Turret Configuration Research Articles

Application of passive flow control techniques to attenuate the unsteady near wake of airborne turrets in subsonic flow

External airborne installations of cylindrically-shaped objects, such as turrets, can lead to severe degradation of flight performance. This engineering challenge is mainly due to an unsteady and separated vortex flow field that evolves in the wake downstream of the turret. This study focuses on providing an engineering solution to attenuate the wake unsteadiness. Experiments were performed in the Israeli Air Force (IAF) low speed wind tunnel, where we investigated various passive flow control methods on a hemispherical dome attached to a cylindrical body turret with a low aspect ratio (AR) of 1.36 at a diameter-based Reynolds number of ReD=3.75×105. Three modifications of the baseline turret geometry were examined. The configurations include the addition of a grit roughness strip, a turbulator zigzag trip tape, and a straight edge protuberance (or a bump strip). The velocity fields in the near wake downstream of the various turret configurations were acquired using a particle image velocimetry (PIV) technique. Results show that tripping the flow using a bump strip is the most effective for the turret studied herein. The bump strip prompts symmetrical vortex shedding downstream, which can potentially eliminate the fluctuating side force on the turret, while also contributing the least to any drag increase (or penalty). Implementing such a passive flow technique on cylindrical installations may assist in resolving large fluctuating side forces and meeting operational requirements during flight.

Wind-tunnel and CFD investigations of UAV landing gears and turrets – Improvements in empirical drag estimation

This paper analyzes the drag characteristics of several landing gear and turret configurations that are representative of unmanned aircraft tricycle landing gears and sensor turrets. A variety of these components were constructed via 3D-printing and analyzed in a wind-tunnel measurement campaign. Both turrets and landing gears were attached to a modular fuselage that supported both isolated components and multiple components at a time. Selected cases were numerically investigated with a Reynolds-averaged Navier-Stokes approach that showed good accuracy when compared to wind-tunnel data. The drag of main gear struts could be significantly reduced via streamlining their cross-sectional shape and keeping load carrying capabilities similar. The attachment of wheels introduced interference effects that increased strut drag moderately but significantly increased wheel drag compared to isolated cases. Very similar behavior was identified for front landing gears. The drag of an electro-optical and infrared sensor turret was found to be much higher than compared to available data of a clean hemisphere-cylinder combination. This turret drag was merely influenced by geometrical features like sensor surfaces and the rotational mechanism. The new data of this study is used to develop simple drag estimation recommendations for main and front landing gear struts and wheels as well as sensor turrets. These recommendations take geometrical considerations and interference effects into account.

Analysis of the Motion Response on the Cylindrical Platform of the Deep Sea

The strategic point of potential tidal energy in Indonesia can be a solution to the energy crisis, and as the development of renewable energy. Several concepts of the floating marine current turbine (MCT) have been offered, one of them is the cylindrical platform. The object of the conducted study is 33 m cylindrical platform with twin horizontal axis MCT installed underneath the platform. The analysis begins with the platform properties which include Centre of gravity, gyration radius and inertial. The environmental loads are 1 m/s and 2 m/s current speed, 2.4 m wave height, and 22 knots wind. The properties will be used as input for motion analysis and mooring line tension. The results of the analysis with turret configuration of three lines and four lines show that the response amplitude operator (RAO) on the largest translational motion on surge motion as far as 4 m and rotational motion of 4.5 degrees. For the analysis of the mooring system the average maximum tension of the mooring chain reaches 2000 kN, with the maximum proof load at the value of 2245.82 kN which resulted to a safety factor of 1,73 and it still complies to API RP 2SK Standard.

A Design of Experiments Methodology for Evaluating Configuration for a Generation Next Main Battle Tank

<p class="p1">Combat vehicles for generation next main battle tank requires state-of-the-art technologies to counter advanced threats both from conventional and un-conventional sources across various theatres of operation. In addition, they require strategic mobility by road, rail, air and sea. Under such conditions, the trend across the world has been to converge on configurations that are lethal, agile, modular systems and interchangeable mission based turret configurations along with higher survivability which imposes limitations on mobility as mass increases. To achieve all the user objectives as laid down in the qualitative requirements, it is prudent to focus the attention on weight management. The traditional approach of weight management is time consuming, for which an alternate approach using design of experiments is proposed in this paper. To carry out this study, two configurations are selected namely evolutionary and revolutionary design. Keeping the outer boundary as the constraint, a simple linear regression and analysis of variance are carried out with mass and volume data from various systems and sub-systems. Subsequently, the accuracy of the analysis is ascertained using a test of hypothesis using PHStat software. Although this study discusses configuration, the factors responsible for reduced system mass and volume namely technology, materials, intelligence etc have not been discussed. Finally, from the outcome of the study it is observed that the revolutionary design configuration fares better compared to the evolutionary design configuration with a combat mass of only 41 t.<span class="Apple-converted-space"> </span></p>

Adaptive-optic system requirements to mitigate aero-optical aberrations as a function of viewing angle

A comparison between the spatial and temporal requirements for designing adaptive-optic correction systems for aero-optical turbulence over the pupil of a turret on the side of an airborne platform is presented. These systems are necessary to mitigate the deleterious aero-optic effects on an optical beam and to reopen the field of regard. The derived technique makes use of the two-dimensional proper orthogonal decomposition to characterize the spatial and temporal frequencies of in-flight measured data from the Airborne Aero-Optics Laboratory. For this study, 13 different viewing angles, which represent various flow topologies around the airborne turret, were chosen. The paper concludes with a discussion that points out the usefulness of the derived technique in characterizing the aero-optical disturbances of various aero-optical environments at different viewing angles and different turret configurations.

