Damping of the loose spring skirt (LSS) of a vibrating pipe under operating conditions was studie... more Damping of the loose spring skirt (LSS) of a vibrating pipe under operating conditions was studied experimentally and numerically. Motion images made using a high speed charge-coupled device (CCD) camera as well as acceleration signals were analyzed in order to correlate the physical states of the LSS pipe system with the vibration transmissibility (TM) through the pipe. Experiments on the pipe undergoing harmonic excitation demonstrate that the damping of the LSS is caused by the same mechanism as with a conventional impact damper. Measurements of the acceleration TM as a function of excitation amplitude verified that the momentum exchange between the pipe and the auxiliary spring is the cause of the damping produced by the LSS pipe. Another finding of this research is that the experimental representation of the resonance shift phenomenon is related to two main operating conditions, namely: 1) the driving frequency and 2) the excitation amplitude. This research demonstrated the occurrence of the resonance shift phenomenon through experimental mapping of the system response at increasing excitation amplitudes using frequency sweep tests. Simulations of the LSS pipe system based on principal coordinate and impact damping analysis were performed in order to investigate and provide better explanations for LSS pipe system damping mechanisms. As a result of this research study, a new damping mechanism is proposed which is different from previous damping models. This research study has also addressed more practical boundary and excitation conditions for LSS pipe systems.
This paper presents the topology optimization of thin plate structures with bending stress constr... more This paper presents the topology optimization of thin plate structures with bending stress constraints. To avoid the stress singularity phenomena, the qp-relaxation is used for local stress interpolation. The local stress constraints are aggregated into a single global constraint based on the p-norm stress measure. The framework of the topology optimization is constructed using the commercial finite element software ANSYS. In the presented work, the volume of the structure is minimized with the global stress constraint. Numerical examples are demonstrated to validate the proposed topology optimization method.
In this paper, we propose horizontal active noise control (ANC) using two-dimensional wave field ... more In this paper, we propose horizontal active noise control (ANC) using two-dimensional wave field information alone. By reducing the control space to a horizontal plane, the number of microphones and speakers was considerably reduced compared with ANC systems using three-dimensional wave field information. The radii of the reference, microphone, and loudspeaker array were determined based on the wave field reproduction error. Accordingly, the simulation and experimental results of the proposed ANC system were presented based on the use of five microphones and loudspeakers using conventional ANC algorithms. Overall, an average noise reduction of 20 dB was observed inside the microphone array with a radius of 0.5 m for tonal noise at 200 Hz. This performance is acceptable with a drastically reduced number of microphones and speakers. The findings of this study, along with further research conducted in a reverberant room, represent a significant contribution to global ANC commercializat...
Optimizing a distribution of resonators on a thin plate for the desired sound radiation
Journal of Sound and Vibration, 2020
Abstract The periodic distribution of mechanical resonators on a thin plate has been studied to i... more Abstract The periodic distribution of mechanical resonators on a thin plate has been studied to improve panel loudspeakers by exploiting the band gap phenomenon (BG), effectively forbidding vibrational modes in certain frequency ranges. Here, we present an optimization procedure to determine the distribution with a minimized number of resonators while achieving the desired sound radiation. A thin aluminum plate with periodic resonators is considered to open a BG from 355 Hz to 710 Hz, which covers an octave band. The structure is modeled using the finite element method. Each resonator is parameterized with a topological design variable, which represents the absence and presence of the resonator. Numerical examples are presented to demonstrate the optimization for the design of a defect and removing ineffective resonators to obtain the desired sound radiation. Experimental validations show good agreement with the numerical results in terms of spectral smoothness and spatial uniformity of sound radiation. In this case, the overall SPL is amplified by 10 dB, and the standard deviation is reduced by 5 dB by comparison with a bare plate.
