Leopoldo P R de Oliveira | Universidade de São Paulo (original) (raw)

Papers by Leopoldo P R de Oliveira

Research paper thumbnail of A state-space modeling approach for active structural acoustic control 1

The demands for improvement in sound quality and reduction of noise generated by vehicles are con... more The demands for improvement in sound quality and reduction of noise generated by vehicles are constantly increasing, as well as the penalties for space and weight of the control solutions. A promising approach to cope with this challenge is the use of active structural-acoustic control. Usually, the low frequency noise is transmitted into the vehicle’s cabin through structural paths, which raises the necessity of dealing with vibro-acoustic models. This kind of models should allow the inclusion of sensors and actuators models, if accurate performance indexes are to be accessed. The challenge thus resides in deriving reasonable sized models that integrate structural, acoustic, electrical components and the controller algorithm. The advantages of adequate active control simulation strategies relies on the cost and time reduction in the development phase. Therefore, the aim of this paper is to present a methodology for simulating vibro-acoustic systems including this coupled model in a...

Research paper thumbnail of On the robustness of a model-based inverse force identification applied on a structure submerged in different media

Journal of the Brazilian Society of Mechanical Sciences and Engineering

This paper addresses an experimental study on the implementation of an Augmented Kalman filter al... more This paper addresses an experimental study on the implementation of an Augmented Kalman filter algorithm complemented by displacement dummy measurements, aiming at identifying a stochastic point force. For this purpose, the present experimental approach features a cantilevered structure instrumented with two pairs of accelerometers. A force sensor is used to measure the actual input force for benchmarking. The main objective of this study is to evaluate the ability of the algorithm to predict forces when the system is perturbed by different fluids surrounding the structure. Firstly, the structure is identified via experimental modal analysis, in two conditions, in air and underwater. Predicted and measured forces, for tests in each media, are compared showing good agreement. Additionally, the method is used to estimate forces applied when the structure is submerged in water while using a system model identified in air, in order to assess the algorithm robustness in scenarios that are either difficult or impossible to be tested. Although results accuracy in such cross-identification conditions depend on the closeness between the reference model and the actual boundary condition, in general, the frequency content of the predicted forces match with those predicted in the direct scheme, allowing qualitative data assessment in an otherwise unfeasible scenario.

Research paper thumbnail of An experimental study on the vibration induced by a two-phase air-water crossflow in a normal triangular tube bundle

Proceedings of the 23rd ABCM International Congress of Mechanical Engineering, 2015

Research paper thumbnail of Multichannel Active Sound Quality Control for Independent-Channel Sound Profiling

Multichannel active noise control algorithms have been proposed to deal with sound propagation in... more Multichannel active noise control algorithms have been proposed to deal with sound propagation in enclosures, which base their operation on sensor/actuator positioning conditions that in some applications could not be easily met. In this paper, we investigate a multichannel active sound quality control algorithm, intended to independently control each sensor position, regardless of the acoustic coupling among channels. The decentralized channels share their adaptive weights among each other, in order to extract the maximum allowed gain that minimizes the cost function at the corresponding error sensor, while keeping distortion at the other error sensors as low as possible. A coupled FE-FE vibro-acoustic model of a scaled vehicle mock-up is used for computer simulations, which properly reproduces acoustic coupling among the error sensors. A pure-sinusoid disturbance is used as the input to the vibroacoustic model, and a 2x2 multichannel algorithm is proposed to independently profile it. Computer simulations demonstrate that, despite of the increased computational burden, as compared with the decentralized leaky-LMS control algorithm, the proposed algorithm is able to deal with the acoustic coupling among the error sensors, thus reaching independent control targets over the disturbance in each error sensor, regardless of their position in an enclosure.

Research paper thumbnail of An adaptive controller for amplitude and relative phase control of periodic disturbance

Most of the active noise and vibration control applications are intended to globally reduce physi... more Most of the active noise and vibration control applications are intended to globally reduce physical quantities such as sound pressure or structural vibration. However, there are other situations where not only through controlling the magnitude but also (or merely) by the relative phase of the components of the periodic disturbance, a system could lead to desired results. Synchronization of chaotic systems, vibration of hysteretic systems and the recently investigated sound quality control based on auditory Roughness are examples of such situations. This paper presents an active control scheme which features the independent controlling of the amplitude and/or relative phase of a number of harmonic components of disturbances such as the internal combustion engine noise. A delayless, frequency-domain approach based on time-domain algorithms such as the PSC-FxLMS and the NEX-LMS is the core of the control scheme. Also, an algorithm for estimating and resolving slight frequency variations is included into the controller, which guarantees relative phase control of the desired components of the disturbance. The proposed scheme can tackle pure harmonic-level problems (e. g. Loudness) as well as more complex multi-harmonic problems (e. g. Auditory Roughness) thus presenting a complete sound quality control system that is capable of exploring a wide range of possibilities in vehicle sound design. Computer simulations are conducted to demonstrate the capabilities of the adaptive control algorithm.

