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Toshiya Takami

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Papers by Toshiya Takami

Numerical Approach for Aerodynamics around a tone hole with a moving pad: an example solving moving boundary problems with topological change

Proceedings of the ICA congress, 2019

In this paper, we discuss the numerical reproducibility of the compressible fluid behavior around... more In this paper, we discuss the numerical reproducibility of the compressible fluid behavior around a tone hole of woodwind instruments by using compressible Large Eddy Simulation (LES). In particular, we focus on the situation that the tone hole is opened and closed with moving a pad above the tone hole, which is regarded as a moving boundary problem with topology change. Our numerical model is based on a 2D analog of Keefe's experimental model, which has a tone hole placed at the center of the resonance tube. To reproduce the opening and closing the tone hole, the pad is moved continuously. Actually, the position of the pad was continuously changed in the order of "open -close -open". Our numerical results agree rather well with Keefe's experimental results. We solved the moving boundary problem with topology change under the situation of acoustics of fluidstructure interaction, and reproduced transitions between resonance and non-resonance states. In addition, the details of complex vortices near the tone holes clarified by this numerical calculation will be reported.

Anti-phase synchronization between the oscillation in the pipe and that in the foot of a flue organ pipe

Proceedings of the ICA congress, 2019

In the recent work (Acoust. Sci. & Tech. vol.40, No.1 pp.29-39 (2019)), we found with the numeric... more In the recent work (Acoust. Sci. & Tech. vol.40, No.1 pp.29-39 (2019)), we found with the numerical study of a 2D flue organ pipe model that the foot works as a Helmholtz resonator. When the frequency of acoustic oscillation in the pipe is higher than the resonance frequency of the Helmholtz resonator by almost the full-width at half-maximum, the most stable oscillation is observed, and the oscillation in the foot is anti-synchronized with that in the pipe. However, if the Helmholtz resonance frequency is nearly equal to the acoustic oscillation frequency, the oscillations in the pipe and foot become rather unstable and the oscillation in the foot lags behind that in the pipe by nearly π/2. In this paper, we study the phase relations among the pressure oscillation in the foot, that in the pipe, and the hydrodynamic oscillation of the jet, which are the key to understanding the mechanism of stabilizing and destabilizing oscillations of the flue organ pipe.

A Study of Data Augmentation for Handwritten Character Recognition using Deep Learning

2018 16th International Conference on Frontiers in Handwriting Recognition (ICFHR), 2018

Building normal ECG models to detect any arrhythmias using deep learning

2020 Computing in Cardiology Conference (CinC), 2020

In the studies of arrhythmias detection using deep learning, most methods train neural networks t... more In the studies of arrhythmias detection using deep learning, most methods train neural networks to categorize input ECGs to major arrhythmias using annotated training ECG data. Such methods can neither detect unknown arrhythmias nor explain why they are considered as arrhythmias. To detect any arrhythmias automatically, this study proposes a method that does not use annotated training data and can explain the reason for its judgment clearly. Methods: Our method builds a model of normal ECGs using CNN (Convolutional Neural Network) and LSTM (Long Short-Term Memory), which are the types of deep learning. The model inputs normal ECGs and trains to predict the succeeding normal ECGs. If an abnormal ECG is given, our model predicts the succeeding ECG far from the actual one and can judge that the input is abnormal. This means that our method can judge any arrhythmias because it uses no prior knowledge about the annotations. Results: To build the model, we used the parts of the normal ECGs in the MIT-BIH arrhythmia database as the training data. Using the other ECGs in the database as the test data, we evaluated our method with ROC curve where the average AUC score was 0.93. As shown in Figure , we also developed GUI for showing in which parts the predicted ECG does not fit the actual one. We show that the proposed method can generate the normal ECG model without training annotated ECG training data and can identify any abnormal ECGs that do not fit the normal ones. In the future, we will investigate the possibility of the ECG analysis in a long period by adjusting the input size and of the classification of arrhythmias by clustering of the output results.

Analysis of the Collective Behavior of Boids

Springer Proceedings in Physics, 2020

Collective behavior of social organisms emerges by simple interactions between individuals, and t... more Collective behavior of social organisms emerges by simple interactions between individuals, and the behavior is often found to be chaotic. Automatic classification of such chaotic motion is, in general, difficult because of a large number of degrees of freedom and the stochastic motion of individuals. First, principal component analysis is applied to the instantaneous variables of motion in order to obtain a low dimensional representation of dynamic states and to try to achieve automatic classification. Second, the complex motion of boids is analyzed by dynamic mode decomposition, by which a time-series of dynamical variables is approximated as a linear time-stepping operator. It is shown that the reconstruction error by the linearized operator relates to the transition of complex behavior. Finally, a simple method based on the error analysis is proposed to detect itinerant motion (of the collective behavior).

