Self-exited Oscillation Research Articles

Control of mechatronic drives considering the type and number of the nonlinearities of a mechanical converter

In this article the particularities of the dynamics study of mechatronic drives that operate at low velocities are discussed; the origins of frictional self-exited oscillations to develop an algorithm for non-linearity correction are analyzed; a drive mathematical model and the qualitative picture of the self-exited oscillations regimes were presented for the three cases: a "system with clearance and friction-free"; a system without clearance with "dry friction" and a system with clearance and "dry friction". Therefore, an algorithm to compensate the frictional self-excited oscillations based on the feedback introduction for the sliding velocity of the linear motion output link was proposed.

Hydrodynamics of Intensive Self-Exited Oscillations of the Reversed Vane in a Plane Diffuser

The problem of the nonstationary flow of a viscous incompressible fluid in a flat diffuser containing a hinged partition in the form of a reverse vane directed toward the flow is considered. The mechanism of excitation and maintenance of the angular auto-oscillation regime of the vane is revealed, accompanied by shock interaction of the vane sock with the channel walls and the formation of two antiphase pulsating jets at the exit from the diffuser. This mode is reproduced in a physical experiment and in numerical simulation.

The Muffler Performance Effect on Pressure Reducing Valve Dynamics

The gas pressure control units are widely used for various applications. Very often such units operate at large flow rates and pressure drops, thus becoming a powerful noise sources. The problem of noise reduction and protection is a formidable challenge for the design and operation of such units. One of the ways for noise reduction is a muffler installation. However, the in-line installation of such devices may cause malfunction of the pressure reducing valve. Any variation in the output line impedance may provoke instability and self-exited oscillation of the regulator. In this paper the muffler's effect on pressure reducing valve dynamics is studied. The subject of research is a muffler installed at the pressure reducing valve outlet. The mathematical model of this system is implemented in the Simulink software to analyze the muffler impact on pressure reducing valve static and dynamic characteristics and to estimate the system noise level. The dependences between the system and muffler parameters are obtained as a result of simulation. The experimental research at the pneumatic bench is implemented for mathematical model verification. The muffler effect on transient process quality is analyzed. Stability domains are calculated and the muffler influence on system stability margin is evaluated. The theoretical results demonstrate acceptable correlation with experimental data.

Study on thermal cycle in oscillating heat pipes by numerical analysis

This paper discusses the thermal cycle found within oscillating heat pipes (OHPs). An OHP is a two-phase heat transfer device using self-exited oscillation. Over the past few decades, a considerable number of studies have been conducted to understand the physics of OHP phenomena. However, little is known about the thermal cycle in OHPs. In this study, we developed a one-dimensional slug flow model to reproduce thermal and hydrodynamic phenomena in OHPs. Fast Fourier transform (FFT) and cross-correlation analysis were used to process oscillation waveform data. A multi-branch OHP consisting of a stainless steel pipe wall and R134a working fluid was simulated. The numerical results revealed pressure propagation within the OHP. Moreover, the results indicated that the vapor volume oscillated with the same frequency as the pressure. Additionally, the vapor plug obtained energy or performed work depending on the direction of pressure propagation. As a result, the propagation of energy was identified as a reason for pressure propagation within the OHP.

Self-Exited Oscillation in a Combustion Chamber Driven by Phase Change in the Liquid Fuel Feed System

A new mechanism for the generation of a self-exited oscillation of combustion in a generic combustion chamber typical for aeroengine combustors is described. The cause of the oscillation is the phase change from liquid to vapour which happens when the preheat temperature of the air flowing through the burner exceeds the boiling temperature at the operating pressure and the fuel flow is so low that heat transfer to the liquid fuel causes evaporation within the fuel channels of the burner. Liquid fuel and vapour alternatively enter the airstream of the burner. This leads to an unstable situation for the flame. Measurements of chemiluminescence and liquid fuel show nearly complete extinction and re-ignition for the limit cycle. Prevention of the oscillation is possible by better thermal management of the fuel path.

Series solutions of coupled Van der Pol equation by means of homotopy analysis method

In this paper, the homotopy analysis method (HAM) is used to give series solutions of self-exited oscillation systems governed by two Van der Pol equations, which are coupled by a linear and a cubic term. The frequency and amplitude of all possible periodic solutions are investigated. It is found that there exist either in-phase or out-of-phase periodic solutions only. Besides, the in-phase periodic oscillations are decoupled, whose periods and amplitudes have nothing to do with the linear and cubic coupled terms. However, the out-of-phase periodic oscillations are strongly coupled, whose period and amplitude can be controlled by the linear and cubic coupled terms.

