Wells turbine for wave energy conversion : a review

In the past twenty years, the use of wave energy systems has significantly increased, generally depending on the oscillating water column (OWC) concept. Wells turbine is one of the most efficient OWC technologies. This article provides an updated and a comprehensive account of the state of the art research on Wells turbine. Hence, it draws a roadmap for the contemporary challenges which may hinder future reliance on such systems in the renewable energy sector. In particular, the article is concerned with the research directions and methodologies which aim at enhancing the performance and efficiency of Wells turbine. The article also provides a thorough discussion of the use of computational fluid dynamics (CFD) for performance modeling and design optimization of Wells turbine. It is found that a numerical model using the CFD code can be employed successfully to calculate the performance characteristics of W-T as well as other experimental and analytical methods. The increase of research papers about CFD, especially in the last five years, indicates that there is a trend that considerably depends on the CFD method

Analisis pengaruh budaya kerja Islami (X1) dan kepuasan kerja (X2) terhadap produktivitas karyawan (Y) di Villa Buana Meteseh Tembalang

Budaya organisasi adalah sistem yang diyakini yang dapat dipelajari dan di terapkan kemudian di kembangkan secara terus-menerus dalam organisasi dan di jadikan pedoman tingkah laku bagi anggota-anggotanya untuk mengatasi masalah yang ada dalam organisasi yang berorientasi pada pencapaian tujuan atau hasil/terget yang di tetapkan Peneliti menggunakan jenis penelitian studi lapangan (field research) dengan pendekatan Kuantitatif yang menekankan analisisnya pada numerikal (angka-angka) yang diolah dengan metode statistika. Field research yang digunakan dalam penelitian Kuantitatif ini menghasilkan data tentang pengaruh Variabel Budaya Kerja Islami dan Kepuasan Kerja baik secara sendiri-sendiri (parsial) maupun bersama-sama (simultan) terhadap Produktivitas Kerja Karyawan di Villa Buana Meteseh. Jumlah sampel yang dilibatkan dalam penelitian ini adalah 100 orang karyawan/responden. Penelitian yang dilakukan menggunakan alat bantu berupa kuesioner yang diukur dengan menggunakan skala likert. Kuesioner ini juga telah melewati uji Validitas dan Reliabilitas dengan hasil Valid dan Reliabel (Handal) Dalam penelitian ini variabel yang diteliti dibagi menjdi dua kelompok, yaitu variabel bebas (independent) berupa Budaya kerja Islami(X1) dan Kepuasan Kerja (X2).dan variabel terikat (dependen) yaitu Produktifitas Kerja Karyawan (Y). Data yang dikumpulkan pada penelitian ini akan dianalisis dengan menggunakan teknik korelasi ganda (multyple correlation) yang menunjukkan arah dan kuatnya hubungan antara dua variabel bebas (X1 dan X2) secara bersama-sama (simultan) dengan variabel yang terikat (Y). Variabel Pelayanan Islami X1 (Budaya Kerja islami) dan X2 (Kepuasan Kerja) memiliki VIF tidak lebih dari 10 dan nilai tolerance tidak kurang dari 0,1 yang dapat disimpulkan bahwa model regresi berganda terbebas dari Multikolenieritas. Berdasarkan uji Heteroskedastisitas dengan metode Glesjer diperoleh nilai signifikan 0.962 dan 0,995 lebih besar dari 0,05 dan nilai t-hitung 0,048 dan 0,006 lebih kecil (<) dari t-tabel 1,661, sehingga dapat disimpulkan bahwa tidak terjadi masalah Heterokedastisitas. Untuk Analisis Regresi Berganda, dengan menggunakan bantuan software SPSS 16.0 bisa diambil kesimpulan bahwa: Terdapat pengaruh yang kurang signifikan antara variabel Budaya Kerja Islami terhadap Produktivitas Kerja Karyawan di Villa Buana Meteseh Tembalang Semarang Yang ditunjukkan pada koefisien regresi Budaya Kerja Islami (X1) sebesar -0,003 dan nilai probabilitas signifikan sebesar 0,973 yang lebih besar dari tingkat kepercayaan sebesar (0,005 < 0,05). Terdapat pengaruh yang juga kurang signifikan antara variabel Kepuasan kerja terhadap Produktivitas Kerja Karyawan di Villa Buana Meteseh Tembalang Semarang Yang ditunjukkan pada koefisien regresi Kepuasan Kerja (X2) sebesar 0,130 dan nilai probabilitas signifikan sebesar 0,239 yang lebih besar dari tingkat kepercayaaan 0,05 (0,000 < 0,05)

Development of design optimization methodology using CFD as the design tool applied to printed circuit heat exchanger /by Artit Ridluan.

