An Algorithm for Classification of Algal Blooms Using MODIS-Aqua Data in Oceanic Waters around India

Increasing incidences and severity of algal blooms are of major concern in coastal waters around India. In this work an automatic algorithm has been developed and applied to a series of MODIS-Aqua ocean color data to classify and monitor four major algal blooms in these waters (i.e., Trichodesmium erythareum, Noctiluca scintillans/miliaris (green/brown), and Cochlodinium polykrikoides (red)). The algorithm is based on unique spectral signatures of these blooms previously reported by various field sampling programs. An examination of the algorithm results revealed that classified blooms agree very well with in-situ data in most oceanic waters around India. Accuracy assessment based on overall, user’s and producer’s accuracy and Kappa accuracy further revealed that the producer’s/user’s accuracy of the four algal blooms were 100% / 100%, 79.16% / 79.16%, 100% / 80%, 100% / 86.95%, respectively. The Kappa coefficient was 1.01. These results suggest that the new algorithm has the potential to classify and monitor these major algal blooms and such information is highly desired by fishermen, fish farmers and public health officials in this region. It should be noted that coefficients with the new algorithm may be finetuned based on more in-situ data sets and the optical properties of these algal blooms in oceanic waters around India.

Stress Analysis and Optimum Design of PDC Die for Offshore Drilling Engineering

The maximum internal tangential stress is a critical parameter for the design of the PDC （polycrystalline diamond compact） die that has been widely applied to offshore oil drilling. A new simple equation for the calculation of the stress is developed, and verified by the test data from Kingdream Corp. of China, the largest bit Company in China. An opti- mum method for the design of the PDC die is presented and demonstrated in detail, and software for the design and FEM analysis of the die is developed on the basis of the method. This software has been used in oil industry in recent years.

An Optical Model for the Remote-Sensing of Absorption Coefficients of Phytoplankton in Oceanic/Coastal Waters

A new model for the remote sensing of absorption coefficients of phytoplankton aph (λ) in oceanic and coastal waters is developed and tested with SeaWiFS and MODIS-Aqua data. The model is derived from a rela-tionship of the remote sensing reflectance ratio Rrs (670)/Rrs (490) and aph (490) and aph (670) (from large in-situ data sets). When compared with over 470 independent in-situ data sets, the model provides accurate retrievals of the aph (λ) across the visible spectrum, with mean relative error less than 8%, slope close to unity and R2 greater than 0.8. Further comparison of the SeaWiFS-derived aph (λ) with in-situ aph (λ) values gives similar and consistent results. The model when used for analysis of MODIS-Aqua imagery, provides more realistic values of the phytoplankton absorption coefficients capturing spatial structures of the massive algal blooms in surface waters of the Arabian Sea. These results demonstrate that the new algorithm works well for both the coastal and open ocean waters observed and suggest a potential of using remote sensing to provide knowledge on the shape of phytoplankton absorption spectra that are a requirement in many inverse models to estimate phytoplankton pigment concentrations and for input into bio-optical models that predict carbon fixation rates for the global ocean.

近海三角张力腿平台钢筋束假定失效研究

Offshore triceratops is one of the successful manifestations of the form-dominant design approaches deployable in ultra-deepwater oil and gas exploration.The deck’s geometric shape and partial isolation from the legs counteract lateral loads.Legs are position-restrained to the sea bed by taut-moored tendons,while ball joints partially isolate the deck from the buoyant legs.However,compliance in the horizontal plane imposes large displacements,intuiting the necessity to examine tendon failure.Numerical analysis of triceratops under wave and wind combined action is carried out under the postulated conditions of a tendon failure.10-yr,100-yr,and 1000-yr post-Katrina hurricane conditions are assumed as loading to the platform.Results confirm a marginal increase in the natural periods of stiff degrees of freedom even under postulated failure conditions,ensuring good adaptability to ultra-deep water.Under postulated failure,the tension of adjacent tendons varies significantly,causing a shift to the mean position of the platform.Fatigue life is significantly reduced under the postulated failure of tendons,making the platform free-floating without affecting its stability.Results also show that the pitch response of the deck is a clear manifestation of the postulated failure,which is otherwise absent due to the presence of ball joints.The attempted study deliberates on the fatigue life of tendons,assessing the platform’s suitability to ultra-deep waters and identifying the vulnerable legs for the chosen load combinations.

