Attenuation Of Electromagnetic Acoustic Noise From A Variable Speed Induction Motor By Using Dynamic Vibration Absorber.pdf

Hingar akustik elektromagnetik mempunyai ciri ton hingar yang dihasilkan oleh motor induksi kelajuan boleh ubah mewujudkan suasana yang tidak selesa kepada pengendali mesin. Hingar yang berlaku pada frekuensi tinggi ini kebiasaannya berlakupada gandaan frekuensi pensuisan pada pembalik. Penyelesaian masalah hingar ini pada umumnya dicapai dengan rekabentuk elektromekanikal dan modulasi lebar denyut untuk membasmi harmonik yang menyebabkan hingar. Penggunaan penyerap getaran dinamik adalah antara alternatif yang dikaji di dalam penyelidikan ini. Ujian spektrum menunjukan bahawa daya tindakan elektromagnetik mempengaruhi secara langsung hingar elektromagnetik yang dihasilkan oleh motor induksi. Gandaan harmonik 3 kHz pada spektrum modulasi lebar denyut berlaku juga pada spektrum getaran permukaan dan spektrum hingar. Analisis mod dan ujian spektrum menunjukan bahawa hingar dengan frekuensi 6 kHz pada kelajuan 1250 rpm dan ke bawah adalah disebabkan oleh getaran paksa. Pada halaju di atas 1250 rpm, hingar 3 kHz adalah disebabkan resonans. Bolt M6 sepanjang 20 mm digunakan sebagai penyerap getaran dinamik dan dipasang pada permukaan motor untuk mengurangkan hingar pada 6 kHz. Penyerap getaran dinamik menyerap getaran sebanyak 20% hingga 86%pada permukaan motor dan pengurangan aras tekanan bunyi sebanyak 12 dB(A) dapat dicapai. Ia juga berkesan pada lokasi lain pada motor dan juga pada semua kelajuan operasi. Penyerap getaran dinamik telah terbukti untuk mengurangkan hingar elektromagnetik daripada motor induksi kelajuan boleh ubah. _________________________________________________________________________________________________________________________ Tonal electromagnetic acoustic noise radiated from variable speed induction motor can be annoying to human operator. Occurring at high frequency, it often occurs at multiples of the inverter switching frequency. Solutions for the noise attenuation have been generally by means of electromechanical design and pulse width modulation (PWM) strategy to remove harmonics leading to noise generation. Dynamic vibration absorber (DVA) as an alternative solution was implemented in this research. Spectral test revealed that the input electromagnetic excitation has direct influence on the radiated electromagnetic acoustic noise from the induction motor. The multiples of 3 kHz harmonics in PWM spectrum was also present in the surface vibration and sound pressure spectrum. From experimental modal analysis and spectral test, it was found that the 6 kHz acoustic noise was due to forced vibration for speed of 1250 rpm and below. While at above 1250 rpm, the 3 kHz noise was due to resonance. A 20mm M6 bolt was used as DVA and attached to a point on the motor housing for targeted noise attenuation at 6 kHz. The DVA was able to absorb the surface vibration in the range of 20 to 86% and maximum sound pressure level reduction of 12 dB (A) was achieved. It was also effective at other locations on motor as well as at different operating speed

A modeling framework and toolset for simulation and characterization of the cochlea within the auditory system

