bluuebunny/crossref_metadata_2025 huggingface dataset:
Recoverable Energy in Natural Gas Pressure Drop Stations: A Case Study of the Khangiran Gas Refinery
Authors: Farzaneh-Gord Mahmood , Deymi-Dashtebayaz Mahdi
Published: September 2008

The natural gas which is supplied to the Khangiran gas refinery comes from a high-pressure natural gas transmission pipeline and passes through a metering and reducing station, sometimes referred to as the pressure drop station. The gas at this reduced pressure enters the refinery for internal uses. It is at the pressure drop station that a lot of energy is wasted, as the pressure of the natural gas is reduced by an expansion-type ball valve. But, the design of the ball valve does not allow any of the energy from the compressed natural gas to be recovered, as it regulates from a higher pressure to a lower pressure. If this energy loss can be captured, it can be converted into electricity. In this study, a comprehensive program has been carried out to record and measure natural-gas properties and flow rates at Khangiran pressure drop station for a year. Based on these data and an accompanying exergy analysis, the amount of available work that can be produced from capturing natural-gas pressure exergy from the station has been calculated. To produce work, a system which consists of preheating and a turbo expander has been proposed and studied. The effect of preheating temperature and turbo expander exergetic efficiency on amount of obtainable work has been studied. The results show that the amount of available energy can meet all electrical demand of the refinery.
Renewable Energy Sources for Sustainable Development in Turkey
Authors: Comakli Kemal , Kaya Mehmet , Sahin Bayram
Published: September 2008

Energy is an essential factor in overall efforts to achieve sustainable development. Countries striving to this end are seeking to reassess their energy systems with a view toward planning energy programs and strategies in line with sustainable development goals and objectives. Turkey's demand for energy and electricity is increasing rapidly. Since 1990, energy consumption has increased at an annual average rate of 4.3%. Turkey is heavily dependent on expensive imported energy resources that place a big burden on the economy and air pollution is becoming a great environmental concern in the country. As would be expected, the rapid expansion of energy production and consumption has brought with it a wide range of environmental issues at the local, regional and global levels. With respect to global environmental issues, Turkey's carbon dioxide (CO2) emissions have grown along with its energy consumption. States have played a leading role in protecting the environment by reducing emissions of greenhouse gases (GHGs). In this regard, renewable energy resources appear to be the one of the most efficient and effective solutions for clean and sustainable energy development in Turkey. Turkey's geographical location has several advantages for extensive use of most of these renewable energy sources. This article presents a review of the potential and utilization of the renewable energy sources in Turkey.
Active Vibration Control Using Delay Compensated LMS Algorithm by Modified Gradients
Authors: Glugla Markus , Schulz Ralf-Kiran
Published: September 2008

Active vibration control (AVC) based on adaptive finite impulse response (FIR) filters inhere delays in conditional signal dispersion. Reasons for these delays are geometrical arrangements, and computational time in analog digital converters (ADCs) and in digital analog converters (DACs). The delays represent a phase shift in periodic signals. These delays avoid instant feedback of the signals through the least mean square (LMS) algorithm. This can lead to instability and even divergence. This study presents a modification of the LMS algorithm by adjusting the underlying gradient descent algorithm. Using analytic considerations, it shows the conditions of convergence for the stepsize as well as the gradient. The result is that all delays occurring can be compensated entirely. Unlike the delayed LMS algorithm, the introduced method considers possible delays analytically and furnishes the possibility for a perfect delay compensation. Modifications are easy to put into practice and were researched and verified using various simulations. Measurements on a duct in a range from 100 Hz to 1000 Hz confirm the success of adjustment and show an excellent convergence over the whole tested frequency range. Signal manipulation, for example, with a low-pass filter, which allows reverse phase shifts between – π and π, results only in a small frequency range and may be omitted by using the delay compensated LMS algorithm. The analytic mathematical derivation of the required modification can be implemented easily.
Theoretical Development of Minimum Effort Active Noise Control with Feedback Inclusion Architecture
Authors: Ahmad Raja Kamil Raja , Tokhi M. O.
Published: September 2008

This paper presents the development of minimum effort active noise control theory for feedforward single-input single output (SISO) architecture, which includes the feedback acoustic path in the controller formulation. The theoretical range of effective minimum effort parameter with respect to level of point cancellation at the observer and the interference pattern generated around the observer for periodic noise control in free-field are investigated. It is found that for a minimum of 6 dB cancellation which corresponds to cancellation factor of 0.75 at the observer, the effort parameter must be specified as less than unity. It is also found that the cancellation pattern characterised by 20 dB, 10 dB and 6 dB zones reduces significantly in terms of size with an increase in the value of the effort term.
Comparative Study of Ion-Exchange and Biosorption Processes for the Removal of Cd2+ and Zn2+ Ions from Aqueous Effluents
Authors: de Britto Julia S. , da Costa Antonio Carlos A. , Luna Aderval S. , Henriques Cristiane A.
Published: September 2008

