Influence of tacking sequence on residual stress and distortion of single sided fillet submerged arc welded joint

Submerged arc welding (SAW) is advantageous for joining high thickness materials in large structure due to high material deposition rate. The non-uniform heating and cooling generates the thermal stresses and subsequently the residual stresses and distortion. The longitudinal and transverse residual stresses and angular distortion are generally measured in large panel structure of submerged arc welded fillet joints. Hence, the objective of this present work is to quantify the amount of residual stress and distortion in and around the weld joint due to positioning of stiffeners tack. The tacking sequence influences the level of residual stress and proper controlling of tacking sequences is required to minimize the stress. In present study, an elasto-plastic material behavior is considered to develop the thermo mechanical model which predicts the residual stress and angular distortion with varying tacking sequences. The simulated result reveals that the tacking sequence heavily influences the residual stress and deformation pattern of the single sided fillet joint. The finite element based numerical model is calibrated by comparing the experimental data from published literature. Henceforth, the angular distortions are measured from an in-house developed experimental set-up. A fair agreement between the predicted and experimental results indicates the robustness of the developed numerical model. However, the most significant conclusion from present study states that tack weld position should be placed opposite to the fillet weld side to minimize the residual stress.     

Installation strength analysis of subsea flowline jumpers

Subsea flowline jumper (FJ) is basic connection component for the wet oil tree, the subsea pipeline and the riser base, playing an irreplaceable role in the subsea production system. During the installation of FJ, collisions often happen between FJ and other equipment, which may cause serious damage. Besides, as the operating water depth increases, the demand for the installation equipments like the crane and winch will increase. The research of deepwater FJ installation in China is still in the primary stage, so an installation method for deepwater FJ is proposed in this paper. Finite element models of a typical M-shape FJ installation system were built to simulate the installation procedures. Analysis results showed that the installation steps designed for the FJ are feasible and valid for deepwater FJ. In order to ensure the safety of the installation process, the collision-sensitive analysis for the FJ was conducted, and results show that it is necessary to set the pick up speed at a proper value, in order to avoid collision in installation process. Besides, the mechanical characteristics of FJ during the installation were investigated under a range of environmental conditions and it was found that the maximum stress of the FJ always happens at its central position. The basic requirements for the installation equipment were also obtained through the analysis of the main installation steps.     

新一代就地成型密封垫圈（FIPG）——用于汽车进气歧管的液态密封胶

进气歧管是发动机上向气缸输送燃油／空气混合物的装置。近来，两段式进气歧管采用了有机硅就地成型密封垫圈（FIPG）。众所周知，由于硅氧烷主链具有灵活性，因此一定数量的汽油可穿透有机硅FIPG层。随着监管规章的日益严格，汽油渗透性也愈加受到重视，由此，一种新型聚丙烯酸酯FIPG便脱颖而出，大大降低了汽油的渗透率。本次研究针对现今汽车传动系统的密封应用，将该项聚丙烯酸酯FIPG密封胶新技术与有机硅FIPG密封胶进行了比较，同时，还针对铝镁合金的粘附性及耐油性进行了探究。     

Evaluation of risk attitude in the shipping freight market under uncertainty

ABSTRACT

The main purpose of this study is to examine how market participants take risks, in other words, what their risk attitude/preference is, and how their risk attitude could be related to the shipping freight and other markets. To address them, we calibrated the risk attitude of participants in shipping freight markets from 2007 to 2013, and provided an example of the application of risk attitude. For market participants, risk attitude/preference has an important role in understanding shipping freight markets and managing risks under uncertainty. However, risk attitude is not directly observable. To achieve this, we applied a framework that consists of structural model and calibration with market data. We interpreted risk attitude and confirmed that a structural break occurred around 2008 for the calibrated risk attitude parameter. The average risk attitude of market participants tended to be more risk-averse after 2010. We conducted an additional analysis to provide an example of the application of calibrated risk attitude, using structural equation modeling to calculate a latent variable that reflected other commodity markets. We compared the risk attitude parameter and the latent variable, and clarified the relationship between the risk attitude parameter and commodity markets.     

