scholarly journals Mathematical Models Based on Transfer Functions to Estimate Tissue Temperature During RF Cardiac Ablation in Real Time

2012 ◽  
Vol 6 (1) ◽  
pp. 16-22
Author(s):  
Jose Alba-Martínez ◽  
Macarena Trujillo ◽  
Ramon Blasco-Gimenez ◽  
Enrique Berjano
Keyword(s):  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Finite Element ◽  
Mathematical Models ◽  
Dynamic System ◽  
Applied Voltage ◽  
Transfer Functions ◽  
Tissue Temperature ◽  
System Response ◽  
Finite Element Models

Radiofrequency cardiac ablation (RFCA) has been used to treat certain types of cardiac arrhythmias by producing a thermal lesion. Even though a tissue temperature higher than 50ºC is required to destroy the target, thermal mapping is not currently used during RFCA. Our aim was thus to develop mathematical models capable of estimating tissue temperature from tissue characteristics acquired or estimated at the beginning of the procedure (electrical conductivity, thermal conductivity, specific heat and density) and the applied voltage at any time. Biological tissue was considered as a system with an input (applied voltage) and output (tissue temperature), and so the mathematical models were based on transfer functions relating these variables. We used theoretical models based on finite element method to verify the mathematical models. Firstly, we solved finite element models to identify the transfer functions between the temperature at a depth of 4 mm and a constant applied voltage using a 7Fr and 4 mm electrode. The results showed that the relationships can be expressed as first-order transfer functions. Changes in electrical conductivity only affected the static gain of the system, while specific heat variations produced a change in the dynamic system response. In contrast, variations in thermal conductivity modified both the static gain and the dynamic system response. Finally, to assess the performance of the transfer functions obtained, we conducted a new set of computer simulations using a controlled temperature protocol and considering the temperature dependence of the thermal and electrical conductivities, i.e. conditions closer to those found in clinical use. The results showed that the difference between the values estimated from transfer functions and the temperatures obtained from finite element models was less than 4ºC, which suggests that the proposed method could be used to estimate tissue temperature in real time.

Thermal-Electric Finite Element Analysis of Electrosurgical Cautery Process

2007 ◽  
Author(s):  
Robert E. Dodde ◽  
Scott F. Miller ◽  
Albert J. Shih ◽  
James D. Geiger
Keyword(s):  
Heat Transfer ◽  
Electrical Conductivity ◽  
Finite Element ◽  
Biological Tissue ◽  
Tissue Temperature ◽  
Temperature Dependent ◽  
Element Analysis ◽  
Temperature Dependent Thermal Conductivity ◽  
Insight Into ◽  
Good Agreement

Cautery is a process to coagulate tissues and seal blood vessels using the heat. In this study, finite element modeling (FEM) was performed to analyze temperature distribution in biological tissue subject to cautery electrosurgical technique. FEM can provide detailed insight into the heat transfer in biological tissue to reduce the collateral thermal damage and improve the safety of cautery surgical procedure. A coupled thermal-electric FEM module was applied with temperature-dependent electrical and thermal properties for the tissue. Tissue temperature was measured at different locations during the electrosurgical experiments and compared to FEM results with good agreement. The temperature-dependent electrical conductivity has demonstrated to be critical. In comparison, the temperature-dependent thermal conductivity does not impact heat transfer as much as the electrical conductivity. FEM results show that the thermal effects can be varied with the electrode geometry that focuses the current density at the midline of the instrument profile.

Development and Comparison of Laplace Domain Models for Nonslender Beams and Application to a Half-Car Model With Flexible Body

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
R. Michael Van Auken
Keyword(s):  
Finite Element ◽  
Wave Equation ◽  
State Space ◽  
Transfer Functions ◽  
Rotary Inertia ◽  
Flexible Body ◽  
Finite Element Models ◽  
Laplace Domain ◽  
Area Of Interest ◽  
Shear Effects

Math models of flexible dynamic systems have been the subject of research and development for many years. One area of interest is exact Laplace domain solutions to the differential equations that describe the linear elastic deformation of idealized structures. These solutions can be compared to and complement finite order models such as state-space and finite element models. Halevi (2005, “Control of Flexible Structures Governed by the Wave Equation Using Infinite Dimensional Transfer Functions,” ASME J. Dyn. Syst., Meas., Control, 127(4), pp. 579–588) presented a Laplace domain solution for a finite length rod in torsion governed by a second-order wave equation. Van Auken (2012, “Development and Comparison of Laplace Domain and State-Space Models of a Half-Car With Flexible Body (ESDA2010–24518),” ASME J. Dyn. Syst., Meas., Control, 134(6), p. 061013) then used a similar approach to derive a Laplace domain solution for the transverse bending of an undamped uniform slender beam based on the fourth-order Euler–Bernoulli equation, where it was assumed that rotary inertia and shear effects were negligible. This paper presents a new exact Laplace domain solution to the Timoshenko model for an undamped uniform nonslender beam that accounts for rotary inertia and shear effects. Example models based on the exact Laplace domain solution are compared to finite element models and to slender beam models in order to illustrate the agreement and differences between the methods and models. The method is then applied to an example model of a half-car with a flexible body.

