Transactions of the Japan Society of Mechanical Engineers Series B
Online ISSN : 1884-8346
Print ISSN : 0387-5016
Volume 73, Issue 734
Displaying 1-28 of 28 articles from this issue
  • Shinichiro ITO
    2007 Volume 73 Issue 734 Pages 1975-1980
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
    JOURNAL FREE ACCESS
    A slipstream is a region of reduced pressure or even suction (negative pressure) formed behind an object in downstream. Even in a marathon event, it is possible to use preceding runners as a shield to reduce aerodynamic drag and to carry out physical strength presservation. These preceding runners are called pacemakers, who maintain a lap time of an main runner. In this research, to confirm the effect of pacemakers' slipstream and to find a suitable arrangement of pacemakers, drag of the main runner was measured using 3 component load cells in a wind tunnel. And the factor of drag reduction was studied by grasping the flow field using a smoke tunnel. Numerical calculations were also carried out in a real Reynolds number and compared with experiments concerning drag and flow field.
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  • Taketo MIZOTA, Yoshiyuki KAWAMURA
    2007 Volume 73 Issue 734 Pages 1981-1986
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
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    Flight trajectory path of side-spin type knuckle balls pitched by a newly developed machine are captured using one digital video camera. Various types of 3D-trajectories data are obtained by processing from these video images. Special attention was focused to observe a quasi-steady assumption during ball flight process. Erratic path behaviors of side direction of the ball trajectory with time duration are clarified, and from these results, side force characteristics in flight and ball rotation angle of maximum side force are clearly recognized. As a result, quasi-steady assumption, which was based on knuckleball flutter theory, was verified.
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  • Taketo MIZOTA, Daisuke NISHIKIORI, Kazuaki KONISHI
    2007 Volume 73 Issue 734 Pages 1987-1992
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
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    Wind tunnel experiments were conducted to measure aerodynamic forces acting on highly spinning baseball balls, which rotate around an axis oriented uniform flow direction. This is called as vertical slider with non-lift force and less drag force compared with other spinning direction ball. A professional pitcher named Daisuke Matsuzaka with powerful ball adopts this U-type rolling spin ball. Experimental results show less drag force in U-type ball than the other X-type one.
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  • Takeshi ASAI, Kazuya SEO, Osamu KOBAYASHI, Shinichiro ITO
    2007 Volume 73 Issue 734 Pages 1993-1998
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
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    The aerodynamic properties and boundary-layer dynamics of a soccer ball are not well under-stood. Here we showed that the critical Reynolds number (Recrit) of a soccer ball was 2.2-3.0×105 in a wind tunnel test. The boundary layer and vortex-trail dynamics of a non-spinning soccer ball in flight were visualized using smoke of titanium tetrachloride, and were compared between the subcritical and supercritical regions. The separation angle between the front-stagnation point (that is, the tip of the ball in the direction of the oncoming flow) and the boundary layer-separation point was about 90°. The vortex rigion was comparatively large when the subcritical ball velocity was 5 m/s. By contrast, the separation point went backward to about 120° from the front-stagnation point and the vortex region shrank when the supercritical ball velocity was about 29 m/s. By counting the number of vortex blobs from smoke visualization images with a wide view angle, the Strouhal number (St) (wide view angle) was estimated to be about 0.5. However, when the vortex blobs seemingly accompanying a vortex ring directly behind the ball were counted from closed up visualization images with a narrower view angle, the frequency increased and St was estimated to be about 1.0. Behind the balls under a knuckle effect were airborne, large scale undulation of the vortex trail were observed when St was about 0.1 or less.
