Search results for "Operations"
showing 10 items of 1692 documents
Investigating the effect of residual stress on hydrogen cracking in multi-pass robotic welding through process compatible non-destructive testing
2021
Abstract In this paper, the effect of Welding Residual Stress (WRS) on the size and morphology of hydrogen-induced cracks (HIC) is studied. Four samples were manufactured using a 6-axis welding robot and in two separate batches. The difference between the two batches was the clamping system used, which resulted in different amounts of welding deformation and WRS. The hydrogen cracks were intentionally manufactured in the samples using a localised water-quenching method, where water was sprayed over a specific weld pass in a predetermined position. The Phased-Array Ultrasonic Testing (PAUT) system was implemented during the welding process (high-temperature in-process method), to detect the …
Minimizing the cycle time in serial manufacturing systems with multiple dual-gripper robots
2006
Robots are being used more and more extensively as material-handling systems for automated manufacturing systems. This is especially true for dual-gripper robots whose in-process buffer (the robot's second gripper) constitutes a further element of flexibility. When the number of stations to be served is high and the set of activities the robot must execute is great, the system throughput may depend on robot capability rather than on process times. In such conditions, the use of several robots leads to an increase in system productivity. Obviously, the design and the management of such a handling system becomes more complex: the minimum number of robots required, the work stations to be serv…
The analytic hierarchy process with stochastic judgements
2014
The analytic hierarchy process (AHP) is a widely-used method for multicriteria decision support based on the hierarchical decomposition of objectives, evaluation of preferences through pairwise comparisons, and a subsequent aggregation into global evaluations. The current paper integrates the AHP with stochastic multicriteria acceptability analysis (SMAA), an inverse-preference method, to allow the pairwise comparisons to be uncertain. A simulation experiment is used to assess how the consistency of judgements and the ability of the SMAA-AHP model to discern the best alternative deteriorates as uncertainty increases. Across a range of simulated problems results indicate that, according to c…
COMPARATIVE ASSESSMENT OF SEVERAL MULTI-CRITERIA DECISION ANALYSIS TOOLS FOR MANAGEMENT OF CONTAMINATED SEDIMENTS
2007
Over the past several decades, environmental decision-making strategies have evolved into increasingly more sophisticated, information-intensive, and complexapproaches including expert judgment, cost-benefit analysis, toxicological risk assessment, comparative risk assessment, and a number of methods forincorporating public and stakeholder values. This evolution has led to an improved array of decision-making aids, including the development of Multi-CriteriaDecision Analysis (MCDA) tools that offer a scientifically sound decision analytical framework. The existence of different MCDA methods and the availability of corresponding software contribute to the possibility of practical implementat…
Locating a Waste Treatment Facility by Multicriteria Analysis
1997
We describe an application of multicriteria decision aid to the location of a waste treatment facility in eastern Finland. In Finland, the Act on Environmental Impact Assessment Procedure requires that when the amount of waste to be dealt with in a facility exceeds 20,000 tons per year, the process of environmental impact assessment (EIA) must be performed. In addition, the opinions of citizens and different interest groups need to be heard. Generally, EIA requires many different factors to be dealt with. Therefore the use of some multicriteria decision aid may be helpful to preserve the information obtained through the EIA in the decision-making process. The alternative locations for the f…
Multicriteria decision support in a technology competition for cleaning polluted soil in Helsinki
2000
Due to expansion of the capital area in Finland, industrial areas are being replanned for residential and commercial use. The soil in these areas is sometimes contaminated, and must therefore be cleaned before building. In spring 1997 the City of Helsinki and the National Technology Agency of Finland declared a contract-based competition for cleaning the polluted soil of the planned Toukolanranta residential area. Nine proposals entered the competition, and the problem was to choose three best candidates for test-cleaning a small part of the region considered. The winner of the test-cleaning phase will get the contract for cleaning the whole area. The proposals were evaluated based on five …
Comparing Performances of Turbo-roundabouts and Double-lane Roundabouts
2012
Starting from assumptions regarding the arrival process of circulating streams and according to models based on the gap-acceptance theory, the paper is aimed at comparing operational performances between basic turbo-roundabouts and double-lane roundabouts. The paper proposes applications of the Hagring model for entry capacity estimations at double-lane roundabouts and turbo-roundabouts, these latter, in particular, featured by movements with only one or two conflicting traffic streams. This model allows to use, in fact, a bunched exponential distribution to quantify the distribution of major vehicle headways; it also considers specific values different by each lane for behavioural paramete…
The role of nano-perovskite in the negligible thorium release in seawater from Greek bauxite residue (red mud)
2016
AbstractWe present new data about the chemical and structural characteristics of bauxite residue (BR) from Greek Al industry, using a combination of microscopic, analytical, and spectroscopic techniques. SEM-EDS indicated a homogeneous dominant “Al-Fe-Ca-Ti-Si-Na-Cr matrix”, appearing at the microscale. The bulk chemical analyses showed considerable levels of Th (111 μg g−1), along with minor U (15 μg g−1), which are responsible for radioactivity (355 and 133 Bq kg−1 for 232Th and 238U, respectively) with a total dose rate of 295 nGy h−1. Leaching experiments, in conjunction with SF-ICP-MS, using Mediterranean seawater from Greece, indicated significant release of V, depending on S/L ratio,…
Multinationality, foreignness and institutional distance in the relation between R&D and productivity
2012
Abstract This paper empirically examines to what extent being foreign and part of a multinational affects the endogenous relation between R&D and productivity. Our findings indicate that multinationals obtain in general higher R&D returns. Also, there is a negative foreignness effect in that domestic-owned multinationals outperform foreign subsidiaries. However, these effects are somehow moderated by the institutional distance between the home and host countries. These results, obtained for a panel of UK firms, are largely consistent with a set of hypotheses derived from the institutional and international business theories.
Forecasting container transshipment in Germany
2009
International audience; In this paper, we examine container transshipment at German ports using the seasonal ARIMA (SARIMA) model and the Holt-Winters exponential smoothing approach. Our models are designed especially to take account of the seasonal behavior of the quarterly data used. We consider the dynamic development in this sector for the whole container throughput and also the destinations Asia, Europe and North America, which are the world's three main economic regions. Our data runs from the first quarter of 1989 to the fourth quarter of 2006. We provide detailed quarterly forecasts for the year 2007 and 2008. According to forecasting error measures such as Mean Square Error and The…