Three-dimensional fluid-structure interaction case study on cubical fluid cavity with flexible bottom

In this paper, we report our study on a numerical fluid-structure interaction problem originally presented by Mok et al.(2001) in two dimensions and later studied in three dimensions by Valdés Vazquez(2007), Lombardi(2012), and Trimarchi(2012). We focus on a 3D test case in which we evaluated the sensitivity of several input parameters on the fluid and structural results. In particular, this analysis provides a starting point from which we can look deeper into specific aspects of these simulations and analyze more realistic cases, e.g., in sails design. In this study, using the commercial software ADINATM, we addressed a well-known unsteadiness problem comprising a square box representing the fluid domain with a flexible bottom modeled with structural shell elements. We compared data from previously published work whose authors used the same numerical approach, i.e., a partitioned approach coupling a finite volume solver(for the fluid domain) and a finite element solver(for the solid domain). Specifically, we established several benchmarks and made comparisons with respect to fluid and solid meshes, structural element types, and structural damping, as well as solution algorithms. Moreover, we compared our method with a monolithic finite element solution method. Our comparisons of new and old results provide an outline of best practices for such simulations.     

基于扩张观测器的船舶动力定位系统反演滑模变结构控制

针对海洋平台船舶动力定位控制系统,结合反演滑模控制与扩张观测器的优势,提出一种基于扩张观测器的船舶动力定位反演滑模控制方法.考虑到系统存在未知外部干扰以及船舶模型参数不确定性的问题,将系统分为内环观测器和外环控制器分别设计,首先利用扩张观测器估计系统的未知状态及不确定项,然后在外环的反演滑模控制器中进行补偿,最后用Lyapunov方法证明系统的稳定性.通过船舶定点控制仿真实验表明,基于扩张状态观测器的反演滑模控制器使得船舶纵荡和横荡的位置及首摇角度逐渐保持在期望值,具有较强的鲁棒性和控制性,能够有效抑制传统滑模控制的抖振问题,有益于船舶工程应用.     

Evaluating air emission inventories and indicators from cruise vessels at ports

This paper provides an estimation of air emissions (CO₂, NO_X, SO_X and PM) released by cruise vessels at the port level. The methodology is based on the “full bottom-up” approach and starts by evaluating the fuel consumed by each vessel on the basis of its individual port activities (manoeuvring, berthing and hoteling). The Port of Barcelona was selected as the site at which to perform the analysis, in which 125 calls of 30 cruise vessels were monitored. Real-time data from the automatic identification system (AIS), factor emissions from engine certificates and vessel characteristics from IHS Sea-web database were also collected for the analysis. The research findings show that the most appropriate indicators are inventory emissions per “port-time gross tonnage”, “port-time passenger” and “port time”. These emission indicators improve our understanding of cruise emissions and will facilitate the work that aims to estimate reliably and quickly the in-port ship emission inventories of cruise ports.     

Shared pilot passage plan and navigational safety during pilotage

Navigating in confined waters with a pilot aboard requires that the pilot’s intention and plan is understood by all present on the bridge. The present study investigates the effect of having a detailed route plan and monitoring it in the context of pilotage. The aim was to see how the presence of a shared pilot passage plan in the Electronic Chart Display and Information System (ECDIS) affects the identification and recovery from navigational errors made by a pilot. Twenty participants, 10 with a shared route plan and 10 without, participated as navigators in a simulator scenario involving pilotage in the Oslofjord. Participants were bachelor students in nautical science. The navigation scenarios involved the intentional error by the pilot just before a predefined way point. Three measurements of relevance to navigational safety were recorded: (1) the time it took the participant to express concern, (2) the time it took the participant to correct the error (‘time to recovery’), and (3) the number of groundings. The study revealed that time to express concern and time to recovery were significantly much shorter for the group with a shared pilot passage plan presented in ECDIS than for the group without such a plan. Providing a bridge team with a shared pilot passage plan in ECDIS during pilotage might improve the ability to identify and correct navigational errors.     

Response-based analysis for Tension Leg Platform

The typical industry practice for Tension Leg Platform (TLP) design focuses on a conventional short-term design recipe, which assumes that an N-year design environment leads to an N-year response. In the response-based design method, the TLP is designed to withstand N-year responses rather than respond to N-year environmental conditions. In this paper, we present an overview and a general procedure for the response-based design method and use a case study to compare the critical TLP responses between the two methods. The results of our comparison show that the conventional short-term design method often contains an element of conservatism and that the response-based design method can reduce the design conditions and thereby achieve cost savings.     

船舶动力定位自适应滤波器设计

传统的陷波滤波器虽然能够很好的滤除一阶高频海浪波,但是滤波的同时也使得信号产生了相位滞后,在时域里面的表现就是信号的延时.卡尔曼滤波器虽然能够解决这一问题,但是其非常依赖于船舶模型.本文针对传统陷波滤波器的缺陷,使用了一种积分补偿型陷波滤波器,对传统的陷波滤波器进行改进.并以某拖轮为仿真对象进行仿真实验,其结果表明,该滤波器不但能够很好的滤除高频海浪波,还能够保持很好的相位特性.同时,递推的最小二乘估计(RLS)方法能够实时的估计出海浪的主导波频,使得陷波滤波器具有很好的自适应性.     

