Dynamic modeling and motion simulation for a winged hybrid-driven underwater glider

PETREL,a winged hybrid-driven underwater glider is a novel and practical marine survey platform which combines the features of legacy underwater glider and conventional AUV (autonomous underwater vehicle).It can be treated as a multi-rigid-body system with a floating base and a particular hydrodynamic profile.In this paper,theorems on linear and angular momentum are used to establish the dynamic equations of motion of each rigid body and the effect of translational and rotational motion of internal masses on the attitude control are taken into consideration.In addition,due to the unique external shape with fixed wings and deflectable rudders and the dual-drive operation in thrust and glide modes,the approaches of building dynamic model of conventional AUV and hydrodynamic model of submarine are introduced,and the tailored dynamic equations of the hybrid glider are formulated.Moreover,the behaviors of motion in glide and thrust operation are analyzed based on the simulation and the feasibility of the dynamic model is validated by data from lake field trials.     

STUDY ON CALCULATION OF OCEAN CURRENT VELOCITY

"Dynamic Computation" used to be calculate only the geostrophic current velocityand the Ekman's drift-current theory applied to compute only the wind-drift current ve-locity are the two basic theorems widely used for easily calculating the current velocitiesof different kinds of ocean currents. But they have their own defects. For easily calcula-ting both the velocity of ocean current produced by the uneven density distribution of seawater and that by the wind and atmospheric pressure of sea surface, the author presentsin this paper a method for solving the equations of motion in consideration of vertical tur-bulence only by using the values of horizontal pressure gradient and the coefficient ofeddy viscosity determined according to a certain fact. With this method We have calculatedthe velocity of ocean current in Kuroshio in the East China Sea, and obtained satisfac-     

Barrier and compensation layers in the East China Sea

Climatology of the isothermal layer depth （ILD） and the mixed layer depth （MLD） has been produced from in-situ temperaturesalinity observations in the East China Sea （ECS） since 1925. The methods applied on the global are used to compute the ILD and the MLD in the ECS with a temperature criterion AT=0. 8 ℃ for the ILD, and a density criterion with a threshold △σθ corresponding to fixed △T=0. 8 ℃ for the MLD, respectively. With the derived climatology ILD and MLD, the monthly variations of the barrier layer （BL） and the compensation layer （CL） in the ECS are analyzed. The BL mainly exists in the shallow water region of the ECS during April-June with thickness larger than 15 m. From December to next March, the area along the shelf break from northeast of Taiwan Island to the northeast ECS is characterized by the CL. Two kinds of main temperature - salinity structures of the CL in this area are given.     

Time-Dependent Reliability Analysis of Offshore Structures

During the life of an offshore structure,its structural strength declines due to various kinds ofdamages related to the time factor.In this paper,four major kinds of damages,including damages causedby fatigue,dent,corrosion and marine life,are discussed.Based on these analyses,formulas for theevaluation of the damaged structure reliability are derived.Furthermore the computer program ISM forthe analysis of structural reliability is developed by the use of Advanced First Order Second Moment meth-od and Monte-Carlo Importance Sampling method.The reliability of a turbular joint and a beam are stu-died as numerical examples.The results show that the theory and the analysis method given in this paperare reasonable and effective.     

An Improved Formulation for the Ultimate Static Strength of Tubular Joints subjected to Combined Loads

"The effect of interaction of loads on the ultimate static strength of tubular joints of offshore fixed platforms, is a practical problem. But there is still absence of rigorous theory to explain available experimental data and empirical criteria for the static strength of tubular joints. The idea of yield at hot spot of tubular joints is introduced in this paper. The interaction equations of plastic capacity for the tubular joints under combined loads (two and three different kinds) are derived. Thereafter the Yura's test data and empirical criteria of ultimate static strength for the tubular joints can be explained. The idea of classification of category of loads in accordance with experimental data and the present theory is suggested. Finally, the improved ultimate capacity equations for tubular joints are recommended. The physical significance of the coefficient of plastic reservation Qp is discussed.     

