Background
A nonlinear isotropic finite element (FE) model of a 29 year old human crystalline lens was constructed to study the effects of various geometrical parameters on lens accommodation.
Methods
The model simulates dis-accommodation by stretching of the lens and predicts the change in the lens capsule, cortex and nucleus surface profiles at select states of stretching/accommodation. Multiple regression analysis (MRA) is used to develop a stretch-dependent mathematical model relating the lens sagittal height to the radial position of the lens surface as a function of dis-accommodative stretch. A load analysis is performed to compare the FE results to empirical results from lens stretcher studies. Using the predicted geometrical changes, the optical response of the whole eye during accommodation was analysed by ray-tracing.
Results
Aspects of lens shape change relative to stretch were evaluated including change in diameter (d), central thickness (T) and accommodation (A). Maximum accommodation achieved was 10.29 D. From the MRA, the stretch-dependent mathematical model of the lens shape related lens curvatures as a function of lens ciliary stretch well (maximum mean-square residual error 2.5×10−3 µm, p<0.001). The results are compared with those from in vitro studies.
Conclusions
The FE and ray-tracing predictions are consistent with EVAS studies in terms of load and power change versus change in thickness. The mathematical stretch-dependent model of accommodation presented may have utility in investigating lens behaviour at states other than the relaxed or fully-accommodated states.
This article investigates different types of compound die piercing punches and double cutting operation parameters in terms of optimization using finite element technique, Taguchi method, regression analysis, and analysis of variance. The article overcomes the current knowledge gap in studying various cutting edges of piercing punches such as flat, chamfered, flat edge with concave hemisphere, and convex shaped when using the compound dies in stamping operations. The analysis of the compound die is carried out using ANSYS software. The main focus is to determine the contribution of key parameters for obtaining optimum cutting tool design. The best piercing punch is selected based on minimum burr height of the product. The values of cutting process parameters and burr heights have been analyzed using Minitab software. The results obtained indicate that the burr heights of the final product are at a minimum when the sheet metals are thicker and larger when the sheets are thinner. The chamfered and convex punches provided minimum burr heights which are as low as 0.034 mm for a typical sheet metal. This study provides a better outcome compared to the available experimental data in the literature. The investigation also designed efficient compound dies resulting in improved product quality.
In this paper, the low frequency vibro-acoustic responses from a submerged hull are attenuated using passive, active, and hybrid control strategies. An analytical model representing a simplified physical model of a submarine hull is developed, including the effects of ring-stiffeners, bulkheads, and external fluid loading. At low frequencies, rotation of the propeller results in discrete tones at the blade passing frequency and its harmonics. The fluctuating forces at the propeller are transmitted through the propulsion system, resulting in excitation of the low frequency hull vibrational modes, which in turn results in a high level of structure-borne radiated noise. In this work tuned vibration absorbers, active vibration control, and hybrid vibration absorbers are used to attenuate the breathing and bending modes of the submerged hull. The control performance of a hybrid vibration absorber is compared to the attenuation achieved using a passive absorber and the control performance of a fully active system. Results show that implementation of the hybrid vibration absorber results in significant attenuation of the structural and acoustic responses of the hull. The hybrid vibration absorber also requires a control force of lower magnitude compared with a fully active control system.
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