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CUBE: A scalable framework for large-scale industrial simulations [article]

Niclas Jansson, Rahul Bale, Keiji Onishi, Makoto Tsubokura
2018 arXiv   pre-print
Writing high performance solvers for engineering applications is a delicate task. These codes are often developed on an application to application basis, highly optimized to solve a certain problem. Here, we present our work on developing a general simulation framework for efficient computation of time resolved approximations of complex industrial flow problems - Complex Unified Building cubE method (Cube). To address the challenges of emerging, modern supercomputers, suitable data structures
more » ... d communication patterns are developed and incorporated into Cube. We use a Cartesian grid together with various immersed boundary methods to accurately capture moving, complex geometries. The asymmetric workload of the immersed boundary is balanced by a predictive dynamic load balancer, and a multithreaded halo-exchange algorithm is employed to efficiently overlap communication with computations. Our work also concerns efficient methods for handling the large amount of data produced by large-scale flow simulations, such as scalable parallel I/O, data compression and in-situ processing.
arXiv:1808.04099v1 fatcat:cenwmeexs5a6npg64ie6yirmgy

Quantifying the COVID19 infection risk due to droplet/aerosol inhalation [article]

Rahul Bale, Akiyoshi Iida, Masashi Yamakawa, ChungGang Li, Makoto Tsubokura
2021 arXiv   pre-print
The dose-response model has been widely used for quantifying the risk of infection of airborne diseases like COVID-19. The model has been used in the room-average analysis of infection risk and analysis using passive scalars as a proxy for aerosol transport. However, it has not been employed for risk estimation in numerical simulations of droplet dispersion. In this work, we develop a framework for the evaluation of the probability of infection in droplet dispersion simulations using the
more » ... sponse model. We introduce a version of the model that can incorporate the higher transmissibility of variant strains of SARS-CoV2 and the effect of vaccination in evaluating the probability of infection. Numerical simulations of droplet dispersion during speech are carried out to investigate the infection risk over space and time using the model. The advantage of droplet dispersion simulations for risk evaluation is demonstrated through the analysis of the effect of humidity on infection risk.
arXiv:2110.04295v1 fatcat:isi45zsyhrh6zfn4p6to33w6qu

Study on the underbody flow of the vehicle

2007 Seisan Kenkyu  
TSUBOKURA, Nobuyuki OSHIMA, Makoto YAMAMOTO, ZHANG Huilai, Keiji OHNISHI, Takuji NAKASHIMA and Toshio KOBAYASHI 研 究 速 報 71.2 時間での解析が可能となった. 2.1.2 計算条件 図 1 に計算対象である ASMO 形状 3) を示す.図 2 に計 算領域を示す.流れ方向 15  ...  %,並列化率 99.6 %を達成し,実時間で 報: LES による CFD 解析:単純化された床下形状の場合-Study on the underbody flow of the vehicle -Report 2: CFD analysis via LES: Case of simplified underbody configurations- し 1 数値解法 1 号 1 号 111 Makoto  ... 
doi:10.11188/seisankenkyu.59.27 fatcat:mxmpqawaabfuhfow7py7ulxx7q

Numerical analysis of the efficiency of face masks for preventing droplet airborne infections [article]

Keiji Onishi, Akiyoshi Iida, Masashi Yamakawa, Makoto Tsubokura
2021 arXiv   pre-print
droplet airborne infections Keiji Onishi,1, a) Akiyoshi Iida,2 Masashi Yamakawa,3 and Makoto  ...  Tsubokura, “Numerical Investigation of Effects of Incisor Angle on Production of Sibilant /s/,” Scientific Reports 11, 16720 (2021). 24 W. O. Fenn and H.  ... 
arXiv:2112.12513v1 fatcat:3zsj5ux3sfd7hml7l5mugiuupq

A one-sided direct forcing immersed boundary method using moving least squares [article]

