Search

This study aims to present the authors' recent research investigating the mechanical and thermo-mechanical properties of commercial polylactic acid (PLA) polymer. Samples were manufactured by 3D printing of fused filament fabrication (FFF) and tests were performed according to ASTM International standards for polymers D638, D695 and D790. All test samples were made using the same printing process parameters. The static mechanical tests consisted of tensile and flexural loadings at various temperature ranges, from room temperature to elevated temperature (25°C, 40°C and 50°C, respectively). For ensuring that the additively manufactured products can resist severities of real-life applications, thermal stability under mechanical load tests (HDT - heat deflection temperature) were carried out. The temperature influence on the mechanical and thermomechanical properties was determined and presented, and a synthesis of the characteristics was made in accordance with the applications of products based on the studied material.

The physically modelled neural and nervous networks pioneered more than two decades ago by Mark Tilden, E. A. Rietman and collaborators, M. Ashkenazi et al. have proven to be a robust and interesting way to obtain powerful emergent behavior by utilizing neuromimetic circuitry. Using a physical representation of biologic neurons, both motor (NU) and cortical (NV) these structures mimic simple reflex arcs present in a large number of evolved organisms. The simple circuits using logic gate oscillators wired as integrators or pulse delay loops with sensors coupled as current injectors or variable resistors of different types demonstrated unexpected emergent „survival” behaviors when connected in chains or loops of several neurons. Mark Tilden calls the simplest functional unit of such looped structures „bicores”-as two neurons linked together in a loop already generate meaningful behavior when their inputs are linked to appropriate sensors. These powerful neuromimetic machines allow for a robust implementation of automated responses in autonomous or semi-autonomous robots. Quadcopters are a very good target for neural network control/stabilization because of their unique flight dynamics and normal control procedures. Obstacle avoidance and stabilization are simple tasks for a well-tuned physical neural network.

Continuing the works debuted in the previous work “Improved Timing for better performance of distributed data acquisition systems” the present paper refines and revisits the concept of a local oscillator with GPS corrections as a source of long-term stable reference clock signals with direct application in distributed data acquisition systems. The system as described herein can generate precise and repeatable clock source signals for trigger and sync of various data acquisition equipment when used in mixed and distributed architectures. These timing signals are a vital part of data acquisition as oftentimes raw data is processed as time series and correlations are made based on timestamps. This paper details improvements in implementation of a cost-effective high precision time base (reference clock) using a GPS receiver as a primary time source and a local high precision real time clock as a secondary oscillator. The improvements to the previous version come both from hardware refinements and from updated software with reduced latencies and reconfigured structure that allows for compensation of internal delays and internal process offsets.

Distributed data acquisition systems are the norm in the great majority of industry branches where the process to be controlled covers a physically large and often fragmented area. Many local smaller data acquisition modules are interfaced and pass raw or pre-processed data along with the timing signals. These timing signals are a vital part of data acquisition as oftentimes raw data is processed as time series and correlations are made based on timestamps. This paper presents a study for implementation of a cost-effective high precision time base (reference clock) using a GPS receiver as a primary time source and a local high precision real time clock as a secondary oscillator.

Strain gage balances provide the most important output of the supersonic wind tunnels. Typically, the time histories of the six forces/moments components must be filtered out, to provide useful results for performance assessment of the models. Various filtering models do exist, from basic regressions, to frequency domain and combinations of piecewise fit polynomials. Results with decoupled piecewise linear fit (moving window) showed the need of more suitable methods, namely piecewise, that must properly connect the neighboring fit curves, to provide continuity up to the first derivative. A polygonal line fit is derived and modified for increased smoothness. A third order cubic spline is derived, offering connectivity up to the first derivative. A fifth order spline is derived with continuity up to the second order derivative. Filtering results are shown for real and synthetic sets of data with conclusions.

A supersonic and high speed transonic Pitot Prandtl is described as it can be implemented in the Trisonic Wind Tunnel for calibration and verification of Mach number precision. A new calculation method for arbitrary precision Mach numbers is proposed and explained. The probe is specially designed for the Trisonic wind tunnel and would greatly simplify obtaining a precise Mach calibration in the critical high transonic and low supersonic regimes, where typically wind tunnels exhibit poor performance. The supersonic Pitot Prandtl combined probe is well known in the aerospace industry, however the proposed probe is a derivative of the standard configuration, combining a stout cone-cylinder probe with a supersonic Pitot static port which allows this configuration to validate the Mach number by three methods: conical flow method – using the pressure ports on a cone generatrix, the Schlieren-optical method of shock wave angle photogrammetry and the Rayleigh supersonic Pitot equation, while having an aerodynamic blockage similar to that of a scaled rocket model commonly used in testing. The proposed probe uses an existing cone-cylinder probe forebody and support, adding only an afterbody with a support for a static port.

