Modified lateral control of an autonomous vehicle by look-ahead and look-down sensing

This paper presents a modified lateral control method for an autonomous vehicle with both look-ahead and look-down sensing systems. To cope with sensor noise and modeling uncertainty in the lateral control of the vehicle, a modified LMI-based H lateral controller was proposed, which uses the look-ahead information of the lateral offset error measured at the front of vehicle and the look-down information of the vehicle yaw angle error between the reference lane and the centerline of the vehicle. To verify the safety and the performance of the lateral control, a scaled-down vehicle was developed, and the positioning of the vehicle was estimated with USAT. The proposed controller, which uses both look-ahead and look-down information, was tested for lane changing and reference lane tracking with both simulation and experiment. The simulation and experimental results show that the proposed controller has better tracking and handling performance compared with a controller that uses only the look-ahead information of the target heading angle error.     

出行者特征要素对公交服务模式的影响分析

公共交通是面向大众的服务,公共交通服务模式的制定与完善需要重点考虑出行者的出行需求,才能从根本上提高公共交通的竞争力。借鉴服务经济学的理论将公共交通服务模式分为公交服务标准、出行者界面、公交服务环境和技术4个维度。基于攀枝花市居民出行调查与公交专项调查数据,应用SPSS定量分析出行者特征要素与公交服务选择的相关性,以考察研究出行者对于公交服务的需求,并提出改善策略。通过研究表明,出行目的、出行时间、职业和年龄与公交服务模式的相关性较大。     

Experimental design influences on stated choice outputs: An empirical study in air travel choice

Discrete choice experiments are conducted in the transport field to obtain data for investigating travel behaviour and derived measures such as the value of travel time savings. The multinomial logit (MNL) and other more advanced discrete choice models (e.g., the mixed MNL model) have often been estimated on data from stated choice experiments and applied for planning and policy purposes. Determining efficient underlying experimental designs for these studies has become an increasingly important stream of research, in which the objective is to generate stated choice tasks that maximize the collected information, yielding more reliable parameter estimates. These theoretical advances have not been rigorously tested in practice, such that claims on whether the theoretical efficiency gains translate into practice cannot be made. Using an extensive empirical study of air travel choice behaviour, this paper presents for the first time results of different stated choice experimental design approaches, in which respective estimation results are compared. We show that D-efficient designs keep their promise in lowering standard errors in estimating, thereby requiring smaller sample sizes, ceteris paribus, compared to a more traditional orthogonal design. The parameter estimates found using an orthogonal design or an efficient design turn out to be statistically different in several cases, mainly attributed to more or less dominant alternatives existing in the orthogonal design. Furthermore, we found that small designs with a limited number of choice tasks performs just as good (or even better) than a large design. Finally, we show that theoretically predicted sample sizes using the so-called S-estimates provide a good lower bound. This paper will enable practitioners in better understanding the potential benefits of efficient designs, and enables policy makers to make decisions based on more reliable parameter estimates.     

Seaport research: A structured literature review on methodological issues since the 1980s

This study aims to investigate how seaport research has been conducted from the methodological perspective. To this end, this study reviews published port literature for the last three decades (1980-2000s). The investigation primarily categorises the literature according to various methodological issues such as research paradigm, research strategy, base-disciplines, research methods and analysis techniques in order to provide meaningful implications on methodological evolution in seaport research for the period. This study suggests methodological bias in port research to a positivistic paradigm, following a quantitative trajectory moving from conceptual to empirical studies. In addition, the increased use of mathematical modelling and advanced statistical analysis methods is clearly observed. The introduction of advanced analytical tools used in other academic disciplines facilitates discussions in particular research area and amplifies the literature in those areas. This paper also suggests research gaps from the methodological perspective and implications for future port research.     

A network option portfolio management framework for adaptive transportation planning

A real option portfolio management framework is proposed to make use of an adaptive network design problem developed using stochastic dynamic programming methodologies. The framework is extended from Smit’s and Trigeorgis’ option portfolio framework to incorporate network synergies. The adaptive planning framework is defined and tested on a case study with time series origin-destination demand data. Historically, OD time series data is costly to obtain, and there has not been much need for it because most transportation models use a single time-invariant estimate based on deterministic forecasting of demand. Despite the high cost and institutional barriers of obtaining abundant OD time series data, we illustrate how having higher fidelity data along with an adaptive planning framework can result in a number of improved management strategies. An insertion heuristic is adopted to run the lower bound adaptive network design problem for a coarse Iran network with 834 nodes, 1121 links, and 10 years of time series data for 71,795 OD pairs.     

