The Experts below are selected from a list of 7170 Experts worldwide ranked by ideXlab platform
Zhen Gao - One of the best experts on this subject based on the ideXlab platform.
-
On the Extreme Value Analysis of the Response of a Turret Moored FPSO
Journal of Offshore Mechanics and Arctic Engineering, 2012Co-Authors: Luis Volnei Sudati Sagrilo, Arvid Naess, Zhen GaoAbstract:One of the standardized procedures used in the design of floating systems and their mooring and production lines is the so-called short-term design approach where the system is analyzed for some specific Extreme Environmental Conditions. Along with this procedure, a nonlinear time-domain coupled dynamic analysis, considering the floater and its risers and mooring lines, can nowadays be incorporated as a feasible part of the design practice. One very important and challenging aspect of this process is concerned with the estimation of the characteristic short-term Extreme values of the system response parameters based on the sampled time-series. In this paper a common procedure used to establish these Extreme values for floater system response parameters, which is based upon a Weibull distribution model for the peaks of the time-series, is reviewed in the light of a recently proposed approach based on a general parametric model for the average Conditional exceedance rate of peaks. It is shown that the former model corresponds to a particular case of the latter one. Numerical results are presented for the response parameters of a turret-moored Floating, Production, Storage and Offloading (FPSO) unit considering a short-term coupled analysis of the whole system under an Extreme Environmental Condition of wind, wave, and current. Specifically, the Extreme response of surge motion, top tension of the most loaded mooring line, and Det norske Veritas (DnV) codes utilization factor for the most critical section of an 0.20 m outer diameter SLWR (steel lazy wave riser) are investigated.
-
Extreme Value Analysis of the Response of a Turret-Moored FPSO
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 2, 2010Co-Authors: Lui´s Volnei Sudati Sagrilo, Arvid Naess, Zhen GaoAbstract:One of the standardized procedures used in the design of floating systems and their mooring and production lines is the so-called short-term design approach where the system is analyzed for some specific Extreme Environmental Conditions. Along with this procedure, a nonlinear time-domain coupled dynamic analysis, considering the floater and its risers and mooring lines, is nowadays feasible to be employed in the design practice. One important and challenging aspect of this process is concerned with the estimation of the characteristic short-term Extreme values of the system response parameters based on the sampled time-series. In this paper a common procedure used to establish these Extreme values for floater system response parameters, which is based on a Weibull distribution model for the time-series peaks, is reviewed in the light of a recently proposed approach based on a general parametric model for the average Conditional exceedance rate of peaks. It is shown that the former model corresponds to a particular case of the latter one. Numerical results are presented for the response parameters of a turret-moored FPSO considering a short-term coupled analysis of the whole system under an Extreme Environmental Condition of wind, wave and current. Specifically, the Extreme response of surge motion, top tension of the most loaded mooring line and DnV’s utilization factor for the most critical section of a 8″ SLWR (Steel Lazy Wave Riser) are investigated.Copyright © 2010 by ASME
-
Dynamic Motion Analysis of Catenary Moored Spar Wind Turbine in Extreme Environmental Condition
2009Co-Authors: Madjid Karimirad, Zhen Gao, Torgeir MoanAbstract:Floating wind turbines can be the most practical and economical way to extract the vast offshore wind energy resources at deep and intermediate water depths. The Norwegian Ministry of Petroleum and Energy is strongly committed to developing offshore wind technology that utilises available renewable energy sources. As the wind is steadier and stronger over the sea than over land, the wind industry recently moved to offshore areas. Analysis of the structural dynamic response of offshore wind turbines subjected to stochastic wave and wind loads is an important aspect of the assessment of their potential for power production and of their structural integrity. Of the concepts that have been proposed for floating wind turbines, spar-types such as the catenary moored spar (CMS) and tension leg spar (TLS) wind turbines seem to be well-suited to the harsh Environmental Conditions that exist in the North Sea. Hywind and Sway are two examples of such Norwegian concepts; they are based on the CMS and TLS, respectively. Floating wind turbines are sophisticated structures that are subjected to simultaneous wind and wave actions. The coupled nonlinear structural dynamics and motion response equations of these turbines introduce geometrical nonlinearities through the relative motions and velocities. Moreover, the hydrodynamic and aerodynamic loading of this type of structure is nonlinear. A floating wind turbine is a multibody aero-hydro-servo-elastic structural system; for such structures, the coupled nonlinear equations of motion considering nonlinear excitation and damping forces, including all wave- and wind-induced features, should be solved