Sea level change along the coast of China relative to the isostatic datum

On the basis of the analyses of significant periods for the sea level observation data taken from recent several decades at 12 tide stations, the monthly mean sea level observations are fitted by a model of linear trend of sea level change superimposed with several variations of different fixed periods. The trends of sea level relative changes and their errors are estimated by the LS method. The results are reduced to the isostatic datum proposed and established in the paper (Huang et al. , 1991, Seismology and Geology , 1, 1-15). The trends of sea level changes in the near future along the coast of China are studied. It is pointed out that the general trend of the sea level change along the coast of China is going up slowly and the rate of the change is not the same in different segments of the coasts. In a few segments, the sea level is even relatively going down. The numerical results given in this paper provide a basis for the predictions of the future sea level changes and their effects.     

Analysis and Research of Ice Loads Acting on Offshore Structures

- Usually, the action of sea ice on offshore engineering structures is one of the controlling loads in cold waters engineering structure design. The reasonable selection of environmental condition and the physical mechanical properties of ice in the region are directly related to the structure design, operation and safety. In this paper, the sea ice force acting on the structure, the physical mechanical properties of ice and the selection of parameters in calculation are discussed. Some suggestions are proposed as to the calculation of various kinds of ice loads acting on the structure.     

Numerical Study on the Probability of Fatigue Failure of a Semi-Submerged Platform Structure

On the basis of Miner's linear cumulative damage theorem, random variables are introduced to evaluate objectively the fatigue damage of a semi-submerged platform structure and a method is presented to analyze the fatigue reliability of the structure in its design life. The reliability of the method is verified through numerical examples and some conclusions are drawn, which have certain guiding and reference value for design and inspection.     

Structural Model Updating of Jacket Platform by Control Theory Using Vibration Measurement Approach

The identification of variations in the dynamic behavior of structures is an important subject in structural integrity assessment.Improvement and servicing of offshore platforms in the marine environment with constant changing,requires understanding the real behavior of these structures to prevent possible failure.In this work,empirical and numerical models of jacket structure are investigated.A test on experimental modal analysis is accomplished to acquire the response of structure and a mathematical model of the jacket structure is also performed.Then,based on the control theory using developed reduction system,the matrices of the platform model is calibrated and updated.The current methodology can be applied to prepare the finite element model to be more adaptable to the empirical model.Calibrated results with the proposed approach in this paper are very close to those of the actual model and also this technique leads to a reduction in the amount of calculations and expenses.The research clearly confirms that the dynamic behavior of fixed marine structures should be designed and assessed considering the calibrated analytical models for the safety of these structures.     

Steady Lateral Growth of Three-Dimensional Particle Laden Density Currents

In this paper the steady lateral growth of three-dimensional turbulent inclined turbidity current is investigated. To simulate the current, an experimental setup is developed to analyze the turbidity current for different regimes in the particle laden density currents environment. The Buckingham's π theorem together with a dimensional analysis is implemented to derive the appropriate non-dimensional variables. The experimental results were normalized and plotted in the form of non-dimensional graphs from which a theoretical model is developed and analyzed. Based on the results obtained for the steady lateral growth, three different regimes, namely, inertia-viscous one as the first regime, buoyancy-viscous and gravity-viscous as the second and third regimes are distinguished within the current.In these regimes, the force balance is between the driving and resisting forces. Namely, in the first regime, the force balance is between the inertia and viscous forces, in the second regime, the buoyancy and viscous forces, and in the third regime, gravity and viscous forces are balanced. The experimental results indicate that the lateral growth rate in the first regime is smaller than that in the second and third regimes due to the magnitude and type of the forces involved in those regimes. According to the graphical results, the three different lateral growth rates appear when the normalized current length is smaller than about 3, between about 3 and 10, and larger than about 10. In those regions,the slopes of the data are different with respect to one another.     

