Imprecision in Engineering Design

Methods for incorporating imprecision in engineering design decision-making are briefly reviewed and compared. A tutorial is presented on the Method of Imprecision (MoI), a formal method, based on the mathematics of fuzzy sets, for representing and manipulating imprecision in engineering design. The results of a design cost estimation example, utilizing a new informal cost specification, are presented. The MoI can provide formal information upon which to base decisions during preliminary engineering design and can facilitate set-based concurrent design.

The Method of Imprecision (MOI) is a multi-objective design method that maximizes the overall degree of both design and performance preferences. Sets of design variables are iteratively selected, and the corresponding performances are approximately computed. The designer’s judgment (expressed as preferences) are combined (aggregated) with the customer’s preferences, to determine the overall preference for sets of points in the design space. In addition to degrees of preference for values of the design and performance variables, engineering design problems also typically include uncertainties caused by uncontrolled variations, for example, measuring and fabrication limitations. This paper illustrates the computation of expected preference for cases where the uncertainties are uncorrelated, and also where the uncertainties are correlated. The result is a “best” set of design variable values for engineering problems, where the overall aggregated preference is maximized. As is illustrated by the examples shown here, where both preferences and uncontrolled variations are present, the presence of uncertainties can have an important effect on the choice of the overall best set of design variable values.

Focusing on the efforts towards a consistent preference representation in decision based engineering design, this paper presents a learning-based comparison and preference modeling process. Through effective integration of a deductive reasoning-based on designer’s outcome ranking in a lottery questions-based elicitation process, this work offers a reliable framework for formulating utility functions that reflect designer’s priorities accurately and consistently. It is expected that this integrated approach will reduce designer’s cognitive burden, and lead to accurate and consistent preference representation. Salient features of this approach include a linear programming based dynamic preference learning method and a logical analysis of preference inconsistencies. The development of this method and its utilization in engineering design are presented in the context of a mechanism design problem and the results are discussed.

Preliminary design information is characteristically imprecise or fuzzy: specifications and requirements are subject to change, and the design description is vague and incomplete. The Method of Imprecision uses the mathematics of fuzzy sets to explicitly represent and manipulate imprecise preliminary design information, enabling the designer to better understand the full range of designs and performances that satisfy an imprecise set of specifications and requirements. This paper discusses the foundations of this methodology, and introduces pragmatic extensions that provide computationally tractable methods to map design imprecision from multiple design variables onto multiple performance variables. These methods attempt to minimize the number of function evaluations required while retaining an appropriate level of accuracy. This is achieved by using optimization to obtain extremal points for each performance variable and selectively applying a linear approximation for the mapping from the design variable space (DVS) to the performance variable space (PVS) to interpolate between extremal points. This linear approximation is constructed using regression techniques adapted from experiment design.

The primary goal of this research is to provide computational tools, or aids, to engineering designers, particularly for the preliminary phase of design. Such aids will be particularly useful in choosing between alternative technologies. Design choices of this nature are perhaps the most critical, and likely to be the most costly if in error. Our approach has been to aid preliminary design decisions with analysis tools developed for computations on imprecise parameters. Contemporary computers and algorithms are not well suited for manipulating imprecise descriptions of objects. To provide these basic tools, we are applying the mathematics of fuzzy sets. This approach (along with “data-driven programming”) appears to be well suited to our problem and has been applied to similar problems in analyzing civil engineering structures and failures.

By using the factorial design method, statistically significant correlations have been developed which enable one to predict steamflood performance in terms of project life, oil recovery and cumulative steam-oil ratio. The effects of various reservoir rock and fluid properties and steamflood design and operating variables on steamflood performance were discusssed.

The advantages of 3D seismic data over conventional 2D geophysical data include: high-density data coverage, improved spatial delimitation of geologic and stratigraphic features, and the ability to visualize geologic, stratigraphic, and structural features in ways not possible with 2D seismic profiles. The widespread availability of 3D exploration seismic data has ushered in a new approach to deepwater hazards and site assessments as well as regional development studies. With the advent of high-powered desktop computers, new software packages, and advanced analysis techniques, these data are now being used for more than the exploration of hydrocarbons, particularly in water depths greater than about 200 m. Exploration 3D data are routinely used to identify and avoid unfavorable drillsites and pipeline routes, thus reducing overall costs. Whereas exploration 3D seismic data generally have sufficient resolution to identify significant drilling hazards and for preliminary pipeline route planning, these data are not adequate for final structure, site or pipeline route selection or for detailed stratigraphic characterization needed for design. In these cases, high-resolution site- and route-specific surveys are still required. The advantages of 3D data are now also available in high-resolution geophysical surveys. These data reduce the need for repeated surveying of the same area and provide details unseen on conventional exploration data. A single high-resolution 3D data set can be used for multiple applications throughout the exploration, production, and development process. These data are used for shallow and intermediate exploration, analyses of seabed topography, geohazards assessments, understanding of complex structural and stratigraphic conditions, well planning, and field development. When integrated with geotechnical soil boring data, high-resolution 3D data provide a detailed understanding of stratigraphic variability necessary for final structure siting and design.

