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Large deformation simulations of geomaterials using moving particle semi-implicit method

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Journal of Rock Mechanics and Geotechnical Engineering 2018年第6期10卷 1122-1132页

作者： Shintaro Nohara Hiroshi Suenaga Kunihiko Nakamura central research institute of electric power industry ChibaJapan

Numerical simulation tools are required to describe large deformations of geomaterials for evaluating the risk of geo-disasters. This study focused on moving particle semi-implicit(MPS) method, which is a Lagrangian gridless particle method, and investigated its performance and stability to simulate large deformation of geomaterials. A calculation method was developed using geomaterials modeled as Bingham fluids to improve the original MPS method and enhance its stability. Two numerical tests showed that results from the improved MPS method was in good agreement with the theoretical ***, numerical simulations were calibrated by laboratory experiments. It showed that the simulation results matched well with the experimentally observed free-surface configurations for flowing sand. In addition, the model could generally predict the time-history of the impact force. The MPS method could be a useful tool to evaluate large deformation of geomaterials.

关键词： Particle method Moving particle semi-implicit(MPS) method Large deformation analysis Geomaterials Bingham model

Creep and creep-fatigue behavior of high chromium steel weldment

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Acta Metallurgica Sinica(English Letters) 2011年第3期24卷 175-182页

作者： Yukio TAKAHASHI Masaaki TABUCHI Materials Science Laboratory Central Research Institute of Electric Power Industry National institute of Material Sciences

Strength of welded joints of high chromium steels is one of the important concerns for fabricators and operators of ultra supercritical thermal power plants. A number of creep as well as creep-fatigue tests with tensile hold have been carried out on the welded joints of two types of high chromium steels widely used in Japan, i.e. Grade 91 and 122 steels. It was found that failure occurred in fine grain heat-affected zone in all the creep-fatigue tests, even at a relatively low temperature and fairly short time where failure occurred in plain base metal region in simple creep testing. Four procedures were used to predict failure lives and their results were compared with the test results. A newly proposed energy-based approach gave the best estimation of failure life, without respect of the material and temperature.

关键词： Creep Creep-fatigue High chromium steel Life prediction Welded joint

Experimental investigation on cohesionless sandy bank failure resulting from water level rising

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International Journal of Sediment research 2018年第1期33卷 47-56页

作者： Ryosuke Arai Kazuyuki Ota Takahiro Sato Yasushi Toyoda Fluid Dynamics Sector Central Research Institute of Electric Power Industry

In the last decade, sediment replenishment forming cohesionless sandy banks below dams has become an increasingly common practice in Japan to compensate for sediment deficits downstream. The erosion process of the placed cohesionless sediment is a combination of lateral toe-erosion and the following mass failure. To explore cohesionless bank failure mechanisms, a series of experiments was done in a soil tank using a compacted sandy soil mass exposed to an increasing water level. Two types of uniform sand(D50= 0.40 mm and 0.17 mm) and two bank heights（50 cm and 25 cm） were used under the condition of a constant bank slope of 75°. The three dimensional（3D） geometry of the bank after failure was measured using a handheld 3D scanner. The motion of bank failure was captured using the particle image velocimetry（PIV） technique, and the matric suction was measured by tensiometers. The compacted sandy soil was eroded by loss of matric suction accompanying the rise in water level which subsequently caused rotational slide and cantilever toppling failure due to destabilization of the bank. The effect of erosion protection resulting from the slumped blocks after these failures is discussed in the light of different failure mechanisms. Tensile strength is analyzed by inverse calculation of cantilever toppling failure events. The tensile strength had non-linear relation with degree of saturation and showed a *** findings of the study show that it is important to incorporate the non-linear relation of tensile strength into stability analysis of cantilever toppling failure and prediction of tension crack depth within unsaturated cohesionless banks.

关键词： Riverbank erosion Matric suction Cohesionless bank Tensile strength

DAMAGE MECHANISMS OF INCONEL 738LC UNDERCREEP-FATIGUE LOADING CONDITIONS

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Acta Metallurgica Sinica(English Letters) 1998年第6期11卷 470-476页

作者： M.Yamamoto T.Ogata central research Inst of electric Power Industry Tokyo Japan

In order to investigate creep-fatigue life characteristics of InConel 738LC, fatigue and creep-fatigue tests were carried out at 850 degree C. Significant life reduction to 30% to 50% of normal fatigue life, occurred when a strain hold period was introduced at the minimum compressive strain. Test results show that the degree of life reduction does not depend on the scale of hold time. To clarify the creep-fatigue damage mechanisms under creep-fatigue loading, in-situ SEM observations were carried out during the tests. In the tensile strain hold test, multi-site grain boundary cracking was observed from the beginning of the test. On the other hand, only a single main crack was observed in the compressive strain hold test. The crack propagates in an intergranular manner, and it is different from the features observed under cyclic fatigue conditions. Through the detailed observations, it was found that the grain boundary sliding damage occurs at most surface grain boundaries. (Edited author abstract) 5 Refs.