Numerical analysis on 2D and 3D edge tones in terms of aerodynamic sound theory

Edge tone is numerically reproduced by compressible LES for 2D and 3D models. To detect the aerod... more Edge tone is numerically reproduced by compressible LES for 2D and 3D models. To detect the aerodynamic sound source, Lighthill’s sound source as well as Howe’s vortex sound source are calculated. We find a marked difference in distribution between the two types of sources originating from the difference in formula: Howe’s vortex sound theory is framed based on the concept that the total enthalpy instead of pressure or air density is true sound, so that the source generating fluctuation of the total enthalpy is different from that generating acoustic pressure. We also calculate mutual correlations among acoustic pressure and the two types of sound sources, i.e., Lighthill’s and Howe’s sources, so as to examine details of interaction among them.

Numerical Analysis on the Lighthill Sound Sources of Oscillating Jet

We numerically have been studying the generation of sound pressure and pseudo-sound pressure from... more We numerically have been studying the generation of sound pressure and pseudo-sound pressure from the oscillating jet based on the Lighthill acoustic analogy[1]. In recent works, it has been found using Howe’s energy corollary that jet oscillations make some amount of acoustic energy, which becomes the sound sources of edge tone and flue instruments[2-5]. However, Howe’s energy corollary is the indirect way for the estimation of aerodynamic sound energy[2]. In order to estimate directly the aerodynamic sound generation, we investigate the role of the Lighthill sound sources of edge tone. The Lighthill sources generate not only acoustic oscillations propagating to a far field but also pseudo-sound pressure (or fluid pressure) in a near field[6]. Thus, we will discuss with numerical simulations how many parts of the energy made by the Lighthill sources are transferred to that of the pseudo-sound pressure and how the small remainder contributes to the generation of the true acoustic os...

Role of the foot chamber in the sounding mechanism of a flue organ pipe

Acoustical Science and Technology, 2019

Two-demensional (2D) models of a flue organ pipe are studied with compressible fluid simulation, ... more Two-demensional (2D) models of a flue organ pipe are studied with compressible fluid simulation, specifically compressible Large Eddy Simulation, focusing on the influence of the geometry of the flue and the foot on the jet motion and acoustic oscillation in the pipe. When the foot geometry is fixed, the models having a flue with chamfers show good performances in stabilizing the acoustic oscillation in the steady state. Furthermore, we find that the foot chamber works as a Helmholtz resonator. If the frequency of the acoustic oscillation in the pipe is higher than the resonance frequency of the Helmholtz resonator by almost the full-width at half-maximum, anti-phase synchronization between the acoustic oscillation in the pipe and that in the foot chamber occurs. In this case, the acoustic oscillation in the pipe grows rapidly in the attack transient and is stabilized in the steady state.

Theoretical Estimation of the Acoustic Energy Generation and Absorption Caused by Jet Oscillation

Journal of the Physical Society of Japan, 2016

We investigate the energy transfer between the fluid field and acoustic field caused by a jet dri... more We investigate the energy transfer between the fluid field and acoustic field caused by a jet driven by an acoustic particle velocity field across it, which is the key to understanding the aerodynamic sound generation of flue instruments, such as the recorder, flute, and organ pipe. Howe's energy corollary allows us to estimate the energy transfer between these two fields. For simplicity, we consider the situation such that a free jet is driven by a uniform acoustic particle velocity field across it. We improve the semi-empirical model of the oscillating jet, i.e., exponentially growing jet model, which has been studied in the field of musical acoustics, and introduce a polynomially growing jet model so as to apply Howe's formula to it. It is found that the relative phase between the acoustic oscillation and jet oscillation, which changes with the distance from the flue exit, determines the quantity of the energy transfer between the two fields. The acoustic energy is mainly generated in the downstream area, but it is consumed in the upstream area near the flue exit in driving the jet. This theoretical examination well explains the numerical calculation of Howe's formula for the two-dimensional flue instrument model in our previous work [ Fluid Dyn. Res. 46, 061411 (2014) ] as well as the experimental result of Yoshikawa et al. [ J. Sound Vib. 331, 2558 (2012) ].

Analytic Approach for Controlling Realistic Quantum Chaotic Systems

AIP Conference Proceedings, 2007

An analytic approach for controlling quantum states, which was originally applied to fully random... more An analytic approach for controlling quantum states, which was originally applied to fully random matrix systems [T. Takami and H. Fujisaki, Phys. Rev. E 75, 036219 (2007)], is extended to deal with more realistic quantum systems with a banded random matrix (BRM). The validity of the new analytic field is confirmed by directly solving the Schrödinger equation with a BRM interaction. We find a threshold of the width of the BRM for the quantum control to be successful.

Multi-physics Extension of OpenFMO Framework

AIP Conference Proceedings, 2007

OpenFMO framework, an open-source software (OSS) platform for Fragment Molecular Orbital (FMO) me... more OpenFMO framework, an open-source software (OSS) platform for Fragment Molecular Orbital (FMO) method, is extended to multi-physics simulations (MPS). After reviewing the several FMO implementations on distributed computer environments, the subsequent development planning corresponding to MPS is presented. It is discussed which should be selected as a scientific software, lightweight and reconfigurable form or large and self-contained form.