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  • Kazuya SEO, Osamu KOBAYASHI, Masahide MURAKAMI
    2007 Volume 73 Issue 734 Pages 1999-2003
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
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    We have measured aerodynamic forces and moments acting on a rugby ball spinning on its transverse axis by wind tunnel experiments. A full-size model of a rugby ball was tested in a low-speed wind tunnel with a 1.5m×1.0m rectangular nozzle. It was made of fiber reinforced plastics by molding a fully-inflated ball. The spinning mechanism was composed of a motor and four shafts inserted the ball along its transverse axis. The results are summarized as follows : the lift increases with increasing the spin rate because of the Magnus force. The Magnus force is at its maximum when the spinning (transverse) axis is perpendicular to the flight direction. The side force depends on the angle between the spinning axis and the direction of flight. The side force is a maximum when this angle is 45°.
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  • Kazuya SEO, Osamu KOBAYASHI, Masahide MURAKAMI
    2007 Volume 73 Issue 734 Pages 2004-2009
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
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    This paper describes the optimal initial conditions for the goal kick in rugby by using an elitist non-dominated sorting genetic algorithm. What is the best way to achieve a satisfactory kick for goal? The primary objective of this paper is to provide the answer. Two objective functions are considered. One is the height difference between the ball position and the crossbar, and the other is the lateral deviation of the distance of the ball position and the center of both goalposts. Seven initial conditions concerning the velocity vector and the angular velocity vector were defined as control parameters. The results are in order to satisfy the Pareto-optimal solutions, the angular velocity vector should be perpendicular to the velocity vector and the longitudinal axis of the ball.
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  • Motomu NAKASHIMA, Yuichi OMODA
    2007 Volume 73 Issue 734 Pages 2010-2017
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
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    The objective of this study was to develop a simulation method for analysis of body behavior in skydiving freefall and to clarify the most stable body position during the freefall. The details of the developed simulation method were firstly described. Using the simulation method, we conducted an optimizing calculation to maximize an objective function with respect to the stability in the freefall. It was found that the most stable position became arched one. In order to clarify the reason why the most stable position became arched, optimization with respect to a simple shaped object which consists of 20 cylinders was conducted. Then the angle to maximize the restoring moment for each cylinder element was analytically calculated and compared with the optimized angle. From the results, we conclude that the most stable position becomes arched mainly since the restoring moment at each part itself becomes maximum at that angle. We also conclude that the magnitude of the arch in the most stable position is determined by the ratio of the normal and tangential drag coefficients.
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  • Ayako AOYAMA, Motomu NAKASHIMA
    2007 Volume 73 Issue 734 Pages 2018-2026
    Published: October 25, 2007
    Released on J-STAGE: August 16, 2011
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    The objective of this study was to investigate the stability during freefall in skydiving, in which the diver has to take various body position in order to control precisely their distance, velocity, and direction relative to the other divers for the group performance. For this objective, the state equation for a simple elliptic cylinder model was firstly derived, considering its equations of motion and the fluid force characteristics. Next, using the form of state equation derived for the elliptic cylinder and the input/output data obtained from the developed simulation method for the body behavior of the skydiver, the state equations of skydiver were identified for various body positions. Finally, roots of the state equations were obtained to investigate the stability. As the results, the causes of instability such as spin and spiral phenomena were clarified as an unstable natural modes, and the stable limit of body position was obtained as a value of parameter which is related to the arch magnitude of the diver's body.
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  • Kazuo MATSUUCHI, Keiichi YAMADA, Takeo NOMURA, Jun SAKAKIBARA, Haruki ...
