In this paper, studies on dynamic modeling, simulation and experiment of power transmission belt drives are comprehensively reviewed. In the past few decades, many investigations are conducted on ...dynamic modeling, simulation and experiment of different kinds of power transmission belt drive systems. In the dynamic modeling and simulation of the belt drive systems, surveys are focused on vibrations of a single axially moving belt span, rotational vibrations of pulley components, coupled belt-pulley vibrations and contact mechanics between the belt and pulley as well as some experimental investigations. Influences of tensioner dry friction and one-way clutch on dynamics of the belt drive systems including system rotational vibrations and coupled belt-pulley vibrations are separately reported. The investigations are also surveyed on modeling and predicting complicated belt-pulley contact behaviors like belt creeps and slips on pulleys, contact force distributions of the belt and pulley, and variation of wrap angles of a belt around pulleys, etc., which are categorized by different approaches including the creep theory, shear theory, multi-body dynamics and finite element methods. Fatigue life estimation and failure analysis of power transmission belt drives are discussed in detail as well. In addition, experimental techniques are reviewed on parameters identifications, and measurements of static and dynamic performances including energy/power loss, system vibration, dynamic belt tension, belt deformation, stress and strain distribution in the belt and pulley, and contact friction force, etc. Finally, conclusion of this work is summarized and topics of future potential studies on the power transmission belt drive systems are suggested.
•A novel general-purpose 3D CSLDV system to measure 3D vibration is developed.•3D full-field ODSs of a turbine blade with a curved surface is measured.•MAC values between ODSs from 3D CSLDV and 3D ...SLDV measurements are larger than 95%.•The 3D CSLDV system can measure 1500 times more points than the 3D SLDV system.•Test time in 3D CSLDV measurement is less than 1/8 of that in 3D SLDV measurement.
Three-dimensional (3D) full-field vibration measurement is significant to structures, especially those with curved surfaces. A triaxial accelerometer and a commercial non-contact 3D scanning laser Doppler vibrometer (SLDV) system are usually used in 3D vibration measurement of a structure. However, the triaxial accelerometer can lead to the mass-loading problem for a light-weight structure, and the 3D SLDV system can take a long time to complete scanning of a structure with a large surface in a step-wise scanning mode. This study proposes a novel general-purpose 3D continuously scanning laser Doppler vibrometer (CSLDV) system to measure 3D full-field vibration of a structure with a curved surface in a non-contact and fast way. The proposed 3D CSLDV system consists of three CSLDVs, a profile scanner, and an external controller, and is experimentally validated by measuring 3D full-field vibration of a turbine blade with a curved surface under sinusoidal excitation and identifying its operating deflection shapes (ODSs). A 3D zig-zag scan path is proposed for scanning the curved surface of the blade based on results from the profile scanner, and scan angles of mirrors in CSLDVs are adjusted based on relations among their laser beams to focus three laser spots at one location, and direct them to continuously and synchronously scan the proposed 3D scan path. A signal processing method that is referred to as the demodulation method is used to identify 3D ODSs of the blade. The first six ODSs from 3D CSLDV measurement have good agreement with those from a commercial 3D SLDV system with modal assurance criterion values larger than 95%. In the experiment, it took the 3D SLDV system about 900 seconds to scan 85 measurement points, and the 3D CSLDV system 115.5 seconds to scan 132,000 points, indicating that the 3D CSLDV system proposed in this study is much more efficient than the 3D SLDV system for measuring 3D full-field vibration of a structure with a curved surface.
Thermoelastic dynamic analysis of micro-/nano-beams is essential in the field of micro-/nano-electro-mechanical systems (MEMSs/NEMSs). However, the classical coupled thermoelastic theory is not ...suitable for the microscopic/nanoscopic case. As elementary parts of MEMSs/NEMSs, the size effect of micro-/nano-beams must be considered in their thermoelastic vibrations. This work originally explores analytical solutions of coupled thermoelastic forced vibrations of micro-/nano-beams based on Rayleigh beam theory and Eringen nonlocal elasticity theory. The heat conductivity equation is obtained by using the type Ⅲ Green-Naghdi theory. Coupled thermoelastic dynamic equations are decoupled by use of Green's function method and expressions of displacements, temperature fields, and thermal moments of micro-/nano-beams are derived. Furthermore, movement behaviors of an “ice core” of the temperature field are used to explain dynamic phenomena of the coupled system. Results from finite element analysis are compared with analytical solutions for verification purposes. This work primarily discusses influences of a small-scale parameter on coupled displacement and temperature fields and those of other important physical parameters, such as heating positions and height-to-length ratios of micro-/nano-beams, on system responses.
