Effect of Explosive Shapes (in Sand Buried Condition) on the Failure of a Circular Clamped Plate of Protective Vehicle

Protective vehicles like armoured personnel carriers (APCs) require assessment of failure of structural elements subjected to impulsive load resulting from explosive blast under sand buried conditions. The explosive shape and location of detonation affect the failure in near field region. In the present study, a circular clamped Rolled Homogenous Armour (RHA) steel plate has been modelled using JC strength & damage model and explosive using JWL equation. Initially, the reflected pressure and specific impulse for a fixed quantity of explosive (3.75 kg) of various shapes i.e. sphere, hemisphere, cylinders with Length to Diameter (L/D) ratio varying from 0.1 to 1 were studied for sand buried at a standoff distance of 118.1 mm. Further, studies were extended for cylindrical charges of φ 213.77 mm with conical 120°-150° and hemispherical cavities with radius of R1.2-R1.8. It was observed that, reflected pressure and specific impulse is much higher for hemispherical cavity of R1.2. The permanent deformation obtained using non-dimensional impulse is valid for explosives without cavities. However, the cavity charges produce failure of plate in the central region of the charge. The critical impulse emerges as an important parameter for assessing failure due to cavity charges. In addition, the scale down experiment is conducted to validate the effectiveness of cavity charges. It can be concluded that cavity charge with hemispherical radius of R1.2 can provide highest damage to RHA plates in close standoff distance

Grasping Mechanism Concepts Oriented to Debris for Removal Applications

Space debris regulation and reduction is an increasingly relevant theme. Several initiatives in the aerospace field on debris removal are pursued by space agencies. In this context, an analysis has been conducted on diverse mechanisms for spacecraft coupling in Low Earth Orbit (LEO) with a robotic arm. Four grasping mechanical concepts for space debris removal applications have been proposed in respect of restrictive requirements. Two concepts are based on probe and drogue mating systems and the other two on finger-like grasping systems. The paper describes the preliminary design and the operation of the proposed mechanisms. In addition, it lays the foundation for a trade-off procedure in order to evaluate advantages and drawbacks for each concept

Terms of the stability for the control valve of the hydraulic impulse drive of vibrating and vibro-impact machines

The working process and regularities of the functioning of vibrating and vibro-impact machines based on hydroimpulse drive with a singlestage valve pulser are analyzed. The essential characteristics determining the conditions for the excitation and existence of periodic oscillations of the valve-pulser shut-off valve are determined. Using the criterion of A. Hurwitz, based on the differential equation of motion, the existence of undamped periodic oscillations of the valve-pulser shut-off valve is analytically justified.Przeanalizowano działanie i regularność pracy maszyn wibracyjnych oraz maszyn poddawanych wibracjom opartych na napędzie hydro-impulsowym z jednostopniowym zaworem impulsowym. Określono podstawowe cechy wpływające na warunki wzbudzenia oraz występowania drgań okresowych zaworu impulsowego. Przy zastosowaniu kryterium A. Hurwitza, opartego na równaniu różniczkowym ruchu, istnienie nietłumionych drgań okresowych zaworu impulsowego jest analitycznie uzasadnione. (Warunki stabilności zaworu sterującego hydraulicznym napędem impulsowym maszyn wibracyjnych oraz maszyn poddawanych wibracjom)

Development of Improved CFD Tools for the Optimization of a Scramjet Engine

In the present work, a plugin has been developed for use with the DoD HPCMP CREATE-AV Kestrel multi-physics solver that adds volumetric source terms to the energy equation. These source terms model the heat released due to combustion, but are much more computationally efficient than a full chemistry model. A thrust-based optimization study was then carried out under the control of Sandia National Laboratories\u27 Dakota toolkit. Dakota was allowed to control the amount of heat added to three regions of the scramjet combustor. The plugin was then extended to consider ignition delay time. By comparing ignition delay time to dwell time, it is possible to determine whether the fuel in a cell should be combusted. Results from this analysis are compared to results gathered using a 22-species chemistry model. The ignition delay source term is shown to capture relevant flow physics at a reduced computational cost. Additionally, the expression for second-law (exergetic) efficiency for a scramjet engine is derived and optimized using Dakota. Finally, Dakota was extended to control the geometry of the scramjet engine, allowing for the numerical optimization of the scramjet expansion system. The results from these computationally-efficient optimizations can then be used to inform researchers of potentially optimal solutions before higher-fidelity models are used

