Investigation of the Split in the Fundamental Air-Cavity Mode of Loaded Tires

It is well known that a tire’s fundamental air-cavity mode, typically near 200 Hz for current passenger car tires, can split into two adjacent features when a tire is loaded and hence deformed, thus creating a fore-aft, horizontal mode and a vertical mode. This split happens because the deformed tires is no longer geometrically symmetric: the air channel in the bottom region of the tire is narrowed, hence effectively increasing the inertia in that region, and thus causing the fore-aft mode, which has a relatively large particle velocity in the bottom part of the tire, to have a lower natural frequency than the vertical mode. These modes are important because they can create dynamic force inputs to the suspension system and thus they can contribute to vehicle interior noise at the modal natural frequencies. In the present work, measurements of the dispersion relations for a set of loaded tires was conducted to determine the range of magnitudes of the modal frequency split. Splits ranging from 3.4 Hz to 12 Hz at rated load have been identified, and it has also been found that the magnitude of the frequency split for a given tire is very nearly quadratically proportional to the applied load

Simulation of the Frequency Split of the Fundamental Air Cavity Mode of a Loaded and Rolling Tire by Using Steady-State Transport Analysis

It has been found that when a tire deforms due to loading, the fundamental air cavity mode splits into two due to the break in geometrical symmetry. The result is the creation of fore-aft and vertical acoustic modes near 200 Hz for typical passenger car tires. When those modes couple with structural, circumferential modes having similar natural frequencies, the oscillatory force transmitted to the suspension can be expected to increase, hence causing increased interior noise levels. Further, when the tire rotates, the frequency split is enlarged owing to the Doppler effect resulting from the airflow within the tire cavity. The current research is focused on determining the influence of rotation speed on the frequency split by using FE simulation. In particular, the analysis was performed by using steady-state transport analysis which enables vibroacoustic analysis in a moving frame attached to tire in the frequency domain. The details of the modeling are described and results are given for a tire under different rotation speeds, presented in terms of dispersion curves that illustrate the interaction between structural and acoustical modes. The results are compared to those for static tires and tires spinning without translational velocity to highlight the effects of rolling

Modeling of Sound Radiation from a Loaded Rolling Tire

In recent work it has been possible to model the surface vibration of a loaded rolling tire, including the influence of the acoustic mode that forms within the tire cavity. For example, it has been found that the acoustic cavity mode splits owing to the deformation of the tire when it is loaded, and that the split widens owing to Doppler effects when the tire is rolling. It has also been demonstrated that the force at the hub that results from the acoustic cavity mode is strongly dependent on interaction with circumferential structural modes of the treadband. The finite element models developed to-date, thus allow a prediction of the tire’s surface vibration. To predict the sound radiation from the deformed, rolling tire, the surface vibration data has been used as the input to boundary element calculations; the effect of the ground surface is modeled by creating an “image” tire. The calculations have been used to illustrate the nature of the exterior sound radiation that results from the acoustic cavity mode, which can be relatively efficient due to the sonic phase speed of the mode within the tire cavity, as opposed to the subsonic structural wave propagation along the treadband

Prediction of Split in Fundamental Air-Cavity Mode of Loaded Tires based on Experimental Observations and Computational Simulations

In previous studies, it was found that a tire’s fundamental air-cavity mode, typically near 200 Hz for current passenger car tires, splits into two features when the tire is loaded. Since the deformed tire is no longer geometrically symmetric, separate fore-aft and vertical modes appear, the former mode appearing at a slightly lower frequency than the vertical mode. These modes are key contributors to dynamic loads on the suspension system and consequently on cabin noise near 200 Hz. In this context, measurements of the dispersion relations for a set of loaded tires were performed to investigate the range of magnitudes of the modal frequency split. Also, finite element analysis of a tire was deployed to model the dispersion in the vicinity of the fundamental air cavity mode. Splits ranging from approximately 3 Hz to 12 Hz at rated load were identified, and it has also been found that the magnitude of the frequency split for a given tire shows a low order polynomial relationship to the applied load

