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
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
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.
This specification covers a synthetic rubber in the form of sheet, strip, tubing, extrusions, and molded shapes. This specification should not be used for molded rings, compression seals, O-ring cords, and molded in place gaskets for aeronautical and aerospace applications without complete consideration of the end use prior to the selection this material.
This SAE Aerospace Recommended Practice (ARP) specifies dimensional and physical requirements of tow bar connections to tractor and aircraft (see Figure 1). It is applicable to all types of commercial transport category aircraft tow bar. The purpose of this SAE Aerospace Recommended Practice (ARP) is to standardize tow bar attachments to airplane and tractor according to the mass category of the towed aircraft, so that one tow bar head with different shear levels can be used for all aircraft that are within the same mass category and are manufactured in compliance with AS1614 or ISO 8267.
This SAE Aerospace Standard (AS) specifies the inside diameters, cross-sections, tolerances, and size identification codes (dash numbers) for O-rings used in sealing applications and for straight thread tube fitting boss gaskets. The dimensions and tolerances specified in this standard are suitable for any elastomeric material provided that suitable tooling is available.
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
This specification covers a fluorosilicone (FVMQ) rubber in the form of molded rings.
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.
This specification covers tungsten carbide-cobalt in the form of powder.
This SAE Standard establishes the minimum circuit identification and requirements for Multi-Voltage Power Distribution Systems (MVPDS) for use on trucks and buses. A Multi-Voltage Power Distribution System is one that distributes two or three voltages, up to 60 VDC, to power the controls, instruments, and devices.
This specification covers procedures for tab marking of bare welding wire to provide positive identification of cut lengths and spools.
This standard establishes the dimensional and visual quality requirements, lot requirements, and packaging and labeling requirements for O-rings molded from AMS7274 rubber. It shall be used for procurement purposes.
This investigation reveals many DoD contractors do not treat integration as a stand-alone activity. Instead, integration is an inherent part of the development process. The contractors did not have a specific documented process for integration beyond calling out integration as an activity in the development process. Integration is an integrator unique step within the development process to meet functional and performance requirements. Identification of the interfaces and engineering to match the interfaces requires substantial individual expertise and heuristics for each integration effort resulting in inconsistent non-repeatable integrations. This increases risk, and limits third party integration effectiveness and utility. This paper identifies steps that can be taken to increase the speed and effectiveness of integration while decreasing the effort and dependency on individual expertise.
Generalized Predictive Control (GPC) is an advanced form of an adaptive control algorithm that uses experimentally acquired data to determine the input-output relationship of complex systems through a process called system identification. GPC has historically been employed for stability augmentation and vibration reduction of dynamically-scaled tiltrotor aircraft wind-tunnel models since the complex nature of these dynamic systems does not lend itself well to traditional control approaches. The present research expands upon previous analytical and experimental work with wind-tunnel experiments that utilize improved GPC techniques. These techniques improved controller robustness such that a working controller was stable across a multitude of model configurations and wind-tunnel conditions and successfully suppressed vibration and vehicle flutter. Advanced GPC (AGPC) enables self-adaptation of a traditional GPC control law. AGPC was also investigated during the present research but was
Dynamic rollovers represent a major hazard for helicopters during near-ground operations, often resulting in significant aircraft damage and passenger injuries. To improve safety in operations, recent studies have focused on developing a Helicopter Flight Data Monitoring framework to provide data-driven insights on operational safety. This work contributes to that effort by proposing an approach to identify precursors to dynamic rollovers. According to NTSB reports, approximately 60% of such incidents occur during in-flight phases like hover, hover-taxi, or landing. To capture the complex non-linear dynamics of helicopters, physics-based simulations were conducted to estimate a first hitting time metric, defined as the time until blade-ground contact, across a wide range of initial conditions for an inflight initial state of the helicopter. Eight parameters were identified as driving the first hitting time, and a probabilistic model was created to predict the distribution of that
This paper deals with the uncertainty estimation of identified frequency and damping trends of whirl flutter modes, obtained by applying system identification methods on experimental data. In particular, two different identification approaches are considered, namely the free-decay analysis by using Matrix Pencil algorithm and the Data-Driven Stochastic Subspace Identification method (SSI), applied to system response to stochastic input. The two approaches lead to as many uncertainty estimation methodologies, both leveraging the bootstrapping statistical process. A full validation procedure is then set up to assess the accuracy of such methods in correctly quantifying the uncertainty of the estimated statistics. To do so, a wing-rotor state-space linear numerical model is used to simulate system response to both dwell and stochastic inputs. The state space numerical system aims to replicate the ATTILA wing-rotor wind-tunnel model, which falls in the framework of Clean Sky 2 European
This paper presents the experimental results of a bare-aircraft model identification of a small-medium sized helicopter. The experimental data were collected using two different approaches, i.e. with manual inputs in open-loop and with automatic inputs in closed-loop. This work demonstrates experimentally that, using a suitable algorithm, the two different experimental approaches converge on equivalent models. The proposed algorithm, i.e., a continuous-time variant of the Predictor Based Subspace Identification Algorithm (PBSID) algorithm, prove to deal properly with data acquired in closed-loop where the correlation between the inputs is very high.
This paper presents an analytical approach for identifying suspension kingpin alignment parameters based on screw axis theorem and differential calculation model. The suspension kingpin caster and inclination alignment parameters can produce additional tire force, which affects vehicle handling dynamics. In wheel steering process, the multi-link suspension control arms lead to movement of the imaginary kingpin, which can cause change in suspension kingpin alignment parameters. According to the structure mechanism of commercial vehicle multi-link independent suspension, the kinematics characteristics of imaginary kingpin were analyzed based on the screw axis theorem. The angular velocity and translation velocity vectors were calculated. In order to avoid the influence of bushing deformation, the unique differential identification model was established to evaluate the suspension kingpin alignment parameters, and the identification results were compared with the ADAMS/Car data. The
Items per page:
50
1 – 50 of 10162