characterization and manufacturing of a paraffin wax as fuel for hybrid rockets

The hybrid propulsion performed with paraffin waxes exhibits most attractive capabilities compared to solid or liquid engines, e.g., throttleability and re-ignition, alongside higher regression rates compared to the conventional hydroxyl terminated polybutadiene (HTPB) hybrid fuel. This is because the paraffin wax forms a thin and hydro-dynamically unstable liquid layer, and then enhances the regression rate with the entrainment of droplets from the liquid-gas interface. Nevertheless, some critical open points on the manufacturing of the paraffin fuel grains still persist, because the paraffin wax exhibits high shrinkage during the solidification phase, leading to the formation of cavities, cracks and internal rips, which may be detrimental to the mechanical properties and the structural integrity of the fuel grain. In this context, this paper deals with a wide calorimetric, thermo-mechanical and physical characterization of the paraffin wax selected to manufacture the hybrid rocket engines (HRE) fuel grain, in order to gain a thorough knowledge of the material necessary to avoid the formation of critical defects. Several manufacturing methods were investigated, and it was found that only laboratory scale processes, based on the use of a heated circular mould-piston apparatus, are able to avoid the formation of critical defects, with the application of both high temperature and pressure. Keywords: Paraffin wax, Hybrid rockets, Manufacturing, SASOL® 0907, Regression rat

Space transportation booster engine configuration study. Addendum: Design definition document

Gas generator engine characteristics and results of engine configuration refinements are discussed. Updated component mechanical design, performance, and manufacturing information is provided. The results are also provided of ocean recovery studies and various engine integration tasks. The details are provided of the maintenance plan for the Space Transportation Booster Engine

Re-Sonification of Objects, Events, and Environments

abstract: Digital sound synthesis allows the creation of a great variety of sounds. Focusing on interesting or ecologically valid sounds for music, simulation, aesthetics, or other purposes limits the otherwise vast digital audio palette. Tools for creating such sounds vary from arbitrary methods of altering recordings to precise simulations of vibrating objects. In this work, methods of sound synthesis by re-sonification are considered. Re-sonification, herein, refers to the general process of analyzing, possibly transforming, and resynthesizing or reusing recorded sounds in meaningful ways, to convey information. Applied to soundscapes, re-sonification is presented as a means of conveying activity within an environment. Applied to the sounds of objects, this work examines modeling the perception of objects as well as their physical properties and the ability to simulate interactive events with such objects. To create soundscapes to re-sonify geographic environments, a method of automated soundscape design is presented. Using recorded sounds that are classified based on acoustic, social, semantic, and geographic information, this method produces stochastically generated soundscapes to re-sonify selected geographic areas. Drawing on prior knowledge, local sounds and those deemed similar comprise a locale's soundscape. In the context of re-sonifying events, this work examines processes for modeling and estimating the excitations of sounding objects. These include plucking, striking, rubbing, and any interaction that imparts energy into a system, affecting the resultant sound. A method of estimating a linear system's input, constrained to a signal-subspace, is presented and applied toward improving the estimation of percussive excitations for re-sonification. To work toward robust recording-based modeling and re-sonification of objects, new implementations of banded waveguide (BWG) models are proposed for object modeling and sound synthesis. Previous implementations of BWGs use arbitrary model parameters and may produce a range of simulations that do not match digital waveguide or modal models of the same design. Subject to linear excitations, some models proposed here behave identically to other equivalently designed physical models. Under nonlinear interactions, such as bowing, many of the proposed implementations exhibit improvements in the attack characteristics of synthesized sounds.Dissertation/ThesisPh.D. Electrical Engineering 201

From Radio to In-Pipe Acoustic Communication for Smart Water Networks in Urban Environments: Design Challenges and Future Trends

The smart management of water resources is an increasingly important topic in today’s society. In this context, the paradigm of Smart Water Grids (SWGs) aims at a constant monitoring through a network of smart nodes deployed over the water distribution infrastructure. This facilitates a continuous assessment of water quality and the state of health of the pipeline infrastructure, enabling early detection of leaks and water contamination. Acoustic-wave-based technology has arisen as a viable communication technique among the nodes of the network. Such technology can be suitable for replacing traditional wireless networks in SWGs, as the acoustic channel is intrinsically embedded in the water supply network. However, the fluid-filled pipe is one of the most challenging media for data communication. Existing works proposing in-pipe acoustic communication systems are romising, but a comparison between the different implementations and their performance has not yet been reported. This paper reviews existing works dealing with acoustic-based ommunication networks in real large-scale urban water supply networks. For this purpose, an overview of the characteristics, trends and design challenges of existing works is provided in he present work as a guideline for future research