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Aerospace Systems Design Laboratory (ASDL)
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ItemUse of Probability of Success as an Independent Variable for Decision-Making(Georgia Institute of Technology, 2004-09) Frits, Andrew P. ; Mavris, Dimitri N.Early phases of design are characterized by risk and uncertainty. Appropriate accounting for this uncertainty is an important requirement for any designer. This work suggests collapsing risk and uncertainty into a single metric called the probability of success, which accounts for the probability of a given design simultaneously meeting all of the design requirements. Optimal or lowest cost designs can then be found for various levels of probability of success. These designs can be compared to each other, creating a trade-off between the cost of a design and its risk. These risk versus cost figures can be generated before a decision-maker commits to the design. Thus, the decision-maker will have all the information regarding the cost and risk of potential designs before making any design decisions. The decision-maker can thus treat the probability of success, or risk, as an independent variable, choosing the level of risk that he or she finds acceptable based upon the cost of the system, with the corresponding
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ItemInclusion of Tactical Considerations for System-of-Systems Optimization of Torpedoes(Georgia Institute of Technology, 2004-08) Frits, Andrew P. ; Weston, Neil R. ; Mavris, Dimitri N.In the current torpedo design process, torpedoes are often designed independently from the tactics with which they are employed. This serial design process, of first developing tactics, then designing the torpedo, then re-developing tactics leads to torpedo designs that are sub-optimal when viewed from the greater system-of-systems perspective. This paper looks at the effects that tactics have on the design of torpedoes. It proposes a new paradigm, of simultaneous tactics development and torpedo design, and looks at the implications of various tactics on the optimal design of torpedo systems.
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ItemBenefits of Non-Dimensionalization in Creation of Designs of Experiments for Sizing Torpedo Systems(Georgia Institute of Technology, 2004-08) Frits, Andrew P. ; Reynolds, Kristen ; Weston, Neil R. ; Mavris, Dimitri N.Non-dimensionalization is useful at many stages in the conceptual design process. One area of usefulness is in the creation and execution of Design of Experiments. A Design of Experiments that is run with dimensional quantities can often have a large number of failed or infeasible cases or require frustratingly small ranges on the design variables in order to execute cleanly. However, with the use of non-dimensional parameters in the Design of Experiments, the dimensional values being used in the analysis tool automatically scale themselves so that appropriate magnitudes of each parameter are always being used. This automatic scaling greatly increases the stability of Design of Experiments when non-dimensional parameters are used, limiting the number of failed cases. This paper explores potential non-dimensional parameters for use in the conceptual design of torpedo systems. The paper shows that traditional non-dimensional parameters used in propulsor design, such as advance ratio and thrust coefficient, also work well as torpedo design parameters. A short example is given where the performance of a Design of Experiments for a torpedo system is improved via the use of non-dimensional parameters.
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ItemUse of a Conceptual Sizing Tool for Conceptual Design of Tactical Missiles (U)(Georgia Institute of Technology, 2002-11) Frits, Andrew P. ; Fleeman, Eugene L. ; Mavris, Dimitri N.This paper illustrates the use of a conceptual sizing tool for the design of tactical missiles. The sizing tool, called the Tactical Missile Design (TMD) spreadsheet, was developed to allow the user to quickly generate estimates of a missile configuration?s performance and other measures of merit such as lethality. This capability allows the user to get a first order estimate of a missile?s ability to meet a set of requirements and allows for fast trade-studies to quickly identify the performance drivers of a system. In order to generate reasonable estimates for missile range and speed, a sizing tool must have analysis methods for aerodynamics, propulsion, weight, and trajectory. In order for the sizing tool to remain useful for conceptual tradeoffs, these analyses must be robust enough to handle a wide range of inputs, yet simple enough to be executed quickly. The analysis methods were constructed with these requirements in mind. The aerodynamics analysis is based upon several physics-derived analytical expressions as outlined in the text ?Tactical Missile Design? by Eugene Fleeman. Propulsion uses a simplified cycle analysis to relate engine parameters (maximum inlet temperature, fuel heating value, expansion ratio) to overall specific impulse (Isp). The propulsion analysis can handle either air-breathing and solid-rocket systems, or a combination thereof. For trajectory, a constant flight path is assumed, with a boost, cruise, and coast phase. These straightforward analysis methods combine to produce a very powerful, yet robust, conceptual missile design tool. The paper first lays out the analysis methods, assumptions, and limitations in the Tactical Missile Design spreadsheet. Next, a comparison is made between the results of the TMD spreadsheet and the performance of historical missile systems. In addition, the paper explores some example trade studies to identify the drivers of a rocket and a ramjet missile system. Finally, the TMD spreadsheet is used to show how easily a tactical missile can be optimized at the conceptual level.