如何在治堵大环境下进行公交线路提速

2013年浙江省各市开展全面治堵工作,其中提高公共交通的服务水平是交通治堵的重点工作,也是城市交通可持续发展的必经之路。公交服务水平的提高不仅追求量的发展,还要保证质的提升,而对公交线路进行提速就是提升公交服务品质的途径之一。本文在城市交通治堵的大环境下,利用治堵的压力和动力,借机调动大量资源,从公交系统内和公交系统外全面、系统、科学地对温州运量最大的前20条线路进行提速。通过方案的逐步落实,3条提速线路效果明显,城市交通也得到进一步改善。     

The importance of being early

This research quantifies the relationship between the cost of earliness and lateness by empirically observing commute trips from two different sources. The first empirical analysis uses individual level travel survey data from six metropolitan regions while the second analysis uses traffic data from the Twin Cities freeway network. The analysis conducted in this research provides a method to estimate the ratio of the costs of earliness to lateness for different datasets. This can be a useful tool for traffic engineers and planners, to assist them in the development and implementation of improved control strategies for congested cities. The results also corroborates the hypothesis of earliness being less expensive than lateness and show that the finding holds steady over time and across different regions and levels.     

Financial lessons from Asian experience in constructing and operating high speed train networks

A serious interest in high speed train has been increasing all over the world. However, recent experiences in Asian countries show that high speed rail projects are not financially viable even in areas seemingly favorable to rail operations. Considering the existing intensive highway and airline network, putting public subsidies to high speed rail projects are barely justifiable from a purely economic point of view. What is required of any government which contemplates high speed rail construction as a policy option is to show taxpayers the cost/revenues difference between constructing a high speed rail line and expanding a capacity of other means, before proceeding.     

Uncertain benefits: Application of Bayesian melding to the Alaskan Way Viaduct in Seattle

Uncertainty is inherent in major infrastructure projects, but public decision-making for such projects ignores it. We investigate the uncertainty about the future effects of tearing down the Alaskan Way Viaduct in downtown Seattle, using an integrated model of housing, jobs, land use and transportation, on outcomes including average commute times. Our methodology combines the urban simulation model UrbanSim with the regional transportation model. We assess uncertainty using Bayesian melding, yielding a full predictive distribution of average commute times on 22 different routes in 2020. Of these routes, 14 do not include the viaduct and eight do. For the 14 base routes that do not include the viaduct, the predictive distributions overlap substantially, and so there is no indication that removing the viaduct would increase commute times for these routes. For each of the eight routes that do include the viaduct, the 95% predictive interval for the difference in average travel times between the two scenarios includes zero, so there is not strong statistical support for the conclusion that removing the viaduct would lead to any increase in travel times. However, the median predicted increase is positive for each of these routes, with an average of 6 min, suggesting that there may be some measurable increase in travel time for drivers that use the viaduct as a core component of their commute.     

Wave impact underneath horizontal decks

The problem of water impact on a fixed horizontal platform deck from regular incident waves was studied. Two-dimensional potential flow was assumed, and the resulting boundary-value problem was solved by three alternative numerical methods, a method based on a generalization of the impact theory by Wagner, and two different nonlinear boundary-element methods. The Wagner-based method used a von Karman approach during the water exit phase, i.e., when the wetted surface decreases. Experiments of the impact on an idealized platform deck have been performed to validate the theory. Comparisons show that the Wagner-based method yields good results for the water entry phase, when the wetted deck area increases, but poor results when the wetted area diminishes. The boundary-element methods compare well with experiments for the entire impact process. A Kutta condition is necessary at the aft body–free surface intersection during water exit and when the flow separates from the aft edge. Gravity effects matter for the water exit phase.