Draft Limits Research Articles

Tight lower bounds for the Traveling Salesman Problem with draft limits

Tight lower bounds for the Traveling Salesman Problem with draft limits

Structural evaluation of a pusher-tug vessel to comply with the requirements for navigation in ice covered waters

The design of a standalone ice breaker vessel destined for inland navigation could be a costly solution for a temporary problem, due to the limited period of time when the vessel is engaged in ice breaking operations. The Romanian Authorities have in their possession a dedicated ice breaker, Perseus, destinated to clear the navigation path on the Maritime Danube River but which cannot navigate upstream on the Fluvial Danube River due to its draft limitations. As a consequence, most vessels trading from Braila and upstream are exposed to high risks due to the possibility of being trapped in ice formations that could be dangerous for both for the crew and vessels during the winter season. A viable solution is represented by designing a removable ice breaker module that could be attached to the existing fleet of pusher vessels. Since it is not a stand-alone vessel, it will not require a dedicated crew onboard and will only operate when ice dams are created along the river and the navigation path needs to be cleared. The existing fleet of pusher vessels is not prepared to navigate in ice covered water and thus structural reinforcement are required to comply with the requirements provided by classification society. The current paper presents the evaluation of the existing structure of a pusher vessel and proposes means of reinforcement to comply with ICE B class notation provided by DNV Class Society. The paper will conclude on the definition of the ice belt area (LIWL, UIWL) along the ship’s side and will provide scantling information for the new structure within the ice belt area.

The Heterogeneous Fleet Vehicle Routing Problem with Draft Limits

Over the past two decades, international maritime transport has been characterized by the advent of ever larger ships. This phenomenon is known as naval gigantism. If, on the one hand, naval gigantism allows to reduce transport costs by exploiting the economies of scale achievable by large ships, on the other hand, it implies a series of operational issues. Indeed, due to their large draft, such giant vessels are not allowed to enter small ports when fully or near-fully loaded, and in some cases, they cannot enter such small ports at all. In fact, their draft can strongly vary depending on the load on board. This implies restrictions for vessels in accessing ports, which impact not only at the strategical level on the fleet sizing problem, but also at the tactical/operational level, on the sequence of port visits among each route. In fact, given a set of ports that a ship has to visit, determining the optimal sequence of visits becomes a very challenging issue, as the sequence that gives the shortest travel distance (i.e., the smallest travel cost) may prove infeasible due to draft limit restrictions for accessing ports. Furthermore, the same sequence of ports, which may be infeasible for a large ship, may become viable if operated by a smaller ship. On the other hand, due to the economy of scale, travel costs per load unit are generally much lower for large ships than for small ones. Therefore, the draft restrictions also affect the fleet sizing problem. In this paper, we introduce the Heterogeneous Fleet Vehicle Routing Problem with Draft Limits (HF-VRP-DL). We propose a mixed integer programming formulation and several valid inequalities to strengthen it. Since the mathematical model is able to handle only small-sized instances, to address larger instances we propose a Large Neighborhood Search matheuristic (LNS) and an Iterated Local Search matheuristic (ILS). Computational tests carried out show excellent performances of the proposed approach. Further analysis is provided on the impact of the instance layout on the computation time required to solve the problem to optimality.

Towards best possible safety – current regulatory research for the German site selection process for high-level radioactive waste disposal

Abstract. The Federal Office for the Safety of Nuclear Waste Management (BASE – Bundesamt für die Sicherheit der nuklearen Entsorgung) is the German federal regulatory authority for radioactive waste disposal. It supervises the German site selection process and is responsible for the accompanying public participation. Task related research is an integral part of BASE's activities. The projects MessEr and übErStand compiled the state-of-the-art science and technology regarding surface based exploration methods suitable for addressing the criteria and requirements specified in the German Site Selection Act. The results support BASE to review and define the surface-based exploration programs to be executed by the national implementer BGE (Bundesgesellschaft für Endlagerung mbH). To support BASE in reviewing the application of the exclusion criteria “active fault zones” according to the Site Selection Act, the project KaStör reviewed the current knowledge on active faults and fault zones in Germany and recommends methodological approaches to date and identify the activity of faulting. For the time being, the Site Selection Act defines 100 ∘C as a draft limit on the temperature at the outer surface of a repository container for all host rocks. The project Grenztemperatur studied the temperature dependency of the different thermal-hydraulic-mechanical-chemical/biological (THMC/B) processes according to available features-events-processes (FEP) catalogues for rock salt, clay stone, and crystalline rock and describes ways to defining host rock specific maximum temperatures based on specific disposal and safety concepts. Safety oriented weighting of different criteria and comparison of different potential regions and sites are key challenges during the siting process. The project MABeSt studied and reviewed methodological approaches to this weighting and comparison problem with special emphasis on multi criteria analysis (MCA) and multi criteria decision analysis (MCDA). A key requirement for safe geological disposal of nuclear waste is barrier integrity. The project PeTroS performed the first triaxial flow-through experiments on natural rock salt samples at disposal relevant p−T conditions and studied potential percolation mechanisms of fluids within rock salt. The data substantiate that the minimum stress criterion and/or the dilatancy criterion are the prime “percolation thresholds” in rock salt. The research results support BASE in fulfilling its tasks as national regulator according to state-of-the-art science and technology and are also relevant to other stakeholders of the siting process.