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ItemA Screening Method for Customizing Designs Around Non-Convergent Regions of Design Spaces(Georgia Institute of Technology, 2002-09) Frits, Andrew P. ; Mavris, Dimitri N.In engineering design, Response Surface Methodology is often used to explore a design space and to generate a meta-model of the space. Designs of Experiments are used in this process to obtain the most behavioral information from the space with the fewest number of runs. Often, the designer discovers that the analysis program cannot converge to an answer for one or more regions of the design space. Traditionally, the designer gets around this problem by shrinking the variable ranges so that there are no regions of non-convergence. Instead of this process, this paper suggests that it is better to treat the non-convergent points as a region of infeasibility. Extra runs can be made to determine the border of this infeasible region, and then a custom Design of Experiments can be constructed to explore the design space while excluding the non-convergent region. This process still generates a valid meta-model yet retains more of the design space than the simple reduction of variable ranges.
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ItemExamination of a Torpedo Performance Space and its Relation to the System Design Space(Georgia Institute of Technology, 2002-09) Frits, Andrew P. ; Weston, Neil R. ; Pouchet, Colin ; Kusmik, Aldo ; Krol, William, Jr. ; Mavris, Dimitri N.In historical torpedo design, mission analysis, which relates torpedo performance to mission success, has been used as a stand-alone tool to derive specific torpedo performance requirements. These performance requirements must then be met by the torpedo designer. However, the incorporation of mission analysis into the engineering design of a torpedo system grants more freedom to the designer. The designer can immediately see the effects of design variable changes on mission success, and can infuse new tactics in addition to new technologies to expand the available design space. This paper serves to explore the performance space of a torpedo, then relate this performance space to the design variables by mapping the performance space directly to the design space and design variables. The paper also studies how granting the designer control of weapon tactics expands the design space, allowing the torpedo and its tactics to be concurrently optimized. This new approach results in significantly greater design freedom and the ability of the find a system-level global optimum.
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ItemAn Evaluation of Green Propellants for an ICBM Post Boost Propulsion System(Georgia Institute of Technology, 2000-11) German, Brian J. ; Branscome, Ewell Caleb ; Frits, Andrew P. ; Yiakas, Nicholas C. ; Mavris, Dimitri N.Propellant toxicity is a major concern in storing, maintaining, and transporting strategic missiles. Many low toxicity green propellants have been developed which hold the potential of increasing the safety and lowering the operation and support costs of liquid-fuelled strategic missile propulsion systems. This study evaluates several green propellants for use in a notional next-generation post-boost propulsion system (PBPS). The mission and physical dimensions for this PBPS were defined by the requirements of the current Minuteman III propulsion system rocket engine (PSRE). Possible propellants were initially screened in terms of toxicity, performance, and technical feasibility for the PBPS application with a multi-attribute ranking method based on an overall evaluation criterion (OEC). Promising propellants were identified, and candidate PBPS concepts were developed and sized for each of these propellants. These concepts were evaluated in terms of weight, cost, and technical risk to determine which concepts, and hence propellants, show the most promise for the application. Probabilistic techniques were employed to explore the effects of uncertainty in the propellant performance and structural weight estimates. The results indicate that high-test peroxide (HTP) combined with either an ethanol-based nontoxic hypergolic miscible fuel (NHMF) or competitive impulse non-carcinogenic hypergol (CINCH) is a very viable propellant solution.