    2007 Volume 73 Issue 734 Pages 2027-2032
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
    JOURNAL FREE ACCESS
    The flow field around a swimmer has been assumed to be steady or quasi-steady in the estimation of flow force acting on hand/arm in spite of its extremely unsteady characters, because the convenient means for measuring the flow field has been lacking. A sophisticated technique called the PIV (Particle Image Velocimetry) was developed and enabled us to estimate the unsteady flow field. The PIV technique can visualize the unsteady flow field and can detect the vortex behavior around a hand. On the other hand, motion analysis has been widely used in the field of biomechanics of sport. This method can also be expected to evaluate the swimmer's complicated motion. Our study is to clarify the relationship between the vortex behavior and the motion of a hand in crawl swimming. Two methods were combined to know the generating mechanism of swimming thrust. Measurements were made for two subjects ; one is a female Olympic swimmer (subject 1) and the other a male with no competitive career (subject2). The trajectory of the plam of the subject 1 was S-shaped motion. From the change of the palm inclination angle, it was suggested that the palm of the subject 1 reversed the orientation of the circulation. On the other hand, the palm of subject 2 did not reverse the orientation of the circulation. It is plausible that subject 2 does not generate any strong and coherent vortices. From the results of visualization of flow field, subject 1 generates strong vortices or vortex pair after the phase turned from in-sweep to out-sweep. In addition, the shed vortex pair follows a jet flow in the direction of the flume flow. In contrast, subject 2 did not shed any vortex pairs. It was confirmed that the hand motion in swimming was closely related to the vortex generation and also to the thrust.
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  • Shinichiro ITO
    2007 Volume 73 Issue 734 Pages 2033-2037
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
    JOURNAL FREE ACCESS
    In general, hand palms are usually moved as if they draw a “8 shape” in sculling action. Although various types of sculling actions exist according to its operation and purposes, all the sculling actions are almost the same in its function which produces lift force in reciprocating movement. Configurations of the hand palms are not standardized but empirically decided by coaches and athletes. In this research, the hydrodynamic characteristics of five kinds of palms were investigated to find a configuration which generates the maximal resultant force as a basic study of steady state flow field
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  • Shinichiro ITO
    2007 Volume 73 Issue 734 Pages 2038-2044
    Published: October 25, 2007
    Released on J-STAGE: August 16, 2011
    JOURNAL FREE ACCESS
    Competitive swimming requires thrust force much greater than recreational swimming. Four configurations of hand paddles are investigated to obtain an optimal form of a hand in freestyle swimming scientifically. These configurations are a cup-shaped hand with fingers spaced apart, a flat one with fingers spaced apart and those with fingers closed. Aerodynamic forces and flow-induced vibration acting on these hand replicas are experimented with a 3 component load cell. The angle of attack into a hand paddle is related to its thrust efficiency and thrust force. The angle of attack for maximal thrust force is affected by the hand forms, especially with the existence of spacing between the fingers in this study. With these facts, the optimal hand forms are different according to a method of swimming such as S-shaped-pull pattern swimming and drag swimming. Moreover, magnitude of fluid-induced vibration acting on a driving hand varies according to the spacing of fingers and the hand forms.
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  • Shinichiro ITO
    2007 Volume 73 Issue 734 Pages 2045-2050
    Published: October 25, 2007
    Released on J-STAGE: August 16, 2011
    JOURNAL FREE ACCESS
    The propelling force in swimming is mainly generated by hands and arms rather than by legs. However, the ratio of the thrust force by a hand to that by the whole forearm with hand has not been experimented. Replicas of a hand and a forearm with hand were made from an excellent swimmer's. Those characteristic data of the lift-drag forces and the propelling force ratio were taken by wind tunnel tests based on the angle of attack and the sweepback angle. The following results were found. As for the S-shaped pull stroke, the thrust force by the whole forearm with hand was 3 to 4 times larger than that by the hand itself in the catch and the finish phases while about 1.8 times larger in the pull phase. In the drag pull type stroke, the I-shaped pull, the thrust force by the whole forearm with hand was 1.8 times larger than that by the hand itself throughout all the three phases. Furthermore, the fluid characteristic of the whole forearm with the hand showed similar to that of the hand itself.
