49 research outputs found
THE APPLICATION OF MODELLING AND SIMULATION TO SHIP DESIGN FOR HELICOPTER OPERATIONS
Modern combat ships, such as frigates and destroyers, routinely operate with maritime helicopters. The challenge of landing the helicopter in bad weather is acknowledged as being both demanding and dangerous; moreover, if the flying conditions are too difficult the helicopter will not be cleared to take off, and an important component of the ship’s capability will be lost. The unsteady air flow over the ship, particularly in the vicinity of the flight deck, is a significant factor that limits the helicopter’s operational envelope. The characteristics of the air flow, known as the ship’s airwake, depend on the wind speed and direction relative to the ship, and the geometry of the ship’s superstructure. The aerodynamics of the ship’s superstructure does not receive much attention at the design stage, compared to, for example, its radar cross-section. This thesis presents an investigation where modelling and simulation has been used to assess and inform the aerodynamic design of a modern warship. The modelling techniques that have been applied are time-accurate computational fluid dynamics, to compute the complex three-dimensional unsteady flow field over the full-size ship, and the mathematical modelling of a helicopter’s flight dynamics, to compute how a helicopter will respond to the unsteady air flow. These modelling techniques have then been used in two simulation applications; one is the Virtual AirDyn, to assess the unsteady loads applied to the helicopter by the ship’s airwake, and the second is piloted flight simulation in a motion-base flight simulator, to assess the effect of the airwake on a pilot’s workload while conducting a deck landing. Collectively the modelling and simulation techniques have been used to assess different design options for a ship’s superstructure. The techniques have also been applied investigate how the ship’s size affects the airwake and the ship’s motion, and how these affect the helicopter and the pilot workload when operating over the landing deck. Air flow modelling has also been used to predict how a ship’s hot engine exhaust gases mix with the airwake to cause fluctuating elevated temperatures over and around the flight deck. It has been demonstrated how relatively small changes to the geometry of the ship’s superstructure ahead of the flight deck can affect the aerodynamic loads on the helicopter, and that these effects can be detected and quantified to provide guidance to the ship designer. It has also been shown that while larger ships create larger and more aggressive airwakes that perturb the helicopter and increase the pilot workload during a landing. Smaller ships, on the other hand, have a more dynamic motion in rough seas, and smaller decks with a closer superstructure. Simulation has been used to show how these different effects combine and how ship size affects the pilot workload during a deck landing. The study has also identified that while offshore oil rig helicopter operators have clear guidelines on limits for air temperature increases, there are no such guidelines when operating a helicopter to a ship, and that the range of temperature increases that can occurs over the flight deck are sufficient to affect the helicopter performance. A significant contribution made by this study has been to inform the design of a real ship, so demonstrating the potential of modelling and simulation in the design of ships for helicopter operations
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Comprehensive aeromechanical measurements of a model-scale, coaxial, counter-rotating rotor system
With the renewed interest in rigid, counter-rotating coaxial rotor designs, and the increased fidelity of fully coupled CFD/CSD simulations, there exists a lack of comprehensive experimental data for a rotor system with which to validate analyses. The goal of this dissertation is to generate a new set of measurements on a model-scale rigid coaxial rotor systems in hover and high speed forward flight. A counter-rotating transmission was built, incorporating 6-component upper and lower rotor load cells for individual hub load measurements. Upper and lower rotor control systems, as well as complementary instrumentation including pushrod load cells, root pitch measurement and blade tip clearance sensors were developed. Two sets of rotor blades were fabricated and characterized using stereoscopic digital image correlation in combination with static and dynamic loads. A novel rotating-frame operational modal analysis successfully identified the first blade flap frequency and aerodynamic damping. Hover testing focused on quantifying the effects of upper and lower coaxial rotor interference when compared to isolated rotors. Statistical analysis of the measured data revealed clear trends with a known confidence level. Due to mutual interference, the upper and lower rotors of the coaxial configuration consumed 18% and 49% more induced power than that of an isolated two-bladed rotor. The coaxial counter-rotating configuration was found to consume 6% less induced power than an isolated, four-bladed single rotor of equal solidity. While torque balanced, the upper rotor was found to produce 54% of the total system thrust regardless of blade loading. Significant four-per-revolution vibratory thrust was observed in the lower rotor, with primary and secondary peaks corresponding to bound vortex and blade thickness interactions respectively. Wind tunnel testing examined the effects of lift offset and rotor phasing at high forward flight speeds. Rotor effective lift-to-drag ratio was found to increase with increasing advance ratio and lift offset, resulting in a 50% peak efficiency gain. The lower coaxial rotor was found to operate at higher lift-to-drag ratio than the upper rotor, due to the reversal of differential upper and lower rotor thrust compared to hover. Lift offset resulted in a decrease in blade tip clearance with a corresponding rise in rotor side force. Vibratory loads increased with advance ratio, with the largest occurring at two and four-per-revolution harmonics. Lift offset decreased vibratory forces while increasing vibratory in-plane moments. The coaxial system experienced reduced vibratory in-plane forces and torque compared to the isolated rotors due to cancellation between upper and lower rotor loads. Adjusting the inter-rotor index angle modified vibratory forces and moments transmitted to the fixed frame, increasing some components while decreasing others.Aerospace Engineerin
Oceanography
How inappropriate to call this planet Earth when it is quite clearly Ocean (Arthur C. Clarke). Life has been originated in the oceans, human health and activities depend from the oceans and the world life is modulated by marine and oceanic processes. From the micro-scale, like coastal processes, to macro-scale, the oceans, the seas and the marine life, play the main role to maintain the earth equilibrium, both from a physical and a chemical point of view. Since ancient times, the world's oceans discovery has brought to humanity development and wealth of knowledge, the metaphors of Ulysses and Jason, represent the cultural growth gained through the explorations and discoveries. The modern oceanographic research represents one of the last frontier of the knowledge of our planet, it depends on the oceans exploration and so it is strictly connected to the development of new technologies. Furthermore, other scientific and social disciplines can provide many fundamental inputs to complete the description of the entire ocean ecosystem. Such multidisciplinary approach will lead us to understand the better way to preserve our "Blue Planet": the Earth
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Energy-efficient mobile Web computing
Next-generation Web services will be primarily accessed through mobile devices. However, mobile devices are low-performance and stringently energy-constrained. In my dissertation, I propose the design of a high-performance and energy-efficient mobile Web computing substrate. It is a hardware/software co-designed system that delivers satisfactory user quality-of-service (QoS) experience on a mobile energy budget. The key insight is that the traditional interfaces between different Web stacks need to be enhanced with new abstractions that express user QoS experience and that expose architectural-level complexities. On the basis of the enhanced interfaces, I propose synergistic cross-layer optimizations across the processor architecture, Web runtime, programming language, and application layers to maximize the whole system efficiency. The contributions made in this dissertation will likely have a long-term impact because the target application domain, the Web, is becoming a universal mobile development platform, and because our solutions target the fundamental computation layers of the Web domain.Electrical and Computer Engineerin