Uncertainty analysis for the prediction of disc brake squeal propensity

© 2017 Institute of Noise Control Engineering. All rights reserved. ACT Since brake squeal was first investigated in the 1930s, it has been a noise, vibration and harshness (NVH) problem plaguing the automotive industry due to warranty-related claims and customer dissatisfaction. Accelerating research efforts in the last decade, represented by almost 70% of the papers published in the open literature, have improved the understanding of the generation mechanisms of brake squeal, resulting in better analysis of the problem and better development of countermeasures by combining numerical simulations with noise dynamometer tests. However, it is still a challenge to predict brake squeal propensity with any confidence. This is because of modelling difficulties that include the often transient and nonlinear nature of brake squeal, and uncertainties in material properties, operating conditions (brake pad pressure and temperature, speed), contact conditions between pad and disc, and friction. Although the conventional Complex Eigenvalue Analysis (CEA) method, widely used in industry, is a good linear analysis tool for identifying unstable vibration modes to complement noise dynamometer tests, it is not a predictive tool as it may either over-predict or under-predict the number of unstable vibration modes. In addition, there is no correlation between the magnitude of the positive real part of a complex eigenvalue and the likelihood that the unstable vibration mode will squeal. Transient nonlinear simulations are still computationally too expensive to be implemented in industries for even exploratory predictions. In this paper, a stochastic approach, incorporating uncertainties in the surface roughness of the lining, material properties and the friction coefficient, is applied to predict the squeal propensity of a full disc brake system by using CEA on a finite element model updated by experimental modal testing results. Results compared with noise dynamometer squeal tests illustrate the potential of the stochastic CEA approach over the traditional deterministic CEA approach

Application of polynomial chaos expansions to analytical models of friction oscillators

Despite past substantial research efforts, the prediction of brake squeal propensity remains a largely unresolved problem. The standard practice to predict the brake squeal propensity is to analyse dynamic instabilities using the complex eigenvalue analysis. However, it is well known that not every predicted unstable vibration mode will lead to squeal and vice-versa. Owing to nonlinearity and problem complexity (e.g. operating conditions), treating brake squeal with uncertainty seems appealing. Another indicator of brake squeal propensity, not often used, is based on negative dissipated energy. In this study, uncertainty analysis induced by polynomial chaos expansions is examined for 1-dof and 4-dof friction models. Results are compared with dissipated energy calculations and standard complex eigenvalue analysis. The potential of this approach for the prediction of brake squeal propensity is discussed. © (2013) by the Australian Acoustical Society

Instability analysis of brake squeal with uncertain contact conditions

© 25th International Congress on Sound and Vibration 2018, ICSV 2018: Hiroshima Calling. All rights reserved. Brake squeal, as a phenomenon of friction-induced self-excited vibrations, has been a noise, vibration and harshness (NVH) problem for the automotive industry due to warranty-related claims and customer dissatisfaction. Intensive research in the past two decades have provided insight into a number of mechanisms that trigger brake squeal. However, brake squeal is a transient and nonlinear phenomenon and many determining factors are not known precisely such as material properties, operating conditions (brake pad pressure and temperature, speed), contact conditions between pad and disc, and friction. As a result, reliable prediction of brake squeal propensity is difficult to achieve and extensive noise dynamometer testings are still required to identify problematic frequencies for the development and validation of countermeasures. Here, the influence of uncertainties in friction modelling and contact conditions on friction-induced self-excited vibrations of a 3 x 3 coupled friction oscillators model is examined by combining the linear Complex Eigenvalue Analysis (CEA) method widely used in industry with a stochastic approach that incorporates these uncertainties. It has been found that unstable vibration modes with consistently high occurrence of instability independent of the contact area, friction modelling and sliding speed could be identified. Such unstable modes are considered to be robustly unstable and are most likely to produce squeal. An example is given to illustrate how instability countermeasures could be designed by repeating the uncertainty analysis for these robustly unstable modes. These results highlight the potential of reliable prediction of brake squeal propensity in a full brake-system using a stochastic approach with the CEA

Revisiting stigmergy in light of multi-functional, biogenic, termite structures as communication channel

