Tail-Equivalent Linearization Method in frequency domain and application to marine structures

An extension of the Tail-Equivalent Linearization Method (TELM) to the frequency domain is presented. The extension defines the Tail-Equivalent Linear System in terms of its frequency-response function. This function is obtained by matching the design point of the nonlinear response with that of the linearized response, thus guaranteeing the equivalence of the tail probability of the latter and the first-order approximation of the tail probability of the nonlinear response. The proposed approach is particularly suitable when the input and response processes are stationary, as is usually the case in the analysis of marine structures. When linear waves are considered, the Tail-Equivalent Linear System possesses a number of important properties, such as the capability to account for multi-support excitations and invariance with respect to scaling of the excitation. The latter property significantly enhances the computational efficiency of TELM for analysis with variable sea states. Additionally, the frequency-response function of the Tail-Equivalent Linear System offers insights into the geometry of random vibrations discretized in the frequency domain and into the physical nature of the response process. The proposed approach is applied to the analysis of point-in-time and first-passage statistics of the random sway displacement of a simplified jack-up rig model.     

Integrating land use and transport knowledge in strategy-making

There is broad and growing consensus regarding the central place of integrated Land Use and Transport (LUT) strategy development in establishing more efficient and sustainable urban environments. However, empirical evidence shows that such integration is hard to achieve in daily planning practice, due to many institutional barriers and substantive differences. More specifically, the tools developed to support LUT strategy development have very low implementation rates in daily planning practice. This paper introduces the concept of ‘knowledge generation’ as a potentially useful mechanism for closing the gap between support tools and planning practice. Through two specific Dutch planning cases, we analyze the applicability of this concept in supporting integrated LUT strategy development. The paper focuses on the developed strategies, how these differ from current practice, and how knowledge generation supported their development. We argue that socialization produces shared strategies and that effective socialization needs to be supported by efficient mutual exchange between tacit and explicit knowledge. We conclude by discussing the implications of this argument for the wider practice of LUT planning integration.     

A methodology to derive the critical demand density for designing and operating feeder transit services

Feeder lines are one of the most often used types of flexible transit services connecting a service area to a major transit network through a transfer point. They often switch operations between a demand responsive and a fixed-route policy. In designing and running such systems, the identification of the condition justifying the operating switch is often hard to properly evaluate. In this paper, we propose an analytical model and solution of the problem to assist decision makers and operators in their choice. By employing continuous approximations, we derive handy but powerful closed-form expressions to estimate the critical demand densities, representing the switching point between the competing operating policies. Based on the results of one-vehicle and two-vehicle operations for various scenarios, in comparison to values generated from simulation, we verify the validity of our analytical modeling approach.     

The transit network design problem with elastic demand and internalisation of external costs: An application to rail frequency optimisation

In this paper we examine the transit network design problem under the assumption of elastic demand, focusing on the problem of designing the frequencies of a regional metro. In this problem, investments in transit services have appreciable effects on modal split. Neglecting demand elasticity can lead to solutions that may not represent the actual objectives of the design. We propose four different objective functions that can be adopted to assume demand as elastic, considering the costs of all transportation systems (car, bus and rail) as well as the external costs, and we define the constraints of the problem. Heuristic and meta-heuristic solution algorithms are also proposed. The models and algorithms are tested on a small network and on a real-scale network.     

Implementing the street-turn strategy by an optimization model

The street-turn option represents a major strategy for the profitability of shipping companies supplying container-based transportation. This option consists in the distribution of trucks delivering loaded containers to import customers, the subsequent allocation of empty containers to export customers and the final dispatch of loaded containers to departure ports. However, the determination of truck routes is a time-consuming activity for shipping companies, because available information can suddenly change while they are making their decisions. In this paper we aim to propose a decision support tool to quickly determine truck routes and implement the street-turn strategy. This tool is based on an optimization model determining the allocation of empty containers between customers and defining truck routes in a post-optimization phase. We compare routes resulting from the proposed model to the decisions of a real shipping company. Early results indicate that this approach represents a promising support for shipping companies in dealing with street-turns. It can significantly reduce distances travelled by trucks and times requested to determine routes.     

