The finite-volume method in computational rheology

The finite volume method (FVM) is widely used in traditional computational fluid dynamics (CFD), and many commercial CFD codes are based on this technique which is typically less demanding in computational resources than finite element methods (FEM). However, for historical reasons, a large number of Computational Rheology codes are based on FEM. There is no clear reason why the FVM should not be as successful as finite element based techniques in Computational Rheology and its applications, such as polymer processing or, more recently, microfluidic systems using complex fluids. This chapter describes the major advances on this topic since its inception in the early 1990’s, and is organized as follows. In the next section, a review of the major contributions to computational rheology using finite volume techniques is carried out, followed by a detailed explanation of the methodology developed by the authors. This section includes recent developments and methodologies related to the description of the viscoelastic constitutive equations used to alleviate the high-Weissenberg number problem, such as the log-conformation formulation and the recent kernel-conformation technique. At the end, results of numerical calculations are presented for the well-known benchmark flow in a 4:1 planar contraction to ascertain the quality of the predictions by this method

Reduced-stress method for efficient computation of time-dependent viscoelastic flow with stress equations of FENE-P type

Most calculation procedures for time-dependent viscoelastic flows require iteration within the time step used to advance the solution, in order to satisfy simultaneously the momentum and the constitutive equations for each stress component. We have devised a way of reformulating the constitutive equation for the FENE-P model, or models described by similar equations expressed in terms of the stress tensor, which enables iterative methods for simulating time-dependent viscoelastic flows to become much more efficient: the number of iterations to obtain a solution with the reformulated stress equations is substantially smaller (by a factor of 5–10) than with a comparable method applied to the original, non- reformulated, constitutive equations. The proposed reformulation is rather simple and consists in considering as dependent variables the reduced stresses obtained by dividing the stress components by the extensibility function of the model. It is tested with three problems of increasing complexity, start-up of channel and square-duct flows, and start-up of a rotating duct flow.info:eu-repo/semantics/publishedVersio

Comparison of DBD plasma actuators flow control authority in different modes of actuation

The principal mechanisms by which DBD plasma actuators influence flow characteristics, and are thus able to control that flow, depend strongly on their modes of actuation. Here two different modes based on steady and unsteady actuation are compared and investigated. A simple sinusoidal voltage distribution and a duty cycled sinusoidal voltage were considered for these purposes. Leading edge separation around a stalled NACA 0012 airfoil at Re=3 ×10^16 is considered as test case. A simplified phenomenological model which uses the correct scale of the plasma body force is considered for the modeling of the plasma actuator effects. The steady actuation results show that flow control can be effectively achieved by this mode of operation with continuous injection of momentum in the boundary layer. Unsteady actuation with an imposed frequency equal to the calculated natural frequencies of the flow gives rise to a resonance actuation effect.info:eu-repo/semantics/publishedVersio

Implementation of the classical plasma–fluid model for simulation of dielectric barrier discharge (DBD) actuators in OpenFOAM

To simulate the coupled plasma and fluid flow physics of dielectric-barrier discharge, a plasma–fluid model is utilized in conjunction with a compressible flow solver. The flow solver is responsible for determining the bulk flow kinetics of dominant neutral background species including mole fractions, gas temperature, pressure and velocity. The plasma solver determines the kinetics and energetics of the plasma species and accounts for finite rate chemistry. In order to achieve maximum reliability and best performance, we have utilized state-of-the-art numerical and theoretical approaches for the simulation of DBD plasma actuators. In this respect, to obtain a stable and accurate solution method, we tested and compared different existing numerical procedures, including operator-splitting algorithm, super-timestepping, and solution of the Poisson and transport equations in a semi-implicit manner. The implementation of the model is conducted in OpenFOAM. Four numerical test cases are considered in order to validate the solvers and to investigate the drawbacks/benefits of the solution approaches. The test problems include single DBD actuator driven by positive, negative and sinusoidal voltage waveforms, similar to the ones that could be found in literature. The accuracy of the results strongly depends to the choice of time step, grid size and discretization scheme. The results indicate that the super-time-stepping treatment improves the computational efficiency in comparison to explicit schemes. However, the semiimplicit treatment of the Poisson and transport equations showed better performance compared to the other tested approaches.info:eu-repo/semantics/publishedVersio