in the time domain. In this thesis, the motion and structural responses for operational and Extreme Environmental Conditions were considered to investigate the performance and the structural integrity of spar-type floating wind turbines. The power production and the effects of aerodynamic and hydrodynamic damping, including wind-induced hydrodynamic and wave-induced aerodynamic damping, were investigated. Negative damping adversely affects the power performance and structural integrity. In this thesis, the controller gains were tuned to remove servo-induced instabilities. The rotor configuration effect on the responses and power production was investigated by comparing the upwind and downwind turbines. To develop robust design tools for offshore wind power, the competencies of the offshore technology and wind technology must be combined. Both the offshore and wind energy industries have begun to extend their existing numerical codes to account for the combined aerodynamic and hydrodynamic effects on the structure. As a result verifications of extended codes by doing experiments and code-to-code comparisons are needed. One of the aspects of the present research was to fill this gap by performing hydrodynamic and hydro-elastic comparison between commercial codes. For both CMS and TLS concepts, the comparisons were carried out prior to using the tools to study the behaviour of the CMS and TLS under wave- and wind-induced loads. Offshore structures encounter a variety of operational and harsh Environmental Conditions. Limit states such as ultimate, fatigue, accidental collapse and serviceability limit states (ULS, FLS, ALS and SLS) are defined as the design criteria for offshore structures. In performing realistic ultimate limit state analysis, the Extreme responses of a floating wind turbine over its life should be estimated. This estimation requires detailed analysis of the Extreme response. In the present thesis, Extreme value analysis for spar-type wind turbines subjected to simultaneous wave and wind actions was preformed. The structural responses and the effect of modelled forces such as turbulence on these responses were investigated. The joint distribution of the Environmental characteristics of the wave and wind was applied through the contour surface method. Stochastic wave and wind analysis showed that, while rigid body modelling was sufficient for obtaining accurate motions, consideration of the elastic behaviour of the tower/support structure was necessary to predict structural responses. The blades structural responses were found to be significantly affected by the turbulent wind. However, the mean and standard deviation of global motion and structural responses were not affected by the turbulence. Thus, to reduce the simulation time in fatigue analysis, a constant wind speed model can be applied. The CMS and TLS wind turbines are inertia-dominated structures, and the hydrodynamic viscous drag did not affect their wave-induced responses, while an increase in viscous drag could effectively reduce the resonant responses of such turbines. Under operational Conditions, aerodynamic damping was found to be active in reducing both wave frequency and resonant responses. The results showed that, for a floating wind turbine, Extreme response could occur in survival Conditions, while for a fixed wind turbine, the Extreme response occurs in operational cases related to the rated wind speed. To estimate the Extreme value responses, extrapolation methods were used to reduce the sample size in Monte Carlo simulations. The accuracy of methods to estimate the Extreme responses as a function of sample size and methods applied was investigated. The normalized responses for both CMS and TLS offshore wind turbines were presented to draw more generalized conclusions.
Saad Mekhilef - One of the best experts on this subject based on the ideXlab platform.
-
an improved particle swarm optimization pso based mppt for pv with reduced steady state oscillation
IEEE Transactions on Power Electronics, 2012Co-Authors: Kashif Ishaque, Zainal Salam, Muhammad Amjad, Saad MekhilefAbstract:This paper proposes an improved maximum power point tracking (MPPT) method for the photovoltaic (PV) system using a modified particle swarm optimization (PSO) algorithm. The main advantage of the method is the reduction of the steady- state oscillation (to practically zero) once the maximum power point (MPP) is located. Furthermore, the proposed method has the ability to track the MPP for the Extreme Environmental Condition, e.g., large fluctuations of insolation and partial shading Condition. The algorithm is simple and can be computed very rapidly; thus, its implementation using a low-cost microcontroller is possible. To evaluate the effectiveness of the proposed method, MATLAB simulations are carried out under very challenging Conditions, namely step changes in irradiance, step changes in load, and partial shading of the PV array. Its performance is compared with the conventional Hill Climbing (HC) method. Finally, an experimental rig that comprises of a buck-boost converter fed by a custom-designed solar array simulator is set up to emulate the simulation. The soft- ware development is carried out in the Dspace 1104 environment using a TMS320F240 digital signal processor. The superiority of the proposed method over the HC in terms of tracking speed and steady-state oscillations is highlighted by simulation and experimental results.
