Distributionally Robust Joint Chance Constrained Vessel Fleet Deployment Problem

2021 ◽  
Author(s):  
Feifeng Zheng ◽  
Zhaojie Wang ◽  
E. Zhang ◽  
Ming Liu
Keyword(s):  
Numerical Experiments ◽  
Historical Data ◽  
Operating Cost ◽  
Liner Shipping ◽  
Total Cost ◽  
Approximation Approach ◽  
Robust Model ◽  
Distributionally Robust ◽  
The Moment ◽  
Fleet Deployment

This work investigates the problem of vessel fleet deployment for liner shipping. The objective is to minimize the total cost, i.e., the sum of vessel chartering cost and vessel-route operating cost. In the considered problem, the shipment demand for each route is uncertain and its distribution is unknown. Due to lacking historical data, we use the moment-based ambiguity set to characterize the unknown distributions of demands. We then introduce a distributionally robust model and propose a new approximation approach to solve this problem. Finally, numerical experiments are conducted to demonstrate the performance of our approximation approach.

Liner Shipping Service Planning Under Sulfur Emission Regulations

2020 ◽  
Author(s):  
Shuaian Wang ◽  
Dan Zhuge ◽  
Lu Zhen ◽  
Chung-Yee Lee
Keyword(s):  
Operations Management ◽  
Operating Cost ◽  
Liner Shipping ◽  
Service Planning ◽  
Planning Problem ◽  
Marine Fuel ◽  
Speed Optimization ◽  
Schedule Design ◽  
Low Sulfur ◽  
Fleet Deployment

Air emissions from ships have become an important issue in sustainable shipping because of the low quality of the marine fuel consumed by ships. To reduce sulfur emissions from shipping, the International Maritime Organization has established emission control areas (ECAs) where ships must use low-sulfur fuel with at most 0.1% sulfur or take equivalent emission-reduction measures. The use of low-sulfur fuel increases the costs for liner shipping companies and affects their operations management. This study addresses a holistic liner shipping service planning problem that integrates fleet deployment, schedule design, and sailing path and speed optimization, considering the effect of ECAs. We propose a nesting algorithmic framework to address this new and challenging problem. Semianalytical solutions are derived for the sailing path and speed optimization problem, which are used in the schedule design. A tailored algorithm is applied to solve schedule design problems, and the solutions are used in fleet deployment. The fleet deployment problem is then addressed by a dynamic programming-based pseudo-polynomial time algorithm. Numerical experiments demonstrate that considering the effect of ECAs in liner shipping operations management can reduce over 2% of the costs, which is significant considering that the annual operating cost of a shipping company’s network can be as high as several billion dollars.

scholarly journals Revisiting a Funding Model for University-led Dental Clinics: The Case of Complete Denture Fabrication Case of Complete Denture Fabrication

2020 ◽  
Vol 27 (2) ◽  
Author(s):  
Rohana Ahmad ◽  
◽  
Nur Amalina Zul ◽  
Siti Anisah Mohtar ◽  
Marc Tennant ◽  
...  
Keyword(s):  
Cost Estimation ◽  
Operating Cost ◽  
Complete Denture ◽  
Government Support ◽  
Patient Records ◽  
Complete Dentures ◽  
Total Cost ◽  
Dental Clinics ◽  
Dental Instruments ◽  
Number Of Visits

Objectives: University-led dental clinics are rarely seen as core to the national healthcare system. Thus, when publicly funded universities experience a decline in government support, dental clinic services operated by students are confronted by a potentially inadequate operating budget. Prompted by the need for strategic resource allocation, this study seeks to quantify the resources consumed in the construction of complete dentures by undergraduate students in an effort to identify opportunities for cost-cutting measures. Methods: Clinical cases were retrieved from the logbooks of graduating students of Class 2015, and patient records were reviewed to identify and quantify all clinical and laboratory procedures involved in constructing a set of complete dentures. Cost estimation was carried out using the activity-based method on the basis of direct medical costs. Results: A total of 83 patient records were reviewed. The average number of visits required to fabricate a set of complete dentures was 10 (range, 6–20 visits) with an average total cost of MYR2131±538 (€450±114). The number of visits contributed substantially to the total cost, and procedures requiring multiple visits included secondary impression and jaw relation recording. The major cost components were dental equipment (44%), laboratory costs (28%), dental consumables (17%), salaries (7%), and dental instruments (3%). Conclusion: The operating cost for training students in denture fabrication is substantial. Schools should formulate strategies to reduce the number of patient visits by ensuring that students optimize the time spent per visit. A financially sustainable model to fund dental training is necessary to ensure that quality of care is not compromised in university-led clinics.