Using EcoYieldSAFE to compare soil carbon dynamics under future climate in two contrasting agroforestry systems

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Calculation Of The Giant Magnetocaloric Effect In The Mnfep 0.45as0.55 Compound

We report the theoretical investigations on the giant magnetocaloric compound MnFeP0.45As0.55. The magnetic state equation used takes into account the magnetoelastic effect that leads the magnetic system to order under first order paramagnetic-ferromagnetic phase transition. The model parameters were determined from the magnetization data adjustment and used to calculate the magnetocaloric thermodynamic quantities. The theoretical calculations are compared with the available experimental data.709944101-094410-5Yu, B.F., Gao, Q., Zhang, B., Mang, X.Z., Chen, Z., (2003) Int. J. Refrig., 26, p. 622Gschneidner Jr., K.A., Pecharsky, V.K., (1997) Rare Earths: Science, Technology and Application III, , edited by R. C. Bautista, C. O. Bounds, T. W. Ellis, and B. T. Kilbourn The Minerals, Metals & Materials Society, WarendaleBrown, G.V., (1976) J. Appl. Phys., 47, p. 3673Pecharsky, V.K., Gschneidner Jr., K.A., (1997) Phys. Rev. Lett., 78, p. 4494Tegus, O., Brück, E., Buschow, K.H.J., De Boer, F.R., (2002) Nature, 415, p. 150. , LondonMorellon, L., Algarabel, P.A., Ibarra, M.R., Blasco, J., García-Landa, B., Arnold, Z., Albertini, F., (1998) Phys. Rev. B, 58, pp. R14721Rodbell, D.S., (1961) Phys. Rev. Lett., 7, p. 1Bean, C.P., Rodbell, D.S., (1961) Phys. Rev., 126, p. 104Bacmann, M., Soubeyroux, J.-L., Barrett, R., Fruchart, D., Zach, R., Niziol, S., Fruchart, R., (1983) J. Magn. Magn. Mater., 134, p. 59Brück, E., Tegus, O., Li, X.W., Deboer, F.R., Buschow, K.H.J., (2003) Physica B, 327, p. 431Tegus, O., Brück, E., Zhang, L., Dagula, Buschow, K.H.J., De Boer, F.R., (2002) Physica B, 319, p. 174Zach, R., Guillot, M., Tobola, J., (1998) J. Appl. Phys., 83, p. 7237Tegus, O., (2003) Novel Materials for Magnetic Refrigeration, , PhD thesis, Van der Waals-Zeeman Instituut, Universiteit van Amsterdam, Printer Partners Ipskamp B. V., ISBN: 9057761076, OctoberVon Ranke, P.J., Grangeia, D.F., Caldas, A., De Oliveira, N.A., (2003) J. Appl. Phys., 93, p. 4055Wada, H., Tanabe, Y., (2001) Appl. Phys. Lett., 79, p. 3302Wada, H., Morikawa, T., Taniguchi, K., Shibata, T., Yamada, Y., Akishige, Y., (2003) Physica B, 328, p. 11

Theoretical Investigation On The Existence Of Inverse And Direct Magnetocaloric Effect In Perovskite Euzro 3

