Energy-Efficient UAV Trajectories: Simulation vs Emulation

This paper uses an emulator to verify an energy-efficient trajectory for an unmanned aerial vehicle (UAV) acting as a portable access point (PAP) to serve a set of users. Specifically, we use the Common Open Research Emulator (CORE), and Extendable Mobile Ad-hoc Network Emulator (EMANE), which allow us to take theoretical assumptions regarding data transfer rates and transmission characteristics and test them in the virtualized wireless networking setting the two tools provide us. The optimal fly-hover-communicate trajectory that maximizes the system's energy efficiency is obtained using a circle-packing algorithm. The CORE-EMANE emulator results match the simulated results, thereby verifying the practicality of the obtained trajectory solution

An experimental and numerical investigation of the role of rivet and die design on the self-piercing riveting joint characteristics of aluminum and steel sheets

We analyze the role of different rivet and die design parameters on the feasibility and quality of the self-piercing riveting (SPR) joining of metallic sheet stacks. In particular, the riveting of a similar aluminum-to‑aluminum sheet stack (AA2019/AA7075-F) and a dissimilar aluminum-to-steel sheet stack (AA7075-F/BA0270) is investigated, both experimentally and numerically. Towards this, the different rivet and sheet materials are experimentally characterized to obtain their elastoplastic and fracture attributes. Thereafter, SPR process finite element models are developed. Initially, the joint feasibility is experimentally probed for specific available rivet and die configurations, thus identifying SPR process parameters that allow for successful joining. Thereafter, a wider range of SPR process parameters is investigated numerically. It is observed that a combination of successful joint formation and high interlock values is obtained over specific ranges of rivet leg thickness and die depth values. Moreover, low rivet leg thickness values and near-unity normalized die depths – with the sum of the die depth and total sheet thickness normalized with respect to the rivet leg length – yield high quality SPR joints for both types of stacks considered. However, the optimum parameter selection is stack-specific, with high-quality AA2019/AA7075-F SPR joints observed to be feasible over a more constrained parametric space compared to the AA7075-F/BA0270 joining case. Further, it is concluded that the mean von Mises stress induced in the sheets after the SPR process is primarily affected by the selection of the die depth, with the induced stress being less sensitive to other design parameters, such as the rivet leg thickness or die shape for both joining cases.ISSN:1526-612

Bayesian identification of the tendon fascicle's structural composition using finite element models for helical geometries

Despite extensive experimental and computational investigations, the accurate determination of the structural composition of biological tendons remains elusive. Here we infer the structural compositions of tendons by coupling a finite element model with fascicle experimental data through a Bayesian uncertainty quantification framework. We present a mechanical model of the fascicle's geometric and material properties based on its constituents and employ the Bayesian framework to infer its parameters. The finite element model is optimized for helical geometries to reduce the computational cost associated with the Bayesian inference. We establish a link between the fiber and the fascicle tendon scale and identify an appropriate range of mechanically compatible material and geometric properties to quantify the tendon properties. These findings could serve as a basis for the design of artificial tendons. © 2016 Elsevier B.V

Cross section shape optimization of wire strands subjected to purely tensile loads using a reduced helical model

This paper introduces a shape optimization of wire strands subjected to tensile loads. The structural analysis relies on a recently developed reduced helical finite element model characterized by an extreme computational efficacy while accounting for complex geometries of the wires. The model is extended to consider interactions between components and its applicability is demonstrated by comparison with analytical and finite element models. The reduced model is exploited in a design optimization identifying the optimal shape of a 1 + 6 strand by means of a genetic algorithm. A novel geometrical parametrization is applied and different objectives, such as stress concentration and area minimization, and constraints, corresponding to operational limitations and requirements, are analyzed. The optimal shape is finally identified and its performance improvements are compared and discussed against the reference strand. Operational benefits include lower stress concentration and higher load at plastification initiation

Co‐evolved genetic programs for stock market trading

The profitability of trading rules evolved by three different optimised genetic programs, namely a single population genetic program (GP), a co‐operative co‐evolved GP, and a competitive co‐evolved GP is compared. Profitability is determined by trading thirteen listed shares on the Johannesburg Stock Exchange (JSE) over a period of April 2003 to June 2008. An empirical study presented here shows that GPs can generate profitable trading rules across a variety of industries and market conditions. The results show that the co‐operative co‐evolved GP generates trading rules perform significantly worse than a single population GP and a competitively co‐evolved GP. The results also show that a competitive co‐evolved GP and the single population GP produce similar trading rules. The profits returned by the evolved trading rules are compared to the profit returned by the buy‐and‐hold trading strategy. The evolved trading rules significantly outperform the buy‐and‐hold strategy when the market trends downwards. No significant difference is identified among the buy‐and‐hold strategy, the competitive co‐evolved GP, and single population GP when the market trends upwards.https://wileyonlinelibrary.com/journal/isaf2021-07-01hj2020Computer Scienc