Domain-specific languages

Domain-Specific Languages are used in software engineering in order to enhance quality, flexibility, and timely delivery of software systems, by taking advantage of specific properties of a particular application domain. This survey covers terminology, risks and benefits, examples, design methodologies, and implementation techniques of domain-specific languages as used for the construction and maintenance of software systems. Moreover, it covers an annotated selection of 75 key publications in the area of domain-specific languages

IPPD Through Robust Design Simulation for an Affordable Short Haul Civil Tiltrotor

Presented at the 53rd Annual Forum of the American Helicopter Society, Virginia Beach, VA, April 29 - May 1, 1997.Beyond the Bell/Boeing 609, the next step in civil tiltrotor evolution will most likely be a larger capacity vehicle (~ 40 passenger class) similar to NASA? vision of a Short Haul Civil Tiltrotor (SHCT). This vehicle will be designed, built and operated in an era being shaped by today? increased emphasis on affordability. This paper discusses the authors?views on the subject and outlines the steps taken to develop a new methodology which will allow a true assessment of the affordability of such a SHCT. Affordability will not be defined by cost metrics alone. Instead, it will be based on the concept of value and tradeoffs between cost and mission effectiveness; measured by maintainability, reliability, safety, etc. In addition, the motivation for this shift in design philosophy and the resulting need for knowledge to be brought forward in the proposed methodology is reviewed. Furthermore, this shift in knowledge calls for a paradigm shift in the design evolution process based on the realization that decisions made during the early design phases are not deterministic in nature and should therefore be handled probabilistically. The approach taken acknowledges this need and defines a suitable probabilistic design environment. The fundamental building blocks of this method are also outlined and discussed including key concepts, tools, techniques, and the approach taken to implement this process

Rotor Fatigue Life Prediction and Design for Revolutionary Vertical Lift Concepts