Hybrid Reynolds-Averaged Navier-Stokes/Large-Eddy Simulation Investigating Control of Flow over a Turret

This investigation explores the flow over a turret atM1 0:4 and ReD 2:4 10 using both hybrid Reynoldsaveraged Navier–Stokes/implicit large-eddy simulation (RANS/ILES) and k-based unsteady Reynolds-averaged Navier–Stokes (URANS) simulations. Additional hybrid RANS/ILES simulations were performed to compare the effectiveness of two steady-suction flow control approaches. The hybrid RANS/ILES computations were obtained using awell-validated high-orderNavier–Stokes flow solver employing a fourth-order compact spatial discretization in conjunction with a sixth-order low-pass spatial filter. The URANS simulations were performed using a secondorder version of the flow solver and kturbulence model. The turret configuration consisted of a half-foot radius hemisphere atop a 4.5-in.-tall circular cylinder base. Both steady suction through a slot and a leeward porous turret shell were explored as forms of flow control. Time-mean hybrid RANS/ILES results, obtained on a 23 10-point mesh, compared reasonably well to experimental pressure coefficient and velocity profiles for the baseline flow. The separation angle was predicted to within 3 deg of experimental observations. The instantaneous hybrid RANS/ILES solutions display complex three-dimensional flow phenomena in the wake of the turret that the kURANS model was unable to resolve. Both steady-suction flow control approaches successfully attached the flow over most the turret dome and significantly reduced the size of the wake.

A Quasi-Explicit Hydrodynamic Model for the Dynamic Analysis of a Moored FPSO Under Current Action

In an earlier work Leite et al (1998) developed a heuristic hydrodynamic model, based on the shrtwing theory, for the horizontal current forces on an FPSO system. The proposed model was quasi-explicit in the sense that it depends on the ship's main dimensions and on only three hydrodynamic coefficients, namely, the friction coefficient Cf for head on incidence, the drag coefficient CY for a cross-flow, and the related yaw moment coefficient lCY. As discussed in Leite et al (1998), these coefficients could even be estimated from the ITTC friction curve and from Hoerner's sectional results, which would then turn the hydrodynamic model explicit. The model has been tested against experimental results for the horizontal force coefficients, obtained both at IPT and at the Marin wave tank, and it has also been confronted with bifurcation experiments for a turret configuration realized at IPT. The agreement rendered good results in all cases tested. The heuristic approach has now been extended to incorporate the yaw velocity terms while preserving the quasi-explicit feature of the original model. The main purpose of the work herein is to present such a development together with some experimental validation. Using Froude scaling of different ships in distinct ballast conditions, the horizontal forces and moment in the yaw rotating tests were measured at IPT and at Marin and compared with those predicted by the heuristic model, the observed agreement again being fair enough. In an accompanying paper in this issue, the derived mathematical model is tested against experiments that emulate a single-point mooring of a tanker ship in order to disclose the model's ability to cope with the main dynamic features of the fishtailing instability problem.

Risk Assessment of Production and Storage Tankers

Abstract Production and storage tankers are being evaluated extensively for development of marginal oil and gas fields in the North Sea. The main safety aspects of these vessels are discussed, based on a number of quantitative risk assessments for these vessel concepts. These studies have confirmed the importance of several important safety features, such as a fire-protected, enclosed escape way along one of the sides of the ship. Other important safety features include weather-vaning capability as a function of the turret location, location and configuration of the flare system, protection of cargo tanks by inert gas blanketing, as well as procedures for strict control of tank intervention. The results, show that the production and storage vessels have favorable safety characteristics, and that these concepts represent an acceptable and feasible solution for the marginal fields.

Determination of turret configuration and hit sequence for optimization of NC turret punch press operation

Abstract This paper addresses the problem of minimization of the time taken to process sheet metal stock on an NC turret punch press. The processing lime of a sheet depends primarily on (1) the sequence in which the hits are made and )2) the arrangement of tools in the turret. Minimization of the processing time for a sheet requires the simultaneous solution of these two coupled sub-problems. Motivated by this view, the paper proposes three heuristics to find a hit sequence and a turret configuration that together minimize the processing time for a sheet. A comparison of the performance of these heuristics is provided. In addition, the paper examines some issues not considered in prior research but essential to the accurate modelling of the operation of an NC turret punch press, and discusses their incorporation in the proposed heuristics.

Integration of CAD/CAM and Production Control in Sheet Metal Manufacturing - The Basis for Automatic Generation of Production Data

An integrated system for design and production planning of sheet metal components is discussed. The functionality of a set of modules is shown. The fundamental integration tool is a common database. The core of the system includes product, process and planning data. The implemented modules communicate via the common database. The structure of the database and the internal representation of parts are described. It is shown how manufacturing data from a feature- based design system is used for the automatic selection of a suitable manufacturing process. Furthermore an algorithm for the calculation of the machine tool turret configuration is explained.