Measuring Impact Noise with Smartphone Apps

The ability of smartphone apps to measure impact noise has not been evaluated. This study was designed to explore the feasibility of using smartphone apps as a means to evaluate impact noise levels in industrial settings. Impact noise was generated by dropping a 4 Kg shotput onto a .5” thick steel plate at heights ranging from 6.5 to 102 cm. Two iPhones and two Android phones were tested with three apps each using both the phone’s built-in microphone and an external microphone. Sound level measurements of each drop were simultaneously recorded by a calibrated smartphone and a gold standard system capable of accurately measuring high intensity impact noise. These experimentally grouped datapoints (phone/app) were analyzed to determine if any smartphone/app/microphone could measure impact noise to within ±2dB SPL of the gold standard system. The results of this study showed that none of the three Android apps tested could measure impact noise with any meaningful degree of accuracy. The absolute mean differences for measurements recorded with Android devices ranged from 29.5 to 53.4 dB SPL. Measurements recorded with iPhones were closer than Android devices to gold standard measurements, with absolute mean differences ranging from 0.3 to 43.1 dB using the internal mic and 0.5 to 44.8 dB with the external mic. Measurements from the SoundMeter iOS app were closest to the gold standard, with absolute mean differences of from 0.5 to 4.8 dB. iv The data recorded using Android phones to measure impact noise in this study indicated that even with an external microphone and proper calibration, Android smartphones and apps are unable to measure impact noise with any degree of accuracy and should not be relied upon to make any decisions regarding occupational impact noise exposure. iOS phones more closely approximated the performance of the gold standard measurements. The SoundMeter app with the iMM-6 external microphone coupled to either the iPhone 6 or iPhone Se approximated the performance of a calibrated Type II sound level meter and would be the preferred instrument combination for impact noise field measurement up to 142 dB peak SPL

Exploring the free-energy landscape of a rotating superfluid

The equilibrium state of a superfluid in a rotating cylindrical vessel is a vortex crystal -- an array of vortex lines which is stationary in the rotating frame. Experimental realisations of this behaviour typically show a sequence of transient states before the free-energy minimising configuration is reached. Motivated by these observations, we construct a new method for a systematic exploration of the free-energy landscape via gradient-based optimisation of a scalar loss function. Our approach is inspired by the pioneering numerical work of Campbell & Ziff (Phys. Rev. B 20, 1979), and makes use of automatic differentiation (AD) which crucially allows us to include entire solution trajectories in the loss. We first use the method to converge thousands of low-free-energy relative equilibria for vortex numbers in the range $10 \leq N \leq 30$, which reveals an extremely dense set of mostly saddle-like solutions. As part of this search, we discover new continuous families of relative equilibria (in the unbounded domain) which are often global minimisers of the free energy. These continuous families all consist of crystals arranged in a double-ring configuration, and we assess which state from the family is most likely to be observed experimentally by computing energy-minimising pathways from nearby local minima -- identifying a common entry point into the family. Finally, we develop an approach to compute homoclinic orbits and use it to examine the dynamics in the vicinity of the minimising state by converging connections for low-energy saddles.Comment: 13 pages, 12 figure

Exact travelling wave solutions in viscoelastic channel flow

Elasto-inertial turbulence (EIT) is a new, two-dimensional chaotic flow state observed in polymer solutions with possible connections to inertialess elastic turbulence and drag-reduced Newtonian turbulence. In this Letter, we argue that the origins of EIT are fundamentally different from Newtonian turbulence by finding a dynamical connection between EIT and an elasto-inertial linear instability recently found at high Weissenberg numbers (Garg et al. Phys. Rev. Lett. 121, 024502, 2018). This link is established by isolating the first known exact coherent structures in viscoelastic parallel flows - nonlinear elasto-inertial travelling waves (TWs) - borne at the linear instability and tracking them down to substantially lower Weissenberg numbers where EIT exists. These TWs have a distinctive ``arrowhead'' structure in the polymer stretch field and can be clearly recognised, albeit transiently, in EIT, as well as being attractors for EIT dynamics if the Weissenberg number is sufficiently large. Our findings suggest that the dynamical systems picture in which Newtonian turbulence is built around the co-existence of many (unstable) simple invariant solutions populating phase space carries over to EIT, though these solutions rely on elasticity to exist

