Double Panel System Research Articles

Vibro-acoustic coupling analysis of dynamic performance of the double panel system with mechanical links

The theoretical prediction model for the dynamic performance of a double panel system that takes into account the effect of mechanical links is developed in this paper. The double panel system is established considering both the vibro-acoustic coupling and the effect of the mechanical links between two flexible panels. Firstly, the modal characteristics of the double panel system are analyzed and compared with the results calculated by the finite element method. The accuracy and efficiency of the proposed model have been validated. Subsequently, the forced response of the double panel system under different external excitations is studied. It is shown that the mechanical link resulted in less response level of the double panel system in in low frequency range due to the structural path in the energy transmission of the double panel system. Finally, the effect of the mechanical link parameters on the dynamic performance of the double panel system is discussed. The results reveal that the stiffness coefficients, location distributions, and number of mechanical links can significantly influence the dynamic behavior of the double panel system. Therefore, the theoretical model can be used in optimization techniques to improve the sound transmission characteristics of the double panel system.

The sound of sustainable structures: Acoustic considerations for mass timber

The use of mass timber in multi-family and commercial buildings poses a range of challenges for acoustic designers, due in part to its recent emergence as a structural technology and relative light weight compared to concrete. The spectral performance of mass timber assemblies differs from that of concrete and of lightweight double-panel systems, such as timber joist floors, even when comparing assemblies with the same single-number airborne and impact sound transmission ratings. Due to the inclusion of mass toppings and damping layers, mass timber floor designs may outperform lightweight double-panel systems at low frequencies, but they are often challenged at mid to high frequencies, resulting in a sound spectrum that differs from established “acoustically acceptable” benchmarks. This study presents initial findings from listening sessions conducted in the Arup SoundLab, as well as various design strategies to balance performance, cost, aesthetics, and sustainability.

An efficient model order reduction of frequency-dependent double panel systems

This paper treats a typical industrial vibroacoustic problem, consisting of a double panel under forced vibration which radiates to the far-field. A finite element model is proposed, where both structural links and porous material are represented as equivalent models. The addition of frequency-dependent elements, as mechanical links and porous material in the cavity, leads to a balance between airborne and structural-borne transmission through panels in the mid-frequency range, which demands a suitable model to represent these phenomena. In order to cope with such large-scale models, a dedicated parametric model order reduction is proposed. The frequency-dependent terms are separated from the system matrices, allowing an offline reduction of the system. The Second-Order Arnoldi procedure is employed to calculate the reduced bases at multiple frequencies, chosen by a rational interpolation scheme. The expansion frequencies are selected by a novel adaptive windowing algorithm, which aims at minimizing the number of frequencies within the frequency range. The proposed approach has shown to be effective in reducing significantly the computational time while maintaining precision compared to the direct method.

Analytical Modelling of Sound Transmission Through Finite Clamped Double-Wall Panels with Magnetic-Linked Stiffness

A theoretical modelling approach is proposed for the vibroacoustic problem of sound transmission across a rectangular double-wall panel clamp mounted on an infinite rigid baffle with magnetically connected stiffness. The magnetic stiffness is derived based on interaction energy between the two rectangular magnets attached to the clamped plates. The exact solution for the vibration of the clamped double plates is taken into account by the method of modal function, and the dynamic response of the structures is obtained by employing the weighted residual (Galerkin) method. This method enabled the coupling of the acoustic and the magnetic stiffness of the link to be done effectively. The accuracy of the theoretical predictions is checked against existing experimental data, with good agreement achieved. The model is then compared with the theoretical formulation in a duct based on a low-frequency range with and without magnetic stiffness. The sound transmission loss (STL) of the two models agrees perfectly in the first resonance, but the mass–air–mass resonance frequency for the current model tends to shift towards a higher value. Furthermore, the influence of magnetic stiffness on the elevation angle and azimuth angle of the STL is investigated. The present method is suitable for double-panel systems with connecting stiffness for practical plates and is applicable for both low- and high-frequency ranges.

Active control of turbulent boundary layer sound transmission into a vehicle interior

In high speed automotive, aerospace, and railway transportation, the turbulent boundary layer (TBL) is one of the most important sources of interior noise. The stochastic pressure distribution associated with the turbulence is able to excite significantly structural vibration of vehicle exterior panels. They radiate sound into the vehicle through the interior panels. Therefore, the air flow noise becomes very influential when it comes to the noise vibration and harshness assessment of a vehicle, in particular at low frequencies. Normally, passive solutions, such as sound absorbing materials, are used for reducing the TBL-induced noise transmission into a vehicle interior, which generally improve the structure sound isolation performance. These can achieve excellent isolation performance at higher frequencies, but are unable to deal with the low-frequency interior noise components. In this paper, active control of TBL noise transmission through an acoustically coupled double panel system into a rectangular cavity is examined theoretically. The Corcos model of the TBL pressure distribution is used to model the disturbance. The disturbance is rejected by an active vibration isolation unit reacting between the exterior and the interior panels. Significant reductions of the low-frequency vibrations of the interior panel and the sound pressure in the cavity are observed.

