Structure-borne Noise Transmission Research Articles

NVH multiobjective and robust optimization of electric motor design, including power losses

As part of electric motor design, compromises between NVH considerations, electrotechnical design and performance targets must be made. Electromagnetic excitation within the airgap results in structure-borne and airborne noise transmission to the vehicle. High-frequency tones are characteristic of this noise. Efficient computation methods exist to estimate these vibration and noise levels. From the early design stage, NVH performance can be diagnosed and optimized. The focus on NVH can no longer be separated from efficiency optimization. Simulation workflows and optimization loops, developed for NVH-related targets, are updated to consider copper and iron losses. The modification of the geometrical design must be addressed to reduce both dynamic excitation and energy loss, or at least offer compromises. Electric motor design optimization requires the handling of multiple objectives and constraints from multiple physics. In addition, design robustness must be ensured as part of the industrial process: manufacturing tolerances have to be considered to define a robust optimized design.

Acoustical performance of steel coil springs for vibration isolation

The acoustical performance of a set of commercially available steel coil springs was evaluated supporting a rigid structure above a slab on grade. The vibration isolation of this simple system is determined by exciting the on-grade slab with a tapping machine and measuring the resulting vibration transmitted into the isolated rigid structure above. Insertion loss of the system is determined by comparing the vibration level on the rigid structure with and without the vibration isolators under the same dynamic forces. The test results reveal the natural frequency, damping ratio, and insertion loss of the system as a function of the loading on the coil springs. The results also reveal the presence of surge frequencies (or wave resonances) that significantly degrade the system performance of at these specific frequencies, which are usually greater than 50 times the natural frequency of the loaded steel spring. Because of potential structure-borne noise transmission through steel coil springs into the supporting structure, designers should be cautioned when considering the use of steel springs to support equipment that can generate strong tonal vibrations in the surge frequency region of the springs.

Evaluating the measurement of the velocity level difference for building constructions which combine Type A and Type B elements

The standard ISO 12354 outlines a method of predicting the transmission of structure-borne noise in buildings based on data measured in a laboratory or in the field, measured in part according to the standard ISO 10848. The ISO 10848 standard describes procedures for the measurement of both the normalized flanking level difference and the velocity level difference of flanking paths through different building constructions and the junctions between them. Both the normalized flanking level difference and the velocity level difference were measured for a hybrid construction of a cross-lamented timber floor (Type A element) connected to lightweight timber walls (Type B elements) in the National Research Council Canada’s four room flanking facility. The predicted normalized level differences are compared against the measured values to evaluate the prediction method for constructions that mix Type A and Type B elements.

Structureborne noise transmission from a sports court

The authors recently investigated a multifamily high-rise building that included a sports court. Noise from bouncing basketballs and similar sources generated undesirable noise transmission in adjacent units. While that was not surprising, the pattern of transmission throughout the building was not as expected. Vibration measurements taken in the building are compared to predicted impact flanking transmission to evaluate the vibration paths through the building. While sports courts are not that common, the results are also applicable to impacts from fitness center sources, and even to prediction of impact noise in lateral and diagonal directions.

The Vibration Reduction Index of Typical Canadian Cross-laminated Timber Junctions

In support of the National Building Code of Canada, The National Research Council Canada has published research report RR-335 which describes the results of measurements of the transmission of structure-borne noise through junctions between mass timber elements. The Code only allows for the use of measured data for the vibration reduction index from the NRC's reports or reports from other research institutes. The Code does not currently allow for the use of empirical data for the calculation of the apparent sound transmission class of mass timber buildings. A lack of published data for typical mass timber junctions used in Canada can result in the overdesign of buildings or buildings which don't meet the acoustic requirements of the Code. The NRC has embarked on a program to measure the vibration reduction index of a number of mock junctions of typical junctions used in Canada including junctions between cross-laminated timber floors and lightweight timber framed walls. The new data will aid in the development of empirical models of typical Canadian mass timber constructions.

Development and Optimization of Vehicle Systems for Improved Road Noise and Prediction Using Vehicle System Model in an Autonomous Vehicle Application

