Optimal design for a VLCC propulsion system based on torsional vibration analysis

AbstractFor main engine changes, shafting torsional vibration of an exported VLCC tanker must be analyzed carefully. With the transition matrix method, the vibration models for the vessel with two different propulsion systems are made. The calculated results show there are forbidden rotated zones which are near to the vessel sailing speed, some necessary measures must be taken to make the forbidden rotated zones change in order that the vessel shafting system is to run safely in the long term instead of main engine changes

Numerical simulations of the sliding impact between an ice floe and a ship hull structure in ABAQUS

This paper studies the hull structural responses of a steel grillage subjected to sliding ice loads, which have been rarely investigated in the literature. Sliding ice loads are modelled using nonlinear finite element analysis (NLFEA) method; and Abaqus Explicit is adopted as the numerical solver. Deformations and damages of ice and steel are both considered. A rigid ice model is also simulated for comparison purposes. The hull’s local structural responses under different load cases, including deformation, contact forces, and energy distribution, have been analysed. The effects of static structure-to-structure friction coefficient and the relative stiffness between ice and structure are studied. It is found that the deformation of structures will increase the total friction coefficient, which is defined as the ratio of the friction force (the tangential contact force) to the normal contact force. When the ice floe is considered rigid, the static friction coefficient has little effect on the local structural responses of the hull. If using a higher-strength steel material for hull structures in the ice-classed ship design, the hull’s deflection and total friction decrease, and the hull dissipates less energy as expected. Moreover, stationary load cases with the same loading condition in the normal direction as sliding load cases are also simulated. When using the deformable ice material model, the simulation results show that the hull’s final contact forces and deflection in stationary load cases are larger than those in sliding load cases. Besides, the effect of steel material is more significant in stationary load cases than in sliding load cases.publishedVersio

OMAE2004-51016 RISK BASED INSPECTION AND REPAIR OPTIMIZATION OF SHIP STRUCTURES CONSIDERING CORROSION EFFECTS

ABSTRACT A theoretical framework of risk based optimal inspection and repair planning is proposed for the ship structures subjected to corrosion deterioration. The planning problem is formulated as an optimization problem where the expected lifetime costs were minimized with a constraint on the minimum acceptable reliability index. The safety margins are established for the inspection events, the repair events and the failure events for ship structures. Moreover, the formulae are derived to calculate failure probabilities and repair probabilities. Based on them, a component subjected to pitting corrosion is investigated to illustrate the process of selecting the optimal inspection and repair strategy. Furthermore, some sensitivity studies were provided. The results show that the optimal inspection instants should take place before the reliability index reaches the minimum acceptable reliability index. The optimal target failure probability is . In addition, a balance can be achieved between the risk cost and total expected inspection and repair costs by using the risk based optimal inspection and repair method, which is very effective in selecting the optimal inspection and repair strategy

OMAE2006-92116 TIME-VARIANT RELIABILITY ASSESSMENT OF FPSO CONSIDERING CORROSION AND COLLISION

ABSTRACT Floating production, storage, and offloading (FPSO) system has been widely used in the offshore oil and gas exploitations. Since it has long intervals of docking for thorough inspection and maintenance, and is exposed to collision risk at sea, the time-variant reliability of FPSO becomes very important as for the risks of corrosion and collision

Analysis of structural strength characteristics of hull girder under ice riding accident

Objectives In order to identify the change in structural strength after an interaction between hull girders and ice, this paper puts forward an analytical technique which can determine the structural strength of hull girders after an ice riding accident and disclose the related structural strength features. MethodsFirst, the hull girder structural strength analysis model and associated load analysis model are constructed in accor-dance with the characteristics of each section. To account for the buoyancy variations brought on by ice riding, the buoyancy distribution of the ice riding conditions is retrieved from the load analysis model and inserted into the structural strength analysis model. Gravity and the reaction force of the ice are then used to determine the structural strength. Finally, an analysis is carried out on the impact of lifting position and height on the buoyancy, shear force, bending moment and local stress distribution of the hull girders. ResultsThe re-sults show that the sites of buoyancy and shear force of the hull girders are situated in the stern part and middle part, and unaffected by changes in the bow lifting height. The shell is closer to the vertical when the lifting position is at the bow of the bulbous bow, making it harder to resist the ice lever support reaction and resulting in the high stress areas becoming comparably larger and more dangerous. ConclusionsThe proposed technique has high computation efficiency and can be used to estimate how hull girders will respond to a signi-ficant bow lift and make preliminary judgments on hull girder construction strength under risky ice riding conditions

