Formulating cargo inventory costs for liner shipping network design

This study examines how to incorporate the inventory costs of containerized cargoes into existing liner service planning models such that the designed networks could be improved while not causing extra modeling/computational burden. Two approaches are compared: (i) not considering the inventory costs at all and (ii) incorporating the inventory costs associated with onboard time and those related to transshipment by assuming a fixed connection time. The two models are compared with the ideal model capturing the exact inventory costs on a route choice problem and a capacity planning problem based on extensive randomly generated and practical numerical experiments. The results show that: first, ignoring the inventory costs in service planning models may lead to network design with much higher costs (poor network design decisions); second, in service planning models assuming weekly frequency, the inventory costs associated with onboard time could be formulated exactly, and those related to the connection time of weekly services could be approximated by assuming fixed connection time of 3.5 days for ports with 1 day’s minimum connection time and 4.5 days for ports with 2 days’ minimum connection time.     

Some economic aspects of conflicts over land use in the coastal zone

Abstract

Recent land use legislation pays particular attention to the coastal zone where age‐old conflicts have recently accelerated. Flexibility is required in policy because visible conflicts are tied into complex physical and social systems which may require changing patterns of land use over time. Public policy is altering property rights and a thorough understanding of the economic and social roles played by those rights is required. Economic models can be used to understand some major changes such as types of alteration of the environment, but may be ignored or misused unless a better understanding of coastal decision processes is developed.     

Oriented review to potential simulator for faults modeling in diesel engine

This paper presents a literature review on most of the faults and their models that are considered on a diesel engine. Several faults that may be produced on diesel engine have been analyzed, classified, modeled, and their influences on the global system have been shown. Thus, this paper aims to prepare an important data base on diesel engine faults which may help researchers to develop precise strategies on diesel engine fault diagnosis and prognosis, and also it helps in the development of diesel engine simulators aiming to study the behavior of the diesel engine in the presence of faults. Different fault models such as analytical, empirical, degradation models which may be represented as function of time or as function of the number of cycles, data driven models such as neural network models, or simply constant are presented and analyzed. The global overall models for diesel engine integrating faults are expressed. And finally, the use of these models with the most common failure density distribution functions is proposed giving a more realistic approach to our study.     

雷达侦察信号环境描述与建模

信号环境仿真是检验雷达侦察设备性能的重要手段。针对雷达侦察信号环境时域、空域、频域、能域分布特点,对雷达侦察信号环境进行了数学描述,建立了雷达辐射源信号环境数学模型,为雷达侦察信号环境仿真奠定基础。     

Using the SKAGEX dataset for evaluation of ocean model skills

Numerical ocean models are now being applied in numerous oceanographic studies. However, the qualities of the model results are often uncertain and there is a great need for standards and procedures for evaluation of the skills of numerical general circulation models. In this paper measurements from repeated hydrographical sections across Skagerrak taken in 1990, the SKAGEX dataset, are used to evaluate the skills of two σ-coordinate ocean models and to study the sensitivity of these models to model parameters. A methodology for quantification of model skills based on observations from repeated hydrographical sections in general is suggested. Area averages of absolute differences are for Skagerrak completely dominated by the discrepancies in the upper few meters of the ocean and may not be used to assess models' abilities to reproduce the fields in the larger and deeper part of the ocean. Therefore, discrepancies between average values in time from the observed fields and time averaged values from model outputs are related to the natural variability of the fields. The numbers produced with the suggested measure are relative numbers that will be specific for each section and for each series of observation. Ideally we would therefore like to see the measures computed for a number of sections for various models and choices of model parameters in order to assess model skills. The value of the SKAGEX dataset as a tool for model improvements is demonstrated. Evidence to support the importance of applying non-oscillatory, gradient preserving advection schemes in areas with sharp density fronts is given. The method is used to identify that the forcing/initial values/boundary values for the temperature field are inferior to the corresponding values for the salinity field. With the present coarse resolution, 11 layers in the vertical, it is shown that it is far from obvious that the quality of the model results improve when replacing simple Richardson number formulations for vertical mixing processes with higher order turbulence closure in the Skagerrak area.     