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  • Shinichiro ITO
    2007 Volume 73 Issue 734 Pages 2051-2057
    Published: October 25, 2007
    Released on J-STAGE: August 16, 2011
    JOURNAL FREE ACCESS
    The dynamics of swimming is considered to be hydrodynamics which acts on a swimmer and the water around the body. Propelling force generated by hand is a resultant force of lift and drag. The propelling force can be divided into two optimal kinds, the maximum mode of propelling force and the minimum mode of energy consumption by lift-drag curves of hand. Driving angles and tilt angles of hand were calculated in a balance state of propelling forces of hand and drag forces of the whole body by utilizing with published data of hand on a quasi-steady state. As a result, the followings were acquired : The hand plane should be almost perpendicular to the direction of motion in each mode. Concerning the maximum mode of propelling force, such as in a competitive swimming, the hand should be driven along the body axis to the advancing direction for drag forces to be used entirely. However, for the minimum energy consumption in swimming, sculling action of hand is important to utilize not only drag force but also lift force.
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  • Shinichiro ITO
    2007 Volume 73 Issue 734 Pages 2058-2061
    Published: October 25, 2007
    Released on J-STAGE: August 16, 2011
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    An underwater camera trucking system was developed to analyze swimming forms. Freestyle swimming forms were compared between a world top ranking swimmer with I-shaped pull stroke, a drug type pull stroke and a skillful swimmer with S-shaped pull stroke. The side views of the two swimming forms were analyzed in a two dimensional wireframe. In the catch and pull phase, the I-shaped pull swimmer moved the arm along the side of the body with the lead lag motion with the arm bent so that the elbow moved almost parallel to the water surface. The S-shaped pull swimmer moved the arm with the rotating motion around the shoulder with the arm straighten. In a stroke period of time, the former had a longer time ratio to generate thrust force and a shorter recovery time than the latter. It means that the I-shaped pull swimmer spent longer time to generate thrust force. In the comparison result of posture aspect ratio, the value of the former is higher because of the smaller vertical value due to the arm bent at the elbow. The rectangular wireframe of the I-shaped pull swimmer is thinner than that of the other.
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  • Ryo ONISHI, Keigo MATSUDA, Keiko TAKAHASHI, Ryoichi KUROSE, Satoru KOM ...
    2007 Volume 73 Issue 734 Pages 2062-2069
    Published: October 25, 2007
    Released on J-STAGE: August 16, 2011
    JOURNAL FREE ACCESS
    We have developed a new simple inversion scheme for retrieving collision kernels from the change of droplet size distributions due to collision growth. Three-dimensional direct numerical simulations (DNS) of colliding droplets in an isotropic steady turbulence are performed in order to investigate the validity of the developed inversion scheme. In the DNS, air turbulence is calculated using a quasi-spectral method, and droplet motions are tracked by a Lagrange method. The initial droplet size distribution is set to be equivalent to that obtained in a wind tunnel experiment. Comparison between collision kernels retrieved by the developed inversion scheme and those obtained by DNS shows that the collision kernel can be retrieved within 15% error. This verifies the feasibility of retrieving collision kernels by using the present inversion scheme.
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  • Masashi YAMAKAWA, Kenichi MATSUNO
    2007 Volume 73 Issue 734 Pages 2070-2076
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
    JOURNAL FREE ACCESS
    From a point of view of grid generation, an overset grid generation method is suitable for a flow around moving complicated-shaped body. The overset grid method treats two grid-types which are a main-grid placed on all over the flow field and a sub-grid placed around the body. However it is difficult to satisfy a physical conservation law since the overset grid method interpolates the value between the main-grid and the sub-grid. To assure the conservation law on the overlapped region, we propose a new method that the overset grid method is combined to the unstructured moving grid finite volume method. In this method the sub-grid and the main-grid are joined by the unstructured grid. The feature of the method is that a control volume on which a space-time unified domain is adopted, and the method assures the geometric conservation law too even if the sub-grid moves and deforms. The method is applied to a problem such that complicated-shaped body flies in supersonic flow.
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  • Shinichi SATAKE, Takafumi ANRAKU, Hiroyuki KANAMORI, Tomoaki KUNUGI, K ...
