The rollers and raceways in cylindrical roller bearings are separated by an extremely thin lubricant film over a narrow region, which is critical to performance. The ultrasound method has been applied successfully to a range of bearings including journal and ball bearings. But the actual maximum speed that can be measured is limited by the repetition frequency of the ultrasonic pulse. Otherwise, a single measurement point cannot image the thickness distribution of the cylindrical roller bearing. This paper describes the measurement of lubricant-film thickness distribution in a roller bearing by moving the ultrasound transducer. A new ultrasonic pulser-receiver is used to get enough effective measurement points. For a range of loads and speeds, the oil-film thicknesses of four positions along the roller are measured. The influences of the rotating speed and radial load on the film thickness measurement are consistent with the theoretical predictions. The limits of the PRR used in measurements are discussed and the averaging effect of the transducer focal zone size is observed.

Although Lagrangian and Hamiltonian analytical mechanics represent perhaps the most remarkable expressions of the dynamics of a mechanical system, these approaches also come with limitations. In particular, there is inherent difficulty to represent dissipative processes and the restrictions placed on end point variations are not consistent with the definition of initial value problems. The present work on poroelastic media extends the recent formulation of a mixed convolved action to address a continuum dynamical problem with dissipation through the development of a new variational approach. The action in this proposed approach is formed by replacing the inner product in Hamilton’s principle with a time convolution. As a result, dissipative processes can be represented in a natural way and the required constraints on the variations are consistent with the actual initial and boundary conditions of the problem. The variational formulations developed here employ temporal impulses of velocity, effective stress, pore pressure and pore fluid mass flux as primary variables in this mixed approach, which also uses convolution operators and fractional calculus to achieve the desired characteristics. The resulting mixed convolved action is formulated in both the time and frequency domains to develop two new stationary principles for dynamic poroelasticity. In addition, the first variation of the action provides a temporally well-balanced weak form that leads to a new family of finite element methods in time, as well as space.

Composite materials and structures are increasingly being applied in aerospace, marine, and wind power industries, as well as in commercial products. One main reason for the scientific interest in composite materials is their tailorable mechanical properties. However, because of the fiber-direction-dependent nature of its physical and mechanical properties, composite material’s property and failure behaviors are usually complex, typically involving various mechanisms depending on applications. Nondestructive testing plays a key role during composite fabrication and maintenance in service. Among the variety of nondestructive techniques available, ultrasound phased array technique has emerged as a promising new approach. Unlike a conventional ultrasound single element transducer, an ultrasound phased array sensor can control and focus acoustic energy to the desired directions and locations. This heightened flexibility and sensitivity is essential given complex shape of modern composite structures. Despite such promise, understanding and application of ultrasound phased array technique is limited due to the anisotropic nature of composite materials, as well as its high acoustic attenuation. Attenuation and velocity dispersion are the two major challenges to the ultrasound evaluation of composite structures; these two factors complicate the control of phased array ultrasound propagation both theoretically and experimentally. This is especially true for thick high attenuation carbon fiber or glass fiber composite materials that have been widely applied in aerospace and wind turbine industries. In our study, ultrasound phased array technique was applied to increase the acoustic penetration power in high acoustic attenuation composite materials. First, ultrasound phased array signal in isotropic materials was studied to calibrate the probe parameters. Then for composite materials, the dependence of ultrasound field on the number of active elements, steering angles, beam focusing laws and on the characteristics of materials was analyzed and optimized through theoretical simulations and experimental evaluations. Results showed that the steering angles and the parameters of beam focusing laws might change the ultrasound beam intensity and uniformity, which had a significant influence on the sensitivity and resolution of the technique; the anisotropic properties of composite materials could distort the ultrasound beam, which made the calibration a necessary and important procedure during practical inspections. The influence of ultrasound frequency and beam angle were also quantitatively evaluated. The proposed research has the potential to apply ultrasound phased array technique to the detection of defects in composite materials and the evaluation of composite structural health. The study of the interaction between ultrasound and composite structures will open the window for the successful application of ultrasound phased array technique.

Gradient index devices for the simultaneous control of the S 0 and A 0 Lamb modes are presented and numerically analysed. It is found a special relationship between the refractive indexes for these two modes which allows their simultaneous control by means of graded phononic crystals and thickness variations of the plate. A flat gradient index lens and a circular Luneburg lens are designed. Numerical simulations show that the performance of these devices is good for the two modes in a broadband frequency region, and that this approach can be used to design more advanced refractive devices for the total control of guided vibrational modes.