DYNAMIC ANALYSIS OF TYPHOON SURGES ALONG THE COASTS OF ZHEJIANG AND JIANGSU PROVINCES

Based on the numerical model shown in Ref. [1], a dynamic analysis is given for the storm surges caused by the four typhoons (i. e. typhoons Nos. 5310, 5612, 6126 and 6207) on the east coast of Zhejiang and Jiangsu Provinces, in which the contributions of various dynamic factors to local surge elevation are calculated numerically, including the Coriolis force, the atmospheric pressure force, the bottom friction, the local topography and the couple nonlinear interactions between surge current and elevation as well as between surge currents themselves. Moreover, the responses of these factors to different kinds of typhoon tracks and water depths are discussed in more detail, and the effects of grid size on the computed results demonstrated.     

Estimation of annual variation of water vapor in the Arctic Ocean between 80°–87°N using shipborne GPS data based on kinematic precise point positioning

The measurement of atmospheric water vapor(WV) content and variability is important for meteorological and climatological research. A technique for the remote sensing of atmospheric WV content using ground-based Global Positioning System(GPS) has become available, which can routinely achieve accuracies for integrated WV content of 1–2 kg/m2. Some experimental work has shown that the accuracy of WV measurements from a moving platform is comparable to that of(static) land-based receivers. Extending this technique into the marine environment on a moving platform would be greatly beneficial for many aspects of meteorological research, such as the calibration of satellite data, investigation of the air-sea interface, as well as forecasting and climatological studies. In this study, kinematic precise point positioning has been developed to investigate WV in the Arctic Ocean(80°–87°N) and annual variations are obtained for 2008 and 2012 that are identical to those related to the enhanced greenhouse effect.     

STUDIES ON THE MANGROVE ECOSYSTEM OF THE JIULONGJIANG RIVER ESTUARY IN CHINA III. ACCUMULATION AND BIOLOGICAL CYCLE OF CALCIUM AND MAGNESIUM IN Kandelia candel COMMUNITY

This is a paper dealing mainly with the accumulation and biological cycle of calcium and magnesium elements of the artificial 20-years old Kandelia candel community in the Jiulongjiang River Estuary of Fujian Province, China. The result of measurements is that the quantities of the two elements in the standing crop are (kg·ha-1) 772.91 for Ca and 526.57 for Mg. In the biological cycle of the two elements, the annual uptakes are 174.86 for Ca and 89.30 for Mg (kg·ha-1); the amounts of Ca and Mg returned via litter fall are estimated to be (kg·ha-1·a-1) 103.28 for Ca and 40.42 for Mg; the annual retention are (kg·ha-1·a-1) 71.58 for Ca and 48.88 for Mg, respectively. The turnover periods of Ca and Mg are 8 and 13 years, respectively.     

New Analytical Solutions for Time Fractional Benjamin–Ono Equation Arising Internal Waves in Deep Water

In this article, the author sets up the abundant traveling wave solutions for time fractional Benjamin–Ono equation which was introduced to describe internal waves in stratified fluids by using Jacobi elliptic function expansion method. The traveling wave solutions are expressed in terms of the hyperbolic functions, the trigonometric functions and the rational functions. It can be seen that the obtained results are found to be important for the statement of some physical demonstrations of problems in mathematical physics and ocean engineering. In ocean engineering Benjamin–Ono equations are generally used in computer simulation for the water waves in deep water and open seas.     

Investigation of Allowable Stresses for Fatigue Design of Fixed Offshore Platforms

Fatigue design method is usually used for estimating whether a platform structure meets the requirements of fatigue resistance. It is described in API RP-2A and ZC rules for fixed offshore platforms, in which the allowable stresses for fatigue design are defined. In this paper discussed are the allowable stresses related factors, such as wave climate, structural response, fatigue behaviour of structural members.     