Why Cost Benefit Analysis is perceived as a problematic tool for assessment of transport plans: A process perspective

Academic discussions on Cost Benefit Analysis (CBA) as an appraisal instrument for integrated land use and transportation plans tend to focus on its technical aspects. However, many issues of CBA also arise from process related matters, especially when assessing integrated plans. Using an inductive research design, we explored how these process related issues play out in Dutch planning practices. In two applied research techniques, focus group sessions and open in depth interviews, we focused on process related issues as perceived by CBA participants ranging from plan makers to CBA testers. This article presents the different perceptions of issues in CBA processes. Through these collected perspectives, we found that these issues are multi-layered and present a number of fundamental dilemmas. After relating our empirical data to theory, we conclude that the biggest challenge lies in decreasing the level of mistrust and communication deficits revealed between plan owners and CBA calculators and their respective frames of thinking when assessing complex integrated land use and transportation plans.     

Understanding ship-grounding events

The paper presents a simple procedure to estimate the damage to a ship bottom and the associated seabed topology that results from a dynamic grounding event. The seabed is modeled as a rigid body and parameterized by a quadratic surface, i.e., a paraboloid, which can in principle model a wide range of seabed topologies. A nonlinear finite element program (LS-DYNA) is used to simulate the contact force versus the lateral penetration, from which the horizontal force component of powered grounding is estimated. The simplified procedure for analyzing dynamic and static grounding events is outlined. Simulations are performed for different ship speeds and for different initial levels of obstruction over the keel. It is shown that a static approach may replace the dynamic grounding simulation, thereby considerably reducing the computational work. The static approach allows for the quick estimation of the energy absorption during powered grounding, which is imperative for decision making during critical situations. The ultimate goal of the study is to provide a near real-time prediction of the risk of rupture of the cargo tanks and hull girder failure. Moreover, the residual strength of damaged ships is an important issue that is related to operations involved in the salvage of wrecked vessels, such as re-floatation and towing.     

A cluster analysis of cyclists in Europe: common patterns,behaviours, and attitudes

Transportation - This study uses cluster analysis on a sample of regular cyclists from six European countries (the U.K., the Netherlands, Sweden, Hungary, Italy, and Spain) to shed light on common...     

Transit network design for small-medium size cities

This paper proposes a novel heuristic to solve the network design problem for public transport in small-medium size cities. Such cities can be defined as those with a diameter of a few kilometers with up to a few hundred thousand residents. These urban centers present a specific spatial configuration affecting the land use and mobility system. Transportation demand is widespread in origin and concentrated in a small number of attraction points close to each other. This particular structure of demand (‘many-to-few’) suggests the need for specific methodologies for the design of a transit system at a network level. In this paper, such design methodologies are defined in terms of models and solution procedures and tested on a selected case study. The solution methods show promising results. The key variables of the model are the routes and their frequencies. The constraints of the problem affect the overall demand to be served, the quality of the proposed service (transfer, load factors) and the definition of routes.     

Factors contributing to bicycle–motorised vehicle collisions: a systematic literature review

Bicycle–motorised vehicle (BMV) collisions account for the majority of the recorded bicyclists’ fatalities and serious injuries. This systematic review intends to examine the main factors contributing to BMV collisions. We performed a comprehensive literature review on Scopus, TRID, ProQuest, and Web of Science databases. Fifty-nine English-language peer-reviewed articles met the eligibility criteria and were included in the final analysis. The main factors contributing to BMV collisions identified were classified in accordance with a recently published conceptual framework for road safety. The majority of studies have identified factors related to road users’ behaviour (59.3%) and infrastructure characteristics (57.6%). A minority of studies identified variables related to exposure (40.7%) and vehicles (15.3%) as contributor factors to BMV collisions. A small but significant proportion of studies (20.3%) provided evidence that environmental factors may also play a role, although to a lesser extent, in determining BMV collisions. In addition to the three factors comprised in the applied conceptual framework for road safety, we identified environmental conditions as a category of factors contributing to BMV collisions.