A knowledge-based system approach to helping engineers understand codes of practice

Civil engineers are increasingly called upon to design according to codes of practice which are foreign, or otherwise unfamiliar to the engineer. Some form of 'tool' to aid such engineers in the safe and effective use of unfamiliar codes, is therefore highly desirable. The argument presented in this thesis, is that a specialised 'knowledge-based system' (KBS) can be successfully constructed in order to provide various sons of insights into the design methods used in certain codes of practice. Three key ideas were used in the implementation produced during the research: the development of a novel set of complementary 'facilities' for examining the design methods used in codes; the support of comparison between the examination of two different codes; and ensuring the system's representation of codes and their examination, could be made readily comprehensible to engineers by using familiar human language phrases. Seven different facilities were developed in the research, including: the ability to view the codes installed in the system in a form close to a human language (such as English or French); the ability to perform parts of a code-based design procedure to various levels of detail; and the ability to inspect the interdependences of design parameters within codes. Use of these symbolic and numerical methods could provide the engineer with the information required to understand how and why an unfamiliar code would specify surprising, or otherwise unusual design parameters in some particular situation. They could also be used in a more exploratory fashion, with t1ie same broad aim of greater understanding of an unfamiliar code. A KBS is a sophisticated computer program that uses the idea of processiilg knowledge information. A characteristic feature of KBSs is that one of their primary components is a 'knowledge base' - a store of human expertise. The KBS built in this research, 'COPES' used an existing abbreviated form of the reinforced concrete (RC) beam design codes as its knowledge base. In particular, it contained 'procedural knowledge'. COPES was implemented using conventional computer systems and progranuning languages (pascal and FORTRAN on a Sun workstation). This is in contrast to most contemporary KBSs, which are often built using a 'shell', or an unconventional declarative programming language such as Prolog. One reason for this choice was that COPES used parts of previous computing work done with RC beam design codes, that had also used conventional computing techniques. However, our research did cover an investigation into the prospects for an alternative approach using a modem expert system shell. (It was confirmed that such an approach was generally less suitable in this particular application.) The COPES system proved to be a useful prototype 'toolbox' of various procedural knowledge extraction operations, which could help an engineer's understanding of an unfamiliar code of practice. To provide a practical system, the various explanatory methods developed could potentially be incorporated into an overall CAD (Computer-Aided Design) environment, or alternatively, wrapped up in a more sophisticated interactive program

The development of an expert systems approach to the statistical analysis of experimental data

This thesis is concerned with the application of expert systems techniques in the field of statistics. An expert statistician in industry has a twofold role; undertaking the design and analysis of data from complex experiments and providing supervision and help for research workers who analyse data from simpler designs. There is, therefore, a potential role for a statistical expert system which could be used by research workers to enable them to carry out valid analyses. The expert statistician would be freed from the more straightforward analyses and would only need to deal with referrals from the system and to initially 'tune' the system to their own application area. The design and development of such a prototype expert system, THESEUS, is the basis of this work. The area of application chosen for the prototype system is completely randomised designs with one trial factor. It was initially important to limit the area of study so that knowledge acquisition for the system would be a manageable task. However, once the difficulties in developing an expert system have been tackled, much of the expertise used in analysing this simple type of study could be readily extended to more complex designs. The knowledge acquisition phase, the most time consuming part of developing any expert system, concentrated on developing a rational prototype rule base by reviewing the available literature, interviewing practising statisticians and undertaking workshops where the analysis of particular data sets was discussed. The prototype software is a production rule system and is written in Turbo Pascal on an IBM-AT. Pascal was chosen because of the need to access statistical routines during the consultation process. The prototype uses a combination of forward and backward chaining to process the rules. Information required by the system can come from the user, the data or the rules. The overall system design also includes facilities for entering and editing data, altering and adding knowledge and a report generator. Implementation of these facilities is not incorporated as part of this thesis. A small number of trial sites were selected for industrial trials in order to validate the system and evaluate the results of the local experts 'tuning' of the rule base to their own particular application area

Development of a novel test rig for the evaluation of aircraft fuel tank sealants

