Scielo RSS <![CDATA[R&D Journal]]> vol. 33 num. lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Development of a combustion visualisation hybrid rocket motor</b>]]> The Phoenix Hybrid Sounding Rocket Programme in the University of KwaZulu-Natal's Mechanical Engineering department has so far only utilised pure paraffin wax and nitrous oxide as the propellant combination in their hybrid rockets. Knowledge of regression rate behaviour is required for the design and performance characterisation of hybrid rocket propulsion systems. The regression rate is the rate at which the fuel recedes in the direction perpendicular to the burning fuel surface. A hybrid slab motor was purpose designed for regression rate analysis. Optimum oxidiser-to-fuel (O/F) ratios obtained from literature and NASA CEA were used with interpolation to define the fuel grain dimensions, and the oxidiser and fuel mass flow rates. The slab motor, with windows for direct regression rate visualisation, was designed based on these parameters. It was manufactured from a combination of brass and stainless steel for structural rigidity, thermal properties and material compatibility with nitrous oxide. The design also includes a compact feed system used to supercharge the nitrous oxide run tank, while minimising pressure losses. The motor was designed to accommodate both pure and aluminised fuel grains. From literature, aluminium additives in the fuel have been shown to increase the regression rate of the system. Different regression rate measurement techniques, discussed in this paper, will be implemented to obtain the relevant data. These include visualisation of the regression process and obtaining the mass flow rate data over the burn time. The pre and post combustion grain volumes will also be significant here in order to calculate the regression rate. The regression rate data obtainedfrom these investigations are imperative in the improvement of future launch vehicles in the Phoenix Programme. <![CDATA[<b>Non-inertial forces in aero-ballistic flow and boundary layer equations</b>]]> This paper derives the non-inertial terms, also referred to as fictitious forces, for aero-ballistic cases using an Eulerian approach. These cases display unsteady rates ofchange in acceleration in all six degrees offreedom. Six fictitious forces are identified in the momentum equation. Their origin and nature ofthese forces are elaborated upon. As shown in previous work, the continuity and energy equations remain invariant. The non-inertial boundary layer equations are derived to determine the effect of fictitious forces in the near-wall region. Through an order of magnitude analysis it was determined that none of the fictitious forces cancels out. It will therefore have an influence on the boundary layer properties. <![CDATA[<b>Heat transfer in a hot stamping process: a review</b>]]> Heat transfer rate during the hot stamping process affects the resultant quality and production rate of the process. This is because the ability of the tool to transfer heat from the blank affects the resultant tensile strength, temperature distribution and cooling time of the formed part. Research efforts have been made on the design of cooling systems that are aimed towards improving the cooling effectiveness of the blanks thereby improving the quality characteristics of the formed parts. The cooling rate is governed by the interfacial heat transfer coefficient (IHTC). A proper design of hot stamping tools requires knowledge of the heat transfer modes during the hot stamping process. It is important to gain an understanding of the heat transfer scenarios during the process to seek opportunities to reduce the cooling time and improve the quality ofparts. The purpose of this article is to review the heat transfer phases during the hot stamping cycle and propose a model for the heat loss by the blank during the process. A review of the models that can be utilized to determine IHTC is presented. <![CDATA[<b>Characterisation of submerged arc welding process using infrared imaging technique</b>]]> Infrared (IR) thermography is a technique used to measure temperature distribution of heat generation in manufacturing processes such as welding. IR thermography is a non-destructive and non-contact method, which makes it favoured for the arc welding process where interference with the welding process must be avoided. In this study, IR thermography is used to record the temperature history during the submerged arc welding (SA W) process experiment; and to validate the numerical model developed to simulate the said SAW process of a multi-pass circumferential weld on pressure vessel steel. The Flir Short Wave Infrared Radiometer (FSIR) is used during SAW experiments with the ESAB welding unit. The weld pool and the surrounding area are continuously monitored and their temperature recorded using a thermal camera. The recorded temperatures are plotted against time on Temperature-Time curves to reveal the temperature profiles of each welding cycle. Comparison of the resultant temperature profiles with those of the numerical model show good agreement. It is therefore concluded that temperature measurement through thermal imaging is a suitable method to characterize the temperature history of the SAW multi-pass circumferential weld, as well as to effectively validate the numerical model developed to simulate the said welding process. <![CDATA[<b>A computational tool for predicting hybrid rocket motor performance</b>]]> A model is described to aid in the design of hybrid rockets and in the prediction of motor performance, specifically with respect to the University of KwaZulu-Natal's Phoenix-1A vehicle. The Hybrid Rocket Performance Code (HRPC), programmed in MATLAB, is segregated into two individual models: i) a preliminary motor design code to analyse and design hybrid rocket motors, and ii) a predictive motor performance code to compute the instantaneous motor performance for a targeted burn time. The predictive motor performance code is based on a one-dimensional unsteady gas flow model through the nozzle and, on a zero-dimensional model of the combustion chamber capturing only the filling and emptying dynamics. The zero-dimensional model is linked to a self-pressurising delivery tank model obtainedfrom literature to simulate the changes in physicochemical properties of nitrous oxide in the tank. HRPC is coupled with NASA-CEA equilibrium chemistry program to determine the thermodynamic properties of the combustion products necessary for solving the governing ordinary differential equations. As such, different propellant combinations can be analysed for motor performances. The HRPC application is validated against hot-fire test data of Phoenix-lA's PV-1 flight motor and against reported performance data from the literature. <![CDATA[<b>Design of a six-component side-wall