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Stochastic crack propagation in offshore structures: The sensitivity of component lifetime to wave distribution models

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JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING-TRANSACTIONS OF THE ASME 1998年第1期120卷 43-49页

作者： Ahmad-Shariff, A Swailes, DC Metcalfe, AV Newcastle Univ Dept Engn Math Newcastle Upon Tyne NE1 7RU Tyne & Wear England

Stress variations induced by wave loading can lead to fatigue crack growth in structural components of offshore structures. This paper is concerned with the influence of the form of the statistical distributions for wave height on the damage accumulation and lifetime of a structural component. Damage accumulation is modeled by a stochastic Paris-Erdogan equation in which the increase in crack size is proportional to a power (m) of the range of the stress intensity factor Analytic expressions for the mean and variance of damage, and approximate mean lifetime, of a component are derived for the case in which m equals 2. It is seen that these depend on both the mean and variance of the stress distribution. The results are compared with those obtained by simulation, and the adequacy of the approximation is demonstrated. Simulation results using Rayleigh and Weibull distributions for wave heights are also given for the case in which m equals 3. It is shown that the Weibull distribution gives a better fit to empirical wave height distributions than does the Rayleigh distribution. Furthermore, when m equals 3, there is a substantial difference between results obtained by fitting Rayleigh and Weibull distributions to wave height data. The former leads to considerable overestimation of lifetimes. Ir is argued that Weibull distributions are more appropriate in determining lifetimes since the two parameters in the distribution allow more accurate representation of the mean and variance of the stress distribution.

关键词： Offshore structures component life Weibull distribution Variance Mean Wave Height mean life Stress distribution distributed parameter Rayleigh distribution statistical distribution Rayleigh offshore

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Design of best management practice applications for diffuse phosphorus pollution using interactive GIS

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WATER SCIENCE AND TECHNOLOGY 2008年第11期57卷 1727-1733页

作者： Kovacs, A. S. Honti, M. Clement, A. Budapest Univ Technol & Econ Dept Sanit & Environm Engn H-1111 Budapest Hungary

The paper presents a complex environmental engineering tool, which is appropriate to support decision making in watershed management. The PhosFate tool allows planning best management practices (BMPs) in catchments and simulating their possible impacts on immissions. The method has two parts: (a) a simple phosphorus (P) fate model to calculate diffuse P emissions and their surface transport, and (b) an interactive tool to design BMPs in small catchments. The fate model calculates diffuse P emissions via surface pathways. It is a conceptual, distributed parameter and long-term (annual) average model. The model also follows the fate of emitted P from each cell to the catchment outlets and calculates the field and in-stream retention. The fate model performed well in the Zala River catchment as a case study. Finally, an interactive design tool was developed to plan BMPs in the catchments and simulate their possible impacts on diffuse P fluxes. Different management scenarios were worked out and their effects evaluated and compared to each other. The results show that the approach is suitable to test BMP scenarios at small catchment scale.

关键词： BMP diffuse emission distributed parameter phosphorus transport

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Effect of kinetic comminution parameters and classification efficiency on output during closed-circuit cement grinding, Part 2

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ZKG INTERNATIONAL 2000年第5期53卷 290-+页

作者： Ito, M

The simulation of closed-circuit grinding was carried out using a comminution kinetics equation containing the parameters k and n and an equation describing classification efficiency derived fi om the operational data of three representative types of classifiers. The results show that the output of finished product from the grinding plant increases the higher the efficiency of classification However the increasing rate decreases with excess-increasing classification efficiency when the fineness is expressed by the specific surface area. The throughput of ground material through the mill, which was used as an indicator of the maximum production late, increased with rising classification efficiency. Under the usual conditions of cement grinding there was a specific relationship between the parameters k (comminution kinetic parameter) and n (particle sized distribution parameter). Under these conditions, the mill output, which was controlled to give a constant specific surface area of the finished product, increased with a decrease in the parameter n.

