Multi-criteria decision-making (MCDM) is one of the most widely used decision methodologies in the sciences, business, and engineering worlds. MCDM methods aim at improving the quality of decisions by making the process more explicit, rational, and efficient. One intriguing problem is that oftentimes different methods may yield different answers to the same decision problem. Thus, the issue of evaluating the relative performance of different MCDM methods is raised. One evaluating procedure is to examine the stability of an MCDM methods mathematical process by checking the validity of its proposed rankings. The ELECTRE II and III methods are two well-known MCDM methods and widely accepted in solving MCDM problems in civil and environmental engineering. However these two methods have never been studied in detail for the validity of their proposed rankings. Thus, the first aim of this thesis is to examine if these two methods suffer of any type of ranking irregularities and analyze the reasons of the phenomenon. As the research results in this thesis revealed, the ELECTRE II and III methods do allow some types of ranking irregularities to happen. For instance, these two methods might change the indication of the best alternative for a given MCDM problem when one of the non-optimal alternatives was replaced by a worse one. The two methods were also evaluated in terms of two other ranking tests and they failed them as well. Two real-life cases are described to demonstrate the occurrence of rank reversals. Then reasons behind the phenomenon are analyzed. Next an empirical study and some real-life case studies were executed and discussed. The results of these examinations show that the rates of those ranking irregularities were rather significant in both the simulated decision problems and the real-life cases studied in this research. However, some recent studies showed that rank reversals could also happen because people may reverse their preferences due to some emotional feelings, like regret and rejoicing. Thus this thesis proposes a new MCDM method which is based on regret and rejoicing. This new method is expected to satisfy a set of critical conditions.

This thesis develops a computer-aided weld inspection methodology based on fuzzy modeling with selected features. The proposed methodology employs several filter feature selection methods for selecting input variables and then builds fuzzy models with the selected features. Our fuzzy modeling method is based on a fuzzy c-means (FCM) variant for the generation of fuzzy terms sets. The implemented FCM variant differs from the original FCM method in two aspects: (1) the two end terms take the maximum and minimum domain values as their centers, and (2) all fuzzy terms are forced to be convex. The optimal number of terms and the optimal shape of the membership function associated with each term are determined based on the mean squared error criterion. The fuzzy model serves as the rule base of a fuzzy reasoning based expert system implemented. In this implementation, first the fuzzy rules are extracted from feature data one feature at a time based on the FCM variant. The total number of fuzzy rules is the product of the fuzzy terms for each feature. The performances of these fuzzy sets are then tested with unseen data in terms of accuracy rates and computational time. To evaluate the goodness of each selected feature subset, the selected combination is used as an input for the proposed fuzzy model. The accuracy of each selected feature subset along with the average error of the selected filter technique is reported. For comparison, the results of all possible combinations of the specified set of feature subsets are also obtained.

The construction industry has one of the highest incidents of fatal and non-fatal accidents/injuries every year. As a high risk industry, there is a need to investigate factors that affect the occurrence of these accidents to be able to protect workers. Traditional approaches to workers safety in the construction industry have focused on the physical and biomechanical aspects of work by improving tools, equipment and task completion methods. However, the impact of psychosocial factors, specifically stress as experienced by construction workers is an area of growing research. Research in the area of occupational stress in the Construction Industry is yielding results that suggest that overall work safety on the construction site, should take into account psychosocial aspects of work. Research is carried out to investigate the relationship existing among occupational stressors, psychological/physical symptoms and accident/injury and work days lost outcomes as experienced by industrial construction manual workers engaged in a range of construction occupations. Workers perceptions about stress levels on specific elements of work as well as responses about physical/psychosocial symptoms were obtained by administering a questionnaire adapted from previous research. Analysis of the data entailed investigation of relationships through correlation and regression analysis, existing between the levels job stressors as experienced by the workers and (a) Company Accident History (OSHA-300 form) reports (b) Employee self-reported injuries and (c) Lost work days in 12 months prior to the survey. Among the occupations surveyed, pipefitters were at the highest risk for getting injured and responded with the most negative levels of occupational stressors. Some of the occupational stressors significantly associated with self-reported and OSHA logged injuries were training, job certainty and safety climate of the company. The OSHA logged injuries were associated with the occurrence of headaches and feelings of tenseness on the job.

In recent years, collaboration in supply chain approach widely discussed in the literature; but most have dealt with the two-echelon systems. This study focuses on the just-in-time delivery policy of three-echelon supply chain by collaborative approach, where any of the information from the supply chain is available to all the subsystems involved; manufacturer, distribution center and retailer. In the first part of the study a simple model has been developed for a three-echelon supply system that consists of a single manufacturer, a single distribution center and a single retailer. The other part of the study extends this model by considering a upstream integrated delivery supply chain system consisting of a single manufacturer, multiple distribution centers and multiple retailers. In both cases the retailer enjoys a permissible delay in payment. The joint annual cost of the supply chain is obtained by summing the annual relevant costs at all the subsystems. Using the convex property of the cost function, the optimum values of the decision values are initially obtained that minimizes the total cost. Then, these values are adjusted according to feasibility criteria of the credit conditions and other constraints using an algorithm. A numerical example illustrating the solution reveals that total supply chain cost is less by the presented collaborative approach compared to typical delivery policy. A sensitivity analysis also showed the robustness of the new model. This model considers lot-splitting and deferred payment simultaneously. That has not been studied for three-echelon system before. Future extension of this study involves assumption of random demand with cross-transfer delivery, unequal cycle time, shortage consideration, etc.