We report on the magnetic and magnetocaloric effect calculations in antiferromagnetic perovskite-type EuZrO 3. The theoretical investigation was carried out using a model Hamiltonian including the exchange interactions between nearest-neighbor and next-nearest-neighbor for the antiferromagnetic ideal G-type structure (the tolerance factor for EuZrO 3 is t = 0.983, which characterizes a small deformation from an ideal cubic perovskite). The molecular field approximation and Monte Carlo simulation were considered and compared. The calculated magnetic susceptibility is in good agreement with the available experimental data. For a magnetic field change from zero to 2 T a normal magnetocaloric effect was calculated and for a magnetic field change from zero to 1 T, an inverse magnetocaloric effect was predicted to occur below T = 3.6 K. © 2011 American Institute of Physics.1098Warburg, E., (1881) Ann. Phys., 13, p. 141. , 10.1002/andv249:5Pecharsky, V.K., Gschneidner Jr., K.A., (1997) Phys. Rev. Lett., 78, p. 4494. , 10.1103/PhysRevLett.78.4494Von Ranke, P.J., De Oliveira, N.A., Gama, S., (2004) J. Magn. Magn. Mater., 277, p. 78. , 10.1016/j.jmmm.2003.10.013De Oliveira, N.A., Von Ranke, P.J., (2008) Phys. Rev. B, 77, p. 214439. , 10.1103/PhysRevB.77.214439Von Ranke, P.J., De Oliveira, N.A., Plaza, E.J.R., De Sousa, V.S.R., Alho, B.P., Magnus, A., Carvalho, G., Reis, M.S., (2008) J. Appl. Phys., 104, p. 093906. , 10.1063/1.3009974Sande, P., Hueso, L.E., Miguens, D.R., Rivas, J., Rivadulla, F., Lopez-Quintela, M.A., (2001) Appl. Phys. Lett., 79, p. 2040. , 10.1063/1.1403317Yamada, H., Goto, T., (2004) Physica B, 346-347, p. 104. , 10.1016/j.physb.2004.01.029Nobrega, E.P., De Oliveira, N.A., Von Ranke, P.J., Troper, A., (2006) Phys. Rev. B, 74, p. 144429. , 10.1103/PhysRevB.74.144429Tishin, A.M., Spichkin, Y.I., (2003) The Magnetocaloric Effect and Its Applications, , 1st ed. (Institute of Physics, Bristol)De Oliveira, N.A., Von Ranke, P.J., (2010) Phys. Rep., 489, p. 89. , 10.1016/j.physre2009.12.006Sasaki, S., Prewitt, C.T., Liebermann, R.C., (1983) Am. Mineral., 68, p. 1189Kuz'Min, M.D., Tishin, A.M., (1991) J. Phys. D: Appl. Phys., 24, p. 2039. , 10.1088/0022-3727/24/11/020Kimura, H., Numazawa, T., Sato, M., Ikeya, T., Fukuda, T., (1995) J. Appl. Phys., 77, p. 432. , 10.1063/1.359349Phan, M.-H., Yu, S.-C., Review of the magnetocaloric effect in manganite materials (2007) Journal of Magnetism and Magnetic Materials, 308 (2), pp. 325-340. , DOI 10.1016/j.jmmm.2006.07.025, PII S0304885306009577Zong, Y., Fujita, K., Akamatsu, H., Murai, S., Tanaka, K., (2010) J. Solid State Chem., 183, p. 168. , 10.1016/j.jssc.2009.10.014Kolodiazhnyi, T., Fujita, K., Wang, L., Zong, Y., Tanaka, K., Sakka, Y., Takayama-Muromachi, E., (2010) Appl. Phys. Lett., 96, p. 252901. , 10.1063/1.3456730Greedan, J.E., Chien, C.-L., Johnston, R.G., (1976) J. Solid State Chem., 19, p. 155. , 10.1016/0022-4596(76)90163-8Nobrega, E.P., De Oliveira, N.A., Von Ranke, P.J., Troper, A., Monte Carlo calculations of the magnetocaloric effect in Gd5(SixGe1-x)4 compounds (2005) Physical Review B - Condensed Matter and Materials Physics, 72 (13), pp. 1-7. , http://oai.aps.org/oai/?verb=ListRecords&metadataPrefix= oai_apsmeta_2&set=journal:PRB:72, DOI 10.1103/PhysRevB.72.134426, 134426Nbrega, E.P., De Oliveira, N.A., Von Ranke, P.J., Troper, A., (2008) J. Magn. Magn. Mater., 320, p. 147. , 10.1016/j.jmmm.2008.02.036Landau, D.P., Binder, K., (2000) A Guide to Monte Carlo Simulations in Statistical Physics, , (Cambridge University Press, Cambridge)Yang, H., Ohishi, Y., Kurosaki, K., Muta, H., Yamanaka, S., (2010) J. Alloys Compd., 504, p. 201. , 10.1016/j.jallcom.2010.05.088Terki, R., Bertrand, G., Aourag, H., Coddet, C., Thermal properties of Ba 1-xSr xZrO 3 compounds from microscopic theory (2008) Journal of Alloys and Compounds, 456 (1-2), pp. 508-513. , DOI 10.1016/j.jallcom.2007.02.133, PII S0925838807005397Bagayoko, D., Zhao, G.L., Fan, J.D., Wang, J.T., (1998) J. Phys. Condens. Matter, 10, p. 5645. , 10.1088/0953-8984/10/25/014Von Ranke, P.J., Mota, M.A., Grangeia, D.F., Carvalho, A.M.G., Gandra, F.C.G., Coelho, A.A., Caldas, A., Gama, S., Magnetocaloric effect in the RNi 5 (R = Pr, Nd, Gd, Tb, Dy, Ho, Er) series (2004) Physical Review B - Condensed Matter and Materials Physics, 70 (13), pp. 1344281-1344286. , DOI 10.1103/PhysRevB.70.134428, 13442