The effects of a wavy wall on the stability of a hypersonic boundary layer on a flared cone are investigated by detailed experimental measurements and direct numerical simulations. The non-contact ...optical measurement method of focused laser differential interferometry is used to measure the disturbance development within the wavy region. The measurement results show that the second mode for the wavy wall is suppressed significantly compared with the smooth wall, and that multiple disturbances at low frequencies appear within the wavy region. Numerical corroboration against experimental measurements reveals good quantitative agreement. It is found that the disturbances at $f=360$ kHz on the wavy wall are suppressed appreciably, which are very significant on the smooth wall. And the disturbances at $f=140$ kHz and $f=260$ kHz develop within the wavy region, and increase considerably. Also, the disturbances achieve a significant increase over the first half of a wavy trough and become more stable over the second half of a wavy trough. The physical mechanism is found to be due to the change in wall geometry and is attributed to the spatially modulated mean flow. The disturbance growth rate is closely related to the level of the mean-flow distortion.
Background and purpose
Alterations in the gut microbial community composition may be influential in neurological disease. Microbial community profiles were compared between early onset pediatric ...multiple sclerosis (MS) and control children similar for age and sex.
Methods
Children ≤18 years old within 2 years of MS onset or controls without autoimmune disorders attending a University of California, San Francisco, USA, pediatric clinic were examined for fecal bacterial community composition and predicted function by 16S ribosomal RNA sequencing and phylogenetic reconstruction of unobserved states (PICRUSt) analysis. Associations between subject characteristics and the microbiota, including beta diversity and taxa abundance, were identified using non‐parametric tests, permutational multivariate analysis of variance and negative binomial regression.
Results
Eighteen relapsing−remitting MS cases and 17 controls (mean age 13 years; range 4–18) were studied. Cases had a short disease duration (mean 11 months; range 2–24) and half were immunomodulatory drug (IMD) naïve. Whilst overall gut bacterial beta diversity was not significantly related to MS status, IMD exposure was (Canberra, P < 0.02). However, relative to controls, MS cases had a significant enrichment in relative abundance for members of the Desulfovibrionaceae (Bilophila, Desulfovibrio and Christensenellaceae) and depletion in Lachnospiraceae and Ruminococcaceae (all P and q < 0.000005). Microbial genes predicted as enriched in MS versus controls included those involved in glutathione metabolism (Mann−Whitney, P = 0.017), findings that were consistent regardless of IMD exposure.
Conclusions
In recent onset pediatric MS, perturbations in the gut microbiome composition were observed, in parallel with predicted enrichment of metabolic pathways associated with neurodegeneration. Findings were suggestive of a pro‐inflammatory milieu.
SnSe is a promising thermoelectric material with record-breaking figure of merit. However, to date a comprehensive understanding of the electronic structure and most critically, the self-hole-doping ...mechanism in SnSe is still absent. Here we report the highly anisotropic electronic structure of SnSe investigated by angle-resolved photoemission spectroscopy, in which a unique pudding-mould-shaped valence band with quasi-linear energy dispersion is revealed. We prove that p-type doping in SnSe is extrinsically controlled by local phase segregation of SnSe
microdomains via interfacial charge transferring. The multivalley nature of the pudding-mould band is manifested in quantum transport by crystallographic axis-dependent weak localisation and exotic non-saturating negative magnetoresistance. Strikingly, quantum oscillations also reveal 3D Fermi surface with unusual interlayer coupling strength in p-SnSe, in which individual monolayers are interwoven by peculiar point dislocation defects. Our results suggest that defect engineering may provide versatile routes in improving the thermoelectric performance of the SnSe family.
A novel three-dimensional (3D) continuously scanning laser Doppler vibrometer (CSLDV) system that contains three CSLDVs and an external controller is developed to measure 3D vibration of a structure ...under random excitation, and a new operational modal analysis method is proposed to estimate its 3D modal parameters, including damped natural frequencies and undamped end-to-end mode shapes, by extending the conventional demodulation method. Calibration among three CSLDVs in the 3D CSLDV system based on the geometrical model of its scan mirrors is conducted to adjust their rotational angles and ensure that three laser spots can continuously and synchronously move along the same scan path on the structure. The extended demodulation method can estimate undamped mode shapes of the structure under random excitation by filtering raw response with a bandpass filter and multiplying the filtered response by sinusoidal signals with its damped natural frequencies obtained from the fast Fourier transform of raw response. Experimental investigation on one-dimensional (1D) and 3D CSLDV measurements for modal parameter estimation is conducted on a beam under white-noise excitation to validate the extended demodulation method and examine the accuracy of the 3D CSLDV system. Modal assurance criterion (MAC) values between the first four undamped mode shapes of the beam from 1D CSLDV measurement and corresponding damped mode shapes from 1D step-wise scanning measurement are larger than 95%. MAC values between the first four undamped mode shapes of the beam from 3D CSLDV measurement and corresponding damped mode shapes from 3D step-wise scanning measurement are larger than 90% in all the three directions of a specified measurement coordinate system.