Simultaneous waterway scheduling, berth allocation, and quay crane assignment: A novel matheuristic approach

Maritime shipment plays a pivotal role in goods transportation worldwide. Ships intending to load/unload a cargo should visit a port. Three main steps are taken during this process. Firstly, ships go through a waterway to reach the berthing area. Secondly, they are allocated to eligible wharves, and quay cranes are assigned to them. At last, ships leave the port area through the waterway. In this paper, the three mentioned stages are considered and solved in an integrated manner. A two-way waterway is deemed with the width limitation for ships moving in opposite directions. Furthermore, ships may arrive during the planning horizon. Tidal impacts, draft limit, and safety distance between ships are prominent maritime limitations included in this paper. As the three stages take place consecutively, the problem appears to resemble a hybrid flow shop scheduling problem with unrelated parallel machines, machine eligibility constraint, and shared resources. Following this attitude, a mathematical model is developed. Due to the problem complexity, three distinct matheuristic approaches are developed by combining the genetic algorithm, discrete differential evolution, and grey wolf optimiser with a mathematical model and tested using randomly-generated numerical instances. At last, developed matheuristics are compared, and some managerial insights are provided.

In-port multi-ship routing and scheduling problem with draft limits

ABSTRACT This paper addresses an in-port multi-ship routing and scheduling problem in maritime transportation. The key objective is to find an optimal routing and schedule for multiple ships that are planned to pick up or deliver cargos located in the various terminals of a port with different draft limits. Using the multiple traveling salesman problem (mTSP) as a base, we formulate a multi-ship routing and scheduling model with draft limits and time windows constraints. To solve the developed model, a two-stage solution method based on dynamic programming and branch-and-bound algorithms is developed. The solution approach is applied to 41 real-sized problem instances. Our experiments revealed that the proposed method outperforms CPLEX by accurately solving the problem instances in a reasonable time. The formulated problem and presented solution can be implemented in fleet operations of autonomous ships in smart maritime transportation systems of the future.

The selective traveling salesman problem with draft limits

This paper introduces the selective traveling salesman problem with draft limits, an extension of the traveling salesman problem with draft limits, wherein the goal is to design a maximum profit tour respecting draft limit constraints at the visited nodes. We propose a mixed integer linear programming (MILP) formulation for this problem. This MILP model is used to solve—to optimality—small size instances and to assess the quality of solutions obtained using a general variable neighborhood search heuristic that explores several neighborhood structures. Our extensive computational experiments confirm the efficiency of the method and the quality of the reported solutions.

A two-phase heuristic for an in-port ship routing problem with tank allocation

This paper addresses an in-port ship routing problem with tank allocation that arises in the chemical shipping industry. The aim is to optimize a tanker’s port call operation that integrates sequencing decisions for visiting terminals and allocating cargo loads to available tanks while taking into account cargo time windows, terminal draft limits and various tank allocation restrictions. We model the problem as a Traveling Salesman Problem with Pickups and Deliveries, Time Windows, Draft Limits and Tank Allocation (TSPPD–TWDLTA), and propose a two-phase heuristic to solve it. Computational studies show that the heuristic is able to provide good solutions to real-sized in-port routing problems with tank allocation in chemical shipping in a reasonable amount of time.