A basic investigation of the removal of Cd(II) and Zn(II) ions from aqueous solutions by Sargassum sp. and NaY zeolite was conducted at room temperature under batch conditions. The results obtained indicated that, for both sorbents, cadmium and zinc ion uptake could be described by the Langmuir adsorption model. The kinetics of the biosorption process followed a pseudo-second-order model, whereas equilibrium in the ion-exchange process was attained so rapidly that the data obtained could not be modelled. The maximum uptake capacities of the sorbents studied were 120 mg/g biomass and 108 mg/g zeolite for cadmium ions and 45.5 mg/g biomass and 70 mg/g zeolite for zinc ions, respectively. This can be considered an excellent result compared with conventional adsorbent materials. Thus Sargassum sp. and NaY zeolite have a great potential for removing cadmium and zinc ions, especially when the concentrations of these ions are low as in wastewater stream samples.
Single-Column Simulated Moving-Bed Process with Recycle Lag: Analysis and Applications
Authors: Araújo João M.M. , Rodrigues Rui C.R. , Silva Ricardo J.S. , Mota José P.B.
Published: September 2008

We report some conceptual and numerical results for a single-column chromatographic process analogous to a simulated moving bed (SMB) with asynchronous port switching. It is shown that the periodic state of the multi-column SMB unit is reproduced by a one-column chromatograph in which the part of its outlet stream that is not recovered as product is recycled back to the column with a lag of (N – 1)τ time units, where N and τ are, respectively, the number of columns and the switching interval of the equivalent SMB unit. This requirement holds true regardless of the port configuration or operational scheme of the analogous multi-column unit. The proposed one-column chromatographic process is a more compact, less expensive and simpler-to-operate alternative to the SMB. By changing the operation of the single-column chromatograph from the classical synchronous port switching to an optimized asynchronous Varicol mode, it is shown that one can easily compensate for a less perfect operation of the plug-flow device that implements the recycle lag.
Hybrid Membrane/PSA Processes for CO2/N2 Separation
Authors: Esteves Isabel A.A.C. , Mota José P.B.
Published: September 2008

New integrated schemes combining membrane permeation and pressure swing adsorption (PSA) have been developed for gas separation. By using the membrane as a pre-bulk separation unit and coupling it to the intrinsically dynamic periodic operation of the PSA, the separation performance of the hybrid scheme is enhanced with respect to that of the two stand-alone units. Instead of constant-composition regular feed, the PSA is fed with a mixture which is progressively enriched in the more adsorbed component during the pressurization and high-pressure adsorption steps of the cycle. This results in sharper concentration fronts.

The hybrid scheme detailed here has been applied successfully to the bulk separation of an 30:70 mol% CO2/N2 mixture over activated carbon. Process performance is reported in terms of product recovery and purity at cyclic steady state. Numerical simulations were validated by experimental work on a composite membrane and a laboratory-scale PSA unit. For the examples studied, product purity and recovery for the hybrid process were increased by 23% and 58% for CO2, and by 14% and 5% for N2, compared to an equivalent stand-alone PSA.
Kinetics of Basic Dye Adsorption onto Sphagnum Magellanicum Peat
Authors: Contreras Elsa G. , Martinez Boris E. , Sepúlveda Luisa A. , Palma Carolyn L.
Published: September 2008

The purpose of this study was to investigate the adsorption of two Basic dyes, i.e. Basic Blue 3 (BB3) and Basic Orange 2 (BO2), onto Sphagnum Magellanicum peat. The equilibrium studies were carried out at 30°C and 45°C, respectively. The equilibrium experimental results were fitted to the Langmuir model to obtain the characteristic parameters. The maximum sorption capacities for each dye were 41 mg/g for BB3 and 92 mg/g for BO2. The magnitude of the aL parameter increased with temperature for both dyes. The batch kinetic studies of Basic dye adsorption onto peat considered the effect of the initial concentrations of the dyes and the peat dosage. The models fitted were first order (Lagergren equation), pseudo-second order (chemisorption mechanism) and intra-particle diffusion. For all the systems studied, the pseudo-second-order model provided the best correlation. The intra-particle diffusion model provided good correlations over the intermediate and final steps of the adsorption process.
Adsorption Isotherms of Mucin on Granules Containing Chitosan Microspheres
Authors: da Silva Classius F. , Martins Fernanda , Santana Maria Helena A.
Published: September 2008

The effect of the excipients used for the preparation of granules containing chitosan microspheres on the adsorption of the muco-polysaccharide mucin was studied. Adsorption isotherms at 37°C were obtained as one strategy for the in vitro evaluation of the muco-adhesive properties of granules carrying drugs. The microspheres were prepared via an ionotropic gelation technique using sodium tripolyphosphate as the cross-linking agent. The resulting microspheres were dried at 40°C until a water content of 75% was achieved and the subsequent extrusion/spherulation process carried out using different excipients, i.e. unmodified chitosan, pre-gelated starch or carboxymethylcellulose. The Langmuir adsorption equation gave a good fit to the experimental data. Mucin exhibited the best affinity to granules containing chitosan as the excipient. Such granules also appeared to have the best muco-adhesive properties.
Adsorption of Myoglobin onto Hydroxyapatite Modified with Metal Ions
Authors: Farinas Cristiane S. , Reis Patrícia C. , Ferraz Helen C. , Salim Vera M.M. , Alves Tito L.M.
Published: September 2008

