This paper presents the boundary element analysis of interference fit problems using axisymmetric boundary elements. A subregional technique is used to calculate the interference pressure and to find ...the von Mises stresses on the hub bore, without using iteration and incremental methods. The shaft and hub are modelled with equal lengths, unequal lengths, a shoulder on the shaft, and a grooved hub. Axisymmetric models of the shaft and hub are used to determine variable interference pressure along the interface line in the axial direction. The hub material is considered as steel and grey cast iron, and the shaft material is taken to be steel. All models used in the analysis are also solved using the finite element method with the ANSYS program. The results are compared with each other.
A comparison of direct integration methods is made and their efficiency is investigated for impact problems. Newmark, Wilson-θ, Central Difference and Houbolt Methods are used as direct integration ...methods. Impact analysis includes that of elastic and large deformation based upon updated Lagrangian including buckling check. The results show that the direct integration methods give different results in different contact-impact cases.
There is widespread clinical interest in assessing the mechanical properties of tissues and vessel walls. This study investigated the importance of the test phantom in providing a realistic ...assessment of clinical wall tracking performance for a variety of ultrasound modalities. B-mode, colour Doppler and Tissue Doppler Imaging (TDI) cineloop images were acquired using a Philips HDI5000 scanner and L12-5 probe. In-vivo longitudinal sections of 30 common carotid arteries and in-vitro images of pulsatile flow of a blood mimicking fluid through walled and wall-less tissue and vessel mimicking flow phantoms were analysed. Vessel wall tracking performance was assessed for our new probabilistic B-mode algorithm (PROBAL), and 3 different techniques implemented by Philips Medical Systems, based on B-mode edge detection (LDOT), colour Doppler (CVIQ) and TDI (TDIAWM). Precision (standard deviation/mean) of the peak systole dilations for respective PROBAL, LDOT, CVIQ and TDIAWM techniques were: 15.4 ± 8.4%, 23 ± 12.7%, 10 ± 10% and 10.3 ± 8.1% for the common carotid arteries; 6.4%, 22%, 11.6% and 34.5% for the wall-less flow phantom, 5.3%, 9.8%, 23.4% and 2.7% for the C-flex walled phantom and 3.9%, 2.6%, 1% and 3.2% for the latex walled phantom. The test phantom design and construction had a significant effect on the measurement of wall tracking performance.
In this study, the stress based finite element method is coupled with the boundary element method in two different ways. In the first one, the ordinary distribution matrix is used for coupling. In ...the second one, the stress traction equilibrium is used at the interface llne of both regions as a new coupling process. This new coupling procedure is presented without a distribution matrix.Several case studies are solved for the validation of the developed coupling procedure. The results of case studies are compared with the distribution matrix coupling, displacement based finite element method, assumed stress finite element method, boundary element method, ANSYS and analytical results whenever possible. It is shown that the coupling of the stress traction equilibrium with assumed stress finite elements gives as accurate results as those by the distribution matrix coupling.
An improved version of the regular boundary element method, the artificial boundary node approach, is derived. A simple contact algorithm is designed and implemented into the direct boundary element, ...regular boundary element and artificial boundary node approaches. The exisiting and derived approaches are tested using some case studies. The results of the artificial boundary node approach are compared with those of the existing boundary element program, the regular element approach, ANSYS and analytical solution whenever possible. The results show the effectiveness of the artificial boundary node approach for a wider range of boundary offsets.
Objective
To compare the location of suspect lesions detected by computational analysis of multimodal magnetic resonance imaging data with areas of seizure onset, early propagation, and interictal ...epileptiform discharges (IEDs) identified with stereoelectroencephalography (SEEG) in a cohort of patients with medically refractory focal epilepsy and radiologically normal magnetic resonance imaging (MRI) scans.
Methods
We developed a method of lesion detection using computational analysis of multimodal MRI data in a cohort of 62 control subjects, and 42 patients with focal epilepsy and MRI‐visible lesions. We then applied it to detect covert lesions in 27 focal epilepsy patients with radiologically normal MRI scans, comparing our findings with the areas of seizure onset, early propagation, and IEDs identified at SEEG.
Results
Seizure‐onset zones (SoZs) were identified at SEEG in 18 of the 27 patients (67%) with radiologically normal MRI scans. In 11 of these 18 cases (61%), concordant abnormalities were detected by our method. In the remaining seven cases, either early seizure propagation or IEDs were observed within the abnormalities detected, or there were additional areas of imaging abnormalities found by our method that were not sampled at SEEG. In one of the nine patients (11%) in whom SEEG was inconclusive, an abnormality, which may have been involved in seizures, was identified by our method and was not sampled at SEEG.
Significance
Computational analysis of multimodal MRI data revealed covert abnormalities in the majority of patients with refractory focal epilepsy and radiologically normal MRI that co‐located with SEEG defined zones of seizure onset. The method could help identify areas that should be targeted with SEEG when considering epilepsy surgery.
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