对称系泊半潜平台在各种可能系泊组合下的动力学分析

In this technologically advancing world,the demand for more energy,oil and gas production is rapidly escalating.To accomplish this,people have inclined more towards completely floating offshore structures,deployed in deep waters.A semi-submersible is selected in the present study,due to its better response characteristics and stability under harsh environmental conditions.The semi-submersible is position restrain with spread mooring lines incorporated with submerged buoy at different locations has been studied.A detailed numerical analysis is carried out using Ansys Aqwa for dynamic response analysis of semi-submersible under the combination of wind,wave,and current forces for 0°,45°,and 90°directions.It was observed that damping ratios and natural periods had been affected based on the position and number of submerged buoys in the mooring system.Also,reduction in mooring force after incorporating buoy in the mooring lines was observed.Subsequently,a Matlab code based on the S-N curve approach was generated and employed to investigate the fatigue damage of mooring lines under dynamic variation of mooring forces.When pegged with submerged buoys,fatigue life of mooring lines is increased under intact and postulated damaged mooring conditions.Moreover,coupling of motion responses of semi-submersible is observed,and unbounded response is not seen in any degrees-offreedom,even during damaged condition of mooring lines.

Optimal Active Control of Wave-Induced Vibration for Offshore Platforms

An obvious motivation of this paper is to examine the effectiveness of the lateral vibration control of a jacket type offshore platform with an AMD control device, in conjunction with H-2 control algorithm, which is an optimal frequency domain control method based on minimization of H-2 norm of the system transfer function In this study, the offshore platform is modeled numerically by use of the finite element method, instead of a lumped mass model This structural model is later simplified to be single-degree-of-freedom (SDOF) system by extracting the first vibration mode of the structure. The corresponding 'generalized' wave force is determined based on an analytical approximation of the first mode shape function, the physical wave loading being calculated from the linearized Morison equation. This approach facilitates the filter design for the generalized force. Furthermore, the present paper also intends to make numerical comparison between H-2 active control and the corresponding passive control using a TMD with the same device parameters.

Buckling analysis of functionally graded plates partially resting on elastic foundation using the differential quadrature element method

We extend the differential quadrature element method (DQEM) to the buckling analysis of uniformly in-plane loaded functionally graded (FG) plates fully or partially resting on the Pasternak model of elastic support. Material properties of the FG plate are graded in the thickness direction and assumed to obey a power law distribution of the volume fraction of the constituents. To set up the global eigenvalue equation, the plate is divided into sub-domains or elements and the generalized differential quadrature procedure is applied to discretize the governing, boundary and compatibility equations. By assembling discrete equations at all nodal points, the weighting coefficient and force matrices are derived. To validate the accuracy of this method, the results are compared with those of the exact solution and the finite element method. At the end, the effects of different variables and local elastic support arrangements on the buckling load factor are investigated.

Effect of Tool Shoulder and Pin Probe Profiles on Friction Stirred Aluminum Welds-a Comparative Study

在海洋的申请，海洋的等级钢通常被使用为拖并且上层建筑。然而，铝也由于它的小质量成为了一种好选择，当铝生锈与钢相比是最小的时。在磨擦上在这糊研究促使铝合金焊接被介绍。现在的调查处理不同磨擦的效果促使在机械强度和铝合金焊接的微观结构性质上焊接工具几何学。有肩膀和工具探查侧面的不同类型的三不同工具几何学根据设计矩阵在调查被使用。焊接上的每个工具肩膀和探查几何学的效果被评估。磨擦搅动焊接工具几何学，这也被观察在焊接加强， microhardness，和焊接强度上有重要效果。

