考虑拱上建筑联合作用的石拱桥有限元分析

建立石拱桥有限元模型时,为使结果更接近实际受力情况,需考虑拱上建筑联合作用影响.以此为基础,提出横向系杆法和等代拱法2种方法改进计算模型,并在工程实例中论证2种方法的可行性和有效性.为石拱桥的承载力评估和加固等提供指导.     

Multi-scale modeling of fatigue crack propagation applied to random sequence of clustered loading

Fatigue crack propagation in marine structures is obviously governed by mechanics of the considerably different four levels of multi-scale problems. Problems of structural response to environmental loads have length scale of several hundred meters, whereas possible detectable size of cracks from initial defects in a weld is of the order of millimeters. Once a fatigue crack initiates, crack tip plasticity is of the order of several grain sizes, while the resulting fatigue crack growth in each load cycle is of the order of nanometers. In our previous work, the first author and their associates have developed the so-called CP-System, which can treat the first two multi-level problems as an integrated system. Furthermore, we have incorporated the third level of mechanics by using the stress intensity range corresponding to the repeated tensile plastic deformation ahead of the crack tip. In the present paper, we shall discuss a more rational integral equation-based formulation in order to integrate the third and fourth levels of micro-mechanics to the first two levels of continuum mechanics.The method is then applied to fatigue crack propagation under the effects of random sequence of clustered loading. As an example of the random sequence of clustered load, we shall use the so-called “storm model”. In the crack propagation simulation, we have to take into account of the plastic wake on the crack surfaces, whose thicknesses are influenced by the material parameters involved in the crack growth model. These parameters are first identified by the fatigue tests under combined constant and random loading using a CT specimen. Then, fatigue crack growth is investigated by numerical simulation and fatigue tests for various random sequences of clustered loading. The experimental and numerical results agree quite well with each other, and fatigue crack propagation is found to be considerably retarded under random sequence loading, so that the conventional equivalent stress approach may provide rather conservative results to the real seaway loading.     

Dynamic calculation of ship exhaust emissions based on real-time AIS data

The activity-based methodology is becoming an increasing way to calculate exhaust emissions from ships in a port. Existing studies make great effort to build and analyze ship emission inventory in a variety of ports by applying this method to historical ship trajectory data. This kind of static emission inventory however, cannot meet the needs of real-time ship emission monitoring. This article proposes a method of dynamic calculation of ship exhaust emissions based on real-time ship trajectory data. Firstly, real-time ship AIS messages are partitioned into continuous data blocks and go through a series of pre-processing operations, including trajectory extraction, association and interpolation. Ship activity parameters are then determined by database querying and regression analysis based on ship attributes. Subsequently, an improved activity-based methodology is employed to estimate exhaust emissions from ships in a distributed way. Based on the grid model, regional ship exhaust emissions can be statistically and dynamically calculated by the spatial allocation of all ship emissions. In a case study, a real-time monitoring platform for ship exhaust emissions in Shenzhen port is developed to demonstrate the effectiveness of the proposed method.     

Efficiency of a highway use reservation system for morning commute

This paper examines the design and efficiency of a highway use reservation system where commuters need reservations to access a highway facility at specific times. We show that, by accommodating reservation requests to the level that the highway capacity allows, traffic congestion can be relieved. Generally, a more differentiated design of the reservation system yields a higher reduction of travel cost and thus achieves a higher efficiency. The efficiency bound of the system is established. We also show that braking or tactical waiting behaviors of drivers would cause a loss of efficiency, which thus need be proactively accommodated. Given that user heterogeneity cause further loss of efficiency, we explore how two specific types of user heterogeneity affect the system efficiency. Auction-based reservation is then proposed to mitigate the efficiency loss.     

LNG-fuelled fishing vessels: A systems engineering approach

Air emissions from fishing vessels must be reduced to comply with progressively stringent environmental regulations. Among the available solutions, liquefied natural gas (LNG) fuel may represent a promising solution, particularly from an environmental perspective. However, the use of LNG as a marine fuel creates different types of hazards than those that exist for traditional fuels. In addition, the increased complexity, safety requirements, and space required for LNG installation increase the capital cost. This article uses a systems engineering approach to clarify the technical aspects of LNG-fuelled systems, their potential implementation costs, and the expertise and training required to operate them safely. Ship owners can use such an approach to aid decision-making and trade-off analyses. Naval architects may also benefit from better information management. Finally, crews may better understand the logic behind the safety actions they are instructed to take.     

Ship emissions and their externalities in cruise ports

This paper presents an estimation and analysis of ship exhaust emissions and their externalities in the popular cruise destinations of Dubrovnik (Croatia) and Kotor (Montenegro) along the eastern coast of the Adriatic Sea. To this extent, the recent record (2012–2014) of cruise ships calling at these ports is used to model and estimate the ship exhaust emission inventories and externalities within the associated bays and ports.The results indicate that cruise ship traffic produces continuously increasing air pollution in both ports over recent years. More importantly, however, the analysis of the ship operating characteristics reveals that for any given ship traffic involving specific vessels using marine fuel of a given quality, the presence of other factors (e.g. berth availability, berth accessibility etc) can also influence the ship emission levels. This is particularly evident in the case of the port of Kotor where berth space insufficiency dictates the need for ship anchorage thus leading to increased air pollution and costs of associated damage.The application and results of the aforementioned ship activity-based methodology to the ports of Dubrovnik and Kotor improves our understanding of ship emissions in cruise bays and ports, and contributes toward the implementation of port policies for the effective control of air quality in such environmentally sensitive locations.     

