61 research outputs found

    A simple animation package

    Get PDF
    This paper discusses a simple animation package that animates sketches drawn by the user through a simple set of operations. The purpose of the animation package is to demonstrate various computer graphics principles to those who are not experienced in the subject. Furthermore, it is an education tool for both art and undergraduate students. An expanded set of utilities allows for journaling for playback as well as a single level undo. This provides for an easy modification or correction of the errors that can be made during any session. The system is written in C language on a Unix workstation environment. User input is handled through a menu driven system and the benefits of an event driven window environment are fully made use of [6]. This obviously simplifies the usage of the package by the merits of such an environment

    Experimental analysis of R134a condensation in vertical narrow channels

    Get PDF
    Herhangi bir ısıl sistemde faz değişimi olması halinde, olmaması haline göre daha fazla ısı geçişinin gerçekleşmesi, araştırmacıları bu alanda çalışma yapmaya sevk etmiştir. Bu husus göz önünde tutularak bu çalışmada; bir faz değişimi olan yoğuşma, deneysel olarak incelenmiştir. Deneysel çalışma kapsamında kurulan deney tesisatında; R134a soğutucu akışkanının, aralarında silindirik tüpün de bulunduğu 5 farklı düşey mini kanaldaki laminer yoğuşması incelenmiştir. Deneylerde kullanılan test üniteleri; silindirik tüp ile 4 adet çok-girişli kanallardır. Pratikte bundy boru olarak adlandırılan silindirik kanalın iç çapı 3.3 mm olup, üzeri bakır kaplı çelikten imal edilmiştir. Çok-girişli kanallar ise; farklı hidrolik çaplarda olmak üzere, 3-girişli, 5-girişli, 6-girişli ve 14-girişli olup alüminyumdan imal edilmiş kanallardır. Söz konusu bu çok-girişli kanalların hidrolik çapları sırasıyla, 4.74 mm, 3.6 mm, 1.53 mm ve 1.02 mm’dir. Böylece; kanal geometrisinin ve hidrolik çapının, R134a yoğuşmasında ısı geçişi ve basınç düşümü üzerindeki etkisi deneysel olarak tespit edilmiştir. Deneyler; farklı doyma sıcaklıkları ve farklı kütlesel akılar için tekrarlanmıştır. Böylece; düşey kanallardaki R134a soğutucu akışkanının yoğuşması, farklı doyma sıcaklıkları ve farklı kütlesel akılar için karşılaştırılabilmiştir. Ayrıca; bütün kanallardaki deneysel sonuçlardan hareketle, soğutucu akışkanların yoğuşması ile ilgili olarak literatürde yaygın bir şekilde yer alan korelasyonlara benzer bir korelasyon geliştirilmiştir. Yoğuşmada Nu sayısı için geliştirilen bu boyutsuz korelasyonun, literatürdeki korelasyonlar ile oldukça uyumlu olduğu görülmüştür. Anahtar Kelimeler: R134a yoğuşması, ısı taşınım katsayısı, sürtünme faktörü, düşey silindirik tüp, çok-girişli kanallar. In any thermal system, the fact that more heat is transferred in the occurrence of phase change is a motivation for the researchers to work on. Furthermore, it has become inevitable to build smaller (more compact) heating and cooling systems, while the technology is improving more and more. This resulted in the necessity of the occurrence of phase changes in smaller spaces. Therefore it is required to know the mechanisms of phase change in narrow spaces and to improve heat transfer. Taking these facts into consideration, this study is performed to investigate condensation, which is a frequently encountered phase change in thermal systems, in experimental aspect. In the experimental study, laminar condensation of coolant R134a is investigated for five different vertical mini channels including the vertical cylindrical tube and the other four multi-port channels. The cylindrical channel with an inner diameter of 3.3 mm is made of steel