1,720,971 research outputs found
Analysis and modeling of container handling equipment activities
No full textAlthough the technical literature contains numerous efforts to simulate container terminal performance,
little attention has been paid to setting up, calibrating and validating models for handling equipment
activities. This paper presents results from the estimation of activity duration concerning three different
types of handling equipment: mobile harbor cranes, gantry cranes and reach stackers. Two estimation
approaches (sample means vs random variables) were investigated with respect to different hypotheses
with regard to activity aggregation and container type (undifferentiated, 20’, 40’, full or empty). A
concise but exhaustive state of art is proposed, an in-depth descriptive analysis of experimental data is
carried out, several probability distribution functions were tested and more than 60 statistical models are
proposed. The results can be easily implemented in any terminal simulation model
Riqualificazione e potenziamento del collegamento ferroviario Salerno-Fisciano-Avellino: simulazione ed analisi degli effetti sul sistema di trasporto
No full textTactical and strategic planning for a container terminal: Modelling issues within a discrete event simulation approach
No full textIn this paper different microscopic discrete event simulation models for a container terminal are presented. The focus is on the best approach to adopt to simulate handling activity time duration and on which level of detail should be pursued with respect to different planning horizons that a decision maker have to face. The models share the same logical architecture but differ in the approaches pursued to estimate handling activity time duration. Terminal operations were broken down into elementary activities pursuing a level of disaggregation not usual in the literature; time duration of each elementary handling activity was modelled through a stochastic approach, distinguishing container type; validation was carried out with respect to different planning horizons (real-time/short-term, long-term) through the definition of local and global indicators and a before-and-after analysis. Modelling issues are discussed for tactical and strategic planning, and operational guidelines are given
Methodology for estimating traffic fuel consumption and vehicle emissions for urban planning
No full textUna mobilità sostenibile nelle aree urbane: stima degli effetti di una riqualificazione del parco veicolare bus a veicoli ibrido-Diesel plug-in
No full textSimulation of a container terminal through a discrete event approach: literature review and guidelines for application
No full textDesign and project appraisal of container terminals may be carried out through two main approaches. optimization or simulation. Simulation can help to achieve different aims: overcome mathematical limitations of optimization approaches, support and let computer generated strategies/policies more understandable, support decision makers in daily decision processes through a “what if” approach.
Although in literature numerous efforts may be found in the field of simulation of a container terminal, most of the existing papers do not pay great attention on the model set-up, its calibration and its validation, but they are only focused on the application and/or on the comparison of design scenarios.
In a container terminal may be distinguished macro-operations, operations and activities. Macro-operations are set up by operations; operations are set up by handling activities. In such a classification, dependent on the level of aggregation chosen, a performance function can be associated to an entire operation (e.g. vessel loading) or to a single handling mean (e.g. a quay crane that load a vessel). In all the cited cases, performance functions can be deterministic or stochastic and are highly influenced by containers typology (e.g. 20 feet vs 40 feet) and by their state (full or empty).
Although the estimation of performance functions should be one of the main issues of all container terminal applications, such a problem does not seem to be treated deeply in most of the application existing in literature. If on the one hand, many contributions do not present any information on performance functions used, the remaining contributions carry out very simple approaches (deterministic) and/or give scanty information: on the estimation approach pursued, on experimental data used, on parameters estimated and on parameters value.
In this paper, drawing on the model architecture proposed in a previous contribution by the same authors, a discrete event simulation model is proposed for the Salerno container terminal (one of the major private container terminal in the South of Italy) in order to address some of the topics introduced before and, in particular, to cope with the following issues:
1. calibration of stochastic distribution function to estimate terminal handling activities,
2. comparison of different stochastic estimation approaches ( Moment, Maximum Likelihood and Kolmogorov-Smirnov),
3. analysis of the effects of different estimation approaches (deterministic, stochastic aggregated, stochastic disaggregated) on the estimation of the whole terminal performances.
The main container terminal operations have been subdivided into elementary activities and each activity has been analyzed individually. In particular, the handling means considered have been: quay cranes, yard crane and reach stackers. The activities taken into account have been:
as regard quay cranes: loading time from dock to vessel, loading time from shuttle to vessel, unloading time from vessel to dock, unloading time from vessel to shuttle;
as regard yard cranes: unloading time (to shuttle/truck), loading time (from shuttle/truck), unloading time (to stack), loading time (from stack), trolley speed (with container), free trolley speed, crane speed;
as regard reach stackers: unloading time from shuttle/truck, loading time to shuttle/truck, stacking time (to tier).
All of them have been analyzed for the following container typologies: undifferentiated, 20’, 40’, 2 x 20’, full and empty.
Starting from the empirical frequency distributions, different distribution functions have been hypothesised (Gamma, Normal, Weibull, LogNormal) and the corresponding parameters have been calibrated starting from real observations obtained from SCT (more than 1.000 vessels monitored) and from an integrative survey (more than 3.000 containers monitored).
The calibration stage has been carried out through the implementation and the comparison of Moment, Maximum Likelihood and Kolmogorov-Smirnov estimation methodologies. For each handling means and for each container typology, deterministic values and distribution function have been obtained, have been compared and have been implemented in a discrete event simulation model. The model simulates operations of SCT, and it has been used to simulate different modelling hypothesis concerning performance functions. The hypotheses envisage:
(1) to use deterministic value;
(2) to pursue a stochastic approach but with an higher level of aggregation: container undifferentiated and no distinction inside loading/unloading activities, e.g. loading from dock and from shuttle are not distinct;
(3) to pursue a stochastic approach with an higher level of disaggregation.
The effects have been evaluated estimating global and local indicators, simulating loading/unloading operations for a set of observed vessels and simulating the trip time for a set of observed containers. Results show remarkable differences among the different hypotheses, but point out how the effects may be not negligible in short-medium term simulation scenarios (real-time management, tactical planning), whereas may be not relevant in strategical planning
STOCHASTIC EQUILIBRIUM ASSIGNMENT WITH VARIABLE DEMAND:THEORETICAL AND IMPLEMENTATION ISSUES
No full textRecently, it has been pointed out that transport models should reflect all significant traveler choice behavior. In particular, trip generation, trip distribution, modal split as well as route choice should be modeled in a consistent process based on the equilibrium between transport supply and travel demand. In this paper a general fixed-point approach that allows dealing with multi-user stochastic equilibrium assignment with variable demand is presented. The main focus was on investigating the effectiveness of internal and external approaches and of different algorithmic specifications based on the method of successive averages within the internal approach. The vector demand function was assumed non-separable, non-symmetric cost functions were adopted and implementation issues, such updating step and convergence criterion, were investigated. In particular the aim was threefold: (i) compare the internal and the external approaches; (ii) investigate the effectiveness of different algorithmic specifications to solve the variable demand equilibrium assignment problem through the internal approach; (iii) investigate the incidence of the number of the links with non-separable and/or asymmetrical cost functions. The proposed analyses were carried out with respect to two real-scale urban networks regarding medium-size urban contexts in Italy
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