    2007 Volume 73 Issue 734 Pages 2077-2084
    Published: October 25, 2007
    Released on J-STAGE: August 16, 2011
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    Micro digital holographic particle tracking velocimetry with high-speed system is constructed by PC grid environment, which is used by Windows XP with AD-POWERs as parallel tool. Two algorithms for high-speed system are evaluated under the same PC grid environment. Both methods are based on the digital hologram algorithm. The first method is a division algorithm based on the time developing for the measurements. The second is a division algorithm based on the spatial reconstruction for the measurement. In case of the former, the performance is achieved for 4.7 times using 5 PC. The utilization of present system is possible to compute the huge hologram images on-site at the experimental facility.
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  • Takuya KUWAHARA, Masashi OHNISHI, Hiroshi YAMAGUCHI, Shigemitsu SHUCHI
    2007 Volume 73 Issue 734 Pages 2085-2091
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
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    In order to evaluate the heat transport capability in the thermomagnetic cycle using temperature sensitive magnetic fluids, a fundamental design work is conducted for practical applications. In the present study, the heat transport characteristics together with pressure characteristics are examined for various magnetic field configurations by means of a numerical analysis and experiments. It is found that the distribution of magnetic field in the radial direction of an electromagnet largely affects the force and the heat transport characteristics. From results, it is shown that the aspect ratio of an electromagnet is the key factor.
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  • Analysis by Means of Mean Field Approximation
    Yasuhiro SAKUDA, Akira SATOH
    2007 Volume 73 Issue 734 Pages 2092-2098
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
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    We have investigated the negative viscosity of a colloidal dispersion composed of ferromagnetic rod-like particles, which have a magnetic moment normal to the particle axis. We have here treated a simple shear flow problem to clarify the particle orientational distribution and rheological properties of such a semi-dense dispersion, under circumstances of an external magnetic field applied in the direction normal to the shear plane of a simple shear flow. In order to take into account magnetic interactions between particles, the mean field approximation has been adopted. The results obtained here are summarized as follows. Characteristic orientational properties of the particle cause negative viscosity, as in the previous study for a dilute dispersion. However, magnetic particle-particle interactions have a function to make such negative viscosity decrease, since the magnetic moment of the particle tends to align in the magnetic field direction more significantly with magnetic particle-particle interactions increasing.
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  • Hitoshi SUGIYAMA, Yoichi SASAKI
    2007 Volume 73 Issue 734 Pages 2099-2106
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
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    Numerical analysis has been performed for three-dimensional fully developed turbulent flow in a helically curved pipe by using an algebraic Reynolds stress model. This kind of duct with helical sharp has been applied for passage employed in air conditioner and heat exchanger in many engineering fields. It is interesting point whether the present method can predict correctly the complicated turbulent flow in helically curved pipe, or not. In the numerical calculation, an algebraic Reynolds stress model is introduced to predict correctly anisotropic turbulence. Besides, boundary fitted-coordinate system is used as the method for coordinate transformation to set boundary conditions along complicated shape of helical curved pipe. Three types of helical pipe with different torsion ratio are selected to calculate turbulent flow structure in this research. Calculated results of streamwise mean velocity, secondary flow vectors and turbulence intensity are compared with the experimental data in order to examine the validity of the presented method. As a result of this calculation, it was found that the present method could predict reasonably the streamwise velocity, i.e., the movement of maximum mean velocity from outer wall to inner wall with increasing torsion ratio is reproduced correctly by the presented method. Besides, calculated results of secondary flow are relatively good agreement with the experiment except for the middle point of rotation flow generated by secondary flow in circular cross section. As for the turbulent intensity, the presented method is able to predict characteristic features of its distribution qualitatively but has tendency to underestimate the experimental results. Six components of Reynolds stresses are presented in helical pipe because there is no data to show these distributions. Calculated results suggest that the presented method can predict the turbulent flow in helical pipe.
