Ergin Tönük

Prediction of automobile tire cornering force characteristics by finite element modeling and analysis

Abstract In this study, a detailed finite element model of a radial automobile tire is constructed for the prediction of cornering force characteristics during the design stage. The nonlinear stress–strain relationship of rubber as well as a linear elastic approximation, reinforcement, large displacements, and frictional ground contact are modeled. Validity of various simplifications is checked. The cornering force characteristics obtained by the finite element tire model are verified on the experimental setup constructed for this purpose.

Numerical Study of the Aerodynamic Effects of Septoplasty and Partial Lateral Turbinectomy

Objectives: To investigate, first, the effects of septal deviation and concha bullosa on nasal airflow, and second, the aerodynamic changes induced by septoplasty and partial lateral turbinectomy, using computational fluid dynamics (CFD).

In vivo indentation of lower extremity limb soft tissues

In vivo rate-controlled indentation tests were conducted on the soft tissues of the residual limbs of five individuals with trans-tibial amputation and the right calf of five nonamputees. Force relaxation trials were also conducted. The cyclic indentation tests indicated that the bulk soft tissue response to compressive load is nonlinear and rate-dependent. Inter- and intrasubject stiffness variations were observed. The force relaxation studies indicated that approximately 55-95% relaxation may occur, with equilibration typically occurring in less than 60 s. Most of this relaxation (35-80%) occurred within 5 s after loading.

The Annular Ligament An Anatomical Study

Background Despite documentations of ligamentous structures of the elbow, the anatomy and clinical and functional importance of the annular ligament has not been comprehensively defined in the orthopaedic literature. Hypothesis The annular ligament is an important component of both the proximal radioulnar and humeroradial joints, as well as an important component of the neighboring muscles and ligaments. Study Design Descriptive laboratory study. Materials and Methods To investigate the annular ligament and its relationship with neighboring structures, macroscopic and microscopic dissections were performed on both upper extremities of 30 cadavers (12 female and 18 male) fixed in 10% formaldehyde and on 1 upper extremity of a fresh cadaver (male). Results The distal ulnar insertion of discrete fibers on the supinator crest was defined as the inferior oblique band of the annular ligament, and the proximal insertion of the annular ligament was defined as the superior oblique band of the annular ligament. These patterns were noted in all specimens. It was difficult to distinguish the fibers of the supinator muscle in every specimen because they were intimately fused with the fibers of the annular ligament. Conclusions The superior and inferior oblique bands of the annular ligament attached proximally and distally onto the ulna, thus helping to secure the annular ligament in place.

Predicting time-dependent remodeling of bone around immediately loaded dental implants with different designs

The purpose of this study was to predict time-dependent biomechanics of bone around cylindrical screw dental implants with different macrogeometric designs under simulated immediate loading condition. The remodeling of bone around a parallel-sided and a tapered dental implant of same length was studied under 100N oblique load by implementing the Stanford theory into three-dimensional finite element models. The results of the analyses were examined in five time intervals consisting loading immediately after implant placement, and after 1, 2, 3 and 4 weeks following implantation. Maximum principal stress, minimum principal stress, and strain energy density in peri-implant bone and displacement in x-(implant lateral direction with a projection of the oblique force) and y-(implant longitudinal direction) axes of the implant were evaluated. The highest value of the maximum and minimum principal stresses around both implants increased in cortical bone and decreased in trabecular bone. The maximum and minimum principal stresses in cortical bone were higher around the tapered cylindrical implant, but stresses in the trabecular bone were higher around the parallel-sided cylindrical implant. Strain energy density around both implants increased in cortical bone, slightly decreased in trabecular bone, and higher values were obtained for the parallel-sided cylindrical implant. Displacement values slightly decreased in time in x-axis, and an initial decrease followed by a slight increase was observed in the y-axis. Bone responded differently in remodeling for the two implant designs under immediate loading, where the cortical bone carried the highest load. Application of oblique loading resulted in increase of stiffness in the peri-implant bone.

An anatomical study of the meniscofibular ligament

We examined the anatomical structure of a ligament (ligamentum meniscofibulare) between apex fibulae and lateral meniscus by macroscopic and microscopic dissection and transillumination method in 50 knees of 25 cadavers (5 were fresh). We analyzed the function of this ligament, which runs between the head of the fibulae and lateral meniscus. The existence of a connection between knee joint and proximal tibiofibular joint was demonstrated by injecting colored liquid into the knee joint space and transillumination. The mensicofibular ligament is a capsular ligament originating from the lateral meniscus that is anterior to the popliteal muscle tendon. The meniscofibular ligament, which is attached to fibula with rotatory motion at one end and to the lateral meniscus at the other, is believed to position the lateral meniscus and therefore to play a key role in the knee joint.