Rahul Bale, Amneet Pal Singh Bhalla, Boyce E. Griffith, Makoto Tsubokura
2021 arXiv   pre-print
This paper presents a one-sided immersed boundary (IB) method using kernel functions constructed via a moving least squares (MLS) method. The resulting kernels effectively couple structural degrees of freedom to fluid variables on only one side of the fluid-structure interface. This reduces spurious feedback forcing and internal flows that are typically observed in IB models that use isotropic kernel functions to couple the structure to fluid degrees of freedom on both sides of the interface.
more » ... e method developed here extends the original MLS methodology introduced by Vanella and Balaras (J Comput Phys, 2009). Prior IB/MLS methods have used isotropic kernel functions that coupled fluid variables on both sides of the boundary to the interfacial degrees of freedom. The original IB/MLS approach converts the cubic spline weights typically employed in MLS reconstruction into an IB kernel function that satisfies particular discrete moment conditions. This paper shows that the same approach can be used to construct one-sided kernel functions (kernel functions are referred to as generating functions in the MLS literature). We also examine the performance of the new approach for a family of kernel functions introduced by Peskin. It is demonstrated that the one-sided MLS construction tends to generate non-monotone interpolation kernels with large over- and undershoots. We present two simple weight shifting strategies to construct generating functions that are positive and monotone, which enhances the stability of the resulting IB methodology. Benchmark cases are used to test the order of accuracy and verify the one-sided IB/MLS simulations in both two and three spatial dimensions. This new IB/MLS method is also used to simulate flow over the Ahmed car model, which highlights the applicability of this methodology for modeling complex engineering flows.
arXiv:2104.07738v1 fatcat:bopatlh6n5ehpiggjlf4yx7g2y

Fluid-Dynamic Force Measurement of Ahmed Model in Steady-State Cornering

Takuji Nakashima, Hidemi Mutsuda, Taiga Kanehira, Makoto Tsubokura
2020 Energies  
Tsubokura et al. [15] and Okada et al.  ... 
doi:10.3390/en13246592 fatcat:jlk6ley3oje2jjg4r2xrts6ina

Topology-free immersed boundary method for incompressible turbulence flows: An aerodynamic simulation for 'dirty' CAD geometry [article]

Keiji Onishi, Makoto Tsubokura
2020 arXiv   pre-print
To design a method to solve the issues of handling 'dirty' and highly complex geometries, the topology-free method combined with the immersed boundary method is presented for viscous and incompressible flows at a high Reynolds number. The method simultaneously employs a ghost-cell technique and distributed forcing technique to impose the boundary conditions. An axis-projected interpolation scheme is used to avoid searching failures during fluid and solid identification. This method yields a
more » ... logy-free immersed boundary, which particularly suits flow simulations of highly complex geometries. Difficulties generally arise when generating the calculation grid for these scenarios. This method allows dirty data to be handled without any preparatory treatment work to simplify or clean-up the geometry. This method is also applicable to the coherent structural turbulence model employed in this study. The verification cases, used in conjunction with the second-order central-difference scheme, resulted in first-order accuracy at finer resolution, although the coarser resolution retained second-order accuracy. This method is fully parallelized for distributed memory platforms. In this study, the accuracy and fidelity of this method were examined by simulating the flow around the bluff body, past a flat plate, and past dirty spheres. These simulations were compared with experimental data and other established results. Finally, results from the simulation of practical applications demonstrate the ability of the method to model highly complex, non-canonical three-dimensional flows. The countermeasure based on the accurate classification of geometric features has provided a robust and reasonable solution.
arXiv:2002.06206v1 fatcat:k2q54si7efejliuqwl3ykwegcy

Numerical visualization of boundary layer transition when negative Magnus effect occurs

Masaya Muto, Makoto Tsubokura, Nobuyuki Oshima
2012 Journal of Visualization  
We previously identified the appearance of negative Magnus lift on a sphere rotating about an axis perpendicular to an incoming flow at a critical Reynolds number using large-eddy simulation and obtained the statistically time-averaged lift and pressure coefficients around the sphere. We have now numerically investigated the unsteady characteristics of the boundary layer around a rotating sphere at three Reynolds numbers (1.0×10 4 , 2.0×10 5 , and 1.14×10 6 ). At a Reynolds number in the
more » ... ical or supercritical region, the direction of the lift force followed the Magnus effect independent of the rotational speed. In contrast, at the critical Reynolds number when a particular rotational speed was imposed, negative lift was observed and a boundary-layer transition occurred only on one side of the sphere, as indicated by the visualization of the vortical structures around the sphere. A change in these structures and a shift of the separation points along with a change in the Reynolds number or rotational speed of the sphere were investigated in the context of boundary layer transition by using visualization around the sphere.
doi:10.1007/s12650-012-0125-2 fatcat:6bikruvgtjbnzakmpglbzv6lrq

Negative Magnus lift on a rotating sphere at around the critical Reynolds number

Masaya Muto, Makoto Tsubokura, Nobuyuki Oshima
2012 Physics of Fluids  
In contrast, the downstream zero-shear line is partially covered by azimuthal 014102-12 Muto, Tsubokura, and Oshima Phys.  ...  Redistribution subject to AIP license or copyright; see Muto, Tsubokura, and Oshima Phys.  ... 
doi:10.1063/1.3673571 fatcat:yd5tufaogbajhhflhpuzgvcfei