<div class="section abstract"><div class="htmlview paragraph">As autonomous vehicles with electric propulsion technology are introduced to the market, the customer expectations may change significantly compared to the conventional ownership models. It is expected that the customers' focus while commuting will shift from driver related to non-driver related tasks and, as a result, more isolation from the environment may be required. Among the many challenges in noise, vibration and harshness (NVH) for an autonomous-electric vehicle, the expectation is that road noise and component noise will require the most amount of development and refinement efforts. As such, a major focus on structure-borne road noise must be considered early in the vehicle development phase to avoid either costly changes late in the program or dissatisfied customers in the market. In order to minimize the amount of structure-borne noise transmission through the body and chassis systems, a vehicle system model for virtual road noise development has been developed at Zoox with close collaboration across vehicle integration, computer-aided engineering (CAE), and tire supplier teams. Vehicle system models for road noise development are generally limited by the tire models used, which are often too simplified and limiting with respect to virtual efforts for system optimization. This paper will review the application of spindle forces and their estimation, an advanced tire-wheel model in a vehicle system model, the proceeding vehicle system analysis, and synthesis of road noise. The tire-wheel model includes the structural dynamic properties of both the tire and wheel with the centrifugal, gyroscopic, fluid-structure coupling and preload effects while the vehicle system model includes vibro-acoustics properties of chassis, powertrain, body and interior systems. A review of other work in the area of road noise excitation methods and application in a vehicle system model will be given, a description of the advanced tire-wheel system model and its application will be introduced, and system optimization will be highlighted. The inclusion of the advanced tire-wheel system model and close collaboration across teams enabled a high level of correlation with experimental tests from 20-400 Hz.</div></div>

Impact of a tunnel on the TL of a vehicle floor in bare and trimmed conditions and investigation on the most suitable simplified geometry able to better represent such impact

NVH engineers are faced with the challenge of designing trim parts for vehicle interior and exterior, like inner dash insulators, carpets, underbody shields or engine encapsulations, which can be made with very different Bills of Materials (BOMs) including among others foams, felts or heavier layers. The measurables commonly used to rank various solutions are Transmission Loss (TL) and absorption. Depending on the numerical analysis method, different approaches may be considered for the evaluation of the TL of an automotive component. In particular, in Statistical Energy Analysis (SEA), automotive components are modeled as an assembly of panels having a simple shape, e.g. flat panels and/or panels with single or double curvature. Furthermore, in SEA the trim is normally modeled by means of the Transfer Matrix Method (TMM), which is essentially a 2-dimensional methodology. This paper intends to analyze in some depth the level of approximation that these practices bring with themselves, specifically in relation to the modelling of an automotive floor. More in detail, the aim of the paper is first to investigate what impact has the presence of the tunnel on the TL of a vehicle floor in bare and trimmed conditions and then to evaluate if the presence of the tunnel can be better modeled by using a semi-cylinder or three flat plates welded together in a trapezoidal shape, both shapes considered as a reasonable simplification of the actual geometry of a typical tunnel. The analysis is carried out at simulation level using FE. To investigate both air bone noise and structure borne noise transmission, two types of excitations are used: a diffuse acoustic pressure field applied to the entire floor surface and an imposed displacement applied to the edge of the floor surface. Furthermore, 3 different kind of trims are taken into consideration in order to analyze if and how the tunnel modeling strategy may influence the evaluation of the trim effectiveness.

Measurements and modelling of dynamic stiffness of a railway vehicle primary suspension element and its use in a structure-borne noise transmission model

The noise inside railway vehicles is transmitted by both structure-borne and airborne paths and, although there are many sources, the rolling noise is often the most important. This paper focuses on the structure-borne transmission of rolling noise in a metro vehicle. Measurements are presented first of the vertical and lateral dynamic stiffness of a primary suspension element consisting of conical rubber/metal elements. Results are presented for various constant preloads over the frequency range 60–600 Hz. An analytical model of the suspension element is also developed, based on a mass-spring system and including wave motion within the rubber elements. The dynamic stiffness results are used in a finite element model of the running gear, consisting of the bogie frame, wheelsets and suspension elements. The excitation is provided by the combined wheel/rail roughness at the contact point. This model is used to calculate the blocked forces at the connection points between the secondary suspension elements and the car body. The blocked forces are combined with measured vibro-acoustic transfer functions from these mounting points to the vehicle interior to determine the structure-borne noise inside the vehicle. The proposed methodology is validated against measurements during operation in terms of acceleration levels, blocked forces and structure-borne noise levels inside the vehicle, showing reasonably good agreement. Including the dynamic stiffness for the primary suspension leads to improved agreement between 100 and 500 Hz compared with using a constant stiffness.

The sound insulation performance of mass timber building elements

Mass timber constructions have been gaining popularity in Canada since provincial building codes were changed to allow for taller buildings of mass timber elements. Common mass timber elements include cross-laminated timber, nail-laminated timber, dowel-laminated timber, and glued laminated timber. Many of these elements have been in use for decades, but much still needs to be learned in terms of the transmission of structure-borne noise between elements and the transmission loss and radiation efficiency of the elements with and without linings. Recent and ongoing studies on cross-laminated and nail-laminated elements conducted at the National Research Council have investigated many of the unknowns and a summary of the results are presented in this paper.