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Biological Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 50-53).Purpose: This research develops a modeling approach and an implementation toolset to simulate reticular lamina displacement in response to excitation at the ear canal and to characterize the cochlear system in the frequency domain. Scope The study develops existing physical models covering the outer, middle, and inner ears. The range of models are passive linear, active linear, and active nonlinear. These models are formulated as differential algebraic equations, and solved for impulse and tone excitations to determine responses. The solutions are mapped into tuning characteristics as a function of position within the cochlear partition. Objectives The central objective of simulation is to determine the characteristic frequency (CF)-space map, equivalent rectangular bandwidth (ERB), and sharpness of tuning (QERB) of the cochlea. The focus of this research is on getting accurate characteristics, with high time and space resolution. The study compares the simulation results to empirical measurements and to predictions of a model that utilizes filter theory and coherent reflection theory. Method We develop lumped and distributed physical models based on mechanical, acoustic, and electrical phenomena. The models are structured in the form of differential-algebraic equations (DAE), discretized in the space domain. This is in contrast to existing methods that solve a set of algebraic equations discretized in both space and time. The DAEs are solved using numerical differentiation formulas (NDFs) to compute the displacement of the reticular lamina and intermediate variables such as displacement of stapes in response to impulse and tone excitations at the ear canal. The inputs and outputs of the cochlear partition are utilized in determining its resonances and tuning characteristics. Transfer functions of the cochlear system with impulse excitation are calculated for passive and active linear models to determine resonance and tuning of the cochlear partition. Output characteristics are utilized for linear systems with tone excitation and for nonlinear models with stimuli of various amplitudes. Stability of the system is determined using generalized eigenvalues and the individual subsystems are stabilized based on their poles and zeros. Results The passive system has CF map ranging from 20 kHz at the base to 10 Hz at the apex of the cochlear partition, and has the strongest resonant frequency corresponding to that of the middle ear. The ERB is on the order of the CF, and the QERB is on the order of 1. The group delay decreases with CF which is in contradiction with findings from Stimulus Frequency Otoacoustic Emissions (SFOAE) experiments. The tuning characteristics of the middle ear correspond well to experimental observations. The stability of the system varies greatly with the choice of parameters, and number of space sections used for both the passive and active implementations. Implication Estimates of cochlear partition tuning based on solution of differential algebraic equations have better time and space resolution compared to existing methods that solve discretized set of equations. Domination of the resonance frequency of the reticular lamina by that of the middle ear rather than the resonant frequency of the cochlea at that position for the passive model is in contradiction with Bekesys measurements on human cadavers. Conclusion The methodology used in the thesis demonstrate the benefits of developing models and formulating the problem as differential-algebraic equations and solving it using the NDFs. Such an approach facilitates computation of responses and transfer functions simultaneously, studying stability of the system, and has good accuracy (controlled directly by error tolerance) and resolution.by Samiya Ashraf Alkhairy.M.Eng

Metamodeling and Audio Signals Design Process, for the Encounter Between Sound and Changing Forms

The context of the following work arises from an exploratory interest around sound and forms, in order to be able to structure fictional architectural envelopes of an audio-reactive nature, whose materialization is achieved through digital visualization techniques, and generative software of art and design. This research implies an interdisciplinary development, between different categories of knowledge, through which unconventional processes are built, where sound is activated as an element that generates random values of information, and that have a direct impact on the configuration and changing behavior of the form and environment. Today, the boundaries that define creative territories are increasingly flexible and adaptive, which allows establishing knowledge networks that expand the ranges of action of design activities

Experimental investigations on the aerodynamic and aeroacoustic characteristics of small UAS propellers

Unmanned aerial system (UAS) is a hot topic in both industry and academia fields. As a popular planform, the rotary-wing system gains more attentions. The small UAS propeller is the most important component in this system, which transfers electric energy into kinetic energy to accomplish fly missions. In the present work, several experimental studies have been performed to investigate the aerodynamic and aeroacoustic characteristics of small UAS propellers. First of all, by conducting force and flow filed measurements, the unsteady dynamic thrust and the wake structure of the propeller has been studied to explore the fundamental physics to help researchers and engineers to obtain a better understanding. Secondly, two kinds of bio-inspired the propellers have been designed and manufactured. Through a set of force, sound, and flow filed measurements, the aerodynamic and aeroacoustic performance of these propellers has been compared to the baseline propeller to evaluate the effects of aerodynamic efficiency and noise attenuation. It was found that the serrated trailing edge propeller could reduce the turbulent trailing edge noise up to 2 dB, and the maple seed inspired propeller could reduce the noise up to 4 dB with no effect on the aerodynamic performance. In addition, since the rotary-wing system consists more than one propeller, the rotor to rotor interaction on the aerodynamic and aeroacoustic performance also has been studied. By enlarging the separation distance between two propellers, the thrust fluctuation and noise generation could be restricted. Not only the design of the device itself has effect on the flying performance, the extreme weather also would affect it. Therefore, an icing research study on the small UAS propeller has been conducted to illustrate how does the ice formed on the propeller and how does the icing influence the aerodynamics performance and power consumption. During these experimental studies, the force measurements were achieved by a high sensitive force and moment transducer (JR3 load cell), which had a precision of ñ0.1N (ñ 0.25% of the full range). The sound measurements were conducted inside of the anechoic chamber located in the aerospace engineering department at Iowa State University. This chamber has a physical dimensions of 12ÃÂ12ÃÂ9 feet with a cut-off frequency of 100 Hz. The detailed flow structure downstream of the propeller was measured by a high-resolution digital PIV system. The PIV system was used to elucidate the streamwise flow structure downstream of the propeller. Both “free-run” and “phase-locked” PIV measurements were conducted to achieve the ensemble-average flow structure and detailed flow structure at certain phase angles