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  • Yohsuke TANAKA, Kazuaki OTSU, Takuya TSUJI, Toshitsugu TANAKA
    2007 Volume 73 Issue 734 Pages 2107-2115
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
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    In the present study, as an elementary physics for modeling a particle-laden turbulent flow, interactions between a single particle and a single Burgers vortex are observed by using 2D-PIV measurement. We used three kinds of particles which have particle Reynolds numbers ranged from 1 258 to 2 854. Their diameters are larger than the Kolmogorov scale. The vortex Reynolds number used is 79. Especially, we focus on the vorticity field and the superficial fluid divergence field induced by the particle motion on a cross-section perpendicular to the vortex axis. It is found that the maximum vorticity is increased when the particle pass through the forced vortex area, and the increase does not occur when the particle pass through the free vortex area.
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  • Hiroyuki KAWAMOTO, Yukikazu MASUNARI, Shinjiro UMEZU
    2007 Volume 73 Issue 734 Pages 2116-2121
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
    JOURNAL FREE ACCESS
    Experimental and theoretical research has been conducted to investigate basic characteristics of an ozone fan utilizing the ionic wind induced in the pin-to-plate corona discharge field. When a high voltage was applied between the electrodes, the ionic wind, which included ozone, flowed from the pin elecrode to a hole of the plate electrode. It was deduced that (1) the ozone concentration is almost linear with respect to the corona current, (2) the ozone concentration was high with the large pin diameter but almost irrelevant with the gap between the electrodes, (3) the energy efficiency of the negative corona was about 14 times higher that of the positive corona, but it was only several %, (4) the ozone generation was reduced at high temperature. It was estimated that the several ppm ozone could be generated and flowed utilizing the negative discharge and the ozone generation was almost eliminated by turning off the polarity.
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  • Contribution of Inter- and Intramolecular Energy Transfer
    Daichi TORII, Takeo NAKANO, Taku OHARA
    2007 Volume 73 Issue 734 Pages 2122-2129
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
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    The molecular dynamics expression of heat conduction flux, which was originally derived by Irving and Kirkwood (1950) for pair-wise potentials, is generalized to systems with many-body potentials defined. The formula, newly derived in the present report, consists of kinetic part and potential part, and the latter term is expressed as a summation of thermal energy transfer in each group of interaction sites for which a many-body potential is defined. Next, the mechanism of the thermal energy transfer involving many-body potentials is clarified by extending the concept of intermolecular energy transfer previously proposed by one of the authors, and the accumulation of the thermal energy transfer over all the potentials and interaction sites in the system is proved to make up the potential part of the expression. A molecular dynamics simulation is conducted for liquid n-octane to examine the applicability of the expression newly obtained, and the contributions of the inter- and intramolecular potentials to heat conduction are elucidated.
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  • Yoshimi KOMATSU, Masahiro SUGAWARA, Seiichi MATSUKAWA, Tadashi FUJITA
    2007 Volume 73 Issue 734 Pages 2130-2137
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
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    Melting of a vertical ice cylinder into a homogeneous calcium chloride aqueous solution inside a rotating cylindrical cavity with several revolution speeds is considered experimentally. Melting mass and temperature are measured on four initial conditions of the solution and four rotating speeds of the cavity. Temperature of liquid layer becomes uniform by the mixing effect resulting from cavity rotation and it enhances the melting rate of ice cylinder. As cavity-rotating speed becomes fast, melting rate increases. Dimensionless melting mass is related to Fourier number and rotating Reynolds number in each initial condition, therefore the experimental equation that is able to quantitatively calculate a dimensionless melting mass is presented. It is seen that melting Nusselt number re-increases in the middle of melting process. Ice cylinder continues to melt in spite of small temperature difference between ice cylinder and solution.
