Mathematical Morphology-Based Artificial Technique for Renewable Power Application

This paper suggests a combined novel control strategy for DFIG based wind power systems(WPS)under both nonlinear and unbalanced load conditions.The combined control approach is designed by coordinating the machine side converter(MSC)and the load side converter(LSC)control approaches.The proposed MSC control approach is designed by using a model predictive control(MPC)approach to generate appropriate real and reactive power.The MSC controller selects an appropriate rotor voltage vector by using a minimized optimization cost function for the converter operation.It shows its superiority by eliminating the requirement of transformation,switching table,and the PWM techniques.The proposed MSC reduces the cost,complexity,and computational burden of the WPS.On the other hand,the LSC control approach is designed by using a mathematical morphological technique(MMT)for appropriate DC component extraction.Due to the appropriate DC-component extraction,the WPS can compensate the harmonics during both steady and dynamic states.Further,the LSC controller also provides active power filter operation even under the shutdown of WPS condition.To verify the applicability of coordinated control operation,the WPS-based microgrid system is tested under various test conditions.The proposed WPS is designed by using a MATLAB/Simulink software.

Dynamic Load Identification in Time Domain

In the time domain method the dynamic load is successfully identified when the accelerations, velocities and displacements or velocities and displacements of the structure are known. But in engineering practice or experiments usually only the acceleration response is recorded. In this paper an improved time domain method is proposed for dynamic load identification. In this method by using of Duhamel integral, only the acceleration response is required for load identification. As an application of the present method, the dynamic ice load on a Bohai offshore platform is identified based on some measured acceleration. The identified values of ice load are in good agreement with the measured ones.

FUZZY ECONOMIC ASSESSMENT FOR OFFSHORE OIL FIELDS

It is understood that economic assessment is a key issue in the development of offshore oil field. In view of uncertainties in exploration, engineering investment etc. the capital investment will take serious risk, especially for small marginal blocks. In order to investigate the relationships between main economic indices and uncertain factors, the upper and lower fuzzy bounds as well as the tolerance are presented in this paper based on the concept of fuzzy mathematics. Quantizing those uncertainties of concerned factors, the risk of investment can then be identified through conventional cash flow table and sensitivity analysis, consequently, the risk can be reduced through careful handling of the uncertainties. As an example, the economic analysis of a reusable platform in a marginal offshore oil field is presented, which shows the process of fuzzy assessment in exposing severe marginality of the field and the performance of discounted cash flow rate of return by the fluctuation of uncertainties.

NONLINEAR BENDING OF THE SHALLOW SPHERICAL SHELLS WITH VARIABLE THICKNESS UNDER AXISYMMETRICAL LOADS

Based on the differential equation of the nonlinear bending of shallow spherical shells with variable thickness under axisymmetrical loads, the numerical solution of the nonlinear differential equation was studied by means of interpolating matrix method. The analysis of the results indicates that the suggested method is easy to implement and has the same high accuracy for both the displacements and the internal forces.

Behavior of Deformation and Strength of Concrete Under Biaxial Stresses

The study of the behavior of concrete under biaxial stresses is essential to the design of offshore concrete platforms. Using the multiaxial test apparatus developed by the authors, the deformation and strength of concrete under biaxial stresses are studied experimentally. Based on the test data, an endochronic damage constitutive model and a failure criterion are proposed. According to the above model, an incremental nonlinear iterative programme is developed, and a plate sample in plane stress state is analyzed.

GENERALIZATION OF THE METHOD OF FULL APPROXIMATION AND ITS APPLICATIONS

This paper presents a generalized form of the method of full approximation. By using the concept of asymptotic linearization and making the coordinate transformations including the nonlinear functionals of dependent variables, the original nonlinear problems are linearized and their higher-order solutions are given in terms of the first-term asymptotic solutions and corresponding transformations. The analysis of a model equation and some problems of weakly nonlinear oscillations and waves with the generalized method shows that it is effective and straightforward.

