Browse Topic: Identification
Gyroscopic effects split circumferential traveling-wave resonances of rotating structures into forward and backward branches. This work first analyzes the splitting in the co-rotating (Lagrangian) frame to provide physical intuition for the evolution of the two branches with spin speed. A transformation to the inertial (Eulerian) frame is then derived, showing that the observed frequencies are shifted by a kinematic Doppler-like term that acts with opposite sign on the forward and backward waves, leading to different Campbell-diagram slopes depending on the observation frame. The resulting framework is validated experimentally on a freely rotating, unloaded tire using two complementary sensing modalities: wireless on-tire accelerometers (co-rotating view) and a scanning laser Doppler vibrometer (inertial view). A frequency-domain SVD-based identification (FDD/ODS-SVD) is used to extract poles and deformation patterns over a range of spin speeds, enabling Campbell diagrams in both frames. The application of the proposed transformation maps the co-rotating branches onto the inertial observations, yielding consistent forward/backward splitting between the two measurement systems.
This paper investigates amplitude effects in the aeroelastic damping and frequency characteristics of the Maryland Tiltrotor Rig across four configurations: gimballed or hingeless hubs, each paired with straight or swept-tip blades. The recovery rate method is used to identify the aeroelastic parameters of the primary modes dominated by out-of-plane and in-plane wing bending from experimental free-decay strain time histories, capturing variations in dynamic behavior with the response amplitude. Results from conventional methods that assume linear (amplitude-independent) behavior are also presented for comparison. The local damping ratio of the examined modes generally decreases with increasing strain amplitude across all configurations, a trend missed by conventional linear estimation methods. The strength of amplitude effects varies as the system approaches instability: for gimballed configurations, they weaken near instability; for hingeless configurations, they become more pronounced. While the local frequency of the mode dominated by out-of-plane wing bending remains relatively constant with strain amplitude, the frequency of the mode dominated by in-plane wing bending displays significant amplitude-dependent shifts, particularly for hingeless hubs. The findings demonstrate the importance of accounting for nonlinear effects in aeroelastic parameter identification based on experimental tiltrotor data and provide insights into tiltrotor nonlinear dynamics.
Wake measurements were performed on a 2-m diameter rotor in forward flight at an advance ratio of 0.2 undergoing sinusoidal collective and cyclic inputs using 2D-3C phase-resolved PIV. Input frequencies of 0.05/rev, 0.1/rev, 0.2/rev, and 0.4/rev were tested. The goal of this study was to characterize the time-varying rotor wake and extract Pitt-Peters dynamic inflow model parameters for the lateral cyclic inflow state. In both input cases, the effects of the pitch inputs manifested as modulation of the local upwash and downwash of the trailing tip vortices near the tip path plane. It was found that additional azimuthal measurements are necessary to improve the extracted value of the steady Pitt-Peters term. However, the extracted mass term was within 12% of the Pitt-Peters value, demonstrating the ability of the presented analysis to resolve the dynamics of the wake with a limited number of azimuthal measurements.
During parking conditions of vehicles, the state of the battery is uncertain as it goes through the relaxation process. In such scenarios, the battery voltage may exceed the functional safety limits. If we cross the functional safety limits, it is hazardous to the driver as well as the occupant. In this case, relaxed voltage plays a crucial role in identifying the safe state of the battery. To estimate the relaxed cell voltage there are methods such as RC filter time constat modeling and relaxation voltage error method. The problem with these solutions is the waiting time and accuracy to determine the relaxation voltage. In this manuscript, a solution is proposed which ensures the above problem is reduced. To achieve the reduction of relaxation voltage estimation time, a python sparse identification of nonlinear dynamics (PySindy) is used which identifies and fits an equation model based on observing the battery characteristics at different SOC and temperatures. The implementation is done and compared with the existing algorithms at different temperature and SOC levels. It is validated that the manuscript predicts relaxation voltage within 1s having Mean Squared Error (MSE) of 0.04mV. In the existing method, it takes minimum 30 seconds of data to estimate relaxation voltage having a mean absolute error of 2.99mV. As a conclusion, manuscript being efficient and accurate to predict the relaxed voltage (OCV) which enhances the estimation of state of battery for functional safety aspects.
Retained surgical items are not as rare as many believe. While stories of sponges left inside patients occasionally make headlines, few realize the actual frequency: according to a systematic review of 21 studies by the Agency for Healthcare Research and Quality (AHRQ), these and other small items are left behind as often as 1.3 times per 10,000 surgical procedures.
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