A study on bunker fuel management for the shipping liner services

In this paper, we consider a bunker fuel management strategy study for a single shipping liner service. The bunker fuel management strategy includes three components: bunkering ports selection (where to bunker), bunkering amounts determination (how much to bunker) and ship speeds adjustment (how to adjust the ship speeds along the service route). As these three components are interrelated, it is necessary to optimize them jointly in order to obtain an optimal bunker fuel management strategy for a single shipping liner service. As an appropriate model representing the relationship between bunker fuel consumption rate and ship speed is important in the bunker fuel management strategy, we first study in detail this empirical relationship. We find that the relationship can be different for different sizes of containerships and provide an empirical model to express this relationship for different sizes of containerships based on real data obtained from a shipping company. We further highlight the importance of using the appropriate consumption rate model in the bunker fuel management strategy as using a wrong or aggregated model can result in inferior or suboptimal strategies. We then develop a planning level model to determine the optimal bunker fuel management strategy, i.e. optimal bunkering ports, bunkering amounts and ship speeds, so as to minimize total bunker fuel related cost for a single shipping liner service. Based on the optimization model, we study the effects of port arrival time windows, bunker fuel prices, ship bunker fuel capacity and skipping port options on the bunker fuel management strategy of a single shipping liner service. We finally provide some insights obtained from two case studies.     

Unmanned aerial vehicle based low carbon monitoring planning

Instead of physically visiting all locations of concern by manpower, unmanned aerial vehicles (UAVs) equipped with cameras are a low-cost low-carbon alternative to carry out monitoring tasks. When a UAV flies to conduct monitoring tasks, it does not have to fly at a fixed speed; instead, it should fly at lower speeds over objects of higher concerns and vice versa. This paper addresses the UAV planning problem with a focus on optimizing the speed profile. We propose an infinite-dimensional optimization model for the problem and transform the model into a linear programming formulation based on characteristics of the problem. Our case study shows the managerial insight that the UAV flies at low speeds on important segments of the path and at its highest speeds on less-important segments. This means more durable batteries should be designed for drones that need to carry out elaborated monitoring tasks. This finding further provides guidance for drone users when purchasing and renting drones.     

Generation of 3-D geoidal surface of the Bay of Bengal lithosphere and its tectonic implications

We compare wind speeds derived from analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF) from 1986 to 1992 with wind speeds retrieved from three space borne instruments: the Geosat altimeter, the Special Sensor Microwave/Imager (SSM/I) microwave radiometer and the European Remote Sensing (ERS-I) scatterometer. The comparison reveals imperfections in both ECMWF and SSM/I wind speeds.

The ECMWF wind speeds are systematically underestimated with respect to the satellite wind speeds in the tropical Pacific and the Atlantic Ocean before May 1989. After the changes to the ECMWF model in May 1989, the differences vanish in the Atlantic and are reduced by about 50 per cent in the Pacific Ocean. However, the differences between ECMWF and satellite wind speeds are greater than those observed between the satellite wind speeds themselves: yearly differences between the satellite and the ECMWF wind speeds are greater than 2 m s^?1 in tropical regions whereas intercomparison of satellite wind speeds reveals differences within ±1m s ^?1. In September 1991 a new version of the ECMWF model was introduced which greatly altered the wind analyses, both in the tropics and in the southern Pacific Ocean. At the global scale, the mean ECMWF-SSM/I wind difference is close to 0m s^?1 before the September 1991 changes and increases to 0·4m s^?1 following the changes, meaning that the ECMWF wind speeds are 5 per cent less than the SSM/I wind speeds, an observation which may also be made from the ECMWF-ERS 1 comparisons.

The SSM/I wind speeds appear as underestimates with respect to the other three data sets in regions of high and moderate wind speeds, in particular in the high northern latitudes and in the Arabian sea, which could result from a Wentz algorithm directional flaw.     

A comparison of algorithms for vertex normal computation

We investigate current vertex normal computation algorithms and evaluate their effectiveness at approximating analytically computable (and thus comparable) normals for a variety of classes of model. We find that the most accurate algorithm depends on the class and that for some classes, none of the available algorithms is particularly good. We also compare the relative speeds of all algorithms.     