Leaks from aircraft fuel tanks have always represented a problem for aircraft manufacturers, airline operators and maintenance crews. The integral fuel tanks within aircraft structures are typically located within the wings and they rely upon sealant materials to prevent leakage past joints and fasteners. However, the wing is designed as a structural member first and as a fuel tank second and there exist many potential leak paths for the fuel from these complex, highly loaded structures. Fuel leaks result in direct loss of fuel which may be dangerous, cause a loss in revenue due to aircraft being withdrawn from service and be difficult and expensive to repair. On top of this there are important health and safety issues involved in the repair of fuel tanks, for example, the Royal Australian Air Force's, F-lll Deseal Reseal Programme 1979 to 2000, where it was found that a significant number of RAAF personnel involved in the Deseal Reseal Programme were suffering from a variety of health problems. Current approaches to fuel tank sealant evaluation embrace immersion in a range of different fluids at different temperatures, of both bulk sealant samples and sealed joints. However, nearly all such tests are of a "static" nature and yet it is acknowledged that joint movement leads to leaks. Thus the missing component of testing is movement coupled with the other key variables. The aircraft industry has been searching for a relatively simple test method that can be used to evaluate sealed joint systems using realistic combinations of materials, joint geometries, imposed stresses and environmental conditions. The aim of this project was to do exactly this. A practical but realistic dynamic test, the Model Sealed System (MSS), was designed, made and evaluated. This unique mechanism consists of an axial stress machine into which fatigue, high and low temperatures and pressures can be programmed for automatic operation. A novel circular lap joint lies at the heart of the MSS in which test sealant is sandwiched between the circular coupons that are then assembled with aerospace fasteners and sealed. This joint configuration is representative of a wing skin butt-strap joint in a real aircraft. The MSS is easy to run, it accurately simulates real world dynamics and conditioning, and it provides results to qualify sealants in a more realistic manner than current testing methods provide. The MSS enables evaluation and comparative testing of sealant systems when used for interfay, fillet and overcoat applications. The information provided is complementary to that obtained from conventional small scale coupon testing; it is not seen as a substitute. Further work is required to refine the test variables and further data are required to provide confidence in the utility of the MSS. Development of the MSS was undertaken with the support of Airbus UK to ensure that the design, materials and all other variables met with the overall requirements of a commercial aircraft manufacturer. Airbus UK have a duplicate MSS of their own, installed by the author, from which they can obtain patterns of data for different combinations of materials and experimental variables

Cutting data for automated turning tool selection in industry

This thesis is concerned with the determination of cutting parameters (cutting speed, feed rate and depth of cut) in turning operations within an industrial environment. The parameters are required for the purposes of tool selection, working with a variety of batches of different materials. Previous work of this nature, little of which has been transferred into industry, has concentrated primarily on deriving optimum cutting conditions, based on a variety of deterministic and non- deterministic approaches, with a general reliance on experimentally-derived input variables. However, this work is only suited to tool selection for a single material. Under industrial conditions tools will frequently need to be selected for more than one material, in tool/material combinations not recommended by tool makers. Consequently, the objective of the research described in this thesis was to employ existing cutting data technology and to use it as the basis for a cutting data system, suitable for multi-batch tool selection. Two companies collaborated in this work, by making available suitable personnel and the provision of shop floor facilities on their premises. The initial work concentrated on the development of an algorithmic model, based on established theory. This was then tested industrially, using the concept of shop floor approved data as a substitute for optimum cutting data. The model was found to work reasonably, but required further development to make it suitable for multi- batch tool selection. This development took three main forms: a) a reduction of input data, particularly in the number of experimentally-derived variables, b) the removal of the tool/material-specific constraints traditionally used in cutting data optimisation, c) a method of data correction based on adjustment of the mean and standard deviation of the data. Further industrial testing was carried out using the resulting system. It was demonstrated that it was possible for a relaxed system with reduced input variables and appropriate data correction to function within an industrial environment