Friction Stir Welding (FSW) is a solid state joining process that uses a non-consumable rotating welding tool to generate frictional heat at the welding location. Large forces are required to produce friction between the welding tool and the work piece which increases the wear rate of the welding tool in welding materials with high melting temperature. Several different approaches have been developed to address this problem. This thesis focuses on a new modification of friction stir welding, called Laser Assisted Friction Stir Welding, a process developed in the last decade. This process uses laser energy to preheat the work piece at a localized area ahead of the rotating tool, thus softening a volume of the work piece ahead of the tool. The work piece is then joined by the rotating tool as in conventional FSW. The amount of heat generated during welding determines the quality of the weld. Hence understanding the temperature distribution is necessary in determining the optimum process parameters for the welding process. In this thesis, a three dimensional model of laser assisted friction stir welding is developed, using FLUENT which is based on finite volume method, to obtain the temperature distribution in the work piece. The developed model can be used to better understand the process, predict the process performance and to determine optimal process parameters. A comparison with pure friction stir welding without laser assistance is also made to show its potential benefits. Parametric studies are designed to understand the effect of variation of certain process parameters such as feed rate, tool rotational speed and laser heat input on temperature distribution in the work piece. Finally, optimal combinations of friction stir welding and laser parameters are determined by a metaheuristic - Ant Colony Optimization.

Forest logging is the process in which trees are cut down for forest management and/or timber harvest. According to OSHA, logging is the most dangerous occupation in the United States. It consistently represents one of the most hazardous industries, with a fatality rate more than 21 times higher than the rate for all workers in the United States. Yet, little research has been performed to determine the long term effect of noise on forest loggers. OSHA regulations state that the maximum permissible hearing in an 8 hour shift should not exceed 90 dB. Occupational noise exposure is recognized as a primary factor on permanent hearing loss (OSHA, 2007). The objective of this study is to determine whether long term hearing loss in forest loggers is associated with noise emitted by logging equipment. This study compares the differences in hearing thresholds of the participants, applying the OSHA age correction tables for audiograms (OSHA, 2008). These tables present the hearing threshold of a normal population at ages ranging from 20 to 60 years. Hearing threshold shift is determined by subtracting the hearing threshold of each participant from age corrected hearing threshold as defined by OSHA (2008) for each specific age. These individuals had never experienced any type of acute or chronic hearing loss. Participants were also separated into age groups of 10 year intervals (20 to 29, 30 to 39, 40 to 49, and 50 to 59) and experience groups of 10 year intervals (1 to 10, 11 to 20, 21 to 30, and 31 to 40). The hearing tests on forest loggers determined that at 4000 Hz, the mean hearing threshold of the participants was significantly higher than the rest of the frequencies. Furthermore, a significant increase in hearing threshold between the participant population and the hearing threshold of a normal population was also determined. The hearing threshold shifts at 1000, 2000, and 4000 Hz were of 4.9, 9.5 and 18.0 dB respectively. A significant decrease in the hearing threshold (of 3.4 dB) was found between those participants who wore hearing protection and those who did not.

Demands at work are associated with an increased risk of cardio vascular diseases, but little is known about its underlying connection. The purpose of this study was to evaluate the effects of physical and mental tasks that induced stress, on Heart Rate Variability (HRV). Another aim was to observe the trends in subjective workload ratings in conjunction with the physiological response of the heart and also to assess the comfort level of the participants while wearing the heart rate monitor and performing tasks. Heart rate was recorded while at rest and while performing the tasks. Subjective workload ratings were obtained from NASA-TLX and the comfort scores from a comfort questionnaire for each task. The power spectral components HF, LF, LF/HF and the time domain RMSSD, were used as the components of HRV in the analysis. The results indicated that all the components of HRV examined were sensitive to physical and mental demands. The HF and RMSSD components decreased with increase in demands from the baseline values. The LF and the LF/HF ratio increased with increase in demands. Overall results indicated reduction in HRV when demanding physical and mental tasks were performed. Subjective workload ratings changed in accordance with the physiological response. Subjective workload rating was high for both the tasks. Overall comfort score indicated that the participants were comfortable while wearing the heart rate monitor and performing the tasks. The evidence from this study suggested that these simulated work factors (physical and mental demands) influence risk factors that may increase risk for CVDs in work places. It is recommended that future research be conducted in the field to quantify HRV and the workplace/tasks be redesigned to reduce excessive physical and mental demands.