Numerical Tidal Current Modeling Using Fine Boundary Fitted Grids for Tidal Flats

Fine grids with small spacing in boundary-fitted coordinates are normally used to treat thecomputation of fluid dynamics for estuarine areas and tidal flats.However,the adoption of Cartesian com-ponents of velocity vectors in this kind of non-orthogonal coordinates will definitely result in a diffculty insolving implicitly the transformed momentum equations,and also complicate the wet-dry point judgementused for flood areas.To solve this problem,equations in terms of generalized contravariant velocityvectors in curvilinear coordinates are derived in the present study,by virtue of which,anAlternative-Direction-Implicit numerical scheme in non-orthogonal grids would then be easily obtained,and wet-dry point judgement would as well be largely simplified.A comparison is made between the explic-it scheme and implicit scheme,showing that the present model is accurate and numerically stable for com-putations of fluid dynamics for estuarine areas and tidal flats.     

Incipient Motion of Sediment Under Currents

Summarized in the paper are the author's studies on incipient motion of sediment in recent 40years.In addition to the forces of gravity,drag and lift,the cohesive force and the additional static pres-sure are important for fine particles.The relations between three stages of incipient motion are defined byuse of instantaneous velocity.Formulas for initial velocity and critical shear stress are given and overallverified by the author's and others'experimental data.     

Nitrogen forms and decomposition of organic carbon in the southern Bohai Sea core sediments

Study on form characteristics of nitrogen in marine sediments is the primary method to research its biogeochemical cycling and nitrogen form characteristics in core sediments can reflect the process and results of early diagenesis in a certain degree. In this paper, Sequential extraction process in natural grain size was used for studying the existent forms of nitrogen in five core sediments of the southern Bohai Sea for the first time. Nitrogen was divided into two parts -transferable and fixed based on whether it could be extracted by the reagent. Distributions and early diagenesis of transferable nitrogen forms in the southern Bohai Sea were researched integratedly. Results indicate that IEF - N and OSF-N are predominant forms in transferable part in the studied core sediments. Contents of different nitrogen forms vary differently with depth, and have different diagenesis process. Decomposition constant of organic nitrogen (ON) and OC are about 15.51 × 10~(-3)a~(-1)and 4.79× 10~(-3)a~(-1) respective     

Risk Assessment of Vertical Breakwaters -A Case Study in Turkey

In the reliability-risk assessment, the second order reliability index (βⅡ ) method and the Conditional Expectation Monte Carlo (CEMC) simulation are interrelated as a new Level Ⅲ approach for the analysis of the safety level of the Dalaman yacht harbor vertical wall breakwater in Turkey. The missing wave data of the Dalaman measurement station are hindcasted by use of multi-layer feed-forward neural networks with the steepest descent and conjugate gradient algorithms. The structural failure probabilities of sliding and overturning failure modes are forecasted by approximation of the failure sur-face with a second-degree polynomial of an equal curvature at the design point. in the new approach, for each randomly generated load and tide combination, the joint failure probability reflects both the occurrence probability of loading condition and the structural failure risk at the limit state. The approach can be applied to risk assessment of vertical breakwaters in short CPU durations of portable comput     

Spatiotemporal shoreline change in Boushehr Province coasts,Iran

Since coastal areas have highly dynamic nature and are one of the most beneficial regions of civilizations,it is of great significance to understand their characteristics and behavior.Changes in shorelines in the form of accretion and erosion can leave devastating effects on businesses and cities located along the shore.In this study,we statistically calculated the tendency of shoreline changes by processing and analyzing historical satellite images of Boushehr Province,Iran.Results show that these shores have experienced both sedimentation and erosion in the past 30 years.Net shoreline movement presents more than 350 m of erosion and 650 m of accretion,which are corresponded to change rates of almost 12 and 22 m/a,respectively.Statistics of shoreline changes are calculated from regression methods including end point rate,linear regression rate,weighted linear regression,and least median of squares.The best-performed method is applied to predict the shoreline position in 2050 and 2100.Potential locations of excessive changes are identified for the predicted shorelines,which should be dealt with properly.