Russian Journal of Biomechanics

Mathematical modelling of the deformation of the eyeball loaded by a heavy stamp with a flat base is performed, which corresponds to Maklakoff tonometry. The modelling is carried out within the framework of the general approach developed by the authors, which represents the eyeball as a set of a deformable two-dimensional surface (cornea) and a zero-dimensional element that responds with a change in volume to changes in intraocular pressure (scleral region). The behavior of both components is assumed to be elastic: linear for the scleral region and non-linear for the cornea. For the latter, an exponential model developed by the authors was used, in which the nonlinearity of the elastic properties of the cornea is characterized by a single parameter. The calculations were carried out in the range of values of the nonlinearity parameter, estimated on the basis of data on tension of an isolated cornea by pressure. It is shown that taking into account the nonlinearity leads to an increase in the difference between the pressures in a loaded and unloaded eye (tonometric difference) and an increase in the slope of the dependence of tonometric pressure on the tonometer weight (pressure difference coefficient) during elastotonometry. The calculated corrections make it possible to propose refinements for the procedure of processing clinical measurement data. However, such conclusions should be considered as preliminary: there are no final estimates of the nonlinearity parameter for living eyes and they should be obtained as a result of comparing the calculation results with clinical studies. In particular, it is necessary to find out to what extent the values of this parameter are individual and may differ for different eyes.

The paper describes the design and software features of an intelligent sensor mounted on the oar shaft to register dynamic parameters characterizing the athlete’s interaction with the oar and the surface of the water in the supporting (water) part of the stroke. As a result of the study, experimental data were obtained, an algorithm was developed to analyze the strain-load curve and calculate the components of the resulting force applied to the oar during rowing. Based on a review of the literature corresponding to the research problem, as well as the data obtained during the pilot experiment, the prospects of using intelligent sensor systems as a means of quantitative description of the performance of sports movements in natural conditions are proved. The presented mathematical algorithm for calculating the values of the individual components of the resulting effort allows us to evaluate the ratio of the efforts made by the athlete and the resulting load on the paddle blades. The results allow us to conclude that the use of the method of mobile wireless tensometry for assessing the biomechanical parameters of sports movements is promising. Ways of further improvement of the developed methodology are determined.

Two algorithms for determination of the rotation matrix of the inertial unit relative to the motion capture 6DOF target are discussed. Solution of this problem is necessary for further co-operative data processing of these sensors in biomechanical researches. In particular, it is required to estimate the acceleration of a moving object in the field of gravity from the data of a 3D accelerometer and a motion capture system. In this case, the local vertical of the well calibrated motion capture system can be used to separate the gravity induced components from the accelerometer data. Both algorithms use measurements obtained for static positions, which differ in orientation of instrumental axes relative to gravitational vertical and at the same time allow us to estimate systematic errors of accelerometers. The first algorithm assumes orthogonality of instrumental axes of inertial unit and does not take into account errors in information on scale coefficients of accelerometers. The algorithm uses equations wich are linearized in the neighborhood of a priori estimates of the unknown values. The second algorithm does not use a priori information about axes of instrumental frame. In this case, the accelerometer unit is recalibrated, and in addition to the zeros and scale factors, the non-orthogonal angles of the instrumental axes of the unit are determined. The immediate result of its work is a matrix, which allows us to determine projections of apparent acceleration on body axes of the motion capture system. Algorithms are tested on experimental data. The comparison criteria is the repeatability of estimated results obtained from different measurement samples. Processing the results of the trial experiment showed that for inaccurate microelectromechanical systems, the second algorithm produced more stable results.

During developing medical equipment and processing results of experiments on the study of biomaterials, it is necessary to describe the process of interaction of the working tool with soft tissues. With this, it is important to take into account not only the mechanical properties of the tissue under study, but also the technical characteristics of the equipment, such as the shape of the tool surface and the speed of the interaction process. For this purpose, a contact model describing the indentation of an axisymmetric rigid cylinder with different foundation surface shape into viscoelastic half-space at a constant speed was constructed. The theory of linear viscoelasticity was used to describe the mechanical behavior of the half-space. A three-parameter model of a standard viscoelastic body was chosen as a viscoelastic model that defines the type of relaxation function of the half-space material. The distribution of contact pressure under the cylinder surface and the dependence of the applied load on the depth of indentation for various forms of the contact surface of the cylinder were obtained. The influence of the shape of the cylinder base surface, the indentation speed and the relaxation properties of the half-space on the characteristics of the contact interaction was studied. For describing the mechanical behavior of biological tissues, a one-dimensional model of a standard viscoelastic body was also considered. For this simplified model, the distribution of the contact pressure under the surface of cylinder with different shape of the base and the dependence of the applied load on time were also obtained. The results obtained using the continuous model and the one-dimensional model were compared. It was shown when it is more appropriate to use the simplified models to describe the interaction of an instrument with biological tissue.

Currently, cardiovascular diseases in many cases can cause premature death (up to 40 % of deaths). In the literature, there are observations about the effect of the temporomandibular joint dysfunction on the state of the cervical portion of the internal carotid artery. Under the influence of the load in the joint, bends and, possibly, looping are formed in the artery, which lead to a decrease in the volume of cerebral circulation and the development of a stroke. To date, there is no strict description of the maxillofacial influence in general and the temporomandibular joint in particular on the brain nutrition, which for the most part goes through the internal carotid artery (up to 80 % of the total blood volume). For the quantitative assessment of the loads influence on blood flow, the model example is considered, and it is shown the 34 % decrease in the carotid artery opening due to forces in the temporomandibular joint. To confirm the hypothesis and explain the action of the effect of loads, it is necessary to develop the biomechanical model of the internal carotid artery and the temporomandibular joint interaction. This study is complicated by the variability of the living structures characteristics from person to person. In the article, it is provided the detailed description of this problem, proposed the formulation of the loading coupled problem on the branch of the carotid artery by forces in the joint and blood flow in this part of the artery and the algorithm for solving this problem through averaging and simpifying the model. The iterative procedure for interaction in the elasticity theory problems and the averaged blood flow problem are presented.