Gaku Hashimoto

Aerodynamic and Structural Numerical Investigation of Unsteady Flow Effects on Last Stage Blades

The aim of this paper is to present some of research results of our current collaborative program to increase steam turbine efficiency with the development of high-performance blade and exhaust hood design methodology using large-scale aerodynamic and structural interaction analysis. Aerodynamic optimum designs of stator blades are already introduced in many designs of actual operating commercial steam turbine units. However, aerodynamic optimum designs of rotating blades are still difficult due to high centrifugal force and vibration stress on rotating blades. This paper focuses on rotating blades and exhaust diffusers that affect the flow field just downstream of last stage long blades. The large-scale high-accuracy CFD analysis of unsteady wet steam flows has been successfully introduced for simulations of low pressure exhaust diffuser using the Earth Simulator of Japan Agency for Marine-Earth Science and Technology. This result shows that the diffuser domain analysis can provide static pressure recovery coefficients and its circumferential deviations with enough accuracy for design use except correct location predictions of separations. The unsteady flow analyses of the typical designed last stage with the measured and calculated downstream static pressure distribution as the outlet boundary condition were conducted. The unsteady flow analyses of the typical designed low pressure exhaust diffuser with the measured and calculated upstream flow conditions as the inlet boundary condition were also conducted. Some of the calculated results were compared with measured data. The large-scale parallel computing Finite Element Analysis of turbine blades with inter-connection parts has been also successfully introduced on the Earth Simulator. The calculation result shows that the eigen frequencies of the present group of loosely-connected rotating blades correspond well to the existing measured data. For the next step, the unsteady structural analysis is being conducted with the calculated unsteady forces on the rotating blades as the FEA boundary conditions. Some of the FEA results are also presented in this paper.Copyright

Numerical Flow Analysis of Electromagnetic Fluid Using GSMAC Finite-Element Method

Numerical calculations for the cavity flow which simulates Joule-heated glass furnace were executed using GSMAC finite element method (GSMAC-FEM). The cavity consists of two main electrode plates on facing sides, two auxiliary electrode at the bottom and constant temperature wall on the top working as a heat sink. Magnetic field effect in Joule-heated glass furnace was verified by flow-electric-magnetic coupling analysis. When the calculation coupled with the flow and electric field was executed, unsteady down flows occurred from the top surface of the cavity. However, from the result of calculation coupled with flow, electric field and magnetic field, a large up flow appeared in the center of the cavity and permanently existed. Consequently, flow behavior including magnetic field was completely different from that excluding magnetic field effect. The results suggest that numerical analysis including magnetic field effect is recommended for accurate understanding of flow behavior in the Joule-heated glass furnaces. On the other hand, the data of velocity field, temperature field and magnetic field are also got by numerical simulation and compared with the result of Japan Atomic Energy Agency.Copyright

Fault Displacement Simulation Analysis of the Kamishiro Fault Earthquake in Nagano Prefecture Using the Parallel Finite Element Method

In recent years, the evaluation of fault displacement has been required for evaluating the soundness of underground structures during an earthquake. Fault displacement occurs as the result of the rupture of the earthquake source fault, and studies have been conducted using the finite difference method, the finite element method, etc. The present study used the nonlinear finite element method to perform a dynamic rupture simulation analysis of the Kamishiro fault earthquake in Nagano Prefecture on November 22, 2014. A model was prepared using a solid element for the crust and a joint element for the fault surface. The Kamishiro fault earthquake in Nagano was a reverse-fault earthquake whose fault plane included a part of the Kamishiro fault and extended northward from there. The total extent was 9 km, and the surface fault displacement confirmed was approximately 1 m at maximum. Initial stress was applied to the fault to intentionally rupture the hypocenter to perform a propagation analysis of the rupture, and the displacement and response time history obtained in the analysis were compared with observational records. At this time, joint elements according to Goodman et al. that had been expanded were introduced to the finite element method code FrontISTR, which can analyze large-scale models, and the simulation analysis was performed.

Effect of GPU Communication-Hiding for SpMV Using OpenACC

In this study, we discuss overlapping possibilities of Sparse Matrix-Vector multiplication (SpMV) in cases where we have multiple RHS-vectors and where the whole sparse matrix data may or may not fit into the memory of the discrete GPU, at once, by using OpenACC. With GPUs, one can take advantage of their relatively high memory bandwidths. However, data needs to be transferred over the relatively slow PCIe bus. We implement communication-hiding to increase performance. In the case of three degrees of freedom and modeling 2,097,152 nodes, we observe a just above 40% performance increase by applying communication-hiding in our routine. This underlines the importance of applying such techniques in simulations, when it is suitable with the algorithmic structure of the problem in relation to the underlying computer architecture.

Numerical investigation of molten glass in a square cavity using finite element method

In this study, natural convection of molten glass in a Joule-heated cavity flow is analyzed using the FEM. The GSMAC-FEM is utilized for incompressible viscous flow. The energy equation and Ampere-Maxwell equation are computed by the node-based FEM and edge-based FEM respectively. The solvers of three fields, i.e. flow field, thermal field and electromagnetic field, are coupled through a staggered scheme to simulate the flow behavior. Two carbon plates are placed on opposing side walls of the cavity model and connected a constant AC voltage to generate an internal heat source. The top surface of the cavity model is cooled by constant temperature. In order to confirm the numerical code, velocity and temperature profile is measured at center of cavity using electric conducting fluid of 80wt% glycerol. The numerical results and experimental data have a good agreement in time histories of temperature. It was confirmed that the upflow behavior of molten glass in the cavity depends on magnetic permeability.