816 コラプシブルチューブ内の気流により生じる自励振動と振動音 : 閉塞型睡眠時無呼吸症候群に対するCPAP療法の体外模擬実験(GS-2 呼吸・血液)

816 コラプシブルチューブ内の気流により生じる自励振動と振動音 : 閉塞型睡眠時無呼吸症候群に対するCPAP療法の体外模擬実験(GS-2 呼吸・血液)

Heat release and flame structure measurements of self-excited acoustically-driven premixed methane flames

An open–open organ pipe burner (Rijke tube) with a bluff-body ring was used to create a self-excited, acoustically-driven, premixed methane–air conical flame, with equivalence ratios ranging from 0.85 to 1.05. The feed tube velocities corresponded to Re = 1780–4450. Coupled oscillations in pressure, velocity, and heat release from the flame are naturally encouraged at resonant frequencies in the Rijke tube combustor. This coupling creates sustainable self-exited oscillations in flame front area and shape. The period of the oscillations occur at the resonant frequency of the combustion chamber when the flame is placed ∼¼ of the distance from the bottom of the tube. In this investigation, the shape of these acoustically-driven flames is measured by employing both OH planar laser-induced fluorescence (PLIF) and chemiluminescence imaging and the images are correlated to simultaneously measured pressure in the combustor. Past research on acoustically perturbed flames has focused on qualitative flame area and heat release relationships under imposed velocity perturbations at imposed frequencies. This study reports quantitative empirical fits with respect to pressure or phase angle in a self-generated pressure oscillation. The OH-PLIF images were single temporal shots and the chemiluminescence images were phase averaged on chip, such that 15 exposures were used to create one image. Thus, both measurements were time resolved during the flame oscillation. Phase-resolved area and heat release variations throughout the pressure oscillation were computed. A relation between flame area and the phase angle before the pressure maximum was derived for all flames in order to quantitatively show that the Rayleigh criterion was satisfied in the combustor. Qualitative trends in oscillating flame area were found with respect to feed tube flow rates. A logarithmic relation was found between the RMS pressure and both the normalized average area and heat release rate for all flames.

単純なフルイディック発振器の安定発振条件(流体工学,流体機械)

A confined jet sometimes causes a self-exited oscillation due to the existence of a downstream target. In this work, the authors study this phenomenon. More specifically, the authors deal with a simple fluidic oscillator; namely, a two-dimensional confined jet into an abruptly-expanding channel with a downstream target of a square cylinder. The authors conduct the velocity measurements by an UVP (ultrasonic velocity profiler). Besides, the flow patterns in the fluidic oscillator are observed by a PIV (particle image velocimetry). As a result, the authors reveal the geometrical effects upon the range of stable jet's oscillation, such as the aspect-ratio effect, the channel-breadth effect, the cylinder-size effect and the cylinder-distance effect, together with the Re effect.

振動流によるエネルギー変換・熱輸送現象と応用技術 熱音響自励振動に関する数値解析

振動流によるエネルギー変換・熱輸送現象と応用技術 熱音響自励振動に関する数値解析

506 境界層理論に基づく熱音響自励振動の数値シミュレーション(OS-7 熱流体の非線形力学とその数値シミュレーション(1))

506 境界層理論に基づく熱音響自励振動の数値シミュレーション(OS-7 熱流体の非線形力学とその数値シミュレーション(1))

Study on Acoustic Absorbers to Suppress Acoustic Resonance in Tube Bundles of Boiler

This paper deals with the acoustic resonance in tube bundles which occurred in actual boiler plants. In-situ measurements revealed that besides the lift-force directional modes, drag-force directional modes which are difficult to suppress, are generated. In order to suppress both types of resonant modes, acoustic absorbers are adopted which are equipped mid-air in the duct. This phenomena is classified as self-exited oscillation and based on the stability criterion, its design method, including the number or placement of absorbers in the duct space for efficient performance, was developed with the use of acoustic FEM. In order to validate this method, scale model test was executed and the same phenomena as those in the actual plant were realized. In the next step acoustic energy absorbers are equipped in the duct and remarkable increase of the critical flow velocity was confirmed. Finally this method was applied to the actual boiler plant and based these results, it was confirmed that the proposed method is the effective countermeasure for the anti-acoustic resonance in heat exchangers.

