Structure-borne Vibration Research Articles

Reduction in Floor Impact Noise Using Resilient Pads Composed of Machining Scraps.

Floor impact noise is a significant social concern to secure a quiescent living space for multi-story building residents in South Korea. The floating floor, consisting of a concrete structure on resilient pads, is a specifically designed system to minimize noise transmission. This floating structure employs polymeric pads as the resilient materials. In this study, we investigated the utilization of helically shaped machining scraps as a resilient material for an alternative approach to floor noise reduction. The dynamic elastic modulus and loss factor of the scrap pads were measured using the vibration test method. The scrap pads exhibited a low dynamic elastic modulus and a high loss factor compared to the polymeric pads. Heavyweight impact sound experiments in an actual building were conducted to evaluate the noise reduction performance. The proposed pads showed excellent performance on the reduction in the structure-borne vibration of the concrete slab and resulting sound generation. The analytical model was used to simulate the response of the floating floor structure, enabling a parametric study to examine the effects of the resilient layer viscoelastic properties. Both experimental and analytical evidence confirmed that the proposed scrap pads contribute to the development of sustainable solutions for the minimization of floor impact noise.

DYNAMIC RESPONSE OF ELASTICALLY-SUPPORTED BRIDGE UNDER OPPOSITE MOVING HIGH-SPEED LOADS

This paper explores the design parameters for elastically supported (ES) bridges, particularly for short to medium under the influence of high-speed trains. It introduces a non-dimensional mathematical framework that conceptualizes the ES as a Euler-Bernoulli beam supported by elastic bearings at its ends and subjected to evenly spaced moving loads. The framework highlights various resonances and speed ratios for cancelling out specific effects based on the stiffness parameter and the distance between loads. The analysis indicates that most of the maximum displacement occurs near the beam's midpoint. Additionally, it shows that lower resonance speeds coupled with higher stiffness parameter values can result in significant amplification of displacement response due to cumulative forces acting on the system. This amplification is a consequence of the cumulative forces acting on the system. Hence, this research provides valuable insights for designers and engineers to optimize foundation design, thereby reducing structure-borne vibrations transmitted to the ground.

DYNAMIC RESPONSE OF ELASTICALLY-SUPPORTED BRIDGE UNDER OPPOSITE MOVING HIGH-SPEED LOADS

This paper explores the design parameters for elastically supported (ES) bridges, particularly for short to medium under the influence of high-speed trains. It introduces a non-dimensional mathematical framework that conceptualizes the ES as a Euler-Bernoulli beam supported by elastic bearings at its ends and subjected to evenly spaced moving loads. The framework highlights various resonances and speed ratios for cancelling out specific effects based on the stiffness parameter and the distance between loads. The analysis indicates that most of the maximum displacement occurs near the beam's midpoint. Additionally, it shows that lower resonance speeds coupled with higher stiffness parameter values can result in significant amplification of displacement response due to cumulative forces acting on the system. This amplification is a consequence of the cumulative forces acting on the system. Hence, this research provides valuable insights for designers and engineers to optimize foundation design, thereby reducing structure-borne vibrations transmitted to the ground.

Analysis and modelling of the dynamic stiffness up to 400 Hz of an air spring with a pipeline connected to a reservoir

The present research addresses the dynamic behaviour of an air spring with a pipeline connected to a reservoir in a frequency range up to 400 Hz, in which structure-borne vibration transmission may occur due to both the structural behaviour of the bellows and fluid dynamics in the pneumatic circuit of the suspension. Based on experimental results, three frequency ranges are distinguished where different resonances of the suspension appear: low (up to 30 Hz) due to the air flow between the bellows and the surge reservoir, intermediate (30–150 Hz) due to the formation of standing waves in the pipeline and high (beyond 150 Hz) due to the structural dynamics of the bellows. A novel modelling technique to predict the dynamic behaviour of the pneumatic system in all these frequency ranges is presented and validated: this consists of an enhanced Finite Element Model (FEM) considering the structural properties of the bellows and the effect of pressurised air in the bellows and in the reservoir, coupled to a model of fluid exchange between the two main air volumes which is defined using a VUFLUIDECH user subroutine developed in ABAQUS. The study focusses on the axial dynamic stiffness of the pneumatic suspension, which plays a key role in determining the transmissibility of the suspension. However, the mathematical model introduced in the paper is capable of predicting also the vibration modes of the suspension in shear and rotation, which may be relevant in some applications, e.g. when air springs are used in vehicle suspensions.