coated with copper. The other four multi-port mini channels, which have 3 ports, 5 ports, 6 ports and 14 ports, are made of aluminum. The hydraulic diameters of these multi-port channels are 4.74 mm, 3.6 mm, 1.53 mm and 1.02 mm, respectively. In this way, the effects of channel configuration and hydraulic diameter on heat transfer and pressure drop for R134a condensation are determined experimentally. In the experimental investigation, the average values of thermal parameters and pressure drop are obtained along the test unit. The experiments are repeated for different saturation temperatures (therefore different saturation pressures) and for different mass fluxes. Condensation data are taken for refrigerant R134a at 32 °C and 42 °C saturation temperatures for all mini channels. Therefore, it has been possible to compare the condensation of coolant R134a in cylindrical and multi-port channels for different saturation temperatures and different mass fluxes. The experimental setup established for this study consists of the following twelve main items: coolant pump, flowmeter to measure the flow rate of the coolant R134a, pre-heating section, heating section (superheater), condensation unit, a transparent Plexiglass heat exchanger covering the condensation unit, a rotameter to measure the flow rate of the cooling water, pre-cooling section, cooling section, a receiver, a thermostatic reservoir for cooling water supply and a data acquisition system. As shown in Figure 1, refrigerant R134a enters the test section at a known vapor quality. It is condensed in the test section against the cooling water flowing in the annulus. The two-phase mixture leaving the test section enters a post- condenser. The subcooled liquid is then passed through a receiver which is in a cooler and the coolant pump. The pump moves the liquid to the pre-heater and the electric post-heater (superheater) which fixes the test section inlet vapor quality. The flowmeter is placed between the pump and the pre-heater to measure refrigerant flow rate in liquid phase. The refrigerant flow rate can be independently controlled by the pump. The inlet vapor quality is determined by the heat input to the electric post heater which can be independently controlled. The test section saturation temperature is controlled by adjusting the cooling water flow rate. The experimental results are investigated in two parts, thermal and hydrodynamic analysis. In the thermal analysis, graphs are obtained for the variation of average heat transfer coefficient with respect to average steam quality. As a result, it is shown that the average heat transfer coefficient increases when the average steam quality is increased. Also, graphs are obtained for the variation of average Nu number with respect to equivalent Re number. Similarly as a result, it is shown that the average Nu number increases when the equivalent Re number is increased. In the hydrodynamic analysis part, graphs are obtained for the variation of the pressure loss due to friction during condensation with respect to average steam quality. Also, other graphs are obtained for the two-phase friction coefficient during condensation with respect to equivalent Re number. As a result, mathematical relations are developed between ftp and Reeq for all mini channels. It is found that the two-phase friction coefficient decreases when the Reeq number is increased similar to Moody chart. As a result, a simple dimensionless correlation is developed for Nu number in refrigerant condensation which is in good agreement with the correlations in literature. Keywords: R134a condensation, heat convective coefficient, friction factor, vertical cylindrical tube, multi-port channels. 

