMs are analyzed by the proposed method. The characteristic impedance of TW-EAMs is more important than microwave index to obtain large modulation bandwidth of TW-EAMs when impedance matching techniques are not used. However, effective refractive index match between microwave and lightwave becomes important as the waveguide length increases. The microwave property closely related to the extinction ratio of output optical powers is the microwave loss. When impedance match is achieved by low-impedance termination, the velocity matching between microwave and lightwave becomes important.     

An approximate nonlinear observer with polynomial coordinatetransformation maps

The state equivalence condition to the nonlinear observer form is stated in terms of the exactness of one-form. Using the definition of the approximate closedness, we relax the equivalence condition, thereby obtaining a necessary and sufficient condition for the approximate observer error linearizability. This approximate observer theory extends the realm of applications. Another great advantage of this approximation method is that the coordinate transformation is directly obtainable as vectors of polynomials, while it is, in general, not possible with the existing method,     

Exact static element stiffness matrices of non‐symmetric thin‐walled curved beams

An evaluation procedure of exact static stiffness matrices for curved beams with non‐symmetric thin‐walled cross section are rigorously presented for the static analysis. Higher‐order differential equations for a uniform curved beam element are first transformed into a set of the first‐order simultaneous ordinary differential equations by introducing 14 displacement parameters where displacement modes corresponding to zero eigenvalues are suitably taken into account. This numerical technique is then accomplished via a generalized linear eigenvalue problem with non‐symmetric matrices. Next, the displacement functions of displacement parameters are exactly calculated by determining general solutions of simultaneous non‐homogeneous differential equations. Finally an exact stiffness matrix is evaluated using force–deformation relationships. In order to demonstrate the validity and effectiveness of this method, displacements and normal stresses of cantilever thin‐walled curved beams subjected to tip loads are evaluated and compared with those by thin‐walled curved beam elements as well as shell elements. Copyright © 2004 John Wiley & Sons, Ltd.     

A study on a generalized parametric interpolator with real-time jerk-limited acceleration

The impossibility of exact arc length computation for ‘standard’ parametric curves such as Bézier/B-spline curves makes it difficult to generate a feedrate profile with desired accelerations in real-time. This paper presents a new recursive trajectory generation method that estimates an admissible path increment and determines the initiation of the final deceleration stage according to the distance left to travel estimated at every sampling time, resulting in exact feedrate trajectory generation through jerk-limited acceleration profiles for the parametric curves. The proposed approach allows the feedrate profile to be dynamically adjusted according to geometrical path constraints for the curved path. The simulation result has been also provided to illustrate the generation of smooth feedrate profile encompassing a sequence of mixed NC blocks including traditional linear and circular blocks.     

Evaluation of fracture toughness degradation of CrMoV rotor steels based on ultrasonic nonlinearity measurements

The objective of this paper is to develop a nondestructive method for estimating the fracture toughness (K _IC) of CrMoV steels used as the rotor material of steam turbines in power plants. To achieve this objective, a number of CrMoV steel samples were heat-treated, and the fracture appearance transition temperature (FATT) was determined as a function of aging time. Nonlinear ultrasonics was employed as the theoretical basis to explain the harmonic generation in a damaged material, and the nonlinearity parameter of the second harmonic wave was the experimental measure used to be correlated to the fracture toughness of the rotor steel. The nondestructive procedure for estimating theK _IC consists of two steps. First, the correlations between the nonlinearity parameter and the FATT are sought. The FATT values are then used to estimateK _IC, using theK _IC versus excess temperature (i.e.,T-FATT) correlation that is available in the literature for CrMoV rotor steel.     

Development of advanced x-ray imaging crystal spectrometer utilizing a large area segmented proportional counter for KSTAR

An advanced x-ray imaging crystal spectrometer (XICS) for KSTAR tokamak has been developed by utilizing a segmented two dimensional (2D) position-sensitive multiwire proportional counter. The XICS for the KSTAR tokamak provides time-resolved measurements of the radial ion and electron temperature profiles, toroidal plasma rotation velocity, and ionization equilibrium. The segmented 2D detector with delay-line readout and supporting electronics has been adopted to improve the photon count rate capability. The current fabrication status of the XICS for the KSTAR tokamak and the first performance test results of the prototype segmented 2D detector are presented.     

Cooling effect of oil cooling method on electric vehicle motors with hairpin winding

Journal of Mechanical Science and Technology - The cooling effect of oil cooling method on electric vehicle motors with hairpin winding is analyzed. A 160 kW motor being developed by a commercial...     

Gaseous Nanocarving‐Mediated Carbon Framework with Spontaneous Metal Assembly for Structure‐Tunable Metal/Carbon Nanofibers

Vapor phase carbon (C)‐reduction‐based syntheses of C nanotubes and graphene, which are highly functional solid C nanomaterials, have received extensive attention in the field of materials science. This study suggests a revolutionary method for precisely controlling the C structures by oxidizing solid C nanomaterials into gaseous products in the opposite manner of the conventional approach. This gaseous nanocarving enables the modulation of inherent metal assembly in metal/C hybrid nanomaterials because of the promoted C oxidation at the metal/C interface, which produces inner pores inside C nanomaterials. This phenomenon is revealed by investigating the aspects of structure formation with selective C oxidation in the metal/C nanofibers, and density functional theory calculation. Interestingly, the tendency of C oxidation and calculated oxygen binding energy at the metal surface plane is coincident with the order Co > Ni > Cu > Pt. The customizable control of the structural factors of metal/C nanomaterials through thermodynamic‐calculation‐derived processing parameters is reported for the first time in this work. This approach can open a new class of gas–solid reaction‐based synthetic routes that dramatically broaden the structure‐design range of metal/C hybrid nanomaterials. It represents an advancement toward overcoming the limitations of intrinsic activities in various applications.     

A preliminary design and structural analysis of the lifting tools for 40° sector sub-assembly and handling ITER components

The purpose-built, ITER tokamak assembly tools, which are to be provided by Korea, should be designed to meet: the assembly plan, space reservations, safety standards, simple operations, efficient maintenance, and so on. It is very important that the ITER assembly tools are able to lift and transfer ITER components or their sub-assemblies to their assembled position safely. Furthermore, the lifting tools will lift and handle very heavy loads that can be more than 1200 tonnes sometimes. Therefore, the ITER lifting tools must be designed to endure these heavy load conditions with regard to their structural integrity. Also, these designs should be verified through an appropriate method. The preliminary design of the sector lifting tool and associated lifting attachments are introduced in this paper. The sector lifting tool was designed especially to lift and handle various ITER components by adjusting the lifting centre. The structural analysis results using ANSYS are described considering the heaviest load condition. The results of the analysis show that; all stresses applied on the lifting tool are lower than the allowable stress of the applied material.