The “Mirror Flags”: Ship registration in globalised ship breaking industry

The incorporation of new international regulations is a rational way to avoid the use of substandard Asian ship-breaking yards. However, more restrictive regulations and agreements could lead to increase the proliferation of the use of third countries in connection with ship recycling industry. The new Open Registries provides ship-owners with legal loopholes in order to avoid strict national legislations and international rules, thus the “genuine link” disappears and the ship-owner’s responsibilities relax. Ship-breaking industry is a complex interconnected system with many important key actors, such as shipping companies, ship-owners, ship registries, brokers, and ship-breaking yards, all of which are discussed in this paper under the vision of a new global ship recycling policy, and focusing in those cases when a ship changes its flag state registration just before scrapping. This paper analyses the most common flags selected in order to send ships for scrapping. Empirical investigation to determine the relation between States and ship-breaking industry has been carried out using the multivariate statistic technic known as “Simple correspondence analysis”. The results show a relation between ship registry selection and ships that are about to end their lives, re-flagging solely for the purpose of scrapping. If we observe the evolution of the different flag states at the end of the ship’s life, we find incremented use of new open registers or “Mirror Flags”. General abuse of new registries in ship-breaking industry would lead to a ship-breaking industry without rules or transparent procedures, which could violate labour and environmental standards.     

Simplified analytical method for evaluating web girder crushing during ship collision and grounding

The paper presents a simplified analytical method to examine the crushing resistance of web girders subjected to local static or dynamic in-plane loads. A new theoretical model, inspired by existing simplified approaches, is developed to describe the progressive plastic deformation behaviour of web girders. It is of considerable practical importance to estimate the extent of structural deformation within ship web girders during collision and grounding accidents. In this paper, new formulae to evaluate this crushing force are proposed on the basis of a new folding deformation mode. The folding deformation of web girders is divided into two parts, plastic deformation and elastic buckling zones, which are not taken into account for in the existing models. Thus, the proposed formulae can well express the crushing deformation behaviour of the first and subsequent folds. They are validated with experimental results of web girder found in literature and actual numerical simulations performed by the explicit LS-DYNA finite element solver. The elastic buckling zone, which absorbs almost zero energy, is captured and confirmed by the numerical results. In addition, the analytical method derives expressions to estimate the average strain rate of the web girders during the impact process and evaluates the material strain rate sensitivity with the Cowper-Symonds constitutive model. These adopted formulae, validated with an existing drop weight impact test, can well capture the dynamic effect of web girders.     

Low carbon maritime transport: How speed,size and slenderness amounts to substantial capital energy substitution

Three responses that reduce energy consumption and CO₂ emissions in maritime transport are slower speeds, larger vessels and slender hull designs. We use crude oil carriers as our illustrative example; these represent nearly a quarter of international sea cargo movements. We estimate the potential and costs in these which can all be described as capital substituting for energy and emissions. At different degrees of flexibility and time scales: speed reductions are feasible immediately when there are vessels available, though more capital will be tied up in cargo. Deployment of larger and more slender vessels to a greater extent requires fleet renovation, and also investments in ports and infrastructure. A novel finding in our analysis is that if bunker costs rise as a result of emission costs (fees, quotas), then this may depress speeds and emissions more than if they result from higher oil prices. The reason is that for higher oil prices, more capital tied up in cargo may give cargo owners an interest in speeding up, partly counteracting the impulse from fuel costs that tends to slow vessels down. Emission costs, in contrast, do not raise cargo values.     

Operational profiles of ships in Norwegian waters: An activity-based approach to assess the benefits of hybrid and electric propulsion

Various regulations are imposed on shipping to increase energy efficiency and reduce environmental impacts. Alternative fuels and power systems are among the solutions for compliance with these regulations. The power system of a ship may not operate optimally because of the diversity of the operational profile during its lifetime. This article uses an activity-based approach and big data from the Automatic Identification System (AIS) to study the operational profiles of eight ship types operating in Norwegian waters around mainland Norway in 2016. The aim is to identify ship types that can benefit from electric and hybrid propulsion through analysis of their operational profiles. Close to shore, the operational profiles of various ship types are similar, and all ships spend a great proportion of their time with lower loads. As the distance from shore increases, the operational profiles of various ship types follow distinct trends. Among the considered ship types, reefers spend more operational time close to the diesel engine design condition. On the other hand, offshore and passenger ships show the most dynamic operational profiles and spend a large percentage of their operational time with a partial load, away from diesel engine design conditions. Such ships can benefit from hybridisation, diesel-electric propulsion, and other electric concepts, such as batteries and fuel cells. Another option is to downsize diesel engines for better operation while fuel cells and batteries supply peak and partial loads. Operational profiles are plotted and details of the approach are presented in the article.