A new formulation is developed for dynamic analysis of a rotating planar Timoshenko beam. The configuration of Timoshenko beam is described using its slope angle and axial and shear strains; hence, ...the shear locking problem can be naturally avoided. Nonlinear partial differential equations of the rotating hub–beam system and associated boundary conditions are derived using Hamilton’s principle. While six boundary conditions are needed for choice of trial functions of three dependent variables, there are only four boundary conditions that can be determined and two boundary conditions are undetermined. An accurate global spatial discretization method is used, where dependent variables are divided into internal and boundary-induced terms. Internal terms only need to satisfy homogeneous boundary conditions, which can be easily chosen as trigonometric functions. Boundary-induced terms are interpolated using dependent variables at boundaries that are taken as generalized coordinates. Nonlinear governing ordinary differential equations of the system are obtained using Lagrange’s equations. When the hub rotates at a constant angular velocity, nonlinear governing equations can be linearized for vibration analysis, and dimensionless vibration equations of the beam are obtained. Natural frequencies and mode shapes of the beam with a constant angular velocity are calculated and compared with available results in the literature. Frequency veering and mode shift phenomena occur. Nonlinear dynamic responses of the system are then calculated and compared with those from the commercial software ADAMS, and they are in good agreement. Axial and shear strains of the beam and their spatial derivatives are also calculated. Since trial functions in the assumed modes method cannot satisfy undetermined boundary conditions, inaccurate results of strains and their spatial derivatives are obtained using the assumed modes method. Hence, use of the accurate global spatial discretization method in the current formulation is essential here.
•A geometrical model of a continuously scanning laser vibrometer is built.•Continuously and synchronously scanning relations among three vibrometers are established.•Vibration measurement of a beam ...and plate is conducted by a 3D continuous scanning system.
This paper presents for the first time an investigation of three-dimensional (3D) vibration measurement by three scanning laser Doppler vibrometers (SLDVs) in a continuously and synchronously scanning mode. Three laser spots from the three SLDVs continuously move along the same scan trajectory and synchronously measure vibration of the same point on a surface of a structure. The three SLDVs, i.e., Top, Left, and Right SLDVs, are from a Polytec PSV-500-3D system and input signals to scan mirrors of each SLDV are controlled by an external dSPACE MicroLabBox control unit. The whole system is called a 3D continuously SLDV (3D-CSLDV) system. Methodologies are developed in this investigation to achieve the continuously and synchronously scanning mode by the system. First, the geometrical model of a CSLDV is built to obtain locations of the three CSLDVs with respect to a specified measurement coordinate system (MCS). Second, a scan trajectory on the measured surface is defined and rotation angles of scan mirrors of the Top CSLDV are obtained by scanning the trajectory. Third, since locations of the three CSLDVs with respect to the MCS have been obtained in the first step, rotation angles of scan mirrors of Left and Right CSLDVs to scan the defined trajectory can be obtained from those of the Top CSLDV based on spatial relations among the three CSLDVs. Experiments to scan a beam and a plate were conducted using the 3D-CSLDV system. Operating deflection shapes (ODSs) of the beam and plate in three directions of the MCS were obtained and they were in good agreement with those obtained by traditional step scanning. The results demonstrate the feasibility of 3D vibration measurement by the 3D-CSLDV system in a continuously and synchronously scanning mode.
A typical engine front end accessory drive system (FEADS) is mathematically modeled through Hamilton’s principle and Newton’s second law. In this model, the belt’s flexural rigidity and pulley’s ...eccentricity are considered. Eccentricities of the pulleys are introduced into governing motion equations of the belt spans through the boundary conditions and then transformed to external forces acting on the belt spans. Vibration modes and natural frequencies of the FEADS are calculated by the state-space technique of the complex mode theory. Dynamic responses of the FEADS at different rotational rates of the crankshaft are calculated by solving the spatially discretized governing equations obtained by Galerkin method. The modeling and solution methods are formulated and programmed in a general purposed code. The study shows that the typical resonance and beat phenomenon happen in a certain portion of the belt spans at a certain rotational rate by the excitations of the pulley’s eccentricity. According to the modal analysis and dynamic response analysis, an optimization method based on a genetic algorithm is proposed. By comparing the vibration amplitudes of belt spans before and after optimization at different rotational rates, this optimization method is verified to be effective in reducing transverse vibrations of the belt spans.
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