| 45811. |
- Shafaghi, Ali Hosseinpour, et al.
(författare)
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On cavitation inception and cavitating flow patterns in a multi-orifice microfluidic device with a functional surface
- 2021
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Ingår i: Physics of fluids. - : AMER INST PHYSICS. - 1070-6631 .- 1089-7666. ; 33:3
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Tidskriftsartikel (refereegranskat)abstract
- During the last decade, hydrodynamic cavitation has been implemented in various applications such as energy harvesting and biomedical applications. Facile hydrodynamic cavitation methods are required for fulfilling the requirements in these applications. In this study, a new generation microfluidic device containing eight parallel micro-orifices with a new design was fabricated and tested with the purpose of intensifying the cavitating flows and early cavitation inception. The roughness elements in the micro-orifices facilitated cavitation inception. This study presents a general perspective of occurrence of different cavitating flow patterns in microscale and addresses the ambiguities about the conditions for the formation of a specific flow pattern. Cavitation inception occurred with the appearance of small bubbles emerging from roughness elements at a rather low upstream pressure in the open loop experimental setup. A reduction in the cavitation number resulted in the formation of different flow patterns such as cavitation clouds, twin cavities, sheet cavities, and bubbly flows. Having several flow patterns with different intensities all together within a single microfluidic device is the main advantage of the proposed device over the state of the art microfluidic devices. Generation of flow patterns with various released energy levels makes this proposed device a unique multi-functional platform, which can be implemented to a lab on a chip platform for applications such as nanoparticle synthesis and wound healing.
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| 45812. |
- Shafiee, Mahmood, 1982, et al.
(författare)
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A Redundancy Optimization Model Applied to Offshore Wind Turbine Power Converters
- 2013
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Ingår i: PowerTech (POWERTECH), 2013 IEEE Grenoble. - 9781467356695
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Konferensbidrag (refereegranskat)abstract
- Unexpected failures, high operation and maintenance (O&M) cost, and low accessibility are critical issues for offshore wind farms. According to existing statistics, power converters are among the most critical components in offshore wind turbines, and suffer from a high failure rate. One efficient way to improve the reliability and availability of the converter system is by adding at least one independent redundant converter, which ensures that the system would still operate in case of a converter failure. However, the redundant converters will increase the system’s cost, volume, and weight. In this paper, we propose a cost-rate minimization model aiming to simultaneously determine the optimal allocation of redundant converters and the optimal number of the converters that are allowed to fail before sending a maintenance crew to the offshore platform. The optimal solution under system-level constraints is derived, and the conditions required to make using redundant converter system beneficial are discussed. Finally, the proposed model has been tested on data collected from an offshore wind farm database and the results are compared with a conventional wind turbine converter system.
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| 45813. |
- Shafiee, Mahmood, 1982, et al.
(författare)
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An Optimal Number-Dependent Preventive Maintenance Strategy for Offshore Wind Turbine Blades Considering Logistics
- 2013
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Ingår i: Advances in Operations Research. - : Hindawi Limited. - 1687-9147 .- 1687-9155. ; Volume 2013 (2013)
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Tidskriftsartikel (refereegranskat)abstract
- In offshore wind turbines, the blades are among the most critical and expensive components that suffer from different types of damage due to the harsh maritime environment and high load. The blade damages can be categorized into two types: the minor damage, which only causes a loss in wind capture without resulting in any turbine stoppage, and the major (catastrophic) damage, which stops the wind turbine and can only be corrected by replacement. In this paper, we propose an optimal number-dependent preventive maintenance (NDPM) strategy, in which a maintenance team is transported with an ordinary or expedited lead time to the offshore platform at the occurrence of the N th minor damage or the first major damage, whichever comes first. The long-run expected cost of the maintenance strategy is derived, and the necessary conditions for an optimal solution are obtained. Finally, the proposed model is tested on real data collected from an offshore wind farm database. Also, a sensitivity analysis is conducted in order to evaluate the effect of changes in the model parameters on the optimal solution.
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| 45814. |
- Shafiee, Mahmood, 1982, et al.
(författare)
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Optimal redundancy and maintenance strategy decisions for offshore wind power converters
- 2015
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Ingår i: International Journal of Reliability, Quality and Safety Engineering. - : World Scientific Publishing Company. - 0218-5393. ; 22:3
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of field failure data collected from various wind farm databases indicates that the power converters are among the most critical components in offshore wind turbines, since they suffer from a high failure rate. One efficient approach to enhance the reliability and availability of the wind power systems is through using a redundant converter design, in which a set of power converters is placed together in parallel. The main advantage of a multiple parallel converter system is that the failure of one converter will not necessarily lead to the failure of the entire system. It may however increase the wind turbine’s acquisition cost, volume, and weight. In this paper, we propose an approach of joint redundancy and maintenance strategy optimization for offshore wind power converters, aiming to simultaneously determine the "optimal allocation of redundant converters" and the "optimal threshold number of converters that are allowed to fail before sending a maintenance crew to the offshore platform". The optimal solution under various system-level constraints (such as reliability, weight, and the available space in nacelle) is derived and the conditions required to make using a redundant system beneficial are discussed. The proposed design is applied to an offshore wind turbine system and its performance is evaluated using a Monte-Carlo simulation technique. Finally, the results are compared with the conventional power converter system and a sensitivity analysis is conducted in order to make the proposed approach applicable for the next generation of wind turbines.