D311 純流体発振素子の特性

A confined jet sometimes causes self-exited oscillations due to an existence of a downstream obstacle.This phenomenon is useful for fluidic oscillators, heat/material mixers and flowmeters, in order to realise a low-cost high-reliability device without mechanically moving components. In the present study, the authors deal with this phenomenon at low Reynolds numbers (Re=500), experimentally. More specifically, the autors conduct a time series of flow visualisations and PIV(Particle Image Verocimatry) analyses, with the measurement by UVP for accuracy check. As a result, the autors propose a new definition of length scale of vertical structures and propose a formula to predict the oscillation frequency using the length scale.

B223 フルイディック発振器内の流れの可視化

A confined jet sometimes causes self-exited oscillations due to an existence of a downstream obstacle. This phenomenon is useful for fluidic oscillators, heat/material mixers and flowmeters, in order to realize a low-cost high-reliability device without mechanically moving components. In the present paper, the authors study this phenomenon at low Reynolds numbers (Re≤1000), experimentally. More specifically, the authors deal with a two-dimensional confined jet into an abruptly expanding channel with a downstream square-cylinder target. As a result, the authors measured the flow patterns by PIV (Particle Image Verocimatry), and are classified into three types. Moreover, as a result of flow visualization by the digital camera, authors revealed that depends for oscillation frequency on the flow of the downstream of a square cylinder.

412 擬似衝撃波を伴う流れの自励振動とジェット騒音との関連性

412 擬似衝撃波を伴う流れの自励振動とジェット騒音との関連性

2001 熱音響自励振動騒音のスリット式消音器による抑制

The boiler, which applies a pre-mixed combustion method, has a strong tendency with the extremely loud combustion noise. The noise depends on the geometric structure of boiler system. The aim of the study is to clarify the characteristic of such noise and reduce it. In this paper, the combustion noise caused by the combustion-driven oscillation is replaced with the noise caused by the self-exited oscillation. This kind of oscillating system is called "Rijke tube", and composed of the electrically heated. Applying the slit type muffler in self-exited oscillation system, it is proposed a method of noise reduction with the muffler by absorbing the sound energy as the result of resonance.

F-1035 能動的抑制法による気柱振動騒音の低減化(G10-5 音響・騒音制御)(G10 機械力学・計測制御部門一般講演)

The boilers applied a pre-mixed combustion method has a strong tendency with the extremely loud combustion noise that depends on the geometric structure of boiler system. This study aimed to clarify the characteristic of such noise and reduce it. In this paper, the combustion noise due to combustion-driven oscillation is replaced by noise due to self-exited oscillation of the air column caused by electrically heated wire called Rijke tube, in order to idealize the heat source. Applying of entrainment phenomenon in self-exited oscillation system, it is proposed noise repression to shift a frequency of self-exited oscillation caused by adding pressure signal at this system. It could be clear that the noise due to heat-driven oscillation is effective for the noise reduction.

亜音速ならびに遷音速流中の二次元パネルのフラッタとダイバージェンス

Analytical studies of the aeroelastic stability of two dimensional flat panels were made for the Mach number range up to one by using the exact linearized aerodynamic forces and adopting GALERKIN method. Flutter instability was predicted for the Mach number range above 0.4 (approx.). However the predicted boundary of static divergence is more critical than that of flutter in the subsonic range. Therefore the possibility of occurence of flutter were examined as a post divergence problem using rather unrealistic rough assumptions to simplify the problem. This examination showed that the tensile axial force which come from the aerodynamic pressure on the diverged panel is strong enough to prevent the panel from going into flutter. The predicted divergence boundaries agreed reasonably well with the experimental results. As for the post divergence phenomena, including the self-exited oscillation (flutter), the experimentally observed phenomena were much more complicated than analytically predicted ones. Most of the tested panels were free from flutter after they were subjected to divergence, but there were two exceptional cases : a panel started flutter in large amplitude and another panel fluttered in small amplitude keeping its divergence shape as the mean deflection of its oscillation. It is felt that a nonlinear analysis, which considers the effect of divergence shape of finite panels on the structural and aerodynamic expression, is necessary to explain the experimental results. The stability boundaries of some simply supported three dimensional panels, of which both surfaces are subjected to the air flow, were tested in order to compare the stabilities of the two dimensional panels. Some distinct differences of instability types were found between them. And the aspect ratio of three dimensional panel was found to be an important parameter to classify the stability character of the panels.

2004 風による円筒の共振時の振幅について

2004 風による円筒の共振時の振幅について