A 2D, plane-strain, finite element model, with perfectly-matched layer elements acting as absorbing boundaries, is used to investigate the effect of soil inhomogeneity on resultant surface vibration. The stiffness and mass matrices for the perfectly-matched layer element is derived and included for reference. Stochastic variability of the soil’s shear wave velocity is introduced using a K-L expansion; the shear wave velocity is assumed to have a log-normal distribution and a modified exponential co-variance kernel. Results suggest that local soil inhomogeneity can significantly affect surface velocity predictions; 90% confidence intervals showing 7dB averages and peak values up to 11dB are computed. This is a significant source of uncertainty and should be considered when using predictions from models assuming homogeneous soil properties.

A structure in service can be subjected to static, dynamic or moving loads. Several situations in practice involve estimation of moving loads which induce vibrations in the structure on which they are applied. An accurate estimation of these loads will ensure product quality and reliability of the final design, and mitigate the cost of structural health monitoring systems. The moving nature of dynamic loads increases the computational difficulty of the problem. One of the types of Inverse Problems involves estimation of the applied load from measured structural response such as strain or accelerations. Measuring response at a limited number of locations causes the unavailability of full set of structural response which can lead to inaccurate results. The unavailability of full structural response is mainly due to three reasons — (i) financial constraints limiting the number of sensors that can be used, (ii) inaccessibility of loading locations to place sensors, and (iii) sensor influence on structural response. The load recovered from such insufficient structural response data will be prone to errors. Ill-conditioning of the inverse problem can be eliminated by choosing optimum sensor locations on the structure, which leads to precise load estimate. No studies could be found which consider optimum sensor placement while recovering dynamic moving loads acting on a structure. In this paper, the recovery of the dynamic moving loads through measurement of structural response at a finite number of optimally selected locations is investigated. The developed algorithm is implemented using ANSYS APDL and MATLAB programming environment. Optimum sensor locations are identified using the D-optimal design algorithm and strain gages are placed at those locations. An algorithm is developed to utilize the strain data measured at optimum locations to estimate the moving load. The developed algorithm is applied to three example problems. The first example deals with the case where two orthogonal dynamic moving loads are applied at the same location. The second example involves a specific vehicle-bridge interaction problem. The vehicle is approximated as a half model consisting of two axles, where the dynamic loads from axles are modeled as point loads which move together. In both the cases, the estimated dynamic moving loads matched closely with the applied loads. In third example, the algorithm is also tested by adding 5% noise to the input response data. Even with random noise present in input strain data, the load estimates are obtained with a high degree of accuracy. Compared to conventional algorithms for estimating moving loads, the developed method makes the dynamic moving load recovery procedure accurate and relatively easy to implement.

Skewing or dislocation installation of a bearing in a spindle will be subjected to uneven loads caused by machining error, assembly error and thermal deformation. Bending moment will be induced by the uneven force around the center of bearing. Non-uniform preload methodology is proposed in this paper aiming to stimulate the skewing installation in a spindle. Wavelet threshold technique for noise reduction and wavelet package method for feature extraction were introduced in order to identify the bearing posture through analyzing the vibration signal of the bearing. To validate the proposed method, the raw vibration signals are reconstructed, the eigenvector is structured and normalization processing is done between uniform preload and non-uniform preload conditions, respectively. The analysis results shows that the wavelet packet threshold de-noising technology can effectively eliminate the noise of the spindle vibration signal. The bearing posture identification and bearing preload identification are realized through the change of frequency energy.

Gas turbine engines often pass through tests in enclosed test facilities. One problem that arises during these tests is the infrasound phenomenon. Infrasound can be a problem for many reasons, ranging from rattling windows to structural damage to the test cell. The aim of this paper is to understand the cause of severe infrasound experienced at Honeywell Aerospace and to evaluate and select a solution using advanced Computational Fluid Dynamics (CFD) techniques. These CFD simulations modeled an entire test cell with an engine in place, which is a more complete approach than what is reported in the literature. The DES turbulence model was applied in a transient, compressible, turbulent simulation in order to capture small pressure fluctuations. Test data taken using an engine/test cell configuration that does not cause problems was used to successfully validate the CFD approach. It was found that the narrow, high-velocity exhaust plume examined in this study impacted the convex blast plate in the aft portion of the test cell having diffused only slightly. The exhaust then rebounded and buffeted the plume, causing extreme dynamic loading. Through a modification to the blast basket, it was shown that the problem would be alleviated and sound pressure levels in the test cell would be reduced by 5 to 32 dB, depending on location in the test cell.