Preventing overloads in wind tunnel model supports is crucial to the integrity of the tested system. Results can only be interpreted as valid if the model support, conventionally called a sting remains sufficiently rigid during testing. Modeling and preliminary calculation can only give an estimate of the sting’s behavior under known forces and moments but sometimes unpredictable, aerodynamically caused model behavior can cause large transient overloads that cannot be taken into account at the sting design phase. To ensure model integrity and data validity an analog fast protection circuit was designed and tested. A post-factum analysis was carried out to optimize the overload detection and a short discussion on aeroelastic phenomena is included to show why such a detector has to be very fast. The last refinement of the concept consists in a fast detector coupled with a slightly slower one to differentiate between transient overloads that decay in time and those that are the result of aeroelastic unwanted phenomena. The decision to stop or continue the test is therefore conservatively taken preserving data and model integrity while allowing normal startup loads and transients to manifest.

The pulsating heated flows are traditionally a difficult subject to treat with conventional hot wire or film methods. Special factors that complicate matters are flow reversal and non linear flow effects of vortices and wire probe wake disturbances on the heat transfer to the hot film or wire sensor in heated pulsating flows. The presence of these strongly nonlinear and unknown terms leads to great difficulties in calibration of hot film probes in this particular regime. The paper analyses the current state of matters in the field and reports a series of solutions that have been practically tested in a case of a high speed pulsated heated flow. Normally such measurements are made in a non-contact fashion using a LDV system or various visualization techniques but there have been recent attempts to use a constant temperature hot wire anemometer system (CTA).To obtain meaningful calibration for hot wire films in hot pulsating flows, a comparison system on other principles (LDV) was used, as well as a specially designed nozzle to replace the calibrator unit that could not be operated with heated fluid due to structural integrity reasons. The method as described below works well for the expected speed range that could be generated using the special nozzle.

Close air support of ground troops especially in densely populated, urban environments has an ever increasing prevalence in the modern warfare. Counter-terrorism activities as well as land-based “surgical strikes” impose a set of special requirements on all the used weapons and equipment so as to minimize weight, cost and complexity and maximize efficiency. Small scale UAVs are in service with all the armed forces around the globe; micro UAVs are emerging as the ground troop close support preferred solution. Endurance and range of these devices is regularly small to very small, and their speed is low. Their small size makes them virtually un-targetable if somewhat still detectable. A new generation of micro-drones is proposed, with a higher speed (up to 350 km/h ground speed averaged) and automatic recovery system. Project SKYLARK consists of a reusable minimal micro-UAV featuring a portable micro-USB camera and an aerodynamically assisted timer-based recovery system.

Schlieren flow visualization methods are an important part of high speed wind tunnel testing, being a fast and reliable method of graphically presenting complex dynamic phenomena that occur in high subsonic, transonic and supersonic regimes. Images can be processed and effects of configuration changes can be understood faster. Quantitative variations of the Schlieren method enable CFD simulations to use real data, resulting in greater precision and thus help improve efficiency of the re-design phase for the aerodynamic object. A modification of the classic Schlieren system is proposed, that would enable extraction of such data with minimal costs.

Preliminary results obtained in developing a numerical model of laser light intensity transverse distribution into undeformed/deformed step index optical fiber are presented. The main purpose of the presented preliminary numerical modelling results consists in developing a simple method of fiber optical sensors interrogation, especially concerning strain and pressure measurements. It is a potential important matter for aeronautical research and industry because of the more extended use of fibre optic sensors in aircraft manufacturing. The developed numerical model relies on solving the equations of electromagnetic waves propagation into optical fibers by using the finite element method technique (FEM). The results of numerical simulation obtained by considering single mode or multimode and various laser wavelengtsh are presented. One important achievement reported in this paper consists in preliminary experimental results concerning the modification of laser intensity transverse distribution observed for multimode optical fiber with and without perpendicular mechanical load. The reported preliminary experimental results confirm to some extent the predictions of numerical simulations regarding laser intensity distribution under low and medium transverse mechanical load. One important conclusion of this paper consists in the future development of fiber optic sensor interrogation techniques based on the reported preliminary experimental and numerical simulation results.