首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
In this study, the dynamics of the tendon/top tension riser(TTR) system of a tension-leg platform(TLP) are investigated through an experiment and by using absolute nodal coordinate formulation(ANCF). First, the model test of the TLP system is conducted in the water tank of Harbin Engineering University to examine the motion response of the TLP and the dynamic response characteristics of the tendon and TTR. The test scale ratio is set to 1: 66.3. Then, on the basis of the ANCF, the stiffness, ext...  相似文献   

2.
This paper presents a review of the different International Maritime Organization(IMO) initiatives to improve the ship energy efficiency of new and existing ships, which is considered one of the essential tasks to reduce Greenhouse Gas(GHG) in the maritime industry. First, the IMO effort and initiatives and the different indices suggested by the IMO are presented till the last version of the Marine Environment Protection Committee(MEPC), showing the effect of different technologies on reducing t...  相似文献   

3.
A novel flywheel energy storage(FES) motor/generator(M/G) was proposed for marine systems.The purpose was to improve the power quality of a marine power system(MPS) and strengthen the energy recycle.Two structures including the magnetic or non-magnetic inner-rotor were contrasted in the magnetostatic field by using finite element analysis(FEA).By optimally designing the size parameters,the average speed of FEA results of was 17 200 r/m,and the current was controlled between 62 and 68 A in the transient field.The electrical machine electromagnetism design was further optimized by the FEA in the temperature field,to find the local overheating point under the normal operation condition and provide guidance for the cooling system.Finally,it can be concluded from the comprehensive physical field analysis that the novel redundant structure M/G can improve the efficiency of the M/G and maintain the stability of the MPS.  相似文献   

4.
Submerged vanes are installed on rivers and channel beds to protect the outer bank bends from scouring. Also, local scouring occurs around the submerged vanes over time, and identifying the effective factors on the scouring phenomena around these submerged vanes is one of the important issues in river engineering. The most important aim of this study is investigation of scour pattern around submerged vanes located in 180° bend experimentally and numerically. Firstly, the effects of various parameters such as the Froude number(Fr), angle of submerged vanes to the flow(α), angle of submerged vane location in the bend(θ),distance between submerged vanes(d), height(H), and length(L) of the vanes on the dimensionless volume of the scour hole were experimentally studied. The submerged vanes were installed on a 180° bend whose central radius and channel width were 2.8 and 0.6 m, respectively. By reducing the Froude number, the scour hole volume decreased. For all Froude numbers, the biggest scour hole formed at θ = 15°. In all models, by increasing the Froude number, the scour hole volume significantly increases. In addition, by increasing the submerged vanes' length and height, the scour hole dimensions also grow. Secondly,using gene expression programming(GEP), a relationship for determining the scour hole volume around the submerged vanes was provided. For this model, the determination coefficients(R~2) for the training and test modes were computed as 0.91 and 0.9,respectively. In addition, this study performed partial derivative sensitivity analysis(PDSA). According to the results, the PDSA was calculated as positive for all input variables.  相似文献   

5.
The effects of the temperature,salinity,and fluid type on the acoustic characteristics of turbulent flow around a circular cylinder were numerically investigated for the Reynolds numbers of 2.25 × 10~4,4.5 × 10~4,and 9.0 × 10~4.Various hybrid methodsReynolds-averaged Navier-Stokes(BANS) with the Ffowcs Williams and Hawkings(FWH) model,detached-eddy simulation(DES) with FWH,and large-eddy simulation with FWH-were used for the acoustic analyses,and their performances were evaluated by comparing the predicted results with the experimental data.The DES-FWH hybrid method was found to be suitable for the aero-and hydro-acoustic analysis.The hydro-acoustic measurements were performed in a silent circulation channel for the Reynolds number of 2.25 × 10~4.The results showed that the fluid temperature caused an increase in the overall sound pressure levels(OASPLs) and the maximum sound pressure levels(SPL T) for the air medium;however,it caused a decrease for the water medium.The salinity had smaller effects on the OASPL and SPLT compared to the temperature.Moreover,the main peak frequency increased with the air temperature but decreased with the water temperature,and it was nearly constant with the change in the salinity ratio.The SPLT and OASPL for the water medium were quite higher than those for the air medium.  相似文献   

6.
第10条 取消条款Cancelling Clause 10. Cancelling Clause (a) Should the Vessel not be ready to load (whether in berth or not)on the cancelling date indi cated in Box 21, the Charterers shall have the option of can celling this Charter Party. (b) Should the Owners anticipate that, despite the exercise of due diligence,  相似文献   