-
An Improved Particle Swarm Optimization (PSO)-Based MPPT for PV With Reduced
2012Co-Authors: Kashif Ishaque, Zainal Salam, Muhammad Amjad, Saad MekhilefAbstract:This paper proposes an improved maximum power point tracking (MPPT) method for the photovoltaic (PV) system using a modified particle swarm optimization (PSO) algorithm. The main advantage of the method is the reduction of the steady- state oscillation (to practically zero) once the maximum power point (MPP) is located. Furthermore, the proposed method has the ability to track the MPP for the Extreme Environmental Condition, e.g., large fluctuations of insolation and partial shading Condition. The algorithm is simple and can be computed very rapidly; thus, its implementation using a low-cost microcontroller is possible. To evaluate the effectiveness of the proposed method, MATLAB sim- ulations are carried out under very challenging Conditions, namely step changes in irradiance, step changes in load, and partial shad- ing of the PV array. Its performance is compared with the con- ventional Hill Climbing (HC) method. Finally, an experimental rig that comprises of a buck-boost converter fed by a custom-designed solar array simulator is set up to emulate the simulation. The soft- ware development is carried out in the Dspace 1104 environment using a TMS320F240 digital signal processor. The superiority of the proposed method over the HC in terms of tracking speed and steady-state oscillations is highlighted by simulation and experi- mental results.
Kashif Ishaque - One of the best experts on this subject based on the ideXlab platform.
-
an improved particle swarm optimization pso based mppt for pv with reduced steady state oscillation
IEEE Transactions on Power Electronics, 2012Co-Authors: Kashif Ishaque, Zainal Salam, Muhammad Amjad, Saad MekhilefAbstract:This paper proposes an improved maximum power point tracking (MPPT) method for the photovoltaic (PV) system using a modified particle swarm optimization (PSO) algorithm. The main advantage of the method is the reduction of the steady- state oscillation (to practically zero) once the maximum power point (MPP) is located. Furthermore, the proposed method has the ability to track the MPP for the Extreme Environmental Condition, e.g., large fluctuations of insolation and partial shading Condition. The algorithm is simple and can be computed very rapidly; thus, its implementation using a low-cost microcontroller is possible. To evaluate the effectiveness of the proposed method, MATLAB simulations are carried out under very challenging Conditions, namely step changes in irradiance, step changes in load, and partial shading of the PV array. Its performance is compared with the conventional Hill Climbing (HC) method. Finally, an experimental rig that comprises of a buck-boost converter fed by a custom-designed solar array simulator is set up to emulate the simulation. The soft- ware development is carried out in the Dspace 1104 environment using a TMS320F240 digital signal processor. The superiority of the proposed method over the HC in terms of tracking speed and steady-state oscillations is highlighted by simulation and experimental results.
-
An Improved Particle Swarm Optimization (PSO)-Based MPPT for PV With Reduced
2012Co-Authors: Kashif Ishaque, Zainal Salam, Muhammad Amjad, Saad MekhilefAbstract:This paper proposes an improved maximum power point tracking (MPPT) method for the photovoltaic (PV) system using a modified particle swarm optimization (PSO) algorithm. The main advantage of the method is the reduction of the steady- state oscillation (to practically zero) once the maximum power point (MPP) is located. Furthermore, the proposed method has the ability to track the MPP for the Extreme Environmental Condition, e.g., large fluctuations of insolation and partial shading Condition. The algorithm is simple and can be computed very rapidly; thus, its implementation using a low-cost microcontroller is possible. To evaluate the effectiveness of the proposed method, MATLAB sim- ulations are carried out under very challenging Conditions, namely step changes in irradiance, step changes in load, and partial shad- ing of the PV array. Its performance is compared with the con- ventional Hill Climbing (HC) method. Finally, an experimental rig that comprises of a buck-boost converter fed by a custom-designed solar array simulator is set up to emulate the simulation. The soft- ware development is carried out in the Dspace 1104 environment using a TMS320F240 digital signal processor. The superiority of the proposed method over the HC in terms of tracking speed and steady-state oscillations is highlighted by simulation and experi- mental results.
Seiji Kojima - One of the best experts on this subject based on the ideXlab platform.
-
Bacterial Motility Measured by a Miniature Chamber for High-Pressure Microscopy
Biophysical Journal, 2015Co-Authors: Masayoshi Nishiyama, Seiji KojimaAbstract:Hydrostatic pressure is one of the physical stimuli that characterize the environment of living matter. Many microorganisms thrive under high pressure and may even physically or geochemically require this Extreme Environmental Condition. In contrast, application of pressure is detrimental to most life on Earth; especially to living organisms under ambient pressure Conditions. To study the mechanism of how living things adapt to high-pressure Conditions, it is necessary to monitor directly the organism of interest under various pressure Conditions. Here, we report a miniature chamber for high-pressure microscopy [1]. The chamber was equipped with a built-in separator, in which water pressure was properly transduced to that of the sample solution. The apparatus developed could apply pressure up to 150 MPa, and enabled us to acquire bright-field and epifluorescence images at various pressures and temperatures. We demonstrated that the application of pressure acted directly and reversibly on the swimming motility of Escherichia coli cells. The present technique should be applicable to a wide range of dynamic biological processes that depend on applied pressures [2, 3].[1] Nishiyama M. and S. Kojima. 2012. Bacterial Motility Measured by a Miniature Chamber for High-Pressure Microscopy. Int. J. Mol. Sci.13: 9225-9239.[2] Nishiyama M. et al. 2013. High Hydrostatic Pressure Induces Counterclockwise to Clockwise Reversals of the Escherichia coli Flagellar Motor. J. Bactetiol.195: 1809-1814.[3] Okuno D. et al., 2013. Single-Molecule Analysis of the Rotation of F1-ATPase under High Hydrostatic Pressure. Biophys. J.105:1635-1642.
