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Turbulent Combustion Properties of Outwardly Propagating Flames
Kimitoshi TANOUE,Fumio SHIMADA,Takashi NASU,Takayuki KAWASHIMA,Toshiro HAMATAKE 한국자동차공학회 2001 한국자동차공학회 Symposium Vol.- No.-
In engine combustion. turbulence generated by flow field motion such as swirl and flimbic, in the cylinder affects the propagating flame initiated by spark plug. resulting in the enhancement or the mass consumption rate or reactants as compared with the corresponding laminar flames. This in turn increases the heat release rate and thus power available from an engine of a given size. In this context the modeling and prediction or turbulent flame properties are or importance from the application point or view. In the present work, turbulent burning velocities or outwardly propagating premixed flames for methane and propane, which are representative of lighter or heavier hydrocarbon respectively, are investigated under the framework or flamelet concept which is based on the assumption that a chemical reaction occurs in thin layers that arc convected and distorted by the turbulent now field. In flamelet concept, the flame-flow interaction can be described in terms of total flame front surface and local flame structure. The local flame properties defined by the displacement speed and reaction rate depend on local hydrodynamic strain rate and curvature effects. Furthermore, the name response to flow divergence and curvature depends strongly on the Lewis number, characterized by the ratio of molecular diffusivity to thermal diffusivity. For non-unity Lewis numbers, differential diffusion of heat and species results in a certain sensitivity of the local flame structure to strain rate and curvature. Although this thermo-diffusive mechanism is well known for laminar names or for low stretched flames, recent studies have showed that it influences the local and global name structure of turbulent premixed combustion with high stretch. The primary objective of the present paper is to study experimentally the turbulent burning velocity and derive the fundamental equations in consideration of interaction between averaged name stretch and Lewis numbers<br/> <br/>
Sato Kimitoshi,Hijikata Yasukazu,Omura Naoki,Miki Takanori,Kakita Hiroto,Yoshida Takashi,Shimizu Fuminori 대한뇌혈관외과학회 2021 Journal of Cerebrovascular and Endovascular Neuros Vol.23 No.3
Objective Acute mechanical thrombectomy (AMT) in patients with acute ischemic stroke from large vessel occlusion (LVO) is performed without directly identifying the occluded vessels. In this study, we evaluated whether 1.5 T magnetic resonance imaging (MRI) with 3D-fast imaging employing steady-state acquisition (FIESTA) could visualize the occluded intracranial middle cerebral artery (MCA) and internal carotid artery (ICA) before AMT. Methods This retrospective study included 21 consecutive patients who underwent time-of-flight magnetic resonance angiography (TOF MRA) and 3D-FIESTA MRI immediately before AMT. The patients also underwent TOF MRA after AMT and achieved TICI 2b or 3 by AMT at our hospital between February 2018 and April 2019. When LVO in the anterior circulation was detected by TOF MRA, 3D-FIESTA MRI was additionally performed. Then, the occluded intracranial MCA and ICA, including their branches, were constructed on the workstation with volume rendering. The obtained images were fused with the TOF MRA images to create combined 3D images. Results The length and top-to-bottom distance of the affected M1 segment (calculated by the ipsilateral-to-contralateral ratio) were 1.29 and 1.17, respectively, on 3D-FIESTA MRI before AMT and 1.34 and 1.24, respectively, on TOF MRA after AMT. We assessed the number of M2 segments branching from the affected M1/M2 junction and visualized the affected anterior temporal artery. The 3D-FIESTA MRI before AMT and TOF MRA after AMT were consistent in all patients, except for two who moved vigorously during imaging. Conclusions Images acquired by 1.5T 3D-FIESTA MRI can visualize to predict the existing path of the occluded MCA and ICA before AMT in patients with LVO of the anterior circulation.
Evaluation of Area- and Volume-based Gradations of Sand-Crushed Stone Mixture by 2D Images
Janaka J. Kumara,Kimitoshi Hayano,Yoshiaki Kikuchi 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.3
Ballast fouling is a challenging issue in ballasted railway tracks due to frequent maintenance works. At present, sieve analysis is conducted to obtain the gradation curve of fresh and fouled ballasts at laboratories. The investigation time is quite long since it requires a sampling. The information obtained from sieve analysis are not sufficient to propose appropriate maintenance plans since it does not produce shape characteristics of the particles properly. In this research, area- and volume-based gradation curves of fresh and fouled ballasts, simulated by laboratory-scale particles, were studied using an image analysis method. A simple method was proposed to obtain the volume-based gradation curve by 2D images. This method can be practised as an in-situ test method since it needs only a camera and a computer. The results suggest that the grain size should be defined appropriately according to the shape assigned for the particles. It was also found that area-based gradation curve produced by an ellipse shape for the crushed stone particles match sieve analysis closer than circle and rectangle shapes. The results also indicate that area-based gradation match sieve analysis closer than number- and volume-based gradations for the crushed stone particles. It was also found that the volume-based gradation curves evaluated by parallel and diagonal passing overestimate and underestimate respectively its grain size compared to sieve analysis. The gradation curve evaluated by an equivalent passing with a grain size correction factor match the sieve analysis for crushed stone, sand and sand-crushed stone samples. The image analysis results also indicate that the crushed stone particles are more angular than sand particles, which is important in numerical analysis to simulate fresh and fouled ballasts.
Importance of particle shape on stress-strain behaviour of crushed stone-sand mixtures
Kumara, Janaka J.,Hayano, Kimitoshi Techno-Press 2016 Geomechanics & engineering Vol.10 No.4
In ballasted railway tracks, ballast fouling due to finer material intrusion has been identified as a challenging issue in track maintenance works. In this research, deformation characteristics of crushed stone-sand mixtures, simulating fresh and fouled ballasts were studied from laboratory and a 3-D discrete element method (DEM) triaxial compression tests. The DEM simulation was performed using a recently developed DEM approach, named, Yet Another Dynamic Engine (YADE). First, void ratio characteristics of crushed stone-sand mixtures were studied. Then, triaxial compression tests were conducted on specimens with 80 and 50% of relative densities simulating dense and loose states respectively. Initial DEM simulations were conducted using sphere particles. As stress-strain behaviour of crushed stone-sand mixtures evaluated by sphere particles were different from laboratory specimens, in next DEM simulations, the particles were modeled by a clump particle. The clump shape was selected using shape indexes of the actual particles evaluated by an image analysis. It was observed that the packing behaviour of laboratory crushed stone-sand mixtures were matched well with the DEM simulation with clump particles. The results also showed that the strength properties of crushed stone deteriorate when they are mixed by 30% or more of sand, specially under dense state. The results also showed that clump particles give closer stress-strain behaviour to laboratory specimens than sphere particles.