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| 45815. |
- Shafiee, Mahmood, 1982
(författare)
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Warranty and Maintenance: under-researched areas
- 2012
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Ingår i: Proceedings of the 5th Asia-Pacific International Symposium on Advanced Reliability and Maintenance Modeling (APARM). ; , s. 414-421
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Konferensbidrag (refereegranskat)abstract
- Warranties (basic and extended) and maintenance (corrective and preventive) are strongly interlinked and of great interest to both researchers from different disciplines and practitioners in different industry sectors. The literature on both warranty and maintenance in separate isvery vast, but the bulk of the research that links these two topics is relatively narrow and discipline specific. This paper briefly reviews the articles that link warranty and maintenance published between 2001 and 2012. It will then discuss some new topics for future research.
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| 45816. |
- Shafiezadeh, N., et al.
(författare)
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Parametric study on the friction angle and dilation angle of intact rock and discontinuities presented in the Siah Bisheh pumping storage hydro-electric power project (HEPP)
- 2006
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Ingår i: Proc. Int. Symp. Int. Soc. Rock Mech., Eurock - Eurock Multiphysics Coupling Long Term Behav. Rock Mech.. - : Taylor & Francis. - 0415410010 - 9780415410014 ; , s. 637-642
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Konferensbidrag (refereegranskat)abstract
- The values of friction angle and dilation angle of rock mass are the effective factors on the visco-elastic displacements around underground structures. The present parametric study was conducted to determine the effect of dilation angle of discontinuities and intact rock, friction angle of discontinuities on the values of visco-elastic displacements based on non-associated flow rule and elasto-viscoplastic theory and statistical Yates method. Elasto-visco plastic analyses of Siah Bisheh Power Cavern have been performed according to non-associated flow rule by FESTO3. In the Yates method, the direct effect and interaction of the concerned parameters on displacements and sensitivity of effects are considered. On the basis of the results, an optimum value can be chosen for the studied parameter. It is found that, the variation of the dilation angle of intact rock and friction angle of discontinuities induced similar variation in the values of displacements, but the sensitivity of these variations is not noticeable. Therefore it is concluded that these parameters are not much effective on the result (visco-plastic displacements). However, changing the dilation angle of discontinuities caused considerable variation in the visco-plastic displacements indicating a direct effect of this parameter on the results. To find out the optimum value of this parameter, the effect of it's variation on the visco-plastic displacement around the cavern is discussed.
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| 45817. |
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| 45818. |
- Shah, S.A., et al.
(författare)
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An experimental study on three-port measurements foracoustic characterization of a perforate
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Multiple analytical, experimental, and numerical studies have been carriedout on perforates to study their properties under operating conditions, resultingin varying hypothesis and models to predict their performance. Theongoing effort of providing experimental results using multiform test setups iscontinued in this study. Incorporating the three-port technique, the passiveacoustic response of a perforated plate is studied under acoustic excitationfrom three directions in presence of grazing flow and high-level excitation.Similar to the in-situ method, usage of the three-port technique has an advantageof being a direct method for impedance determination and is not boundby any boundary conditions traditionally considered in presence of grazingflow. Extending the observations of previous studies, a semi-empirical modelis determined for the real part of the transfer impedance of a perforate, wherethe characterisation of the determined impedance on the testing parameterslike the Strouhal number, particle velocity, flow velocity and shear numberis displayed.
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| 45819. |
- Shah, Shail A., 1993-
(författare)
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Experimental Investigation of the Acoustic Properties of Perforate using Acoustic Three-Ports
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis discusses the aero-acoustic characterisation of a perforate sample using a three-port technique. A rectangular T-junction with a flush mounted perforated sample at the intersection form the acoustical three-port. Under acoustic excitation from three different directions a direct method of impedance determination is incorporated to experimentally determine the passive acoustic properties of the perforate. The three-port scattering matrix and the normalised transfer impedance are calculated in the presence of grazing flow and for high-level excitation and the behaviour of these characteristics is studied. Validation of the determined results in the linear range is carried out by comparing it with existing models. Moreover, based on the experimental results for low grazing flow velocities the dependence of the real part of the transfer impedance on the grazing flow parameters as well as dimensionless numbers is described, and a semi-empirical model quantifying the behaviour is proposed.Furthermore, the thesis explains some experimental errors pertaining to standing wave patterns and operating conditions, and corrections are suggested to reduce the errors.
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| 45820. |
- Shah, S. A., et al.
(författare)
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Nonlinear three-port measurements for the determination of high-level excitation effects on the acoustic properties of perforates
- 2022
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Ingår i: Proceeding of the 28th AIAA/CEAS Aeroacoustics 2022 Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics (AIAA).
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Konferensbidrag (refereegranskat)abstract
- The effect of high-level excitation on the acoustic properties of perforates, and formulation of the non-linear part of the impedance is under scientific discussion. Analytical models including the non-linear properties, as well as various experimental studies give varying results for the acoustic impedance. This paper aims to provide detailed results obtained under high-level excitation with different acoustic wave incidence and flow configurations. Contrary to the well-established two-port configuration, here, a three-port measurement technique is used to observe the acoustic impedance of the perforated plate using excitation from the three different directions. Plane wave propagation is considered and physical quantities such as in-hole particle velocity, which is calculated at the perforate sample, are used as the controlling parameters. This paper is an attempt to study the effect of high-level excitation on the acoustic behavior of the perforates with grazing and normal acoustic incidence. Moreover, the non-linear behavior of the perforate determined in presence of an external grazing flow is also discussed.
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