    Termoakustik soğutucu analizi

    Get PDF
    Acoustic waves consist of pressure, displacement and temperature oscillations as a response to the pressure variations. The interaction of these effects in gas close to a solid surface generates thermoacoustic oscillations. At the solid surface heat can be extracted or supplied to the gas. The result of this interaction is that acoustic work is absorbed in order to transport heat, generating a temperature gradient along the solid surface. While in the reverse case a sound wave is sustained in case of a large temperature gradient along the solid surface. Utilizing this effect, heat can be transferred from a low temperature source to a high temperature source by a thermoacoustic refrigerator, while the opposite process can be achieved by a thermoacoustic prime mover which converts heat applied on solid surface to acoustical work. Thermoacoustic effects have attracted the scientist's attention for over two centuries. But a quantitatively accurate understanding was not achieved until Rott's (1969) studies, which has been confirmed experimentally by Yazaki et al (1979). Many thermoacoustic engines have been constructed and analyzed till now with an increasing interest. One reason for the increasing interest in thermoacoustics is from its potentiality of environment protection. Conventional refrigerators with freon gas as their working fluid are being prohibited because of its destruction of ozone layer. But the thermoacoustic engines do not use any harmful working fluid. They use mainly helium, or helium with argon, neon, xenon or such inert gaseous. The other reason is that conventional systems have moving parts, so they are less reliable and more expensive than thermoacoustic devices. Because thermoacoustic devices use no moving parts, no close tolerances, no exotic materials, the interests on thermoacoustic engines have increased a lot. In this study a thermoacoustic cooler working with atmospheric air was designed and constructed. A systematical approach was followed to design the device which had been proposed by Tijani. The system was constructed with a speaker as the acoustical source, resonator, stacks at different lengths, stack holder, signal generator, amplifier, temperature and pressure measurement system. After constructing the thermoacoustic device, pressure distributions in the resonator at various resonance frequencies were examined. The resonance frequencies of the system were approximately measured at 112 Hz, 180 Hz and 300 Hz starting from the first harmonics. The theoretical and experimental pressure distributions were compared. Changes of pressure antinode position with respect to acoustical source amplitude at resonance frequencies were studied theoretically and experimentally. The analytical and experimental results were  compared. Three stacks at different lengths were constructed. After that the temperature distributions on the stack at different stack positions were examined and compared to the theoretical results with and without taking care of axial conduction effects. The maximum temperature difference, measured between the tips of the stacks are 20.4oC (10 cm length stack), 21.4oC (15 cm length stack), 27.6oC (22 cm length stack). It was concluded that the axial conduction effects are important in a system at low power. It was also measured the steady state temperature distribution on stack, and it was seen that it was linear as it should be. Later it was examined how the existence and the position of the stack affects the pressure distribution and the resonance frequency of the system. It was concluded that the existence and the position of the stack in the resonator affects the resonance frequency and pressure antinode position. In the experiments, it was measured that the resonance frequency of the system was changed between 108 Hz and 112 Hz depending on the stack position while the resonance frequency of the empty resonator is 112 Hz. Despite the fact that pressure antinode position from open end of the resonator was measured 72 cm at empty resonator resonance frequency, it was observed that the pressure antinode position decreased down to 66 cm as a result of the stack inside the resonator. At the end it was examined how slight frequency changes affects the system performance. It was measured that a few Hertz frequency changes does not affect the system performance a lot, but there is a sharp decrease at the system performance if the frequency changes are larger than a few Hertz. Keywords: Thermoacoustics, thermoacoustic cooler, thermoacoustic engine.Ses dalgaları içerisindeki basınç salınımları ile birlikte gerçekleşen sıcaklık salınımları sonucu  akışkan ve akışkana temas eden katı yüzey arasındaki ısıl etkileşimler termoakustik olarak adlandırılır. Termoakustik sistemlerin maliyetlerinin düşük, yapılarının basit olması, atmosfere zarar veren gazlar kullanmaması, hareketli parçalarının bulunmaması gibi sebeplerle, klasik soğutma sistemlerine göre pratikteki verimlerinin düşük olmalarına rağmen üzerlerindeki ilgi artarak devam etmiştir. Termoakustik soğutucular geleceğin soğutma teknolojilerinden birisi olmaya adaydır. Bu çalışmada atmosferik hava ile çalışan basit bir termoakustik soğutucu dizayn ve inşa edilmiş, daha sonra sistem üzerinde çeşitli inceleme ve analizler yapılmıştır. Sistemin rezonans frekansları birinci harmonikten itibaren yaklaşık olarak 112 Hz, 180 Hz, 300 Hz olarak ölçülmüştür. Akustik kaynak olarak bir hoparlör kullanıldığından ideal rezonans tüpünden farklı olarak kapalı uçta hız nodunun oluşmadığı görülmüştür. Daha sonra sistemdeki basınç dağılımının şeklinin akustik kaynak genliğine bağlı olarak değişimi incelenmiştir. Ardından üç farklı uzunlukta yığın kullanılarak farklı yığın pozisyonlarında yığın üzerindeki sıcaklık dağılımları ve yığın uçları arasındaki sıcaklık farkları ölçülmüş ve teoriyle karşılaştırılmıştır. Yığınların her iki ucu arasında en yüksek 27.6oC sıcaklık farkı ölçülmüştür. Daha sonra rezonans tüpü içerisinde yığının varlığının ve pozisyonunun sistemin basınç dağılımı ve rezonans frekansı üzerine etkileri incelenmiştir. Yığının sistem içindeki varlığının ve pozisyonunun sistem çalışma frekansını ve basınç antinod pozisyonunu etkilediği gözlenmiştir. Son olarak sistemin çalışma frekansındaki kaymaların sistem performansı üzerine etkileri incelenmiştir. Anahtar Kelimeler: Termoakustik, termoakustik soğutucu, termoakustik makine.&nbsp

