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Seismic pounding and collapse behavior of neighboring buildings with different natural periods

Natural Science 2012年第8期4卷 686-693页

作者： Daigoro Isobe tokiharu ohta Tomohiro Inoue Fujio Matsueda Collaborative Research Center Ashikaga Institute of Technology Ashikaga-shi Japan Division of Engineering Mechanics and Energy University of Tsukuba Tsukuba-shi Japan Kyoryo Consultants Ltd. Tokyo Japan Science Programs Division Japan Broadcasting Corporation Tokyo Japan

Seismic pounding phenomena, particularly the collision of neighboring buildings under long-period ground motion, are becoming a significant issue in Japan. We focused on a specific apartment structure called the Nuevo Leon buildings in the Tlatelolco district of Mexico City, which consisted of three similar buildings built consecutively with narrow expansion joints between the buildings. Two out of the three buildings collapsed completely in the 1985 Mexican earthquake. Using a finite element code based on the adaptively shifted integration (ASI)-Gauss technique, a seismic pounding analysis is performed on a simulated model of the Nuevo Leon buildings to understand the impact and collapse behavior of structures built near each other. The numerical code used in the analysis provides a higher computational efficiency than the conventional code for this type of problem and enables us to address dynamic behavior with strong nonlinearities, including phenomena such as member fracture and elemental contact. Contact release and recontact algorithms are developed and implemented in the code to understand the complex behaviors of structural members during seismic pounding and the collapse sequence. According to the numerical results, the collision of the buildings may be a result of the difference of natural periods between the neighboring buildings. This difference was detected in similar buildings from the damages caused by previous earthquakes. By setting the natural period of the north building to be 25% longer than the other periods, the ground motion, which hada relatively long period of 2 s, first caused the collision between the north and the center buildings. This collision eventually led to the collapse of the centerbuilding, followed by the destruction of the north building.

关键词： Seismic Pounding Collapse Behavior Neighboring Buildings Natural Period Asi-Gauss Technique

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The deterministic condition for the ground reaction force acting point on the combined knee valgus and tibial internal rotation moments in early phase of cutting maneuvers in female athletes

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Journal of Sport and Health Science 2024年第3期13卷 376-386页

作者： Issei Ogasawara Ken ohta Gajanan S.Revankar Shoji Konda Yohei Shimokochi Hideyuki Koga Ken Nakata Department of Health and Sport Sciences Graduate School of MedicineOsaka UniversityToyonaka 560-0043Japan Sports Sensing Co. LTD.Fukuoka 815-0035Japan Department of Neurology Graduate School of MedicineOsaka UniversitySuita 565-0871Japan Department of Health and Sport Management Osaka University of Health and Sport SciencesSennan-gun 590-0496Japan Department of Joint Surgery and Sports Medicine Graduate School of Medical and Dental SciencesTokyo Medical and Dental UniversityBunkyo-ku 113-8519Japan

Background:Combined knee valgus and tibial internal rotation(VL+IR)moments have been shown to stress the anterior cruciate ligament(ACL)in several in vitro cadaveric *** utilize this knowledge for non-contact ACL injury prevention in sports,it is necessary to elucidate how the ground reaction force(GRF)acting point(center of pressure(CoP))in the stance foot produces combined knee VL+IR moments in risky maneuvers,such as ***,the effects of the GRF acting point on the development of the combined knee VL+IR moment in cutting are still ***:We first established the deterministic mechanical condition that the CoP position relative to the tibial rotational axis differentiates the GRF vector’s directional probability for developing the combined knee VL+IR moment,and theoretically predicted that when the CoP is posterior to the tibial rotational axis,the GRF vector is more likely to produce the combined knee VL+IR moment than when the CoP is anterior to the tibial rotational ***,we tested a stochastic aspect of our theory in a lab-controlled in vivo *** females performed 60˚cutting under forefoot/rearfoot strike conditions(10 trials each).The positions of lower limb markers and GRF data were measured,and the knee moment due to GRF vector was *** trials were divided into anterior-and posterior-CoP groups depending on the CoP position relative to the tibial rotational axis at each 10 ms interval from 0 to 100 ms after foot strike,and the occurrence rate of the combined knee VL+IR moment was compared between trial ***:The posterior-CoP group showed significantly higher occurrence rates of the combined knee VL+IR moment(maximum of 82.8%)at every time point than those of the anterior-CoP trials,as theoretically predicted by the deterministic mechanical ***:The rearfoot strikes inducing the posterior CoP should be avoided to reduce the risk of non-contact ACL injury associated with the com