Research paper thumbnail of Frequency-Domain Delayless Adaptive Control for Roughness

In previous works in the field of Active Noise Control (ANC) applied to passenger car cavities, i... more In previous works in the field of Active Noise Control (ANC) applied to passenger car cavities, it has been shown that the psychoacoustic metric known as Loudness can be modified in a rather efficient manner, influencing the internal sound field and overall vehicle perception. In that sense, engine orders can be controlled either to have their amplitudes increase or decrease, which directly affects Loudness and might also indirectly influence other sound quality attributes. A rather important metric that should be targeted whenever engine noise is concerned, is Roughness. This paper aims at demonstrating that Roughness can be modified by means of an ANC system that changes amplitude and/or phase of certain engine orders, leading to the desired noise attributes targeted at the vehicle´s conceptual design phase. The proposed control scheme is implemented in the frequency domains with the aid of the Fx-LMS and also inspired in some recent developments such as the PSC-FxLMS and the NEX-LMS. The proposed frequency-domain active controller can tackle pure harmonic-level problems as well as more complex multi-harmonic problems thus presenting a complete sound quality control system that is able to explore a wide range of design possibilities in vehicle sound.

Research paper thumbnail of An experimental analysis on the characteristics of a dynamic struc-ture for the study of multiphase flow-induced vibrations in tube bun-dles

Research paper thumbnail of Customized Road TPA to Improve Vehicle Sensitivity to Rumble Noise from Tires/Wheels Lateral Forces

Research paper thumbnail of Design and Analysis of a Dynamic Structure for the Study of Multiphase Flow Induced Vibration

Flow-Induced Vibration (FIV) in tube bundles is an important issue in the design of heat exchange... more Flow-Induced Vibration (FIV) in tube bundles is an important issue in the design of heat exchangers, due to the potential damage that may result from it. Many test benches have been constructed to study the flow-structure interactions that occur in those equipments, however, some vibration mechanisms, mostly those related to multiphase flow, are not yet fully understood. Therefore, in this work, the design and analysis of a dynamic device consisting of an instrumented flexibly suspended tube for the study of the FIV are presented. The function of this system is to allow the suspended tube to vibrate under the excitation of multiphase flow, as part of a tube bundle test bench that represents a steam generator of a nuclear plant. Several suspension devices used in FIV studies have been reviewed as well as academic and real systems were considered during the conceptual design phase. Based on the literature review and the particular features of the complete test bench currently under construction, a wire system solution is devised and constructed. This paper also presents some preliminary tests carried out on the dynamic subsystem, aiming at addressing the mode shapes and resonance frequency range provided by the proposed suspension. The results are compared with data of previous FIV experimental studies.

Research paper thumbnail of A Mimo Control Strategy for the Sound Quality of Multi-Harmonic Disturbances Transmitted Into Cavities

Active sound quality control in automotive applications is devised to attain predefined sound qua... more Active sound quality control in automotive applications is devised to attain predefined sound quality perceptions of the engine noise at the driver's head position. Similarly, it can be desirable guaranteeing the same or even other perceptions of the multi-harmonic disturbance in other locations into the cavity, e.g. at the passengers' positions, which implies taking into account the multiple vibroacoustic transfer paths in the design and implementation of a control algorithm. This paper presents a decentralized, multiple-input/multiple-output strategy for controlling the sound quality of multi-harmonic disturbances, based on the amplitude and relative-phase of their narrowband components. Control effort restrictions are required in the single-input, single-output formulation of the SF-cFxLMS algorithm, core of the proposed adaptive control strategy, for keeping the decentralized systems at suitable levels, thus avoiding cross-action effects that could lead to instabilities, when implemented in a MIMO setup. Computer simulations of the proposed algorithm demonstrate the feasibility of simultaneously reaching predefined sound quality perceptions at two locations inside a fictitious cavity, in terms of the assessment of the obtained time histories and relevant psychoacoustic metrics such as Loudness and Roughness, even though when impulsive occurrences could emerge through the operation of the proposed MIMO system.

Research paper thumbnail of Loudness scattering due to vibro-acoustic model variability

The use of numerical simulation in the design and evaluation of products performance is ever incr... more The use of numerical simulation in the design and evaluation of products performance is ever increasing. To a greater extent, such estimates are needed in an early design stage, when physical prototypes are not available. When dealing with vibro-acoustic models, known to be computationally expensive, a question remains, which is related to the accuracy of such models in view of the well-known variability inherent to the mass manufacturing production techniques. In addition, both the academia and industry have recently realized the importance of actually listening to a products sound, either by measurements or by virtual sound synthesis, in order to assess its performance. In this work, the scatter of significant parameter variations on a simplified vehicle vibro-acoustic model is calculated on loudness metrics using Monte Carlo analysis. The mapping from the system parameters to sound quality metric is performed by a fully-coupled vibro-acoustic finite element model. Different loudness metrics are used, including overall sound pressure level expressed in dB and Specific Loudness in Sones. Sound quality equivalent sources are used to excite this model and the sound pressure level at the driver's head position is acquired to be evaluated according to sound quality metrics. No significant variation has been perceived when evaluating the system using regular sound pressure level expressed in dB and dB(A). This happens because of the third-octave filters that average the results under some frequency bands. On the other hand, Zwicker Loudness presents important variations, arguably, due to the masking effects.