Evaluation of Cd, Cr, Cu, Ni, and Pb in selected cosmetic products from Jordanian, Sudanese, and Syrian markets

ObjectivesThere is no sufficient data that evaluate heavy metal content in cosmetic products in Jordan as well as Sudan and Syria. This study aims to assess metal levels which include Cadmium (Cd), Chromium (Cr), Copper (Cu), Nickel (Ni), and Lead (Pb) in cosmetic products. These elements have draft limits because they are identified as potential impurities and are known to be toxic. This study aims to provide information to the population that may be beneficial to public health. Study designSamples were collected from different brands obtained from markets in Jordan, Sudan, and Syria. Some of the selected cosmetic products were eyeliner, eye pencil, mascara, lipstick, powder, face cream, body cream, sun block, Vaseline, and the traditional eye cosmetic (kohl). The heavy metal content in these samples were determined by atomic absorption spectrometry (AAS). Based on analysis of variance analysis, a significant difference in heavy metal levels was found for samples obtained from Jordanian and Sudanese markets. MethodsThe acid digestion method used in this study was based on procedures recommended by Nnorom et al. with some modifications as follows. (i) A weight of 2.0 g of cosmetic sample was dissolved in a mixture of 6 mL of high quality concentrated 69% nitric acid (HNO3; Merck, Darmstadt, Germany) and 4 mL of concentrated 37% hydrochloric acid (Scharlau, Spain) in a porcelain crucible and heated on a hotplate to near dryness. (ii) An aliquot of 15 mL HNO3 (1.00 M) was added to the digested sample and filtered through a Whatman No. 40 filter paper. (iii) The digested sample was transferred quantitatively into a 25 mL volumetric flask and then diluted with deionized water. (iv) Each digested sample was evaporated at 70 °C to about 1 mL and transferred into a polyethylene flask and diluted with 25 mL deionized water. (v) Blank was treated in the same procedure. ResultsIn Jordan the concentration ranges of heavy metals in the collected samples were: Cd (0.03–0.10 μg/g), Cr (0.0–1.00 μg/g), Cu (0.60–7.40 μg/g), Ni (0.50–3.60 μg/g), and Pb (0.30–15.4 μg/g). Whereas, in Sudanese market the concentration ranges were: Cd (0.01–0.15 μg/g), Cr (0.00–27.9 μg/g), Cu (0.60–10.10 μg/g), Ni (0.00–5.70 μg/g), and Pb (0.02–3.80 μg/g). Also, the concentration ranges of heavy metals in Syrian market were: Cd (0.04–0.056 μg/g), Cr (0.24–0.83 μg/g), Cu (0.61–1.27 μg/g), Ni (0.73–1.41 μg/g), and Pb (4.85–27.70 μg/g). Results revealed that kohl samples have the highest concentration of most of the studied metals, particularly Pb. ConclusionsBased on the results obtained, it is likely to conclude the following: (i) It is not possible to completely eliminate the presence of heavy metals from cosmetic products after manufacturing. However, the quality of the products can be improved by careful selection of raw materials, taking in consideration heavy metal levels. (ii) Heavy metal concentration in lipstick differs with different manufacturers' colors and shade. Statistically significant associations between Pb level and the cosmetic type were found. (iii) Heavy metals levels including Cd, Cr, Cu, Ni, and Pb may impose risk in daily use and repeated application as well as in ingestion through the mouth even at concentration below the allowed limits. (iv) It is the manufacturers' responsibility to ensure that the finished cosmetic product contains the lowest levels possible of heavy metals. So it does not exceed the limits set by health authorities.

The traveling salesman problem with pickups, deliveries, and draft limits

We introduce a new generalization of the traveling salesman problem with pickup and delivery, that stems from applications in maritime logistics, in which each node represents a port and has a known draft limit. Each customer has a demand, characterized by a weight, and pickups and deliveries are performed by a single ship of given weight capacity. The ship is able to visit a port only if the amount of cargo it carries is compatible with the draft limit of the port. We present an integer linear programming formulation and we show how classical valid inequalities from the literature can be adapted to the considered problem. We introduce heuristic procedures and a branch-and-cut exact algorithm. We examine, through extensive computational experiments, the impact of the various cuts and the performance of the proposed algorithms.