Optimization of the purification process remains a challenge in the production of proteins for pharmaceutical or industrial applications. In this context, the purpose of this work was to study the adsorption of myoglobin onto hydroxyapatite (HAp) modified with metal ions (Cu2+, Ni2+, Zn2+), with the aim of its purification from a complex medium. The influence of pH and ionic strength on the adsorption process was evaluated using experimental design methodology. Experiments for determining the kinetics and adsorption isotherms were undertaken, allowing the determination of important equilibrium parameters required for scale-up. High adsorption capacities (ca. 90 mg myoglobin/g modified HAp) and rapid adsorption kinetics were observed. These results indicate the applicability of HAp as a support for pseudo-affinity chromatography.
Adsorption of Zinc Ions from Water Using Zeolite/Iron Oxide Composites
Authors: Fungaro Denise A. , Graciano José E. A.
Published: September 2008

The adsorption characteristics of zeolites synthesized from fly ash were combined in a composite with the magnetic properties of iron oxides to produce adsorbents which were magnetic materials. Such zeolite/iron oxide magnetic composites were prepared with weight ratios of 3:1, 2:1 and 1:1. The experimental data for the equilibrium adsorption isotherms of Zn2+ ions onto the composites were modelled using the Freundlich and Langmuir equations. The presence of iron oxide had no significant effect on the adsorption capacities of the magnetic composites.

The experimental data were also employed to determine the kinetic characteristics of the adsorption process. The adsorption of Zn2+ ions was found to follow pseudo-second-order type kinetics. Although intra-particle diffusion occurred in the adsorption processes, it could not be accepted as the primary rate-determining step. The evaluated thermodynamic parameters indicated that the adsorption of Zn2+ ions onto zeolite/iron composites was spontaneous and endothermic.
Adsorption of Reactive Blue 5G Dye by Activated Carbon and Pyrolyzed Shale Oil Residue
Authors: Lambrecht Rafael , Barros Maria Angélica S.D. , Cossich Eneida S. , Silva Edson A. , Matta Gleisy Kelly L. , Stachiw Rosalvo
Published: September 2008

This work was aimed at the study of the adsorption mechanism of Reactive Blue 5G dye on activated carbon derived from babassu shells and pyrolyzed oil shale residue. Experiments were undertaken employing a fixed bed reactor at 30°C using continuous systems. To minimize diffusional resistances, the influence of the flow rate was investigated via breakthrough curves at a feed concentration of 35 mg/ l. Breakthrough curves for flows in the range 2–10 m l/min were carried out using bed height of 15.5 cm for activated carbon and 9.5 cm for pyrolyzed oil shale residue, with an inlet diameter of 1.01 cm. From the calculated mass-transfer parameters, it was shown that the minimum resistance to flow occurred at 4 m l/min for activated carbon and at 2 m l/min for pyrolyzed oil shale residue. It was concluded that the sizes of the pores in the adsorbents play an important role in the adsorption mechanism.
Determination of the Acidity of MCM-41 with Different Si/Al Ratios by the Temperature Programmed Desorption of Pyridine
Authors: Souza Marcelo J.B. , Lima Stevie H. , Araujo Antonio S. , Pedrosa Anne M. Garrido , Coutinho Ana C.S.L.S.
Published: September 2008

Mesoporous catalysts of MCM-41 type with different Si/Al ratios were synthesized by the hydrothermal method and characterized by X-ray diffraction, nitrogen adsorption and thermogravimetric analysis. Their acidic properties were determined via the temperature programmed desorption of pyridine. Vyazovkin kinetic models were used to correlate the total acidity as a function of the Si/Al ratio with the apparent activation energy for pyridine desorption. The results obtained indicated that the catalysts possessed weak and medium acidic sites. An increase in the Si/Al ratio led to an increase in the activation energy for pyridine desorption.
Optimized Design of a Steel-Glass Parabolic Vault Using Evolutionary Multi-Objective Algorithms
Authors: Amadio Claudio , Fragiacomo Massimo , Lucia Pasquale , de Luca Olindo
Published: September 2008

The paper explores the possibilities offered by evolutionary multi-objective algorithms in structural design. The developed procedure includes the parameterization of a 3D structure, the automatic generation of a finite element (FE) model, and the optimum design. The search of the optimum solution is dealt with using two commercial software packages: Straus7, for FE analysis, and modeFrontier, for optimal search, interlinked by a program purposely developed ( SCU, system control unit). The optimum design of a structure needs a different approach with respect to the traditional design. The paper presents a possible approach and describes more in detail the data pre and post processing including the choice of the solutions on the Pareto's front. A case study, a steel-glass vault roof built in Badenweiler (Germany), is used to demonstrate the effectiveness of the proposed approach. A significant economical saving can be achieved when the optimum design solution is used. The proposed algorithm can then be employed as a useful tool to help the designer in the complex design process.
Structural Design of a Spherical Cable Dome with Stiff Roof
Authors: Zhang Zhi-Hong , Dong Shi-Lin , Fu Xue-Yi
Published: September 2008