Research paper thumbnail of A multi-objective optimization procedure for guilding the active sound quality control of multi-harmonic disturbances in cavities

The refinement of the sound quality of the engine disturbance perceived in vehicle cavities can b... more The refinement of the sound quality of the engine disturbance perceived in vehicle cavities can be accomplished by means of active control algorithms, oriented by psychoacoustic metrics. Loudness, Roughness and Tonality, as the most regarded metrics in designing sound quality targets for low frequency disturbances, are commonly investigated on an individual basis, which leads to tackle one or some of them, while-possibly-degrading the others. This paper contributes to the design and implementation stages of the sound quality for low-frequency, multi-harmonic disturbances by presenting a multi-objective optimization procedure. The optimization tools correspond to the NSGA-II and SPEA-II algorithms, which have been extensively used in the engineering community for solving problems with conflictive objectives, as is the Loudness/Roughness/Tonality case and its combinations by pairs. Both the NSGA-II's and SPEA-II's operators and parameters are selected from the specialized literature. Computer simulations of the SF-cFxLMS control algorithm implemented over a synthesized internal combustion engine disturbance show the feasibility of attaining the obtained Pareto frontier solutions, thus demonstrating a complete method for controlled designing and implementing of sound fields in cavities.

Research paper thumbnail of Transfer Path Analysis of Road Noise: Overview and Customized Approaches for Road Rumble Noise

SAE Technical Paper Series, 2010

Research paper thumbnail of State-of-the-Art Review on Flow Patterns, Superficial Void Fraction and Flow-Induced Vibration During Two-Phase Flows Across Tube Bundles

Volume 2: Fora, 2012

This paper presents a comprehensive review on the open literature concerning two-phase flow acros... more This paper presents a comprehensive review on the open literature concerning two-phase flow across horizontal tube bundles. Initially, experimental studies available in the literature are described in an organized manner. This detailed description includes bundle configurations and the experimental techniques used for evaluating flow patterns, void fraction and flow-induced vibration. Most of studies were performed having air-water as working fluids. Several excitation mechanisms can be reproduced such as flow periodicity, fluid-elasticity and turbulence. Flow patterns are discussed and their predictive methods are compared. Void fraction predictive methods are also discussed and comparisons among them are presented. It was found that the predictive methods worked reasonably well when compared against the databases used during their development. Generally, the studies have obtained bundle average measurements which are not representative of the local conditions and, therefore, are not recommendable to be used as accurate designing tools. Most studies concerning fluid-induced vibration have addressed this problem through simplified bench structures, usually consisting of a single rigid tube over a flexible suspension.

Research paper thumbnail of Effect of parametric uncertainties on the effectiveness of discrete piezoelectric spatial modal filters

Modal filters may be obtained by a weighted sum of the signals of an array of sensors distributed... more Modal filters may be obtained by a weighted sum of the signals of an array of sensors distributed on the host structure. However, the effect of parametric uncertainties on the effectiveness of the modal filter has received little attention. This work presents some numerical and experimental results on the effect of uncertainties of sensor array spatial distribution and weighting coefficients on the modal filtering effectiveness. For that, a free rectangular plate with twelve bonded piezoelectric sensors is considered. The spatial distribution of the array of piezoelectric sensors was optimized in a previous work to improve the effectiveness and frequency range of a set of modal filters. An experimental implementation of the modal filters was performed through a voltage divider and summing amplifier circuits and used to validate the performance of the modal filters. From numerical and experimental analysis, it was noticed, however, that the effectiveness of the modal filters are quite sensitive to the array spatial distribution and weighting coefficients. First, the effect of uncertainties of the array spatial distribution on the output of the modal filters was analyzed numerically using a finite element model. In this case, the main challenge was the cost of function evaluation and, thus, focus was put on solutions for the parameters sampling and approximations using response surface methods. Then, the effect of uncertainties of the weighting coefficients was evaluated using stochastic modeling combined with the measurement of individual responses of piezoelectric sensors. Confidence intervals for the modal filters output were evaluated and compared to experimental results with satisfactory results.