Altered functional connectivity during speech perception in Congenital Amusia

Individuals with congenital amusia have a lifelong history of unreliable pitch processing. Accordingly, they downweight pitch cues during speech perception and instead rely on other dimensions such as duration. We investigated the neural basis for this strategy. During fMRI, individuals with amusia (N=15) and controls (N=15) read sentences where a comma indicated a grammatical phrase boundary. They then heard two sentences spoken that differed only in pitch and/or duration cues, and selected the best match for the written sentence. Prominent reductions in functional connectivity were detected in the amusia group, between left prefrontal language-related regions and right hemisphere pitch-related regions, which reflected the between-group differences in cue weights in the same groups of listeners. Connectivity differences between these regions were not present during a control task. Our results indicate that the reliability of perceptual dimensions is linked with functional connectivity between frontal and perceptual regions, and suggest a compensatory mechanism

멀티로터형 비행체의 공력소음: 비행 제어 시스템과 공기역학적 상호작용의 영향

학위논문(박사) -- 서울대학교대학원 : 공과대학 항공우주공학과, 2022. 8. 이수갑.Multirotor configurations using a distributed electric propulsion (DEP) system have different aerodynamic and aeroacoustic characteristics from conventional rotorcrafts. Generally, DEP systems use electric motors to control the rotational speed (revolutions per minute, RPM) of individual rotors to perform flight control. Besides, aerodynamic interactions between multiple rotors occur significantly. The main objective of this study is prediction-based evaluations of RPM-controlled multirotor noise. Therefore, three numerical studies are conducted from the perspective of the flight control system and aerodynamic interactions. First, a comprehensive multirotor noise assessment (CONA) framework is developed for real-time noise prediction and psychoacoustic analyses of RPM-controlled multirotor configurations. The CONA framework utilizes flight control, aerodynamics, tonal and broadband noise prediction, and psychoacoustics modules. By this framework, it is possible to conduct the real-time noise assessment in actual flight environments considering the mission profile and gusty wind conditions. A high-resolution time-frequency analysis technique is introduced to analyze the frequency and amplitude modulation characteristics of rotor tonal noise. The Griffin-Lim algorithm is used for the phase reconstruction for time signal synthesis of predicted rotor broadband noise in the 1/3 octave band. Using the CONA framework, the noise of quadrotor configurations is analyzed in representative mission profiles, such as cruise, takeoff, and loitering flights. As flight parameters, flight speed, wind speed, and quadrotor flight type are selected, and the effects of each parameter on acoustic signatures are evaluated. Second, wake interaction effects of multirotor configurations are analyzed by developing the MultiPA framework based on the free-wake vortex lattice method. The aerodynamic and aeroacoustic performance of individual rotors is compared with that of a single rotor with RPM, forward velocity, and incidence angle as variables in two flight types of the quadrotor. Besides, induced circulation is introduced to analyze wake interactions quantitatively. Wake interaction effects are divided into wake-, rotor-, and motion-induced circulation. By circulation analyses, it is quantitatively confirmed that wake effects depend on the flight conditions and