The Giant Anisotropic Magnetocaloric Effect In Dyal2

We report on calculations of the anisotropic magnetocaloric effect in DyAl2 using a model Hamiltonian including crystalline electrical field effects. The anisotropic effect is produced by the rotation of a constant magnetic field from the easy to a hard magnetic direction in the crystal and is enhanced by the first order nature of the field induced spin reorientation transition. The calculated results indicate that for a field with modulus of 2 T rotating from a hard to the easy direction, the isothermal magnetic entropy (Δ Siso) and adiabatic temperature (Δ Tad) changes present peak values higher than 60% the ones observed in the usual process, in which the field direction is kept constant and the modulus of the field is varied. © 2008 American Institute of Physics.1049Tishin, A.M., Spichkin, Y.I., (2003) The Magnetocaloric Effect and Its Applications, , 1st ed. (Institute of Physics, Bristol)Warburg, E., (1881) Ann. Phys. (N.Y.), 13, p. 141. , 0003-4916Brown, G.V., (1976) J. Appl. Phys., 47, p. 3673. , 0021-8979 10.1063/1.323176Pecharsky, V.K., Gschneidner Jr., K.A., (1997) Phys. Rev. Lett., 78, p. 4494. , 0031-9007 10.1103/PhysRevLett.78.4494Von Ranke, P.J., De Oliveira, N.A., Mello, C., Garcia, D.C., De Souza, V.A., Magnus, A., Carvalho, G., (2006) Phys. Rev. B, 74, p. 054425. , 0163-1829 10.1103/PhysRevB.74.054425Hill, T.W., Wallace, W.E., Craig, R.S., Inuone, T.J., (1973) Solid State Chem., 8, p. 364. , 10.1016/S0022-4596(73)80036-2De Oliveira, I.G., Garcia, D.C., Von Ranke, P.J., (2007) J. Appl. Phys., 102, p. 073907. , 0021-8979 10.1063/1.2783781Lima, A.L., Tsokol, A.O., Gschneidner Jr., K.A., Pecharky, V.K., Lograsso, T.A., Schlagel, D.L., (2005) Phys. Rev. B, 72, p. 024403. , 0163-1829 10.1103/PhysRevB.72.024403Von Ranke, P.J., De Oliveira, I.G., Guimarães, A.P., Da Silva, X.A., (2000) Phys. Rev. B, 61, p. 447. , 0163-1829 10.1103/PhysRevB.61.447Von Ranke, P.J., De Oliveira, N.A., Garcia, D.C., De Sousa, V.S.R., De Souza, V.A., Magnus, A., Carvalho, G., Reis, M.S., (2007) Phys. Rev. B, 75, p. 184420. , 0163-1829 10.1103/PhysRevB.75.184420Purwins, H.G., Leson, A., (1990) Adv. Phys., 39, p. 309. , 0001-8732 10.1080/00018739000101511Von Ranke, P.J., Pecharsky, V.K., Gschneidner Jr., K.A., (1998) Phys. Rev. B, 58, p. 1211