Causal feedforward control of a stochastically excited fuselage structure with active sidewall panel.

This paper provides experimental results of an aircraft-relevant double panel structure mounted in a sound transmission loss facility. The primary structure of the double panel system is excited either by a stochastic point force or by a diffuse sound field synthesized in the reverberation room of the transmission loss facility. The secondary structure, which is connected to the frames of the primary structure, is augmented by actuators and sensors implementing an active feedforward control system. Special emphasis is placed on the causality of the active feedforward control system and its implications on the disturbance rejection at the error sensors. The coherence of the sensor signals is analyzed for the two different disturbance excitations. Experimental results are presented regarding the causality, coherence, and disturbance rejection of the active feedforward control system. Furthermore, the sound transmission loss of the double panel system is evaluated for different configurations of the active system. A principal result of this work is the evidence that it is possible to strongly influence the transmission of stochastic disturbance sources through double panel configurations by means of an active feedforward control system.

Performance of active feedforward control systems in non-ideal, synthesized diffuse sound fields.

The acoustic performance of passive or active panel structures is usually tested in sound transmission loss facilities. A reverberant sending room, equipped with one or a number of independent sound sources, is used to generate a diffuse sound field excitation which acts as a disturbance source on the structure under investigation. The spatial correlation and coherence of such a synthesized non-ideal diffuse-sound-field excitation, however, might deviate significantly from the ideal case. This has consequences for the operation of an active feedforward control system which heavily relies on the acquisition of coherent disturbance source information. This work, therefore, evaluates the spatial correlation and coherence of ideal and non-ideal diffuse sound fields and considers the implications on the performance of a feedforward control system. The system under consideration is an aircraft-typical double panel system, equipped with an active sidewall panel (lining), which is realized in a transmission loss facility. Experimental results for different numbers of sound sources in the reverberation room are compared to simulation results of a comparable generic double panel system excited by an ideal diffuse sound field. It is shown that the number of statistically independent noise sources acting on the primary structure of the double panel system depends not only on the type of diffuse sound field but also on the sample lengths of the processed signals. The experimental results show that the number of reference sensors required for a defined control performance exhibits an inverse relationship to control filter length.

VIBRATORY BEHAVIOR OF A DOUBLE PANEL SYSTEM BY THE OPERATIONAL MODAL ANALYSIS

The present study tackles the vibratory behavior of a double panel system by operational modal analysis (OMA) using one of the major techniques of blind source separation (BSS), which is the independent component analysis (ICA). For this purpose, the OMA method and the ICA concept are presented and exploited in order to identify the eigenmodes of a double panel system. Then, results obtained by the OMA technique are presented and compared with those achieved by the modal recombination method. Since a good argument is observed, this approach can be used in conjunction with experimental works.

A study on the characteristic behavior of mass inclusions added to a poro-elastic layer

Heterogeneous (HG) blankets consist of a layer of poro-elastic media with small embedded masses that replicate the behavior of a distributed mass–spring–damper system. The concept of an HG blanket used to control the sound transmission through an aircraft double-panel system has already been developed and cited in the present literature. However, deficiencies in methodical property control exist; therefore, the prime objective of this research is to provide a simple method to predict and control material properties of the heterogeneous blankets through alteration of mass and stiffness parameters. Mass inclusion size, shape, and placement were varied. If optimized heterogeneous (HG) blankets targeted to specific applications are to be successfully developed, control of these parameters is necessary. This research offers a detailed analysis of the behavior of the mass inclusions, highlighting controlled stiffness variation of the mass–spring–damper systems inside the HG blanket. Characteristic parameters of the HG blanket like the “footprint,” “effective area,” and the “mass interaction distance” are defined and confirmed through mathematical calculations and experimental results. A novel, empirical approach to predict the natural frequency of different mass shapes embedded in porous media was derived and experimentally verified for many different types of porous media, including melamine foam, polyurethane, and polyamide. A maximum error of 8% existed for all the predictions made in this document.

Validation of a polyimide foam model for use in transmission loss applications.