Despite recent technological advancements, rotorcraft still lag behind their fixed-wing counterparts in the areas of flight safety and operating cost. Competition with fixed-wing aircraft is difficult for applications where vertical takeoff and landing (VTOL) capabilities are not required. Both must be addressed to ensure the continued competitiveness of vertical lift aircraft, especially in the context of new military and civilian rotorcraft programs such as Future Vertical Lift and urban air mobility, which will require orders-of-magnitude improvements in reliability, availability, maintainability, and cost (RAM-C) metrics. Lifecycle costs and accident rates are strongly driven by scheduled replacement or failure of flight-critical components. Rotor blades are life-limited to ensure that they are replaced before fatigue damage exceeds critical levels, but purchasing new blades is extremely costly. Despite aggressive component replacement times, fatigue failure of rotor blades continues to account for a significant proportion of inflight accidents. Fatigue damage in rotorcraft is unavoidable due to the physics of rotary-wing flight, but new engineering solutions to improve fatigue life in the rotor system could improve rotorcraft operating costs and flight safety simultaneously. Existing rotorcraft design methods treat fatigue life as a consequence, rather than a driver, of design. A literature review of rotorcraft design and fatigue design methods is conducted to identify the relevant strengths and weaknesses of traditional processes. In rotorcraft design, physics-based rotor design frameworks are focused primarily on fundamental performance analysis and do not consider secondary characteristics such as reliability or fatigue life. There is a missing link between comprehensive rotor design frameworks and conceptual design tools that prevents physics-based assessment of RAM-C metrics in the early design stages. Traditional fatigue design methods, such as the safe life methodology, which applies the Miner's rule fatigue life prediction model to rotorcraft components, are hindered by a lack of physics-based capabilities in the early design stages. An accurate fatigue life quantification may not be available until the design is frozen and prototypes are flying. These methods are strongly dependent on extrapolations built on historical fatigue data, and make use of deterministic safety factors based on organizational experience to ensure fatigue reliability, which can lead to over-engineering or unreliable predictions when applied to revolutionary vertical lift aircraft. A new preliminary fatigue design methodology is designed to address these concerns. This methodology is based on the traditional safe life methodology, but replaces several key elements with modern tools, techniques, and models. Three research questions are proposed to investigate, refine, and validate different elements of the methodology. The first research question addresses the need to derive physics-based fatigue load spectra more rapidly than modern comprehensive analysis tools allow. The second investigates the application of different probabilistic reliability solution methods to the fatigue life substantiation problem. The third question tests the ability of the preliminary fatigue design methodology to evaluate the relative impact of common preliminary fatigue design variables on the probability of fatigue failure of a conceptual helicopter's rotor blade. Hypotheses are formulated in response to each research question, and a series of experiments are designed to test those hypotheses. In the first experiment, a multi-disciplinary analysis (MDA) environment combining the rotorcraft performance code NDARC, the comprehensive code RCAS, and the beam analysis program VABS, is developed to provide accurate physics-based predictions of rotor blade stress in arbitrary flight conditions. A conceptual single main rotor transport helicopter based on the UH-60A Black Hawk is implemented within the MDA to serve as a test case. To account for the computational expense of the MDA, surrogate modeling techniques, such as response surface equations, artificial neural networks, and Gaussian process models are used to approximate the stress response across the flight envelope of the transport helicopter. The predictive power and learning rates of various surrogate modeling techniques are compared to determine which is the most suitable for predicting fatigue stress. Ultimately, shallow artificial neural networks are found the provide the best compromise between accuracy, training expense, and uncertainty quantification capabilities. Next, structural reliability solution methods are investigated as a means to produce high-reliability fatigue life estimates without requiring deterministic safety factors. The Miner's sum fatigue life prediction model is reformulated as a structural reliability problem. Analytical solutions (FORM and SORM), sampling solutions (Monte Carlo, quasi-Monte Carlo, Latin hypercube sampling, and directional simulation), and hybrid solutions importance sampling) are compared using a notional fatigue life problem. These results are validated using a realistic helicopter fatigue life problem \jnr{which incorporates the fatigue stress surrogate model and is based on a probabilistic definition of the mission spectrum to account for fleet-wide usage variations. Monte Carlo simulation is found to provide the best performance and accuracy when compared to the exact solution. Finally, the capabilities of the preliminary fatigue design methodology are demonstrated using a series of hypothetical fatigue design exercises. First, the methodology is used to predict the impact of rotor blade box spar web thickness on probability of fatigue failure. Modest increases in web thickness are found to reduce probability of failure, but larger increases cause structural instability of the rotor blade in certain flight regimes which increases the fatigue damage rate. Next, a similar study tests the impact of tail rotor cant angle. Positive tail rotor cant is found to improve fatigue life in cases where the center of gravity (CG) of the vehicle is strongly biased towards the tail, but is detrimental if the CG is closer to the main rotor hub station line. Last, the effect of design mission requirements like rate of climb and cruising airspeed is studied. The methodology is not sensitive enough to predict the subtle impact of changes to rate of climb, but does prove that a slower cruising airspeed will decrease probability of fatigue failure of the main rotor blade. The methodology is proven to be capable of quantifying the influence of \jnr{rotor blade design variables, vehicle layout and configuration, and certain design mission requirements}, paving the way for implementation in a rotorcraft design framework. This thesis ends with suggestions for future work to address the most significant limitations of this research, as well as descriptions of the tasks required to apply the methodology to conventional rotorcraft or conceptual revolutionary vertical lift aircraft.Ph.D

A small perturbation based optimization approach for the frequency placement of high aspect ratio wings

Design denotes the transformation of an identified need to its physical embodiment in a traditionally iterative approach of trial and error. Conceptual design plays a prominent role but an almost infinite number of possible solutions at the outset of design necessitates fast evaluations. The traditional practice of empirical databases loses adequacy for novel concepts and an ever increasing system complexity and resource scarsity mandate new approaches to adequately capture system characteristics. Contemporary concerns in atmospheric science and homeland security created an operational need for unconventional configurations. Unmanned long endurance flight at high altitudes offers a unique showcase for the exploration of new design spaces and the incidental deficit of conceptual modeling and simulation capabilities. The present research effort evolves around the development of an efficient and accurate optimization algorithm for high aspect ratio wings subject to natural frequency constraints. Foundational corner stones are beam dimensional reduction and modal perturbation redesign. Local and global analyses inherent to the former suggest corresponding levels of local and global optimization. The present approach departs from this suggestion. It introduces local level surrogate models to capacitate a methodology that consists of multi level analyses feeding into a single level optimization. The innovative heart of the new algorithm originates in small perturbation theory. A sequence of small perturbation solutions allows the optimizer to make incremental movements within the design space. It enables a directed search that is free of costly gradients. System matrices are decomposed based on a Timoshenko stiffness effect separation. The formulation of respective linear changes falls back on surrogate models that approximate cross sectional properties. Corresponding functional responses are readily available. Their direct use by the small perturbation based optimizer ensures constitutive laws and eliminates a previously necessary optimization at the local level. The great economy of the developed algorithm makes it suitable for the conceptual phase of aircraft design.Ph.D.Committee Chair: Mavris, Dimitri; Committee Member: Bauchau, Olivier; Committee Member: Schrage, Daniel; Committee Member: Volovoi, Vitali; Committee Member: Yu, Wenbi

