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1.
Steady-state heat conduction problems arisen in connection with various physical and engineering problems where the functions satisfy a given partial differential equation and particular boundary conditions, have attracted much attention and research recently. These problems are independent of time and involve only space coordinates, as in Poisson's equation or the Laplace equation with Dirichlet, Neuman, or mixed conditions. When the problems are too complex, it is difficult to find an analytical solution, the only choice left is an approximate numerical solution. This paper deals with the numerical solution of three-dimensional steady-state heat conduction problems using the meshless reproducing kernel particle method (RKPM). A variational method is used to obtain the discrete equations. The essential boundary conditions are enforced by the penalty method. The effectiveness of RKPM for three-dimensional steady-state heat conduction problems is investigated by two numerical examples. 相似文献
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Coastal disposal of waste water can be idealized as the problem of a jet under random waves. Understanding of this phenomenon is important for engineering design and environmental impact assessment. The present study aims to simulate such phenomenon by using a 3D numerical model based on the solution of the spatially filtered and σ-transformed Navier–Stokes equations with dynamic sub-grid scale model of turbulence. The numerical solution procedures are split into three steps: advection, diffusion and pressure propagation, and a Lagrange–Euler method is used to track the free surface. Cases of vertical jet in stagnant water, pure random waves and vertical jet in random waves are simulated with the same grid system for comparative study. Different methods of generating jet inflow turbulence have been tested and the method of jet azimuthal modes is found to be the optimum. The numerical results reproduce the distinct characteristics of jet in waves, including faster decay of centerline velocity, wider lateral spreading and the occurrence of wave tractive mechanism. 相似文献
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Reverse tip jets are strong low-level winds with easterly component that form near the southern tip of Greenland. In the present study, a reverse tip jet case which occurred from 21 to 22 December 2000 was examined to clarify its fine structure using a numerical model with a horizontal resolution of 3 km. The reverse tip jet, showing the supergeostrophic wind speed with a maximum wind speed in excess of 45 m s−1 , extended from the east coast of Greenland to the west of Cape Farewell with anticyclonic curvature. A cloud free region coincided with the jet indicated that there was a mesoscale downdraft. Along the eastern edge of the jet, a banded cloud formed between the upstream easterly wind and the colder northerly wind that is a part of the jet and is located along the east coast. This cloud was associated with large gradients in surface wind speed, temperature, moisture, and heat flux. A maximum surface total heat flux of 300 W m−2 coincided with the location of the jet. It is suggested that the orographic deflection by Greenland's large-scale topography as well as small-scale downslope winds behind mountains with fiords causes the reverse tip jet. 相似文献
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Through the flexural behavior test of coral aggregate reinforced concrete beams (CARCB) and ordinary Portland reinforced concrete beams (OPRCB), and based on the parameters of concrete types, concrete strength grades and reinforcement ratios, the crack development, failure mode, midspan deflection and flexural capacity were studied, the relationships of bending moment-midspan deflection, load-longitudinal tensile reinforcement strain, load-maximum crack width were established, and a calculation model for the flexural capacity of CARCB was suggested. The results showed that with the increase in the reinforcement ratio and concrete strength grade, the crack bending moment (Mcr) and ultimate bending moment (Mu) of CARCB gradually increased. The characteristics of CARCB and OPRCB are basically the same. Furthermore, through increasing the concrete strength grade and reinforcement ratio, Mcr/Mu could be increased to delay the cracking of CARCB. As the load increased, crack width (w) would also increase. At the beginning of the loading, w increased slowly. And then it increased rapidly when the load reached to the ultimate load, which then led to beam failure. Meanwhile, with a comprehensive consideration of the effects of steel corrosion on the loss of steel section and the decrease of steel yield strength, a more reasonable calculation model for the flexural capacity of CARCB was proposed. 相似文献