Injuries of the neck and shoulders are common among workers who perform overhead tasks. In order to develop an injury-free working environment with regards to occupational musculoskeletal stress, it is pivotal to understand the pathophysiology of mechanical stress on the musculoskeletal system. The objective of this research was to study the effect of overhead lifting on the sternocleidomastoid and upper Trapezius muscles. Upper body joint angles were also analyzed using APAS during the overhead lifting. This study was conducted using two devices. The set of equipment incorporates an electromyography device, and the APAS. Two electrodes were placed at the muscle belly of the sternocleidomastoid and the upper Trapezius muscles to record the muscle activity. Each participant was asked to lift 15%, 30% and 45% of his/her MVC, The MVC was determined by a non dynamic lifting task. ANOVA was performed to test the effect of different loads on the muscle activity. Correlation analysis was performed to observe the effect of increasing the lifted weight on the joint angles of the upper body extremities. Results of this research show a strong relationship between neck muscle activities and overhead lifting. The level of sternocleidomastoid activity increased 11.8% from a 15% MVC load to a 30% MVC load and increased 16.53% from a 30%MVC to a 45% MVC. All these values were statistically significant. At the trapezius: a 10.64% increase from 15% MVC to 30% MVC, and a 7.76 % increase from 30% MVC to 45% MVC. The significance level of alpha = 0.05 reveals that weight increase has a significant effect on the MAV EMG of the neck muscles. A slight increase in the elbow joint angle of 0.1% was recorded from 15% MVC to 30% MVC. A 2.88% increase in elbow joint angle was recorded from 30% MVC to 45% MVC, with an overall 2.98% increase from 15% MVC to 45% MVC. There was no effect of changing elbow angles on the sternocleidomastoid muscle. On the other hand, flexion of the shoulder angle in the sagital plane had a significant effect on both the Trapezius and the sternocleidomastoid muscles.

This thesis research implemented an existing thermomechanical model of friction stir welding process, and studied the surrogate model-based optimization approach to obtain optimal process parameters for the modeled friction stir welding process. As an initial step, the thermomechanical model developed by Zhu and Chao for friction stir welding of 304L stainless steel was replicated using ANSYS. The developed model was then used to conduct parametric studies to understand the effect of various input parameters like total rate of heat input, welding speed and clamping location on temperature distribution and residual stress in the workpiece. With the data from the simulated model, linear and nonlinear surrogate models were constructed using regression analysis to relate the selected input process parameters with response variables. Constrained optimization models were formulated using surrogate models and optimization of process parameters for minimizing cost and maximizing throughput was carried out using improved harmony search algorithm. To handle the constraints, Debs parameter-less penalty method was used and implemented in the algorithm. It is learned from this research that: (1) heat input is mainly constrained by the lower bound of the temperature for making good welds; (2) the optimal welding speed must balance the loss of heat input and the gain in productivity; (3) clamping closer to the weld is better than away from the weld in terms of lowering the peak residual stresses. Moreover, the nonlinear surrogate models resulted in a slightly better optimal solution than the linear models when wide temperature range was used. However, for tight temperature constraints, optimization on linear surrogate models produced better results. The implemented improved harmony search algorithm seems not able to converge to the best solution in every run. Nevertheless, the non-converged solution it found was very close to the best.

Track and field runners, especially sprinters and mid-distance runners, face many problems due to walking in spike shoes. Due to the fact that track and field spike shoes are designed specifically for running, the runners feet remain in an uncomfortable, flexed position when walking between workouts and races. Problems caused by the dangerous foot-positioning include, but are not limited to, the following: back pain, shin splints, bone spurs, blisters, and overall decreased level of running performance. Over time, runners wearing improper footwear for walking may face chronic injuries such as plantar fasciitis, shin splints, Achilles tendinitis, chondromalacia, and iliotibial band syndrome. To address this problem, a modified spike shoe was tested. The modification consists of adding a removable heel to the shoe. The removable heels were attached to the sole after exercise or between races to shoe angle of flexion, so that the foot can be leveled. The modified shoes were tested in terms of health and comfort through the use of two experimental protocols. Nine healthy, resistance-trained participants volunteered to perform walking drills on a treadmill. They walked with regular spikes at 2 mph and 3 mph. Then, they repeated the drill with the redesigned spike shoes. EMG measurements were used to evaluate the participants muscle activity, fatigue, and stress during the exercise. The analyzed muscles were the tibialis anterior and the medial gastrocnemius. The statistical tool used for the mathematical interpretation of the data was ANOVA, the hypotheses being tested with the softwares Statistix 9.0. and SAS 9.0 English version. Complementarily, participants were individually asked to rate their discomfort on a scale of 1 to 10, using a body map as a further evaluation of the effects of the removable heel. Results showed a 22 % average decrease in EMG muscle activity from walking without heels to walking with heels in the tibialis anterior and a 24.25% average decrease in the gastrocnemius. Results were consistent for all participants. Similarly, when rating discomfort from walking without heels to walking with heels, the body map survey results indicate that participants noticed an average superior comfort of 2.7 points in the knees, 2.6 points in the calves, 3.9 points in the ankles, and 4.2 points in the feet on an ergonomic scale of 10 discomfort points. Thus, results showed that the removable heel helps reduce muscle fatigue and stress and therefore its related musculoskeletal problems.