Automatic Generation of the Planning Tunnel High Speed Craft Hull Form

一艘轮船到的几何模型的创造决定特征静水力学并且水动力学，并且也在轮船设计过程为结构的设计和设备安排是那么重要的。计划隧道高度速度手艺是在的手艺之一，到他们的最高的速度的成就是更重要的。有隧道的使用的这些手艺有飞行器水动力学的性质减少抵抗，好经得起海上风浪的行为，减少撞击并且避免 porpoising。因为隧道的存在，这些手艺的壳形式产生更复杂、困难。在这份报纸，它试图基于几何学创造指南并且与最少的控制和壳形式调整参数的一个条目提供一个方法，到自动地产生计划的壳形式隧道手艺。起初，数学模型的方程被描述并且随后，基于现在的方法产生的三个不同模型被比较并且分析。显然，产生模型在设计的早阶段有更多的申请。

Modeling phase equilibria of semiclathrate hydrates of CH_4,CO_2 and N_2 in aqueous solution of tetra-n-butyl ammonium bromide

Semiclathrate hydrates of tetra-n-butyl ammonium bromide （TBAB） offer potential solution for gas storage, transportation, separation of flue gases and CO2 sequestration. Models for phase equilibria for these systems have not yet been developed in open literatures and thus require urgent attention. In this work, the first attempt has been made to model phase equilibria of semiclathrate hydrates of CH4, CO2 and N2 in aqueous solution of TBAB. A thermodynamic model for gas hydrate system as proposed by Chen and Guo has been extended for semiclathrate hydrates of gases in aqueous solution of TBAB. A correlation for the activity of water relating to the system temperature, concentration of TBAB in the system and the nature of guest gas molecule has been proposed. The model results have been validated against available experimental data on phase equilibria of semiclathrate hydrate systems of aqueous TBAB with different gases as guest molecule. The extended Chen and Guo＇s model is found to be suitable to explain the promotion effect of TBAB for the studied gaseous system such as, methane, carbon dioxide and nitrogen as a guest molecule. Additionally, a correlation for the increase in equilibrium formation temperature （hydrate promotion temperature, ATp） of semiclathrate hydrate system with respect to pure gas hydrate system has been developed and applied to semiclathrate hydrate of TBAB with several gases as guest molecules. The developed correlation is found to predict the promotion effect satisfactorily for the system studied.

The Effect of Key Design Parameters on the Global Performance of Submerged Floating Tunnel under Target Wave and Earthquake Excitations

This study presents a practical design strategy for a large-size Submerged Floating Tunnel(SFT)under different target environments through global-performance simulations.A coupled time-domain simulation model for SFT is established to check hydro-elastic behaviors under the design random wave and earthquake excitations.The tunnel and mooring lines are modeled with a finite-element line model based on a series of lumped masses connected by axial,bending,and torsional springs,and thus the dynamic/structural deformability of the entire SFT is fully considered.The dummy-connection-mass method and constraint boundary conditions are employed to connect the tunnel and mooring lines in a convenient manner.Wave-and earthquake-induced hydrodynamic forces are evaluated by the Morison equation at instantaneous node positions.Several wave and earthquake conditions are selected to evaluate its global performance and sensitivity at different system parameters.Different BuoyancyWeight Ratios(BWRs),submergence depths,and tunnel lengths(and mooring intervals)are chosen to establish a design strategy for reducing the maximum mooring tension.Both static and dynamic tensions are critical to find an acceptable design depending on the given target environmental condition.BWR plays a crucial role in preventing snap loading,and the corresponding static tension is a primary factor if the environmental condition is mild.The tunnel length can significantly be extended by reducing BWR when environmental force is not that substantial.Dynamic tension becomes important in harsh environmental conditions,for which high BWR and short mooring interval are required.It is underscored that the wet natural frequencies with mooring are located away from the spectral peaks of design waves or earthquakes.