Identifying Real Stiffness Properties of Structural Elements of Adapted Finite-Element Models of Buildings and Structures - Part 1: Problem Setting

2014 ◽  
Vol 670-671 ◽  
pp. 732-735 ◽  
Author(s):  
Pavel I. Novikov
Keyword(s):  
Finite Element ◽  
Mathematical Models ◽  
Dynamic Characteristics ◽  
Finite Element Models ◽  
Structural Elements ◽  
Reliable Analysis ◽  
Adaptive Procedures ◽  
Stiffness Properties ◽  
The Creation ◽  
Problem Setting

The distinctive paper is devoted to problem of identification the dynamic characteristics of mathematical models based on the measured dynamic characteristics of real constructions. It is describes a problem of discrepancy of measured and modeling eigen pairs. It is shown that the problem is systemic. The creation and verification processes of mathematical (finite element) models used in the design constructions need some work and adjustments. For a reliable analysis of the construction ways are suggested to overcome the identified gaps using adaptive procedures.

scholarly journals Analysis of the Pump Strength to Extend its Lifetime

2018 ◽  
pp. 30-35 ◽  
Author(s):  
O. Larin ◽  
A. Kelin ◽  
R. Naryzhna ◽  
K. Potopalska ◽  
O. Trubayev
Keyword(s):  
Thermal Conductivity ◽  
Finite Element ◽  
Thermal Shock ◽  
Thickness Measurement ◽  
Operating Conditions ◽  
The Body ◽  
Finite Element Models ◽  
Body Parts ◽  
Strained State ◽  
Actual Geometry

The paper deals with the estimation of the residual strength of the body of water jet pump SN-10 /50K type operating in the beyond design lifetime in the line of NPP unit sprinkler pumps. The results of theoretical studies of its stressed-strained state are presented taking into account change in the geometry of body parts, which was observed after completion of the design lifetime. Static strength assessment was carried out for the main operating modes of the pump operation (normal operating conditions and hydraulic tests), as well as for conditions of an emergency situation. Corresponding researches were carried out in the framework of numerical computer simulation on the basis of the finite element method using up-to-date software complexes. 3D finite element models have been developed that take into account actual geometry of the pump components and the forecast of its possible change for a period of extended lifetime. The change in the design geometry is taken into account based on the extrapolation of the data of thickness measurement of the pump body walls obtained during the long service period. Based on the built finite-element models, the tasks of thermal conductivity and thermoelasticity have been consistently solved. The phenomenon of thermal shock on body parts was simulated that allow assessing residual pump strength in case of an emergency. Corresponding simulation was carried out by solving the problems of nonstationary thermal conductivity and the related problem of quasi-static thermoelasticity. Such an approach made it possible to determine the distribution of the temperature field over time under thermal shock, and the distribution of the stressed-strained state parameters of the pump at certain time moments.

scholarly journals Finite Element Analysis of Lightning Damage Factors Based on Carbon Fiber Reinforced Polymer

Materials ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5210
Author(s):  
Yansong Zhu ◽  
Yueke Ming ◽  
Ben Wang ◽  
Yugang Duan ◽  
Hong Xiao ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Carbon Fiber ◽  
Fiber Reinforced Polymers ◽  
Fiber Direction ◽  
Fiber Reinforced ◽  
Element Analysis ◽  
Carbon Fiber Reinforced

While carbon-fiber-reinforced polymers (CFRPs) are widely used in the aerospace industry, they are not able to disperse current from lightning strikes because their conductivity is relatively low compared to metallic materials. As such, the undispersed current can cause the vaporization or delamination of the composites, threatening aircraft safety. In this paper, finite element models of lightning damage to CFRPs were established using commercial finite element analysis software, Abaqus, with the user-defined subroutines USDFLD and HEAVEL. The influences of factors such as the structural geometry, laminate sequence, and intrinsic properties of CFRPs on the degree of damage to the composites are further discussed. The results showed that when a current from lightning is applied to the CFRP surface, it mainly disperses along the fiber direction in the outermost layer. As the length of the CFRP increases, the injected current has a longer residence time in the material due to the increased current exporting distance. Consequently, larger amounts of current accumulate on the surface, eventually leading to more severe damage to the CFRP. This damage can be alleviated by increasing the thickness of the CFRP, as the greater overall resistance makes the CFRP a better insulator against the imposed current. This study also found that the damaged area increased as the angle between the first two layers increased, whereas the depth of the damage decreased due to the current dispersion between the first two layers. The analysis of the electrical conductivity of the composite suggested that damage in the fiber direction will be markedly reduced if the conductivity in the vertical fiber direction increases approximately up to the conductivity of the fiber direction. Moreover, increasing the thermal conductivity along the fiber direction will accelerate the heat dissipation process after the lightning strike, but the influence of the improved thermal conductivity on the extent of the lightning damage is less significant than that of the electrical conductivity.