In this paper, the 3-D unsteady turbulent flow inside a centrifugal pump is investigated by computational fluid dynamics (CFD) in ANSYS CFX, using Detached Eddy Simulation (DES) as the turbulence approach. The pump has a single end-suction and a single volute discharge. The impeller is semi-open (unshrouded with baseplate) and has five backswept blades and pump-out back blades. The CFD model of the pump consists of the inlet, the impeller, and the volute. A sliding mesh technique has been applied to the interfaces in order to allow unsteady interactions between the rotating impeller and the stationary parts. These unsteady interactions generate pressure fluctuations over the volute casing and blade surfaces that are hydroacoustic dipoles according to Lighthill’s acoustic analogy theory. The pressure fluctuation spectra at the volute tongue show that pressure fluctuations are generated mainly by the discrete components related to the impeller rotation at low frequencies, especially the blade-passing frequency (BPF) component. This component is approximately 1% of the reference dynamic pressure 0.5 ρν2 2 where ν 2 is the circumferential velocity at the impeller outlet. The discrete components with frequency larger than 4 times BPF are no longer obvious in the spectra. Compared to the experimental results, the CFD simulation predicts much lower amplitudes for the broad band pressure fluctuations. This is reasonable, because DES combines a classical Reynolds averaged Navier Stokes (RANS) simulation with elements of Large Eddy Simulation (LES), and both RANS and LES use average methods which filter out the high frequency fluctuations. Nevertheless, CFD is capable of accurately predict the BPF component. The pressure fluctuations on the casing and blade surfaces are extracted and modelled as the stationary and rotary dipoles, respectively, according to the Ffowcs Williams and Hawkings (FW-H) equation of the acoustic analogy theory. After Fast Fourier Transform, the spectra of the pressure fluctuations are obtained, and are used to predict the tonal hydrodynamic sound radiation at BPF and its low order harmonics. The sound radiation of casing surface dipoles is calculated by extracting the tonal components, and performing a surface integration with the fundamental solution to Helmholtz equation as the kernel. A frequency domain formulation of the FW-H equation with the moving surface dipole is employed to predict the tonal blade noise. The results from these acoustical simulations show that the sound power generated by the casing surface dipole is three orders of magnitude higher than that of the blade surface dipole, and the main hydroacoustic sources are located at the volute tongue.

Thermoacoustic instability has been reported in various combustion systems including industrial combustors (heaters, boilers, etc.), propulsion systems (rockets, afterburners) and gas turbine combustors. Thermoacoustic instability can be addressed by adding acoustic damping to the combustion environment. In larger industrial applications, tonal acoustic damping solutions such as quarter wave tubes and/or Helmholtz resonators or even active acoustic damping solutions can be used to quiet this instability. This paper discusses the numerical investigation of mitigating the 30 Hz thermoacoustic instability in a fire-tube 600 horsepower steam boiler. By conducting finite element analysis of the acoustics of the combustion chamber and all the fire-tubes, the 30 Hz mode sympathizing with the heat release dynamics of the chamber is identified. Subsequently, a number of tuned acoustic absorption solutions are experimented with, numerically (on the finite element model of the boiler’s acoustics), and the most suitable (in terms of effectiveness and ease of implementation) candidate solution is identified. Currently, work is underway to implement this solution on the boiler.

In this paper, we present a new design for waveguide-based phononic crystal (PnC) resonators in pillar-based piezoelectric membranes at the GHz frequency range based on mode-gap waveguide termination. The mode confinement in these resonators is achieved by a smooth transition from a phononic waveguide to another phononic waveguide that does not support (and therefore reflects) the guided modes of the first waveguide over a certain frequency range. These resonators can be utilized for applications including wireless communications and sensing [1, 2] where high-Q and high-frequency resonators are highly desirable.

This research employed acoustic analysis software and established an analytical method for sound transmission loss, which is a sound-insulation performance measure for glass windows. In addition to prediction of transmission loss through vibration of the glass, the research estimated acoustic characteristics that considered transmission loss in the vibration of the frame. Acoustic analysis was conducted with 3D CAD for glass windows of 8 mm plate thickness through preparation of an analysis model under the same conditions as a vibration test. The acoustic analysis also considered both the glass pane and aluminum frame on the side of the sound source. This paper evaluated the results based on analytical values and experimentally observed values.