In this paper, the use of polyimide foam as a lining in double panel applications is considered. Polyimide foam has a number of attractive functional attributes, not the least of which is its high fire resistance, thus making its use desirable in some sound transmission applications. The configuration studied here consisted of two 0.04×94 thick, flat aluminum panels separated by 5 in., with a 3 in. thick layer of foam centered in that space. Random incidence transmission loss measurements were conducted on this buildup, and conventional poro-elastic models were used to predict the performance of the lining material. The Biot parameters of the foam were determined by a combination of direct measurement (for density, flow resistivity and Young’s modulus) and inverse characterization procedures (for porosity, tortuosity, viscous and thermal characteristic length, Poisson’s ratio, and loss factor). The inverse characterization procedure involved matching normal incidence standing wave tube measurements of absorption coefficient and transmission loss of the isolated foam with finite element predictions. When the foam parameters determined in this way were used to predict the performance of the complete double panel system, reasonable agreement between the measured transmission loss and predictions made using commercial statistical energy analysis codes was obtained.

Formula omitted] and [formula omitted] feedforward and feedback compensators for acoustic isolation

This paper investigates through numerical simulations the limits of performance for a class of feedforward and feedback compensators used for structural acoustic isolation, where the emphasis is on controlling the structural vibration that is responsible for the sound radiation. The proposed designs aim to attenuate the sound pressure transmitted through a double panel system filled with absorption material. The controller must reduce the noise radiated through the back panel when the front panel is excited by an external force that causes structural vibration. A point moment simulating a piezoelectric patch attached to the back panel is the actuator. In the feedforward setting, the pre-filter assumes full information of the exogenous disturbance. On the other hand, the feedback designs assume full information of the state. The H 2 and H ∞ norms are the optimality criteria used for both the filter design and the control design. All four designs are cast in the linear matrix inequality framework and incorporate parametric uncertainties described by a bounded convex polyhedral domain. It is shown that the performance of the feedforward and the feedback compensators are equivalent when model uncertainties are not taken into account. Otherwise, considering uncertainties, the feedback compensators have a more robust behavior.

Increase in transmission loss of a double panel system by addition of mass inclusions to a poro-elastic layer: A comparison between theory and experiment

This paper is concerned with the modeling and optimization of heterogeneous (HG) blankets, which are used in this investigation to reduce the sound transmission through double panel systems. HG blankets consist of poro-elastic media with small embedded masses, which act similarly to a distributed mass–spring–damper-system. HG blankets have shown significant potential to reduce low frequency radiated sound from structures, where traditional poro-elastic materials have little effect. A mathematical model of a double panel system with an acoustic cavity and HG blanket was developed using impedance and mobility methods. The predicted responses of the source and the receiving panel due to a point force are validated with experimental measurements. The presented results indicate that proper tuning of the HG blankets can result in broadband noise reduction below 500 Hz with less than 10% added mass.

Vibroacoustic behavior of clamp mounted double-panel partition with enclosure air cavity

A theoretical study on the vibroacoustic performance of a rectangular double-panel partition clamp mounted in an infinite acoustic rigid baffle is presented. With the clamped boundary condition taken into account by the method of modal function, a double Fourier series solution to the dynamic response of the structure is obtained by employing the weighted residual method (i.e., the Galerkin method). The double series solution can be considered as the exact solution of the problem, as the structural and acoustic-structural coupling effects are fully accounted for and the solution converges numerically. The accuracy of the theoretical predictions is checked against existing experimental data, with good agreement achieved. The influence of several key parameters on the sound isolation capability of the double-panel configuration is then systematically studied, including panel dimensions, thickness of air cavity, elevation angle, and azimuth angle of incidence sound. The present method is suitable for double-panel systems of finite or infinite extent and is applicable for both low- and high-frequency ranges. With these merits, the proposed method compares favorably with a number of other approaches, e.g., finite element method, boundary element method, and statistical energy analysis method.

Multi‐bay double panel system with heterogeneous blanket treatment: A comparison between theory and experiment

This study is part of an effort to improve the low frequency performance of acoustic blankets used to reduce the noise inside aircraft cabins. This is achieved by embedding small masses inside the poro‐elastic layer such that they act like distributed mass spring damper systems. These mass‐spring‐damper systems can then be designed to reduce the sound transmission through the double panel system at low frequencies where traditional poro‐elastic materials have little effect. A mathematical model of a multi‐bay double panel system with frames, stringers, an acoustic cavity and porous/mass layer was developed using impedance and mobility methods (IMM). The multi‐bay double panel system includes four skin pockets with four HG blankets of different dimensions such that the interaction between the panels can be analyzed. The predicted responses of the source and receiver panel due to a point force are validated with experimental measurements. The results indicate that proper tuning of the mass insertions can improve the broadband noise reduction below 500 Hz with less than 10% added mass without losing the performance of the acoustic foam at high frequencies.