A traveling salesman problem with pickups and deliveries, time windows and draft limits: Case study from chemical shipping

This paper introduces and studies a real in-port ship routing and scheduling problem faced by chemical shipping companies. We show that this problem can be modeled as a Traveling Salesman Problem with Pickups and Deliveries, Time Windows and Draft Limits (TSPPD-TWDL). We propose a mathematical formulation for the TSPPD-TWDL and suggest a solution method based on forward dynamic programming (DP) to solve the problem. A set of label extension rules are also proposed to accelerate and enhance the performance of the algorithm. Computational studies show that the label extension rules are essential to the DP-algorithm, and the proposed solution method is able to solve real-sized in-port routing and scheduling problems in chemical shipping efficiently.

Quantitative assessment of the oxidation potential of sulfide-bearing aggregates in concrete using an oxygen consumption test

In the presence of oxygen and humidity, the iron sulfide minerals present in some concrete aggregates can oxidize creating damage to concrete infrastructure. An oxygen consumption test was developed to assess the oxidation potential of concrete aggregate. A compacted layer of aggregate material is exposed to oxygen (O2) in a hermetic cell, and the O2 consumption is monitored. Optimized parameters included a 10 cm compacted layer of aggregate material with particle size <150 μm kept at 40% saturation degree with a 10-cm headspace left at the top of the cell. The consumption of the O2 present in the headspace is monitored over a 3-h testing period at 22 °C. The test was able to discriminate the eight sulfide-bearing and control aggregates selected when using a threshold limit of 5% O2 consumed. This draft limit will, however, require to be confirmed through the testing of a larger number of aggregates.

A general variable neighborhood search variants for the travelling salesman problem with draft limits

In this paper, we present two General Variable Neighborhood Search for the Traveling Salesman Problem with Draft Limits (TSPDL), a recent variant of the Traveling Salesman Problem. TSPDL arises in the context of maritime transportation. It consists of finding optimal Hamiltonian tour for a given ship which has to visit and deliver products to a set of ports while respecting the draft limit constraints. The proposed methods are tested on a set of benchmarks from the literature and computational experiments show their efficiency.

Toxic metals contained in cosmetics: A status report

The persistence of metals in the environment and their natural occurrence in rocks, soil and water cause them to be present in the manufacture of pigments and other raw materials used in the cosmetic industry. Thus, people can be exposed to metals as trace contaminants in cosmetic products they daily use. Cosmetics may have multiple forms, uses and exposure scenarios, and metals contained in them can cause skin local problems but also systemic effects after their absorption via the skin or ingestion. Even this, cosmetics companies are not obliged to report on this kind of impurities and so consumers have no way of knowing about their own risk. This paper reviewed both the concentration of metals in different types of cosmetics manufactured and sold worldwide and the data on metals’ dermal penetration and systemic toxicology. The eight metals of concern for this review were antimony (Sb), arsenic (As), cadmium (Cd), chromium (Cr), cobalt (Co), mercury (Hg), nickel (Ni) and lead (Pb). This was because they are banned as intentional ingredients in cosmetics, have draft limits as potential impurities in cosmetics and are known as toxic.

Exact algorithms for the traveling salesman problem with draft limits

This paper deals with the Traveling Salesman Problem (TSP) with Draft Limits (TSPDL), which is a variant of the well-known TSP in the context of maritime transportation. In this recently proposed problem, draft limits are imposed due to restrictions on the port infrastructures. Exact algorithms based on three mathematical formulations are proposed and their performance compared through extensive computational experiments. Optimal solutions are reported for open instances of benchmark problems available in the literature.

Black Carbon, Trace Elements and Particulate Matter levels in the ambient air of the Jomo Kenyatta International Airport-Nairobi

There have not been any air pollution studies at airports in Africa and indeed at the Jomo Kenyatta International Airport (JKIA), Nairobi, despite a growing global concern on the effect of airports on air pollution. Airport related emission sources pose a direct threat to the health of airport workers, users and surrounding communities. The study was carried out at JKIA between May 6th 2011 and May 17th 2011 with the aim of assessing particulate air pollution at the airport and its implications on human health. Sampling for outdoor and indoor air pollutants was done using an Andersen TM dichotomous impactor and cyclonic personal samplers. These air samplers collect particulate matter (PM) of size PM10 and PM2.5 (Particles with aerodynamic diameters less than 10 µm and 2.5 µm respectively) on Teflon™ filters. Outdoor air sampling was carried out for 12 hours and for eight hours indoors. In both cases, sampling was done twice a day i.e. day time and night time. The shorter indoor period was chosen to mimic the normal working hours of staff at the airport. Atmospheric mass concentration levels of PM (PM10 and PM2.5) were determined gravimetrically, black carbon (BC) by use of a reflectometer while trace elements were determined using Energy Dispersive X-Ray Fluorescence (EDXRF) spectroscopy. Median day time outdoor PM10 and PM2.5 atmospheric mass concentrations (41 µg m-3 and 9 respectively) at JKIA were found to be lower than the Kenyan draft limits (50 µg m-3 and 35 respectively). Median day time outdoor BC concentrations in the PM10 and PM2.5 size fractions were 4.0 µg m-3 and 3.3 respectively. The maximum night time outdoor elemental concentrations for zinc (Zn) and lead (Pb) were 1000 ng m-3 and 51 respectively in the PM2.5 size fraction particles. The concentrations of PM and detected elements indicate that the air at JKIA is not more polluted than at other public places in Nairobi and Africa.