ON THE NONLINEAR STABILITY OF SYMMETRICALLY LAMINATED CYLINDRICALLY ORTHOTROPIC SHALLOW SPHERICAL SHELLS

In this paper, the large deflection theory of symmetrically laminated cylindrically orthotropic shallow spherical shells is established. Based on this theory, applying the modified iteration method, the analytic solution for critical buckling loads of the shells with rigidly clamped edges under actions of uniform pressure has been obtained.

PERTURBATION SOLUTION TO THE NONLINEAR PROBLEM OF OBLIQUE WATER EXIT OF AN AXISYMMETRIC BODY WITH A LARGE EXIT-ANGLE

In this paper, a nonlinear, unsteady 3-D free surface problem of the oblique water exit of an axisymmetric body with a large water exit-angle was investigated by means of the perturbation method in which the complementary angle a of the water exit angle was chosen as a small parameter. The original 3-D problem was solved by expanding it into a power series of a and reduced to a number of 2-D problems. The integral expressions for the first three order solutions were given in terms of the complete elliptic functions of the first and second kinds. The zeroth-order solution didn't turn out to be a linear problem as usual but a nonlinear one corresponding to the vertical water exit for the same body. Computational results were presented for the free surface shapes and the forces exerted up to the second order during the oblique water exit of a series of ellipsoids with various ratios of length to diameter at different Froude numbers.

GENERALIZED VARIATIONAL PRINCIPLES ON NONLINEAR THEORY OF ELASTICITY WITH FINITE DISPLACEMENTS

Two generalized variational principles on nonlinear theory of elasticity with finite displacements in which the σij, eij and ui are all three kinds of independent functions are suggested in this paper. It is proved that these two generalized variational principles are equivalent to each other if the stress-strain relation is satisfied as constraint. Some special cases, i.e. generalized variational principles on nonlinear theory of elasticity with small deformation, on linear theory with finite deformation and on linear theory with small deformation together with the corresponding equivalent theorems are also obtained. All of them are related to the three kinds of independent variables.

NONLINEAR DRIFT MOTION SIMULATION OF MULTI-CHAIN MOORING BUOY IN TIME DOMAIN

This paper deals with the nonlinear effect of the drift motion of multi-chain mooring buoys. The buoy's motion in time domain is determined for the case that the wave and mooring force are nonlinear. The Kotorayama's method of hydrodynamic effect in a single mooring chain is expanded to multi-mooring chains. The time history of drift motion of the mooring buoy in regular waves and wave groups is calculated. The relation between the drift motion and the wave height or difference frequency is discussed. It can be shown that the effect of the hydrodynamic force acting on the mooring chain has remarkable influence on the total drift motion of the mooring buoy. In a wave group, its amplitude is mainly controled by the wave height and has little relation with difference frequency.

PERIODIC SOLUTION TO A KIND OF SINGULARLY PERTURBED DIFFERENTIAL EQUATIONS OF PARABOLIC TYPE IN CHEMICAL KINETICS

This paper deals with the problem on the periodic solution for the singularly perturbed differential equations of parabolic type originating from chemical kinetics stratified media. A uniformly valid asymptotic solution is constructed and the related asymptotic estimate is given.

ON THE COMPUTATION OF THE MAIN EIGEN-PAIRS OF THE CONTINUOUS-TIME LINEAR QUADRATIC CONTROL PROBLEM

The degeneration of the eigenvalue equation of the discrete-time linear quadratic control problem to the continuous-time one when Δt&rarr0 is given first. When the continuous-time n-dimensional eigenvalue equation, which has all the eigenvalues located in the left half plane, has been reduced from the original 2n-dimensional one, the present paper proposes that several of the eigenvalues nearest to the imaginary axis be obtained by the matrix transformation Ae = eA. All the eigenvalues of Ae are in the unit circle, with the eigenvectors unchanged and the original eigenvalues can be obtained by a logarithm operation. And several of the eigenvalues of Ae nearest to the unit circle can be calculated by the dual subspace iteration method.