3107 二重壁構造の振動と騒音の統合的能動制御(OS3-4 振動,騒音,乗り心地の制御,OS3 交通・物流システムの制御,オーガナイズド・セッション)

3107 二重壁構造の振動と騒音の統合的能動制御(OS3-4 振動,騒音,乗り心地の制御,OS3 交通・物流システムの制御,オーガナイズド・セッション)

Control of aircraft interior noise using heterogeneous (HG) blankets

This study is concerned with the passive control of vibration and sound radiation of interior cabin noise in aircraft at low frequencies (<500 Hz) using heterogeneous (HG) blankets. HG blankets consist of poroelastic media with small embedded masses, which act similar to a distributed mass-spring-damper system. HG blankets have shown significant potential to reduce low-frequency radiated sound from structures, where traditional poroelastic materials have little effect. A mathematical model of a double panel system with an acoustic cavity and HG blanket was developed using mobility and impedance matrix methods. Theoretical predictions are validated with experimental measurements. Results indicate that proper tuning of the HG blankets can achieve in broadband reductions in sound transmission through the double panel system with less than 10% added mass. Future work includes expanding the model and experiment to multiple panel systems.

Active noise control of a mechanically linked double panel system coupled with an acoustic enclosure

Active control of sound transmission through a mechanically linked double-wall structure into an acoustic enclosure is investigated in this paper. Based on a fully coupled vibro-acoustic model, the effect of mechanical links on the selection of control strategies is studied by examining (a) cavity control using acoustic sources inside the air gap and (b) structural control using structural actuators between the two panels. The relationship between the transmission path and the control strategies is explored. Numerical results show that cavity control can provide good noise attenuation for soft links when acoustic transmitting path dominates, while either structural or cavity controls can be used with the increase of stiffness of links depending on the frequency range of interest. For each case, the dominant control mechanism is examined and the alteration in the structural–acoustic coupling is analyzed to explain the mechanisms of attenuation. The effect of the acoustic mode (0,0,0) on active control of energy transmission is also discussed, giving guidance to choosing the appropriate control arrangement to ensure the maximum control performance.

An analytical and experimental investigation of active structural acoustic control of noise transmission through double panel systems

An analytical and experimental investigation of active control of sound transmission through double panel systems has been performed. The technique used was active structural acoustic control (ASAC) where the control inputs, in the form of piezoelectric actuators, were applied to the structure while the radiating pressure field was minimized. Results verify earlier experimental investigations and indicate the application of control inputs to the radiating panel of the double panel system resulted in greater transmission loss (TL) due to its direct effect on the nature of the structural-acoustic (or radiation) coupling between the radiating panel and the receiving acoustic space. Increased control performance was seen in a double panel system consisting of a stiffer radiating panel due to its lower modal density and also as a result of better impedance matching between the piezoelectric actuator and the radiating plate. In general the results validate the ASAC approach for double panel systems, demonstrating that it is possible to take advantage of double panel system passive behavior to enhance control performance, and provide design guidelines.

Active Control of Structure-Borne and Airborne Sound Transmission Through Double Panel

This paper presents a theoretical study of the active control of both structure-borne and airborne noise transmission through a double-panel system. The physical and geometrical characteristics of the system were chosen to be similarto those of the fuselage of a civil aircraft. The total sound power transmitted by the double-panel system was used to evaluate the active control performance of four different strategies for the control system: e rst, active mounts connecting the two panels and loudspeakers placed between the two panels were driven to minimize the total sound powerradiated by thepanel (thereference case );second, activemounts connecting the two panels were driven to cancel the out-of-plane velocities at the connecting points on the radiating panel; third, loudspeakers placed between the two panels were driven to cancel the acousticpressure at points neareach control loudspeaker; and fourth, active mount and control loudspeaker systems were used simultaneously as already stated. The simulations show that the control loudspeakers are able to produce large attenuation of the sound transmission at low frequencies close to the mass-air-mass resonance of the double panel. The performance is signie cantly better if the loudspeakers are driven to minimize radiated sound power, rather than cancel pressure between the panels. The active mount cone guration studied in this paper does not producesignie cant reductions of the sound transmission except in the case where it is used in combination with the control loudspeakers. I. Introduction

A comparison of active control strategies for the reduction of sound transmission through double panels

A theoretical study of the active isolation of air-borne and structure-borne sound transmission through a double panel system is presented. The reductions in the radiated sound are investigated for three different families of control approaches. The first and the second families are based on the minimization of total sound power radiation or the minimization of the weighted sum of the square values of the sound pressure at a set of positions between the two panels and the square values of the velocities at a set of positions of the radiating panel using either active mounts or/and control loudspeakers. The third family considers: first, the cancellation of out-of-plane velocities underneath the mounts using active mounts; second, the cancellation of sound pressure near each loudspeaker using loudspeakers; and third, the cancellation of both velocities and the sound pressure using both loudspeakers and mounts. The third family does not give good performances except at low frequencies. Alternatively, the minimization of weighted square values of plate velocities and cavity pressures gives good results which are comparable with those obtained with the optimal control approach of total sound power minimization. In general, the control loudspeakers give better control in all control approaches considered.