Modeling,Identification, and Control of an Unmanned Surface Vehicle

This paper describes planar motion modeling for an unmanned surface vehicle (USV), including a comparative evaluation of several experimentally identified models over a wide range of speeds and planing conditions. The modeling and identification objective is to determine a model that is sufficiently rich to enable effective model‐based control design and trajectory optimization, sufficiently simple to allow parameter identification, and sufficiently general to describe a variety of hullforms and actuator configurations. We focus, however, on a specific platform: a modified rigid hull inflatable boat with automated throttle and steering. Analysis of experimental results for this vessel indicates that Nomoto's first‐order steering model provides the best compromise between simplicity and fidelity at higher speeds. At low speeds, it is helpful to include a first‐order lag model for sideslip. Accordingly, we adopt a multiple model approach in which the model structure and parameter values are scheduled based on the nominal forward speed. The speed‐scheduled planar motion model may be used to generate dynamically feasible trajectories and to develop trajectory tracking control laws. The paper describes the development, analysis, and experimental implementation of two trajectory tracking control algorithms: a cascade of proportional‐derivative controllers and a nonlinear controller obtained through backstepping. Experimental results indicate that the backstepping controller is much more effective at tracking trajectories with highly variable speed and course angle. © 2013 Wiley Periodicals, Inc.     

Power optimization for dynamic configuration in heterogeneous web server clusters

To reduce the environmental impact, it is essential to make data centers green, by turning off servers and tuning their speeds for the instantaneous load offered, that is, determining the dynamic configuration in web server clusters. We model the problem of selecting the servers that will be on and finding their speeds through mixed integer programming; we also show how to combine such solutions with control theory. For proof of concept, we implemented this dynamic configuration scheme in a web server cluster running Linux, with soft real-time requirements and QoS control, in order to guarantee both energy-efficiency and good user experience. In this paper, we show the performance of our scheme compared to other schemes, a comparison of a centralized and a distributed approach for QoS control, and a comparison of schemes for choosing speeds of servers.     

Simulation and control of hybrid electric vehicles

This research develops a typical model for a parallel hybrid electric vehicle. Model predictive controllers and simulations for this model have been built to verify the ability of the system to control the speeds and to handle the transitional period for the clutch engagement from the pure electrical driving to the hybrid driving. If the output constraints are the measured speeds and the unmeasured torques which are not strictly imposed and can be violated somewhat during the clutch engagements, a modified model predictive controller with soften output constraints has been developed. Simulations show that the new model predictive controller can control the speeds very well for rapid clutch engagements, which enhance the driving comfort and reduce the jerk on the parallel hybrid electric vehicles.     

Optimal state-free, size-aware dispatching for heterogeneous -type systems

We consider a cluster of heterogeneous servers, modeled as M/G/1 first-come first-serve queues with different processing speeds. A dispatcher that assigns jobs to the servers takes as input only the size of the arriving job and the overall job-size distribution. This general model captures the behavior of a variety of real systems, such as web server clusters. Our goal is to identify assignment strategies that the dispatcher can perform to minimize expected completion time and waiting time. We show that there exist optimal strategies that are deterministic, fixing the server to which jobs of particular sizes are always sent. We prove that the optimal strategy for systems with identical servers assigns a non-overlapping interval range of job sizes to each server. We then prove that when server processing speeds differ, it is necessary to assign each server a distinct set of intervals of job sizes in order to minimize expected waiting or response times.     