Users’ perceptions and willingness to pay in interurban toll roads: identifying differences across regions from a nationwide survey in Spain

Users’ acceptability is considered one of the key drivers for the successful implementation of transport policy measures. This is especially crucial in the case of toll roads since they are financed through drivers’ contributions. Previous literature in this field has mainly focused on measuring users’ attitudes towards urban congestion pricing strategies. However limited research has been developed concerning interurban toll roads. Previous research shows that socioeconomic variables are not conclusive to explain users’ perceptions towards tolls. By contrast, other drivers such as regional differences seem to play a more important role, especially when charging conditions within the same nation greatly vary across regions. This paper analyzes regional differences in users’ attitudes within an asymmetrical distribution of the toll road network across regions. Based on a nationwide survey conducted to road users in interurban toll roads in Spain, we develop both a binomial logit and a censored regression (tobit) model to explore drivers’ perceptions and willingness to pay. The research concludes that users from regions with a more extensive tolled network generally show a more negative attitude towards charges, but not necessarily a lower willingness to pay. The paper also points out that an asymmetrical distribution of toll roads across regions may result in negative perceptions among those users perceiving to be unfairly treated when compared to citizens in other regions.     

An activity-based approach of investigating travel behaviour of older people

The paper presents the results of an investigation on daily activity-travel scheduling behaviour of older people by using an advanced econometric model and a household travel survey, collected in the National Capital Region (NCR) of Canada in 2011. The activity-travel scheduling model considers a dynamic time–space constrained scheduling process. The key contribution of the paper is to reveal daily activity-travel scheduling behaviour through a comprehensive econometric framework. The resulting empirical model reveals many behavioural details. These include the role that income plays in moderating out-of-home time expenditure choices of older people. Older people in the highest and lowest income categories tend to have lower variations in time expenditure choices than those in middle-income categories. Overall, the time expenditure choices become more stable with increasing age, indicating that longer activity durations and lower activity frequency become more prevalent with increasing age. Daily activity type and location choices reveal a clear random utility-maximizing rational behaviour of older people. It is clear that increasing spatial accessibility to various activity locations is a crucial factor in defining daily out-of-home activity participation of older people. It is also clear that the diversity of out-of-home activity type choices reduces with increasing age and older people are more sensitive to auto travel time than to transit or non-motorized travel time.     

Bicycle mode share in China: a city-level analysis of long term trends

In the past 15 years, cities in China have experienced big changes in socioeconomic and traffic conditions, resulting in a long term change in bicycle use. This study aims to quantify the changes in bicycle mode share in Chinese cities and explore the potential causes. Based on data from 51 cities, it is found that bicycle mode share at the city level decreased gradually in the past. Conventional bicycle mode share decreased with a rate of 3 % per year, but electric bicycle mode share increased with a rate of 2 % per year. The correlations between city features such as demographics and built environments and bicycle mode share at different city sizes are compared. The generalized linear models are estimated to relate the changes in the share of different trip modes to various city-level factors. The results show that the bicycle mode share in a city is impacted by factors including city area size, population density, number of cars, percentage of local road mileage among all roads, and trip purpose. Possible reasons for the changes in bicycle uses in Chinese cities are explored and policy implications are discussed.     

Cost and time damping: evidence from aggregate rail direct demand models

There is a significant body of evidence from both disaggregate choice modelling literature and practical travel demand forecasting that the responsiveness to cost and possibly to time diminishes with journey length. This has, in Britain at least, been termed ‘Cost Damping’, and is recognised in guidance issued by the UK Department for Transport. However, the consistency of the effect across modes and data types has not been established. Cost damping, if it exists, affects both the forecasting of demand and our understanding of behaviour. This paper aims to investigate the evidence for cost and time damping in rail demand using aggregate rail ticket sales data. The rail ticket sales data in Britain has, for many years, formed the basis of analysis of a wide range of impacts of rail demand. It records the number of tickets sold between station pairs, and it is generally felt to provide a reasonably accurate reflection of travel demand. However, the consistency of these direct demand models with choice modelling and highway demand model structures has not been investigated. Rail direct demand models estimated by ticket sales data indicate only slight variation in the fare elasticity with distance, as is evidenced in the largest meta-analysis of price elasticities conducted to date (Wardman in J Transp Econ Policy 48(3):367–384, 2014). This study of UK elasticities shows strong variation between urban and inter-urban trips, presumably a segmentation at least in part by purpose, but less remaining variation by trip length. A lack of variation by length supports the hypothesis of cost damping, because constant cost sensitivity would imply that fare elasticity would increase strongly with distance, because of the increasing impact of higher fares at longer distances. In this paper we indicate that rail direct demand models have some consistency of behavioural paradigm with utility based choice models used in highway planning. We go on to use rail demand data to estimate time and fare elasticities in the context of various cost damping functions. Our empirical contribution is to estimate time elasticities on a basis directly comparable with cost elasticities and to show that the phenomenon of cost damping is strongly present in ticket sales data. This finding implies that cost damping should be included in models intended for multimodal analysis, which may otherwise give incorrect predictions.