Preliminary design of a practical spherical cable dome with a diameter of 122m was carried out in China Construction (Shenzhen) Design International (CCDI) in 2006. Stiff roof (roof system with steel purlins and metallic skin) has been chosen for the project of a multifunctional gymnasium in preference to a flexible membrane (PTFE, ETFE). In the present paper the whole structural design procedure of this real cable dome is described: Load conditions, technical conditions required by performance based structural design, a novel force finding method-linear deduction method, optimal analysis of feasible initial internal force level, load analysis, nonlinear buckling analysis, cable breaking simulation, and construction animation. Technical details of joint design are also given out.
Modelling System Failures to Optimise Wind Turbine Maintenance
Authors: Andrawus Jesse A. , Watson John , Kishk Mohammed
Published: September 2008

Modelling System Failures (MSF) is a unique quantitative maintenance optimisation technique which permits the evaluation of life-data samples and enables the design and simulation of the system's model to determine optimum maintenance activities. In this paper, the approach of MSF is used to assess the failure characteristics of a horizontal axis wind turbine. Field failure data are collated and analysed using the Maximum Likelihood Estimation in the Weibull Distribution; hence shape ( β) and scale (η) parameters are estimated for critical components and subsystems of the wind turbine. Reliability Block Diagrams are designed to model the failures of the wind turbine and of a selected wind farm. The models are simulated to assess the reliability, availability and maintainability of the wind turbine and the farm; taking into account the costs and availability of maintenance crew and spares holding. Optimal maintenance activities are determined to minimise the total life-cycle cost of the wind farm.
Rotor Speed Stability of Grid Connected Wind Energy Conversion Systems
Authors: Jayashri R. , Devi R.P. Kumudini
Published: September 2008

This paper examines the dynamics of grid connected wind energy conversion systems under the concept of ‘rotor speed stability’. The majority of wind turbines installed in India have induction generators, which are directly connected to the grid. Consequently, wind turbines interact with the power system in a way that differs from synchronous generators. Therefore, it is more appropriate to study the impacts in terms of rotor speed stability that focuses on torque-speed dependence of asynchronous generators, similar to the rotor-angle stability that focuses on the torque-angle dependence of synchronous generators. In this paper, the rotor-speed stability of the system considered is analysed for step change in wind velocity, gust speed and for three-phase faults at key locations in the system. Simulation studies are done on an 11-bus radial system, using C++ programming language and the results obtained are presented. The results help to understand the rotor-speed stability phenomena in fixed speed windfarms and could help in designing the rotor-speed stability requirements of such systems.
A Novel SFL-SM Controller for Statcom to Improve the Dynamic Performance of a Power System with Integrated Wind Generation
Authors: Subramanian D. Padma , Devi R. P. Kumudini
Published: September 2008

A novel Single Input Fuzzy Logic (SFL) based Sliding Mode Controller (SMC) is proposed for Static Synchronous Shunt Compensators (STATCOM1) to improve the dynamic performance of a power system having much integration of wind generation using induction generators. The proposed controller consists of an equivalent control term, a switching term and a fuzzy control term. It employs only one input signal, which is the deviation of STATCOM capacitor voltage from its reference value. The major drawback of the basic SMC approach is the undesired ‘chattering’, due to high-frequency; this switching is reduced by introducing a boundary layer in the proposed controller. Using the SFL control term, the improvements of dynamic performance are: maintaining constant voltage at the point of common coupling (PCC) for greater loading, delaying the incidence of Hopf bifurcation (HBF) and saddle node bifurcation (SNB). Hence an increase in load limit is achieved. The effectiveness of the proposed controller is demonstrated through bifurcation analysis of a 10 bus system, in which a Wind Energy Conversion System (WECS) is integrated to the main transmission grid at the eighth bus. Steady state bifurcation diagrams are constructed for the test system and improvement of dynamic response by the proposed controller is illustrated in a bifurcation perspective.
Analysis of Wind Power Penetration in Autonomous Greek Islands
Authors: Caralis George , Zervos Arthouros
Published: September 2008

Greek islands are characterized by excellent wind-energy potential for isolated island grid power, but face curtailment by the system operator of surplus wind-generated power during periods of low demand. The ability to balance demand with wind power, defines the wind capacity to be installed and the wind power to be absorbed by the grid. In this paper, isolated island electrical systems are simulated and the impacts of large penetration of wind power are evaluated using a parametrical approach. The simulation is based on the non-dynamic analysis of the system, in order to calculate the annual wind energy which can be absorbed by the electrical system. The conclusions are focused on the prospects of wind power decreasing the electrical system's cost. The results show that a proportionately large penetration of wind power in autonomous islands may decrease the system's electricity production cost, provided that a larger instantaneous wind penetration can be allowed.
Modelling and Fault-Ride-Trough Tests of Siemens Wind Power 3.6 MW Variable-Speed Wind Turbines
Authors: Nielsen Jørgen Nygaard , Akhmatov Vladislav , Thisted Jan , Grøndahl Erik , Egedal Per , Frydensbjerg Michael Nørtoft , Jensen Kim Høj
Published: September 2008