Multi-directional active vibration control of 1D smart structure inspired by automotive engine mounting system

Recently, active mounting system is being gradually applied to automotive engine mounts for mitigating structure-borne vibration effectively throughout the whole vehicle chassis. This paper presents modeling, analysis, and control of a source structure with an active mounting system in multi-directions, considering position and direction of actual automotive engine mounts. The active mount consists of a piezoelectric stack actuator in series with an elastomeric (rubber) mount. When harmonic excitation forces are employed, secondary force required for each active mount is calculated mathematically and the control signal can reduce the vibration through the destructive interference with input signal. In addition, the horizontal vibration can also be mitigated by setting a variable parameter through the dynamic relation of source structure. A series of simulation results demonstrate that the excitation vibration could be reduced along with this multi-directional (vertical and horizontal) active mounts. Based on this result, it can be expected that noise vibration harshness(NVH) performance can be improved by controlling the vibration of the actual automotive engine structure with rubber mount and secondary force of actuators in both vertical and horizontal directions.

Active Mitigation Strategy of Structure-Borne Vibration with Complex Frequency Spectra from Asymmetric Plate-like Mounting Systems in Next Generation Mobilities

The complicated spectrum produced by electric and hybrid car engines is particularly sensitive to the mid-frequency range. Furthermore, sensor placement in future mobility is crucial because when the positions and orientations of sensors are altered by excessive vehicle vibration, it results in the malfunctioning of autonomous driving systems. Smart structure-based active mounting approaches have been developed to reduce engine-induced vibration. These are made to continually adjust the mounts’ dynamic properties and enhance their performances in terms of noise, vibration, and harshness (NVH) under diverse operating circumstances. It can take the place of the engine support system’s current mount technique. The performance of the source part for reducing vibration when the structure is triggered by a sinusoidal and multi-frequency signal is the main subject of this study. The overall structure, which has two active mounts based on the source-paths-receiver structure, was modeled using a lumped parameter model. In the source section, sinusoidal, amplitude modulation (AM), and frequency modulation (FM) signals were used in order to assess the effectiveness of vibration reduction in the mid-frequency band. The normalized least mean-square (NLMS) technique was utilized to assess the effectiveness of an active mounting system, and a tracking signal was employed as a control signal. The algorithm was further expanded to the multi-NLMS algorithm to monitor the complex spectral signal. This demonstrates how an active mounting system can successfully reduce vibrations when the structure is activated by many mid-frequency complex signals.

Analytical Research on the Mitigation of Structure-Borne Vibrations from Subways Using Locally Resonant Periodic Foundations

Filtering properties of locally resonant periodic foundations (LRPFs) have inspired an innovative direction towards the mitigation of structural vibrations. To mitigate the structure-borne vibrations from subways, this study proposes an LRPF equipped with a negative stiffness device connecting the resonator and primary structure. The proposed LRPF can exhibit a quasi-static band gap covering the ultra-low frequency range. These frequency components have the properties of strong diffraction and low attenuation and contribute the most to the incident wave fields impinging on nearby buildings. By formulating the interaction problem between the tunnel-ground and LRPF-superstructure systems, the mitigation performance of the proposed LRPF is evaluated considering the effects of soil compliance and superstructure. The performance depends on the dynamic properties of the ground, foundation, and superstructure as well as their coupling. Transmission analyses indicate that the superstructure responses can be effectively attenuated in the quasi-static band gap by adjusting the negative stiffness. Considering the coupling of the flexible ground, the peak responses of the LRPF-superstructure system occur not only at its eigenfrequencies but also at coupled resonance frequencies due to the contribution of the soil compliance. This study provides an analytical tool for mitigating the structure-borne vibrations from subways with the LRPF.

Analysis of the axial and transversal stiffness of an air spring suspension of a railway vehicle: mathematical modelling and experiments

ABSTRACT The secondary suspension of railway vehicles is fundamental for their dynamic behaviour. This paper outlines a model-based procedure for predicting and evaluating the influence of different parameters in the static stiffness and vibration transmission of an air spring employed in the secondary suspension system of a railway vehicle. For that aim, a detailed and experimentally validated finite element model of the air spring is defined. It includes the behaviour of the reinforced elastomer, the inner pressure-deformation coupling and the thermodynamic interactions taking place inside the bellow. A Computer Aided Design of Experiments is employed to evaluate the influence of seven construction parameters of the bellow. Experimental tests and simulation results show that the air spring has natural frequencies below 100 Hz, in the frequency range where structure-borne vibration transmission occurs. The cord angle modifies the axial-transversal stiffness relation and a larger separation between adjacent layers and fibres delay the vibration transmissibility.

