Coordinates and maps of the Apollo 17 landing site

We carried out an extensive cartographic analysis of the Apollo 17 landing site and determined and mapped positions of the astronauts, their equipment, and lunar landmarks with accuracies of better than ±1 m in most cases. To determine coordinates in a lunar body‐fixed coordinate frame, we applied least squares (2‐D) network adjustments to angular measurements made in astronaut imagery (Hasselblad frames). The measured angular networks were accurately tied to lunar landmarks provided by a 0.5 m/pixel, controlled Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) orthomosaic of the entire Taurus‐Littrow Valley. Furthermore, by applying triangulation on measurements made in Hasselblad frames providing stereo views, we were able to relate individual instruments of the Apollo Lunar Surface Experiment Package (ALSEP) to specific features captured in LROC imagery and, also, to determine coordinates of astronaut equipment or other surface features not captured in the orbital images, for example, the deployed geophones and Explosive Packages (EPs) of the Lunar Seismic Profiling Experiment (LSPE) or the Lunar Roving Vehicle (LRV) at major sampling stops. Our results were integrated into a new LROC NAC‐based Apollo 17 Traverse Map and also used to generate a series of large‐scale maps of all nine traverse stations and of the ALSEP area. In addition, we provide crater measurements, profiles of the navigated traverse paths, and improved ranges of the sources and receivers of the active seismic experiment LSPE

A non-linear model of rubber shear springs validated by experiments

Vibrating flip-flow screens provide an effective solution for screening highly viscous or fine materials. However, yet, only linear theory has been applied to their design. Yet, to understand deficiencies and to improve performance an accurate model especially of the rubber shear springs equipped in screen frames is critical for its dynamics to predict e.g. frequency- and amplitude-dependent behaviour. In this paper, the amplitude dependency of the rubber shear spring is represented by employing a friction model in which parameters are fitted to an affine function rather constant values used for the classic Berg’s model; the fractional derivative model is used to describe its frequency dependency and compared to conventional dashpot and Maxwell models with its elasticity being represented by a nonlinear spring. The experimentally validated results indicate that the proposed model with a nonlinear spring, friction and fractional derivative model is able to more accurately describe the dynamic characteristics of a rubber shear spring compared with other models

Determining periodic orbits via nonlinear filtering and recurrence spectra in the presence of noise

© 2017 The Authors. Published by Elsevier Ltd. In nonlinear dynamical systems the determination of stable and unstable periodic orbits as part of phase space prediction is problematic in particular if perturbed by noise. Fourier spectra of the time series or its autocorrelation function have shown to be of little use if the dynamic process is not strictly wide-sense stationary or if it is nonlinear. To locate unstable periodic orbits of a chaotic attractor in phase space the least stable eigenvalue can be determined by approximating locally the trajectory via linearisation. This approximation can be achieved by employing a Gaussian kernel estimator and minimising the summed up distances of the measured time series i.e. its estimated trajectory (e.g. via Levenberg-Marquardt). Noise poses a significant problem here. The application of the Wiener-Khinchin theorem to the time series in combination with recurrence plots, i.e. the Fourier transform of the recurrence times or rates, has been shown capable of detecting higher order dynamics (period-2 or period-3 orbits), which can fail using classical FouRiER-based methods. However little is known about its parameter sensitivity, e.g. with respect to the time delay, the embedding dimension or perturbations. Here we provide preliminary results on the application of the recurrence time spectrum by analysing the Hénon and the Rössler attractor. Results indicate that the combination of recurrence time spectra with a nonlinearly filtered plot of return times is able to estimate the unstable periodic orbits. Owing to the use of recurrence plot based measures the analysis is more robust against noise than the conventional Fourier transform

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

International Entrepreneurship Education

Entrepreneurship for engineering students must be taught within the global context. Lacking that, graduates will be ill prepared to be internationally competitive. Any engineering graduate who does not scour the earth for new ideas, developments and designs is not competitive. And any engineer who does not look at the total world marketplace for sale of products is limiting potential success. This paper will outline what every entrepreneurially minded student should have in the way of competencies, attitudes, communication strategies, cultural understandings, business mores, multinational corporate logistics, and macroeconomics understandings. It will outline cultural soft skills needed, as well as hard-nosed business skills. Many US universities may be prepared to work effectively with internationally minded students, but engineering students typically do not get involved ñ only 2 to 3 percent of engineering students get a meaningful international exposure prior to graduation. Among other constraints, engineering faculty members are less than aggressive in encouraging them to get such experience. To meet the needs of engineering students, institutional and individual partnerships must be created to promote international collaborations, including design projects, international internships, exposure to successful entrepreneurs from other parts of the world including developing countries, etc

Research and development of an air-puff excitation system for lightweight structures

© 2019 International Group of Operational Modal Analysis. Lightweight, thin-walled structures appear in numerous engineering and natural structures. Due to their sensitivity, vibration excitation by, now traditional, contacting techniques, such as modally-tuned impact hammers or electrodynamic shakers, to investigate their dynamics is challenging since it typically adds substantial mass and/or stiffness at the excitation location. The research presented in this article, therefore, is intended to yield a system for the non-contact excitation of thin-walled structures through small, controlled blasts of air. An air-puff system, consisting of two fast-acting solenoid-controlled valves, a small air outlet nozzle and bespoke control software with a programmable valve control sequence, is researched and developed. The excitation impulse characteristics are investigated experimentally and described in detail for varying input control parameters. Ultimately, suitability of the system for the excitation of thin-walled structures is explored, for both a 3D-printed micro-satellite panel and a natural bee honeycomb, with promising results when compared to that of an impact hammer