Texture development and coercivity enhancement in cast alnico 9 magnets

The effect of Y addition and magnetic field on texture and magnetic properties of arc-melted alnico 9 magnets has been investigated. Small additions of Y (1.5 wt.%) develop a (200) texture for the arc-melted alnico 9 magnet. Such a texture is hard to form in cast samples. To achieve this goal, we set up a high-field annealing system with a maximum operation temperature of 12500 C. This system enabled annealing in a field of 45 kOe with subsequent draw annealing for the solutionized buttons; we have been able to substantially increase remanence ratio and coercivity, from 0.70 and 1200 Oe for the Y-free alnico 0 to 0.90 and 1400 Oe for the Y-doped alnico 9, respectively. A high energy product of 7.3 MGOe has been achieved for the fully heat-treated Y-doped alnico 9. The enhancement of coercvity is believed to arise from the introduction of magnetocrystalline anisotropy from 80 nm Y2Co17- type grains, which are exchange-coupled to the main-phase alnico rods

Transcription factors NF-YB involved in embryogenesis and hormones responses in Dimocarpus Longan Lour

IntroductionNF-YB transcription factor is an important regulatory factor in plant embryonic development.ResultsIn this study, 15 longan NF-YB (DlNF-YB) family genes were systematically identified in the whole genome of longan, and a comprehensive bioinformatics analysis of DlNF-YB family was performed. Comparative transcriptome analysis of DlNF-YBs expression in different tissues, early somatic embryogenesis (SE), and under different light and temperature treatments revealed its specific expression profiles and potential biological functions in longan SE. The qRT-PCR results implied that the expression patterns of DlNF-YBs were different during SE and the zygotic embryo development of longan. Supplementary 2,4-D, NPA, and PP333 in longan EC notably inhibited the expression of DlNF-YBs; ABA, IAA, and GA3 suppressed the expressions of DlNF-YB6 and DlNF-YB9, but IAA and GA3 induced the other DlNF-YBs. Subcellular localization indicated that DlNF-YB6 and DlNF-YB9 were located in the nucleus. Furthermore, verification by the modified 5'RNA Ligase Mediated Rapid Amplification of cDNA Ends (5' RLM-RACE) method demonstrated that DlNF-YB6 was targeted by dlo-miR2118e, and dlo-miR2118e regulated longan somatic embryogenesis (SE) by targeting DlNF-YB6. Compared with CaMV35S- actuated GUS expression, DlNF-YB6 and DlNF-YB9 promoters significantly drove GUS expression. Meanwhile, promoter activities were induced to the highest by GA3 but suppressed by IAA. ABA induced the activities of the promoter of DlNF-YB9, whereas it inhibited the promoter of DlNF-YB6.DiscussionHence, DlNF-YB might play a prominent role in longan somatic and zygotic embryo development, and it is involved in complex plant hormones signaling pathways

A study on the optimization strategies for the service trade structure of Guangdong-Hong Kong-Macao Greater Bay Area

The construction of urban agglomerations and integration of regional economics have become the new trends in Chinese economic development. The economy of Guangdong-Hong Kong-Macao Greater Bay Area plays a significant role in driving regional development and stimulating technological innovation. In this paper, through study on the current situation of trade in service in Guangdong-Hong Kong-Macao Greater Bay Area, the reasons for the improper trade structure are concluded. Through data and case analysis, the factors affecting service trade structure are located. The results of case analysis can offer some useful and viable recommendations for the optimization of service trade structure, which can facilitate the industrial transformation and upgrading in Guangdong-Hong Kong-Macao Greater Bay Area as well as give a fresh impetus to economic growth