7.
With the fast improvement of the technology of refrigeration in reefer containers (hereinafter referred to as 'reefer' or 'reefers'),the scope of containerizable reefer cargos is expanded continuously in the past years,from the fish that should be frozen at minus 60 degrees Celsius to the flower bulbs at 30 degrees Celsius and from the temperature-sensitive goods whose deviation should be less than 1 degree Celsius to the fresh fruits and vegetables controlled by humidityventilation adjustment system.Being an important node in the logistics chain,the container terminal (hereinafter referred to as ‘CT') should pay more attention to these state-of-the-art techniques and adopt the accordingly suitable technology to optimize its reefer monitoring business in order to provide the highly cost-effective services to ship owners (or their agents) and shippers / consignees (or their brokers).  相似文献   

8.
The aim of the present work is to assess the offshore wave energy potential along the Atlantic coast of Morocco. Research works of this paper focus on the identification of the most energetic sites for wave energy converters(WECs) deployment. For this purpose, 11 sites have been explored; all of them are located at more than 40 m depth on the Moroccan Atlantic coast. The wave power at each site is computed on the basis of wave data records in terms of significant wave height and energy period provided by the Wave Watch three(WW3) model. Results indicate that the coast sites located between latitudes 30° 30′ N and 33° N are the most energetic with an annual average wave power estimated at about 30 kW· m~(-1), whereas, in the other sites, the wave power is significantly lower. Moreover, the study of the monthly and seasonal temporal variability is found to be uniform in the powerful sites with values four times greater in winter than in summer. The directional investigation on the significant wave height has shown that for almost all the powerful sites, the incoming waves have a dominant sector ranging between Northern(N) and Western-Northern-Western(WNW) directions.  相似文献   

9.
In the Lagrangian meshless(particle) methods, such as the smoothed particle hydrodynamics(SPH), moving particle semi-implicit(MPS) method and meshless local Petrov-Galerkin method based on Rankine source solution(MLPG_R), the Laplacian discretisation is often required in order to solve the governing equations and/or estimate physical quantities(such as the viscous stresses). In some meshless applications, the Laplacians are also needed as stabilisation operators to enhance the pressure calculation. The particles in the Lagrangian methods move following the material velocity, yielding a disordered(random) particle distribution even though they may be distributed uniformly in the initial state. Different schemes have been developed for a direct estimation of second derivatives using finite difference, kernel integrations and weighted/moving least square method. Some of the schemes suffer from a poor convergent rate. Some have a better convergent rate but require inversions of high order matrices, yielding high computational costs. This paper presents a quadric semi-analytical finite-difference interpolation(QSFDI) scheme,which can achieve the same degree of the convergent rate as the best schemes available to date but requires the inversion of significant lower-order matrices, i.e. 3 × 3 for 3D cases, compared with 6 × 6 or 10 × 10 in the schemes with the best convergent rate. Systematic patch tests have been carried out for either estimating the Laplacian of given functions or solving Poisson's equations. The convergence, accuracy and robustness of the present schemes are compared with the existing schemes. It will show that the present scheme requires considerably less computational time to achieve the same accuracy as the best schemes available in literatures, particularly for estimating the Laplacian of given functions.  相似文献   

10.
Fracture processes in ship-building structures are in many cases of a 3-D character.A finite element (FE) model of an all fracture mode (AFM) specimen was built for the study of 3-D mixed mode crack fracture behavior including modes I,II,and III.The stress intensity factors (SIFs) were calculated by the modified virtual crack closure integral (MVCCI) method,and the crack initiation angle assessment was based on a recently developed 3-D fracture criterion––the Richard criterion.It was shown that the FE model of the AFM-specimen is applicable for investigations under general mixed mode loading conditions,and the computational results of crack initiation angles are in agreement with some available experimental findings.Thus,the applicability of the FE model of the AFM-specimen for mixed mode loading conditions and the validity of the Richard criterion can be demonstrated.  相似文献   

11.
The development of a two dimensional numerical wave tank (NWT) with a rocker or piston type wavemaker based on the high order boundary element method (BEM) and mixed Eulerian-Lagrangian (MEL) is examined. The cauchy principle value (CPV) integral is calculated by a special Gauss type quadrature and a change of variable. In addition the explicit truncated Taylor expansion formula is employed in the time-stepping process. A modified double nodes method is assumed to tackle the corner problem, as well as the damping zone technique is used to absorb the propagation of the free surface wave at the end of the tank. A variety of waves are generated by the NWT, for example; a monochromatic wave, solitary wave and irregular wave. The results confirm the NWT model is efficient and stable.  相似文献   

12.
In this paper, we present our analysis of the non-cavitating and cavitating unsteady performances of the Potsdam Propeller Test Case(PPTC) in oblique flow. For our calculations, we used the Reynolds-averaged Navier-Stokes equation(RANSE) solver from the open-source Open FOAM libraries. We selected the homogeneous mixture approach to solve for multiphase flow with phase change, using the volume of fluid(Vo F) approach to solve the multiphase flow and modeling the mass transfer between vapor and water with the Schnerr-Sauer model. Comparing the model results with the experimental measurements collected during the Second Workshop on Cavitation and Propeller Performance – SMP'15 enabled our assessment of the reliability of the open-source calculations. Comparisons with the numerical data collected during the workshop enabled further analysis of the reliability of different flow solvers from which we produced an overview of recommended guidelines(mesh arrangements and solver setups) for accurate numerical prediction even in off-design conditions. Lastly, we propose a number of calculations using the boundary element method developed at the University of Genoa for assessing the reliability of this dated but still widely adopted approach for design and optimization in the preliminary stages of very demanding test cases.  相似文献   

