This work presents an alternate method for producing the finite helical axes for tibial motion. The method includes two procedures. In the first procedure, coordinates of the tibia in each specified position throughout full knee flexion to extension are measured in spatial Cartesian form. In the second procedure, the Rodrigues displacement equation is used to calculate finite helical axis parameters from the tibial displacements.
The purpose of this study is to estimate material properties of articular cartilage by curve fitting method using finite element (FE) analysis. While various material tests have been conducted to predict the behavior of articular cartilage, one of the recent interests was the accurate estimation of material properties under physiological and dynamic condition. In this study, cylindrical indentation was experimentally conducted in high compressive amount and high compression rate in considering the physiological condition. Each single specimen was sequentially exposed to compressive tests at definite deflection with different compressive amount and different compression rates and compressive creep test. The time-dependent compressive force given by a precise compression tester was utilized for estimation of material properties by curve fitting method with FE analysis. Five typical material properties, which represented total apparent Young's modulus, strain dependent permeability and fibril reinforcement by collagen network, were selected for the estimation process with depth-dependency of Young's modulus. In the curve fitting processes by FE analysis, each material property had specific roles on reproducing experimental time-dependent reactional force. A single material property set estimated in this study successfully reproduced the four different experimental time-dependent behaviors.
Upon the arrival of the osteosynthesis, technological advancement has revolutionized the orthopedic surgery, producing increasingly efficient prostheses. Nevertheless, it turns out that over the years of lifetime these orthopedic implants presents complications in vivo. This requires in most cases a reoperation. To improve the total hip replacement lifetime it is imperative to investigate the effects of dynamic loading on the replaced joint. For this reason, we initially studied the mechanical behavior of their different components, according to the nature of hip's movements, the exerted forces on the femoral head and particularly the muscular forces acting on hip-femur system. Then, we performed numerical simulations of a femur carrying a cemented hip prosthesis type (CMK3), the boundary conditions used in the simulations are identical to those applied in vivo during the daily activities.
The objective of this study is to calculate the tibiofemoral and patellofemoral forces at deep squatting and kneeling including seiza, which is the Japanese sedentary sitting. These postures are usually seen in daily life, especially in Japan or some regions in Asia or Arab. Thus it is expected to develop the artificial knee joint which is capable of making the posture, because the conventional prostheses cannot ensure deep knee flexion. We measured the joint angles of a lower limb and thigh-calf contact force at four postures. Then the tibiofemoral and patellofemoral joint forces were calculated, by using the force and moment equilibrium conditions on the muscloskeltal model at saggital plane. As a result, the thigh-calf contact force was the smallest at heel-contact squatting (0.60BW) and was the largest at heel-rise squatting (1.16BW). The knee flexion angle at these postures were almost the same, therefore the force might be effected the angles of hip and ankle joint. The tibiofemoral force was the smallest at seiza (0.64BW) and was the largest at heel-rise squatting (1.87BW). The patellofemoral force was also the smallest at seiza (0.74BW) and was the largest at heel-rise squatting (1.72BW). Neglecting the thigh-calf contact force, the joint forces were 3.8 times larger on average. Considering the thigh-calf contact force, which might be affected by not only knee joint angle but also hip and ankle joint angle, the knee joint force decreased extremely and the comparison between the postures underwent significant change.
Motivated by the dynamic, i.e., “delayed” stall mechanism in bio-inspired flapping wing aerodynamics that can achieve high lift production at high angles of attack (AoA) we utilize a simplified revolving wing model to explore the novel mechanisms in concert with stall phenomenon at low Reynolds numbers. The dynamic stall-based leading-edge vortex structure recognized as the primary reason for lift augment in insect flapping flight is also observed in revolving wings in low Reynolds (Re) number regime. However, it is still unclear why this “delayed” stall at low Res performs remarkably distinguished from that at high Res. In this study, we built a hawkmoth wing-like geometric model and a revolving kinematic model with an impulsive accelerated start as the quasi-steady model of flapping wings. We carried out a systematic parametric study on stall characteristics in terms of Res effects over a wide range from 100 up to 5.4×105. Our results show that in the low Res regime where most insects fly, the revolving wing likely does not stall in a conventional sense: there is no trend that lift turns to reduce at some critical AoA but keeps increasing with increasing AoAs. Moreover, the Reynolds number effect on aerodynamic forces augment is mostly pronounced at Res less than 5400 during both unsteady acceleration and steady rotation phases. Our results imply that micro air vehicles (MAV) with rotary wings will suffer a rapid drop in aerodynamic performance probably at operating Res less than 5,400, which may point to the importance of the employment of flapping wings for insect-sized MAV design.
This study presents a computational mechanical model of coil placement in cerebral aneurysms with using realistic coil properties. The mechanical behavior of the coil is expressed by solving a variational problem including the kinetic and elastic energies of the coil and geometric constraints due to the multiple contacts. The coil is discretized as a set of beam elements obeying Timoshenko beam theory, in which these elastic properties are determined based on the actual shape and material property of the coil. Numerical examples of the coil placement are presented for four cases with different coil properties in terms of the elastic property (hard and soft) and reference configurations (helical loop and complex loop) within the realistic range. These results exhibit the effects of the coil properties on not only the transition of the coil configuration during the placement process but also the contact force of the coil against the aneurysm wall which has a fatal risk of bleeding in the operation. The proposed computational model will assist surgeons to select the appropriate coil and coil deployment protocol to achieve the sufficient treatment effectiveness with minimizing the risk of bleeding in the view of the mechanical sense.
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