The modelling of dry bulk and tanker markets: a survey

This paper provides an overview of the development of the quantitative modelling techniques that have been applied to the analysis of dry bulk shipping markets. Of necessity it will be dated by the time it is published. The principal points that emerge from the survey are fourfold: first:-reduced form rather than structural modelling, has become the standard approach in the past 15 years. Second, there is a greater focus on modelling rate variability rather than rate levels, using models that estimate the behaviour of both the conditional mean freight rate and its conditional variance. Third, the introduction of models of financial derivatives and their application to shipping markets has been very marked, as finance models of risk management have been adapted to shipping markets. Fourth, the use of segmented models of different ship types, and higher frequency data is now standard. It is argued that the relative neglect of structural models means that estimating fully specified structural econometric models may be a fruitful research agenda for the future.     

The modelling of dry bulk and tanker markets: a survey

This paper provides an overview of the development of the quantitative modelling techniques that have been applied to the analysis of dry bulk shipping markets. Of necessity it will be dated by the time it is published. The principal points that emerge from the survey are fourfold: first:-reduced form rather than structural modelling, has become the standard approach in the past 15 years. Second, there is a greater focus on modelling rate variability rather than rate levels, using models that estimate the behaviour of both the conditional mean freight rate and its conditional variance. Third, the introduction of models of financial derivatives and their application to shipping markets has been very marked, as finance models of risk management have been adapted to shipping markets. Fourth, the use of segmented models of different ship types, and higher frequency data is now standard. It is argued that the relative neglect of structural models means that estimating fully specified structural econometric models may be a fruitful research agenda for the future.     

Mass and heat transports in the NE Barents Sea: Observations and models

The strait between Novaya Zemlya and Frans Josef Land, here called the Barents Sea Exit (BSX) is investigated using data obtained from a current-meter array deployed in 1991–1992, and two numerical models (ROMS and NAME). Combining the observations and models the net volume flux towards the Arctic Ocean was estimated to 2.0 ± 0.6 Sv (1 Sv = 10⁶ m³s^? 1). The observations indicate that about half of this transport consists of dense, Cold Bottom Water, which may penetrate to great depths and contribute to the thermohaline circulation. Both models give quite similar net transport, seasonal variations and spatial current structures, and the discrepancies from the observations were related to the coarse representation of the bottom topography in the models. Also the models indicate that actual deployment did not capture the main in- and outflows through the BSX. A snapshot of the hydrographic structure (CTD section) indicates that both models are good at reproducing the salinity. Nevertheless, they react differently to atmospheric cooling, although the same meteorological forcing was applied. This may be due to the different parameterisation of sea ice and that tides were included in only one of the models (ROMS). Proxies for the heat transport are found to be small at the BSX, and it can not be ruled out that the Barents Sea is a heat sink rather than a heat source for the Arctic Ocean.     

An empirical model for estimating berth and sailing times of mega container ships

ABSTRACT

We provide two empirical models for calculating the sailing time and berth time of maritime container liner networks to effectively model the ambiguity associated with sea and port contingency for ex-ante decisions of fleet deployment and route planning. The models are based on recorded AIS data of 110 mega vessels including all the operating container mega vessels with a capacity of 16,000 TEU or more during the summer of 2015. The models are able to estimate the sailing time (with R² of 0.974) and the berth time (with R² of 0.895) without knowledge of any operational-level explanatory variables. The models are validated against the published East Asia–North Europe services. Moreover, the study reveals that vessel operators adopt different berthing and sailing strategies even under the same conditions.     

船舶电站冗余系统可靠性建模与分析

为解决船舶电站冗余系统的可靠性计算问题,从船舶电站冗余系统主要冗余方式的基本模型出发,提出了基于马尔柯夫过程的船舶电站冗余系统可靠性分析方法,建立了船舶电站冗余系统的可靠性数学模型,从而推导出船舶电站冗余系统的可靠度与平均无故障工作时间,为船舶电站冗余设计提供重要理论依据。所述基本思想及结论不但适用于船舶电站冗余系统,对其它形式的电站系统也有参考价值。     

Test of large-eddy simulation models for homogeneous-shear turbulence in stratification

