Purpose: To evaluate the in vitro biomechanical characteristics of patellar tendon ligaments (BTB) when stored as fresh frozen or as glycerol cryopreserved allografts. Methods: Seventy patellar tendons were harvested from 35 cadaveric human donors and randomly assigned into seven groups. Grafts in group FRESH were mechanically tested within 2 h of harvesting. FROZ-3, FROZ-6, and FROZ-9 were deep-frozen to -80 degrees C for 3, 6, and 9 months, respectively. Grafts in groups CRYO-3, CRYO-6, and CRYO-9 were initially incubated with 10 % glycerol in a phosphate-buffered saline for 1 h and then stored in glycerol solution (10 % glycerol in PBS) at -80 degrees C for 3, 6, and 9 months, respectively. Grafts were mechanically tested with two cycling modes (50-250 degrees N and 150-500 degrees N) and then loaded to failure. Results: Cryopreserved grafts demonstrated more consistent results and expressed lower elongation rates after both cycling loading protocols compared to their frozen counterparts at all storage times. During load-to-failure analysis, ultimate stiffness levels were predominantly higher (23.9-61.5 %) in cryopreserved grafts compared with frozen grafts, and ultimate stress levels were 26 % (13.3-47.7 %) higher, regardless of the storage time. Moreover, cryopreserved grafts revealed similar ultimate elongation and uniformly higher ultimate stiffness and ultimate stress levels compared to fresh grafts. Conclusion: The results of this in vitro study demonstrated superior mechanical properties of cryopreserved grafts compared to frozen grafts within a preservation period of 9 months. Cryopreservation with glycerol solution might be used to further improve the quality of preserved soft-tissue allografts.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 30380505When estimating a structure's fatigue life during vibrational test the stress frequency- response function (SFRF) to the base excitation is required.The response to this base excitation can be numerically obtained by solving the equilibrium equations for each frequency of interest. In this research we propose a new method, that can be used to obtain the SFRFof a base-excited structure using the modal model of the unconstrained structure, only. By further developing the idea of a structural modification using the response function this research significantly reduces the computation time and the amount of data sent to the fatigue-analysis software.The new method is presented on two numerical examples: a simple beam structure and a Y-shaped structure. Using numerical examples, the effects of the modal truncation, the matrix singularity and the damping are discussed
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 12882459The article introduces a simple and efficient higher-order explicit numerical scheme for the integration of a system of ordinary differential equations. The scheme is based on the truncated Taylor expansion of the constraint equation with order h of the scheme being determined by the highest exponent in the truncated Taylor series. In conjunction with a direct solution technique used to solve the boundary value problem, the scheme is very convenient for integrating constitutive models in plasticity. The general opinion that the implicit backward-Euler scheme is much more accurate than the thus-far known explicit schemes is seriously challenged by the introduction of the developed scheme. The accuracy of the new higher-order explicit scheme in the studied cases is significantly higher than the accuracy of the classical backward-Euler scheme, if we compare them under the condition of a similar CPU time consumption.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 11946779Vortex wake interaction of a rectangular prism is numerically investigated. The wind barrier is accurately geometrically represented with a three-dimensional model in the numerical simulation. The barrier model consists of horizontal bars with different inclination angles. The unsteady Reynolds-averaged Navier-Stokes (URANS) computation is applied because the flow is not statistically stationary. The shear stress transport (SST) k- turbulence model is used because it shows good behavior in adverse and separated flows. Experimental study is performed to confirm the numerical data. The aim is to enhance the present level of understanding regarding bluff body wake interference flow and analyze the barriers bar inclination effect on the sheltered object. As the bar inclination angle decreases, the bleed flow gets stronger, which results in a smaller reduction of the drag imposed on the sheltered object. The turbulent structures between the barrier and the sheltered object decrease as the bar inclination angle decreases.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 13194011A new method based on Muller's algorithm for solving nonlinear equations has been developed. The classic Muller's method is based on an interpolating polynomial built on the last three points of an iterative sequence. Unfortunately, Mullers method is not globally convergent. In order to ensure the global convergence a bracketing is introduced. The proposed method does not require the use of a derivative of the function and is more rapidly convergent than a classical regula falsi method. The method is good alternative to other bracketing methods.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 12740379