From design perspective, structural modification including material modification and geometry modification in a brake system is the most common approach in reducing the brake squeal. Research of this paper will focus on the modification of the largest noise-generating part in motorcycle’s brake system-the circular disc rotor, based on an existing product available in Taiwan. To reach the best geometry design of a circular disc rotor for specific vibration reduction criteria, parametric studies will be carried out in understanding effects of two evenly distributed modifications in the disc — the bolts and ribs. This paper aims to find a criterion in dealing with the design of a pattern on a disk through finite element analyses and experimental modal analyses. From which results, a new criterion for frequency splitting is developed and a mode-veering phenomenon is observed. The outcome has engineering application in reducing specific squeal noise caused by split doublet modes and shifting natural frequencies of a brake disc without creating a new one.

An ‘acoustic fiber’, analogous to optical fiber, is presented as a means of long-distance data and energy transfer. Low-loss axial guided waves are produced along a cable-like waveguide, which is composed of a solid core and a cladding layer, where the cladding’s acoustic speeds of sound, both longitudinal and transverse, exceed those of the core. A similar condition exists in glass fiber optic cables consisting of a core surrounded by a cladding of lower index of refraction. This results in total internal reflection of light at the core-cladding interface and effective confinement of light to the core. A specific acoustic waveguide construction is analyzed, composed of an aluminum cladding with longitudinal wave speed of 6.198 km/s and shear wave of 3.122 km/s and copper core with longitudinal speed of 4.505 km/s, and shear speed of 2.164 km/s. Finite element simulations show that a guided wave mode that is confined largely to the core exists and is capable of propagating long distances with very little loss to the surroundings. A 6 mm diameter aluminum-cladded copper core (2 mm diameter) fiber was found to have a propagation loss of 0.023 dB/m when operating at 2 MHz predict (neglecting material attenuation). When including material attenuation, the same waveguide produced a propagation loss of 0.24 dB/m. Similarly, a 12 mm cladding with 4.8 mm core at 1 MHz had losses of 0.10 dB/m, and a 22 mm diameter cladding with 9 mm core at 500 kHz had losses of 0.062 dB/m. Relationships were found between frequency, total diameter and core diameter yielding the highest efficiencies. The minimum total dimension of an aluminum-clad-copper acoustic fiber was found to have an inverse relationship with frequency. The optimum ratio of core to total diameter was about 0.45 but between values of 0.35 and 0.5, attenuation was relatively constant (insensitive to frequency). Outside of that range, attenuation climbed rapidly. Due to this property, attenuation in properly designed fibers should always be dominated by, and roughly equivalent to, the material attenuation rather than attenuation due to leakage.

The purpose of this paper is to introduce the concept of entropy for a main resonator attached to a “fuzzy structure”. This structure is described explicitly using the Lagrangian method, and is treated as a layer of discrete resonators. A generic entropy formulation is then developed for the layer of resonators, which is used to determine the individual oscillator entropies. The combined entropy of the linear resonator system is then determined and compared numerically to the sum of the individual oscillator entropies. The entropy behavior of the system is then related to the energy behavior of the system and explained in regards to the the “artificial damping” of the main resonator.

Inhomogeneous electric field induces internal stress in flexoelectric materials, which is known as the converse flexoelectric effect . The atomic force microscope (AFM) probe can be applied to actuate the flexoelectric patch laminated on flexible structures and, in turn, induce structural vibrations. In this study, multiple actuators (i.e., combination of multiple AFM probes and flexoelectric patches) are used to suppress the vibration of an elastic cantilever beam. The displacement of the beam under control is obtained by superposition of a mechanical force induced part and an actuator induced part. The optimal actuator positions are selected when the minimal tip displacement of the cantilever beam is achieved. In case studies, only three actuators are used and only first three beam modes are considered. Under resonance conditions where only one mode participates, the optimal positions are obtained and they only depend on the relationship between actuation factor and actuator’s position. The influence of the patch length is discussed, followed by the analysis of control voltages applied to actuators. When the control voltage is so small as to the induced displacement is far less than that induced by the mechanical force, the optimal actuation positions do not vary with the voltage magnitude; while when the voltage is relatively large the actuators keep adjusting their relative optimal positions with respect to the control voltage and the system becomes unstable. Furthermore, as long as the control voltage is relatively small below the stability threshold, the optimal positions do not change as the position where mechanical force placed along the beam. Under the small voltage condition, a smooth relationship between optimal positions and vibration frequency is obtained. There are four jump points of optimal positions and they are related to the tip displacement-actuator position curves under different frequencies. This study serves as the foundation of flexoelectric vibration control with multiple AFM/flexoelectric actuators on flexible structures.

