著者

鯰江 一也 栗田 裕 松村 雄一

出版者

一般社団法人 日本機械学会

雑誌

Dynamics & Design Conference 2006 (ISSN:24242993)

巻号頁・発行日

pp._164-1_-_164-6_, 2006-08-06 (Released:2017-06-19)

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This paper describes a transitional wave phenomenon in synchronous flashing of fireflies. We used self-excited oscillator, consists of amplification element, saturation element and phase delay element. To simulate a transitional wave phenomenon, the self-excited oscillator simulated the firefly shouldn't be late from the detection of the flashing of other self-excited oscillator. The period of self-excited oscillator in the transient state depends on strength of own flashing and changes. Strengthening strength of own flashing, perceived the flashing of other self-excited oscillators, the timing of flashing shifts and withdraws by correcting it at a constant period. This is a transitional wave phenomenon.

著者

中井 幹雄 川口 和也

出版者

一般社団法人 日本機械学会

雑誌

Dynamics & Design Conference 2006 (ISSN:24242993)

巻号頁・発行日

pp._109-1_-_109-6_, 2006-08-06 (Released:2017-06-19)

被引用文献数

1 1

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ピアノ弦のような曲げ剛性をもつ弦の振動における倍音周波数より高い周波数の系列であるInharmonicityの第1系列と異なる第2の系列について述べる. Inharmonicityの第1系列における第n次の周波数計算では, f_n=nf_0√<1+Bn^2>が一般的に用いられている.ここで, f_0は弦の曲げ剛性を考慮しない場合の固有振動数である.また, Bは非調和度と呼ばれる無次元量である.第1系列と異なる第2の系列では,その非調和度は第1系列の1/4の値となることが経験的にわかっている.打弦および撥弦時のInharmonicityの第2系列の発生機構について実験を行った.周波数スペクトルから各次数のピーク周波数を読み取り,その次数の倍音周波数との差を固有振動数で除し,無次元化した値を各次数について計算する.それらの結果とともに第1系列の周波数値を用いて,和および差の周波数を表す格子線を図A1に示す.実線,点線は第1,2系列を示す.図において,微小なピークはほぼ格子点に一致し,第1系列周波数の和および差の周波数をもつことが明らかとなった.また,この格子線は包絡線をもっており,包絡線周辺は格子点の間隔が狭くなり,数多くのピークが集中することが明らかとなった.この包絡線が,理論的に正確に第1系列の非調和度の1/4の値をもつ曲線となっていることがわかり,第2系列を含むすべての微小なピークの周波数特性が明らかとなった.これらの微小なピークは,弦が大変形するという幾何学的非線形性が原因となって発生すると考えられるので,弦の横振動および縦振動を考慮した次式のような非線形方程式を用いて第2系列について検討した. ρA(∂^2u)/(∂t^2)=EA(∂^2u)/(∂x^2)-(T_0-EA)(∂^2w)/(∂x^2)(∂w)/(∂x) (A1) ρA(∂^2w)/(∂t^2)=T_0(∂^2w)/(∂x^2)-EI(∂^42)/(∂x^4)-C_D(∂w)/(∂t)-(T_0-EA){(∂^2w)/(∂x^2) (∂u)/(∂x)+(∂w)/(∂x) (∂^2u)/(∂x^2)+3/2((∂w)/(∂x))^2(∂^2w)/(∂x^2)} (A2) 図A2(a), (b)は数値計算した横振動と縦振動の変位の周波数分析結果を示す.この図で黒丸が第1系列,白丸が第2系列を示している.この図から,8次モードから第2系列が生じ始めることおよび縦振動のピークと第2系列がほぼ一致していることがわかる.このことは式(A1)におけるwの2次の非線形項が横振動の2つの周波数の和あるいは差をもつ外力として縦振動に作用するとみなすことができることからわかる.さらに,横振動の周波数分析結果に和および差の周波数をもつピークが主に現れることがわかった.しかし,横振動には主に任意の2つの第1系列周波数の和・差の組み合わせ周波数からなる第2系列を含む微小なピークのほかのピークも含まれている.したがって,さらに,横振動については,方程式を検討する必要がある.