Research paper thumbnail of Active control of engine noise transmitted into cavities: simulation, experimental validation and sound quality assessment

Active control has been proposed as a possible solution to cope with low frequency noise reductio... more Active control has been proposed as a possible solution to cope with low frequency noise reduction in vehicles. Active noise control systems tend to be designed with a target on the sound pressure level reduction. However, the perceived control efficiency for the occupants can be more accurately assessed if psychoacoustic metrics are taken into account. The aim of this paper is to evaluate, numerically and experimentally, the effect of (i) a collocated velocity feedback controller and (ii) an adaptive feedforward controller on the engine sound quality in a vehicle mockup. The simulation scheme is described and experimentally validated. The engine excitation is provided by a sound quality equivalent engine simulator, running on a real-time platform that delivers harmonic excitation in function of the driving condition. The controller performance is evaluated in terms of sound quality metrics such as Roughness, Zwicker-and Specific-Loudness. As a result of the control action, Loudness is significantly reduced while Roughness can either be increased or decreased, depending on the role of the controlled order in the modulation mechanism. Eventually, engine sound quality is improved overall.

Research paper thumbnail of A state-space modeling approach for active structural acoustic control

The demands for improvement in sound quality and reduction of noise generated by vehicles are con... more The demands for improvement in sound quality and reduction of noise generated by vehicles are constantly increasing, as well as the penalties for space and weight of the control solutions. A promising approach to cope with this challenge is the use of active structural-acoustic control. Usually, the low frequency noise is transmitted into the vehicle's cabin through structural paths, which raises the necessity of dealing with vibro-acoustic models. This kind of models should allow the inclusion of sensors and actuators models, if accurate performance indexes are to be accessed. The challenge thus resides in deriving reasonable sized models that integrate structural, acoustic, electrical components and the controller algorithm. The advantages of adequate active control simulation strategies relies on the cost and time reduction in the development phase. Therefore, the aim of this paper is to present a methodology for simulating vibro-acoustic systems including this coupled model in a closed loop control simulation framework that also takes into account the interaction between the system and the control sensors/actuators. It is shown that neglecting the sensor/actuator dynamics can lead to inaccurate performance predictions.

Research paper thumbnail of An Experimental Investigation on the Modal Characteristics of an Off-Road Competition Vehicle Chassis

This paper presents the results of an experimental modal analysis performed on a prototype chassi... more This paper presents the results of an experimental modal analysis performed on a prototype chassis of an off-road competition vehicle. The vehicle was designed by the Mini Baja EESC-USP team for the annual competition promoted by SAE Brasil. The goal of this ...

Research paper thumbnail of On the force drop off phenomenon in shaker testing in experimental modal analysis

The Electrodynamic Vibration Exciter (shakers) has been one of the most employed excitation sourc... more The Electrodynamic Vibration Exciter (shakers) has been one of the most employed excitation sources in modal tests. The shaker is an electromechanical device that provides a mechanical motion due to the input signal sent to its coil. Despite being widely used, it is well known that the shaker interacts with the structure under test. In particular, when the structure passes through a given resonance, the force delivered by the shaker abruptly decreases, causing the so called drop off phenomenon. This paper aims to study this force drop off phenomenon in the single shaker modal testing. Analytical models are developed to help in understanding the physical principles involved in the interaction between the shaker and the structure under test. Experimental analyses are performed using different shakers as well as excitation signals, in order to evaluate the effects of the input signal, as well as the power amplifier operational modes, on the structure dynamics. Preliminary tests revealed that significant distortions might occur during vibration tests using shakers and these distortions significantly affect the determination of the structure response.

Research paper thumbnail of Concurrent mechatronic design approach for active control of cavity noise

Journal of Sound and Vibration, 2008

Active control is a potential solution to many noise and vibration problems for improving the low... more Active control is a potential solution to many noise and vibration problems for improving the low-frequency performance. Cavity noise reduction as encountered for instance in aircraft cabins and vehicle interiors is a typical example. However, the conventional design of these active solutions may lead to suboptimal products, since the interaction between the vibro-acoustic plant dynamics and control dynamics is usually not considered. A proper way to design such active systems would be considering control and plant parameters concurrently. To cope with this approach, a methodology to derive a fully coupled mechatronic model that deals with both the vibro-acoustic plant dynamics as well as the control parameters is proposed. The inclusion of sensor and actuator models is investigated, since it contributes to the model accuracy as it can confer frequency, phase or amplitude limitations to the control performance. The proposed methodology provides a reduced state-space model derived from a fully coupled vibro-acoustic finite element model. Experimental data on a vibro-acoustic vehicle cabin mock-up are used to validate the model reduction procedure. Regarding noise reduction, optimization results are presented considering both vibro-acoustic plant features, such as thicknesses, and control parameters, such as sensor and actuator placement and control gains. A collocated sensor/ actuator pair is considered in a velocity feedback control strategy. The benefits of a concurrent mechatronic design when dealing with active structural-acoustic control solutions are addressed, illustrated and experimentally validated. r