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Ping Wu Yang Guo Dayong Zhu Weiliang Jin Zhenhua Zhang Rongzhu Liang 《Marine Georesources & Geotechnology》2020,38(5):518-526
AbstractThis study developed prestressed high-strength concrete (PHC) piles reinforced with high-strength materials (glass fiber-reinforced polymer (GFRP) bars) for flexural performance enhancement. Flexural strengths and behaviors of PHC piles reinforced with hybrid GFRP and steel bars were experimentally investigated, respectively. Large-scale specimens with total lengths of 12,000?mm and diameters of 600?mm were constructed and tested under bending, accompanied by evaluation of effects of non-prestressed reinforcement type and longitudinal reinforcement ratio. J-factors were calculated to evaluate deformability of all the specimens. PHC piles reinforced with GFRP bars were demonstrated to have much higher flexural capacity than those reinforced with steel bars. Moreover, strains at the midspans of cross sections of all the specimens basically conformed to the assumption of plane section. Failure of PHC piles reinforced with GFRP bars was attributable to gradual concrete crushing, while that of PHC piles reinforced with steel bars resulted from steel yielding. Results of this study were expected to provide theoretical basis for wide engineering applications of PHC piles reinforced with hybrid GFRP bars and steel bars in marine structures. 相似文献
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The submerged 3D turbulent jet flow behavior around a pile on a rigid bed and on a scoured bed was studied experimentally and numerically. ADV was used to obtain the jet velocity distributions and Realizable k–ε turbulence model was used for the prediction of flow field around a pile. The jet flow area was three-dimensional and thus numerical model was a three-dimensional model. The numerical results were used to predict the velocity close to the pile and bed shear stress on the bed. In general, the results indicated that the flow field was also in agreement with the findings of previous experiments in literature and the related principles in the subject area. The experimental results demonstrated that Acoustic Doppler Velocimeter (ADV) measurements were almost identical with the Realizable k–ε turbulence model results for turbulence intensity I=10%. 相似文献
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提出一种随机分布点蚀损伤的模拟方法,模拟点蚀在构件表面的随机生长过程,并建立了随机态点蚀损伤圆管截面的有限元分析模型;设计了三个受不同腐蚀深度点蚀损伤的圆管构件,并开展轴压试验,利用试验结果校验有限元模型的计算精度;在多种腐蚀情形下(点蚀强度和腐蚀深度变化),研究点蚀分布模式变化引起的极限强度退化及其变异性;比较随机分布点蚀模型与传统腐蚀模型(规则分布点蚀和均匀腐蚀)在计算强度和结构失效行为方面的差异。研究结果表明,点蚀的随机分布模式会引起显著的极限强度变异,且蚀坑深度越大,强度变异越大,蚀坑分布造成的强度极差与强度均值相比达到5%;随机分布点蚀相比于传统腐蚀模型,除了引起更为严重的强度削减,还会改变结构的破坏模式。提出的随机点蚀损伤的模拟方法,可替代昂贵的构件试验,应用于评估点蚀损伤圆管截面的极限强度,增强评估结果的可靠性。 相似文献
10.
Chen Tieyun Zhang Huiyuan Proefessor Shanghai Jiao Tong University Shanghai
Engineer Shenzhen Shipbuilding Trading Co. LTD Shenzhen 《中国海洋工程》1993,(4)
- The formulation for the stress concentration matrix of multiplanar tubular joint with braces subjected to combined load is established in this paper. The formulations for SCF values of multiplanar tubular joints are compared with those by Wordsworth and Efthymiou. The stiffening effect and load-interaction effect are discussed. A spatial offshore jacket with braces subjected to combined load is computed as a numerical example. The maximum stress of each multiplanar tubular joint and its location are found through SCF matrix. Finally, the difference between the maximum stresses of multiplanar tubular joints and their corresponding uniplanar tubular joints are discussed. 相似文献
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ZHAO Shunbo Ass. Prof. North China Institute of Water Conservancy Hydroelectric Power Zhengzhou P. R. China. 《中国海洋工程》1998,(4)
An experimental program was carried out to study the shear behavior of the reinforced con-crete composite beam(RCCB)subjected to two-phase uniformly distributed load.A total of 12 reinforcedconcrete composite beams were tested:10 of them were the RCCB subjected to two-phase uniformly dis-tributed load,the other 2 were the comparative reinforced concrete beams cast at the same time as theRCCB subjected to one-phase uniformly distributed load.The interface of precast unit and recast concretewas natural and rough.The test range of the main composite factors:the ratio of precast section depth tocomposite section depth was from 0.35 to 0.65,the ratio of first-phase load moment to precast section ulti-mate bearing moment was from 0.25 to 0.65.Based on the test results,the stresses of the longitudinal rein-forcements and stirrups,the load-bearing properties of the interface,the crack state and the failure charac-teristics of the RCCB under uniformly distributed load are discussed.The effects of the stirrups,the 相似文献