An experimental study on thermal characteristics of nanofluid with graphene and multi-wall carbon nanotubes

High-thermal conductivity enhancement of nanofluid is one of the promising topics of the nanoscience research field. This work reports the experimental study on the preparation of graphene(GN) and multi-walled carbon nanotubes(MWCNTs) based nanofluids with the assistance of sodium dodecyl benzene sulfonate(SDBS) and sodium dodecyl sulfate(SDS) surfactants, and their thermal behaviors. The present work suggests not a solution, but a solution approach and deduces a new conclusion by trying to resolve the agglomeration problem and improve the dispersibility of nanoparticles in the base fluid. The analysis results of FESEM, thermal conductivity, diffusivity, effusivity and heat transfer coefficient enhancement ratio of nanofluid with surfactants SDS and SDBS expose strong evidence of the dispersing effect of surfactant on the making of nanofluid.

An Improved Modal Strain Energy Method for Damage Detection in Offshore Platform Structures

柔韧的损坏察觉方法为的发展近海结构是关键的阻止结构的失败引起的大祸。在这研究，我们为检测损坏在开发了一个改进形式的紧张精力(IMSE ) 方法近海站台基于一个传统的形式的紧张精力方法(Stubbs 索引方法) 组织。从 Stubbs 索引方法的最重要的差别是形式的频率的应用程序。目标是改进传统的方法的坚韧性。表明建议 IMSE 方法的有效性和实物，数字、试验性的研究用夹克衫站台结构为不同损坏情形被进行。当仅仅有限、空间地不完全、弄脏噪音的形式的数据是可得到的时，结果在损坏地点表明了 IMSE 方法的有效性。比较研究证明 IMSE 索引超过了 Stubbs 索引并且展出了更强壮的坚韧性，证实建议途径的优势。

Effect of Upward Internal Flow on Dynamics of Riser Model Subject to Shear Current

Numerical study about vortex-induced vibration （V/V） related to a flexible riser model in consideration of internal flow progressing inside has been performed. The main objective of this work is to investigate the coupled fluid-structure interaction （FSI） taking place between tensioned riser model, external shear current and upward-progressing internal flow （from ocean bottom to surface）. A CAE technology behind the current research which combines structural software with the CFD technology has been proposed. According to the result from dynamic analysis, it has been found that the existence of upward-progressing internal flow does play an important role in determining the vibration mode （/dominant frequency）, vibration intensity and the magnitude of instantaneous vibration amplitude, when the velocity ratio of internal flow against external current is relatively high. As a rule, the larger the velocity of intemal flow is, the more it contributes to the dynamic vibration response of the flexible riser model. In addition, multi-modal vibration phenomenon has been widely observed, for asymmetric curvature along the riser span emerges in the case of external shear current being imposed.

Numerical Investigation of Contra Rotating Vertical-Axis Tidal-Current Turbine

In this study,the performance of a contra rotating vertical-axis tidal-current turbine was investigated.The incompressible unsteady Reynolds-averagedNavier-Stokes(U-RANS)equations were solved via two-dimensional(2D)numerical simulation using ANSYS Fluent computational fluid dynamics(CFD)code.An algorithm known as SIMPLE from the CFD code was used to calculate the pressure-velocity coupling and second-order finite-volume discretization for all the transport equations.The base turbine model was validated using the available experimental data.Three given scenarios for the contra rotating turbine were modeled.The contra rotating turbine performs better in a low tip speed ratio(TSR)than in a high TSR operation.In a high TSR operation,the contra rotating turbine inefficiently operates,surviving to rotate in the chaotic flow distribution.Thus,it is recommended to use contra rotating turbine as a part of new design to increase the performance of a vertical-axis tidal-current turbine with a lower TSR.