著者

金子 淳一 細矢 直基 古屋 耕平

出版者

一般社団法人 日本機械学会

雑誌

Dynamics & Design Conference 2010 (ISSN:24242993)

巻号頁・発行日

pp._111-1_-_111-6_, 2010-09-14 (Released:2017-06-19)

被引用文献数

2 3

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This paper discuses the way to reduce the noise and vibration of thin plate structures. This paper focuses on the musical saw, a kind of musical instrument. The musical saw is thin plate and it is need to bend the saw as S-curve, to play the instrument. Thin plate structures used for various products. In some case, curvature is laid on thin plate structures to enhance the rigidity. If musical saw and thin plate structures conditions are matched, it will be noise problem. Investigating that the relationship between the sound pressure, S-curve, boundary condition, and aspect ratio of the saw by experiment and FEA, it is discussed to apply the investigation result to the thin plate structures.

著者

裘 進浩 原口 正和 吉田 誠 谷 順二

出版者

一般社団法人 日本機械学会

雑誌

Dynamics & Design Conference 2003 (ISSN:24242993)

巻号頁・発行日

pp._604-1_-_604-6_, 2003-09-16 (Released:2017-06-19)

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This paper describes a study of active noise isolation using an advanced composite board with embedded piezoelectric elements, which are used as both sensors and actuators. The identification system, which estimates the radiated sound from the voltage signals of the piezoelectric elements in the smart board, was constructed based on Rayleigh's integral formula so that no external microphone is needed for noise control. Since the control system was implemented to minimize the estimated value of noise by suppressing the vibration of the smart board, it can reduce the sound transmission through the board. The technique of self-sensing actuator was also used to reduce the number of piezoelectric need for the control. Experiments were performed and the results showed that the transmitted noise level was successfully reduced at several resonant peaks.

著者

滝田 好宏 樫谷 賢士

出版者

一般社団法人 日本機械学会

雑誌

Dynamics & Design Conference 2016 (ISSN:24242993)

巻号頁・発行日

pp.431, 2016 (Released:2017-06-19)

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This paper investigates a VTOL UAV with tailless wing configuration. In the previous our work for multi-rotor UAV, a trirotor geometry with four rotors was built and experimented flight in the laboratory. VTOL type UAV enables the flight without take-off and landing spaces. So, there many researches for VTOL type UAVs, but the effective configuration of wing and electric propulsion unit is not discovered. This paper proposes a tailless wing configuration combined with the trirotor geometry for VTOL UAV. The Tailless wing airplane has advantage of low friction force, simple structure and lighter than the normal airplane with same wing area. The disadvantage of tailless wing type is that low stability in pitch and yaw motions. In order to overcome these problems, a stable airfoil with low moment coefficient is used and designed the configuration the wing. The experimental model of tailless wing for VTOL UAV is built and experimented flight in the field. Experimental results show the maneuver of designed tailless wing UAV.

著者

谷田 涼 内野 敬太 松村 雄一

出版者

一般社団法人 日本機械学会

雑誌

Dynamics & Design Conference 2010 (ISSN:24242993)

巻号頁・発行日

pp._740-1_-_740-6_, 2010-09-14 (Released:2017-06-19)

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This paper clarified the excitation mechanism of picking the strings of a guitar. The picking excites forced vibration and free vibration of the strings by giving the strings impact force, friction force and initial condition. At first, separate influence of these force and initial condition was experimentally examined. Then, generation mechanism of transient responses of the strings was examined for ordinary picking technique, by the viewpoint of the influence of impact force, friction force and initial condition.