Research paper thumbnail of A state-space modeling approach for active structural acoustic control 1

The demands for improvement in sound quality and reduction of noise generated by vehicles are con... more The demands for improvement in sound quality and reduction of noise generated by vehicles are constantly increasing, as well as the penalties for space and weight of the control solutions. A promising approach to cope with this challenge is the use of active structural-acoustic control. Usually, the low frequency noise is transmitted into the vehicle’s cabin through structural paths, which raises the necessity of dealing with vibro-acoustic models. This kind of models should allow the inclusion of sensors and actuators models, if accurate performance indexes are to be accessed. The challenge thus resides in deriving reasonable sized models that integrate structural, acoustic, electrical components and the controller algorithm. The advantages of adequate active control simulation strategies relies on the cost and time reduction in the development phase. Therefore, the aim of this paper is to present a methodology for simulating vibro-acoustic systems including this coupled model in a...

Research paper thumbnail of On the robustness of a model-based inverse force identification applied on a structure submerged in different media

Journal of the Brazilian Society of Mechanical Sciences and Engineering

This paper addresses an experimental study on the implementation of an Augmented Kalman filter al... more This paper addresses an experimental study on the implementation of an Augmented Kalman filter algorithm complemented by displacement dummy measurements, aiming at identifying a stochastic point force. For this purpose, the present experimental approach features a cantilevered structure instrumented with two pairs of accelerometers. A force sensor is used to measure the actual input force for benchmarking. The main objective of this study is to evaluate the ability of the algorithm to predict forces when the system is perturbed by different fluids surrounding the structure. Firstly, the structure is identified via experimental modal analysis, in two conditions, in air and underwater. Predicted and measured forces, for tests in each media, are compared showing good agreement. Additionally, the method is used to estimate forces applied when the structure is submerged in water while using a system model identified in air, in order to assess the algorithm robustness in scenarios that are either difficult or impossible to be tested. Although results accuracy in such cross-identification conditions depend on the closeness between the reference model and the actual boundary condition, in general, the frequency content of the predicted forces match with those predicted in the direct scheme, allowing qualitative data assessment in an otherwise unfeasible scenario.

Research paper thumbnail of An experimental study on the vibration induced by a two-phase air-water crossflow in a normal triangular tube bundle

Proceedings of the 23rd ABCM International Congress of Mechanical Engineering, 2015

Research paper thumbnail of Multichannel Active Sound Quality Control for Independent-Channel Sound Profiling

Multichannel active noise control algorithms have been proposed to deal with sound propagation in... more Multichannel active noise control algorithms have been proposed to deal with sound propagation in enclosures, which base their operation on sensor/actuator positioning conditions that in some applications could not be easily met. In this paper, we investigate a multichannel active sound quality control algorithm, intended to independently control each sensor position, regardless of the acoustic coupling among channels. The decentralized channels share their adaptive weights among each other, in order to extract the maximum allowed gain that minimizes the cost function at the corresponding error sensor, while keeping distortion at the other error sensors as low as possible. A coupled FE-FE vibro-acoustic model of a scaled vehicle mock-up is used for computer simulations, which properly reproduces acoustic coupling among the error sensors. A pure-sinusoid disturbance is used as the input to the vibroacoustic model, and a 2x2 multichannel algorithm is proposed to independently profile it. Computer simulations demonstrate that, despite of the increased computational burden, as compared with the decentralized leaky-LMS control algorithm, the proposed algorithm is able to deal with the acoustic coupling among the error sensors, thus reaching independent control targets over the disturbance in each error sensor, regardless of their position in an enclosure.

Research paper thumbnail of An adaptive controller for amplitude and relative phase control of periodic disturbance

Most of the active noise and vibration control applications are intended to globally reduce physi... more Most of the active noise and vibration control applications are intended to globally reduce physical quantities such as sound pressure or structural vibration. However, there are other situations where not only through controlling the magnitude but also (or merely) by the relative phase of the components of the periodic disturbance, a system could lead to desired results. Synchronization of chaotic systems, vibration of hysteretic systems and the recently investigated sound quality control based on auditory Roughness are examples of such situations. This paper presents an active control scheme which features the independent controlling of the amplitude and/or relative phase of a number of harmonic components of disturbances such as the internal combustion engine noise. A delayless, frequency-domain approach based on time-domain algorithms such as the PSC-FxLMS and the NEX-LMS is the core of the control scheme. Also, an algorithm for estimating and resolving slight frequency variations is included into the controller, which guarantees relative phase control of the desired components of the disturbance. The proposed scheme can tackle pure harmonic-level problems (e. g. Loudness) as well as more complex multi-harmonic problems (e. g. Auditory Roughness) thus presenting a complete sound quality control system that is capable of exploring a wide range of possibilities in vehicle sound design. Computer simulations are conducted to demonstrate the capabilities of the adaptive control algorithm.