Numerical Simulation of Turbulent Non-Premixed Flame in a Furnace

2000 Seisan Kenkyu  
TSUBOKURA, Nobuyuki TANIGUCHI and Toshio KOBAYASHI 研 究 速 報 * 東京大学生産技術研究所 第 2 部 ** 東京工業大学大学院総合理工学研究科 *** 東京大学国際・産学共同研究センター - - - - - - - - ここで, ,flamelet data: 密度の空間平均値は以下の式で与えられる. ≥≥≥≥≥≥≥≥≥≥≥≥≥≥≥≥≥≥≥≥  ...  Turbulent Non-Premixed Flame in a Furnace -Development of Solution Method for LES of Turbulent Non-Premixed Flame- 弘 畑 幹 鐘 * ・伊 藤 裕 一 * ・坪 倉 誠 ** ・谷 口 伸 行 * ・小 林 敏 雄 *** Mikikane HIROHATA, Yuichi ITOH, Makoto  ... 
doi:10.11188/seisankenkyu.52.63 fatcat:gdji7dd4sfdvhpbg5hgy6mq3zq

Assessment of the Eddy Viscosity Type Models in Dynamic SGS Model

1998 Seisan Kenkyu  
-1 3 Ë ij ˜kk = -2C ∆ 2 S S ij ˜ij ≈ u i ′ u j ′ ˜ij = u i u j -u i u j ダイナミック SGS モデルにおける渦粘性型モデルの評価 Assessment of the Eddy Viscosity Type Models in Dynamic SGS Model 坪 倉 誠 * ,小 林 敏 雄 ** ,谷 口 伸 行 *** Makoto  ...  TSUBOKURA, Toshio KOBAYASHI and Nobuyuki TANIGUCHI 特 集 6 研 究 速 報 研 究 速 報 * 日本学術振興会特別研究員 ** 東京大学国際・産学共同研究センター *** 東京大学生産技術研究所第 2 部 に乗じる.そして生成項に含まれる ˜ij に対してその対角 成分を ˜ij のトレースを用いて与え,非対角成分について はゼロと仮定する(弱非等方性  ... 
doi:10.11188/seisankenkyu.50.23 fatcat:2ylu4i4u4newrh4l25rktarzuu

Large Eddy Simulation of the Flow-Field around a Full-Scale Heavy-Duty Truck

Prasanjit Das, Makoto Tsubokura, Tomofuyu Matsuuki, Nobuyuki Oshima, Kozo Kitoh
2013 Procedia Engineering  
In this paper, Large Eddy Simulations (LES) of flow field around two different full-scale heavy-duty truck with air deflector and without an air deflector model are presented. The full-scale truck model is considered which contains a number of details such as bumpers, underbody, tractor chassis, wheels and axles. The numerical simulations have been conducted with two virtual wind tunnels at different yaw angle at 0°, 5° and 10°. The models are placed at different yawing angles in the virtual
more » ... d tunnels with a blockage ratio of about 10%, which is same as the experimental wind tunnel. To compare the corrected experimental results with the ideal case, other simulations are also conducted with a larger cross section at the blockage ratio of about 1%. A detailed survey of both instantaneous and timeaveraged flow is presented. The steady state simulations with tetrahedral meshes predict the drag coefficient ( d C ) accurately within 3.3%, 4.5% and 3.3% of with air deflector model and 1.3%, 4.1% and 7% of without an air deflector model to corresponding experimental values at 0 o , 5 o and 10 o yaw cases, respectively. It is observed that aerodynamic coefficients such as drag coefficient ( d C ), side force coefficient ( s C ) and lift force coefficient ( l C ) depend on yaw angles and as well as vehicle geometry.
doi:10.1016/j.proeng.2013.03.155 fatcat:noolkg4uczbdhnulvn42vljcsi

Effect of posture on the aerodynamic characteristics during take-off in ski jumping