Coarse-Grained Picture for Controlling Quantum Chaos

Advances in Chemical Physics, 2005

We propose a coarse-grained picture to analyze control problems for quantum chaos systems. Using ... more We propose a coarse-grained picture to analyze control problems for quantum chaos systems. Using optimal control theory, we first show that almost perfect control is achieved for random matrix systems and a quantum kicked rotor. Second, under the assumption that the controlled dynamics is well described by a Rabi-type oscillaion between unperturbed states, we derive an analytic expression for the optimal field. Finally we numerically confirm that the analytic field can steer an initial state to a target state in random matrix systems.

Open-architecture Implementation of Fragment Molecular Orbital Method for Peta-scale Computing

We present our perspective and goals on highperformance computing for nanoscience in accordance w... more We present our perspective and goals on highperformance computing for nanoscience in accordance with the global trend toward "peta-scale computing." After reviewing our results obtained through the grid-enabled version of the fragment molecular orbital method (FMO) on the grid testbed by the Japanese Grid Project, National Research Grid Initiative (NAREGI), we show that FMO is one of the best candidates for peta-scale applications by predicting its effective performance in peta-scale computers. Finally, we introduce our new project constructing a peta-scale application in an open-architecture implementation of FMO in order to realize both goals of highperformance in peta-scale computers and extendibility to multiphysics simulations.

Sound Generation by a Turbulent Flow in Musical Instruments - Multiphysics Simulation Approach

Total computational costs of scientific simulations are analyzed between direct numerical simulat... more Total computational costs of scientific simulations are analyzed between direct numerical simulations (DNS) and multiphysics simulations (MPS) for sound generation in musical instruments. In order to produce acoustic sound by a turbulent flow in a simple recorder-like instrument, compressible fluid dynamic calculations with a low Mach number are required around the edges and the resonator of the instrument in DNS, while incompressible fluid dynamic calculations coupled with dynamics of sound propagation based on the Lighthill's acoustic analogy are used in MPS. These strategies are evaluated not only from the viewpoint of computational performances but also from the theoretical points of view as tools for scientific simulations of complicated systems.

Parareal Acceleration of Matrix Multiplication

The parareal-in-time algorithm has been used in time-domain parallelism of scientific problems de... more The parareal-in-time algorithm has been used in time-domain parallelism of scientific problems described by ordinary differential equations and partial differential equation. In this paper, applicability of this algorithm to a simple linear transformation is studied through convergence and speedup ratio. In particular, the convergence of the procedure is analyzed for calculations of series of vectors defined by matrix multiplications. The actual speedup ratio is measured in a distributed parallel machine and compared to theoretical prediction. Finally, appropriate problem sizes for this scheme is presented based on these results.

Performance Tuning of Parallel Fragment Molecular OrbitalProgram (OpenFMO) for Effective Execution on K-computer

Journal of Computer Chemistry, Japan, 2013

3D Calculation with Compressible LES for Sound Vibration of Ocarina

Sounding mechanism is numerically analyzed to elucidate physical processes in air-reed instrument... more Sounding mechanism is numerically analyzed to elucidate physical processes in air-reed instruments. As an example, compressible large-eddy simulations (LES) are performed on both two and three dimensional ocarina. Since, among various acoustic instruments, ocarina is known as a combined system consisting of an edge-tone and a Helmholtz resonator, our analysis is mainly devoted to the resonant dynamics in the cavity.

Quantum Classical Correspondence in Nonintegrable Systems with Continuous Parameter

Progress of Theoretical Physics Supplement, 1994

ABSTRACT We study quantum classical correspondence in nonintegrable systems with a continuous par... more ABSTRACT We study quantum classical correspondence in nonintegrable systems with a continuous parameter. In a stadium billiard with an aspect ratio as a parameter, we show that the slope of the parametric motion of eigenvalues is mainly due to the first derivative of periodic orbit length with respect to the parameter. We also present a viewpoint for scarred wavefunctions in a continuous change of the systems.

Semiclassical interpretation of avoided crossings for classically nonintegrable systems

Physical Review Letters, 1992

We study an origin of avoided crossings for classically nonintegrable systems. Using a diabatic t... more We study an origin of avoided crossings for classically nonintegrable systems. Using a diabatic trans- formation, we show that characteristic features of "scars" continuously change along diabatic lines. Moreover, through Fourier transformation of an energy level density, we suggest that avoided crossings in fully chaotic systems originate from the long periodic orbits winding around scars.

Analytic approach for controlling quantum states in complex systems

Physical Review E, 2007

We examine random matrix systems driven by an external field in view of optimal control theory (O... more We examine random matrix systems driven by an external field in view of optimal control theory (OCT). By numerically solving OCT equations, we can show that there exists a smooth transition between two states called "moving bases" which are dynamically related to initial and final states. In our previous work [J. Phys. Soc. Jpn. 73 (2004) 3215-3216; Adv. Chem. Phys. 130A (2005) 435-458], they were assumed to be orthogonal, but in this paper, we introduce orthogonal moving bases. We can construct a Rabi-oscillation like representation of a wavpacket using such moving bases, and derive an analytic optimal field as a solution of the OCT equations. We also numerically show that the newly obtained optimal field outperforms the previous one.