rotor topology. Finally, numerical techniques are developed to simulate the torque ripple in the hovering flight of multirotor configurations. In the MultiPA framework, a periodic RPM signal is applied to the numerical analysis. In the CONA framework, a statistical technique that introduces a periodic random RPM signal is used to implement uncertainties in torque ripple numerically. Based on the results of each framework, the effects of torque ripple are illustrated in aerodynamic and aeroacoustic characteristics. The implications can be derived that torque ripple should be considered in the noise assessment of RPM-controlled multirotor configurations using an electric motor. The frameworks developed in this study are specialized in analyzing the unique aerodynamic and aeroacoustic characteristics according to the flight control system and wake interaction effects of DEP systems. The entire process of the CONA framework can be utilized for various multirotor configurations to perform real-time noise prediction and noise impact assessment. The MultiPA framework and induced circulation concepts can be utilized to analyze the wake interaction effect and develop efficient wake models of multirotor configurations. This study illustrates the effects of the flight control system and wake interactions from various perspectives. It is expected that the research of low-noise and high-efficient urban air mobility will be possible through perception-based evaluations using the developed frameworks.멀티로터형 비행체는 분산 전기 추진(Distributed electric propulsion, DEP) 시스템을 활용하여 기존 회전익기와는 다른 공력 및 공력 소음 특성을 가진다. 일반적으로 DEP 시스템은 전기 모터를 이용하여 개별 로터의 회전속도(revolutions per minute, RPM)를 제어하여 비행 제어를 수행하며, 다수의 로터 사이에 공기역학적 상호작용이 뚜렷하게 발생한다. 본 연구의 주된 목적은 RPM 제어 멀티로터 소음의 해식 기반 평가이다. 따라서, 세 가지 수치적 연구가 비행 제어 시스템과 공기역학적 상호작용의 측면에서 수행되었다. 먼저, RPM 제어 멀티로터의 실시간 소음 예측과 심리음향학적 분석을 위한 CONA (Comprehensive multirotor noise assessment) 프레임워크를 개발하였다. CONA 프레임워크는 비행 제어, 공기역학, 로터 톤 및 광대역 소음 해석, 심리음향 해석 모듈을 활용하며, 멀티로터형 비행체의 임무 형상과 대기 바람 조건을 부여한 실제 비행 환경에서의 실시간 소음 해석이 가능하다. 로터 톤 소음의 주파수 및 진폭 변조 특성을 분석하기 위해 고해상도 시간-주파수 분석 기법을 도입하였고, 1/3 옥타브 밴드로 해석되는 로터 광대역 소음을 시간 신호로 변환하기 위하여 그리핀-림 알고리즘을 활용한 음원 합성을 수행하였다. 개발한 CONA 프레임워크로 대표적인 임무 형상인 순항, 수직 이륙, 선회 비행에서 쿼드로터의 소음 특성을 분석하였다. 비행 변수로 비행 속도, 바람 속도, 쿼드로터 비행 타입을 선정하여 각 변수의 공력 소음 특성에 대한 영향을 평가하였다. 두 번째로, 자유 후류 와류 격자 기법 기반의 MultiPA 프레임워크를 개발하여, 멀티로터형 비행체의 후류 상호작용 효과를 분석하였다. 쿼드로터의 두 가지 비행 타입에서 RPM, 전진 속도, 전진각을 변수로 하여 개별 로터의 공력 및 공력 소음 성능을 단일 로터와 비교하였다. 또한, 후류 상호작용 효과를 정량적으로 분석할 수 있는 유도 순환 지표를 도입하였다. 후류 상호작용 효과는 유도 순환 지표를 통해서 후류-유도 순환, 로터-유도 순환, 그리고 로터의 구동에 따른 순환으로 구분되며, 비행 조건과 로터 배치에 따라 후류 영향이 달라짐을 정량적으로 확인하였다. 마지막으로, 멀티로터형 비행체의 제자리 비행 시 발생하는 토크 리플의 수치적 모사 기법을 고안하였다. MultiPA 프레임워크에서는 주기적인 RPM 신호를 해석에 적용하였고, CONA 프레임워크에서는 불확실성이 강한 토크 리플을 수치적으로 구현할 수 있도록 주기적인 무작위 RPM 신호를 도입한 통계적 기법을 활용하였다. 각각의 해석 결과를 바탕으로 토크 리플에 의한 공력 및 공력 소음 특성을 분석하였고, 전기 모터를 활용한 RPM 제어 비행체의 소음 평가 시 토크 리플을 고려해야 한다는 시사점을 도출하였다. 본 연구에서 개발한 프레임워크들은 DEP 시스템의 비행 제어 시스템과 후류 상호작용 효과에 따른 독특한 공력 및 공력 소음 특성을 분석하는 데 특화되어 있다. CONA 프레임워크의 전체 해석 프로세스는 다양한 멀티로터형 비행체에 활용되어 실시간 소음 해석과 소음 영향 평가를 수행할 수 있다. MultiPA 프레임워크와 유도 순환 지표는 후류 상호작용의 효과를 분석하고, 멀티로터형 비행체의 효율적인 후류 모델을 개발하는 데 활용될 수 있다. 