Identifying Structure-Borne Noise Transmission in Building

This paper presents an identification of the noise and vibration transmission in a building. The study includes noise measurements and noise mapping for two lecture rooms as well as vibration measurements on the floor in an office room. The results shows that the background noise level of the empty lecture rooms have exceeded the recommended limit by ANSI 12.2-2008, i.e. above 35 dB(A) due to the excessive noise radiated from the structure-borne source coming from the VAV system above the ceiling. The VAV system also transmits waves of vibration through the floor to the office on the level above causing annoying low frequency vibration. From the measured signal on the VAV, it is found that the system suffers from mechanical rotating looseness which must be solved to reduce the transmission of noise and vibration in the building.

Sound insulation performance of prefabricated cabins in cruise ships

In this paper, sound insulation performance of a prefabricated cabin mock-up is studied. The cabin mock-up consists of two identical rooms whose partition, ceiling, and side walls are sandwich panels composed of thin metal sheets and mineral wools. The floor is a steel plate with stiffeners, and plate thickness is 6 mm. It is shown that sealing gap between the floor and the partition improves STL (Sound Transmission Loss) significantly above 2000 Hz. Even after all gaps are sealed, the weighted sound reduction index Rw of the partition measured in the mock-up is lower than that from laboratory measurement by 9 dB. To find out how flanking transmission of noise degrades Rw of the partition, we measure structure-borne noise (SBN) of room surfaces. It is found that SBN of the steel floor is the most important factor in flanking transmission of SBN. Although SBNs of sandwich panels in the source room are larger than that of the floor, they decrease rapidly as they propagate to the receiving room, because sandwich panels provide considerably more damping than the steel floor. Consequently, SBN of the floor becomes dominant in the receiving room. Statistical energy analysis is performed, where SBN transmission along the floor is investigated. It is concluded that that the most effective way to reduce flanking transmission of SBN is to increase damping of the floor

Tire Surface Vibration and Sound Radiation Resulting from the Tire Cavity Mode

Abstract It is well-known that acoustical modes exist in tire cavities. Previous research on tire cavity modes has focused on the transmission of structure-borne noise to the vehicle interior due to the force that the tire cavity mode exerts on the wheel hub. In contrast, here the major concern is the identification of the tire surface vibration and the sound radiation from the tire surface that can be attributed to the tire cavity mode. The surface normal vibration of a point-driven tire has been measured over a complete circumference by using a scanning laser Doppler vibrometer. When the space-frequency data is transformed to the wave number-frequency domain, a clear feature that can be attributed to the tire cavity mode becomes visible. Although the magnitude of the surface vibration resulting from the tire cavity mode is small, its radiation efficiency is high owing to the high phase speed of the acoustical waves that create the tire cavity mode. It has also been found, that, as expected, tire vibration features associated with the tire cavity mode disappear when the tire is filled with fibrous, sound-absorbing material. Finally, measurements of sound radiation from a tire driven by a steady-state, point-input, and from a tire driven by a uniform impact over the contact patch area are presented, and the features associated with the tire cavity mode are highlighted.

Effective control of machinery noise on offshore platforms

Offshore noise control must consider operational noise levels in the Topsides work areas from the perspective of hearing conservation. At the same time, for human comfort, it must consider both direct and structure-borne noise transmission from the Topsides sources to the occupied spaces. This paper will summarize design stage case studies for controlling centrifugal compressor and water injection pump noise integrating commercially available outdoor and indoor noise modeling packages and statistical energy analysis software. Practicality and economics of achieving the specified noise limits will be demonstrated based on cost effectiveness and noise reduction capacity of mitigation measures such as acoustic insulation, acoustic blankets, in-line silencers, enclosures, anti vibration mounts, and damping cassettes. For centrifugal compressor noise control, controlling the piping radiated noise by acoustical insulation provides the greatest benefit. For water injection pump noise control, controlling the base plate radiated noise through viscoelastic damping proves most effective. Economic and technical barriers to effective employment of the advanced analysis tools to the field of offshore noise control will be discussed.

Control of radiated noise from a ship’s cabin floor using a floating floor

In order to develop the noise control design for a ship's cabin, a series of acoustic tests were carried out in a large scale noise test facilities with two reverberation rooms and deckhouse mock-up. From the tests, it was found that the combined noise level of a cabin was dominated by the radiated noise from the floor structure, which is a combination of a stiffened steel deck and deck covering. In this paper, the dynamic characteristics of floor structure are firstly identified through the structure-borne noise transmission test in the deckhouse mock-up. Based on the result, multi-layer floating floor systems were applied on the steel deck to reduce the radiated noise from the floor structure. Before the application, numerical simulations using assumed modes and structure-borne noise transmission tests are carried out for the floating floor itself to extract the optimum structure. Finally, the considered floating floor systems were applied in the cabin of deckhouse mock-up and the cabin noise reductions are compared. Through a series of numerical simulations and structure-borne noise transmission tests, it is found that the cabin noise reduction of a multi-layer floating floor can be greatly improved over the entire frequency range if the visco-elastic deck covering is installed between the steel deck and the mineral wool of floating floor