著者

岡村 宏 大石 久己 土屋 賢康 長谷川 浩志

出版者

一般社団法人 日本機械学会

雑誌

Dynamics & Design Conference 2016 (ISSN:24242993)

巻号頁・発行日

pp.339, 2016 (Released:2017-06-19)

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We report the result of test that has given the acoustic excitation to the new guitar in the aging cell with using the Bach's cello suites. The sound quality effect of playing the guitar for five years is the same as one of the four weeks aging test with the high load. However, the too much aging gives the new guitar the adverse effects. In this time, we were able to have the good balance results with the light load aging. But there were few effects in the upper position sounds of the guitar. The sound range of the cello is not enough to the acoustic excitation of high frequency zone. So, we will try soon the aging test with playing the violin pieces.

著者

北林 研人 石原 匡 鞍谷 文保 吉田 達哉 小出 俊雄 水田 泰次 長村 光造

出版者

一般社団法人 日本機械学会

雑誌

Dynamics & Design Conference 2016 (ISSN:24242993)

巻号頁・発行日

pp.340, 2016 (Released:2017-06-19)

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Cymbals are thin domed plates used as percussion instruments. When cymbals are stuck, they vibrate and radiate sound. Cymbals are made through spin forming, hammering, and lathing. The sound radiated from a cymbal depends on its vibration characteristics that are determined by the shape and dimension. The hammering produces plastic deformation on the cymbal's surface, generating residual stresses throughout it. Although the vibration characteristics are changed by the hammering to adjust cymbal sound, the effect of the hammering on the cymbal sound is not clear. In this paper, we reveal the effect of the hammering on the vibration and the sound radiation characteristics. The stress distribution within the cymbal produced by hammering is reproduced by thermal stress analysis and the change in natural frequency of the modes are calculated by the vibration analysis with the stress distribution. The change (i.e., increase or decrease) in natural frequency for each mode is explained by the stress and modal strain energy distributions.

著者

金沢 純一 田中 幸和 小澤 健悟 岡村 宏 菅原 淳一

出版者

一般社団法人 日本機械学会

雑誌

Dynamics & Design Conference 2006 (ISSN:24242993)

巻号頁・発行日

pp._725-1_-_725-4_, 2006-08-06 (Released:2017-06-19)

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Front soundboard of classical guitar is the most important as part giving a sound. Because, it emit many sound energy. And, sound board has braces to reinforce it. We examined a difference of bracing pattern by investigating a vibration characteristic and an acoustic feature.

著者

秋田 涼佑 梶原 逸朗 細矢 直基

出版者

一般社団法人 日本機械学会

雑誌

Dynamics & Design Conference 2016 (ISSN:24242993)

巻号頁・発行日

pp.343, 2016 (Released:2017-06-19)

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This paper proposes a health monitoring system for detecting a hole opened on a pipe based on laser plasma acoustic excitation and acoustic measurement. In this system, the acoustic excitation is applied to the pipe by the laser-induced plasma in the air, which is generated by a high-power Nd: YAG pulse laser. Non-contact acoustic impulse excitation can be realized by laser-induced plasma. A microphone is used for measuring the time response of acoustic pressure. In this study, the detection of the hole on the pipe is focused. The time response of acoustic pressure changes due to reflection of acoustic wave caused at the hole opened on the pipe. The position of the hole is identified by applying continuous wavelet transform to time response of with/without the hole.

著者

林 裕介 渡辺 昌宏 原 謙介

出版者

一般社団法人 日本機械学会

雑誌

Dynamics & Design Conference 2010 (ISSN:24242993)

巻号頁・発行日

pp._260-1_-_260-6_, 2010-09-14 (Released:2017-06-19)

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This paper deals with theoretical stability analysis of an active feedback control of web flutter which occurs to the web with both ends fixed and tensioned. In this paper, a non-contact active feedback control method of web flutter by using movable plates set at inlet or outlet of the passage are developed and its analytical model is constructed. The equations of motion of the flexible sheet coupled with the fluid flow controlled by the movable plates are obtained. The characteristic equation of the system is derived as a function of the flow velocity in the narrow gap. As a result, it is shown that the web flutter occurs to the web with increasing the flow velocity, and is effectively suppressed by the proposed non-contact flow control devices and active feedback control method. Furthermore, calculation results are verified by the experiments.