Transmission system operators and developers require dynamic wind turbine models to evaluate fault-ride-through capability and to investigate power system stability associated the grid incorporation of large windfarms. Siemens Wind Power has developed a dynamic model of a 3.6 MW variable-speed wind turbine which is one of the world's largest, most advance and competitive offshore wind turbines. The model is implemented in commercially available power system simulation tools, such as DIgSILENT PowerFactory and Siemens PTI PSS/E. The model has been validated successfully with fault-ride-through tests.
Offshore Coastal Wind Speed Gradients: Issues for the Design and Development of Large Offshore Windfarms
Authors: Barthelmie R.J. , Badger J. , Pryor S.C. , Hasager C.B. , Christiansen M.B. , Jørgensen B.H.
Published: September 2008

Simulations, from mesoscale numerical models, and analyses of in-situ and remote sensing data from offshore wind farms in Denmark, are used to examine both horizontal and vertical gradients of wind speeds in the coastal zone. Results suggest that the distance from the coastline over which wind speed vertical profiles are not at equilibrium with the sea surface (which defines the coastal zone) extends to 20 km and possibly 70 km from the coast. Using this operational definition of the coastal zone, these results thus imply the typical width of the coastal zone in northern Europe is between 20 and 70 km. The width of the coastal zone, and the wind's vertical (shear) and horizontal gradients within the coastal zone, depend on atmospheric stability. Although vertical wind speed profiles above 50 m are likely responding to additional factors such as the height of the boundary-layer, using a stability correction improves predictions of wind speed compared with the logarithmic profile. Modelling indicates that within the coastal zone, wind speeds at typical turbine hub-heights can change by 2 m/s over the horizontal extent of a large wind farm, depending on stability. However, if the fetch is sufficiently long (or the windfarm is further from the coast) both horizontal and vertical wind speed gradients over the area of the wind farm appear to be small and negligible.
Market-Based Ancillary Services in the Australian National Electricity Market for Increased Levels of Wind Integration
Authors: Thorncraft Stuart R. , Outhred Hugh R. , Clements David J. , Barker Filita K.
Published: September 2008

This paper provides an overview of Australia's National Electricity Market (NEM) with a focus on its design and implementation features that benefit an increasing level of wind generation. The NEM design is discussed both in terms the ability of the system operator to manage threats to the security of the power system that an increasing level of wind integration may pose through the use of market-based frequency control ancillary services (FCAS) as well as the extent to which the commercial decision-making processes are suitable for participation of wind farm operators in the electricity market. In this way, the features of the NEM that facilitate wind integration are identified along with aspects of the market design that could be refined. This allows for comparisons to be made to other electricity market designs in terms of their ability to support an increasing level of wind integration.
Noise Management on Modern Wind Turbines
Authors: Romero-Sanz Ignacio , Matesanz Álvaro
Published: September 2008

This paper describes the activities in which the wind turbine industry is taking part to reduce the noise emission. The produced noise could risk the development of this technology in populated areas and it has become one of the most important environmental impacts of wind energy. The turbulent nature of the incoming flow, the presence of the terrestrial boundary layer, the elastic deformations and the moving geometry makes the problem difficult to solve. In this context the reasonable alternative is to find semi-empirical methods that could be applied to reduce noise with the time constraints imposed by the market. The beginning of this paper introduces the most relevant noise sources for wind turbines and their theoretical treatment, then the description of the strategies that are used to reduce noise levels are discussed, and finally the current research projects where the industry is participating for noise reduction are presented.
O&M Planning — Key to Increased Project Availability and Revenue
Authors: Ait-Driss Bouaziz , Deane Paul , Chittaranjan Govindarajan
Published: September 2008

A major factor influencing the profitability of wind projects, after the construction budget, is the cost of operation and maintenance (O&M). Inadequate reserves or cost provisions of a poorly planned O&M budget can compromise project operability and trigger significant revenue losses of even a well-designed project. O&M is therefore to be considered as a key element to help ensure component longevity and project success. Though advances in wind turbine technology have lessened the burden of O&M on projects, wind farms still require a sound O&M programme to achieve expected levels of performance and consistent revenues. This paper will highlight the main elements to be considered in developing an O&M plan, while showing the evolution of various O&M budget costs as a function of advances in technology. Hélimax's findings are mostly based on publicly available O&M history in Europe, though relevant parameters relative to harsh climate will also be discussed.
Control of Rotor Geometry and Aerodynamics: Retractable Blades and Advanced Concepts
Authors: McCoy Timothy J. , Griffin Dayton A.
Published: September 2008

