Optimum Mass Matrices for Short Wave Pulse Propagation Finite Element Models

The matrices of a substructure ensuring minimum modal errors of the whole structure are obtained by using optimization approach. The mass and stiffness matrices of a small component domain of selected dimension are obtained by applying the modal synthesis of a limited number of closeto-exact modes such that after assembling a larger joined domain model the modal convergence rate of the latter should be as high as possible. The goal is achieved by formulating the minimization problem for the penaltytype target function representing the cumulative relative modal error of the joined domain and by applying the gradient descent minimization method. After the optimum matrices of a component domain are obtained, they can be used in any structure as higher-order elements or super-elements. The “combined” mass matrices can be treated as a special case of the presented approach. The performance of the obtained dynamic models is demonstrated by solving short wave pulse propagation problems by using a only few nodal points per pulse length

Investigation of thermo-elastic damping of vibrations of rectangular and ring-shaped mems resonators

The paper deals with finite element analysis of damped modal vibrations Q-factor values determined by taking into account the thermally-elastic damping. Modal properties of square- and ring-shaped MEMS resonators have been investigated by taking into account the layered structure of MEMS and the influence of the geometry of the clamping zone. The calculations have been performed by employing the COMSOL Multiphysics finite element software. The solution method has been verified comparing numerically and analitically obtained damped modal properties of cantilever MEMS resonator. Experimental investigations of Q-factor values have been performed. The comparison of calculated and experimentally obtained resonant frequencies and Q-factor values indicated good agreement of tendencies of change of the quantities against temperatur

The Structure Modeling of Material Composed of the Orthotropic Crystals

In this paper the model of a elastic composite medium which consists of a matrix containing a set of orthotropic crystals with the random orientation of the anisotropy axes is presented. The axes orientation is described by the Gauss distribution. The numerical investigation is proposed for rectangular plate, when the normal strains are given in the one side. Other sides are free of strain. The finite - difference technique is used for model discretization

Investigation of vibrations of line scale calibration systems

The paper treats the issue of embedding the traceable length metrology directly into technological process by performing precise dynamic measurements of line scale in real industrial environment. It addresses the error-related problems specific to line scale calibration in dynamic mode of operation that are caused primarily by static and dynamic loads as well as geometrical deviations of the calibration system components. Introducing the dynamic regime of calibration leads to the dynamic calibration error originating due to vibration sources in the structure. This term should be considered and implicated in the measurement uncertainty budget. A new 3D finite element model has been developed in order to both investigate the influence of dynamical excitations of a long stroke comparator structure and evaluate possible influence of vibrations on geometrical dimensions of the line scale. The experiments have been conducted on the new interferometer-controlled comparator setup with a moving microscope in order to evaluate the performance of the precision scale calibration proces

Optimization of ultrasound beam transmission path within measurement channel of ultrasonic flowmeter

The numerical simulation of the water flow through the semicircular duct is presented. The results of the simulation show that by implementing such duct into ultrasonic time-of-flight flowmeters it is possible to get an almost flat and linear function of hydrodynamic correction. The optimal choice of the dimension of ultrasonic transducers and the optimal positioning of them allows us to achieve a hydrodynamic function with the slope ~ 4%. It is expected that flat hydrodynamic calibration function gives the possibility to expand the dynamic measurement range of ultrasonic flowmeters and to increase stability and repeatability of the measurement result

Finite element analysis of thermo-elastical modal damping of mems vibrations

The paper deals with finite element analysis of damped modal vibrations Q-factor values determined by thermal-elastic damping in micro-electrical-mechanical systems (MEMS). Mathematically the problem is formulated as a complex eigenvalue problem. Verification problems have been solved by using several computational environments and different presentations of model equations in order to comprehend and reduce the influence of rounding errors. The analysis of damped modal properties of selected real MEMS resonator revealed the main features of thermal-elastic damping by taking into account 3D geometry of the resonator and anchoring (clamping) structur

Investigation of thermo-elastic damping of vibrations of rectangular and ring-shaped mems resonators

The paper deals with finite element analysis of damped modal vibrations Q-factor values determined by taking into account the thermally-elastic damping. Modal properties of square- and ring-shaped MEMS resonators have been investigated by taking into account the layered structure of MEMS and the influence of the geometry of the clamping zone. The calculations have been performed by employing the COMSOL Multiphysics finite element software. The solution method has been verified comparing numerically and analitically obtained damped modal properties of cantilever MEMS resonator. Experimental investigations of Q-factor values have been performed. The comparison of calculated and experimentally obtained resonant frequencies and Q-factor values indicated good agreement of tendencies of change of the quantities against temperatur

Computer modeling of an impedance-controlled pulsing protocol for RF tumor ablation with a cooled electrode

