• Journal of applied mathematics & informatics
• /
• v.7 no.2
• /
• pp.391-408
• /
• 2000

In the curved geometries, from the solution of the classical Riemann problem in the plane, the asymptotic solutions of the compressible Euler equation are presented. The explicit formulae are derived for the third order approximation of the generalized Riemann problem form the conventional setting of a planar shock-interface interaction.

• Transactions of Materials Processing
• /
• v.11 no.5
• /
• pp.405-413
• /
• 2002

A process planning system for cold forging of non-axisymmetric parts of comparatively simple shape was developed in this study. Programs for the system have been written with Visual LISP in AutoCAD. Shape of the product must be drawn with the solid line and the hidden line, and with the plane and front view, as well. At the plane, the system recognizes the external shape of non-axisymmetric portions - the number of the sides of the regular polygons and the radii of circles inscribing and circumscribing the polygon. At the front view, the system cognizes the diameter of axisymmetric portions and the height of the primitive geometries such as polygon, cylinder, cone, concave, convex, etc. The system perceives that the list developed from the solid line must be formed by the operation of forward extrusion or upsetting, and that the list developed from the hidden line must be formed by the operation of backward extrusion. The system designs the intermediate geometries again by considering clearance between workpiece and die, and then finally the billet diameter, in reverse order from the finished product, on the basis of volume constancy and using the operations, the forming sequence, the number of operations and the intermediate geometries which were already designed. The design rules and knowledges for the system were extracted from the plasticity theories, handbook, relevant reference and empirical knowledge of field experts. Suitability of the process planning was analyzed using SuperForge of FVM simulation package. The results of analysis showed good formability.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.25 no.6
• /
• pp.324-330
• /
• 2013

The main objective of this work is to experimentally investigate the effect of inlet geometries on the distribution of two-phase annular flow at header-channel junctions simulating the corresponding parts of compact heat exchangers. The cross-section of the header and the channels were fixed to $16mm{\times}16mm$ and $12mm{\times}1.8mm$, respectively. Experiments were performed for the mass flux and the mass quality ranges of $30{\sim}140kg/m^2s$ and 0.3~0.7, respectively. Air and water were used as the test fluids. Three different inlet geometries of the header were tested:no restriction (case A), a single 8 mm hole at the center (case B), and nine 2 mm holes around the center (case C) at the inlet, respectively. The tendencies of the two-phase flow distribution were different, in each case. For cases B and C (flow resistance exists), more uniform flow distribution results were seen, compared with case A(no flow resistance), due to the flow pattern change to mist flow from annular flow at the inlet, and the flow recirculation near the end plate of the header.

• Wind and Structures
• /
• v.32 no.3
• /
• pp.205-217
• /
• 2021

Cold regions with high air density and wind speed attract wind energy producers across the globe exhibiting its potential for wind exploitation. However, exposure of wind turbine blades to such cold conditions bring about devastating impacts like aerodynamic degradation, production loss and blade failures etc. A series of wind tunnel tests were performed to investigate the effect of icing on the aerodynamic properties of wind turbine blades. A baseline clean wing configuration along with four different ice accretion geometries were considered in this study. Aerodynamic force coefficients were obtained from the surface pressure measurements made over the test model using MPS4264 Simultaneous pressure scanner. 3D printed Ice templates featuring different ice geometries based on Icing Research Tunnel data is utilized. Aerodynamic characteristics of both the clean wing configuration and Ice accreted geometries were analysed over a wide range of angles of attack (α) ranging from 0° to 24° with an increment of 3° for three different Reynolds number in the order of 105. Results show a decrease in aerodynamic characteristics of the iced aerofoil when compared against the baseline clean wing configuration. The key flow field features such as point of separation, reattachment and formation of Laminar Separation Bubble (LSB) for different icing geometries and its influence on the aerodynamic characteristics are addressed. Additionally, attempts were made to understand the influence of Reynolds number on the iced-aerofoil aerodynamics.

• Journal of the Korean Vacuum Society
• /
• v.20 no.5
• /
• pp.374-380
• /
• 2011

Carbon coils could be synthesized on nickel catalyst layer-deposited silicon oxide substrate using $C_2H_2$ and $H_2$ as source gases and $SF_6$ as an additive gas under thermal chemical vapor deposition system. The characteristics (formation density and morphology) of as-grown carbon coils according to the injection stage of $SF_6$ gas incorporation were investigated. A continuous injecting of $SF_6$ gas flow could give rise to many types of carbon coils-related geometries, namely linear tub, micro-sized coil, nano-sized coil, and wave-like nano-sized coil. However, the limitation of the geometry as the nano-sized geometries of carbon coils could be achieved by the incorporation of $SF_6$ in a short time (1 min) during the initial deposition stage. A delayed injection of a short time $SF_6$ gas flow can deteriorate the limitation of the geometries. It confirms that the injection time and its starting point of $SF_6$ gas flow would be very important to determine the geometries of carbon coils.