An existing defect on the bearing raceway may evolve with the interactions between the bearing elements, and the evolutions of the defect may be divided into different stages. In this study, a dynamic model for a cylindrical roller bearing with localized defects on raceways is developed to investigate vibration character of the bearing in these stages. The coupling of centrifugal forces, gravity forces and the slipping of the roller are considered. The half sine function and step function are used to construct time-varying models of defects in different stages, which is reflected on the local deflection. The system dynamic equations are solved by the fourth-order Runge-Kutta integration method with variable steps. Time domains and frequency domains are used to analyze dynamic responses of the bearing in every defect stage, which can be used as a reference of fault diagnosis. An experimental comparison in the previous study is carried out to validate the proposed model.

Engine mounts need to satisfy three design requirements: (1) firmly support engine weight, (2) isolate structure from the engine’s noise and vibration, and (3) control engine motion when large shocks or engine resonances are present. In addition to these three criteria, which are common for designing all types of engine mounts (passive, semi-active, and active), two more design requirements need to be satisfied for active engine mounts. First, they should be designed such that if there is any malfunction with the actuator, the controller, or the sensors, the active engine mount should still safely operate as a passive mount. Second, the power consumption, the size and weight of the required actuator and its controller should be kept as low as possible. The current paper aims to present an active hydraulic (or fluid) engine mount design by using an electromagnetic actuator and capacitive circuit such that it is able to act as a passive mount, semi-active mount, and an active mount. In addition, the presented design has the capability to be converted to a damper as and when needed. The multi-functional capability of the proposed engine mount design (passive, semi-active, active, and damper) distinguishes the current design from the previously designed active engine mounting systems, and this multi-functional capability is explained in the paper. The proposed design consists of a conventional passive hydraulic (fluid) mount, an electromagnetic actuator (voice coil) and a capacitive circuit. The voice coil is placed in the lower chamber of the passive hydraulic mount and it can change the volumetric stiffness of the bottom chamber actively such that the engine mount has low dynamic stiffness in a wide range of frequencies. The capacitive circuit is paralleled with the voice coil and in situations when large shock inputs are present; it adds capacitance to the electromagnetic circuit and changes the characteristics of the mount from an isolator to a damper. Since the active engine mount design of this paper involves several energy domains, bond graph modeling technique is used for mathematical modeling. MATLAB simulation results are shown for an automotive application and the performance of the proposed active engine mount design is evaluated as an isolator and as a damper. Finally, an adaptive controller, based on Filtered-X LMS algorithm, is proposed and its performance is investigated. The proposed design can eliminate transmitted force from the engine to the structure in a frequency range of 15 Hz to 125 Hz.

The location of leaks in water distribution pipes are traditionally identified by cross correlating two vibro-acoustic signals measured with accelerometers either side of the leak, but this method provides little information about the features of the signal (such as the leak flow rate) and does not differentiate between the leak signal and background noise. Due to its capability to provide time and frequency information, wavelet analysis can be used to extract features about the leak. However one of the greatest challenges is the selection of the mother wavelet, and there has been limited studies investigating how varying the mother wavelet can produce alternate results in the context of leaks in water distribution systems. This study demonstrates the potential of the wavelet transform to distinguish between the different features composed in the signal, including the leak noise, ambient noise, pump noise and leak type on plastic pipe when applied to data from a test rig. Variables such as the influence of pressure or distance from the leak are also included in order to demonstrate the efficacy of the wavelet transform in providing information about the signal. Moreover, this research gains an understanding of how the choice of different mother wavelet can influence the information provided by the leak signal. The results demonstrate that an appropriate mother wavelet can be identified and that the wavelet transform can localise features of the signal, including pump noise, background noise and the leaks characteristics.

A numerical study using our source code to acquire the acoustic properties of subsonic flow past an open cavity with different modified geometries will be presented in this paper. A Modified Curle’s analogy will be applied to solve the far field acoustics of the flow. Several cases with different leading edge of cavity fillet radii will be analysed and the effects will be investigated. It is important to find a way to attenuate the sound generation by the cavity, as it is an undesired situation for most applications. In this work a passive system, fillet modification to the leading edge of the cavity, is suggested and the effects of it on the sound generation is investigated.