This research focuses on the combination of two areas: aerodynamics and controls for wind turbine load reduction. The goal of the study is to develop baseline estimates of the cost benefits available from the use of advanced control of wind turbine rotors. The first category includes devices or methods that can be used to actively alter the local aerodynamic properties of the rotor blade. These devices have response times at least as fast as a full-span, variable-pitch system. The second category is geometry control, based on extendable length blades. These technologies are applied to a virtual turbine design with a 90-m diameter and a 2.5 MW rating, variable-speed, and variable-pitch. The approach will include simulations using MSC-ADAMS and detailed cost modeling based on the simulated loads. The control algorithms will employ linear state space methods that include individual blade pitch and multi-input, multi-output control of the selected aerodynamic devices.
Simulated Onshore-Fault Ride through of Offshore Wind Farms Connected through VSC HVDC
Authors: Arulampalam A. , Ramtharan G. , Caliao N. , Ekanayake J.B. , Jenkins N.
Published: September 2008

Effective Onshore-Fault Ride Through was demonstrated by simulation for a Fixed Speed Induction Generator (FSIG) offshore wind farm connected through a Voltage Source Converter HVDC link. When a terrestrial grid fault occurs, power through the onshore converter reduces and the DC link voltage increases. A control system was then used to block the offshore converter. The offshore AC network voltage was reduced to achieve rapid power rejection. Reactive power at the onshore converter was controlled to support the AC network voltage according to the GB Grid Code requirements. Two cases, a 200 ms terrestrial fault and a 50% retained voltage fault of duration 710 ms, at the grid connection point were studied. The simulation results show that power blocking at the offshore converter was effective and the DC link voltage was controlled.
Impact of FACTS Controllers on the Dynamic Stability of Power Systems Connected with Wind Farms
Authors: Kumar N. Senthil , Khan M. Abdullah
Published: September 2008

The increasing power demand has led to the growth of new technologies that play an integral role in shaping the future energy market. Keeping in view of the environmental constraints, grid connected wind turbines are promising in increasing system reliability. This paper presents the impact of Flexible A.C. Transmission System (FACTS) controllers on the dynamic stability of power systems connected with wind energy conversion systems. The wind generator model considered is a variable speed doubly - fed induction generator model. The stability assessment is made first for a three phase short circuit without the FACTS controllers in the power network and then with the FACTS controllers. The dynamic simulation results yield information on (i) The impact of faults on the performance of induction generators/wind turbines. (ii) The change in controllable parameters of the FACTS controllers following the disturbance. (iii) Transient rating of the FACTS controllers for enhancement of rotor speed stability of induction generators and angle stability of synchronous generators.
Non-Linearity in MCP with Weibull Distributed Wind Speeds
Authors: Clive Peter J M
Published: September 2008

Conventional MCP (Measure Correlate Predict) techniques often employ linear regression to model the relationship between wind speeds at two sites and use this model to predict the long term wind regime at one site from the long term wind regime at the other. In considering sites whose wind speeds are Weibull distributed it can be demonstrated analytically that linear relationships do not, in fact, hold. The general relationship is found to be of the form y = m xα + c where α is the ratio of the shape parameters of the Weibull distributions. Linearity prevails only when the shape parameters are equal. This is seen to have implications for MCP analysis.
Practical Implementation of Hysteresis Control for Maximum Power Point Tracking of a Permanent Magnet Generator Wind Turbine
Authors: Riahy G. , Freere P.
Published: September 2008

A permanent magnet wind turbine is to track a dynamically changing wind from measurements of the wind speed and the rotor speed. Issues of determining the effective wind speed at the turbine rotor are investigated as well as the optimum control strategy to maintain operation at the maximum power point. This is implemented using a hysteresis control system based on the turbine tip speed ratio and then tested on a permanent magnet generator wind turbine in a dynamic wind environment. This showed a small increase in the energy output using the controller. Methods to increase the energy output further are investigated by simulation.
Variable Speed Wind Generators Participation in Primary Frequency Control
Authors: Courtecuisse Vincent , Robyns Benoit , Francois Bruno , Petit Marc , Deuse Jacques
Published: September 2008

To maintain a power reserve to contribute to the primary frequency control with variable speed wind generators, two control strategies are analysed in this paper: a torque control strategy and a fuzzy logic based multivariable control strategy. The first and most simple strategy allows to maintain a regular reserve only when the wind turbine generator works at full load and needs the determination of a power reference value a priori or by the network manager. The second control strategy allows to overcome these limits without any wind speed measurement; it determines in real time the generator power reference value to maintain a fixed minimum reserve. The main result of this paper is to shown that it is possible to maintain a regular reserve on a large range of the wind speed. This reserve is still more regular when considering a wind farm owing to the wind speed dispersion. The performance of the proposed primary frequency control strategies is shown with the help of simulations by considering a wind farm including three wind generators.
On Embedded Energy Storage for High Penetration of Wind Power
Authors: Yang T C
Published: September 2008