A methodology for rapid vehicle scaling and configuration space exploration

Drastic changes in aircraft operational requirements and the emergence of new enabling technologies often occur symbiotically with advances in technology inducing new requirements and vice versa. These changes sometimes lead to the design of vehicle concepts for which no prior art exists. They lead to revolutionary concepts. In such cases the basic form of the vehicle geometry can no longer be determined through an ex ante survey of prior art as depicted by aircraft concepts in the historical domain. Ideally, baseline geometries for revolutionary concepts would be the result of exhaustive configuration space exploration and optimization. Numerous component layouts and their implications for the minimum external dimensions of the resultant vehicle would be evaluated. The dimensions of the minimum enclosing envelope for the best component layout(s) (as per the design need) would then be used as a basis for the selection of a baseline geometry. Unfortunately layout design spaces are inherently large and the key contributing analysis i.e. collision detection, can be very expensive as well. Even when an appropriate baseline geometry has been identified, another hurdle i.e. vehicle scaling has to be overcome. Through the design of a notional Cessna C-172R powered by a liquid hydrogen Proton Exchange Membrane (PEM) fuel cell, it has been demonstrated that the various forms of vehicle scaling i.e. photographic and historical-data-based scaling can result in highly sub-optimal results even for very small O(10-3) scale factors. There is therefore a need for higher fidelity vehicle scaling laws especially since emergent technologies tend to be volumetrically and/or gravimetrically constrained when compared to incumbents. The Configuration-space Exploration and Scaling Methodology (CESM) is postulated herein as a solution to the above-mentioned challenges. This bottom-up methodology entails the representation of component or sub-system geometries as matrices of points in 3D space. These typically large matrices are reduced using minimal convex sets or convex hulls. This reduction leads to significant gains in collision detection speed at minimal approximation expense. (The Gilbert-Johnson-Keerthi algorithm is used for collision detection purposes in this methodology.) Once the components are laid out, their collective convex hull (from here on out referred to as the super-hull) is used to approximate the inner mold line of the minimum enclosing envelope of the vehicle concept. A sectional slicing algorithm is used to extract the sectional dimensions of this envelope. An offset is added to these dimensions in order to come up with the sectional fuselage dimensions. Once the lift and control surfaces are added, vehicle level objective functions can be evaluated and compared to other designs. For each design, changes in the super-hull dimensions in response to perturbations in requirements can be tracked and regressed to create custom geometric scaling laws. The regressions are based on dimensionally consistent parameter groups in order to come up with dimensionally consistent and thus physically meaningful laws. CESM enables the designer to maintain design freedom by portably carrying multiple designs deeper into the design process. Also since CESM is a bottom-up approach, all proposed baseline concepts are implicitly volumetrically feasible. Furthermore the scaling laws developed from custom data for each concept are subject to less design noise than say, regression based approaches. Through these laws, key physics-based characteristics of vehicle subsystems such as energy density can be mapped onto key system level metrics such as fuselage volume or take-off gross weight. These laws can then substitute some historical-data based analyses thereby improving the fidelity of the analyses and reducing design time.Ph.D.Committee Chair: Dr. Dimitri Mavris; Committee Member: Dean Ward; Committee Member: Dr. Daniel Schrage; Committee Member: Dr. Danielle Soban; Committee Member: Dr. Sriram Rallabhandi; Committee Member: Mathias Emenet

The design and application of power line carrier communication and remote meter reading for use in integrated services and broadband - integrated services digital networks

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN009939 / BLDSC - British Library Document Supply CentreGBUnited Kingdo