Vibration impact of rock excavation on nearby sensitive buildings: An assessment framework

As a common construction activity, rock excavation using hydraulic breakers often generates high-level ground- and structure-borne vibrations, which may adversely affect nearby buildings in terms of structural safety, occupant comfort, and ultraprecision equipment functionality. However, building vibrations induced by rock excavation have not been well investigated and understood in the literature. For example, the coupling attenuation at column bases and the floor-to-floor vibration attenuation inside a building have rarely been quantitatively studied. Moreover, traditional dynamic analysis methods in earthquake engineering may not apply to simulations of rock excavation-induced building vibrations. This paper proposed a novel assessment framework based on the mechanical impedance concept, which can quantify the coupling attenuation at column bases and the floor-to-floor vibration attenuation inside a building in a computationally efficient manner. Systematic finite element simulations of rock excavation were performed to characterize vibration propagation in the ground and buildings. The finite element simulations and field measurements successfully verified the accuracy of the proposed prediction formulas, which offers a convenient vibration impact assessment framework to construction practitioners.

Feasibility study of measuring instantaneous angular speed of helical gears with magnetoresistive sensors

The digitalization of industrial processes with e.g. the goal to increase the availability of production processes in general and to support the individualization of many products in particular leads to an increasing demand in sensor data. The state of the art for condition monitoring of involute gear trains is the measurement of structure-borne vibration with acceleration sensors. New approaches, such as measuring the instantaneous angular speed (IAS), are gaining in popularity. Machine manufacturers usually wish to use existing sensors or measurement points, where little or no effort is needed to implement the sensor concept. Magnetoresistive (MR) sensors fulfil this complex set of requirements to a high degree: They are comparatively easy to integrate, can be added as an optional component and provide sufficient accuracy.The authors have developed different sensor concepts using MR sensors for measuring IAS in a 1-stage helical gear box. Multiple tests with artificial tooth flank damages have been carried out to evaluate the damage detection potential of the sensor concepts. Finally, a spectrum analysis of the first gear mesh frequency and surrounding sidebands demonstrates the capability for detecting tooth flank damage with different MR sensor concepts.

A Review on Vibro-Acoustic Analysis of a Launch Vehicle Structure

Abstract: Space vehicles are subjected to significant dynamic pressure loads when their rocket propulsion systems are in use during flying missions. During the aerodynamic and launch phases, launch vehicles, payloads, and their parts are subjected to extremely high random acoustic loads. The noise from the engine exhaust gas, aerodynamic boundary layer noise, transonic buffering, structure-borne vibration, engine thrust fluctuation, etc. is the source of these loads, which also result in a secondary acoustic load. When the vehicle is lifting off and traveling at a speed greater than Mach number, acoustic stresses to the spacecraft and payload are very harsh and significant. This loading causes the structure to vibrate randomly, which could be dangerous for some vehicle parts, avionics, propulsion systems, and payloads like satellites. This paper discusses the vibration of the structure subjected to acoustic excitation on a diffuse acoustic field and the software used for the analysis.

Raising the bar for jack-up floating floors—Understanding laboratory test results and proposed future test methodologies

The jack-up concrete floating floor has been a staple in the field of architectural acoustical design for decades. Compatible with both spring and elastomeric isolators, the jack-up concrete floating floor system is often specified when the highest level of airborne and structure-borne vibration isolation separation is desired, and assurance of a decoupled floor is needed. Recent laboratory testing for jack-up floating floors under various configurations has yielded interesting and perhaps unexpected results. This paper will review the results from laboratory testing and dissect which factors appear to influence the airborne and/or the structure-borne isolation performance. A preview of future testing will be discussed, including new testing methodologies to validate existing conclusions and identify the influence of additional factors that may influence the airborne and/or structure-borne isolation performance.

Legal consequences of train-induced structure borne noise and vibration in residential buildings