A new wind retrieval algorithm for Jason-1 at high wind speeds

The altimeter wind speed algorithm at high wind speeds remains unsolved because of lack of observed data. In this study data at high wind speeds were generated using Yin's typhoon model, which consists of the Rankine vortex model and the angular momentum model with typhoon parameters, provided by the Joint Typhoon Warning Centre (JTWC). The accuracy of Yin's typhoon model can be validated by comparing it with recorded data from a weather station. By comparing the normalized radar backscatter cross‐section (NRCS) detected by the Jason‐1 altimeter with wind speed data inferred by Yin's typhoon model, an empirical algorithm valid for a range of wind speeds between 10 and 40 m s^–1 is developed and proposed. The proposed algorithm is compared with the Jason‐1 operational algorithm and Young's altimeter wind retrieval algorithm. The study shows that, for the proposed algorithm and the operational algorithm for Jason‐1, the root mean square (RMS) errors are 3.38 and 3.60 m s^–1, respectively, and the average relative errors are 18% and 19%, respectively, for wind speeds less than 27 m s^–1. Hence, the proposed algorithm is in agreement with the operational algorithm for the Jason‐1 altimeter for wind speeds in the range 10–27 m s^–1. However, the Jason‐1 operational algorithm is inaccurate for wind speeds above 27 m s^–1 because the wind speeds used in the algorithm training process came from scatterometer wind products, and are significantly lower than those in strong wind and heavy rain conditions. Comparison of the proposed algorithm and Young's algorithm shows that the RMS errors are 6.27 and 15.18 m s^–1, respectively, and the average relative errors are 16% and 59%, respectively, for wind speeds greater than 20 m s^–1. The Holland typhoon model cannot accurately determine the outer wind field of typhoons since it extends cyclonic wind speeds to infinity. Young's altimeter wind retrieval algorithm depends on the Holland typhoon model, and the latter results in some errors. Compared with Young's altimeter wind retrieval algorithm, the proposed algorithm retrieves wind speeds with better accuracy. Therefore, the proposed algorithm, suitable for retrieving sea surface wind speeds in typhoons and other strong wind conditions, can be considered as supplementary to the Jason‐1 operational algorithm.     

Vehicle scheduling problems with time-varying speed

The vehicle scheduling problem with time-varying speed (VSPTS) is a generalization of the vehicle scheduling problem in which the travel speed between two locations depends on the passing areas and time of day. We propose a simple model for estimating time-varying travel speeds in the VSPTS that relieves much burden for the data-related problems. We present three heuristics for the VSPTS, developed by extending and modifying existing heuristics for conventional vehicle scheduling problems. The results of computational experiments demonstrate that the proposed estimation model performs well and the saving method is the best among the three heuristics.     

Multimedia object modeling and storage allocation strategies

The improvements in disk speeds have not kept up with improvements in processor and memory speeds. Many techniques have been proposed and utilized to maximize the bandwidths of storage devices. These techniques have proven useful for conventional data, but when applied to multimedia data, they tend to be insufficient or inefficient due to the diversified data types, bandwidth requirements, file sizes and structures of complex objects of multimedia data. In this paper, we discuss the design of an efficient multimedia object allocation strategy that strives to achieve the expected retrieval rates and I/O computational requirements of objects; and also effectively balances the loads on the storage devices. We define a multimedia object model, describe the multimedia object and storage device characteristics, the classification of the multimedia objects according to their I/O requirements, and the fragmentation strategies. We use a bipartite graph model for mapping of fragments to storage devices. A cost function based on a disk utilization per allocated space, the amount of free space, and the bandwidth of a storage device is used to determine the optimal allocation for an object's data.     

Collision avoidance using a model of the locust LGMD neuron

The lobula giant movement detector (LGMD) system in the locust responds selectively to objects approaching the animal on a collision course. In earlier work we have presented a neural network model based on the LGMD system which shared this preference for approaching objects.We have extended this model in order to evaluate its responses in a real-world environment using a miniature mobile robot. This extended model shows reliable obstacle detection over an eight-fold range of speeds, and raises interesting questions about basic properties of the biological system.     

WCDMA高速上行变速率数据业务传输技术研究

论文分析了3GWCDMA系统使用较高传输速率支持上行变速率业务传输的接入约束模型,并利用该模型提出了一种上行方向支持WWW浏览业务的传输方案,给出了支持变速率传输的传输格式设计方案和接入控制规则,并仿真了不同可用系统负载情况下传输速率分布情况和系统拥塞概率。     

A new relationship between radar cross-section and ocean surface wind speed using ERS-t scatterometer and buoy measurements

The ERS–I spacecraft scatterometer, C-band VV polarization, acquired radar cross-section measurements over the global oceans during 1992 and 1993. We investigate the cross-section dependence on mean wind speed U using collocated buoys within ±25km of the scatterometer cells. These collocated measurements result in over 75000 matches in two diITerent oceanic regions. The buoys measure hourly mean wind speeds from 0·2–10 mS ¹ and 0·2–18ms ^-1 in the equatorial Pacific Ocean and at mid^-latitudes off the North American coasts, respectively. We present experimental evidence for a new and compact exponential model dependence on wind speed. The previously used power–law form inadequately characterizes the cross-section measurements based on a single index over a large wind speed range. The cross-sectional slope varies from about zero dB/ms^-1 at high wind speeds U=18ms ^-1 and small incidence angles 0=20° to about 1·3dB/ms ^-1 at low wind speeds U=3ms ^-1 and large incidence angles, 0=55°. The CMOD4 model significantly underestimates the radar cross section measurements for U≤3ms ^-1 whereas the exponential model exhibits less bias.     

