Hydroelastic analysis of a rectangular plate subjected to slamming loads

A hydroelastic analysis of a rectangular plate subjected to slamming loads is presented. An analytical model based on Wagner theory is used for calculations of transient slamming load on the ship plate. A thin isotropic plate theory is considered for determining the vibration of a rectangular plate excited by an external slamming force. The forced vibration of the plate is calculated by the modal expansion method. Analytical results of the transient response of a rectangular plate induced by slamming loads are compared with numerical calculations from finite element method. The theoretical slamming pressure based on Wagner model is applied on the finite element model of a plate. Good agreement is obtained between the analytical and numerical results for the structural deflection of a rectangular plate due to slamming pressure. The effects of plate dimension and wave profile on the structural vibration are discussed as well. The results show that a low impact velocity and a small wetted radial length of wave yield negligible effects of hydroelasticity.     

Reliability analysis of ship hulls made of composite materials under sagging moments

An approach is presented to assess the reliability of ship hulls made of composite materials under sagging moments. Buckling, first-ply failure, and ultimate collapse are regarded as the three possible failure modes of ship hulls of composite materials under sagging moments. Reliability estimates were carried out by a combination of the first-order second-moment method and the response surface methodology. A ship hull of composite materials under sagging moments was evaluated and the results showed that the effects on reliability estimates of the model uncertainty in the longitudinal strength of the ship hull, the model uncertainty of the sagging moments, and the sagging moments were significant, whereas the influences of the stochastic characteristics of material elastic moduli were relatively unimportant.     

Behavioral modeling of on-demand mobility services: general framework and application to sustainable travel incentives

Transportation - This paper presents a systematic way of understanding and modeling traveler behavior in response to on-demand mobility services. We explicitly consider the sequential and yet...     

Wheel life prediction model – an alternative to the FASTSIM algorithm for RCF

In this article, a wheel life prediction model considering wear and rolling contact fatigue (RCF) is developed and applied to a heavy-haul locomotive. For wear calculations, a methodology based on Archard's wear calculation theory is used. The simulated wear depth is compared with profile measurements within 100,000?km. For RCF, a shakedown-based theory is applied locally, using the FaStrip algorithm to estimate the tangential stresses instead of FASTSIM. The differences between the two algorithms on damage prediction models are studied. The running distance between the two reprofiling due to RCF is estimated based on a Wöhler-like relationship developed from laboratory test results from the literature and the Palmgren-Miner rule. The simulated crack locations and their angles are compared with a five-year field study. Calculations to study the effects of electro-dynamic braking, track gauge, harder wheel material and the increase of axle load on the wheel life are also carried out.     

An equilibrium algorithm for the spatial aggregation problem of traffic assignment

Present traffic assignment methods require that all possible origins and destinations of trips taking place within a study area be represented as if they were taking place to and from a small set of points or centroids. Each centroid is supposed to represent the location of all trip-ends within a given zone, and this necessarily misrepresents points located at the edges of the zone.In order to alleviate this problem (which we refer to as the spatial aggregation problem) one could use smaller zones and more centroids, but existing traffic assignment algorithms cannot efficiently handle many centroids.This paper introduces an algorithm procedure which is designed to handle a substantially larger number of centroids. In the paper that follows, the technique is further developed to take into account a continuous distribution of population.     

Compressive tests on short continuous panels

Results of eight tests on stiffened panels under axial compression until collapse and beyond are presented. The tests consider panels with different combinations of mechanical material properties and geometric configurations for the stiffeners including the use of ‘U’-shaped stiffeners. The specimens are three bay panels with associated plate made of high tensile steel S690. Four different configurations are considered for the stiffeners that are made of mild or high tensile steel for bar stiffeners and mild steel for ‘L’ and ‘U’ stiffeners. The influence of the stiffener's geometry on the ultimate strength of the stiffened panels under compression is analyzed.     

Study of damaged ship motions taking into account floodwater dynamics

This paper presents an application of shallow water theory to describe the motion of floodwater inside a rolling ship in damage condition. The time domain theoretical approach to the coupled problems of ship and water inside compartment motions is briefly described, including the method used to solve for the water motion characteristics and forces exerted on the ship. This approach is applied to the study of the behaviour of a passenger Ro–Ro ship in regular beam seas and numerical results are given for the intact and damaged conditions. Comparison is made with experimental results. For the damaged condition, the characteristics of the floodwater motion are studied in the time domain for a number of different wave frequencies. The shape of the free-surface and phase of water motion in relation to the ship roll motion are shown for several wave frequencies. The dynamic floodwater roll moment is also shown and compared with the static roll moment (flat horizontal free surface), allowing the conclusion that the dynamic roll moment is much larger than the static roll moment, for high wave frequencies, and is in phase opposition in relation to the roll motion.     

Productivity assessment of African seaports with biased technological change

Abstract

This paper analyses the productivity of a representative sample of African seaports from 2002 to 2008. Productivity scores are decomposed, based on the Luenberger productivity indicator, and the nature of technological change is analysed. The paper finds that Nigerian seaports are the most efficient, followed by Angola and Mozambique. Discussions of the results as well as related policy implications are provided.     

The smoothing effect of carpool lanes on freeway bottlenecks

Real data show that reserving a lane for carpools on congested freeways induces a smoothing effect that is characterized by significantly higher bottleneck discharge flows (capacities) in adjacent lanes. The effect is reproducible across days and freeway sites: it was observed, without exception, in all cases tested. Predicted by an earlier theory, the effect arises because disruptive vehicle lane changing diminishes in the presence of a carpool lane. We therefore conjecture that smoothing can also be induced by other means that would reduce lane changing.The benefits can be large. Queueing analysis shows that the smoothing effect greatly reduces the times spent by people and vehicles in queues. For example, by ignoring the smoothing effect at one of the sites we analyzed one would predict that its carpool lane increased both the people-hours and the vehicle-hours traveled by well over 300%. In reality, the carpool lane reduced both measures due to smoothing. The effect is so significant that even a severely underused carpool lane can in some instances increase a freeway bottleneck’s total discharge flow. This happens for the site we analyzed when carpool demand is as low as 1200 vph.