Iterative multi-domain BEM solution for water wave reflection by perforated caisson breakwaters

The oxidative coupling of methane (OCM) is a direct path for converting methane into ethene (ethylene), which is one of the most important building blocks for the chemical industry. Carbon dioxide is generated as a byproduct in the reactor and must be separated in order to produce the pure olefin. This step is commonly achieved by amine scrubbing, in which a significant amount of energy is consumed for regenerating the amine. In this contribution, a hybrid system employing gas separation membranes and absorption is modeled and simulated in order to carry out preliminary engineering design and economic evaluations to assess the feasibility of applying this process on industrial scale. It is demonstrated that the hybrid process offers economic advantage when compared to the standalone absorption process when carbon dioxide is used as diluent in the OCM reactor.

This study presents a detailed assessment of wave conditions in the Gulf of Oman based on numerical simulations during the passage of three cyclones that have caused severe impacts to the coastal communities. The cyclone-generated waves for Gonu (2007), Phet (2010) and Kyarr (2019) are validated against satellite altimeter data and offshore wave buoy measurements. Simulation results obtained at four locations indicate that significant wave heights decrease as waves propagate into the Gulf. The maximum significant wave heights occurred during cyclone Gonu with values between 4.0 and 7.2 m within the Gulf of Oman whilst for the other two cyclones were just over 2.0 m. Longer peak wave periods were obtained for cyclone Kyarr (12.9 s). Although wave heights tend to decrease with increasing distance from the entrance of the Gulf of Oman, peak wave periods remain constant. The study provides valuable information on cyclonic-wave conditions for coastal management and planning, risk assessment studies and preliminary engineering design. The cyclone model, together with additional marine observation buoys, is an essential set of tools in measuring and forecasting wave conditions for future cyclones and, consequently, to increase safety of coastal populations and infrastructure.

The National Ignition Facility (NIF) Project officially began in December of 1995. In October of 1996, advanced conceptual design studies, complete environmental impact study, facilitization of the manufacturing capabilities of optics vendors began. The Title I preliminary engineering design had not yet began until the end of December, but it is expected to be on schedule. It is expected that the conventional facilities design will be completed first. The Independent Cost Estimate (ICF) process will begin after the facilities design is complete. Other elements of the design will be submitted in one- or two-week intervals. This phase method of completing Title I was also used at the end of Complete Design Report and proved to be efficient. 9 refs., 11 figs.

LinguisticBelief is a Java computer code that evaluates combinations of linguistic variables using an approximate reasoning rule base. Each variable is comprised of fuzzy sets, and a rule base describes the reasoning on combinations of variables fuzzy sets. Uncertainty is considered and propagated through the rule base using the belief/plausibility measure. The mathematics of fuzzy sets, approximate reasoning, and belief/ plausibility are complex. Without an automated tool, this complexity precludes their application to all but the simplest of problems. LinguisticBelief automates the use of these techniques, allowing complex problems to be evaluated easily. LinguisticBelief can be used free of charge on any Windows XP machine. This report documents the use and structure of the LinguisticBelief code, and the deployment package for installation client machines.

Fuzzy [formula omitted]-neighbourhood spaces: Part 2— [formula omitted]-neighbourhood systems

North American undergraduate mechanical engineering design education has failed to meet the needs of industry in educating students in effective design philosophies typified by the concurrent engineering design philosophy. Current programmes emphasize traditional engineering analysis courses, leaving little room for truly educating the students in the fundamentals of mechanical engineering design. This paper uses the concurrent engineering design paradigm to design a programme for the education of students in mechanical engineering design. The basics of concurrent engineering design are outlined, the failings of typical design education stated, and an exploration of the required features of a new design curriculum presented.

Magnetic diagnostics are essential tools for operation and control of the Korea Superconducting Tokamak Advanced Research (KSTAR) device and for understanding the plasma behavior. For this purpose, a concept and preliminary engineering design for the KSTAR magnetic diagnostics have been prepared. An overview and engineering design of the KSTAR magnetic diagnostics are presented.