Realistic Three-dimensional Finite Element Model Research Articles

INVESTIGATION OF DAMAGE ON DERBENDIKHAN DAM DURING EARTHQUAKE EXCITATION

In this study, the performance of a damaged dam was evaluated through a three-dimensional finite element model. The dam is located in Derbendikhan city of Northern Iraq and damaged during a 7.3 magnitude earthquake which was happened 30 kilometers south of Halabja city. Derbendikhan dam which was built between the years 1956-1961 is a clay-core rock fill dam. The damage of the dam was investigated at the site right after the earthquake and some cracks were observed in the main body of the dam. The main goal of this work is to present the results of the survey which was conducted at the site and investigating the damage development mechanism through a realistic three-dimensional finite element model of the dam. As complying with the observations at the site, the finite element analysis has shown that the primary failure mechanism is due to the separation of the core and rock fill sections at the downstream side of the dam.

Analysis of trans tibial prosthetic socket materials using finite element method

The objective of this work was to analyze in a parametric study for optimum design solution of prosthetic socket material by finite element method. A realistic three-dimensional finite element model of the PTB socket was developed to find out the stress distribution pattern under physiologically relevant loading condition during normal walking. The CAD model of the rectified socket was collected from a CMET 250 non-tactile high accuracy (0.06 mm) white light scanner and analyses were carried out using finite element Method in ANSYS®. All structural materials used in the analysis were assumed to be linearly elastic, homogeneous and isotropic. Different materials were used for socket and only polypropylene was used for socket adopter. Analysis was prepared at 2 mm, 3 mm, 4 mm, 5 mm & 6 mm thickness of socket in different materials commonly used in developing countries. The bottom line of socket was made to zero displacement constraints and vertical loads in relation to stance phase of gait cycle were applied under static condition at the patella tendon brim. The 3 mm laminated composite sockets was found to be optimum in terms of strength, weight and factor of safety.

Conservation of a slender historical Mamluk-style minaret by passive control techniques

During the Egypt/Dahshur 1992 earthquake, a large number of historical Islamic minarets, especially those built during the Mamluk era, were significantly damaged. The level of damage in Mamluk-style minarets was assigned to their massive size, and their irregular distribution of mass and stiffness along their heights. In this paper, the seismic vulnerability of a representative Mamluk-style minaret, namely Manjaq Al-Yusufi (1349 A.D.) is investigated and some seismic protection techniques are proposed and evaluated. Geometrical, material, and geotechnical data were determined at the site. A realistic three-dimensional finite element model of the minaret that reflects those properties was constructed. Ambient vibration tests were then performed on the minaret, and its modal parameters such as fundamental periods and mode shapes were obtained. The ambient vibration test results were then used to update the finite element model. The seismic hazard at the minaret location was evaluated, and a seismic risk study of the minaret was performed with the conclusion that the minarets will be highly vulnerable during moderate earthquakes. A seismic protection technique that includes the use of high damping rubber bearings HDRB and vertical steel anchoring bars is proposed and evaluated. The proposed technique was found to efficiently reduce the seismic risk of the minaret under investigation. Copyright © 2004 John Wiley & Sons, Ltd.

A realistic three dimensional FEM of the human head

A realistic three-dimensional finite element model (FEM) of the human headhas been developed. Separate layers for the scalp, skull, cerebrospinalfluid (CSF) and brain were modelled. Hexahedral elements, a special mastermatrix assembly technique and an iterative successive over-relaxation (SOR)solution scheme were employed. This approach enabled rapid modelling withminimal memory requirements, which makes this method practical if used forelectrical impedance tomography (EIT) or source localization inverseproblems. Compared to scalp electrodes, subdural voltage sensing electrodeswere three to four times more sensitive close to an oedema or sourceregion, if it was peripheral, but this decreased to 30%-40% for centraloedema or source regions. Scalp current injecting electrodes arepreferable, since the maximum allowable current is 10 times larger thanthat of the subdural ones. The distance of voltage sensing electrodes froma region to be imaged highly affects sensitivity, so depth electrodes willbe more sensitive, provided that they are close to the region of interest.Finally, the electrode size has significant effects on the input ortransfer impedance.

Effects of local skull inhomogeneities on EEG source estimation

The accuracy of the head model affects the solutions of the EEG inverse problems. If a simple three-sphere model and standard conductivity values for brain, skull and scalp regions are used, significant errors may occur in the dipole localisation. One of the most sensitive head model parameters is the conductivity of the skull. A realistic three-dimensional finite-element model provides a method to study the effect of inhomogeneities of the skull on the solutions of EEG inverse problems. In this paper the effect of a local skull conductivity inhomogeneity on source estimation accuracy is analyzed by computer simulations for different numbers of electrodes. It is shown that if the inhomogeneity of the skull conductivity is not taken into account, localisation errors of approximately 1 cm can be encountered in the equivalent current dipole estimation. This modelling error introduces a bias to the solution which cannot be compensated by increasing the number of electrodes.

Simulated internal defibrillation in humans using an anatomically realistic three-dimensional finite element model of the thorax.

Determination of the optimal electrode configuration during implantable cardioverter defibrillator (ICD) implantation remains largely an empirical process. This study investigated the feasibility of using a finite element model of the thorax to predict clinical defibrillation metrics for internal defibrillation in humans. Computed defibrillation metrics from simulations of three common electrode configurations with a monophasic waveform were compared to pooled metrics for similar electrode and waveform configurations reported in humans. A three-dimensional finite element model was constructed from CT cross-sections of a human thorax. Myocardial current density distributions for three electrode configurations (epicardial patches, right ventricular [RV] coil/superior vena cava [SVC] coil, RV coil/SVC coil/subcutaneous patch) and a truncated monophasic pulse with a 65% tilt were simulated. Assuming an inexcitability threshold of 25 mA/cm2 (10 V/cm) and a 75% critical mass criterion for successful defibrillation, defibrillation metrics (interelectrode impedance, defibrillation threshold current, voltage, and energy) were calculated for each electrode simulation. Values of these metrics were within 1 SD of sample-size weighted means for the corresponding metrics determined for similar electrode configurations and waveforms reported in human clinical studies. Simulated myocardial current density distributions suggest that variations in current distribution and uniformity partially explain differences in defibrillation energy requirements between electrode configurations. Anatomically realistic three-dimensional finite element modeling can closely simulate internal defibrillation in humans. This may prove useful for characterizing patient-specific factors that influence clinically relevant properties of current density distributions and defibrillation energy requirements of various ICD electrode configurations.

Effect of paddle placement and size on defibrillation current distribution: a three-dimensional finite element model

A realistic three-dimensional finite element model of the conductive anatomy of a canine thorax was constructed for use in the study of transthoracic electrical defibrillation. The model was constructed from a series of 21 cross-sectional CT scans of a 14.5 kg beagle, each separated by 0.82 cm. The electrical conductive properties of 8 distinct tissues were incorporated, including the anisotropic properties of skeletal muscle. Current density distributions were obtained for six paddle pairings and two paddle sizes. A quantitative basis for comparing the resulting distributions was formulated. Our results suggest that placing one or both of the paddles near the heart delivers a higher fraction of current to the heart. However, such paddle placements also produce a less uniform myocardial current density distribution and thus have a higher potential for causing damage. We found that some paddle positions can produce myocardial current densities close to the threshold for damage in successful defibrillations. Results obtained for 8 and 12 cm paddles indicate that 12 cm paddles may offer modest advantages over 8 cm paddles in clinical defibrillation. Comparison of our results to available in vivo experimental data confirm the validity of the finite element method for examining continuum field variables pertinent to electrical defibrillation.