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

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 topology-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.Comment: 33 pages, 23 figure

CURRENT STATUS ON HIGH PERFORMANCE COMPUTING FOR VEHICLE AERODYNAMICS USING LARGE EDDY SIMULATION

ABSTRACT The world's largest class unsteady turbulence simulations of flow around vehicles were conducted using Large Eddy Simulation (LES) on the Earth Simulator in Japan. The main objective of our study is to investigate the validity of LES, as an alternative to a conventional wind tunnel measurement or the Reynolds Averaged Navier-Stokes method, for the assessment of vehicle £ Address all correspondence to this author

包括的凝固/線溶動態に基づく敗血症性DIC（播種性血管内凝固）の病態解明

Background: The functional dynamics of coagulation and fibrinolysis in patients with disseminated intravascular coagulation (DIC) vary due to the pathology and severity of various underlying diseases. Conventional measurements of hemostasis such as thrombin-antithrombin complex, plasmin-α2-plasmin-inhibitor complex, and fibrinogen-fibrin degradation products may not always reflect critical pathophysiologic mechanisms in DIC. This article aims to clarify the pathology of sepsis-associated DIC using assessment of comprehensive coagulation and fibrinolysis. Methods: Plasma samples were obtained from 57 patients with sepsis-associated DIC at the time of initial diagnosis. Hemostasis parameters were quantified by clot-fibrinolysis waveform analysis (CFWA) and thrombin/plasmin generation assays (T/P-GA). The results were expressed as ratios relative to normal plasma. Results: CFWA demonstrated that the maximum coagulation velocity (|min1|) ratio modestly increased to median 1.40 (min - max: 0.10 - 2.60) but the maximum fibrinolytic velocity (|FL-min1|) ratio decreased to 0.61 (0 - 1.19). T/P-GA indicated that the peak thrombin (Th-Peak) ratio moderately decreased to 0.71 (0.22 - 1.20), whereas the peak plasmin (Plm-Peak) ratio substantially decreased to 0.35 (0.02 - 1.43). Statistical comparisons identified a correlation between |min1| and Th-Peak ratios (ρ = 0.55, p < 0.001), together with a strong correlation between |FL-min1| and Plm-Peak ratios (ρ = 0.71, p < 0.001), suggesting that CFWA reflected the balance between thrombin and plasmin generation. With |min1| and |FL-min1| ratios, DIC was classified as follows: coagulation-predominant, coagulation/fibrinolysis-balanced, fibrinolysis-predominant, and consumption-impaired coagulation. The majority of patients in our cohort (80.7%) were coagulation-predominant. Conclusion: A pathological clarification of sepsis-associated DIC based on the assessment of coagulation and fibrinolysis dynamics may be useful for the hemostatic monitoring and management of optimal treatment in these individuals.博士（医学）・甲第786号・令和3年3月15日© 2020. Thieme. All rights reserved.This is a non-final version of an article published in final form in "http://dx.doi.org/10.1055/s-0040-1713890

Computational visualization of unsteady flow around vehicles using high performance computing

One of the largest-scale unstructured Large Eddy Simulation (LES) of flow around a full-scale road vehicle is conducted on the Earth Simulator in Japan. The main objective of our study is to look into the validity of LES for the assessment of vehicle aerodynamics, especially in the context of its possibility for unsteady or transient aerodynamic forces. Firstly, the aerodynamic LES proposed is quantitatively validated on the ASMO simplified model by comparing the mean pressure distributions on the vehicle surface with those obtained by a conventional Reynolds-Averaged Navier-Stokes simulation (RANS) or a wind tunnel measurement. Then, the method is applied to the full-scale vehicle with complicated geometry to qualitatively investigate the capability of capturing organized flow structures around the vehicle. Finally, unsteady aerodynamic forces acting on the vehicle in transient yawing-angle change are estimated and relationship between the flow structures and the transient aerodynamic forces is mentioned. As a result, it is demonstrated that LES will be a powerful tool for the vehicle aerodynamic assessment in the foreseeable future, because it can provide precious aerodynamic data which conventional wind tunnel tests or RANS simulations are difficult to provide