Numerical tests of various subgrid-scale (SGS) models were conducted for turbulence in thermally stratified homogeneous-shear flow at a relatively low Reynolds number. Compared with a direct numerical simulation (DNS), we found that nondynamic isotropic SGS models are not able to represent the energy spectrum very well because the energy decays considerably during the transition between an initial random stage and a stage of coherent turbulent structures. Dynamic models performed well for simulating the energy spectrum and the change of GS properties with time; anisotropy is not a necessary feature under the present simulation conditions, although one of the special features of stratified turbulence is anisotropy. This may be because the present grids for large-eddy simulation were fine enough to resolve the patches of counter-gradient heat fluxes, which play an important role in the evolution of turbulent energy in stratified turbulence. With respect to the domain-averaged values of SGS stresses, only the dynamic two-parameter mixed (DTM) model produced results of the same order of magnitude as those of filtered DNS. This is because of the terms arising from re-decomposing of the SGS stresses in the DTM model. It was also found that this incompetence in simulating the SGS stress is not necessary to simulate GS energy evolution, as is known for wall turbulence. Updated from the Japanese original (J Soc Nav Archit Jpn 2001; 190:27–39)     

舰艇编队智能防空决策模型研究

海上战机稍纵即逝,指挥决策时间的长短往往可以决定小到1艘舰艇大到1支舰队的命运。在抗击来袭的空中目标问题上,已有的火力分配模型都存在一定的局限性,不能更好满足舰艇编队的防空需求。本文试图引入作为通用智能基础的Soar系统,对来袭的空中目标进行智能决策,建立舰艇编队智能防空决策模型。以Soar作为决策推理引擎,对所有来袭目标威胁程度不断循环推理,以期优化打击方案,大大降低决策时间,更好地满足实战需要,提高海上编队的防空作战能力。     

船舶操纵模拟器中三维场景库的雷达图像模拟

现有船舶操纵模拟器中雷达图像的模拟多是基于二维海图,生成的图像和真雷达图像之间有一定的差距。根据雷达所在位置及扫描范围,基于三维场景库模拟雷达图像,实时访问场景库获取模型的相关信息。采用圆周扫描方式,以射线组模拟雷达电磁波的波束,并利用射线与三角形求交计算物标的回波位置,在计算回波强度时考虑了物标反射面自身因素的影响。经模拟得出了较好的雷达图像。     

Experimental investigation of the strength and stability of submarine pressure hulls with and without artificial corrosion damage

A submarine may have to operate for a period of time with local corrosion damage in the pressure hull if a suitable repair method is unavailable or too expensive for implementation. This paper describes collapse tests on twenty ring-stiffened aluminium cylinders, which were conducted to study the effect of corrosion damage on hull strength and stability. Artificial hull thinning was found to reduce the collapse strength of experimental models through high local stresses in the corroded region, leading to early onset of yielding and inelastic buckling. Bending associated with the eccentricity due to one-sided thinning was found to further increase the local stresses in the hull. Overall collapse pressures were more severely affected by corrosion damage than interframe collapse pressures. The percentage reduction in overall collapse pressure, compared with intact experimental models, was found to be closely related to the percentage depth of thinning. The accuracy of conventional collapse pressure predictions for the experimental models was significantly better for intact than for corroded cylinders.     

Optimal investment priority in container port development

The aim of this paper is to develop realistic and relevant investment planning models for inland container transportation systems. The models may be utilized to identify the most effective investment plan for inland transportation infrastructure development and to evaluate the inland container transportation system. The procedure enables determination of the optimal locations, sizes and time of container port developments as well as the optimal container cargo flows through transportation networks. A heuristic algorithm was developed for the purpose of evaluating alternative investment plans. Dynamic and linear programming methods are applied to each of the two planning problems: the former for the optimum container port capacity development problem and the latter for the optimal allocation of inland container traffic movements. The model has been applied to concrete inland container transportation system problems in Korea.     

Optimal investment priority in container port development

The aim of this paper is to develop realistic and relevant investment planning models for inland container transportation systems. The models may be utilized to identify the most effective investment plan for inland transportation infrastructure development and to evaluate the inland container transportation system. The procedure enables determination of the optimal locations, sizes and time of container port developments as well as the optimal container cargo flows through transportation networks. A heuristic algorithm was developed for the purpose of evaluating alternative investment plans. Dynamic and linear programming methods are applied to each of the two planning problems: the former for the optimum container port capacity development problem and the latter for the optimal allocation of inland container traffic movements. The model has been applied to concrete inland container transportation system problems in Korea.     