ITERATIVE PROCESS FOR LIPSCHITZ LOCAL STRICTLY PSEUDOCONTRACTIVE MAPPINGS

Supposed that K was a non-empty subset of an uniformly smooth Banach space X. Let T:K&rarrX be a Lipschitz local strictly pseudocontractive mapping. It is shown that the iterative sequence given strongly converges to the unique fixed point of T. A related result deals with the problem that the Ishikawa iteration process converges strongly to a solution of the equation TX=f where T is Lipschitz and local strongly accretive in X.

Crystallite Orientation Analysis for a Multidirectionally Cold Rolled α-Ti Alloy (TA7) Thin Sheet

A microcomputer software determining the crystallite orientation distribution functions (ODFs) and inverse pole figures of hexagonal materials with or without orthorhombic physical symmetry has been worked out the first time. The texture measurements and the ODF calculations were performed for a multidirectionally cold rolled α-Ti alloy (TA7) sheet by the application of this software. It is shown that the rolling planes of most grains in the sheet tend to be parallel to (0001) with a deviation to the extent of 40° and is shown a predominance of the orientation zone containing (1016), while the rolling directions are, as a whole, uniformly distributed along all the directions over the rolling planes. Of all the texture components, (2¯117) [01¯10] is slightly stronger than the other.

Interfacial Characters of Organophosphoric and Phosphonic Acid Extraction Systems

Dynamic interfacial properties are investigated for solvent extraction systems of metals by organophosphoric or phosphonic acid. The relationship between interfacial properties and kinetic parameters shows that the dynamic interfacial properties are important to mass transfer processes in liquid-liquid extraction. The authors develop a two-film adsorption model which may offer a basis for researching interfacial activity in mass transfer processes.

Prediction of the Gibbs Free Energies of Formation of Intermediate Compounds in a Binary System

A method for predicting the Gibbs free energies of intermediate compounds in a binary system has been presented, based upon the regulations of the Gibbs free energies of formation of intermediate compounds in the system. The application of this procedure to the V-O system demonstrates that this method is feasible.

NONLINEAR BENDING OF SHALLOW SPHERICAL SHELLS ON THE PASTERNAK FOUNDATIONS

Based on Karman's nonlinear fundamental differential equations, the new approach, which combines modified iteration method with Galerkin's one, has been put forward to solve nonlinear bending of shallow spherical shell with concave base and clamped edges on the Pasternak foundation under uniform loads in this paper. Mathematical expression of load-deflection has been given; furthermore, results obtained are in good agreement with existent ones.

TRANSIENT TEMPERATURE FIELDS AND RESIDUAL STRESS FIELDS OF METALLIC MATERIALS UNDER WELDING

Based on the situation of welding thermal conduction and thermo-elasto-platicity research, this paper explores some problems in this field. First, the boundary element method for nonlinear problems is improved by linearization of nonlinear problems and used in welding thermal conduction analysis. Second, the thermo-elasto-plastic finite element method is used for the welding stress calculation, in which the phase transformation is considered by the 'equivalent linear expansion coefficient method'. The comparison of the calculated results with experimental data shows that the methods provided in this paper are available.

Dynamic Response Analysis of Interaction System of R.C. Gravity Single-Leg Platform

In this paper, the responses of the interaction system of R.C. gravity single-leg platform to seismic excitation are mainly analysed. A set of nonlinear equations for the interaction system are established by using the wave, one is the soil-structure interaction and the other is the fluid-structure interaction. The seismic response of the interaction system is analysed for the influence of the asymmetric structure, fluid action, etc. with the input of seismic SH waves in any direction. The numerical results are given for a simple example.

ON J-INTEGRALS IN THE PLANE FRACTURE

In this paper, we discuss J-integrals near models I and II crack tips for the plates of linear-elastic isotropic homogeneous material and orthotropic composite material, using the theories of complex function and calculus, and obtain the result as follows: (1) The various J-integrals are transformed into standard form of line integrals with respect to coordinates: J = ∫rP(x, y)dx+Q(x, y)dy. (2) Independence of path of the various J-integrals is proved. (3) Computing formulae of J-integrals are derived.