본 연구에서는 다양한 관점으로 비행 제어 시스템과 후류 상호작용 효과를 분석하였으며, 개발한 프레임워크를 활용해 인지-기반 평가를 통한 저소음 고효율 도심 항공 모빌리티의 연구를 수행할 수 있을 것으로 기대된다.1 Introduction 1 1.1 Background 1 1.1.1 Multirotor configurations 1 1.1.2 Noise assessment of novel aerial vehicles 3 1.2 Frequency-modulated multirotor noise 5 1.2.1 Frequency and amplitude modulation 5 1.2.2 Time-frequency analysis of the noise signal 7 1.2.3 Perception-influenced evaluation of aerial vehicles 8 1.3 Wake interactions in multirotor configurations 9 1.3.1 Wake interaction phenomena 9 1.3.2 Previous research on wake interactions 10 1.4 Research objectives and scope 12 1.4.1 Real-time noise prediction 13 1.4.2 Wake interactions in multirotor configurations 15 1.5 Dissertation organization 16 2 Real-time noise prediction framework 19 2.1 Flight control module 21 2.2 Aerodynamics module 22 2.2.1 HBEM with aerodynamic models 22 2.2.2 Beddoes wake models 24 2.2.3 Unsteady aerodynamic corrections 26 2.3 Time reconstruction module 28 2.4 Tonal noise prediction module 29 2.5 Time-frequency analysis module 31 2.6 Broadband noise prediction module 34 2.6.1 Semi-empirical model 34 2.6.2 Amiet's theory with wall-pressure spectrum models 35 2.7 Phase reconstruction module 36 2.7.1 Step 1: Narrowband spectrogram synthesis 36 2.7.2 Step 2: Time signal synthesis 37 2.8 Psychoacoustics module 38 3 Free-wake vortex lattice method solver 41 3.1 Aerodynamic and aeroacoustic solver 41 3.1.1 Free-wake vortex lattice method 41 3.1.2 Additional aerodynamic models 43 3.1.3 Acoustic analogy 44 3.2 Quantification factors for wake interaction 45 3.2.1 Wake interaction relations 45 3.2.2 Concepts of induced circulation 46 3.2.3 Quantification factors derived by induced circulation 47 4 Verification, validation, and numerical setup 49 4.1 CONA framework verification and validation: Flight control, aerodynamics, and tonal noise 49 4.1.1 UAV: Single rotor hovering flight 49 4.1.2 UAV: Single rotor forward flight 52 4.1.3 UAV: Quadrotor forward flight 57 4.1.4 UAM: Quadrotor forward flight 63 4.2 CONA framework verification and validation: Broadband noise and psychoacoustics 66 4.2.1 UAV: Airfoil self-noise 66 4.2.2 UAV: Single rotor hovering flight 69 4.2.3 UAV: Single rotor forward flight 73 4.2.4 UAV: Quadrotor forward flight 75 4.2.5 UAV: Quadrotor hovering flight 77 4.3 Free-wake vortex lattice method solver 79 4.3.1 Reference model for wake interaction analyses 79 4.3.2 Test matrix and target outputs 82 4.3.3 Solver validation 83 4.4 Torque ripple modeling 87 4.4.1 Sinusoidal RPM signal approach 89 4.4.2 Random periodic RPM signal approach 90 5 Frequency-modulated multirotor noise 93 5.1 Flight simulation for quadrotor configurations 93 5.1.1 Mission profile and numerical settings 93 5.1.2 Flight control results 96 5.2 High-resolution time-frequency analyses 101 5.2.1 Flyover noise 102 5.2.2 Takeoff noise 104 5.2.3 Loitering noise 107 5.3 Prediction-based psychoacoustic analyses 109 5.3.1 Auralization process 109 5.3.2 Flyover noise 114 5.3.3 Takeoff noise 119 5.3.4 Loitering noise 122 6 Wake interactions in multirotor configurations 125 6.1 Wake interactions in quadrotor hovering flight 125 6.2 Performance of quadrotor forward flight 129 6.2.1 Aerodynamic and aeroacoustic performance 129 6.2.2 Comparison of polynomial regression 133 6.3 Physics of quadrotor forward flight 140 6.3.1 Wake dynamics of quadrotor configurations 140 6.3.2 Distribution of induced circulation 146 6.3.3 Temporal characteristics of wake interaction 161 7 Torque ripple modeling 167 7.1 Sinusoidal RPM signal approach 167 7.1.1 Aerodynamic characteristics 167 7.1.2 Aeroacoustic characteristics 173 7.1.3 Effects of the angular frequency of RPM variations 176 7.2 Random periodic RPM signal approach 180 7.2.1 Effects on noise spectrum 180 7.2.2 Effects on noise directivity 182 8 Conclusions and recommendations 185 8.1 Conclusions 185 8.2 Recommendations for future work 187 8.2.1 Applications of the CONA framework 187 8.2.2 Applications of the MultiPA framework 189 Bibliography 191 Appendix A Control outputs of the CONA framework 205 국문초록 215박