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Efficient Approximate Method of Global Reliability Analysis for Offshore Platforms in the Ice Zone 总被引：1，自引：0，他引：1
Ice load is the dominative load in the design of offshore platforms in the ice zone, and the extreme ice load is the key factor that affects the safety of platforms. The present paper studies the statistical properties of the global resistance and the extreme responses of the jacket platforms in Bahai Bay, considering the randomness of ice load, dead load, steel elastic modulus, yield strength and structural member dimensions. Then, based on the above results, an efficient approximate method of the global reliability analysis for the offshore platforms is proposed, which converts the implicit nonlinear performance function in the conventional reliability analysis to linear explicit one. Finally, numerical examples of JZ20-2 MSW, JZ20-2NW and JZ20-2 MUQ offshore jacket platforms in the Bahai Bay demonstrate the satisfying efficiency, accuracy and applicability of the proposed method. 相似文献
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海洋平台的灌浆卡箍技术研究 总被引：4，自引：0，他引：4
在国内外文献研究的基础上，对钢质近海结构物的修理，加固方法做了较为深入的研究，利用丹麦学者N．S．Ottosen提出的多轴应力状态下混凝土强度理论Ottosen破坏准则，建立了钢与混凝土组合结构T型灌浆卡箍管节点的轴向受控，受压和面内弯矩作用下的非线性有限元计算模型，采用分级加载计算分析了相应的极限承载能力，并与试验结果进行比较分析，计算结果表明，经灌浆卡箍维修后的管节点应力分布，变形和极限承载能力都得到了明显的改善，所得结果较好地反映了实际结构的力学特性。 相似文献
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The effectiveness of constructing a geogrid-reinforced and pile supported embankment on soft ground to reduce differential settlement has been studied by pilot scale field tests and numerical analysis. Three-by-three pile groups with varying pile spacing were driven into a layer of soft ground, and a layer of geogrid was used as reinforcement over each pile group. Further, a 2-D numerical analysis has been conducted using the computer program FLAC 2D. The mechanisms of load transfer can be considered as a combination of embankment soil arching, geogrid tension, and stress transfer due to the difference in stiffness between pile and soft ground. Based on the pilot scale field tests and results of numerical analysis, we find that the geosynthetic reinforcement slightly interferes with soil arching, and helps reduce differential settlement of the soft ground. Also, the most effective load transfer and vertical stress reduction at the midspan between piles occurs when the pile cap spacing index D/b (D: pile cap spacing, b: diameter of pile) is 3.0. 相似文献
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Turbulent heat transfer in a swinging tube with a serrated twist tape insert was experimentally examined to reveal the effects of swinging oscillations on heat transfer for such a swirl tube under sea-going conditions. This swirl tube swings about two orthogonal axes under single and compound rolling and pitching oscillations. A selection of Nusselt number (Nu) measurements illustrates the influences of swinging oscillations with and without buoyancy interaction on heat transfer performances. Single rolling or pitching oscillation with the swinging frequencies ranging from 0.333 to 1 Hz reduces heat transfer levels from the static references. Synergistic effects of compound rolling and pitching oscillations with either harmonic or non-harmonic rhythms improve heat transfer performances. Buoyancy effects in the swinging swirl tube elevate local Nu, but are weakened as the relative strength of swinging force increases. A set of heat transfer correlations is derived that permits the individual and interactive effects of single and compound swinging force effects with buoyancy interactions on the developed flow heat transfer value () to be quantified. 相似文献
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对传统可拆式板式换热器进行了改良,以适用于海洋温差能发电系统工况,并对改良后的板式换热器进行了理论数值分析。研建了海洋温差发电系统测试平台,对系统内的换热器换热特性进行测试,在不同工况下对换热器换热特性进行了实验研究,得到了板式换热器瞬态运行特性,同时还得到了换热器换热特性随热流密度的变化曲线及压降随工质流量的变化关系。结合实验数据拟合了换热器换热特性经验关联式和压降随工质流量关联式,预测值和实验值偏差均在20%以内。结果表明:在实验系统运行工况范围内,换热器的换热系数随着热流密度的增加而增大,当热流密度大于3 kW/m2时,换热系数随热流密度变化的曲线斜率变小;换热器压降随着工质流量增大而增加,压降随工质流量变化的曲线斜率变大。 相似文献
17.