关键词： Center of pressure Deterministic condition Foot strike pattern Injury mechanism Moment of ground reaction force

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An Improved Coupled Level Set and Continuous Moment-of-Fluid Method for Simulating Multiphase Flows with Phase Change

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Communications on Applied Mathematics and Computation 2024年第2期6卷 1034-1069页

作者： Zhouteng Ye Cody Estebe Yang Liu Mehdi Vahab Zeyu Huang Mark Sussman Alireza Moradikazerouni Kourosh Shoele Yongsheng Lian Mitsuhiro ohta M.Yousuff Hussaini ZJUI Institute Zhejiang UniversityHaining 314400ZhejiangChina Department of Mathematics Florida State UniversityTallahasseeUSA Department of Mechanical Engineering Florida State UniversityTallahasseeUSA Mechanical and Aerospace Engineering Mathworks NatickMAUSA School of Aerospace Engineering Tsinghua UniversityBeijing 100084China Department of Mechanical Engineering University of LouisvilleLouisvilleUSA Department of Mechanical Science Tokushima UniversityTokushimaJapan

An improved algorithm for computing multiphase flows is presented in which the multimaterial Moment-of-Fluid(MOF)algorithm for multiphase flows,initially described by Li et al.(2015),is enhanced addressing existing MOF difficulties in computing solutions to problems in which surface tension forces are crucial for understanding salient flow *** Continuous MOF(CMOF)method is motivated in this *** CMOF reconstruction method inherently removes the"checkerboard instability"that persists when using the MOF method on surface tension driven multiphase(multimaterial)*** CMOF reconstruction algorithm is accelerated by coupling the CMOF method to the level set method and coupling the CMOF method to a decision tree machine learning(ML)*** flow examples are shown in the two-dimensional(2D),three-dimensional(3D)axisymmetric"RZ",and 3D coordinate *** include two material and three material multiphase flows:bubble formation,the impingement of a liquid jet on a gas bubble in a cryogenic fuel tank,freezing,and liquid lens dynamics.

关键词： Moment-of-Fluid(MOF) Surface tension Two phase flow Phase change Deforming boundaries with change(s)in topology Two-dimensional(2D) Three-dimensional(3D)axisymmetric 3D

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Behavior of Vaneless Diffuser Stall in a Centrifugal Compressor

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Journal of Thermal Science 2022年第1期31卷 3-12页

作者： AGARI Yuki YAMAO Yoshifumi FUJISAWA Nobumichi ohta Yutaka Department of Applied Mechanics and Aerospace Engineering Waseda UniversityTokyo 169-8555Japan

The rotating stall in a centrifugal compressor with a vaneless diffuser was investigated both experimentally and numerically with focus on the effect of the internal flow field within the impeller on the diffuser *** numerical analysis,the boundary layer separation at the impeller outlet was found to play an important role in the expansion and rotation processes of the diffuser *** particular,the expanded boundary layer separation near the hub side at the outlet of the main blade(M.B.)suction surface passage was considered to be the main cause of the expansion and rotation processes.A longitudinal vortex existed at the throat of the ***,and the mass flow rate in the *** was significantly reduced by the blockage *** addition,the longitudinal vortex induced the rolling up flow near the hub side at the impeller ***,the boundary layer separation expanded.