Multistability of elasto-inertial two-dimensional channel flow

Elasto-inertial turbulence (EIT) is a recently discovered two-dimensional chaotic flow state observed in dilute polymer solutions. It has been hypothesised that the dynamical origins of EIT are linked to a center-mode instability, whose nonlinear evolution leads to a travelling wave with an 'arrowhead' structure in the polymer conformation, a structure also observed instantaneously in simulations of EIT. In this work we conduct a suite of two-dimensional direct numerical simulations spanning a wide range of polymeric flow parameters to examine the possible dynamical connection between the arrowhead and EIT. Our calculations reveal (up to) four co-existent attractors: the laminar state and a steady arrowhead, along with EIT and a 'chaotic arrowhead'. The steady arrowhead is stable for all parameters considered here, while the final pair of (chaotic) flow states are visually very similar and can be distinguished only by the presence of a weak polymer arrowhead structure in the 'chaotic arrowhead' regime. Analysis of energy transfers between the flow and the polymer indicates that both chaotic regimes are maintained by an identical near-wall mechanism and that the weak arrowhead does not play a role. Our results suggest that the arrowhead is a benign flow structure that is disconnected from the self-sustaining mechanics of EIT.Comment: 17 pages, 10 figure

Music\u27s Emotional Journey

Music has an emotion-evoking effect on its audience through form. This is exemplified throughout history, but we will be focusing on \u27Don\u27t Stop Believin\u27 \u27 by Journey as a prime example. Part of this influence is due to the fact that it contrast with other widely-used forms. Presentation Time: Thursday, 3-4 p.m

Recurrent flow patterns as a basis for turbulence: predicting statistics from structures

A dynamical systems approach to turbulence envisions the flow as a trajectory through a high-dimensional state space transiently visiting the neighbourhoods of unstable simple invariant solutions (E. Hopf, Commun. Appl. Maths 1, 303, 1948). The hope has always been to turn this appealing picture into a predictive framework where the statistics of the flow follows from a weighted sum of the statistics of each simple invariant solution. Two outstanding obstacles have prevented this goal from being achieved: (1) paucity of known solutions and (2) the lack of a rational theory for predicting the required weights. Here we describe a method to substantially solve these problems, and thereby provide the first compelling evidence that the PDFs of a fully developed turbulent flow can be reconstructed with a set of unstable periodic orbits. Our new method for finding solutions uses automatic differentiation, with high-quality guesses constructed by minimising a trajectory-dependent loss function. We use this approach to find hundreds of new solutions in turbulent, two-dimensional Kolmogorov flow. Robust statistical predictions are then computed by learning weights after converting a turbulent trajectory into a Markov chain for which the states are individual solutions, and the nearest solution to a given snapshot is determined using a deep convolutional autoencoder. To our knowledge, this is the first time the PDFs of a spatio-temporally-chaotic system have been successfully reproduced with a set of simple invariant states, and provides a fascinating connection between self-sustaining dynamical processes and the more well-known statistical properties of turbulence

Exact coherent structures in two-dimensional turbulence identified with convolutional autoencoders

Convolutional autoencoders are used to deconstruct the changing dynamics of two-dimensional Kolmogorov flow as $Re$ is increased from weakly chaotic flow at $Re=40$ to a chaotic state dominated by a domain-filling vortex pair at $Re=400$. The highly accurate embeddings allow us to visualise the evolving structure of state space and are interpretable using `latent Fourier analysis' (Page {\em et. al.}, \emph{Phys. Rev. Fluids} \textbf{6}, 2021). Individual latent Fourier modes decode into vortical structures with a streamwise lengthscale controlled by the latent wavenumber, $l$, with only a small number $l \lesssim 8$ required to accurately represent the flow. Latent Fourier projections reveal a detached class of bursting events at $Re=40$ which merge with the low-dissipation dynamics as $Re$ is increased to $100$. We use doubly- ($l=2$) or triply- ($l=3$) periodic latent Fourier modes to generate guesses for UPOs (unstable periodic orbits) associated with high-dissipation events. While the doubly-periodic UPOs are representative of the high-dissipation dynamics at $Re=40$, the same class of UPOs move away from the attractor at $Re=100$ -- where the associated bursting events typically involve larger-scale ($l=1$) structure too. At $Re=400$ an entirely different embedding structure is formed within the network in which no distinct representations of small-scale vortices are observed; instead the network embeds all snapshots based around a large-scale template for the condensate. We use latent Fourier projections to find an associated `large-scale' UPO which we believe to be a finite-$Re$ continuation of a solution to the Euler equations

The Ursinus Weekly, October 26, 1967

Six seek Homecoming title • Peace march rocks heart of Washington • IF weekend features Soul Survivors\u27 sound • Students honor Scott Pierce • UC awarding degrees in Founders\u27 assembly • Open letter to Ursinus students • Editorial • On aggression • Warmakers confronted! • Letters to the editor • Dr. Rice scales fine rail models • Dialogue is coming • Three chosen as student-faculty representatives • Hartzells dig German way: A like affection shared by all and beer is lighter in Munich • Cross country: Dynasty in the making; Footballers impress • Grads view pre-med program • Bruins edged by Garnet after defeat by Wilkes • Booters\u27 spirit good despite four losses • Greek gleaningshttps://digitalcommons.ursinus.edu/weekly/1179/thumbnail.jp