Interval estimation in the calibration of certain trip distribution models

This paper argues for interval, rather than point, estimation when calibrating some variants of the trip distribution “gravity” models. Analytic expressions are derived for the approximate asymptotic covariances of least squares and maximum likelihood estimates of the parameters in the impedance function under a variety of conditions. A comparative numerical example, and an application using migration flows, are also presented.     

新转化膜在汽车行业内的应用近况

1 引言 伴随着20世纪初Thomas Coslett及其他众多人士的研究工作,在1943年引入了Jernstadt磷酸盐后,诞生了今天人们所熟知的用于镀锌工艺前预浸处理的含钛磷酸氢二钠溶液.使用该磷酸盐后,可以更快地形成更为细小的磷酸锌晶体组织.过去60多年间,这种基础工艺在众人的努力下愈发精细,但是基本的化学特性及功能仍然保持不变.     

Dynamic stability in following seas: predictive and experimental approaches

This article presents work based on the development of a performance-based stability assessment method. It describes a numerical method used to determine the survival limit for a dynamic intact stability assessment procedure. The numerical method utilises a time-domain vessel motion program to assess the limit for a range of vertical centres of gravity (KG). The appropriateness of the numerical predictions was examined through comparison with model experiment results. Free-running model tests were conducted in regular following waves at discrete KGs. A comparison between the survival limits determined through the numerical and experimental methods is presented. The current International Maritime Organisation (IMO) stability criteria are also evaluated against the numerical and experimental dynamic performance-based stability assessment methods.     

Slam events of high-speed catamarans in irregular waves

Slam events experienced by high-speed catamarans in irregular waves were characterised through experiments using a hydroelastic segmented model. The model was designed to represent the dynamic behaviour of the full-scale Incat 112 m vessel and to allow the measurement of the slam load on the centrebow and wet deck. It was tested in irregular head seas at two speeds relating to Froude numbers of 0.32 and 0.60. Nearly 300 slams were identified in the test data and analysed with respect to kinematic parameters. Slams were found to have a large range of magnitudes, with the largest equivalent to 1785 tonnes full scale (approximately 70% of vessel displacement); however, the majority of events were of relatively low severity. Differences in slam characteristics were found for the two model speeds tested; slams at the slower speed generally occurred further forward on the hull, prior to the wave crest and with a bow down pitch angle. Immersion of the centrebow to the two-dimensional filling height of the cross-section between the centrebow and demihulls is shown to be a better indicator of slam occurrence than immersion to the top of the archway.     

An insight into the slamming behaviour of large high-speed catamarans through full-scale measurements

The slamming behaviour of a large high-speed catamaran has been investigated through the analysis of full-scale trials data. The US Navy conducted the trials in the North Sea and North Atlantic region on a 98 m wave piercer catamaran, HSV-2 Swift, designed by Revolution Design Pty Ltd and built by Incat Tasmania. For varying wave headings, vessel speeds and sea states the data records were interrogated to identify slam events. An automatic slam identification algorithm was developed, considering the measured rate of change of stress in the ship’s structure coupled with the vessel’s pitch motion. This has allowed the slam occurrence rates to be found for a range of conditions and the influence of vessel speed, wave environment and heading to be determined. The slam events have been further characterised by assessing the relative vertical velocity at impact between the vessel and the wave. Since the ship was equipped with a ride control system, its influence on the slam occurrence rates has also been assessed.