关键词： centrifugal compressor vaneless diffuser pressure and velocity measurement CFD rotating stall

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Unsteady Behavior and Control of Vortices in Centrifugal Compressor

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Journal of Thermal Science 2014年第5期23卷 401-411页

作者： Yutaka ohta Nobumichi Fujisawa Department of Applied Mechanics and Aerospace Engineering Waseda University3-4-1OkuboShinjukuTokyo169-8555Japan Graduate School of Fundamental Science and Engineering Waseda University3-4-1OkuboShinjukuTokyo169-8555Japan

Two examples of the use of vortex control to reduce noise and enhance the stable operating range of a centrifugal compressor are presented in this *** the case of high-flow operation of a centrifugal compressor with a vaned diffuser,a discrete frequency noise induced by interaction between the impeller-discharge flow and the diffuser vane,which appears most notably in the power spectra of the radiated noise,can be reduced using a tapered diffuser vane(TDV) without affecting the performance of the *** longitudinal vortices produced by leakage flow passing through the tapered portion of the diffuser vane induce secondary flow in the direction of the blade surface and prevent flow separation from the leading edge of the *** use of a TDV can effectively reduce both the discrete frequency noise generated by the interaction between the impeller-discharge flow and the diffuser surface and the broadband turbulent noise *** the case of low-flow operation,a leading-edge vortex(LEV) that forms on the shroud side of the suction surface near the leading edge of the diffuser increases significantly in size and blocks flow in the diffuser *** formation of an LEV may adversely affect the performance of the compressor and may cause the diffuser to *** a one-side tapered diffuser vane to suppress the evolution of an LEV,the stable operating range of the compressor can be increased by more than 12 percent,and the pressure-rise characteristics of the compressor can be *** results of a supplementary examination of the structure and unsteady behavior of LEVs,conducted by means of detailed numerical simulations,are also presented.

关键词：压缩机控制不稳定离心式行为涡流叶片表面扩散器离散频率

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Coexisting State of Surge and Rotating Stall in a Two-Stage Axial Flow Com-pressor using a Double-Phase-Locked Averaging Technique

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Journal of Thermal Science 2017年第1期26卷 38-46页

作者： Yuu SAKATA Yutaka ohta Graduate school of Fundamental Science and Engineering Waseda University 3-4-10kuboShinjuku Tokyo 169-8555 Japan. Department of Applied Mechanics and Aerospace Engineering Waseda University 3-4-10kubo Shinjuku Tokyo169-8555 Japan.

The interaction between surge and rotating stall in an axial flow compressor was investigated from the viewpoint of an unsteady inner flow structure. The aim of this study was to identify the key factor that determines the switching phenomenon of a surge cycle. The main feature of the tested compressor is a shock tube connected in series to the compressor outlet through a diaphragm, slits, and a concentric duplex pipe: this system allows surge and rotating stall to be generated by connecting the shock tube with the compressor, or enables the compression plane wave injection. The unsteady characteristics and the internal flow velocity fluctuations were measured in detail, and the stall cell structure was averaged and visualized along the movement of the operation point under a coexisting state of surge. A coefficient of the cell scale fluctuation was calculated using the result of the averaging, and it confirmed that the processes of inner flow structure change differed from each other according to the next cycle of the surge. The result suggests that the key factor that determines the next cycle is the transformation of the internal flow structure, particularly between the stall cell and the entire circumferential stall, in both the recovering and stalling processes.

关键词： Axial flow compressor, Rotating stall, Surge, Double-phase-locked measurement, Compression wave.

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Review: Prediction of Unexpected Fluid-Induced Vibration in Pipeline Network

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World Journal of Mechanics 2022年第2期12卷 17-40页

作者： Ryuhei Yamaguchi Makoto ohta Institute of Fluid Science Tohoku University Sendai Japan

This review considers unexpected destructive disasters involving fluid power plants, such as nuclear electric power plants and fluid power plants. It specifically addresses the possibility of fluid vibration induced in a pipeline network of such a plant. The authors investigate the flow oscillation induced within a T-junction for laminar steady flow at a Reynolds number less than 103 and clarify that there is a periodic fluid oscillation with a constant Strouhal number independent of several flow conditions. Generally, a nuclear electric power plant is constructed using straight pipes, elbows, and T-junctions. Indeed, a T-Junction is a basic fluid element of a pipeline network. The flow in a fluid power plant is turbulent. There are peculiar flow phenomena that occur at high Reynolds numbers, which are also seen in other flow situations;e.g., Kaman vortices are observed around a circular cylinder in low Reynolds numbers, around structures like bridges and downstream of islands in oceans. Although the flow situation of a T-junction and elbow in a fluid power plant, such as the fluid suddenly changing its flow direction is turbulent flow, the authors mention the possibility of the fluid-induced vibration of a pipeline network.