A qualidade das bases de dados como factor crucial em estudos ambientais: condições de referência e tipologia com base piscícola para rios portugueses

Com base num conjunto superior a 1000 amostragens piscícolas em rios portugueses (troços vadeáveis) realizadas por diversas entidades nacionais nos últimos 10 anos, seleccionou-se um grupo de 459 locais que cumprem critérios de normalização de amostragem, procedimentos no terreno, e acuidade nas identificações taxonómicas. Estes locais representam a diversidade de condições naturais e de impactos humanos em Portugal Continental. Para caracterizar a magnitude e tipo de perturbação humana em cada local foram aplicadas 15 variáveis de pressão – ao nível do troço, segmento e bacia – classificadas de acordo com o desvio às condições naturais (de 1 para ausência de desvio, até 5 para forte degradação). Este passo envolveu um longo período de trabalho e baseou-se na análise de várias fontes de informação geográfica e documental, em inquéritos e no conhecimento do terreno. Durante as fases de selecção de locais e construção das bases de dados ambientais e biológicas, toda a informação foi sujeita a procedimentos de controle de qualidade de dados. É proposta uma metodologia para a selecção de sítios de referência; desta forma, foram incluídos neste grupo os locais com pontuação 1 ou 2 em, pelo menos, 80% das variáveis, permitindo a classificação 3 em 20% (três variáveis), excepto para a variável “abundância de indivíduos exóticos”, que obrigatoriamente correspondeu à pontuação 1 ou 2. Uma abordagem estatística multivariada suportou os dois passos seguintes: a definição da tipologia com base nas ictiocomunidades e a alocação de todos os locais num tipo. Utilizando os sítios de referência, e com base na classificação de grupos funcionais piscícolas, foram estabelecidos 6 tipos (t.): t. salmonícola da região norte; t. transição salmonícola-ciprinícola da região norte; t. ciprinícola de pequena dimensão das regiões norte interior e sul; t. ciprinícola de média dimensão da região norte; t. ciprinícola de média dimensão da região sul e t. ciprinícola da região norte litoral. A análise discriminante múltipla (ADM) suportou a tipologia piscícola, alocando correctamente 71 a 93% dos locais para os seis grupos; temperatura média em Julho, área de drenagem, altitude, precipitação média anual e uma variável categórica de enquadramento geográfico foram as variáveis retidas pelo modelo final. A ADM evidenciou elevada robustez ao classificar a maioria dos locais de não referência num dos tipos da respectiva região geográfica e ao detectar variações longitudinais das comunidades piscícolas ao longo de vários rios

Generic Pareto local search metaheuristic for optimization of targeted offers in a bi-objective direct marketing campaign

Cross-selling campaigns seek to offer the right products to the set of customers with the goal of maximizing expected profit, while, at the same time, respecting the purchasing constraints set by investors. In this context, a bi-objective version of this NP-Hard problem is approached in this paper, aiming at maximizing both the promotion campaign total profit and the risk-adjusted return, which is estimated with the reward-to-variability ratio known as Sharpe ratio. Given the combinatorial nature of the problem and the large volume of data, heuristic methods are the most common used techniques. A Greedy Randomized Neighborhood Structure is also designed, including the characteristics of a neighborhood exploration strategy together with a Greedy Randomized Constructive technique, which is embedded in a multi-objective local search metaheuristic. The latter combines the power of neighborhood exploration by using a Pareto Local Search with Variable Neighborhood Search. Sets of non-dominated solutions obtained by the proposed method are described and analyzed for a number of problem instances