Abstract The development of subways in cities has provided great comfort to the citizens, but it has brought adverse effects to the residents of the buildings adjacent to the subway lines. The main effects are Structure Borne Noise (SBN) and Structure Borne Vibration (SBV), which are identified as environmental challenges. In this research, the extent and seriousness of SBV and SBN annoyances to people were investigated. This is made in two steps; first a thorough field test was made to evaluate the level of train-induced noise and vibration; then, a comprehensive investigation was made on the level of people annoyance from train-induced vibration and noise, using results obtained from interviews and questionnaires. The results obtained indicate that health concerns, economic losses, building damages and social harms were the most important factors, which cause annoyance of the citizens. These annoyances caused citizens to take their complaints to judiciary system in the world. In the second part of this research, the effectiveness and sufficiency of the current laws and legislation to protect the citizen against SBV/SBN annoyance are evaluated. The results indicate that there are limitations in the current laws in regard to crime determination, criminal identification, estimation of damages to citizens, citizen rights regarding the annoyance caused by SBV/SBN. Also, there is a lack of legal awareness among the citizens who do not know how to get their legal rights. The results of this research showed that the judicial bodies should improve and extend the current laws and make more low-enforcement to protect people against the growing problem of SBV/SBN. Also, there is a need to make people more familiar with their civil rights in regard to SBN and SBV.

Structural Dynamics, Noise and Vibration: Buildings Adjacent to Train Lines

In architecture and civil engineering there is a growing interest in the study of the dynamics of structures. The dynamic effects are due to various actions, but their influence is widened or reduced according to the design of the structure. Structures can be highly susceptible to the action of dynamic loads produced by the action of wind, earthquake, industrial activities, blasting activities, construction sites, road vehicles, trains, building services and human activities. Noise and vibration can have significant environmental impact on buildings and structures and can damage track components, crack roadways, unsettle foundations, affect sensitive equipment, impact human comfort and damage structures. Structure-borne noise and vibration can be a major and often overlooked consideration in the planning, design and operation of existing or new developments. A reliable, considered approach to assessing noise and vibration is needed to achieve outcomes that meet client expectations while maintaining on-going compliance with relevant standards and regulatory and planning requirements. The proposed paper will focus on a general overview of the structure-borne noise and vibration risks, associated with new developments that are adjacent to existing rail lines during the early design stages, from commercial and residential buildings to sensitive research facilities. It will further explain the general description of the design process, including problem descriptions, measurements of ground and structural vibration levels at the proposed site, vibration criteria, finite element analysis and provisions of the isolation system required to be considered at the building to achieve the relevant criteria.

On the concept of embedded resonators for passive vibration control of tyres

An investigation is carried out on structure-borne vibrations of tyre models at low frequencies. The idea is to use embedded resonant meta-materials to damp the tyres’ vibrations and thus reduce the transferred energy to the main attached structures. A simplified tyre model is used, being the investigation of the effects of the embedded substructures the main target of the work; internal pressure and tyre rotation effects are neglected at this stage. Different configurations are tested targeting different natural modes of the tyre, while mechanical excitation is assumed on one section of the tyres. The results show how the proposed designs open new possible and feasible solutions for the vibration control.

Analysis of traveling waveform of flexible waveguides containing absorbent material along flanged junctions

The traveling waveform of a flexible waveguide bounded by elastic plates and with an inserted expansion chamber having flanges at two junctions and a finite elastic membrane atop is investigated through a mode-matching technique. The modeled problem is governed by Helmholtz’s equation and includes Dirichlet and higher-order boundary conditions. An acoustically absorbent lining is placed along the inner sides of the flanges at the junctions while their outer sides are kept rigid. Moreover, the edge conditions are imposed to define the physical behavior of the elastic membrane and plates at finite edges. The configuration is excited with the structure as well as fluid-borne modes. The influence of the imposed edge conditions at the connections of the plates and the prescribed incident forcing on the transmission-loss along the duct is elaborated. Specifically, the effects of edge conditions on the transmission-loss of structure-borne vibrations and fluid-borne noise are specified. The performance of low-frequency approximation is compared with that of the benchmark mode-matching method and is found to be in good agreement with relative merits. Apposite numerical simulations are performed to substantiate the validity of the mode-matching technique.

Idle shake vibration optimization of an engine mounting system through the practical application of transfer path analysis

This article presents a practical application of experimental transfer path analysis (TPA) for optimizing idle shake vibrations of a front-wheel-drive car with a transversely mounted four-cylinder diesel engine. Performance control of the vehicle engine mounting system must take into account the multiple dynamic interactions between the engine mounting system, subframe modes and the vehicle suspension. Experimental methods can be used in conjunction with simulations to design and optimize the engine mounting system. TPA is a powerful tool for the diagnosis of vibration and noise transmission via multiple solid paths. TPA allows a quick diagnosis of the engine mounting system performances on vehicle comfort. A strong synergy between numerical model and experimental data finally makes it possible to find better design alternatives, not necessarily obvious to the designer. This study is the guideline for an optimization of the engine mount noise vibration and harshness (NVH) performances by using a hybrid approach, combining an analytical approach and measurement data. First, a diagnosis of the transmission of structure-borne vibrations via the engine mounting system to the seat floor is done at constant idle speed. This method is used to rank individual engine mount contributions in the low-frequency vibration level inside the vehicle. Then, an original approach allows the optimization of the vibration level at idle speed by offsetting contributions of the engine mount paths by adding damping in the right engine mount. This approach has led to the design and validation of an original double inertia-track hydroelastic mount prototype which allows a 5-dB reduction on the seat floor vibration level. The future development of a new version is planned to confirm and optimized the obtained results. The length of the second inertia track will be increased to reach the targeted characteristics, and the adjustment system will be removed to respect the overall dimension constraints of the mount.