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  • Yoshihisa SATO, Yukinori TANABE
    2007 Volume 73 Issue 734 Pages 2138-2144
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
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    It is necessary to develop a new power generation system using the unused thermal energy around 100 degrees C from a viewpoint of global warming prevention. Even if a shape memory alloy is bent in normal temperature, when it is heated, it has the feature which returns to the original straight form. Using this feature of a shape memory alloy, unused thermal energy will be able to transform into rotation energy, and finally it can change into electric energy. This research aims to develop the new power generation system which collects the unused thermal energy from the steam turbine which thrown away into the sea, the river, etc. The research was done from both sides of theory and an experiment about the rotation mechanism of the SMA engine, and its output characteistics. The theoretical formula for calculating predicts the rotation speed (ω) and the output power (P) of the SMA engine, was drawn from the size of a SMA belt, Young's modulus, and the radiuses of high-temperature and low-temperature rings. In addition, we conducted the experiment about rotation speed of SMA engine, and verified the part of validity of this theory indirectly.
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  • 1st Report, A Comparative Analysis of the Growth Patterns
    Shinichi TSUDA, Shu TAKAGI, Yoichiro MATSUMOTO
    2007 Volume 73 Issue 734 Pages 2145-2152
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
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    The growth of bubble nuclei in a decompressed liquid has been investigated using molecular dynamics (MD) simulations. In the case of one-component liquid in which no impurities were dissolved, we observed rapid growth of bubble nuclei with weak inter-bubble interaction in the early stage while seeing a competing coarsening that looks like Ostwald ripening in the late stage. In the case of two-component liquid in which a noncondensable gas was dissolved, we observed frequent coalescence of bubble nuclei through all stages. We pointed out that the different growth patterns in the two cases originated from the time characteristic of the pressure propagation and that of the diffusion of the noncondensable gas.
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  • 2nd Report, An Extraction of a Growth Law of the Bubble Nuclei
    Shinich TSUDA, Shu TAKAGI, Yoichiro MATSUMOTO
    2007 Volume 73 Issue 734 Pages 2153-2159
    Published: October 25, 2007
    Released on J-STAGE: March 03, 2011
    JOURNAL FREE ACCESS
    In this report, we have extracted the exponent for coarsening rate of the mean radius of the bubble nuclei using microcanonical molecular dynamics simulations. The objects of the simulations are one-component liquid argon and liquid argon with a moncondensable gas, as in the case of the 1st report. Although the same coarsening rate (n=1/2) was obtained between the two cases, we have confirmed that the different characteristics are reflected in the change of the total radius and in the change of the number of the nuclei with the coarsening. We show that the differences reflect the characteristics of the radius change of each nucleus and those of the size distribution function.
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  • Yasuo YAMAMOTO, Akira ISHII, Kenji AMAGAI, Tomohiko FURUHATA, Masataka ...
    2007 Volume 73 Issue 734 Pages 2160-2168
    Published: October 25, 2007
    Released on J-STAGE: August 16, 2011
    JOURNAL FREE ACCESS
    In order to develop effective combustion and gasification system of waste plastics, thermal decomposition and combustion characteristics of plastics compounds flame retardant were investigated. Polypropylene (PP) with flame retardant, which was composed by Al (OH) 3 or (NH4PO3) n, was decomposed in an image furnace. Mass reduction during thermal decomposition and combustion was measured by an electric micro-balance. The gas components produced by the thermal decomposition and combustion were analyzed with gas analyzer. Soluble organic fraction (SOF) components in a condensable emission during the decomposition process were analyzed with a PM analyzer. SOF and solid carbon in the remains after the thermal decomposition were also analyzed by the PM analyzer. The oxygen concentration was changed from 0% to 21% and the content of flame retardant was changed from 0% to 50%. It was found that flame retardant had small effect on the thermal decomposition temperature. Gas components produced by thermal decomposition and combustion were changed corresponding to the content of flame retardant.
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