Fatigue of jack-ups: Simplifying calculations

Simplification of calculations for fatigue of jack-ups is essential in order to understand the primary influences and the uncertainties involved. Considerable simplification is possible for jack-ups because calculations for fatigue are dominated by the few worst loading conditions, while the large number of lesser conditions can be ignored. The dominating conditions are likely to be — during operations, the resonant sway and surge motions at the natural period of the structure; and during towage, the 1 or 2 days of maximum roll and pitch motions. Examples for both situations examine loading conditions and demonstrate simplified calculations.     

荷兰铁路最新研究成果

荷兰铁路最新研究集中在开发用户友好工具以利用标准的列车检测数据对车站晚点列车进行实验分析、建立不同线路列车到发晚点时间分布的随机模型。根据位于荷兰车站Hague HS的轨道电路对近10000次列车运行自动检测可以证明，TNV－Prepare软件工具可以很好地记录列车占用和释放时间以及列车速度。若一条线路上晚点时间很短（1分钟以下）或晚点时间长（5分钟以上）的次数不是太大，发车晚点分布在很多情况下符合一种指数分布。用一种新的工具对大铁路网的时刻表以及在中转车站的相互连接的线路之间的晚点的扩散进行了分析，将列车描述成一个基于Max-Plus线性系统的间断事件系统（DES）。它有助于确定网络中的关键环路，交叉线路时刻表的剩余间隙以及网络中的晚点扩散。另一个铁路研究领域是线路基础设施养护维修与更新改造的寿命周期成本估算的决策支持系统，该系统经证明对不同线路上部结构设计的寿命周期成本的估算非常有效，对轨道和道岔养护维修与更新改造计划规则的修改也十分有效。     

Generalized magnetorheological (MR) damper model and its application in semi-active control of vehicle suspension system

In this paper, analytical characterization of the magneto-rheological (MR) damper is done using a new modified algebraic model. Algebraic model is also more preferable because of its low computational expenses compared to differential Bouc-Wen’s model which is highly computationally demanding. This model along with the obtained model parameters is used as a semi-active suspension device in a quarter car model and the stationary response of the vehicle traversing on a rough road is obtained. The control part consists of two nested controllers. One of them is the system controller which generates the desired damping force and the other is the damper controller which adjusts the voltage level to MR damper so as to track the desired damping force. For the system controller a model reference skyhook Sliding Mode Controller (SMC) is used and for the damper controller a continuous state algorithm is built to determine the input voltage so as to gain the desired damping force. The analytical model is subsequently used in the quarter car vehicle model and the vehicular responses are studied. A simulation study is performed to prove the effectiveness and robustness of the semi-active control approach. Results show that the semi-active controller can achieve compatible performance as that of active suspension controller except for a little deterioration.     

In-situ measurement of loading stresses with X-ray diffraction for yield locus determination

The application of the X-ray diffraction method is introduced to solve the problem of inhomogeneous deformation fields in the specimens used for sheet metal characterization. In this method, strains are measured on one side of a specimen with optical measurement systems. On the other side, loading stresses on a specimen are captured with an X-ray diffractometer mounted on a universal testing machine. By this way, the whole stress-strain history of a material point is tracked during testing. The method was first applied to uniaxial tension tests, whereby the applicability of the theory of stress factors and effective X-ray elastic constants were tested. The relaxation behavior of a sheet material which shows itself as stress drops during in-situ experimentation was characterized and compensated by a visco-plastic material model for different stress states. The proposed method was applied to characterize aluminum alloy AA5182 under plane strain tension and shear conditions and the results were compared with the conventionally obtained yield locus. Numerical analyses of a workpiece with the Vegter and Yld2000-2D material models show that the enriched yield locus definition with accurate plane strain tension and shear stresses captures the experimentally obtained surface strains more precisely.     

Tollroads are only part of the overall trip: the error of our ways in past willingness to pay studies

With rare exception, actual tollroad traffic in many countries has failed to reproduce forecast traffic levels, regardless of whether the assessment is made after an initial year of operation or as long as 10 years after opening. Pundits have offered many reasons for this divergence, including optimism bias, strategic misrepresentation, the promise to equity investors of early returns on investment, errors in land use forecasts, and specific assumptions underlying the traffic assignment models used to develop traffic forecasts. One such assumption is the selection of a behaviourally meaningful value of travel time savings (VTTS) for use in a generalised cost or generalised time user benefit expression that is the main behavioural feature of the traffic assignment (route choice) model. Numerous empirical studies using stated choice experiments have designed choice sets of alternatives as if users choose a tolled route or a free route under the (implied) assumption that the tolled route is tolled for the entire trip. Reality is often very different, with a high incidence of use of a non-tolled road leading into and connecting out of a tolled link. In this paper we recognise this feature of route choice and redesign the stated choice experiment to account for it. Furthermore, this study is a follow up to a previous study undertaken before a new toll road was in place, and it benefits from real exposure to the new toll road. We find that the VTTS is noticeably reduced, and if the VTTS is a significant contributing influence on errors on traffic forecasts, then the lower estimates make sense behaviourally.     

A measure of linked‐trip accessibility

The concept of accessibility has been variously interpreted as being the “nearness to places,” the “nearness to activities” and more recently the “ease of participating in activities.” With each of these qualitative interpretations, there has also been a variety of quantitative definitions of accessibility. This paper shows that many of the proposed definitions of accessibility can in fact be gathered together to form a spectrum of accessibility measures. These measures differ with respect to the factors included in their formulation and their degree of behavioural interpretation.

Existing measures of accessibility are shown to be deficient in one major aspect. That is, they assume that for any one measure of accessibility there is but one origin of trips. Thus, in estimating the accessibility of a point within a region it is assumed that all potential trips, which contribute to the accessibility of that point, start from that single point. In view of the considerable amount of evidence demonstrating the widespread, and increasing, occurrence of trip‐linking such a proposition must be viewed as being rather doubtful.

In the light of this, the paper proceeds to develop a measure of accessibility which explicitly accounts for the linking of trips. The implications of this measure, compared to a conventional unlinked‐trip accessibility measure, are discussed as are some problems which are foreseen in the practical implementation of such a measure.     

Valuing Estuarine Resource Services Using Economic and Ecological Models: The Peconic Estuary System Study

This article summarizes four integrated economic studies undertaken to contribute to resource preservation and restoration decisions for the Peconic Estuary System of Suffolk County, NY. Completed as part of the National Estuary Program, the studies apply distinct resource valuation methods to a wide range of resource issues. The principal goals of this article are to highlight different methodologies that may be used to assess nonmarket economic values in a coastal management context, and characterize differences in the results that one may expect from each approach. We also emphasize potential relationships among values estimated by different nonmarket methodologies, and comment on the implications of these relationships for the interpretation and use of economic value estimates.