Gergana Nikolova

Interface Behavior of a Bimaterial Plate under Dynamic Loading

The paper deals with interface behavior of bimaterial ceramic-metal composites under dynamic time-harmonic load. The first plate is precracked with a normal crack touching the interface between the plates. It is assumed that the respective restriction for the ratio of energy release rates of the plates allowing the occurrence of an interface single delamination before the initiation of the normal crack in the second plate is satisfied. The growth of interface delamination is not considered. The used approximate shear-lag dynamic approach gives a possibility to obtain solutions in a closed form for axial and shear stresses of the structure. At an elastic-brittle interface behavior theoretical predictions for single debond length of two bimaterial structures are calculated. The parametric analysis reveals the sensitivity of the interface single debond length and shear stress to the type of bimaterial structure and to the characteristics of the dynamic load—in particular its frequency and amplitude. All results are illustrated in figures and tables and are discussed.

Anthropometric Measurements and Model Evaluation of Mass-Inertial Parameters of the Human Upper and Lower Extremities

Based on our own anthropometric measurements of 50 Bulgarian men and 52 women that complement the representative anthropological investigation [1] of the Bulgarian population aged 30-40 years, we present a method for determining the mass-inertial characteristics of upper and lower arm, thigh and shank of the human body using 3D geometrical modelling. The segments are modeled via threedimensional versions of right elliptical stadium solids. The comparison performed between our model results and data reported in literature demonstrates that this modelling is successful being closer to the real shape of the segments envisaged.

Intelligent control design in robotics and rehabilitation

For control purposes in robotics or rehabilitation, we may use properly simplified dynamic models with a reduced number of degrees of freedom. First, we define a set of variables that best characterize its dynamic performance in the required motion task. Second, driving forces/torques are properly assigned in order to achieve the required dynamic performance in an efficient way. The usual performance requirements are for positioning accuracy, movement execution time, and energy expenditure. We consider complex biomechatronic systems (BMS) like human with active orthosis or robotic arm that have to perform two main types of motion tasks: goal-directed movements and motion/posture stabilization. We propose new design concepts and criteria for BMS based on necessary and sufficient conditions for their robust controllability. Using simplified, yet realistic, models, we give several important examples in robotics and rehabilitation to illustrate the main features and advantages of our approach.

Computer and Mathematical Modelling of the Female Human Body: Determination of Mass-inertial Characteristics in Basic Body Positions.

The aim of the current article is: 1) to present 16-segmental biomechanical model of the female human body generated within a SolidWorks medium. 2) to determine the mass-inertial characteristics of the human body of the average Bulgarian female on the basis of the model. These parameters are needed in order to design wearable or rehabilitation robots and devices properly; 3) to verify the model via comparing its results for the segments of the body with analytical results from our previous investigation of these segments; 4) to predict the inertial properties of a human body in various body positions. The comparison performed between our model results and data reported in literature gives us confidence that this model could be reliably used to calculate these characteristics at random postures of the body.

Determination of Mass-Inertial Characteristics of the Human Body in Basic Body Positions: Computer and Mathematical Modelling

The aim of the current article is: 1) to determine the mass-inertial characteristics of the human body of the Bulgarian male on the basis of 16-segmental biomechanical model generated within a SolidWorks medium. They are needed in order to design wearable or rehabilitation robots and devices properly; 2) to verify the model via analytical results from our previous investigation; 3) to predict the inertial properties of a human body in various body positions. The comparison performed between our model results and data reported in literature gives us confidence that this model could be used to calculate these characteristics at random postures of the body.

An Evolution Equation of Blood Flow in a Dilated Artery

In this study we derive an evolution equation for propagation of nonlinear waves in a blood-filled artery with a local dilatation (an idealized aneurysm) in a long–wave approximation. The equation is a version of the perturbed Korteweg-deVries-Burgers equation with variable coefficients. Exact travelling-wave solution of this equation is obtained by the modified method of simplest equation where the differential equation of Riccati is used as simplest equation. A numerical example of the obtained exact solution is presented and discussed from the point of view of arterial disease mechanics.

Modelling of the Bending Behaviour of a Double-Reinforced Beam from Recycled Materials for Application in NZEBs

A number of design approaches of nearly zero energy buildings (NZEBs) are known in literature. The aim of the present paper is to study the bending behavior of a structural bi-material element of a recycled concrete beam reinforced along its lower and upper side by highly-tough thin layers. On one hand, the design of such a structural element would produce a light weight element, since no conventional reinforcement would be involved, and on the other hand, the recycled aggregate of the concrete matrix would make the element applicable to NZEBs. Thus, natural energy resources may be saved. Moreover, thin reinforcing layers guarantee good bearing capacity due to their high toughness, excellent crack resistance under dynamic impacts, as well as fire resistance when fabricated from special polymer materials. The approach of employing such lightweight structural bi-material elements in constructions is energy saving and innovative. The study provides a method of specifying the thickness of the reinforcing layer assuming the existence of a transition area between the two materials and smooth transition between the reinforcing layer and the concrete bulk. It is also assumed that the element operates within the materials linear-elastic zone, without generation of macrocracks within concrete and debonding along the interface. The analytical results found are verified by subsequent experimental evidence available in literature.

CONTROL STRATEGY AND STRUCTURE IDENTIFICATION FOR EFFICIENT MOTION REHABILITATION

We propose control strategy for humans that have to perform goal-directed motion tasks and/or posture stabilization tasks. First, we define a set of variables that best characterize the dynamic performance of the controlled system in the required motion task. Second, driving forces/torques are properly assigned in order to achieve the required dynamic performance in an efficient way. The usual performance requirements are for positioning accuracy, movement response, and energy expenditure. For control purposes, we may use properly simplified dynamic models with a reduced number of degrees of freedom. It means that, with given motion task, we have to work with models that sufficiently well represent the kinematics, dynamics, and control functions. We can generate such models employing a general 3D computer model of the human body with 16 segments. Using simplified, yet realistic, models, we give two important examples to explain the basic features of our approach: upward posture stabilization and active ankle-foot orthosis.