13.
Responses of the very large floating Structures(VLFS) can be mitigated by implementing oscillating water columns(OWCs). This paper explores the fundamental mechanism of present wave interactions with both structures and examines the hydrodynamic performance of VLFS equipped with OWCs(VLFS-OWCs). Under the linear potential flow theory framework, the semi-analytical model of wave interaction with VLFS-OWCs is developed using the eigenfunction matching method. The semi-analytical model is verified ...  相似文献   

14.
《集装箱化》1998,(10):31-31
In order to standardize the market management of china‘s intemational container multimodal transport and promote china‘s foreign trade,the ministry of commuications and the ministry of railways of the people‘s republic of china(hereinfter referred to as the two ministries)jointly promulgated on march1997 the “regulations for the managemetnt of intemational container multimodal transport ”(hereinafter referred to as the regulations )and began to enforce the regulations on oct.1.1997.  相似文献   

15.
A numerical analysis based on the boundary element method (BEM) was presented for the hydrodynamic performance of a high skew propeller (HSP) which is employed by an underwater vehicle (UV). Since UVs operate at two different working conditions (surface and submerged conditions), the design of such a propeller is a cumbersome task. This is primarily due to the fact that the resistance forces as well as the vessel efficiency under these conditions are significantly different. Therefore, some factors are necessary for the design of the optimum propeller to utilize the power at the mentioned conditions. The design objectives of the optimum propeller are to obtain the highest possible thrust, minimum torque, and efficiency. In the current study, a 5-bladed HSP was chosen for running the UV. This propeller operated at the stern of the UV hull where the inflow velocity to the propeller was non-uniform. Some parameters of the propeller were predicted based on the UV geometrical hull and operating conditions. The computed results include the pressure distribution and the hydrodynamic characteristics of the HSP in open water conditions, and comparison of these results with those of the experimental data indicates good agreement. The propeller efficiency for both submerged and surface conditions was found to be 67% and 64%, respectively, which compared to conventional propellers is a significantly higher efficiency.  相似文献   

16.
On the 20th of December,2012,Det Norske Veritas (DNV) and Germanischer Lloyd (GL) respectively published the news on their home pages that a merger agreement had been signed by both parties.With the advent of the Christmas holiday,the media has enteredinto a quiet period.However,the merger between DNV and GL has undoubtedly had a significant and profound influence on the international maritime industry,and the birth of the super classification society might be just a new beginning.  相似文献   

17.
The surface wave generated by flow around a ship hull moving near free surface of water is simulated numerically in this study. The three-dimensional implicit finite volume method(FVM) is applied to solve Reynolds averaged Navier-Stokes(RANS) equation. The realizable k-ε turbulence model has been implemented to capture turbulent flow around the ship hull in the free surface zone. The volume of fluid(VOF) method coupled with the Stokes wave theory has been used to determine the free surface effect of water. By using is a six degrees of freedom model, the ship hull's movement is numerically solved with the Stokes wave together. Under the action of Stokes waves on the sea, the interface between the air and water waves at the same regular pattern and so does the pressure and the vertical velocity. The ship hull moves in the same way as the wave. The amplitude of the ship hull's heave is less than the wave height because of the viscosity damping. This method could provide an important reference for the study of ships' movement, wave and hydrodynamics.  相似文献   

18.
19.
This research presents a review and classification of the published work related to applied risk analysis and risk management in the maritime liquefied natural gas(LNG) sector from 2000 to 2023. The papers are categorised under two primary contexts. The first is the risk analysis theory context which represents the classification with respect to(w. r. t.) the used risk analysis method, the used risk analysis tool, and the objective of risk analysis, whereas the second is the presented case in th...  相似文献   

20.
In order to solve the distributed detection fusion problem of underwater target detection, when the signal to noise ratio (SNR) of the acoustic channel is low, a new strategy for united detection fusion and communication using multiple sensors was proposed. The performance of detection fusion was studied and compared based on the Neyman-Pearson principle when the binary phase shift keying (BPSK) and on-off keying (OOK) modes were used by the local sensors. The comparative simulation and analysis between the optimal likelihood ratio test and the proposed strategy was completed, and both the theoretical analysis and simulation indicate that using the proposed new strategy could improve the detection performance effectively. In theory, the proposed strategy of united detection fusion and communication is of great significance to the establishment of an underwater target detection system.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号