基于噪音受益的快速图像分割算法

图像分割是指将一幅图像分解为若干互不交迭的区域的集合。当用已有的改进高斯混合模型于图像分割时,如何加快其分割过程是一个有研究意义的课题。基于最新的噪音受益EM算法,通过人工加噪来加快已有的改进高斯混合模型的收敛速度,从而达到加快图像分割的目的。当添加的噪声满足噪音受益EM定理时,加性噪声加快了EM算法收敛到局部最大值的平均收敛速度。改进的高斯混合模型是EM算法的特例,因此,噪音受益EM定理同样适用于改进的高斯混合模型。实验表明,提出的算法进行图像分割时,其收敛速度明显加快,时间复杂度明显变小。     

Asymptotic continuous Petri nets

A Petri net is basically a discrete model. However, continuous Petri nets, such that the markings are real numbers have been defined. Two continuous Petri net models involving time have been drawn up. They differ by the calculation of the instantaneous firing speeds of the transitions. Both can be used to approximate a timed Petri net. The former considers constant firing speeds (CCPN) and is very easy to simulate (few events have to be considered, even when it approximates a timed Petri net with many reachable markings). The latter considers firing speeds depending on the marking (VCPN). Although it provides a better approximation, its simulation is longer because the markings and speeds are given by differential equations. This paper introduces a third model (ACPN) which presents the advantages of the two preceding ones. In most cases, this model represents the asymptotic behavior of the VCPN. Then their precisions are similar. Since the firing speeds of the ACPN are constant, it is as easy to simulate as the CCPN.     

基于单线圈的速度估计混合模型

实时准确预测出交通速度对于成功的快速路管理系统来说足至关重要的。然而,交通速度并不能直接从单线圈检测器测量出来。该文提出了一种基于单线圈输出量进行速度估计的混合模型方法。该方法分别考虑自由流和拥挤两种不同状态下分别采用不同的模型进行交通速度的估计。模型系数的计算采用已知的单线圈输出量信息和交通流模型进行估计。整个算法采用matlab仿真软件仿真检验,结果表明利用该方法估计出来的速度非常接近于双线圈测量的速度观测值。与以往的算法相比,该方法简单实用并且明显地改善了速度估计。     

Diffusive approximation of fisher's equation

We show that Fisher's Equation is the relaxation limit of a discrete kinetic model with two speeds, in which the collision term contains a source. The analysis can be directly applicable to obtain a numerical approximation to Fisher's Equation in terms of the relaxing system.     

Dynamic modeling of a wave glider

We propose a method to establish a dynamic model for a wave glider, a wave-propelled sea surface vehicle that can make use of wave energy to obtain thrust. The vehicle, composed of a surface float and a submerged glider in sea water, is regarded as a two-particle system. Kane’s equations are used to establish the dynamic model. To verify the model, the design of a testing prototype is proposed and pool trials are conducted. The speeds of the vehicle under different sea conditions can be computed using the model, which is verified by pool trials. The optimal structure parameters useful for vehicle designs can also be obtained from the model. We illustrate how to build an analytical dynamics model for the wave glider, which is a crucial basis for the vehicle’s motion control. The dynamics model also provides foundations for an off-line simulation of vehicle performance and the optimization of its mechanical designs.     

Verification and falsification of programs with loops using predicate abstraction

Predicate abstraction is a major abstraction technique for the verification of software. Data is abstracted by means of Boolean variables, which keep track of predicates over the data. In many cases, predicate abstraction suffers from the need for at least one predicate for each iteration of a loop construct in the program. We propose to extract looping counterexamples from the abstract model, and to parametrise the simulation instance in the number of loop iterations. We present a novel technique that speeds up the detection of long counterexamples as well as the verification of programs with loops.