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251.
Undoubtedly, the main advantage of the additive manufacture technology is to allow building miniature structural parts with a large degree of complexity such as to replicate structural details of real-scale marine structures. This work presents a new technique for reproducing the structural response of large-scale thin-walled metallic structures when subjected to crushing loadings by using scaled-down additive manufactured models. This technique couples scaling laws for strain rate sensitive materials and a thickness distortion technique based on the structural collapse mode. In order to validate this coupled technique, the structural response of a large-scale crushing test of a web girder structure was experimentally replicated by using a 1/40 scale reduction model. The results and conclusions summarize the prospects and limitations of additive manufacturing of miniature complex marine structures for structural purposes and crashworthiness verification. 相似文献
252.
为分析波浪对船舶快速性和耐波性的影响,必须对波浪中航行的船舶阻力增值进行准确预报。本文基于计算流体力学软件FINE/Marine建立了Wigley船模的数值模型,对不同规则波波长下的船体运动和波浪增阻进行了计算,并与试验结果进行对比,验证了数值模型的可行性与准确性。同时计算分析了船舶在规则波中航行时的波浪增阻与浪向之间的变化关系。通过研究发现:随着浪向角的增大船舶波浪增阻逐渐增加,在60°浪向角时波浪增阻达到最大值,浪向角对波浪增阻的影响较大。本文的研究方法可用于船舶有航速下的不同浪向波浪增阻的数值预报。 相似文献
253.
The exposure temperature significantly affects the diffusion of chloride ions in concrete, and, as such, it must be taken into consideration in the development of service-life prediction models for structures exposed to chloride-bearing environments. Most of the earlier studies have used cement paste to assess the effect of exposure temperature on chloride diffusion. In the reported study, chloride diffusion in Type I and fly ash (20% fly ash) cement concrete was evaluated under field and laboratory conditions. The laboratory concrete specimens were exposed to chloride solution maintained at four temperatures (22, 35, 50 and 60 °C) for 365 days. Beam specimens were exposed in the tidal zone of a marine exposure site, along the Arabian Gulf coast, for up to 10 years to study the chloride diffusion in the field specimens. The coefficient of chloride diffusion (Da) in the concrete specimens exposed to 22 or 35 ᵒC in the laboratory was less than that in the concrete specimens exposed to 50 and 60 ᵒC. The Da for Type I cement concrete specimens increased by 3.6 times as the temperature was increased from 22 to 60 ᵒC while this increase was 2.3 times for the fly ash cement concrete specimens for a similar increase in the temperature. The Da decreased with the period of exposure in the field specimens. The values of activation energy that can be used for predicting the chloride diffusion for exposure temperature within the range of 22–60 °C were developed based on the laboratory data. In addition, mathematical models were developed relating the coefficient of chloride diffusion in the field and laboratory concrete specimens. The developed models can be utilized to ascertain chloride diffusion in field specimens, utilizing the laboratory values, and hence calculate the useful service-life of structures. 相似文献
254.
Maintenance is playing an important role in integrity management of marine assets such as ship structures, offshore renewable energy platforms and subsea oil and gas facilities. The service life of marine assets is heavily influenced by the involvement of numerous material degradation processes (such as fatigue cracking, corrosion and pitting) as well as environmental stresses that vary with geographic locations and climatic factors. The composition of seawater constituents (e.g. dissolved oxygen, salinity, temperature content, etc.) is one of the major influencing factors in degradation of marine assets. Improving the efficiency and effectiveness of maintenance management strategies can have a significant impact on operational availability and reliability of marine assets. Many research studies have been conducted over the past few decades to predict the degradation behaviour of marine structures operating under different environmental conditions. The utilisation of structural degradation data – particularly on marine corrosion – can be very useful in developing a reliable, risk-free and cost-effective maintenance strategy. This paper presents an overview of the state-of-the-art and future trends in asset maintenance management strategies applied to corroded steel structures in extreme marine environments. The corrosion prediction models as well as industry best practices on maintenance of marine steel structures are extensively reviewed and analysed. Furthermore, some applications of advanced technologies such as computerized maintenance management system (CMMS), artificial intelligence (AI) and Bayesian network (BN) are discussed. Our review reveals that there are significant variations in corrosion behaviour of marine steel structures and their industrial maintenance practices from one climatic condition to another. This has been found to be largely attributed to variation in seawater composition/characteristics and their complex mutual relationships. 相似文献
255.
孔晓丽 《武汉船舶职业技术学院学报》2011,(5):97-99,106
文章针对航海院校轮机管理专业学生的三管轮适任证书考试,从把握考试大纲、熟悉教材和题库,多种方式相结合教学,系统复习、融会贯通和加强学生应试能力的训练四个方面论述了如何提高"轮机工程基础"课程的考证一次通过率。 相似文献
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257.
Chains usually form the upper part of moorings systems used for maritime structures such as floating production storage and offloading (FPSO) vessels, increasingly employed in the offshore oil and gas industry particularly in very deep waters. Current design rules do not differentiate between corrosion and inter-link wear. Laboratory experiments are described to determine the rate of wear of model (i.e. small-scale) mooring chains for up to 200,000 wear cycles. Various axial loadings and specific angular displacement were used with testing under either dry or wet conditions and for un-corroded and corroded chain. The results show that tensile force has a significant but non-linear effect on the inter-link wear. The amount of wear is similar for un-corroded and for corroded chains and is lower in wet conditions. 相似文献
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