Browsing by Subject "Fuzzy sets"
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Item A fuzzy sets based model of the interaction between stresses involved in manual lifting tasks(Texas Tech University, 1982-12) Karwowski, WaldemarThe primary objectives of this research were: 1. Development and testing of a mathematical, fuzzy sets based model for the acceptability of the stresses involved in lifting activity. 2. Evaluation of the hypothesis that a combination of the acceptability of the biomechanical and physiological stresses leads to an overall measure of lifting task acceptability, namely the acceptability of the psychophysical stress. 3. Development of a general criterion for establishing maximum permissible weights of load to be lifted safely. 4. Comparison and evaluation of existing recommendations versus this proposed general criterion. The group of acceptable weights of load that can be lifted safely was defined as a class with no sharp transition from membership to nonmembershlp. The acceptability measure of the stresses were associated with fuzziness, rather than randomness. Measures of acceptability were expressed by membership functions which describe the degree to which the stresses were acceptable for the human operator (with respect to the chosen design criteria). A synergistic effect was used as the basis to combine the biomechanical and physiological stresses into one category. The psychophysical methodology was used to carry out an experiment with nine male subjects to provide the data needed for the model development. An iterative procedure was used to generate conditions for membership functions which resulted in the minimum (or near-minimum) mean value of the Hamming distance between the acceptability measures of these stresses. The combined stress was then compared with the psychophysical one using the similarity measure between them. The conditions under which the acceptability of the psychophysical stress were similar to the acceptability of the combined stress were found. The points of reference for the biomechanical stress where the hypothesis holds true were also deterniined. A general criterion for the acceptability of the lifting task was proposed as one which considers the effect of both biomechanical and physiological stresses on the human operator's performance during manual lifting activities.Item Effect of cue type on situation awareness(Texas Tech University, 1996-12) Jones, Debra GipsonSituation Awareness (SA) is a vital element of decision making in dynamic environments. As such, SA errors can impede and degrade decision making performance. One particularly troublesome SA error is the representational error which occurs when the wrong mental model is used to interpret information (resulting in an inaccurate understanding of the situation), when in fact it should provide a cue that the wrong mental model is in effect. This dissertation investigates what characteristics of information are likely to cause a person to adjust a mental model rather than falling prey to a representational error. Since the literature on this issue is sparse, findings from schema literature were used as a starting point for investigating this question. From the schema Iherature, two hypotheses were formulated involving the effect of cues on SA: (1) schema bizarre information will impact SA more than schema irrelevant information, and (2) schema unexpected information will impact SA more than the absence of schema expected information. A high fidelity simulation of an air traffic control task was used to test these hypotheses. Certain misinformation was provided to the controllers and then cues to this error were provided in the form of schema bizarre cues or irrelevant cues, schema unexpected cues or absence of expected cues. The controllers were expected to ascertain from these cues that the current mental model was not adequate to account for the cue (thus, the cue signified that an error had been committed) and that the error needed correcting. If the significance of the information was comprehended, an overt action was required.Item Fuzzy neural networks(Texas Tech University, 1998-12) Guven, MuratSince the development of computer technology, methods have been developed and investigated to mimic the processes of the human brain. The human brain is a collection of billions of neurons interconnected with each other. Interconnected neurons are modeled with artificial neural networks (ANNs or NNs). Neural networks, mathematically speaking, are a system of linked parallel equations that are solved simultaneously and iteratively. Initial research can be found in papers by McCulloch-Pitts (1943), Hebb (1949), Rosenblatt (1958), Minsky-Papert (1969), and Hopfield (1982). Since 1982, research into neural networks has exploded and the use of neural networks to solve complex nonlinear problems has expanded (from pattem recognition to actual learning to playing games). Many different neural network architectures (the feedforward network, CMAC, Hopfield network, Kohonen network) have been developed to aid in the solution of these problems. In this paper, we are interested in the feedforward network.Item Fuzzy-based wind damage model for single-family housing(Texas Tech University, 2001-05) Kumar, AlokResidential construction is generally non-engineered and sustains the most damage of all the construction types in the event of a windstorm. With extensive development along the hurricane prone coastal areas, more and more residential property is exposed to hurricane risk. As a result, a probabilistic estimate of damage to these structures is crucial to the insurance industry. In the present work of developing a wind damage model, the authors have proposed a methodology for damage prediction that takes into account both expert opinion and strength of components and connections in a building, as provided in the literature. A building is considered to be an aggregation of components and connections that are assembled together according to standard construction practices. The strength of each component and connection is represented by a suitable probability distribution. To account for the uncertainty in the strength, a probability distribution is represented by fuzzy membership functions. The effect of damage to the building envelope is included in the analysis by updating the wind load acting on components when the building envelope is breached. Expert opinion is used to establish the fraction of interior damaged given there is damage to any of the exterior components. A component exposure parameter, based on expert opinion, defines the maximum fraction of damage to a component at any given wind speed. These expert supplied parameters are represented by fuzzy membership functions to account for uncertainty in the expert judgment. A fuzzy model of building damage as a function of wind speed is then developed. .Item Modeling hurricane evacuation using transportation models, fuzzy set, and possibility theory(Texas Tech University, 2001-05) Tiglioglu, Tufan SuhaNot available