Finite element modelling of transportation tunnels

The aim of this thesis is to determine the ground deformation and stress distribution around highway tunnels at various stages of excavation and for several support conditions using finite element modelling techniques. When ground is excavated and material removed the subsequent redistribution of stress in the remaining surrounding material needs to be treated by one of three methods. These are the gravity difference method, the stress reversal technique and the relaxation approach. The first two methods were chosen for the simulation of excavation in this study. The tunnel data are in the form of the dimensions of the tunnel, heights of the rock layers, details of the shotcrete lining and tunnel support systems. A pre-processing program was written to transform this information into a finite element mesh in a format suitable for use by PAFEC-FE software. This enables different tunnel models and meshes to be produced with minimum error and time. The lack of adequate post-processing facilities available in PAFEC-FE dictated that computer programs needed to be written in order to reformat the textual output files and process the mesh stress and displacement outputs for graphical display using UNIRAS. In this way repeated use could be made of PAFEC-FE without time-consuming and error-prone manual retrieval of data. The tunnels were modelled at various stages of excavation and with such support provided at those stages as to allow the computed displacements to be compared with measurements made on highway tunnels in Turkey. The stresses generated in the tunnel supports and surrounding ground were also calculated to enable the possibility of damage or failure of the support structure or ground to be assessed and the selection of an optimal support system. Insertion of a support system into the model has a marginal effect on the development of rock strength around an excavation boundary

Assessment of catheter-manometer systems used for invasive blood pressure measurement

Direct measurement of blood pressure using a fluid-filled catheter and an electromechanical transducer is widely accepted in clinical practice. However, errors associated with the measurement are often not appreciated and these catheter-manometer systems are frequently unable to accurately reproduce applied pressures. To assess the accuracy of catheter-manometer systems used for invasive arterial blood pressure measurements, in vitro and in vivo evaluations were performed. The frequency response (described in terms of damped natural frequency and damping factor) for a variety of cannulae, pressure tubing and stopcocks (and combinations thereof) and their dependence on various parameters (catheter length, lumen diameter, fluid temperature and catheter material) were measured using an hydraulic pressure generator. The design and construction details of the pressure generator are presented. It was found that the damped natural frequency of the catheter-manometer system is directly proportional to lumen diameter of the pressure tubing/catheter. Furthermore, damping factor is inversely related to the damped natural frequency and stiffer catheter material (for identical radius ratios) results in higher damped natural frequency. Catheter length is inversely related to damped natural frequency and the resonant frequency decreases for an increase in fluid operating temperature. It was established that all catheter-manometer systems tested were under-damped (0.15 < β < 0.37) and that the damped natural frequency ranged from 10.5 Hz for 1500 mm to 27.0 Hz for pressure tubing of 300 mm in length. Furthermore, catheter-manometer systems which had pressure tubing in excess of 300 mm in length did not comply with the bandwidth requirements for accurate dynamic blood pressure measurement. For the in vivo assessment of the catheter-manometer system, the blood pressure waveform was analysed in the time and frequency domains. It was established that in 60 percent of the cases, the systolic pressure peak was higher when measured by a narrow bandwidth catheter-manometer system compared to that measured by a wide bandwidth system. Furthermore, values of dp/dt maximum were lower for wide bandwidth catheter-manometer systems than those measured by narrow bandwidth systems for heart rates above 90 beats per minute. In the frequency domain analysis, artifact was sometimes found to occur at frequencies higher than the bandwidth of the catheter-manometer system. This high frequency artifact was found to distort the blood pressure waveform and resulted in false high dp/dt and peak systolic pressures

Research reports: 1990 NASA/ASEE Summer Faculty Fellowship Program

Reports on the research projects performed under the NASA/ASEE Summer Faculty Fellowship Program are presented. The program was conducted by The University of Alabama and MSFC during the period from June 4, 1990 through August 10, 1990. Some of the topics covered include: (1) Space Shuttles; (2) Space Station Freedom; (3) information systems; (4) materials and processes; (4) Space Shuttle main engine; (5) aerospace sciences; (6) mathematical models; (7) mission operations; (8) systems analysis and integration; (9) systems control; (10) structures and dynamics; (11) aerospace safety; and (12) remote sensin

Wave-front reconstruction of optical disturbances using digital image processing

This thesis is concerned with the development of a practical digital image processing system for recording and subsequent reconstruction of the magnitude and phase of an optical wave-front arriving from a coherently illuminated object disturbance. Since the wave-fronts of concern are coherent, the magnitude and phase of such waves are generally independent functions in the sense that the knowledge of one is not sufficient to uniquely deduce the other. To uniquely reconstruct and characterize optical disturbances both the magnitude and phase are required. In general, all recording media respond only to light intensity and no difficulty is encountered in recording the intensity and therefore the magnitude, because it is the square root of the intensity. [Continues.