Thermal-Electric Finite Element Analysis and Experimental Validation of Bipolar Electrosurgical Cautery

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Robert E. Dodde ◽  
Scott F. Miller ◽  
James D. Geiger ◽  
Albert J. Shih
Keyword(s):  
Heat Transfer ◽  
Electrical Conductivity ◽  
Finite Element ◽  
Temperature Distribution ◽  
Tissue Temperature ◽  
Temperature Dependent ◽  
Element Analysis ◽  
Temperature Dependent Thermal Conductivity ◽  
Insight Into ◽  
Good Agreement

Cautery is a process to coagulate tissues and seal blood vessels using heat. In this study, finite element modeling (FEM) was performed to analyze temperature distribution in biological tissue subject to a bipolar electrosurgical technique. FEM can provide detailed insight into the tissue heat transfer to reduce the collateral thermal damage and improve the safety of cautery surgical procedures. A coupled thermal-electric FEM module was applied with temperature-dependent electrical and thermal properties for the tissue. Tissue temperature was measured using microthermistors at different locations during the electrosurgical experiments and compared to FEM results with good agreement. The temperature- and compression-dependent electrical conductivity has a significant effect on temperature profiles. In comparison, the temperature-dependent thermal conductivity does not impact heat transfer as much as the temperature-dependent electrical conductivity. Detailed results of temperature distribution were obtained from the model. The FEM results show that the temperature distribution can be changed with different electrode geometries. A flat electrode was modeled that focuses the current density at the midline of the instrument profile resulting in higher peak temperature than that of the grooved electrode (105 versus 96°C).

scholarly journals Up-to-date mathematical models lines of development of information technologies in the field of numerical methods of structures strength calculations

2018 ◽  
Vol 44 ◽  
pp. 00060
Author(s):  
Vladimir Meleshko
Keyword(s):  
Finite Element ◽  
Numerical Methods ◽  
Mathematical Models ◽  
Information Technologies ◽  
Structural Mechanics ◽  
High Dimensionality ◽  
Finite Element Models ◽  
Systems Of Equations ◽  
Distinctive Features ◽  
Complex Program

In order to carry out reliable calculations of structures adequate to reality, in particular, for taking into account plastic resource, it is necessary to use complex program systems and build finite element models of high dimensionality. This work provides a comparison of different mathematical models, which can be used for numerical analysis. Consideration was given to basic variation principles and methods of calculating structural mechanics. Distinctive features of forming systems of equations of classical methods of structural mechanics and known numerical methods were demonstrated. Possible advantages of methods with respect to accuracy and rate of calculations were revealed. Consideration was given to possible improvements of existing mathematical models in elastoplastic domain. Possible directions of development in the field of engineering methods for calculating strength were proposed.

Numerical prediction of thermal conductivity in ZrB2-particulate-reinforced epoxy composites based on finite element models

2018 ◽  
Vol 25 (2) ◽  
pp. 337-342
Author(s):  
Yicheng Wu ◽  
Zhiqiang Yu
Keyword(s):  
Thermal Conductivity ◽  
Finite Element ◽  
Volume Fraction ◽  
High Volume ◽  
Epoxy Composites ◽  
Spherical Particles ◽  
Homogeneous Distribution ◽  
Finite Element Models ◽  
Negative Effect ◽  
Thermal Conductivities

AbstractEpoxy composites reinforced by Zirconium diboride (ZrB2) particles were investigated by finite element models (FEMs). It helped to explore the relationship between the thermal conductivity of composites and the volume fraction, size, shape, orientation, and arrangement of the ZrB2particles. The results showed that the thermal conductivity performance of composites was improved effectively when filled with ZrB2particles. Specifically, epoxy composites filled with 50 vol% spherical ZrB2particles had 12.05 times the thermal conductivity of epoxy resin. At the same volume fraction, the number of ZrB2particles in the epoxy matrix has little influence on thermal conductivity due to the dimensionless models. At a high volume fraction, rectangular ZrB2particles improved thermal conductivity more effectively than spherical particles. In the comparison of thermal conductivities among composites reinforced by rectangular fillers, the thermal conductivities of composites were clearly affected by the length-width ratios of fillers, and this effect was monotonically increasing. The vertical orientations of particles could conduct heat most effectively compared with slant and parallel orientations. The agglomerate distribution of ZrB2particles has the negative effect of thermal diffusion in a certain direction compared with homogeneous distribution.

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