Termite mounds are fascinating because of their intriguing composition of nu- merous geometric shapes and materials. However, little is known about these structures, or of their functionalities. Most research has been on the basic com- position of mounds compared with surrounding soils. There has been some targeted research on the thermoregulation and ventilation of the mounds of a few species of fungi-growing termites, which has generated considerable inter- est from human architecture. Otherwise, research on termite mounds has been scattered, with little work on their explicit properties. This review is focused on how termites design and build functional structures as nest, nursery and food storage; for thermoregulation and climatisation; as defence, shelter and refuge; as a foraging tool or building material; and for colony communication, either as in indirect communication (stigmergy) or as an information channel essential for direct communication through vibrations (biotremology). Our analysis shows that systematic research is required to study the prop- erties of these structures such as porosity and material composition. High res- olution computer tomography in combination with nonlinear dynamics and methods from computational intelligence may provide breakthroughs in un- veiling the secrets of termite behaviour and their mounds. In particular, the ex- amination of dynamic and wave propagation properties of termite-built struc- tures in combination with a detailed signal analysis of termite activities is re- quired to better understand the interplay between termites and their nest as superorganism. How termite structures serve as defence in the form of disguis- ing acoustic and vibration signals from detection by predators, and what role local and global vibration synchronisation plays for building are open ques- tions that need to be addressed to provide insights into how termites utilise materials to thrive in a world of predators and competitors

Methylation of miR-155-3p in mantle cell lymphoma and other non-Hodgkin's lymphomas

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An immersed boundary-lattice Boltzmann method for fluid-structure interaction problems involving viscoelastic fluids and complex geometries

An immersed boundary-lattice Boltzmann method (IB-LBM) for fluid-structure interaction (FSI) problems involving viscoelastic fluids and complex geometries is presented in this paper. In this method, the fluid dynamics and the constitutive equations of viscoelastic fluids are both solved using the lattice Boltzmann method. In order to enhance numerical stability in solving the constitutive equations, an artificial damping is introduced which does not affect the numerical results if the damping effect is much smaller than the relaxation and the convective effects. The structural dynamics including 2D and 3D capsules, 2D and 3D rigid particles and flags, are solved by the finite difference method (2D capsules, 2D and 3D rigid particles and flags) and the finite element method (3D capsules). The interaction between the solid structure and the fluid is enforced by an immersed boundary method. The overall framework of this method is very simple, enabling modelling FSI problems involving viscoelastic fluids and the inertia of both fluids and structures. It is very efficient for FSI problems involving high Weissenberg numbers flows, large deformations and complicated geometries without any preconditioner. This work uses IB-LBM to solve for the first time, flows involving viscoelastic fluids coupled with non-massless deforming structures. The method is also capable of solving very high Weissenberg number problems, as demonstrated by simulations of flexible particle flows at . The present method and models are validated by several cases including a 2D rigid particle migration in a Giesekus Couette flow, a spherical particle rotation in an Oldroyd-B shear flow, a spherical particle settling in a FENE-CR fluid, 2D and 3D capsules deformation in a Newtonian shear flow, and a 3D flag flapping in a Newtonian free stream. In addition, the present method is also applied to simulate the deformation of 2D and 3D capsules in an Oldroyd-B shear flow, a 3D flag flapping in an Oldroyd-B free stream, and elastic capsule movement in a contraction-expansion channel filled with an Oldroyd-B fluid. Deformation of the capsules decreases with the increase of the Weissenberg number and the capsules experience monotonically increasing deformation when the Weissenberg number is above a critical value which is respectively 10 for 2D and 2 for 3D simulations. Viscoelasticity of the Oldroyd-B fluid hinders the flapping motion of the 3D flag. For elastic capsules passing through a periodic contraction-expansion channel, the capsules mix up after a short-term evolution, and then migrate to the bottom of the channel and almost follow two steady trajectories after a long-term evolution. The validations and applications provide extensive data which may be used to expand the currently limited database available for FSI benchmark studies

Sensing of minute airflow motions near walls using pappus-type nature-inspired sensors

This work describes the development and use of pappus-like structures as sensitive sensors to detect minute air-flow motions. We made such sensors from pappi taken from nature-grown seed, whose filiform hairs' length-scale is suitable for the study of large-scale turbulent convection flows. The stem with the pappus on top is fixated on an elastic membrane on the wall and tilts under wind-load proportional to the velocity magnitude in direction of the wind, similar as the biological sensory hairs found in spiders, however herein the sensory hair has multiple filiform protrusions at the tip. As the sensor response is proportional to the drag on the tip and a low mass ensures a larger bandwidth, lightweight pappus structures similar as those found in nature with documented large drag are useful to improve the response of artificial sensors. The pappus of a Dandelion represents such a structure which has evolved to maximize wind-driven dispersion, therefore it is used herein as the head of our sensor. Because of its multiple hairs arranged radially around the stem it generates uniform drag for all wind directions. While still being permeable to the flow, the hundreds of individual hairs on the tip of the sensor head maximize the drag and minimize influence of pressure gradients or shear-induced lift forces on the sensor response as they occur in non-permeable protrusions. In addition, the flow disturbance by the sensor itself is limited. The optical recording of the head-motion allows continuously remote-distance monitoring of the flow fluctuations in direction and magnitude. Application is shown for the measurement of a reference flow under isothermal conditions to detect the early occurrence of instabilities

Improved Measurement of Electron Antineutrino Disappearance at Daya Bay

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