    Motion control for realistic walking behavior using inverse kinematics

    Get PDF
    This study presents an interactive hierarchical motion control system for the animation of human figure locomotion. The articulated figure animation system creates movements using motion control techniques at different levels, like goal-directed motion and walking. Inverse Kinematics using Analytical Methods (IKAN) software, developed at the University of Pennsylvania, is utilized for controlling the motion of the articulated body. © 2007 IEEE

    Automated LASCO CME catalog for solar cycle 23: are CMEs scale invariant?

    Full text link
    In this paper we present the first automatically constructed LASCO CME catalog, a result of the application of the Computer Aided CME Tracking software (CACTus) on the LASCO archive during the interval September 1997 - January 2007. We have studied the CME characteristics and have compared them with similar results obtained by manual detection (CDAW CME catalog). On average CACTus detects less than 2 events per day during solar minimum up to 8 events during maximum, nearly half of them being narrow (< 20 degrees). Assuming a correction factor, we find that the CACTus CME rate is surprisingly consistent with CME rates found during the past 30 years. The CACTus statistics show that small scale outflow is ubiquitously observed in the outer corona. The majority of CACTus-only events are narrow transients related to previous CME activity or to intensity variations in the slow solar wind, reflecting its turbulent nature. A significant fraction (about 15%) of CACTus-{\it only} events were identified as independent events, thus not related to other CME activity. The CACTus CME width distribution is essentially scale invariant in angular span over a range of scales from 20 to 120 degrees while previous catalogues present a broad maximum around 30 degrees. The possibility that the size of coronal mass outflows follow a power law distribution could indicate that no typical CME size exists, i.e. that the narrow transients are not different from the larger well-defined CMEs.Comment: 13 pages. ApJ, accepte

    Investigation of heat transfer in moving liquid column

    Get PDF
    Bu &ccedil;alışmada, halkasal zorlanmış salınımlı akışta ısı ge&ccedil;işi deneysel ve sayısal olarak incelenmektedir.&nbsp; Halkasal kesit i&ccedil;inde akışkan bir piston-silindir d&uuml;zeneği ile farklı frekans, genlik ve ısı y&uuml;k&uuml;nde titreştirilmektedir. Deneyler farklı ısı akıları ve frekanslar i&ccedil;in yapılmış olup bu frekanslara karşılık gelen Nusselt sayıları bulunarak, boyutsuz sayılar cinsinden bir korelasyon eşitliği ile verilmektedir. Ayrıca sonlu hacimler ayrıklaştırma y&ouml;ntemine g&ouml;re &ccedil;&ouml;z&uuml;m yapan FLUENT yazılımı kullanılarak Hareketli Sıvı Kolonunda ısı ge&ccedil;işi sayısal olarak da incelenmektedir. Yapılan incelemelerde, sıvı i&ccedil;erisindeki hız ve sıcaklık dağılımı elde edilerek ısı ge&ccedil;iş mekanizması a&ccedil;ıklanmaktadır. Isı ge&ccedil;işinde etkili olan mekanizmanın akışın merkezini takip edemeyen hidrodinamik sınır tabakadan kaynaklandığı ve bunun ısı ge&ccedil;işini artırdığı anlaşılmıştır. Sayısal &ccedil;&ouml;z&uuml;m i&ccedil;inde bir &ccedil;evrimde suya ge&ccedil;en ısı i&ccedil;in Nusselt sayıları bulunarak deneysel sonu&ccedil;larla karşılaştırılmaktadır. &nbsp;Anahtar Kelimeler: Hareketli sıvı kolonu, salınımlı akış, Nusselt sayısı.In this study, the heat transfer from a surface heated with constant heat flux to an oscillating vertical annular liquid column having an interface with the atmosphere is investigated experimentally and numerically.  The reciprocating motion of water column is created using a piston cylinder mechanism. The space-cycle heat transfer rate from heater to water was calculated by using experimental measurements. The analysis was carried out for the case of different oscillation frequencies while the displacement amplitude remains constant.  Based on the experimental data a correlation equation was obtained for the cycle-averaged Nusselt number as a function of kinetic Reynolds number.  Heat transfer in the moving liquid column was also investigated numerically using the FLUENT program.  Fluent uses a control-volume-based technique to convert the governing equations to algebraic equations that can be solved numerically. This control volume technique consists of integrating the governing equations about each control volume, yielding discrete equations that conserve each quantity on a control-volume basis. It is clear that heat transfer rate depends on velocity and temperature profile.  The numerical results reveal that there is a phase difference between hydrodynamic boundary layer and core flow, which improves the heat transfer.  The averaged heat transfer rate is found to increase with the frequency. The space-cycle averaged Nusselt number was found numerically and compared with experimental results. The numerical solution is in good agreement with the experimental data. Keywords: Oscillating liquid column, reciprocating flow, Nusselt number

