Prediction of forces and moments for flight vehicle control effectors. Part 2: An analysis of delta wing aerodynamic control effectiveness in ground effect

Many types of hypersonic aircraft configurations are currently being studied for feasibility of future development. Since the control of the hypersonic configurations throughout the speed range has a major impact on acceptable designs, it must be considered in the conceptual design stage. Here, an investigation of the aerodynamic control effectiveness of highly swept delta planforms operating in ground effect is presented. A vortex-lattice computer program incorporating a free wake is developed as a tool to calculate aerodynamic stability and control derivatives. Data generated using this program are compared to experimental data and to data from other vortex-lattice programs. Results show that an elevon deflection produces greater increments in C sub L and C sub M in ground effect than the same deflection produces out of ground effect and that the free wake is indeed necessary for good predictions near the ground

QUANTIFYING AND MANAGING RISK IN AGRICULTURE

Risk and Uncertainty,

A Study to Determine Feasible Government Development Strategies for Farms in Nimboran Irian Jaya

The study was undertaken to establish what factors constrain small-farmers in Nimboran Irian Jaya from increasing their net cash incomes (NCI) and to determine how these constraints can best be relaxed. The constraints are viewed within the wider context of transforming local subsistence agriculture towards a commercial agriculture. A decision theoretic approach, combined with subjective equilibrium theory and subsistence affluence theory is used. The selected basic model is stochastic discrete programming, wherein a lexicographic decision rule is specified which explains that resources will be allocated to cash activities only after subsistence food requirements have been met. A field survey was conducted to interview 30 of the 357 farm households estimated to be found in the region, to collect farm data, elicit utility functions and subjective probabilities of the states of nature. ... The result of the analysis showed that the availability of female labour was the most limiting factor. The level of crop activities between the two utility groups appeared to be the same. Only the expected NCI varied. The expected NCI of the better educated farmers group appeared to be lower and closer to the value of expected consumption than that of the majority of the farmers group. The possible interpretation of these facts is that the pattern of resource allocation or the level of crop activities is the best - given the existing resources, technology and institutional conditions - regardless of whether the aspirations have increased or not. The best available farm development strategy is expanding cash crops such as coconut and cocoa, where reallocation of resources may still be possible to generate higher expected NCI. Given the Nimboran farmers subjective assessment, the introduction of rice could be difficult since it appeared to have increased resources - land and labour - used, but added extremely little to the expected NCI

Aerodynamic Requirements for BVI Noise Control

As a rotor blade moves through the air, it sheds vortices. These vortices shed along the length of the blade over time form the wake. The strongest vortices of the wake are those trailing from the tip of the blade. When a rotating blade system moves under certain operating conditions, each blade will impinge on the tip vortices shed by itself or other blades. This impingement is called a blade-vortex interaction, or BVI. Although the blade and trailing tip vortices interact with many different orientations, one of the two extremes, either parallel or perpendicular interaction, is usually modelled. In a perpendicular interaction, the portion of the blade that is actually interacting with the travelling vortex at any given time is very small. A parallel interaction, however, has the largest concurrent interaction with the blade, as a result this case is given the most attention. One of the most commonly studied occurrences of blade-vortex interactions is associated with low-speed descending rotorcraft flight. BVI occur when the tip vortices shed by the blades intersect the plane of the rotor. BVI cause local pressure changes over the blades which are responsible, in part, for the acoustic signature of the rotorcraft. The local pressure changes also cause vibrations which lead to fatigue of both the blades and the mechanical components driving the blades

Decision making in horticultural firms

Before looking at decision making in the horticultural firm in detail, it is desirable to briefly describe the types of decisions, that are made along with the nature of the environment within which the horticultural firm typically exists. Decision making in horticultural firms is characterised by a diversity of decision types which maybe categorised for convenience on the basis of time scales. In the long term, decisions need to be made concerning the legal form of the business structure, the crop plan choice, scale of operation and location of operation. In the medium term will be decisions concerning investment in equipment, machines and storage facilities. As a result of these medium and long term decisions, there is a requirement in the short term for decisions relating to crop production methods and husbandry matters (e.g. pest and disease control), labour, harvesting and marketing. Marketing policy may in fact be a medium term decision requiring short term decisions for its implementation. Set-out in Figure 1 is one version of an abbreviated decision making cycle (Rae, 1977). The horticultural firm, especially for small family operations, is characterised by a close relationship between the operations of the household and the firm. Both entities consume funds and labour resources and may be in conflict with one another. Horticultural firms maybe legally structured in several ways such as sole ownership, partnerships, companies or as a co-operative. While these forms of business structure determine responsibility for consequences of management decisions, they may not necessarily be an accurate reflection of who makes particular decisions. Having considered briefly the system of the horticultural firm and the types of decisions it is involved in making, we now briefly consider the environment within which the firm exists, as it will markedly influence decision making

Analysis of the project fire re-entry package flow field final technical report

Theoretical prediction of state of gas in flow field surrounding Apollo type vehicle in reentry at hypersonic speed

Roll stabilization for fast monohulls by using passive and active lifting appendages

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2004.Includes bibliographical references (p. 91-92).Roll stabilization for monohulls is an important issue in naval architecture. Several methods including roll stabilization tanks, active control fins, rudder roll stabilization systems, and bilge keels are commonly used for roll stabilization purposes and each one of them has its own advantages and disadvantages. In this thesis roll stabilization is studied by using passive and active roll stabilization configurations with hydrofoils. The main objective of this research is to identify an effective roll stabilization system for use on high- speed monohull vessels. The analysis of the performance of a passive hydrofoil configuration is used as a starting point for the development of active control mechanisms. A generic fast monohull was created for study purposes and the SWAN-2 code (ShipWaveANalysis), a state-of-the-art time domain simulation program, was used for the analysis of the linear free-surface flow around the vessel. Simulations were carried out in regular waves incident at angles ranging from 90⁰, 105⁰,120⁰,135⁰ and 150⁰ degrees relative to the ship axis, 900 being beam waves and 180⁰ degree being head waves. The ship was equipped with a hydrofoil fixed amidships, quarter to aft and aft to determine the sensitivity of roll motion on the longitudinal position of the lifting appendage.(cont.) It was found that the most efficient location for the hydrofoil is amidships leading to a 20% to 60% roll motion reduction (depending on the wave angle and ship speed) of the RMS value of roll motion in an ISSC spectrum. Also studies were performed to determine the planform area of the hydrofoil for optimal roll motion reduction. In addition, four different Froude numbers are used, ranging from 0.3 to 0.9, to evaluate the effect of the speed on the effectiveness of the lifting appendage. As expected, higher speeds lead to better seakeeping performance, namely better roll reduction compared to lower speeds. Passive hydrofoils were found to be very effective in reducing the rolling motion. Active roll control mechanisms were also investigated by seeking the optimal time-dependent variation of the modulus and phase of the hydrofoil angle of attack and found to be very effective leading to increased roll reduction. The development of such optimal control algorithms is expected to lead to an enhanced roll seakeeping performance over a broader range of sea state conditions and ship speeds.by Talha Ulusoy.S.M