A Practical Approach to Energy Optimization Using Pinch Analysis: A Case Study of an Oil Refinery

2021 ◽  
Author(s):  
Paschal Uzoma Ndunagu ◽  
Emeka Emmanuel Alaike ◽  
Theophile Megueptchie
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Energy Savings ◽  
Operating Cost ◽  
Energy Optimization ◽  
Distillation Unit ◽  
Pinch Analysis ◽  
Cost Index ◽  
Heat Exchanger Network ◽  
Total Cost

Abstract The objective of this paper is to perform an energy optimization study using pinch analysis on the Heat Exchanger Network (HEN) of a Crude Distillation Unit to maximum heat recovery, minimize energy consumption and increase refining margin. The heat exchanger network (HEN) considered comprises exchangers from the pre-heat section of the atmospheric distillation unit, which recovers heat from the product streams to incrementally heat the crude oil feed stream before entering the furnace. This paper illustrates how to perform a detailed HEN retrofitting study using an established design method known as Pinch Analysis to reduce the operating cost by increasing energy savings of the HEN of an existing complex refinery of moderate capacity. Analysis and optimization were carried out on the HEN of the CDU consist a total of 19 heat exchangers which include: process to process (P2P) heat exchangers, heaters and coolers. In the analysis, different feasible retrofit scenarios were generated using the pinch analysis approach. The retrofit designs included the addition of new heat exchangers, rearrangement of heat exchanger (re-sequencing) and re-piping of existing exchangers. Aspen Hysys V9 was used to simulate the CDU and Aspen Energy Analyser was used to perform pinch analysis on the HEN of the pre-heat train. Several retrofit scenarios were generated, the optimum retrofit solution was a trade-off between the capital cost of increasing heat exchanger surface area, payback time, energy / operating cost savings of hot and cold utilities. Results indicated that by rearrangement (Re-sequencing), the pre-heat train can reduce hot (fired heat) and cold (air and cooling water) utilities consumption to improve energy savings by 8% which includes savings on fired heat of about 4.6 MW for a payback period of 2 years on capital investment. The results generated were based on a ΔTmin of 10°C and pinch temperature of 46.3°C. Initial sensitivity analysis on the ΔTmin indicated that variation of total cost index is quite sensitive and increases with increase in ΔTmin at the temperature range of 14.5-30°C, however total cost index remains constant and minimal at a temperature range between 10°C-14.5°C for the CDU preheat train under study. In addition, the implementation of the optimum retrofit result is straightforward and feasible with minimum changes to the existing base case/design.

scholarly journals Thermal-economic multiobjective optimization of heat pipe heat exchanger for energy recovery in HVAC applications using genetic algorithm

2014 ◽  
Vol 18 (suppl.2) ◽  
pp. 375-391 ◽  
Author(s):  
Sepehr Sanaye ◽  
Davood Modarrespoor
Keyword(s):  
Genetic Algorithm ◽  
Heat Exchanger ◽  
Heat Pipe ◽  
Operating Cost ◽  
Design Parameters ◽  
Nsga Ii ◽  
Pipe Length ◽  
Total Cost ◽  
Continuous And Discrete Variables ◽  
Pipe Heat

Cost and effectiveness are two important factors of heat pipe heat exchanger (HPHE) design. The total cost includes the investment cost for buying equipment (heat exchanger surface area) and operating cost for energy expenditures (related to fan power). The HPHE was thermally modeled using e-NTU method to estimate the overall heat transfer coefficient for the bank of finned tubes as well as estimating pressure drop. Fast and elitist non-dominated sorting genetic algorithm (NSGA-II) with continuous and discrete variables was applied to obtain the maximum effectiveness and the minimum total cost as two objective functions. Pipe diameter, pipe length, numbers of pipes per row, number of rows, fin pitch and fin length ratio were considered as six design parameters. The results of optimal designs were a set of multiple optimum solutions, called ?Pareto optimal solutions?. The comparison of the optimum values of total cost and effectiveness, variation of optimum values of design parameters as well as estimating the payback period were also reported for various inlet fresh air volume flow rates.

