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991.
[Objective]This paper aims to establish a dynamic model of a floating raft vibration isolation system with a liquid tank in order to study the mass effect of the liquid medium, tank form, structural stiffness and loading rate on acoustic performance. [Methods]A floating raft system with a cuboidal or cylindrical liquid tank is taken as the research object, and a fluid-structure coupling finite element dynamic model is established. The dynamic force transmission rate and power flow are then used to evaluate the acoustic performance of the system. The influence of the mass effect of the liquid medium, tank form, structural stiffness and loading rate of tank volume on the acoustic performance of the floating raft system are analyzed.[Results]The results show similar laws obtained through the calculation and analysis of the floating raft system with two types of tanks. The structural stiffness of the tank affects the mass effect of the liquid medium in the tank to a certain extent. [Conclusions]If full advantage is to be taken of the liquid mass effect in the tank with a large loading rate to improve the acoustic performance of the floating raft system, the design of the liquid tank and raft structure must have sufficient stiffness. In addition, under the condition that the floating raft structure has sufficient stiffness, its acoustic performance will improve significantly as the tank loading rate increases in the relevant low frequency range. © 2022 Journal of Clinical Hepatology. All rights reserved. 相似文献
992.
为揭示复杂地应力红层泥岩隧道持续底鼓特征及底鼓原因,以某隧道为研究对象,通过长期变形监测、地下水位监测、隧底围岩位移监测等方法对底鼓变形特征进行了统计分析,并结合钻孔取芯岩样分析、地应力测试、围岩膨胀力测试、岩石蠕变试验、数值模拟分析等手段对可能导致隧道底鼓的因素逐一进行了分析。结果表明:受控于近水平层状泥岩以及复杂地应力,隧道部分段落呈现出底鼓时间“不收敛”、底鼓段落“不连续”、底鼓程度“不均衡”的三大特征;隧道岩层产状近水平,岩性为粉砂质泥岩,属于软质岩,未达到膨胀岩判定标准,具有中—低蠕变特性,隧址区地应力场以水平构造应力为主,水平应力在9.5~13.73 MPa之间;隧道开挖后,局部应力集中导致围岩发生蠕变,当蠕变产生的形变压力过大时,仰拱局部进入塑性状态,隧道即产生底鼓。 相似文献
993.
Transportation - The mediation of work practices by information and communication technologies enables knowledge workers to telework from remote non-office locations such as their homes, or to work... 相似文献
994.
Dewan Md Zahurul Islam J. Fabian Meier Paulus T. Aditjandra Thomas H. Zunder Giuseppe Pace 《Research in Transportation Economics》2013
In this paper an introduction to the principles and methods used in logistics and supply chain management is presented. It begins by a discussion on fundamentals and explains the relevant terms. Next policy and practice associated with logistics and freight services are regarded with a focus on the EU policy for the sector which greatly influences the development of logistics chains and services. Mathematical formulation of typical transport and logistics-related problems is also presented followed by a discussion on the concept of sustainability. 相似文献
995.
L. P. Perera J. P. Carvalho C. Guedes Soares 《Journal of Marine Science and Technology》2011,16(1):84-99
This paper focuses on a fuzzy logic based intelligent decision making system that aims to improve the safety of marine vessels
by avoiding collision situations. It can be implemented in a decision support system of an oceangoing vessel or included in
the process of autonomous ocean navigation. Although Autonomous Guidance and Navigation (AGN) is meant to be an important
part of future ocean navigation due to the associated cost reduction and improved maritime safety, intelligent decision making
capabilities should be an integrated part of the future AGN system in order to improve autonomous ocean navigational facilities.
In this study, the collision avoidance of the Target vessel with respect to the vessel domain of the Own vessel has been analyzed
and input, and output fuzzy membership functions have been derived. The if–then rule based decision making process and the
integrated novel fuzzy inference system are formulated and implemented on the MATLAB software platform. Simulation results
are presented regarding several critical collision conditions where the Target vessel fails to take appropriate actions, as
the “Give way” vessel to avoid collision situations. In these situations, the Own vessel is able to take critical actions
to avoid collisions, even when being the “Stand on” vessel. Furthermore, all decision rules are formulated in accordance with
the International Maritime Organization Convention on the International Regulations for Preventing Collisions at Sea (COLREGs),
1972, to avoid conflicts that might occur during ocean navigation. 相似文献
996.
A new simple and accurate shell FE-based structural Hot Spot Stress (HSS) determination method for web-stiffened cruciform joints has been proposed. Local stress of welded joints in full-scale bulk carrier (BC)’s lower stool models subject to bending and pressure loadings are examined. HSSs determined by the proposed method are compared with those derived by Lotsberg’s method and the conventional 0.5t-1.5t extrapolation. As results, following are found:
- (1)
- The local stress of full-scale BC lower stool models with various stool angle and plate thickness can be calculated accurately solely from shell FE results by means of the proposed method.
- (2)
- HSSs of welded joints in full-scale BC lower stool models subject to bending and pressure loadings derived by the proposed method show good agreement with the target HSSs determined from fine solid models. This demonstrates the validity of the proposed method for actual ship structures under the real load.
- (3)
- The excessive safety allowance of HSS determined by the conventional 0.5t-1.5t extrapolation can be reduced substantially by adopting Lotsberg’s method or our proposal. The proposed HSS determination method gives more accurate estimates compared to Lotsberg’s method under the conditions chosen, and the application range of the proposed method is equal to or wider than Lotsberg’s method.
997.
This paper presents an integrated design procedure for determination of structural arrangement and scantlings for the complete structure of small high-speed craft. The purpose of the procedure is to serve as a tool in the preliminary design stage where it enables generation of weight minimized designs with very limited effort. The design procedure is applied in a material concept study for a high-speed patrol craft. The various concepts include single skin and sandwich composites, aluminum and steel. It is demonstrated that the mass of the aluminum hull structure can be reduced from the original 11.7 tonnes to 9.6 tonnes through application of the presented design procedure. The most weight efficient material concept is a carbon-fiber foam-cored sandwich with a structural mass of 4.8 tonnes, which is about 50% less than the refined aluminum version. Through simple hydromechanic analysis, potential for fuel and CO2 emission reductions of 8% for the refined aluminum version and 27% for the carbon-fiber sandwich version in relation to the original craft are indicated. 相似文献
998.
The use of spatial computable general equilibrium (SCGE) models for assessing the economic impacts of transport projects is one of the key items on the research agenda for project appraisal in the Netherlands. These models are particularly suitable for analysing indirect effects of transport projects through linkages between the transport sector and the wider economy. Potentially, according to the literature, indirect effects that are additional to first-order direct cost reductions can turn out to be up to almost 80% in magnitude of the direct impacts. Given the relevance of these models for policy appraisal, experiences with this new modelling approach are important to report. After two years of development and application of SCGE models for transport appraisal, we found that the translation of theory behind the spatial equilibrium models into practical model specifications and empirical applications is a challenging task, and may lead to problems in project appraisal in terms of inaccuracies in the assessment of impacts. This paper discusses some key challenges we encountered with the specification of the Dutch SCGE model RAEM. This chapter is especially useful for researchers developing SCGE applications for use in transport appraisal and those who want to get a better understanding of differences between theoretical and computable SCGE modelling. 相似文献
999.
1000.