Keizo Yamamoto, Makoto Tsubokura, Jun Ikeda, Keiji Onishi, Sophie Baleriola
2016 Journal of Biomechanics  
Ecole Nationale SuMrieure de Mecanique et d'Aerotechnique, Paris, ~r a n c e~ The purpose of this study was to quantify the aerodynamic characteristics during takeoff using computational fluid dynamics (CFD). The CFD method adopted for this study is based on LargeEddy Simulation. Body surface data were obtained by 3-D laser scanning of an active ski jumper. A model was generated by dividing the data into A 5 segments with joint mobility. Based on video analysis of the actual takeoff movement at
more » ... a jumping hill, two sets of motion data were generated (world-class jumper A and less-experienced junior jumper B). The incoming velocity was set to 23.23 mls. The aerodynamic force, flow velocity, and vortices for each model were compared between models. Comparison of the two models shows that aerodynamic forces acting upon models might be influenced by the airflow condition around the model's back. Expansion of the low air-speed domain of jumper B can be caused by a large trunk angle of attack (Meile et al., 2006) . The trunk and upper arm motion might cause the flow structure difference of the wake. Two distinct vortexes generated by the arms produced a downwash flow in the wake of jumper A. It is considered that the positioning of the arms in a very low position strongly influences the flow structure. These results suggested that the vortexes generated by the arms seem to be very important for the aerodynamic lift generation. KEY WORDS: ski jumping, computational fluid dynamics, aerodynamic force, vortex.
doi:10.1016/j.jbiomech.2016.09.037 pmid:27743629 fatcat:hq6mfge6vvhwfmj6a4mq2xlxyy

An implicit turbulence model for low-Mach Roe scheme using truncated Navier–Stokes equations

Chung-Gang Li, Makoto Tsubokura
2017 Journal of Computational Physics  
資源タイプ Resource Type Journal Article / 学術雑誌論文 版区分 Resource Version author 権利 Rights ABSTRACT The original Roe scheme is well-known to be unsuitable in simulations of turbulence because the dissipation that develops is unsatisfactory. Simulations of turbulent channel flow for Reτ=180 show that, with the 'low-Mach-fix for Roe' (LMRoe) proposed by Rieper [J. Comput. Phys. 230 (2011) 5263-5287], the Roe dissipation term potentially equates the simulation to an implicit large eddy simulation (ILES)
more » ... low Mach number. Thus inspired, a new implicit turbulence model for low Mach numbers is proposed that controls the Roe dissipation term appropriately. Referred to as the automatic dissipation adjustment (ADA) model, the method of solution follows procedures developed previously for the truncated Navier-Stokes (TNS) equations and, without tuning of parameters, uses the energy ratio as a criterion to automatically adjust the upwind dissipation. Turbulent channel flow at two different Reynold numbers and the Taylor-Green vortex were performed to validate the ADA model. In simulations of turbulent channel flow for Reτ=180 at Mach number of 0.05 using the ADA model, the mean velocity and turbulence intensities are in excellent agreement with DNS results. With Reτ=950 at Mach number of 0.1, the result is also consistent with DNS results, indicating that the ADA model is also reliable at higher Reynolds numbers. In simulations of the Taylor-Green vortex at Re=3000, the kinetic energy is consistent with the power law of decaying turbulence with −1.2 exponents for both LMRoe with and without the ADA model. However, with the ADA model, the dissipation rate can be significantly improved near the dissipation peak region and the peak duration can be also more accurately captured. With a firm basis in TNS theory, applicability at higher Reynolds number, and ease in implementation as no extra terms are needed, the ADA model offers to become a promising tool for turbulence modelling.
doi:10.1016/ fatcat:rildc654rfde3habbbltboieb4

Coupled analysis of unsteady aerodynamics and vehicle motion of a road vehicle in windy conditions

Takuji Nakashima, Makoto Tsubokura, Mariano Vázquez, Herbert Owen, Yasuaki Doi
2013 Computers & Fluids  
The two-way coupling of full-scale vehicle motion and the surrounding turbulence motion has been realized on a developed unsteady aerodynamic simulator for a road vehicle. A large-eddy simulation (LES) technique has been applied to reproduce the unsteady turbulence motion, and an unstructured finite volume method has been adopted to explain the complicated geometry of a full-scale road vehicle. Three-degree-of-freedom equations of the vehicle's dynamic motion are incorporated into the developed
more » ... LES code, and the motion is numerically reproduced by coupling the arbitrary Lagrangian-Eulerian (ALE) method and Navier-Stokes equations in a non-inertial reference frame. The simulation code is implemented on a massively parallel processor to meet the demands of the large-scale, long-term aerodynamic simulations of full-scale road vehicles. As a typical application of the coupled analysis, an unsteady aerodynamics simulation of a simplified heavy-duty truck in windy conditions is demonstrated, and the effects of the unsteady aerodynamics on the truck's motion are investigated. The obtained results are compared with the results of a conventional quasi-steady analysis, and certain differences in the vehicle path and the yaw angle are identified. The effects of the transitional aerodynamics on variables related to driver's perception are significant. These results clearly indicate the importance of estimating the unsteady aerodynamic forces in a vehicle motion analysis.
doi:10.1016/j.compfluid.2012.09.028 fatcat:dbhh2lhidfcdtizhy4c2rklama
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