Research paper thumbnail of Frequency-Domain Delayless Adaptive Control for Roughness

In previous works in the field of Active Noise Control (ANC) applied to passenger car cavities, i... more In previous works in the field of Active Noise Control (ANC) applied to passenger car cavities, it has been shown that the psychoacoustic metric known as Loudness can be modified in a rather efficient manner, influencing the internal sound field and overall vehicle perception. In that sense, engine orders can be controlled either to have their amplitudes increase or decrease, which directly affects Loudness and might also indirectly influence other sound quality attributes. A rather important metric that should be targeted whenever engine noise is concerned, is Roughness. This paper aims at demonstrating that Roughness can be modified by means of an ANC system that changes amplitude and/or phase of certain engine orders, leading to the desired noise attributes targeted at the vehicle´s conceptual design phase. The proposed control scheme is implemented in the frequency domains with the aid of the Fx-LMS and also inspired in some recent developments such as the PSC-FxLMS and the NEX-LMS. The proposed frequency-domain active controller can tackle pure harmonic-level problems as well as more complex multi-harmonic problems thus presenting a complete sound quality control system that is able to explore a wide range of design possibilities in vehicle sound.

Research paper thumbnail of An experimental analysis on the characteristics of a dynamic struc-ture for the study of multiphase flow-induced vibrations in tube bun-dles

Research paper thumbnail of Customized Road TPA to Improve Vehicle Sensitivity to Rumble Noise from Tires/Wheels Lateral Forces

Research paper thumbnail of Design and Analysis of a Dynamic Structure for the Study of Multiphase Flow Induced Vibration

Flow-Induced Vibration (FIV) in tube bundles is an important issue in the design of heat exchange... more Flow-Induced Vibration (FIV) in tube bundles is an important issue in the design of heat exchangers, due to the potential damage that may result from it. Many test benches have been constructed to study the flow-structure interactions that occur in those equipments, however, some vibration mechanisms, mostly those related to multiphase flow, are not yet fully understood. Therefore, in this work, the design and analysis of a dynamic device consisting of an instrumented flexibly suspended tube for the study of the FIV are presented. The function of this system is to allow the suspended tube to vibrate under the excitation of multiphase flow, as part of a tube bundle test bench that represents a steam generator of a nuclear plant. Several suspension devices used in FIV studies have been reviewed as well as academic and real systems were considered during the conceptual design phase. Based on the literature review and the particular features of the complete test bench currently under construction, a wire system solution is devised and constructed. This paper also presents some preliminary tests carried out on the dynamic subsystem, aiming at addressing the mode shapes and resonance frequency range provided by the proposed suspension. The results are compared with data of previous FIV experimental studies.

Research paper thumbnail of A Mimo Control Strategy for the Sound Quality of Multi-Harmonic Disturbances Transmitted Into Cavities

Active sound quality control in automotive applications is devised to attain predefined sound qua... more Active sound quality control in automotive applications is devised to attain predefined sound quality perceptions of the engine noise at the driver's head position. Similarly, it can be desirable guaranteeing the same or even other perceptions of the multi-harmonic disturbance in other locations into the cavity, e.g. at the passengers' positions, which implies taking into account the multiple vibroacoustic transfer paths in the design and implementation of a control algorithm. This paper presents a decentralized, multiple-input/multiple-output strategy for controlling the sound quality of multi-harmonic disturbances, based on the amplitude and relative-phase of their narrowband components. Control effort restrictions are required in the single-input, single-output formulation of the SF-cFxLMS algorithm, core of the proposed adaptive control strategy, for keeping the decentralized systems at suitable levels, thus avoiding cross-action effects that could lead to instabilities, when implemented in a MIMO setup. Computer simulations of the proposed algorithm demonstrate the feasibility of simultaneously reaching predefined sound quality perceptions at two locations inside a fictitious cavity, in terms of the assessment of the obtained time histories and relevant psychoacoustic metrics such as Loudness and Roughness, even though when impulsive occurrences could emerge through the operation of the proposed MIMO system.

Research paper thumbnail of Loudness scattering due to vibro-acoustic model variability

The use of numerical simulation in the design and evaluation of products performance is ever incr... more The use of numerical simulation in the design and evaluation of products performance is ever increasing. To a greater extent, such estimates are needed in an early design stage, when physical prototypes are not available. When dealing with vibro-acoustic models, known to be computationally expensive, a question remains, which is related to the accuracy of such models in view of the well-known variability inherent to the mass manufacturing production techniques. In addition, both the academia and industry have recently realized the importance of actually listening to a products sound, either by measurements or by virtual sound synthesis, in order to assess its performance. In this work, the scatter of significant parameter variations on a simplified vehicle vibro-acoustic model is calculated on loudness metrics using Monte Carlo analysis. The mapping from the system parameters to sound quality metric is performed by a fully-coupled vibro-acoustic finite element model. Different loudness metrics are used, including overall sound pressure level expressed in dB and Specific Loudness in Sones. Sound quality equivalent sources are used to excite this model and the sound pressure level at the driver's head position is acquired to be evaluated according to sound quality metrics. No significant variation has been perceived when evaluating the system using regular sound pressure level expressed in dB and dB(A). This happens because of the third-octave filters that average the results under some frequency bands. On the other hand, Zwicker Loudness presents important variations, arguably, due to the masking effects.