CP and MIP Methods for Ship Scheduling with Time-Varying Draft

Existing ship scheduling approaches either ignore constraints on ship draft (distance between the waterline and the keel), or model these in very simple ways, such as a constant draft limit that does not change with time. However, in most ports the draft restriction changes over time due to variation in environmental conditions. More accurate consideration of draft constraints would allow more cargo to be scheduled for transport on the same set of ships. We present constraint programming (CP) and mixed integer programming (MIP) models for the problem of scheduling ships at a port with time-varying draft constraints so as to optimise cargo throughput at the port. We also investigate the effect of several variations to the CP model, including a model containing sequence variables, and a model with ordered inputs. Our model allows us to solve realistic instances of the problem to optimality in a very short time, and produces better schedules than both scheduling with constant draft, and manual scheduling approaches used in practice at ports.

The Traveling Salesman Problem with Draft Limits

In maritime transportation, routing decisions are sometimes affected by draft limits in ports. The draft of a ship is the distance between the waterline and the bottom of the ship and is a function of the load onboard. Draft limits in ports can thus prevent ships to enter these ports fully loaded and may impose a constraint on the sequence of visits made by a ship. This paper introduces the Traveling Salesman Problem with Draft Limits (TSPDL), which is to determine an optimal sequence of port visits under draft limit constraints. We present two mathematical formulations for the TSPDL, and suggest valid inequalities and strengthened bounds. We also introduce a set of instances based on TSPLIB. A branch-and-cut algorithm is applied on both formulations for all these instances. Computational results show that introducing draft limits make the problem much harder to solve. They also indicate that the proposed valid inequalities and strengthened bounds significantly reduce both the number of branch-and-bound nodes and the solution times.

Baseball’s Accidental Racism: The Draft, African-American Players, and the Law

Major League Baseball has recently experienced two puzzling upheavals. First, the number of foreign players has grown, to twenty-eight percent of all players. At the same time, the fraction of African-American players has declined, and is now at its lowest level in more than thirty years. The solution to the puzzle lies within the league itself. In 1965, MLB instituted two regulations that penalized domestic players: the draft and age minimums. Because the regulations applied only to U.S. players, teams shifted their scouting and development resources to foreign countries. Our empirical analysis, using a new data set, shows that the shift has caused growth in the numbers of foreign MLB players and a decline in U.S. players, especially harming disadvantaged groups such as African-Americans. The regulations violate the Civil Rights Act of 1964 in two ways. First, because they explicitly burden only U.S. players, they constitute intentional discrimination based on national origin. Second, because the regulations’ impact falls disproportionately on African-Americans, the league has engaged in unlawful racial discrimination. The appropriate remedy is that the draft and age limits should be eliminate.

Kolkata Port Trust: A Turnaround Story

Kolkata Port (KoPT) had achieved a turnaround from having made a loss of Rs 7.5 crores (cr) in the year 2000–01 to a net surplus of Rs 465.1 cr in the year 2006–07. A variety of initiatives had been taken during the intervening years with a focus on tariff rationalization, revenues from alternate sources, infrastructure development and productivity improvements. While these had yielded results, there was a fundamental issue of operational complexity and inability to compete due to the locational disadvantage. KoPT was a riverine port with two locations, 232 kms and 115 kms upstream on the Hooghly with draft limitations. Two significant studies having implications for future strategies of KoPT had recently been submitted in March and November 2007. The top management of the port, including the Chairman who was responsible for driving many of the initiatives, was concerned that it may not be possible to achieve long term sustainable growth continuing with the strategies used so far. A well thought out future roadmap, breaking away from the present thinking, was essential sustained growth.