[EN] Purpose: To develop computer models to mimic the impedance-controlled pulsing protocol implemented in radiofrequency (RF) generators used for clinical practice of radiofrequency ablation (RFA), and to assess the appropriateness of the models by comparing the computer results with those obtained in previous experimental studies.Methods: A 12-min RFA was modelled using a cooled electrode (17G, 3cm tip) inserted in hepatic tissue. The short (transverse) diameter of the coagulation zone was assessed under in vivo (with blood perfusion (BP) and considering clamping) and ex vivo (at 21 degrees C) conditions. The computer results obtained by programming voltage pulses were compared with current pulses.Results: The differences between voltage and current pulses were noticeable: using current instead of voltage allows larger coagulation zones to be created, due to the higher energy applied by current pulses. If voltage pulses are employed the model can accurately predict the number of roll-offs, although the waveform of the applied power is clearly not realistic. If current voltages are employed, the applied power waveform matches well with those reported experimentally, but there are significantly fewer roll-offs. Our computer results were overall into the ranges of experimental ones.Conclusions: The proposed models reproduce reasonably well the electrical-thermal performance and coagulation zone size obtained during an impedance-controlled pulsing protocol.This work was supported by the Spanish Plan Estatal de Investigacion, Desarrollo e Innovacion Orientada a los Retos de la Sociedad under grant number TEC2014-52383-C3-R (TEC2014-52383-C3-1-R). The authors alone are responsible for the content and writing of the paper.Trujillo Guillen, M.; Bon Corbín, J.; Rivera Ortun, MJ.; Burdio, F.; Berjano, E. (2016). Computer modeling of an impedance-controlled pulsing protocol for RF tumor ablation with a cooled electrode. International Journal of Hyperthermia. 32(8):931-939. doi:10.1080/02656736.2016.1190868S931939328Hocquelet, A., Balageas, P., Laurent, C., Blanc, J.-F., Frulio, N., Salut, C., … Trillaud, H. (2015). Radiofrequency ablation versus surgical resection for hepatocellular carcinoma within the Milan criteria: A study of 281 Western patients. International Journal of Hyperthermia, 31(7), 749-757. doi:10.3109/02656736.2015.1068382Fukushima, T., Ikeda, K., Kawamura, Y., Sorin, Y., Hosaka, T., Kobayashi, M., … Kumada, H. (2015). Randomized Controlled Trial Comparing the Efficacy of Impedance Control and Temperature Control of Radiofrequency Interstitial Thermal Ablation for Treating Small Hepatocellular Carcinoma. Oncology, 89(1), 47-52. doi:10.1159/000375166Goldberg, S. N., Stein, M. C., Gazelle, G. S., Sheiman, R. G., Kruskal, J. B., & Clouse, M. E. (1999). Percutaneous Radiofrequency Tissue Ablation: Optimization of Pulsed-Radiofrequency Technique to Increase Coagulation Necrosis. Journal of Vascular and Interventional Radiology, 10(7), 907-916. doi:10.1016/s1051-0443(99)70136-3Ahmed, M., Liu, Z., Humphries, S., & Nahum Goldberg, S. (2008). Computer modeling of the combined effects of perfusion, electrical conductivity, and thermal conductivity on tissue heating patterns in radiofrequency tumor ablation. International Journal of Hyperthermia, 24(7), 577-588. doi:10.1080/02656730802192661Lobo, S. M., Liu, Z.-J., Yu, N. C., Humphries, S., Ahmed, M., Cosman, E. R., … Goldberg, S. N. (2005). RF tumour ablation: Computer simulation and mathematical modelling of the effects of electrical and thermal conductivity. International Journal of Hyperthermia, 21(3), 199-213. doi:10.1080/02656730400001108Solazzo, S. A., Liu, Z., Lobo, S. M., Ahmed, M., Hines-Peralta, A. U., Lenkinski, R. E., & Goldberg, S. N. (2005). Radiofrequency Ablation: Importance of Background Tissue Electrical Conductivity—An Agar Phantom and Computer Modeling Study. Radiology, 236(2), 495-502. doi:10.1148/radiol.2362040965Barauskas, R., Gulbinas, A., & Barauskas, G. (2007). Investigation of radiofrequency ablation process in liver tissue by finite element modeling and experiment. Medicina, 43(4), 310. doi:10.3390/medicina43040039Haemmerich, D., & Wood, B. J. (2006). Hepatic radiofrequency ablation at low frequencies preferentially heats