Modeling the Effects of Tool Shoulder and Probe Profile Geometries on Friction Stirred Aluminum Welds Using Response Surface Methodology

现在的论文讨论当模特儿磨擦上的效果搅动铝焊接使用的工具几何学反应表面方法论。磨擦促使焊接工具基于一个设计矩阵与不同肩膀和工具探查几何学被设计。为设计的工具的矩阵为定义肩膀表面类型和探查侧面几何学各为工具的三种类型被做，基于探针的三种类型，与三个层次。然后，工具肩膀的效果和磨擦上的探查几何学搅动了铝焊接试验性地关于焊接强度，焊接十字节区域，焊接的谷物尺寸和 thermo 机械地影响的地区的谷物尺寸被调查。这些效果被建模用多重并且反应表面回归分析。当模特儿的反应表面回归被发现为定义磨擦适当搅动焊接特征。

Study on Deformation Law of Circular Foundation Under Combined Loading

The foundations of some ocean engineering structures are built to withstand not only the vertical gravity load V, but also the horizontal load H induced by sea waves and current. The horizontal load includes the concentrated force load, the moment load M, and the torque load T termed also as combined loading. It is of academic and engineering significance to study the deformation law of submarine seabed due to combined loading. On the basis of the three-dimensional elastic mechanics solution of circular foundation, numerical methods are used to analyze the deformation law of submarine soil under circular foundation with six degrees of freedom. The finite element analysis results give the elastic deformation law of soil in three dimensional spaces, modify the theoretical elasticity solution, and presents nonlinear soil deformation mechanism under the circular foundation with six degrees of freedom.

Free vibration analysis of non-homogeneous orthotropic plates resting on Pasternak elastic foundation by Rayleigh-Ritz method

Free vibration analysis of non-homogeneous orthotropic plates resting on a Pasternak type of elastic foundation is investigated. A set of admissible orthogonal polynomials are generated with Gram-Schmidt orthogonalization procedure and adopted in the Rayleigh-Ritz method. Accuracy and applicability of the method are examined by comparison of the results for different boundary conditions and material types with those available in literature. It is found that this method has good accuracy regardless of type of boundary condition and yields very accurate results even with low number of terms of orthogonal polynomials for the first mode of vibration. For higher modes of vibration, higher terms of orthogonal polynomials should be used. The effects of foundation parameter, density and non-homogeneity parameters on natural frequency are examined. It is concluded that natural frequency of plates are more sensitive to shearing layer coefficient rather than Winkler coefficient and density parameter has weakening effect on natural frequency.

CFD-Based Numerical Analysis of a Variable Cross-Section Cylinder

Using ANSYS-CFX, a general purpose fluid dynamics program, the vortex-induced vibration(VIV) of a variable cross-section cylinder is simulated under uniform current with high Reynolds numbers. Large eddy simulation(LES) is conducted for studying the fluid-structure interaction. The vortex shedding in the wake, the motion trajectories of a cylinder, the variation of drag and lift forces on the cylinder are analyzed. The results show that the vortices of variable cross-section cylinder are chaotic and are varying along the cylinder. In places where cross-sections are changing significantly, the vortices are more irregular. The motion trail of the cylinder is almost the same but irregular. The drag and lift coefficients of the cylinder are varying with the changes of diameters.

Response Analysis of Tension-Based Tension Leg Platform Under Irregular Waves

Tension Leg Platform（TLP） is a hybrid structure used as oil drilling and production facility within water depths of 1200 m. The extension of this TLP concept to deeper waters is a challenge and warrants for some innovative design concepts. In this paper, a relatively new concept of TLP which is christened as Tension-Based Tension Leg Platform（TBTLP） and patented by Srinivasan（1998） has been chosen for study. Response analysis of TLP with one tension base under irregular waves for three different sea states has been performed using hydrodynamic tool ANSYS？ AQWA？. Results are reported in terms of RAOs, response spectrums for surge, heave and pitch degrees of freedom from which spectral statistics have been obtained. The statistics of TBTLP have been compared with TLPs（without tension base） for two different water depths to highlight the features of the new concept. The effect of viscous damping and loading effects on the RAOs are also investigated.