Personal audio provides an independent sound space that can reduce auditory disturbances by creat... more Personal audio provides an independent sound space that can reduce auditory disturbances by creating a listening zone with the desired sound field and a quiet zone with a low sound pressure level (SPL). The performance of personal audio is assessed based on the difference in SPL between the listening and quiet zones as well as the accuracy of sound reproduction in the listening zone. There is a tradeoff relationship between the two performances, and the required performance depends on the usage environment and user preferences. Therefore, the performance of personal audio needs to be adjusted based on the user's evaluation. This paper describes the development of a personal audio performance controller. A performance controller should vary the performance of personal audio based on user feedback in real-time. In addition, it should be possible to fine-tune the performance, and the performance can vary linearly with respect to user inputs. To satisfy these conditions, the source weight traces of the loudspeaker array are modeled as simple and continuous functions that employ piecewise linear approximations, based on the change in performance. As a result, the performance changes for user input are made efficient, continuous, and linear. The proposed personal audio performance controller is verified using numerical simulations and experiments.
Personal audio provides an independent sound space that can reduce auditory disturbances by creat... more Personal audio provides an independent sound space that can reduce auditory disturbances by creating a listening zone with the desired sound field and a quiet zone with a low sound pressure level (SPL). The performance of personal audio is assessed based on the difference in SPL between the listening and quiet zones as well as the accuracy of sound reproduction in the listening zone. There is a tradeoff relationship between the two performances, and the required performance depends on the usage environment and user preferences. Therefore, the performance of personal audio needs to be adjusted based on the user's evaluation. This paper describes the development of a personal audio performance controller. A performance controller should vary the performance of personal audio based on user feedback in real-time. In addition, it should be possible to fine-tune the performance, and the performance can vary linearly with respect to user inputs. To satisfy these conditions, the source weight traces of the loudspeaker array are modeled as simple and continuous functions that employ piecewise linear approximations, based on the change in performance. As a result, the performance changes for user input are made efficient, continuous, and linear. The proposed personal audio performance controller is verified using numerical simulations and experiments.
A refrigerator consumes 20~40% of the total electric energy in a house. And most of the electrici... more A refrigerator consumes 20~40% of the total electric energy in a house. And most of the electricity in the refrigerator is consumed for operating the compressor. Therefore, developing a high efficiency compressor is necessary to increase the energy efficiency. To increase the efficiency of the linear motor, a new linear motor design with a reduced electrical loss is needed. Also, the loss analysis is preceded to design the linear motor having higher efficiency. In this paper, the iron loss analysis is implemented by using the analytical and numerical methods. The iron loss analysis of the linear motor is performed by using ANSYS, the commercial FEA tool and tested iron loss curve made by the manufacturer. The proposed methods are applied to the iron loss analysis of the linear motor. For the validation of the iron loss analysis result, the experiment measuring the iron loss of the linear motor is performed and this result is compared with that of ion loss analysis result.
Development of the Design Process for Laser Scanned Model
Recent engineering process requires fast development and manufacturing of the products. This pape... more Recent engineering process requires fast development and manufacturing of the products. This paper mainly discusses the process of rapid product development (RPD) from the reverse engineering to the optimal design. A laser scanning system scans a product and the efficient data processing method reduces the scanned point data. The reduced (scanned) points model is transformed to a finite element model without the construction of a CAD model. Since CAD modeling is a time-consuming work, skipping this step can save much time. This FE model is updated from the result based on the structural characteristics from modal test of the real model. For FE model updating, Response Surface Method is adopted. Finally, the updated FE model is optimized using the reliability-based topology optimization, which is developed recently. All these processes are applied to the design of an upper part model of a cellular phone.
Generally, it is time consuming to confirm operating deflection shape or modeshape of a structure... more Generally, it is time consuming to confirm operating deflection shape or modeshape of a structure by experiment. In order to overcome this problem, recently, a researcher proposed Hilbert Huang Transform (HHT) technique to extract modeshape from the measurement which continuously measures vibration of an interesting region of a structure with noncontact laser sensor. In this previous research, however, two technical processes were required before applying HHT to obtain un-damped impulse response for each mode. The purpose of this study is to improve and complement the previous research; modal analysis approach is adapted to obtain an accurate un-damped impulse response of each mode for continuous measurement instead of using the two technical processes. For this purpose, Frequency Response Functions (FRFs) for each type of beam are derived, hence, making it possible to measure continuous measurement in a straight profile. In this process, technical limitation and drawback of the pro...