Research paper thumbnail of A multi-objective optimization procedure for guilding the active sound quality control of multi-harmonic disturbances in cavities

The refinement of the sound quality of the engine disturbance perceived in vehicle cavities can b... more The refinement of the sound quality of the engine disturbance perceived in vehicle cavities can be accomplished by means of active control algorithms, oriented by psychoacoustic metrics. Loudness, Roughness and Tonality, as the most regarded metrics in designing sound quality targets for low frequency disturbances, are commonly investigated on an individual basis, which leads to tackle one or some of them, while-possibly-degrading the others. This paper contributes to the design and implementation stages of the sound quality for low-frequency, multi-harmonic disturbances by presenting a multi-objective optimization procedure. The optimization tools correspond to the NSGA-II and SPEA-II algorithms, which have been extensively used in the engineering community for solving problems with conflictive objectives, as is the Loudness/Roughness/Tonality case and its combinations by pairs. Both the NSGA-II's and SPEA-II's operators and parameters are selected from the specialized literature. Computer simulations of the SF-cFxLMS control algorithm implemented over a synthesized internal combustion engine disturbance show the feasibility of attaining the obtained Pareto frontier solutions, thus demonstrating a complete method for controlled designing and implementing of sound fields in cavities.

Research paper thumbnail of Transfer Path Analysis of Road Noise: Overview and Customized Approaches for Road Rumble Noise

SAE Technical Paper Series, 2010

Research paper thumbnail of State-of-the-Art Review on Flow Patterns, Superficial Void Fraction and Flow-Induced Vibration During Two-Phase Flows Across Tube Bundles

Volume 2: Fora, 2012

This paper presents a comprehensive review on the open literature concerning two-phase flow acros... more This paper presents a comprehensive review on the open literature concerning two-phase flow across horizontal tube bundles. Initially, experimental studies available in the literature are described in an organized manner. This detailed description includes bundle configurations and the experimental techniques used for evaluating flow patterns, void fraction and flow-induced vibration. Most of studies were performed having air-water as working fluids. Several excitation mechanisms can be reproduced such as flow periodicity, fluid-elasticity and turbulence. Flow patterns are discussed and their predictive methods are compared. Void fraction predictive methods are also discussed and comparisons among them are presented. It was found that the predictive methods worked reasonably well when compared against the databases used during their development. Generally, the studies have obtained bundle average measurements which are not representative of the local conditions and, therefore, are not recommendable to be used as accurate designing tools. Most studies concerning fluid-induced vibration have addressed this problem through simplified bench structures, usually consisting of a single rigid tube over a flexible suspension.

Research paper thumbnail of Effect of parametric uncertainties on the effectiveness of discrete piezoelectric spatial modal filters

Modal filters may be obtained by a weighted sum of the signals of an array of sensors distributed... more Modal filters may be obtained by a weighted sum of the signals of an array of sensors distributed on the host structure. However, the effect of parametric uncertainties on the effectiveness of the modal filter has received little attention. This work presents some numerical and experimental results on the effect of uncertainties of sensor array spatial distribution and weighting coefficients on the modal filtering effectiveness. For that, a free rectangular plate with twelve bonded piezoelectric sensors is considered. The spatial distribution of the array of piezoelectric sensors was optimized in a previous work to improve the effectiveness and frequency range of a set of modal filters. An experimental implementation of the modal filters was performed through a voltage divider and summing amplifier circuits and used to validate the performance of the modal filters. From numerical and experimental analysis, it was noticed, however, that the effectiveness of the modal filters are quite sensitive to the array spatial distribution and weighting coefficients. First, the effect of uncertainties of the array spatial distribution on the output of the modal filters was analyzed numerically using a finite element model. In this case, the main challenge was the cost of function evaluation and, thus, focus was put on solutions for the parameters sampling and approximations using response surface methods. Then, the effect of uncertainties of the weighting coefficients was evaluated using stochastic modeling combined with the measurement of individual responses of piezoelectric sensors. Confidence intervals for the modal filters output were evaluated and compared to experimental results with satisfactory results.