关键词： Output Manufactured products CLOSED LOOP mill Natural Increase classification efficiency Comminution operating data distributed parameter milling SPECIFIC AREA

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Control Loop Design and Control Performance Study on Direct Internal Reforming Solid Oxide Fuel Cell

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FUEL CELLS 2009年第5期9卷 722-728页

作者： Zhang, H. Weng, S. Su, M. Shanghai Jiao Tong Univ Key Lab Power Machinery & Engn Educ Minist Shanghai 200240 Peoples R China

A solid oxide fuel cell (SOFC) stack is a complicated nonlinear power system. Its system model includes a set of partial differential equations that describe species, mass, momentum and energy conservation, as well as the electrochemical reliction models.. The validation and verification of the control system by experiment is very expensive and difficult. Based on the distributed and lumped model of I one-dimensional SOFC, the dynamic performance with different control loops for SOFC is investigated. The simulation result proves that the control system is appropriate and feasible, and can effectively satisfy the requirement of variable load power demand This simulation model not only can prevent some latent dangers of the fuel cell system but also predict the distributed parameters characteristics inside the SOFC system.

关键词： Control Loop Design Control Performance distributed parameter Dynamic Simulation Solid Oxide Fuel Cell

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Mechanisms of surface alloy segregation on faceted core-shell nanowire growth

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2017年 100卷 21-44页

作者： Zhang, Qian Voorhees, Peter W. Davis, Stephen H. Northwestern Univ Dept Engn Sci & Appl Math 2145 Sheridan Rd Evanston IL 60208 USA Northwestern Univ Dept Mat Sci & Engn 2225 Campus Dr Evanston IL 60208 USA

A general two-dimensional faceted model that accounts for capillarity and deposition of an A(x)B(1-x) alloy is developed for the growth of the shell on a hexagonal core. With this model, the surface alloy segregation and morphological evolution in the processes of the faceted core-shell nanowire growth are studied both analytically and numerically. Mechanisms of formation of Al-rich stripes along {112} facets and Al-poor quantum dots/wires at the apices of {112} facets are identified. More specifically, it is found that diffusion tends to move the atoms from {112} facets to {110} facets. The formation of Al-rich stripes along the {112} facets is due to the large ratios of mobilities of Al atoms and Ga atoms on {112} facets, even though Al atoms diffuse slower than Ga on the {110} facets. In addition, the difference of interaction parameters in the enthalpy on different facets can also lead to lines of enhanced concentration of Al behind {112} facets. If the attachment rates of Al on the {112} facets are smaller than that on {110} facets, Al-poor dots will grow at the end of the Al-rich stripes because the growth process switches from diffusion dominant to deposition dominant when the size of the nanowire gets large. Moreover, influences of different parameters on the distribution of concentrations of the atoms in the shell are investigated in details.

关键词： Interaction parameters Gallium flat surfaces Atoms linear patterned slopes Stripes aluminium Nanowire capillarity distributed parameter shelling surface alloy

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THE COMPUTATION OF VISIBLE-SURFACE REPRESENTATIONS

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IEEE TRANSACTIONS ON PATTERN ANALYSIS AND MACHINE INTELLIGENCE 1988年第4期10卷 417-438页

作者： TERZOPOULOS, D Schlumberger Palo Alto Res. CA USA

A computational theory of visible-surface representations is developed. The visible-surface reconstruction process that computes these quantitative representations unifies formal solutions to the key problems of: (1) integrating multiscale constraints on surface depth and orientation from multiple-visual sources; (2) interpolating dense, piecewise-smooth surfaces from these constraints; (3) detecting surface depth and orientation discontinuities to apply boundary conditions on interpolation; and (4) structuring large-scale, distributed-surface representations to achieve computational efficiency. Visible-surface reconstruction is an inverse problem. A well-posed variational formulation results from the use of a controlled-continuity surface model. Discontinuity detection amounts to the identification of this generic model\'s distributed parameters from the data. Finite-element shape primitives yield a local discretization of the variational principle. The result is an efficient algorithm for visible-surface reconstruction.

关键词： efficient algorithm representations Interpolation Surface reconstruction discontinuities distributed parameter

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Thermal stability of a nonuniformly heat generating annular fluid layer

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2006年第1-2期49卷 269-280页

作者： Saravanan, S Kandaswamy, P Bharathiar Univ UGC DRS Ctr Fluid Dynam Dept Math Coimbatore 641046 Tamil Nadu India

The thermal stability of two dimensional parallel convective motion in a fluid confined between two vertical cylinders is studied. The convective motion is induced by nonuniformly distributed heat sources in the fluid layer. A spectral collocation method is employed to solve the axisymmetric perturbed equations arising in the linear stability analysis. The stability boundary depends on the source distribution parameter, source strength parameter, Prandtl number and radius ratio. In general the flow remains least stable when the source distribution parameter is maximum in the middle of the two bounding cylinders. Thermal buoyancy mode of instability is introduced by the source distribution parameter for lower values of the radius ratio. (c) 2005 Elsevier Ltd. All rights reserved.