• Bulletin of the Korean Chemical Society
• /
• v.35 no.3
• /
• pp.775-782
• /
• 2014

The importance of including spin-orbit interactions for the correct description of structures and vibrational frequencies of haloiodomethanes is demonstrated by density functional theory calculations with spin-orbit relativistic effective core potentials (SO-DFT). The vibrational frequencies and the molecular geometries obtained by SO-DFT calculations do not match with the experimental results as well as for other cations without significant relativistic effects. In this sense, the present data can be considered as a guideline in the development of the relativistic quantum chemical methods. The influence of spin-orbit effects on the bending frequency of the cation could well be recognized by comparing the experimental and calculated results for $CH_2BrI$ and $CH_2ClI$ cations. Spin-orbit effects on the geometries and vibrational frequencies of $CH_2XI$ (X=F, Cl, Br, and I) neutral are negligible except that C-I bond lengths of haloiodomethane neutral is slightly increased by the inclusion of spin-orbit effects. The $^2A^{\prime}$ and $^2A^{{\prime}{\prime}}$ states were found in the cations of haloiodomethanes and mix due to the spin-orbit interactions and generate two $^2E_{1/2}$ fine-structure states. The geometries of $CH_2XI^+$ (X=F and Cl) from SO-DFT calculations are roughly in the middle of two cation geometries from DFT calculations since two cation states of $CH_2XI$ (X=F and Cl) from DFT calculations are energetically close enough to mix two cation states. The geometries of $CH_2XI^+$ (X=Br and I) from SO-DFT calculations are close to that of the most stable cation from DFT calculations since two cation states of $CH_2XI$(X=Br and I) from DFT calculations are energetically well separated near the fine-structure state minimum.

• Nuclear Engineering and Technology
• /
• v.49 no.7
• /
• pp.1405-1413
• /
• 2017

To investigate the heat loads imposed on a reactor vessel through the natural convection of core melts in severe accidents, mass transfer experiments were performed based on the heat transfer/mass transfer analogy, using two- (2-D) and three-dimensional (3-D) facilities of various heights. The modified Rayleigh numbers ranged from $10^{12}$ to $10^{15}$, with a fixed Prandtl number of 2,014. The measured Nusselt numbers showed a trend similar to those of existing studies, but the absolute values showed discrepancies owing to the high Prandtl number of this system. The measured angle-dependent Nusselt numbers were analyzed for 2-D and 3-D geometries, and a multiplier was developed that enables the extrapolation of 2-D data into 3-D data. The definition of $Ra^{\prime}_H$ was specified for 2-D geometries, so that results could be extrapolated for 3-D geometries; also, heat transfer correlations were developed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.19 no.8
• /
• pp.569-576
• /
• 2007

The desiccant rotor is the most essential component of desiccant cooling system, but one of its drawbacks to spread out is rotor size. To reduce the size of rotor the analysis of rotor performance is crucial. Systematic examination on the effect of desiccant and channel geometries has been conducted based on the numerical program previously developed. Considered parameters related to channel geometries are channel shape and cross section area of channel, and parameters related to desiccant are mass fraction, heat capacity, density, maximum water uptake and separation factor of isotherm. Considerable reduction of rotor size is expected by adjusting the parameters.

• Korea-Australia Rheology Journal
• /
• v.13 no.2
• /
• pp.67-81
• /
• 2001

The development of new techniques for the dynamic measurement of linear viscoelastic properties is an active area of rheometry, and this paper surveys some novel deformation geometries which have been recently reported e.g. oscillating probe-type devices which are imbedded in or placed on the surface of the sample. Small amplitude band-limited pseudorandom noise is used for the displacement signal, with Fourier analysis of the complex waveform of the resistance force yielding the frequency dependent viscoelastic material functions (e.g. storage and loss moduli G", G"). Theoretical calculations of the fundamental equations relating force to displacement and instrument geometry, were carried out with the aid of the correspondence principle of linear viscoelasticity. The rapidity of the tests and flexibility in terms of sample preparation and stiffness mean that this basic technique should find many applications in rheometry. Three examples of oscillatory tests are presented in detail squeeze flow, imbedded needle and concentric sliding cylinder geometries.eometries.

• Journal of Electrical Engineering and Technology
• /
• v.9 no.6
• /
• pp.2079-2088
• /
• 2014

In this paper, we propose new physically based threshold voltage models for short channel Surrounding Gate Silicon Nanowire Transistor with two different geometries. The model explores the impact of various device parameters like silicon film thickness, film height, film width, gate oxide thickness, and drain bias on the threshold voltage behavior of a cylindrical surrounding gate and rectangular surrounding gate nanowire MOSFET. Threshold voltage roll-off and DIBL characteristics of these devices are also studied. Proposed models are clearly validated by comparing the simulations with the TCAD simulation for a wide range of device geometries.