Granular Response to Impact: Topology of the Force Networks

Impact of an intruder on granular matter leads to formation of mesoscopic force networks seen particularly clearly in the recent experiments carried out with photoelastic particles, e.g., Clark et al., Phys. Rev. Lett., 114 144502 (2015). These force networks are characterized by complex structure and evolve on fast time scales. While it is known that total photoelastic activity in the granular system is correlated with the acceleration of the intruder, it is not known how the structure of the force network evolves during impact, and if there is a dominant features in the networks that can be used to describe intruder's dynamics. Here, we use topological tools, in particular persistent homology, to describe these features. Persistent homology allows quantification of both structure and time evolution of the resulting force networks. We find that there is a clear correlation of the intruder's dynamics and some of the topological measures implemented. This finding allows us to discuss which properties of the force networks are most important when attempting to describe intruder's dynamics. Regarding temporal evolution of the networks, we are able to define the upper bound on the relevant time scale on which the networks evolve

A study of sound generation in subsonic rotors, volume 2

Computer programs were developed for use in the analysis of sound generation by subsonic rotors. Program AIRFOIL computes the spectrum of radiated sound from a single airfoil immersed in a laminar flow field. Program ROTOR extends this to a rotating frame, and provides a model for sound generation in subsonic rotors. The program also computes tone sound generation due to steady state forces on the blades. Program TONE uses a moving source analysis to generate a time series for an array of forces moving in a circular path. The resultant time series are than Fourier transformed to render the results in spectral form. Program SDATA is a standard time series analysis package. It reads in two discrete time series and forms auto and cross covariances and normalizes these to form correlations. The program then transforms the covariances to yield auto and cross power spectra by means of a Fourier transformation

A study of sound generation in subsonic rotors, volume 1

A model for the prediction of wake related sound generation by a single airfoil is presented. It is assumed that the net force fluctuation on an airfoil may be expressed in terms of the net momentum fluctuation in the near wake of the airfoil. The forcing function for sound generation depends on the spectra of the two point velocity correlations in the turbulent region near the airfoil trailing edge. The spectra of the two point velocity correlations were measured for the longitudinal and transverse components of turbulence in the wake of a 91.4 cm chord airfoil. A scaling procedure was developed using the turbulent boundary layer thickness. The model was then used to predict the radiated sound from a 5.1 cm chord airfoil. Agreement between the predicted and measured sound radiation spectra was good. The single airfoil results were extended to a rotor geometry, and various aerodynamic parameters were studied

Formalizing homogeneous language embeddings.

The cost of implementing syntactically distinct Domain Specific Languages (DSLs) can be reduced by homogeneously embedding them in a host language in cooperation with its compiler. Current homogeneous embedding approaches either restrict the embedding of multiple DSLs in order to provide safety guarantees, or allow multiple DSLs to be embedded but force the user to deal with the interoperability burden. In this paper we present the \mu-calculus which allows parameterisable language embeddings to be specified and analysed. By reducing the problem to its core essentials we are able to show how multiple, expressive, language embeddings can be defined in a homogeneous embedding context. We further show how variant calculi with user-defined safety criteria can be defined

Language factories

Programming languages are the primary mechanism by which software is created, yet most of us have access to only a few, fixed, programming languages. Any problem we wish to express must be framed in terms of the concepts the programming language provides for us, be they suitable for the problem or not. Domain Specific Languages (DSLs) suggest an appealing escape route from this fate, but since there is no real technology or theory underpinning them, new DSLs are rare. In this paper we present the Language Factories vision, which aims to bring together the theory and practice necessary to realise DSLs in a systematic way. In so doing, we hope to lower the barrier for language creation significantly, ultimately allowing software creators to use the languages most suited to them and their needs

Using icon-derived technologies to drive model transformations.

Model transformations are currently the object of much interest and research. Current proposals for model transformation languages can be divided into two main camps: those taking a ‘declarative’ approach, and those opting for an ‘imperative’ approach. The Icon programming language is a SNOBOL derivative which contains several unique constructs which make it particularly well suited to the job of analyzing and transforming strings. In this paper we discuss model transformations, analyze the relevant parts of Icon that lend themselves to transforming strings, and then propose how some of Icon’s unique features could be incorporated into a model transformation approach that partially blurs the distinction between ‘declarative’ and ‘imperative’ approaches

Issues surrounding model consistency and QVT.

This document is intended to outline some of the issues surrounding model consistency in the context of QVT. As far as possible this document is intended to be independent of any particular QVT submission, although we do borrow some terminology from the QVT-Partners submission

Model transformations in converge.

Model transformations are currently the focus of much interest and research due to the OMG’s QVT initiative. Current proposals for model transformation languages can be divided into two main camps: those taking a ‘declarative’ approach, and those opting for an ‘imperative’ approach. In this paper we detail an imperative, meta-circular, object orientated, pattern matching programming language Converge which is enriched with features pioneered by the Icon programming language, amongst them: success/failure, generators and goal-directed evaluation. By presenting these features in a language suitable for representing models, we show that we are able to gain some of the advantages of declarative approaches in an imperative setting

Investigation of the effects of inlet shapes on fan noise radiation

The effect of inlet shape on forward radiated fan tone noise directivities was investigated under experimentally simplified zero flow conditions. Simulated fan tone noise was radiated to the far field through various shaped zero flow inlets. Baseline data were collected for the simplest baffled and unbaffled straight pipe inlets. These data compared well with prediction. The more general inlet shapes tested were the conical, circular, and exponential surfaces of revolution and an asymmetric inlet achieved by cutting a straight pipe inlet at an acute angle. Approximate theories were developed for these general shapes and some comparisons with data are presented. The conical and exponential shapes produced directivities that differed considerably from the baseline data while the circular shape produced directivities similar to the baseline data. The asymmetric inlet produced asymmetric directivities with significant reductions over the straight pipe data for some angles