    Right-triangular subdivision for texture mapping ray-traced objects

    Get PDF
    The introduction of global illumination and texture mapping enabled the generation of high-quality, realistic looking images of computer graphics models. We describe a fast and efficient 2D texture mapping algorithm that uses triangle-to-triangle mapping, taking advantage of mapping an arbitrary triangle to a right triangle. This requires fewer floating point operations for finding the 2D texture coordinates and little preprocessing and storage. Texture mapping is combined with ray tracing for better visual effects. A filtering technique alternative to area sampling is developed to avoid aliasing artifacts. This technique uses linear eye rays, and only one eye ray per pixel is fired. A uniform supersampling filtering technique eliminates aliasing artifacts at the object edges

    Tests of sunspot number sequences: 1. Using ionosonde data

    Get PDF
    More than 70 years ago it was recognised that ionospheric F2-layer critical frequencies [foF2] had a strong relationship to sunspot number. Using historic datasets from the Slough and Washington ionosondes, we evaluate the best statistical fits of foF2 to sunspot numbers (at each Universal Time [UT] separately) in order to search for drifts and abrupt changes in the fit residuals over Solar Cycles 17-21. This test is carried out for the original composite of the Wolf/Zürich/International sunspot number [R], the new “backbone” group sunspot number [RBB] and the proposed “corrected sunspot number” [RC]. Polynomial fits are made both with and without allowance for the white-light facular area, which has been reported as being associated with cycle-to-cycle changes in the sunspot number - foF2 relationship. Over the interval studied here, R, RBB, and RC largely differ in their allowance for the “Waldmeier discontinuity” around 1945 (the correction factor for which for R, RBB and RC is, respectively, zero, effectively over 20 %, and explicitly 11.6 %). It is shown that for Solar Cycles 18-21, all three sunspot data sequences perform well, but that the fit residuals are lowest and most uniform for RBB. We here use foF2 for those UTs for which R, RBB, and RC all give correlations exceeding 0.99 for intervals both before and after the Waldmeier discontinuity. The error introduced by the Waldmeier discontinuity causes R to underestimate the fitted values based on the foF2 data for 1932-1945 but RBB overestimates them by almost the same factor, implying that the correction for the Waldmeier discontinuity inherent in RBB is too large by a factor of two. Fit residuals are smallest and most uniform for RC and the ionospheric data support the optimum discontinuity multiplicative correction factor derived from the independent Royal Greenwich Observatory (RGO) sunspot group data for the same interval
    corecore