关键词： Fluid-Induced Vibration Flow Oscillation Tube Flow Laminar Steady Flow Fluid Power Plant

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The thermal conductivity of the Earth's core and implications for its thermal and compositional evolution

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National Science Review 2021年第4期8卷 18-20页

作者： Kenji ohta Kei Hirose Department of Earth and Planetary Sciences Tokyo Institute of Technology Earth-Life Science Institute Tokyo Institute of Technology Department of Earth and Planetary Science The University of Tokyo

The thermal conductivity of iron alloys is a key to understanding the mechanism of convection in the Earth’s liquid core and its thermal history. The Earth’s magnetic field is formed by a dynamo action that requires... 详细信息

关键词： ELECTRICAL-RESISTIVITY HIGH-PRESSURE IRON ALLOYS SI NI

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Unsteady Behavior of Leading-edge Vortex and Diffuser Stall in a Centrifugal Compressor with Vaned Diffuser

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Journal of Thermal Science 2016年第1期25卷 13-21页

作者： Nobumichi FUJISAWA Shotaro HARA Yutaka ohta Graduate Student Graduate School of Fundamental Science and EngineeringWaseda University 3-4-10kuboShinjukuTokyo 169-8555Japan Department of Applied Mechanics and Aerospace Engineering Waseda University 3-4-1 OkuboShinjukuTokyo 169-8555Japan

The characteristics of a rotating stall of an impeller and diffuser and the evolution of a vortex generated at the diffuser leading-edge(i.e., the leading-edge vortex(LEV)) in a centrifugal compressor were investigated by experiments and numerical analysis. The results of the experiments revealed that both the impeller and diffuser rotating stalls occurred at 55 and 25 Hz during off-design flow operation. For both, stall cells existed only on the shroud side of the flow passages, which is very close to the source location of the LEV. According to the CFD results, the LEV is made up of multiple vortices. The LEV is a combination of a separated vortex near the leading-edge and a longitudinal vortex generated by the extended tip-leakage flow from the impeller. Therefore, the LEV is generated by the accumulation of vorticity caused by the velocity gradient of the impeller discharge flow. In partial-flow operation, the spanwise extent and the position of the LEV origin are temporarily transmuted. The LEV develops with a drop in the velocity in the diffuser passage and forms a significant blockage within the diffuser passage. Therefore, the LEV may be regarded as being one of the causes of a diffuser stall in a centrifugal compressor.

关键词：叶片扩压器离心压缩机失速特性前缘涡扩散器稳态行为数值分析方法离心式压缩机

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Coexisting Phenomena of Surge and Rotating Stall in an Axial Flow Compressor

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Journal of Thermal Science 2013年第6期22卷 547-554页

作者： Takuya ABE Hiroaki MITSUI Yutaka ohta Graduate Student Graduate School of Science and EngineeringWaseda University Department of Applied Mechanics and Aerospace Engineering Waseda University

The unsteady inner flow structure of a single-stage axial flow compressor under the coexisting conditions of surge and rotating stall was experimentally investigated via detailed measurements of the unsteady characteristics and the internal flow velocity fluctuations. The main relevant feature of the tested compressor is a shock tube with a capacity tank connected in series to the compressor outlet through slits and a concentric duplex pipe: surge and rotating stall can both be generated by connecting the shock tube. Research attention is focused on the unsteady behavior of a rotating stall during the surge cycle. The size of the rotating stall cell during the recovery process of an irregular surge cycle was experimentally determined by the circumferential flow velocity fluctuations ahead of the rotor blade. The results suggested that the size of the rotating stall cell at the switching point of the performance curve between large and small cycles is considered to be the key parameter in determining the following surge cycle. In addition, the surge cycle is largely influenced by the unsteady behavior of the rotating stall cell.

关键词：旋转失速轴流压气机浪涌非定常特性共存相关特征转子叶片恢复过程

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