-
Bacterial motility measured by a miniature chamber for high-pressure microscopy.
International journal of molecular sciences, 2012Co-Authors: Masayoshi Nishiyama, Seiji KojimaAbstract:Hydrostatic pressure is one of the physical stimuli that characterize the environment of living matter. Many microorganisms thrive under high pressure and may even physically or geochemically require this Extreme Environmental Condition. In contrast, application of pressure is detrimental to most life on Earth; especially to living organisms under ambient pressure Conditions. To study the mechanism of how living things adapt to high-pressure Conditions, it is necessary to monitor directly the organism of interest under various pressure Conditions. Here, we report a miniature chamber for high-pressure microscopy. The chamber was equipped with a built-in separator, in which water pressure was properly transduced to that of the sample solution. The apparatus developed could apply pressure up to 150 MPa, and enabled us to acquire bright-field and epifluorescence images at various pressures and temperatures. We demonstrated that the application of pressure acted directly and reversibly on the swimming motility of Escherichia coli cells. The present technique should be applicable to a wide range of dynamic biological processes that depend on applied pressures.
Arvid Naess - One of the best experts on this subject based on the ideXlab platform.
-
On the Extreme Value Analysis of the Response of a Turret Moored FPSO
Journal of Offshore Mechanics and Arctic Engineering, 2012Co-Authors: Luis Volnei Sudati Sagrilo, Arvid Naess, Zhen GaoAbstract:One of the standardized procedures used in the design of floating systems and their mooring and production lines is the so-called short-term design approach where the system is analyzed for some specific Extreme Environmental Conditions. Along with this procedure, a nonlinear time-domain coupled dynamic analysis, considering the floater and its risers and mooring lines, can nowadays be incorporated as a feasible part of the design practice. One very important and challenging aspect of this process is concerned with the estimation of the characteristic short-term Extreme values of the system response parameters based on the sampled time-series. In this paper a common procedure used to establish these Extreme values for floater system response parameters, which is based upon a Weibull distribution model for the peaks of the time-series, is reviewed in the light of a recently proposed approach based on a general parametric model for the average Conditional exceedance rate of peaks. It is shown that the former model corresponds to a particular case of the latter one. Numerical results are presented for the response parameters of a turret-moored Floating, Production, Storage and Offloading (FPSO) unit considering a short-term coupled analysis of the whole system under an Extreme Environmental Condition of wind, wave, and current. Specifically, the Extreme response of surge motion, top tension of the most loaded mooring line, and Det norske Veritas (DnV) codes utilization factor for the most critical section of an 0.20 m outer diameter SLWR (steel lazy wave riser) are investigated.
-
Extreme Value Analysis of the Response of a Turret-Moored FPSO
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 2, 2010Co-Authors: Lui´s Volnei Sudati Sagrilo, Arvid Naess, Zhen GaoAbstract:One of the standardized procedures used in the design of floating systems and their mooring and production lines is the so-called short-term design approach where the system is analyzed for some specific Extreme Environmental Conditions. Along with this procedure, a nonlinear time-domain coupled dynamic analysis, considering the floater and its risers and mooring lines, is nowadays feasible to be employed in the design practice. One important and challenging aspect of this process is concerned with the estimation of the characteristic short-term Extreme values of the system response parameters based on the sampled time-series. In this paper a common procedure used to establish these Extreme values for floater system response parameters, which is based on a Weibull distribution model for the time-series peaks, is reviewed in the light of a recently proposed approach based on a general parametric model for the average Conditional exceedance rate of peaks. It is shown that the former model corresponds to a particular case of the latter one. Numerical results are presented for the response parameters of a turret-moored FPSO considering a short-term coupled analysis of the whole system under an Extreme Environmental Condition of wind, wave and current. Specifically, the Extreme response of surge motion, top tension of the most loaded mooring line and DnV’s utilization factor for the most critical section of a 8″ SLWR (Steel Lazy Wave Riser) are investigated.Copyright © 2010 by ASME