We present a method to design noise barriers with acoustic topology optimization by considering t... more We present a method to design noise barriers with acoustic topology optimization by considering the Zwicker’s Loudness around the barrier. The main objective of this research is to minimize the main specific loudness of target critical band by optimizing distribution of absorbing and reflecting material of noise barriers by formulating an acoustical topology optimization problem. The Helmholtz equation modeling the wave propagation is solved using finite element method. The sensitivity is calculated using adjoint variable method and chain rule. The method supposes given source and receiver position and the calculation provides an optimal design for the barrier to reduce the Zwicker’s Loudness at receiver point over a critical band. Different examples are presented to estimate the influence of the sources and receiver positions. A reduction of the loudness when using optimized barriers is achieved compared to utilizing conventional noise barriers.
Bandgap refers to a frequency band where free waves do not propagate. One of the characteristics ... more Bandgap refers to a frequency band where free waves do not propagate. One of the characteristics of a bandgap is its ability to block the propagation of bending waves in a specific frequency band with a periodic structure. Additionally, it has been reported in previous studies that the vibration-reduction performance of a bandgap is superior to that of other reduction methods. A bandgap can be generated in various frequency bands through a simple parameter change in the unit structure. However, the bandgap for a desired frequency band can be determined accurately only with intensive simulations. To overcome this limitation, we have mathematically derived the bandgap using a serpentine spring as a unit structure. The bandgap equation is derived from the general mass–spring system and the final bandgap is derived by substituting the system into the serpentine resonator. The error map for the major design parameter is confirmed by comparing the derived bandgap with the simulation resul...
An optimal filter design method for a virtual mechanical impedance (VMI) control system is presen... more An optimal filter design method for a virtual mechanical impedance (VMI) control system is presented in this report. Existing passive methods for reducing machinery noise have limited applications because of weight reduction, cooling, and appearance problems. The VMI control method, which does not require a sensor and can be implemented using a small number of actuators, is an active approach that can be used to replace passive methods when mechanical tuning is difficult. However, VMI control methods can only reduce single-tone noise. In this regard, we improved the VMI control system to reduce the radiated sound power of the enclosure panel at multiple frequencies. To achieve this, we propose an optimal filter design method for a multichannel feedback controller. Unlike conventional VMI control, the presented technique is capable of multifrequency control and considers the radiation efficiency, damping, and estimates the errors of the structural-acoustic system. The controller designed using the proposed method satisfies the required robustness and minimum steady-state error in the target frequency band. Thus, this filter design method facilitates the quantitative determination of several criteria that are needed to evaluate system parameter changes such as radiation efficiency, damping, and estimation error, which are overlooked in a standard active structural acoustic controller. The results obtained using a finite element-based model and experimental investigations show that the radiated sound power of the enclosure panel is reduced at multiple target frequencies after the implementation of control. INDEX TERMS Virtual mechanical impedance control, multichannel feedback controller, multifrequency, enclosure panel, radiated sound power.
This paper presents a new approach regarding both magnetic and thermal characteristics associated... more This paper presents a new approach regarding both magnetic and thermal characteristics associated with design of a scroll compressor that is the low-pressure type. In the scroll compressor, the single-phase induction motor (SPIM) does not only play a role of source for dynamic force, but also generates high heat exerting negative influence on both lifetime and performance. Thus, it is necessary to design the scroll compressor considering two physical disciplines in order to improve the performance and to be protected against overheating. In this paper, firstly, numerical analysis of electromagnetic field is carried out by the nonlinear transient finite element method (FEM). Secondly, the linear static FEA of magneto-thermal field is implemented by applying source current computed by the nonlinear transient analysis. FE results are validated in terms of electromagnetics and heat transfer by experiments. And then, the pseudo-transient topology optimization using a multi-objective function is performed.
A design sensitivity formulation of Zwicker’s loudness is presented using the adjoint variable me... more A design sensitivity formulation of Zwicker’s loudness is presented using the adjoint variable method (AVM). The dynamic behaviour of a structure is analyzed by the frequency-response method. Acoustic pressure radiated from the vibrating structure is obtained by the Boundary Element Method (BEM). The global acoustic sensitivity is calculated using AVM, and the sensitivity of main specific loudness with respect to the design variables is obtained using the chain rule. The proposed sensitivity result is compared to finite difference sensitivity. It turned out that the computational time for calculating sensitivity is extremely reduced, and the sensitivity result is similar to the result of the finite difference method.
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