Passive isolator design for jitter reduction in the Terrestrial Planet Finder Coronagraph

Terrestrial Planet Finder (TPF) is a mission to locate and study extrasolar Earth-like planets. The TPF Coronagraph (TPF-C), planned for launch in the latter half of the next decade, will use a coronagraphic mask and other optics to suppress the light of the nearby star in order to collect visible light from such planets. The required contrast ratio of 5e-11 can only be achieved by maintaining pointing accuracy to 4 milli-arcseconds, and limiting optics jitter to below 5 nm. Numerous mechanical disturbances act to induce jitter. This paper concentrates on passive isolation techniques to minimize the optical degradation introduced by disturbance sources. A passive isolation system, using compliant mounts placed at an energy bottleneck to reduce energy transmission above a certain frequency, is a low risk, flight proven design approach. However, the attenuation is limited, compared to an active system, so the feasibility of the design must be demonstrated by analysis. The paper presents the jitter analysis for the baseline TPF design, using a passive isolation system. The analysis model representing the dynamics of the spacecraft and telescope is described, with emphasis on passive isolator modeling. Pointing and deformation metrics, consistent with the TPF-C error budget, are derived. Jitter prediction methodology and results are presented. Then an analysis of the critical design parameters that drive the TPF-C jitter response is performed

Background, analysis, and performance guide for Edison Denisov\u27s Sonata for flute and piano

After composer Edison Vasilievich Denisov (1929–1996) finished his graduate work at the Moscow Conservatoire, he launched into an independent examination of composers whose music had been banned by the Soviet authorities during his conservatory years (1951–1959). It was during this time in his compositional development that he composed his Sonata for Flute and Piano (1960). The first section of this document provides a biographical summary of Edison Denisov and the circumstances surrounding the composition of the flute sonata. The second section is devoted to formal, harmonic, and stylistic analysis of the sonata. The final section of the document provides a guide for performing and teaching the piece, and includes information for available audio recordings