Dynamic function of the fibula. Gait analysis evaluation of three different parts of the shank after fibulectomy: proximal, middle and distal

The purpose of this case study was to investigate the dynamic features of fibular movement to gait pattern by analyzing the gait of individuals with three different parts of the fibula resected. Gait analyses revealed that proximal fibula resection impaired knee stability, whereas distal fibula resection disturbed ankle kinematics significantly. Except a mild secondary quadriceps weakness, middle fibula resection did not cause a significant biomechanical disturbance on gait.

Predicting bone remodeling around tissue- and bone-level dental implants used in reduced bone width

The objective of this study was to predict time-dependent bone remodeling around tissue- and bone-level dental implants used in patients with reduced bone width. The remodeling of bone around titanium tissue-level, and titanium and titanium-zirconium alloy bone-level implants was studied under 100 N oblique load for one month by implementing the Stanford theory into three-dimensional finite element models. Maximum principal stress, minimum principal stress, and strain energy density in peri-implant bone and displacement in x- and y- axes of the implant were evaluated. Maximum and minimum principal stresses around tissue-level implant were higher than bone-level implants and both bone-level implants experienced comparable stresses. Total strain energy density in bone around titanium implants slightly decreased during the first two weeks of loading followed by a recovery, and the titanium-zirconium implant showed minor changes in the axial plane. Total strain energy density changes in the loading and contralateral sides were higher in tissue-level implant than other implants in the cortical bone at the horizontal plane. The displacement values of the implants were almost constant over time. Tissue-level implants were associated with higher stresses than bone-level implants. The time-dependent biomechanical outcome of titanium-zirconium alloy bone-level implant was comparable to the titanium implant.

Impact of fibular torsion and rotation on chronic ankle instability

BACKGROUND The fibula is known not to involve in transmission of weight but known simply as an ankle stabilizer. However, its main function in stabilizing the ankle remains obscure. Since the fibula has an impact on torsion and rotation of the ankle, its effect on lateral ankle instability should be investigated. MATERIALS AND METHODS Twenty patients with lateral ankle instability (Group 1) and 19 healthy volunteers (Group 2) were included in the study. The tibiofibular and talofibular relationships were evaluated using MRI images. Fibular torsion and rotation angles were calculated using a new method. Range of motion of the ankle joint was investigated while the knee was at flexion (90°) and extension (0°). The comparisons performed between the 2 groups and independent from the groups were statistically evaluated and, the p value of <0.05 was considered as statistically significant. RESULTS A significant difference was found between the two groups for age (p<0.05). There were no statistically significant differences between the right and left sides for all measurements in the group 1 and 2 (p>0.05). There was a statistically significant difference between the two groups in dorsal flexion when the knee is at flexion (90°) and extension (0°) position. There was also a statistically significant difference between the two groups in plantar flexion which was measured while the knee was at extension (0°) position. No statistically significant difference was found between both groups in terms of fibular torsion and rotation. However, independent from the groups when the patients were divided into 2 groups according to whether the fibula localized posteriorly or not, in patients with posteriorly localized fibula it was demonstrated that the fibular torsion and rotation was increased significantly. CONCLUSION We did not detect any relationship between fibular torsion and rotation and ankle instability. However, independent from the groups when the patients were divided into 2 groups according to whether the fibula localized posteriorly or not, we realized that in patients with posteriorly localized fibula, fibular torsion and rotation significantly increased. This finding did not explain the cause of instability. However, it may gain significance with new further studies regarding ankle instability.

Effects of custom-made insole on gait pattern of patients with unilateral displaced intra-articular calcaneal fracture: evaluation with computerized gait analysis

OBJECTIVE The aim of this study was to investigate whether use of custom-fabricated insoles improves the gait pattern in patients with displaced intra-articular calcaneal fractures. METHODS Fourteen patients (7 female, 7 male; mean age: 39 ± 12 years) and 11 healthy individuals (mean age: 42 ± 13 years) were included in the study. Treatment protocol included conservative treatment involving immobilization, with or without closed reduction, active exercises, wear of a custom-fabricated insole and prospective follow-up. All patients were evaluated by physical examination, axial and lateral radiographs, computerized tomography, and computerized gait analysis. RESULTS The use of custom-made insoles significantly improved step and stride lengths and the peak values of fore-aft component in the involved foot and tended to increase plantar flexor moment and total ankle power. The majority of patients (71%) continued to have substantial mechanical abnormalities by computerized gait analysis. Plantar flexion moment, total ankle power, vertical component of ground reaction forces (GRFs), and total sagittal plane excursion were significantly decreased in the involved foot when compared to the uninvolved foot. Plantar flexion moment, total ankle power, vertical, fore-aft and mediolateral components of GRFs were significantly decreased in the involved foot when compared to the healthy control group. CONCLUSION Use of a custom-made insole improves advancement of limb and weight-bearing in patients with a displaced intra-articular calcaneal fracture. Nevertheless, mechanical abnormalities persist in the affected limb, which does not appear to recover a gait pattern similar to that of normal walking.