It is recognised that to enable high penetration of wind power it is essential for modern wind farms to meet some technical requirements. These requirements are specified, or planned to be included, in grid codes by some utilities around the world. In this paper it is shown that having an Embedded Energy Storage (EES) unit, a battery bank, in a wind turbine can help to meet these requirements and to reduce the overall wind farm development and system integration costs. After a review of wind power integration and power system load frequency control, two cases are presented. These are based on (a) the statistics of the wind speeds measured at Dunstaffnage, Scotland, (b) the manufacturers' data for two turbine generators, and (c) some mild assumptions used for the calculations. In the first case, for the same amount of wind energy annual output and a specified frequency control requirement: the delta production constraint, a wind farm of 50 wind turbines can be replaced by 10 wind turbines with an EES in each of them plus 33 ordinary wind turbines. In the second case, again for the same amount of wind energy annual output, wind turbines with EESs can meet the absolute power constraint and at the same time the ratings of transformers, transmission lines and other equipments associated with a wind farm development can be reduced, leading to a significant reduction in costs. Wind farms with such wind turbines can also provide some vital support in an emergency, for example, the event in Denmark on the 8th January 2005, when the total wind power output dropped suddenly from the scheduled 1843MW to 126MW, due to the shut down of most wind turbines under strong winds.
Noise Generation by Vacuum Cleaner Suction Units
Authors: Čudina Mirko , Prezelj Jurij
Published: September 2008

Among all household appliances, the vacuum cleaner is the most powerful source of noise. The built-in suction unit, consisting of an electric motor and a centrifugal blower, represents the main source of noise; this is partially aerodynamic, mechanical and electromagnetic in origin. The contribution of the particular origin of noise generation to the total noise level depends on the geometry of the suction unit and operating conditions. The aerodynamically generated noise within the blower mostly prevails in the total emitted noise at design and off-design operations, and is especially distinct at partial flow rates when rotating stall and surge appear. The vaned diffuser built into the blower has an important effect on the emitted noise, so on the airborne as well as on the structure-borne noise and their spectra. Detailed analyses of measurement results have shown that the built-in vaned diffuser has numerous disadvantages, including: increase in the tonal and turbulent noise, increase in production costs and reduction of the flow rate, therefore, it could be omitted or replaced by a vaneless one. In this paper, an overview of the effects of the vaned diffuser on the aerodynamic, mechanical and electromagnetic noise origins at different operating conditions is given.
Time Delay Based Noise Control in Centrifugal Fans
Authors: Golmohammadi Rostam , Rahimi Jamshid , Mossavi Saeid Hossien , Mahjub Hossien
Published: September 2008

The most common noise control systems are already based on passive and active techniques. Passive noise control is a typical technique for high frequency noise and active noise control also for low frequency noise. In this paper, a simple and cheap method is proposed to determine the difference between sound waves of two centrifugal fans based on time delay in power starting to control low frequency noise.

The highest level in the noise level analysis shown in study fans is at 250 Hz. In the interference stage of study, noise measurements were recorded in the time delay of 3, 6 and 8 ms for power start for one of the fans. Results showed that an 8 ms time delay resulted in 1.3 – 2.3 dB(L) reduction in total sound pressure level of fans. This method is suggested for noise control of low frequency in the same sources.
Annoyance Due to Single and Combined Sound Exposure from Railway and Road Traffic
Authors: Öhrström Evy , Barregärd Lars , Andersson Eva , Skänberg Annbritt , Svensson Helena , Ängerheim Pär
Published: September 2008

Environmental noise is a growing and well recognized health problem. However, in many cases people are exposed not to a single noise source—for example, road, railway, or aircraft noise—but to a combination of noise exposures and there is only limited knowledge of the effects on health of exposure to combined noise sources. A socio-acoustic survey among 1953 persons aged 18–75 years was conducted in residential areas exposed to railway and road traffic noise with sound levels ranging from LAeq,24h 45–72 dB in a municipality east of Gothenburg, Sweden. The objectives were to assess various adverse health effects, including annoyance, and to elucidate the impact of exposure to single and combined noise sources. In areas exposed to both railway and road traffic, the proportion annoyed by the total traffic sound environment (total annoyance) was significantly higher than in areas with one dominant noise source rail or road traffic with the same total sound exposure ( LAeq,24h,tot). This interaction effect was significant from 59 dB and increased gradually with higher sound levels. Effects of the total sound exposure should be considered in risk assessments and in noise mitigation activities.
Screening Performance of Pairs of Diffusively Reflecting Traffic Noise Barriers: Theory and Experiments
Authors: Cianfrini Claudio , Corcione Massimo , Fontana Lucia
Published: September 2008

An easy-to-apply computational procedure for the study of the acoustic performance of pairs of diffusively reflecting roadside barriers is described in detail, and an experimental verification of its predictions, carried out on a 1:10 scale model, is presented and discussed. It is shown that, in comparison with pairs of more traditional specularly reflecting noise barriers, significant attenuation benefits are obtained not only in the shadow zone behind the barriers, but also in the unprotected zone immediately above the barriers, which proves that diffusive traffic faces of the barriers may effectively help in counteracting multiple reflection effects.
Implications of New Radiobiological Insights for the Long Term Management of High Level Radioactive Waste
Authors: Baverstock Keith
Published: September 2008

The IAEA has laid down nine principles of radioactive waste management [1], the first of which covers the protection of human health and demands that radioactive waste will be managed in such a way as to provide an acceptable level of protection. The fourth principle demands that future generations are protected in terms of the level of predicted impacts at the same level of protection as applies today. Recent developments in the understanding of the effects of ionising radiation, particularly at low doses and especially for some of the radiation qualities that characterise long lived components of radioactive waste, suggest that there may have been an underestimation of the predicted impact on health of future generations should radioactive waste products reach the biosphere. This could undermine the existing management framework upon which radiological protection is based and may lead to violation of the fourth principle.