tumour tissue. International Journal of Hyperthermia, 22(7), 563-574. doi:10.1080/02656730601024727Haemmerich, D., Chachati, L., Wright, A. S., Mahvi, D. M., Lee, F. T., & Webster, J. G. (2003). Hepatic radiofrequency ablation with internally cooled probes: effect of coolant temperature on lesion size. IEEE Transactions on Biomedical Engineering, 50(4), 493-500. doi:10.1109/tbme.2003.809488Schutt, D. J., & Haemmerich, D. (2008). Effects of variation in perfusion rates and of perfusion models in computational models of radio frequency tumor ablation. Medical Physics, 35(8), 3462-3470. doi:10.1118/1.2948388Zhang, B., Moser, M. A. J., Zhang, E. M., Luo, Y., & Zhang, W. (2015). Numerical analysis of the relationship between the area of target tissue necrosis and the size of target tissue in liver tumours with pulsed radiofrequency ablation. International Journal of Hyperthermia, 31(7), 715-725. doi:10.3109/02656736.2015.1058429Solazzo, S. A., Ahmed, M., Liu, Z., Hines-Peralta, A. U., & Goldberg, S. N. (2007). High-Power Generator for Radiofrequency Ablation: Larger Electrodes and Pulsing Algorithms in Bovine ex Vivo and Porcine in Vivo Settings. Radiology, 242(3), 743-750. doi:10.1148/radiol.2423052039Abraham, J. P., & Sparrow, E. M. (2007). A thermal-ablation bioheat model including liquid-to-vapor phase change, pressure- and necrosis-dependent perfusion, and moisture-dependent properties. International Journal of Heat and Mass Transfer, 50(13-14), 2537-2544. doi:10.1016/j.ijheatmasstransfer.2006.11.045Pätz, T., Kröger, T., & Preusser, T. (2009). Simulation of Radiofrequency Ablation Including Water Evaporation. World Congress on Medical Physics and Biomedical Engineering, September 7 - 12, 2009, Munich, Germany, 1287-1290. doi:10.1007/978-3-642-03882-2_341Trujillo, M., Alba, J., & Berjano, E. (2012). Relationship between roll-off occurrence and spatial distribution of dehydrated tissue during RF ablation with cooled electrodes. International Journal of Hyperthermia, 28(1), 62-68. doi:10.3109/02656736.2011.631076Hall, S. K., Ooi, E. H., & Payne, S. J. (2015). Cell death, perfusion and electrical parameters are critical in models of hepatic radiofrequency ablation. International Journal of Hyperthermia, 31(5), 538-550. doi:10.3109/02656736.2015.1032370Chang, S.-J., Yu, W.-J., Chang, C.-C., & Chen, Y.-H. (2010). 7 PROTEOMICS ANALYSIS OF MALE REPRODUCTIVE PHYSIOLOGY BY TOONA SINENSIS ROEM. Reproductive BioMedicine Online, 20, S3-S4. doi:10.1016/s1472-6483(10)62425-xBeop-Min Kim, Jacques, S. L., Rastegar, S., Thomsen, S., & Motamedi, M. (1996). Nonlinear finite-element analysis of the role of dynamic changes in blood perfusion and optical properties in laser coagulation of tissue. IEEE Journal of Selected Topics in Quantum Electronics, 2(4), 922-933. doi:10.1109/2944.577317Doss, J. D. (1982). Calculation of electric fields in conductive media. Medical Physics, 9(4), 566-573. doi:10.1118/1.595107Jo, B., & Aksan, A. (2010). Prediction of the extent of thermal damage in the cornea during conductive keratoplasty. Journal of Thermal Biology, 35(4), 167-174. doi:10.1016/j.jtherbio.2010.02.004Belous, A., & Podhajsky, R. J. (2009). The effect of initial and dynamic liver conditions on RF ablation size: a study in perfused and non-perfused animal models. Energy-based Treatment of Tissue and Assessment V. doi:10.1117/12.809597Song, K. D., Lee, M. W., Park, H. J., Cha, D. I., Kang, T. W., Lee, J., … Rhim, H. (2015). Hepatic radiofrequency ablation:in vivoandex vivocomparisons of 15-gauge (G) and 17-G internally cooled electrodes. The British Journal of Radiology, 88(1050), 20140497. doi:10.1259/bjr.20140497Cha, J., Choi, D., Lee, M. W., Rhim, H., Kim, Y., Lim, H. K., … Park, C. K. (2009). Radiofrequency Ablation Zones in Ex Vivo Bovine and In Vivo Porcine Livers: Comparison of the Use of Internally Cooled Electrodes and Internally Cooled Wet Electrodes. CardioVascular and Interventional Radiology, 32(6), 1235-1240. doi:10.1007/s00270-009-9600-0Lee, J. M., Han, J. K., Chang, J. M., Chung, S. Y., Kim, S. H., Lee, J. Y., … Choi, B. I. (2006). Radiofrequency Ablation of the Porcine Liver In Vivo: Increased Coagulation with an Internally Cooled Perfusion Electrode. 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