Numerical and experimental validation of a hybrid finite element-statistical energy analysis method

The finite element (FE) and statistical energy analysis (SEA) methods have, respectively, high and low frequency limitations and there is therefore a broad class of "mid-frequency" vibro-acoustic problems that are not suited to either FE or SEA. A hybrid method combining FE and SEA was recently presented for predicting the steady-state response of vibro-acoustic systems with uncertain properties. The subsystems with long wavelength behavior are modeled deterministically with FE, while the subsystems with short wavelength behavior are modeled statistically with SEA. The method yields the ensemble average response of the system where the uncertainty is confined in the SEA subsystems. This paper briefly summarizes the theory behind the method and presents a number of detailed numerical and experimental validation examples for structure-borne noise transmission.

On-resonance transmissibility methodology for quantifying the structure-borne road noise of an automotive suspension assembly

In this paper, a methodology is presented for the analysis of the structure-borne noise transmission paths for an automotive suspension assembly. First, a fully-instrumented test bench consisting of a wheel/suspension/lower suspension A-arm assembly was designed in order to identify the vibro-acoustic transmission paths (up to 250 Hz) for white noise excitation of the wheel. Second, frequency response function measurements between the excitation signal and each suspension/chassis linkages are used to characterize the different transmission paths that transmit energy through the chassis of the car. Finally, a synthesis of the major resonances of the suspension is drawn, with the objective of indicating which suspension transfer paths contribute the most to the structural forces transmitted to the chassis. On-resonance force transmissibility factors (ORTF) were calculated to provide an overall classification of the system resonances to the vibration transmission through the individual suspension linkages and in all axes.

611 カーペットによるフロア振動の低減効果を考慮したFEモデルの構築(振動利用・振動低減,振動基礎(1))

The behavior of a carpet composed of two layers is studied. The vibration measurements of the panel with or without the carpet describes that it works as well as viscous damping. We have developed an FE model of the carpet that is based on spring, mass and damper system. The FE model is checked by parameter study and prediction of the behavior of another carpet. And the model is also applied to predict the change of structure-borne noise transmission of an L-shaped structure due to the placement of the carpet using FEM combined with SEA. A part of an automotive car body is also used to test the FE model.

Analytical Model of Tire Cavity Resonance and Coupled Tire/Cavity Modal Model

Abstract The acoustic resonance of the air cavity in the tire/wheel assembly may be a contributor to vehicle interior noise through the structure-borne noise transmission path. This problem has been examined in the past using approximate closed form solutions (based on plane wave theory for a two-tube model) and numerically, using FEA. The coupling between the cavity resonance and structural resonance of the wheel may result in higher levels of interior noise as noted previously. The two primary goals of this paper are (1) to develop simple analytical models to gain fundamental understanding of some observed phenomena and for a quick estimation of cavity resonance frequency to assist in the design process, and (2) to develop tire modal models incorporating the acoustic cavity to predict coupled system natural frequencies and response. An improved analytical model for accurate calculation of acoustic cavity resonance frequencies of a static, unloaded tire is developed using variational principles. The sensitivities of the cavity resonance frequencies to tire width and aspect ratio are examined. For the case of a loaded tire, an improved analytical formulation based on plane wave propagation (for linearly varying cross-sectional area) is developed. Deformed structure geometry from FEA is used as input to the analytical model. The FEA-based methodology used in the tire/cavity coupling analysis is as follows: The tire structural modes are calculated, ignoring the effect of the acoustic cavity. The tire cavity modes are calculated using deformed cavity geometry only. Next, the structural/acoustic coupling matrix is calculated. Finally, a coupled cavity-structure modal model is generated from modal mass and stiffness of the tire/wheel assembly, the cavity modal matrices, and the coupling matrix. This process is an improvement over conventional tire modal models, which only include structural modes.

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

Structure-borne noise transmission in the Propfan Test Assessment aircraft

Estimates of the level of structure-bor ne noise transmission in the Propfan Test Assessment (PTA) aircraft were carried out for the first three blade passage frequencies. The procedure used combined the frequency response functions of cabin sound pressure level to wing strain response obtained during ground test of the PTA aircraft with in-flight measured wing strain response data. The estimated structure-borne noise levels varied from 64 to 84 dB showing very little dependence on engine/propel ler power, flight altitude, or flight Mach number. In general, the bare cabin in-flight noise levels decreased with increasing propeller tone frequency, giving rise to a plausible structure-borne noise transmission problem at the higher frequency blade passage tones. Without knowledge of the effects of a high insertion loss sidewall treatment on structure-bor ne noise transmission of the bare cabin no quantitative conclusions could be made on the level of structure-borne noise transmission in a treated production aircraft.