Resolving room volume and structural vibration transfer issues at UW Green Bay’s Studio Arts Building

The primary rehearsal spaces for the orchestral, band, and choral programs in the Music Department at the University of Wisconsin—Green Bay are hosted at the campus’ Studio Arts building, which was constructed in the early 1970’s and had not been significantly updated since then. The goal of the building’s renovation was to improve room acoustic response for both spaces, improve on the insufficient acoustic isolation between the large instrumental and choral rehearsal rooms, and to update HVAC services. Because of the many years of wear and undocumented alterations to the building, exploratory testing of airborne and structure-borne vibration paths was necessary to determine the contributing means of sound transfer between spaces. Acoustically isolated construction ultimately was utilized to increase separation between rooms as well as to introduce acoustic shaping to the choral rehearsal room, to maximize reverberation and avoid the typical acoustic pitfalls of a roughly cubic room volume. A new reflector array was installed in the large instrumental rehearsal room, as well as targeted absorptive and diffusive treatments. New variable acoustic treatments were designed and installed in both rooms, while noise and vibration control for new HVAC equipment realized suitably low background noise levels for both.The primary rehearsal spaces for the orchestral, band, and choral programs in the Music Department at the University of Wisconsin—Green Bay are hosted at the campus’ Studio Arts building, which was constructed in the early 1970’s and had not been significantly updated since then. The goal of the building’s renovation was to improve room acoustic response for both spaces, improve on the insufficient acoustic isolation between the large instrumental and choral rehearsal rooms, and to update HVAC services. Because of the many years of wear and undocumented alterations to the building, exploratory testing of airborne and structure-borne vibration paths was necessary to determine the contributing means of sound transfer between spaces. Acoustically isolated construction ultimately was utilized to increase separation between rooms as well as to introduce acoustic shaping to the choral rehearsal room, to maximize reverberation and avoid the typical acoustic pitfalls of a roughly cubic room volume. A new reflecto...

Effect of inner stiffeners on vibration and noise levels of gearbox housing without changing the mass

Especially, with the advancement of technology, mechanical parts need to be designed to be lighter and more durable. In the industry, gears are the most common power transmission equipment, and for this equipment, increasing durability and rigidity has an essential importance. During power transmission, undesired vibration and noise arise in gear systems. In addition to gear design, gearbox housing design is also essential to reduce the radiation of undesired structure-borne noise and vibration. In order to reduce noise and vibration levels, some modifications are frequently used on gearbox housings. In this study, three different gearbox housing designs (basic, cross and cellular) are formed and analysed by using ANSYS® software. The design alternatives for housings have been formed inside of the structure as different quantities of longitudinal and transverse stiffeners. In addition, all the external dimensions and the mass of these three housing designs are equal in order to observe just vibration and noise reduction. Fast Fourier Transform (FFT), statistical properties of vibration signals and sound levels of the gearbox have used for comparisons to determine which gearbox have better vibration and sound levels.

High-frequency structure- and air-borne sound transmission for a tractor model using Dynamical Energy Analysis

Dynamical Energy Analysis (DEA) is a mesh-based high frequency method for modelling structure borne sound in complex built-up structures. Vibro-acoustic simulations are performed directly on finite element meshes, circumventing the need for re-modelling strategies. DEA provides detailed spatial information about the vibrational energy distribution within a complex structure in the mid-to-high frequency range. We will present here progress in the development of the DEA method towards handling complex FE-meshes including Rigid Body Elements and sound radiation. We also provide, for the first time, a detailed comparison of the simulations with measurements on a complex engineering structure consisting of the chassis and cabin of a tractor. Both structure borne vibrations and sound pressure levels (SPL) inside the cabin were considered. For the latter, a combined DEA/SEA analysis has been developed. The simulation results compare favourably with measurement results, both for vibration levels measured across the structure and for SPLs inside the cabin.