Accommodating perceptual conditioning in the valuation of expected travel time savings for cars and public transport

Travel time variability (i.e., random variations in travel time) leads to a travel time distribution for a repeated trip from a fixed origin to destination (e.g., from home to work). To represent travel time variability, a series of possible travel times per alternative (departure time, route or mode) are often used in stated choice experiments. In the traditional models, the probabilities associated with different travel scenarios (e.g., arriving early, on time and late) shown in the experiments are directly used as weights. However, evidence from psychology suggests that the shown probabilities may be transformed (underweighted or overweighted) by respondents. To account for this transformation of probabilities, this study incorporates perceptual conditioning through a non-linear probability weighting function into a utility maximisation framework, within which the empirical estimate of the value of expected travel time savings is estimated. The key advantage of this framework is that the estimated willingness to pay value can be directly linked to the source of utility (i.e., the probability distribution of travel time), while taking into account the perceptual transformation of probabilities.     

Forecasting container throughput based on wavelet transforms within a decomposition-ensemble methodology: a case study of China

To improve predictive accuracy, new hybrid models are proposed for container throughput forecasting based on wavelet transforms and data characteristic analysis (DCA) within a decomposition-ensemble methodology. Because of the complexity and nonlinearity of the time series of container throughputs at ports, the methodology decomposes the original time series into several components, which are rather simpler sub-sequences. Consequently, difficult forecasting tasks are simplified into a number of relatively easier subtasks. In this way, the proposed hybrid models can improve the accuracy of forecasting significantly. In the methodology, four main steps are involved: data decomposition, component reconstruction based on the DCA, individual prediction for each reconstructed component, and ensemble prediction as the final output. An empirical analysis was conducted for illustration and verification purposes by using time series of container throughputs at three main ports in Bohai Rim, China. The results suggest that the proposed hybrid models are able to forecast better than do other benchmark models. Forecasting may facilitate effective real-time decision making for strategic management and policy drafting. Predictions of container throughput can help port managers make tactical and operational decisions, such as operations planning in ports, the scheduling of port equipment, and route optimization.     

Error correction of a predictive ocean wave model using local model approximation

Constructing models from time series with nontrivial dynamics is a difficult problem. The classical approach is to build a model from first principles and use it to forecast on the basis of the initial conditions. Unfortunately, this is not always possible. For example, in fluid dynamics, a perfect model in the form of the Navier–Stokes equations exists, but initial conditions and accurate forcing terms are difficult to obtain. In other cases, a good model may not exist. In either case, alternative approaches should be examined. This paper describes an alternative approach of combining observations and numerical model results in order to produce an accurate forecast. The approach is based on application of a method inspired by chaos theory for building nonlinear models from data called Local Models. Embedding theorem based on the time lagged embedded vectors is the basis for the local model. This technique is used for analysis and updating of numerical model output variables to forecast and correct the errors created by numerical model. The local model approximation is a powerful tool in the forecasting of chaotic time series and has been employed for wave prediction in a forecasting horizon from a few hours to 24 h. The efficacy of the local model as an error correction tool (by combining the model predictions with the observations) compared with the predictions of linear auto regressive models has been brought up. In the present study, the parameters driving the local model are optimized using evolutionary algorithms.     

Uncertainty analysis of extreme mooring loads associated with environmental contours and peak tension distributions

This paper aims to assess the uncertainty on the extreme mooring loads of floating system considering short-term variability. Two environmental contour approaches based on the inverse First and Second Order Reliability Methods are employed to identify critical sea states that may give rise to extreme loads. The uncertainty related to the construction of environmental contours is addressed including significant differences due to marginal distribution fitting, parameter estimation methods and joint models. Three measured datasets are analysed using a known conditional joint distribution and proposed mixed copula model. 3-h time domain numerical simulation for each sea state is conducted and the characteristic extreme responses of mooring lines subjected to design loads are assessed. The uncertainties due to various statistical models including the average conditional exceedance rate method as well as global maxima, peak-over-threshold method combined with Gumbel distribution, Generalized Extreme Value distribution, Generalized Pareto distribution and 3-parameter Weibull distribution are investigated and quantified. It is observed that marginal distributions, joint models and parameters estimation methods have apparent effect on design loads estimation, and the extreme tensions of the semi-submersible platform shows significant difference using various probabilistic models. The results indicate that those epistemic uncertainties should be account for in the reliability analysis or safety factor calibration for mooring systems.