balance using optical fibre sensors</b>]]> <![CDATA[<b>A numerical evaluation of dunnage bag pressure drop subject to a single void reduction cycle</b>]]> A method using a simple response model is used to replicate the results of an industry standard certification test for a dunnage bag. The method makes use of numerical optimization tools, standard commercial FEA software and a simple material response model to predict the pressure drop in a dunnage bag caused by material plastic deformation under a compressive cycled load. The results of the response model are evaluated to ensure that the overall response of the model matches that of the measured system. Calibration of the model is done by numerical optimization and the resulting model predicts the pressure drop over one cycle to within one standard deviation of the measured results. <![CDATA[<b>Investigation of nozzle contours in the CSIR supersonic wind tunnel</b>]]> The existing nozzle contour profiles of the CSIR's supersonic or High Speed Wind Tunnel (HSWT) produce weak waves in the test section region, which effectively degrades the air flow quality in the test section. This paper describes a calculation method developed to improve the flow quality in the test section region subject to the HSWT's limitations. The wind tunnel geometry and constraints were employed in accordance with the Sivells' nozzle design method and the method of characteristics technique to design the nozzle profiles for the full supersonic Mach number range 1<M<4.5 of the facility. Automatic computation was used for the profile design and a computational method analysed the test section flow characteristics. A boundary layer correction was applied to the profiles to account for the reduction in Mach number due to viscous effects. The method used, achieved uniform and shock-free test section flow, such that the Mach number distribution and flow angularity were within the acceptable quality limits of the HSWT. <![CDATA[<b>Upgrading the BMT120 KS micro gas turbine</b>]]> This study evaluates the performance of the BMT 120 KS micro gas turbine engine. The analysis involves matching the existing engine components as well as redesigned elements using engine characteristic maps. An experimental investigation was conducted to measure the baseline performance parameters of the engine. Analytical calculations were used to review the thermodynamic cycle of the engine. A numerical component sensitivity analysis was also used to evaluate the engine's output. The performance predictions of the engine and its modifications showed good correlation with test results and available engine data. <![CDATA[<b>Development and testing of a scale model Clamshell mucker</b>]]> The aim of the research was to develop a scaled experimental model of a Clamshell mucker and assess its performance over a range of operating parameters, including bucket closure angular velocity, bucket starting height (translating into increased depth of penetration and bucket fill), bucket angle of attack, and location of the bucket relative to a boundary wall. An experimental rig was developed consisting of a 1/6th scale model opposed bucket arrangement which was actuated by means of hydraulic cylinders. The digging performance was assessed in two materials: a mixture of hard plastic spheres (of diameters 19 and 25 mm), and 13 mm decomposed granite stone aggregate. Flow visualisation tests conducted in the plastic spheres and stone aggregate revealed that particles move initially downwards ahead of the bucket jaws before rising to the interior of the buckets. Tests conducted in decomposed granite revealed that force chains developed between the particles which resisted the motion of the buckets. The force chains resulted in local peaks in the bucket torques. The peak torque required to scoop material was found to increase with increasing depth ofpenetration, was not affected significantly by angular velocity of the buckets (although the number of local peaks associated with force chains decreased), bucket torque was found to increase in the presence of a smooth boundary within one particle width of the buckets, and was not significantly affected by different angles of penetration. An initial estimate of the energy required to fill the buckets indicated that the least amount of energy was required for lower bucket angular velocities. However, at low angular velocities there was a propensity for bucket stall due to the wedging of particles. <![CDATA[<b>Simulation system to aid in vehicle simulator design</b>]]> Vehicle simulators aim to provide the user with a driving experience that replicates the sensations experienced in a real vehicle. An important aspect is the replication of motion cues. The replication of motion cues in the vehicle simulator is limited by platform workspace and the selected position control systems performance. In this work a Matlab/Simulink setup that incorporates the various aspects involved in replication of motion sensations was created. This includes input data scaling, classical washout algorithm and inverse kinematic implementations. By adjusting the input data scaling and classical washout algorithm filter parameters platform motion that adheres to the actuator motion constraints was assured. Therefore this simulation system makes the design process easier since no parameter adjusting was done on the actual motion platform. This simulation system also ensures safe operation of the vehicle simulator system for the user and ensures safety of the vehicle simulator mechanical structure. Additionally the system allowed for the derived inverse kinematic equations to be verified and evaluated the effectiveness of the classical washout motion cueing algorithm. <![CDATA[<b>The National Wind Resource Assessment Project of Namibia</b>]]> With eleven tall masts equipped with modern wind data acquisition systems, the National Wind Resource Assessment Project (NWRAP) of Namibia is the most comprehensive dedicated wind measurement project undertaken in the country to date. The objective of NWRAP is the provision of high-quality wind data from which reliable wind climates can be identifiedfor relevant parts of the country. The article provides a brief background to the project and proceeds with a description of the development and location thereof, the equipment employed to produce wind data and the processes and methods used to analyse the data. The statistics pertaining to the observed wind climates as identifiedfrom wind speed data observed at two elevations at each of the masts are presented in the results section. The statistics include Weibull parameters and mean wind power density. It is inter alia shown that the best wind resource exists at the site located close to the Southern coastal town of Lüderitz where a resource of 411 W/m² at approximately 46 m above ground level was identified.