关键词： superalloy creep-fatigue grain boundary sliding

Numerical model of local scour considering the unsteady sediment inflow and sediment sorting: Application to scour upstream of slit weir

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International Journal of Sediment research 2022年第4期37卷 469-483页

作者： Kazuyuki Ota Takahiro Sato Ryosuke Arai Meteorology and Fluid Science Division Central Research Institute of Electric Power Industry

The current study proposes a novel framework for the numerical model for estimating the temporal scour considering unsteady sediment inflow and the sediment sorting process. The framework was applied to local scour upstream of a slit weir. The scour model is based on an ordinary nonlinear differential equation derived from sediment continuity and scour rate equations. A one-dimensional(1-D)Boussinesq-type model coupled with nonequilibrium sediment transport was incorporated in the scour model to consider unsteady sediment inflow. In addition, a mixing layer approach was incorporated to determine temporal variations in particle size in the scour hole. The proposed framework was validated using scour experiments conducted under conditions that include non-uniform sediment, live-bed scour,and unsteady flow rate. The simulation results showed satisfactory agreement with experimental results for the scour upstream of a slit weir. The proposed model appropriately explained the hysteresis process for flow unsteadiness, refilling process for live-bed scour, and armoring process for non-uniform sediments. In addition, the model framework proposed in the current study is applicable to local scour around other hydraulic structures(e.g., bridge piers) upon establishing the scour rate equation. Therefore, the current study provides a novel approach for modeling temporal scour that is required to consider unsteady sediment inflow and sediment sorting.

关键词： Local scour Temporal scour Mixing layer theory Slit weir Non-equilibrium bed load

Foreword for the special issue of the 7th China-Japan bilateral symposium on high temperature strength of materials

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Acta Metallurgica Sinica(English Letters) 2011年第2期24卷 I0001-I0002页

作者： Shan-Tung TU Yukio TAKAHASHI East China University of Science and Technology central research institute of electric power industry

The 7th China-Japan Bilateral Symposium on High Temperature Strength of Mate- rials was held at Dalian, China, during the period August 23-27, 2010. The symposium was co-organized by the High Temperature Strength and Materials Committee, the So- ciety of Materials, Chinese Mechanical Engineering Society and the Committee on High Temperature Strength of Materials, the Society of Materials Science Japan.

关键词： 7th China-Japan bilateral symposium on high temperature strength of materials lecture Japan friendship

A new model for evaluating the dynamic shear strength of rocks based on laboratory test data for earthquake-resistant design

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Journal of Rock Mechanics and Geotechnical Engineering 2019年第5期11卷 979-989页

作者： Tetsuji Okada Tomohiro Naya central research institute of electric power industry ChibaJapan Dia Consultants Co. Ltd.SaitamaJapan

The dynamic shear strength of rocks is required for the earthquake-resistant design of nuclear power plants in *** research aims to propose a mathematical model for estimating the dynamic strength and to validate the *** different types of specimens were prepared for the model validation,and the monotonic and cyclic loading tests were conducted to obtain the mathematical model ***,multistep cyclic loading tests were performed,followed by simulations using the mathematical *** test results demonstrated that the dynamic shear strength exceeded the static shear strength,which agreed with previous ***,the dynamic shear strength calculated using the mathematical model was generally consistent with that obtained from the experimental data.

关键词： Dynamic shear strength Static shear strength Cyclic loading Strain rate Fatigue Mathematical model

Analysis on EAST LHCD Operation Space by Using Simple Core-SOL-Divertor Model

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Plasma Science and Technology 2009年第4期11卷 389-393页

作者： R.HIWATARI A.HATAYAMA S.ZHU Y.TOMITA central research institute of electric power industry Faculty of Science and Technology Keio University institute of Plasma Physics Chinese Academy of Sciences National institute for Fusion Science

A simple core-SOL-divertor model （CSD model） was developed to investigate qual- itatively the overall features of the operational space for the integrated core and edge plasma. In the CSD model, the core plasma model of ITER physics guidelines and the two-point SOL-divertor model are applied, This CSD model is validated by the two dimensional divertor transport code （B2-EIRINE） and by the JT-60U divertor recycling database, and this model is applicable to the low- and high-recycling state of the divertor plasma. The CSD model is applied to the study of the EAST operational space with lower hybrid current drive under various kinds of trade-off for the basic plasma parameters, and the relationship between the operational space and the plasma discharge duration is also discussed.

关键词： core transport SOL-divertor transport operation space EAST LHCD

Nonlinear numerical simulation method for galloping of iced conductor

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Applied Mathematics and Mechanics(English Edition) 2009年第4期30卷 489-501页

作者：刘小会严波张宏雁周松 Department of Engineering Mechanics Chongqing University Sichuan electric power Test and research institute Sichuan electric power industry Commission and Test institute

Based on the principle of virtual work, an updated Lagrangian finite element formulation for the geometrical large deformation analysis of galloping of the iced conductor in an overhead transmission line is developed. In numerical simulation, a three-node isoparametric cable element with three translational and one torsional degrees-of-freedom at each node is used to discretize the transmission line. The nonlinear dynamic system equation is solved with the Newmark time integration method and the Newton-Raphson nonlinear iteration. Numerical examples demonstrate the efficiency of the presented method and the developed finite element program. A new possible galloping mode, which may reflect the saturation phenomenon of a nonlinear dynamic system, is discovered under the condition that the lowest order of vertical natural frequency of the transmission line is approximately two times of the horizontal one.

关键词： iced conductor galloping geometric nonlinearity numerical method