著者

齋藤 彰 久能 友宏

出版者

一般社団法人 日本機械学会

雑誌

Dynamics & Design Conference 2019 (ISSN:24242993)

巻号頁・発行日

pp.351, 2019 (Released:2020-02-25)

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In this paper, applicability of Dynamic Mode Decomposition (DMD) to the extraction of modal properties of linear mechanical systems from their time-domain dynamic responses, i.e., experimental modal analysis is discussed. Of particular interest is its capability to extract modal parameters, i.e., natural frequencies, damping ratios and mode shapes, from measured time histories of displacement of discrete and distributed mechanical systems. First, theoretical background of DMD is briefly reviewed from the viewpoint of structural dynamics. It is shown that the modal parameters can be extracted from the DMD eigenvalues and the associated eigenvectors. The DMD is then applied to analytical solutions of transient response of discrete mass-spring-damper mechanical systems to discuss the applicability of the DMD to extract the modal parameters from the transient response. Furthermore, the effects of measurement errors on the identified modal parameters are discussed. With relatively large measurement errors, it is shown that DMD produces erroneous results especially for the damping ratios. Finally, DMD is applied to experimentally-obtained impulse response of displacement field of a cantilevered beam with many measurement points, and its modal parameters are extracted. It is shown that the modal parameters extracted by DMD are as accurate as the ones obtained by the existing modal parameter extraction method.

著者

小池 関也 見邨 康平

出版者

一般社団法人 日本機械学会

雑誌

Dynamics & Design Conference 2016 (ISSN:24242993)

巻号頁・発行日

pp.506, 2016 (Released:2017-06-19)

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Previous studies, which calculate dynamic contributions of the whole-body joint torques to the generation of bat head speed by using the equation of motion for whole-body with bat system, showed that the motion-dependent term is the largest contributor to the generation of the bat head speed at the ball impact, and also showed that joint torques of the upper limb joints and the torso joint are the main contributors to the head speed with consideration of the generating factors of the motion-dependent term. These results do not tell us the roles of the lower limb joints in the bat head speed generating mechanism. So in order to quantify the roles of the lower limb joints in the mechanism, we quantify the dynamic contributions of the whole-body joint torques to the generation of forward/backward rotational motion of the lower trunk segment during baseball batting motion. Five collegiate baseball players participated in this experiment. They performed hitting a teed ball as strong as possible. Kinetic data of each hand and each foot were obtained by using an instrumented bat equipped with 28 strain gauges and 3 force platforms, respectively. From the results, the flexion/extension torque of both hip joints showed the largest contribution to the forward angular velocity of the lower trunk segment against the large negative contribution due to the torso joint torque. This result indicates that these hip joint torques play an important role to exert large rotational torque at the torso joint, and these hip joint torques show indirect contributions to the bat head speed.

著者

相原 洋人 田中 信雄

出版者

一般社団法人 日本機械学会

雑誌

Dynamics & Design Conference 2007 (ISSN:24242993)

巻号頁・発行日

pp._340-1_-_340-6_, 2007-09-25 (Released:2017-06-19)

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There have been a number of reports on active noise control (ANC). However, conventional ANC using a voice coil loudspeaker promises attenuation only at targeted local points. Then ANC using a parametric array loudspeaker as a control source is discussed. A parametric array loudspeaker exploits nonlinear interactions of finite amplitude ultrasounds in the air. Characteristics of a parametric array loudspeaker have already been reported by a number of researchers. However, there are few investigations of simulation or experimental result of ANC using a parametric array loudspeaker. This paper addresses control effect of feed forward ANC using a parametric speaker as a control source. The control effect is more than 20dB by ANC using a parametric array loudspeaker as a control source at 1000Hz. Distribution maps of sound pressure of ANC using a conventional speaker and a parametric speaker as a control source are shown by numerical analyses and experiments.