Bao Yingbin Li Runpei Gu Yongning
Ph. D. Candidate School of Naval Architecture Ocean Engineering Shanghai Jiao Tong University Shanghai Professor School of Naval Architecture Ocean Engineering Shanghai Jiao Tong University Shanghai 《中国海洋工程》1998,(1)
This paper studies intensively the problems of ship-platform collision.The ship and platformare treated as one structural system connected with spring elements and then motion equation of the colli-sion system is established.A nonlinear force-displacement relationship is derived for the simulation of lo-cal dent in a hit member and the yield surface of a dented tubular section is developed to consider the re-duction of load carrying capacity of hit members.Large deformations,plasticity and strain-hardening ofthe beam-column element are taken into account by combining the elastic large displacement analysis theo-ry with the plastic node method.The effect of the hydrodynamic forces acting on the platform,the rubberfender the property of the local dent and the buckling behavior of beam-column on collision are analyzed.The numerical simulation of the nonlinear dynamic response is carried out by Wilson θ method with updat-ed Newton-Raphson iteration.And the numerical example of the dynamic response of a offs 相似文献
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The need to assess the structural capability of curved marine composite structures that support the keel of high performance yachts has increased due to the rise in the number of accidents and human casualties. The top hat stiffener is the basic structural member of the yacht to sustain the tensile and bending load of the keel. This paper characterises the mechanical strength of E-glass/vinylester composite top hat stiffeners subjected to transverse loading. The out-of-plane load transfer was studied and failure modes were identified for the three different composite layups which were tested to failure. Experimental results obtained from mechanical testing were compared with FEA predictions, based on the quadratic interlaminar stress criterion. Secondary reserve strength from the unidirectional fibres was identified and the potential to use this secondary strength was further investigated. 相似文献
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Reinforcement and Arching Effect of Geogrid-Reinforced and Pile-Supported Embankment on Marine Soft Ground 总被引：1，自引：0，他引：1
The effectiveness of constructing a geogrid-reinforced and pile supported embankment on soft ground to reduce differential settlement has been studied by pilot scale field tests and numerical analysis. Three-by-three pile groups with varying pile spacing were driven into a layer of soft ground, and a layer of geogrid was used as reinforcement over each pile group. Further, a 2-D numerical analysis has been conducted using the computer program FLAC 2D. The mechanisms of load transfer can be considered as a combination of embankment soil arching, geogrid tension, and stress transfer due to the difference in stiffness between pile and soft ground. Based on the pilot scale field tests and results of numerical analysis, we find that the geosynthetic reinforcement slightly interferes with soil arching, and helps reduce differential settlement of the soft ground. Also, the most effective load transfer and vertical stress reduction at the midspan between piles occurs when the pile cap spacing index D/b (D: pile cap spacing, b: diameter of pile) is 3.0. 相似文献
20.
The calculative method of heat transfer coefficient between ice cover and water is analyzed considering the heat balance at ice cover bottom firstly. The heat transfer coefficient is calculated with the meteorological, oceanographic data and sea ice conditions measured on the JZ20-2 Oil/Gas Platform in the Bohai Sea during the winter of 1997/1998. From the results, it is shown that the heat transfer coefficient is smaller in the freezing and melting periods, which is about 0.16× 10-3 and 0.04× 10-3 respectively. In the middle of ice season, the heat transfer coefficient has a larger value, which is about 0.5 × 10-3. Lastly, the influences of ice thickness and ice type on the heat transfer coefficient are discussed. With the heat transfer coefficient determined above, the oceanic heat flux in the winter of 1997～1998 is calculated, and its trend in the winter is analyzed. This study can be referenced in the sea ice numerical simulation and prediction in the Bohai Sea. 相似文献