Overcoming Overconfidence for Active Learning

It is not an exaggeration to say that the recent progress in artificial intelligence technology depends on large-scale and high-quality data. Simultaneously, a prevalent issue exists everywhere: the budget for data labeling is constrained. Active learning is a prominent approach for addressing this issue, where valuable data for labeling is selected through a model and utilized to iteratively adjust the model. However, due to the limited amount of data in each iteration, the model is vulnerable to bias; thus, it is more likely to yield overconfident predictions. In this paper, we present two novel methods to address the problem of overconfidence that arises in the active learning scenario. The first is an augmentation strategy named Cross-Mix-and-Mix (CMaM), which aims to calibrate the model by expanding the limited training distribution. The second is a selection strategy named Ranked Margin Sampling (RankedMS), which prevents choosing data that leads to overly confident predictions. Through various experiments and analyses, we are able to demonstrate that our proposals facilitate efficient data selection by alleviating overconfidence, even though they are readily applicable

Finite Element Modeling of Force Amplification at the Spindle due to a Tire’s Cavity Mode: Experimental Verification

Reduction of tire road noise is an important issue when developing luxury cars and electric vehicles. In this context, the air cavity mode is an important source of spindle forces transmitted to the suspension that then increase interior noise levels. When a tire rotates, the cavity mode near 200 Hz splits into two adjacent modes due to a Doppler effect and tire deformation. That split can lead to increased levels of both longitudinal and vertical spindle forces at the spindle since the two acoustic modes each contribute to both forces when the tire rotates. Thus, it is important to develop tools to identify the contributions of the split air cavity modes to the spindle force. A FE simulation of the spindle force for a steady state rolling tire has been verified by a comparison with laboratory test results obtained by using a wheel force transducer mounted on Purdue’s Tire Pavement Test Apparatus. It was observed that the frequency split expands as the rotation speed increases and that the vertical spindle force increases when aligned with an odd numbered circumferential structural mode

Force Amplification at the Wheel Hub Due to the Split in the Air-Cavity Mode for a Rolling Tire

Reduction of tire/road noise has become an important issue for EVs since powertrain noise has largely been eliminated. A tire’s air-cavity mode is known to be a significant contributor to increased forces at the wheel hub, which can result in significant interior noise levels near 200 Hz. Moreover, the single natural frequency of a static, undeformed tire can separate into two neighboring frequencies for a rolling, deformed tire due to the combination of the tire’s asymmetry, and the Doppler effect resulting from the tire’s rotation. In this study, the evolution of the Doppler-related frequency split with increasing speed was observed in Tire Pavement Test Apparatus (TPTA) tests by measuring the dynamic force at the hub under rotation and load. Similar results were obtained using FE simulations. Through the FE simulation, it has been shown that there can be force amplification at the hub when the split frequencies couple with adjacent treadband structural modes near 200 Hz. In addition, material modifications were applied to the base model in the simulations to find values that would reduce force levels at the split frequencies. Finally, it is suggested that a target speed needs to be determined when evaluating a tire since the two split, natural frequencies are strongly influenced by rotation speed

Development of a Chaff Dispense Program for Target Tracking Radar Deception

This study aims to develop an appropriate chaff dispensing program to deceive the target tracking radar (TTR) effectively. Chaff is a countermeasure commonly used by fighter aircraft to deceive TTR. However, there has been a lack of methodology for calculating chaff dispense programs that take into account the specific characteristics of the fighter, chaff, and TTR. This study proposes a methodology that considers these variables to calculate chaff dispense programs and addresses this gap. The proposed method is demonstrated through TESS engagement, which shows its effectiveness in various engagement situations

A Laboratory Procedure for Measuring the Dispersion Characteristics of Loaded Tires

It is of interest to be able to measure the wave dispersion characteristics of tires, since that information can be used to identify the types and speeds of waves propagating within them. The latter information can be used, for example, to identify the waves that preferentially radiate sound or create structure-borne disturbances that can propagate into the vehicle interior. This type of measurement is usually performed by driving an unloaded tire at one point on its treadband with a shaker, and then measuring the resulting radial vibration around the tire circumference by using a laser vibrometer. The latter spatial data can then be Fourier transformed, one frequency at-a-time, to reveal the tire’s dispersion characteristics. However, it is well known that loading a tire has a significant impact on its dynamic response, causing circumferential modes of both the carcass and interior air space to split, for example. In this paper, the design and construction of an experimental rig that allows dispersion measurements to be made on a loaded tire will be described. Here, the focus was on relatively low frequencies, so the rig was designed to be dynamically rigid below 300 Hz