In engineering design, optimization methods are typically based on trial-and-error design and local search approaches. In nuclear reactor design, conservative approaches are directly linked to safety margin in operation under anticipated and unanticipated off-normal scenarios. These approaches require iterative experimentation and analyses (time) to locate the optimum. Moreover, the actual response surface (design solution within design space) may have multiple, regional maxima and minima. The search process may only yield a local optimum, not an absolute optimum. Thus, these practices in reactor engineering need to be changed when applied to advanced nuclear systems. Design conservatism must be reduced in search of efficiency with respect to performance, while meeting regulatory (licensing) requirements.;This dissertation proposes, develops, and demonstrates a new systematic design optimization methodology. Three key elements (tools), Computational Fluid Dynamics (CFD), Artificial Neural Network (ANN), and Response Surface Methodology (RSM) are integrated into the design engineering process to limit, reduce, and eliminate past conservative methodologies and to improve the optimization process. To test this methodology, the Printed Circuit Heat Exchanger (PCHE) was selected as a Case Study since the PCHE is being considered as the Next Generation Nuclear Plant's (NGNP) Intermediate Heat Exchanger (IHX). Further, a thermally efficient IHX is key to an optimal NGNP balance-of-plant.;Foremost, modeling and simulation results for each key design tool were collected, to determine the capability and accuracy of each tool. The first result showed that CFD simulation can capture unsteady phenomena; vortex shedding, using unsteady RANS-based CFI) simulation The second CFD simulation predicted key thermohydraulic parameters, friction coefficient and Nusselt number. Thus via benchmarking, CFD can be used as a design tool and integrated into the proposed design optimization process. The third result showed that ANN, EBaLM [Error-Back (Propagation) and Levenberg-Marquardt] algorithm, adapts well to thermophysical property nonlinearities and to system fluctuations (in thermal-hydraulics) under relevant conditions. Most importantly, EBaLM provided a means to consistently enhance the dataset within the design space so as to reduce CFD simulations. It became clear that ANN can be used as a design tool and integrated into the proposed design optimization process.;In NGNP PCHE design optimization Case Study, the design parameters considered were the vertical (t) and horizontal (p) distances between channels, channel diameter (d), and streamwise (l) and spanwise (h) zigzagged lengths of the channels. With five levels of each design parameter, the total combination of parametric variations requires as many as 3.125 (5{esc}p5{esc}s) CFD runs. Under the proposed design optimization methodology, this number of simulations is systematically and effectively reduced to 52 runs.;Benchmarked CFD simulation was used to generate PCHE thermal effectiveness (E), hot-sided and cold-sided pressure drops (DPh and DPc). The design space of pressure drops was first globally explored using Uniform Design theory. A candidate subregion that can satisfy functional requirements was then identified. Based on CFD simulations, RSM was then used to develop surface equations to represent the PCHE response in terms of E, DPh, and DPc. These surface equations were then used to determine the optimal design parameters using a Generalized Reduced-Gradient (GRG) algorithm.;The unique contribution is the development and demonstration of a design optimization methodology. Specifically, the results showed that the optimization method is systematic and effective for following reasons: (1) exploration of a large design space facilitates the search of a subregion that can meet the defined constraint, (2) only 52 CFD simulations were performed, (3) for given input and output conditions, the effectiveness was improved ~19% relative to simplified PCHE configurations (straight channel); ~6.5% and 15% reduction in DPh, and DPc were observed relative to a simplified configuration, and (4) the design optimization process was completed in two steps, thus eliminating the iterative search process.Thesis (Ph. D., Mechanical Engineering)--University of Idaho, June 2009

UNSTEADY ISOTHERMAL FLOW THROUGH A STAGGERED TUBE BUNDLE ARRAY

ABSTRACT Two-dimensional Unsteady simulations of isothermal flow through a staggered tube bundle array at three different Reynolds numbers 54, 72, and 90 were investigated. The Navier-Stokes equations are numerically solved. Based on the CFD simulation results, the unsteady flow patterns were developed behind the rear row of the array, while for the other rows, the steady separated and reattached flow behaviors were observed, small, short, and closed separation bubble behind the rods. At Reynolds Number of 54, the transient flow was perfectly periodic. The complicated patterns of unsteady flow could be observed at Reynolds numbers of 72 and 90. The shedding patterns of vortices from the last rods were different and no longer periodic as found at Reynolds number of 54. The degree of chaos is increased as Reynolds number progressed INTRODUCTION The development and design for high efficient heat exchange devices has received much attention for many years. Most investigations have been concentrated on various shapes of fines such as circular and rectangular configurations. Engineering applications often involve the complex flow phenomenon over complex geometries, in which the fin bundle can be arranged in a variety of ways. Therefore, the considerable improvement of heat transfer performance is based on the improvement on external fluid flow of the arrangement of fins. Most arrangements are affected by the complex formations and interactions of vortices. In compariso

Computational study of decaying annular vortex flow using the R-epsilon/K-epsilon turbulence model

In this article, we present three dimensional CFD study of turbulent vortex flow in an annular passage using OpenFOAM 1.6. The vortex flow is generated by introducing the flow through a tangential entry to the passage. For the analysis presented in this article, turbulence was modeled using the Re/k - e model, in addition, a comparison between such model with the standard k - e model was conducted and discussed. The main characteristics of the flow such as vortex structure and recirculation zone were investigated. It was found that flow is subjected to Rankine vortex structure with three forced vortex regimes and a free vortex region near to the outer wall. The phenomenon of vortex decay was investigated by depicting the swirl number trend along the axial direction of the flow domain. It was found that the vortex decay is subjected to an exponential decay behavior. New coefficients for the exponential decay correlation were derived based on local values of velocity components in different radial planes