Research paper thumbnail of Active control of engine noise transmitted into cavities: simulation, experimental validation and sound quality assessment

Active control has been proposed as a possible solution to cope with low frequency noise reductio... more Active control has been proposed as a possible solution to cope with low frequency noise reduction in vehicles. Active noise control systems tend to be designed with a target on the sound pressure level reduction. However, the perceived control efficiency for the occupants can be more accurately assessed if psychoacoustic metrics are taken into account. The aim of this paper is to evaluate, numerically and experimentally, the effect of (i) a collocated velocity feedback controller and (ii) an adaptive feedforward controller on the engine sound quality in a vehicle mockup. The simulation scheme is described and experimentally validated. The engine excitation is provided by a sound quality equivalent engine simulator, running on a real-time platform that delivers harmonic excitation in function of the driving condition. The controller performance is evaluated in terms of sound quality metrics such as Roughness, Zwicker-and Specific-Loudness. As a result of the control action, Loudness is significantly reduced while Roughness can either be increased or decreased, depending on the role of the controlled order in the modulation mechanism. Eventually, engine sound quality is improved overall.

Research paper thumbnail of A state-space modeling approach for active structural acoustic control

The demands for improvement in sound quality and reduction of noise generated by vehicles are con... more The demands for improvement in sound quality and reduction of noise generated by vehicles are constantly increasing, as well as the penalties for space and weight of the control solutions. A promising approach to cope with this challenge is the use of active structural-acoustic control. Usually, the low frequency noise is transmitted into the vehicle's cabin through structural paths, which raises the necessity of dealing with vibro-acoustic models. This kind of models should allow the inclusion of sensors and actuators models, if accurate performance indexes are to be accessed. The challenge thus resides in deriving reasonable sized models that integrate structural, acoustic, electrical components and the controller algorithm. The advantages of adequate active control simulation strategies relies on the cost and time reduction in the development phase. Therefore, the aim of this paper is to present a methodology for simulating vibro-acoustic systems including this coupled model in a closed loop control simulation framework that also takes into account the interaction between the system and the control sensors/actuators. It is shown that neglecting the sensor/actuator dynamics can lead to inaccurate performance predictions.

Research paper thumbnail of An Experimental Investigation on the Modal Characteristics of an Off-Road Competition Vehicle Chassis

This paper presents the results of an experimental modal analysis performed on a prototype chassi... more This paper presents the results of an experimental modal analysis performed on a prototype chassis of an off-road competition vehicle. The vehicle was designed by the Mini Baja EESC-USP team for the annual competition promoted by SAE Brasil. The goal of this ...

Research paper thumbnail of On the force drop off phenomenon in shaker testing in experimental modal analysis

The Electrodynamic Vibration Exciter (shakers) has been one of the most employed excitation sourc... more The Electrodynamic Vibration Exciter (shakers) has been one of the most employed excitation sources in modal tests. The shaker is an electromechanical device that provides a mechanical motion due to the input signal sent to its coil. Despite being widely used, it is well known that the shaker interacts with the structure under test. In particular, when the structure passes through a given resonance, the force delivered by the shaker abruptly decreases, causing the so called drop off phenomenon. This paper aims to study this force drop off phenomenon in the single shaker modal testing. Analytical models are developed to help in understanding the physical principles involved in the interaction between the shaker and the structure under test. Experimental analyses are performed using different shakers as well as excitation signals, in order to evaluate the effects of the input signal, as well as the power amplifier operational modes, on the structure dynamics. Preliminary tests revealed that significant distortions might occur during vibration tests using shakers and these distortions significantly affect the determination of the structure response.

Research paper thumbnail of Concurrent mechatronic design approach for active control of cavity noise

Journal of Sound and Vibration, 2008

Active control is a potential solution to many noise and vibration problems for improving the low... more Active control is a potential solution to many noise and vibration problems for improving the low-frequency performance. Cavity noise reduction as encountered for instance in aircraft cabins and vehicle interiors is a typical example. However, the conventional design of these active solutions may lead to suboptimal products, since the interaction between the vibro-acoustic plant dynamics and control dynamics is usually not considered. A proper way to design such active systems would be considering control and plant parameters concurrently. To cope with this approach, a methodology to derive a fully coupled mechatronic model that deals with both the vibro-acoustic plant dynamics as well as the control parameters is proposed. The inclusion of sensor and actuator models is investigated, since it contributes to the model accuracy as it can confer frequency, phase or amplitude limitations to the control performance. The proposed methodology provides a reduced state-space model derived from a fully coupled vibro-acoustic finite element model. Experimental data on a vibro-acoustic vehicle cabin mock-up are used to validate the model reduction procedure. Regarding noise reduction, optimization results are presented considering both vibro-acoustic plant features, such as thicknesses, and control parameters, such as sensor and actuator placement and control gains. A collocated sensor/ actuator pair is considered in a velocity feedback control strategy. The benefits of a concurrent mechatronic design when dealing with active structural-acoustic control solutions are addressed, illustrated and experimentally validated. r