关键词： Stability analysis ANNULAR Fluid Heat sources Cylinders Cylinders distributed parameter thermal stability

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Energy based discretization of a class of distributed parameters processes Comparison with classical approach

Energy based discretization of a class of distributed parame...

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Proceedings of the 46th IEEE Conference on Decision and Control, Pages 3678-4134

作者： H. Peng A. Baaiu F. Couenne Y. Le Gorrec University of Lyon France

ISBN: (纸本)9781424414970;1424414970

This paper deals with model reduction of infinite dimensional systems described by PDEs. It focuses on one dimensional systems as tubular reactors and adsorption processes derived from mass transport phenomena. The proposed method is based on energetic considerations. First, concepts of network modeling are used to stress the structure of the power transmission within the spatial domain and through the boundary. It is shown how to define the port variables such that the interconnection between dissipation and accumulation elements is power preserving. Based on this definition, the discretization method aims at preserving the structure associated with mass and power balances during the reduction. Finally the proposed methodology is compared with a finite difference method on an adsorption process. It is shown that in the centered approximation case, the proposed method avoids oscillations obtained from finite difference method.

关键词： Discretization Finite difference methods ADSORPTION PROCESS power transmission Energy sources Multidimensional systems distributed parameter spatial domain Reduced order model One dimensional Differentiation

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A distributed parameters model for electric hot water tanks

A distributed parameters model for electric hot water tanks

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American Control Conference

作者： Nathanael Beeker Paul Malisani Nicolas Petit MINES ParisTech PSL Research University CAS 60 bd Saint-Michel 75272 Paris Cedex FRANCE EDF Lab EnerBat Avenue des Renardieres - Ecuelles 77818 Moret-sur-Loing Cedex FRANCE

ISBN: (纸本)9781479917730

To quantify the potential of electric hot water tanks (EHWT) in load shifting and other demand response programs, there is a need for a simple model allowing to reproduce their experimentally observed behavior. The input output response of this system is in fact relatively complex. This paper presents a model of an EHWT in the form of two simple one-dimensional partial differential equations, followed by an experimental validation. The model permits to quantify the effective energy available for consumption which is an important variable for control and optimization purposes.

关键词： Load shifting hot water distributed parameter Demand-Responsive Electricity INPUT-OUTPUT available energy

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Modeling Heat Flow in Measuring Cell of Differential Scanning Calorimeter as a Control Object with distributed parameters

Modeling Heat Flow in Measuring Cell of Differential Scannin...

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International Conference on Complex Systems: Control and Modeling Problems

作者： Alexandr Nechaev Yurij Moshchenskij Samara State Technical University SamaraRussian Federation

Modern differential scanning calorimeter (DSC) is a complex information-measuring system used to obtain different temperature and thermal characteristics of the investigated substances. The main subsystem of DSC is a heat block including heaters, measuring cells, and heat conducting elements. Measuring cells in the thermal block are often located symmetrically in relation to the center. However, the heat flow coming from the main heater affects them unevenly. At different overall parameters of reference and test substances uneven cells heating leads to measurement error increase. Since the defining of thermal characteristics of materials using DSC is carried out in a dynamic mode it is necessary to take into account not only the dependence of measuring cell parameters on time, but also the spatial distribution of the external thermal impact affecting it. Measuring cell DSC mathematical model is given as a block with a distributed input and concentrated output effect. The model takes into account the uneven spatial distribution of the thermal field in the thermal block, as well as heat removal from the substrate through the sensing elements considered to be inertial links. A structural model of the heat flow control system in a heat block DSC was constructed on the basis of the measurement cell mathematical model. The model shows the following: basic elements and their relationships, radiation influence on heat flow formation reaching the measuring cell and additional heat formation from micro aggregates, its influence on the measuring cell. After a number of experiments, a computer model of the automatic heat flow control system in the measuring cell of the differential scanning calorimeter DSC-500 was built as a control object with distributed parameters. This model serves as the basis for numerical experiments required to adjust the regulators parameters of the main and additional heaters in the thermal block of the DSC at different modes of this information-measu

关键词： differential scanning calorimetry heat systems heat transfer measurement errors thermal engineering Differential scanning calorimetry measurement elements Heat flow Thermal engineering Error measure Heating systems thermal characteristics Heaters Heat transfer scanning calorimeter distributed parameter controlled object

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