Some unsettling maritime terms: the interpretation of found, cargo, ballast and voyage

This paper examines the meaning of four common maritime and admiralty terms: found, cargo, ballast and voyage . These terms are problematic because their definitions are elastic which makes application of the terms difficult. The four terms are important because significant legal consequences are attached to each of them, particularly for seamen on flags of convenience (FOC) and crews of convenience (COC) vessels in US ports. The findings of the author are based on personal experience as well as research conducted in preparation as an expert witness in several maritime cases in both the US District Courts and in Louisiana State Courts, personal interviews with seamen on FOC/COC vessels, interviews with legal and economic experts on the international maritime industry and officials of national and international labour organizations.     

Mesoscale subduction at the Almeria–Oran front: Part 1: Ageostrophic flow

This paper presents a detailed diagnostic analysis of hydrographic and current meter data from three, rapidly repeated, fine-scale surveys of the Almeria–Oran front. Instability of the frontal boundary, between surface waters of Atlantic and Mediterranean origin, is shown to provide a mechanism for significant heat transfer from the surface layers to the deep ocean in winter. The data were collected during the second observational phase of the EU funded OMEGA project on RRS Discovery cruise 224 during December 1996. High resolution hydrographic measurements using the towed undulating CTD vehicle, SeaSoar, traced the subduction of Mediterranean Surface Water across the Almeria–Oran front. This subduction is shown to result from a significant baroclinic component to the instability of the frontal jet. The Q-vector formulation of the omega equation is combined with a scale analysis to quantitatively diagnose vertical transport resulting from mesoscale ageostrophic circulation. The analyses are presented and discussed in the presence of satellite and airborne remotely sensed data; which provide the basis for a thorough and novel approach to the determination of observational error.     

Estimates of vertical mixing during a Lagrangian experiment off the Galician coast

An adjoint 1-D model was used to determine vertical diffusivity coefficients from temperature profiles collected within a filament escaping from the Galician coast following an upwelling event. The optimisation scheme ended with relatively high diffusivity values within the thermocline (9×10⁻⁵ m² s⁻¹). Such high values are relevant for biogeochemical exchanges between surface and deep waters in stratified areas.The optimised values were several orders of magnitude higher than the bulk of diffusivity measurements recorded with a free-falling device; however, the optimisation solution was consistent with the arithmetic mean of the measurements in the thermocline (7.7×10⁻⁵ m² s⁻¹), giving more weight to the few largest values. Below the thermocline, the data assimilation method failed because of the three-dimensional nature of the advective field of the upwelling system. Ignoring this advective forcing in the model led to estimates that were two orders of magnitude too high.The results suggest that turbulent mixing is a random process where a few intense events determine the average mixing that drives the long-term evolution of the water column structure. This statistical property is very important when one wants to use instantaneous diffusivity measurements for modelling purposes.     

Response of carbon fiber trapezoidal corrugated sandwich structure under air explosion loading北大核心CSCD

The effects of the thickness of the face plate, angle of the wall plate and height of the core layer on the anti-explosion performance of carbon fiber reinforced composite trapezoidal corrugated sandwich structures were investigated. [Methods]First, based on the 3D Hashin failure criterion, a subroutine module of the damage evolution of fiber reinforced composites is developed using the VUMAT user subroutine interface in ABAQUS. Second, through comparison with experiments in the public literature, the effectiveness of the dynamic response simulation method of carbon fiber reinforced composites based on a development subroutine under explosion impact loading is verified. Finally, a parametric study on the explosion resistance of carbon fiber reinforced composite trapezoidal corrugated plates is carried out based on the numerical method. [Results]The results show that, compared with increasing the thickness of the blast face panel, increasing the thickness of the back blast face panel can improve the explosion resistance of the sandwich plate more obviously; when the folding angle of the core wall plate decreases from 45° to 30°, the explosion resistance increases by 1.3%; when it decreases from 60° to 45°, the explosion resistance increases by 6.3%; and whenthecoreheightincreasesfrom8mmto20mm, theexplosionresistanceincreasesby27.7%.[Conclusions]The results of this study can provide references for the explosion-proof design of carbon fiber reinforced composite sandwich structures. © 2023 Journal of Nanjing Agricultural University. All rights reserved.     

RECENT DEVELOPMENT OF PROCESS SIMULATION AND ITS APPLICATIONS TO MANUFACTURING PROCESSES

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