Automated Optimum Design of Refrigerated Warehouses

1979 ◽  
Vol 101 (4) ◽  
pp. 633-639
Author(s):  
B. D. Gupta ◽  
S. S. Rao
Keyword(s):  
Optimum Design ◽  
Meteorological Data ◽  
Operating Cost ◽  
Building Envelope ◽  
Penalty Function Method ◽  
Functional Requirements ◽  
Existing Building ◽  
Total Cost ◽  
Initial Cost ◽  
Average Maximum

The main consideration in the design of refrigerated commercial warehouses, apart from energy required for operation, is the total cost (initial plus operating costs). There is no simple explicit relation between the total cost and the energy required to maintain the desired inside conditions. Qualitatively, one feels that a design involving less initial cost requires larger energy input and hence a higher operating cost. With limited energy resources, it is necessary to conserve energy or use it optimally. A unified approach to find the optimal combination of initial cost and operating cost (energy) is presented in this paper. Since the thickness of insulation is one of the important factors to be considered in reducing the external load and hence the energy requirements, the optimum building envelope and insulation thicknesses are found for a specified volume and location by using the interior penalty function method of optimization. The procedure outlined in this paper can be used for new as well as existing building to fulfill the functional requirements optimally and thus conserve the energy to the greatest possible extent. For the computation of heat gain, the design day, based on the average maximum solar air temperature computed from the hourly meteorological data, is chosen. The resulting computer program is used to find the effect of some of the parameters like wall thickness, type of insulation, orientation of building and economics model on the optimum design.

Fleet deployment in liner shipping: a case study

2009 ◽  
Vol 36 (5) ◽  
pp. 397-409 ◽  
Author(s):  
Kjetil Fagerholt ◽  
Trond A. V. Johnsen ◽  
Haakon Lindstad
Keyword(s):  
Liner Shipping ◽  
Fleet Deployment

Routing and fleet deployment in liner shipping with spot voyages

2015 ◽  
Vol 57 ◽  
pp. 188-205 ◽  
Author(s):  
Rodrigo Moretti Branchini ◽  
Vinícius Amaral Armentano ◽  
Reinaldo Morabito
Keyword(s):  
Liner Shipping ◽  
Fleet Deployment

Characterization of the Quorum Sensing Regulon in Acidithiobacillus ferrooxidans

2013 ◽  
Vol 825 ◽  
pp. 129-132 ◽  
Author(s):  
Sigde Mamani ◽  
Yan Denis ◽  
Danielle Moinier ◽  
Mohamad Sabbah ◽  
Laurent Soulère ◽  
...  
Keyword(s):  
Cell Adhesion ◽  
Quorum Sensing ◽  
Acidithiobacillus Ferrooxidans ◽  
Operating Cost ◽  
Second Step ◽  
Low Grade ◽  
Mineral Surface ◽  
Homoserine Lactones ◽  
The Moment

Bioleaching is the solubilization of metals from ores by microorganisms. This process is more efficient than conventional methods in the metal recovery from low grade ores while decreasing the operating cost and the environmental impact. Among the bioleaching bacteria, the Gram-negative chemolithoautotrophic acidophilic Acidithiobacillus ferrooxidans has the ability to adhere to mineral surface and to form biofilm. The genes involved in the production of this biofilm are controlled by a cellular communication system called Quorum Sensing (QS). The QS occurs mainly through the production of acyl homoserine lactones (AHLs). A functional QS system has been identified in At. ferrooxidans with an acyl synthase (AfeI) and a transcriptional regulator (AfeR). Here, our purpose is to characterize the quorum sensing regulon and particularly the genes involved in biofilm formation in At. ferrooxidans. This has been done by cell adhesion experiments comparing At. ferrooxidans grown with or without Tetrazol, an AHL analogue that activates the cell adhesion to mineral surface. The second step has been to compare the expression of some genes predicted to be involved in the QS regulon in At. ferrooxidans grown in the presence/absence of Tetrazol using real-time PCR. These two different strategies are expected to give insight on the moment at which the At. ferrooxidans QS regulon is switched on. The formation of biofilm could improve the bioleaching operation and therefore the understanding of the QS regulon is of primordial importance.

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