This paper addresses, from an “in principle” perspective, the issues that new radiobiological evidence and recent developments in biology and genetics have raised in the context of determining radiological risk from internal contamination. Special emphasis is placed on radiation qualities, low energy beta particles, Auger electrons and alpha particles, which characterise the nuclides that are associated with long-lived radioactive decay processes. While absorbed tissue dose remains a guide to one aspect of the risks incurred by exposure (called herein type A risk), evidence is accumulating that other cellular processes may contribute to additional risk (type B risk). These processes are the induction of genomic instability and the bystander effect. Risk assessment in these cases cannot readily and convincingly be based on absorbed tissue dose and require addressing at the levels of the individual cell and the specific track structural features of the different radiation qualities. A potential framework for assessing type B risk is proposed.

It is concluded that there is no basis to assume other than that the linear no threshold (LNT) hypothesis will apply to risks (types A and B) from exposure to environmental radioactivity deriving from leakage of buried radioactive wastes.
Disposing of Britain's Nuclear Waste: The Corwm Process
Authors: Wallis Max K.
Published: September 2008

The Committee on Radioactive Waste Management (CoRWM) set up in 2003 was tasked to oversee a review of options for managing UK radioactive waste and to engage the public in choosing a long-term solution with the objective of inspiring public confidence. This paper reviews the Committee's processes against their remit and guidance on public engagement. It shows that CoRWM assumed proof-of-concept for geological disposal, despite the contrary verdict of the Sellafield inquiry, and biased the framing of options against ‘interim storage plus ongoing R&D’ (Netherlands option). CoRWM also failed to propose technical criteria comparable to those used internationally, and to resolve the deep disagreement on timescale between key stakeholders. The paper points out vested interests operated via CoRWM's programme manager (AMEC-NNC) and sees the checking role of Defra's chief scientist as also undermining the proclaimed independence of the Committee.

CoRWM did recognise their need to range much wider than scientific and technical issues, introducing concepts of institutional breakdown, volunteerism, and socio-cultural timescales. However, these concepts were not subjected to stakeholder consultation and public judgement. The audit of public and stakeholder engagement omitted questions of procedural norms, imbalance of power, and lack of consultation on novel judgements. Two late ‘show stoppers' were ignored in a desire to complete the task, resulting in a fudged compromise papering over deep divisions between members.

Their final choice of ‘Phased Deep Geological Disposal’ expressed qualified confidence in the concept, yet favoured keeping the repository open while continuing R&D into other options. The substantial scientific uncertainties associated with this choice, the problematic process by which this decision was reached, and the concerns associated with the modes of public engagement, mean that their ‘solution’ is more rhetorical than real. The technical problems and requirements for public confidence remain obscured and unresolved. The reasons for this problematic outcome are located in the current UK policy push for substantial new nuclear power plants and in a culture tolerant of vested interest in nuclear policy-making and civil service warping of the science process.
Public Participation - Potential and Pitfalls
Authors: Oughton Deborah
Published: September 2008

Over the past ten years there has been an increased awareness of the importance of stakeholder involvement and public participation in policy making. However, despite a general acceptance that stakeholder participation is important within decision-making, it is less clear as to how that participation should be undertaken, who should be involved, and how the various methods for participation should be evaluated. By first reflecting on some of the philosophical assumptions behind the view that stakeholder engagement is important, this paper presents a number of possible evaluation criteria for such involvement. It suggests that the appraisal of processes needs to include consideration of the legitimacy of the procedure, in addition to the more common efficiency evaluation of procedures and outcomes. Using experience from case studies, these criteria are then used to highlight the main promises and pitfalls of the various participation procedures.
Drinking Water from Solar Stills: A Renewable Technology for Sudan
Authors: Omer Abdeen Mustafa
Published: September 2008

The harsh climate in the Red Sea area, for example the Sudan, presents unique challenges in meeting growing demands for power and water. The international demand for water increases compared to the available water resources. Many areas, and especially in the Red Sea areas already experience a serious shortage of potable water and this is likely to grow. These areas enjoy, however, a high intensity of solar energy. Among the renewable energy options that have received special attention are solar stills. A solar still was built based on the principle of the packed tray array for tandem distillation and heat recovery. This article provides a brief overview of efforts to expand such renewable technologies in the Sudan in a cost-effective and sustainable way, and the environmental benefits associated with displacing fossil fuels.