Journal of Engineering and Thermal Sciences
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Calculation of vibrations of an incompressible elastic structure
Get PDFRubber and photo-elastic materials at elevated temperatures exhibit incompressible behavior. The vibrations of a structure by taking the incompressibility constraint into account by the penalty method are analyzed. Reduced order numerical integration of the penalty term is performed. Graphical representation of volumetric strains at the points of reduced integration is proposed for validation of the calculated eigenmodes
Development of mortar simulator with shell-in-shell system – problem of internal ballistics
Get PDFThe shell-in-shell system used in the mortar simulator raises a number of non-standard technical and computational problems starting from the requirement to distribute the propelling blast energy between the warhead and the ballistic barrel, finishing with the requirement that the length of warhead’s flight path must be scaled to combat shell firing tables. The design problem of the simulator is split into two parts – the problem of external ballistics where the initial velocities of the warhead must be determined, and the problem of internal ballistics – where the design of the cartridge and the ballistic barrel must be performed. Initial velocities of the warhead determined in the problem of external ballistics form the set of initial data for the problem of internal ballistics of mortar simulator with shell-in-shell system. The ballistic barrel (reusable component of the mimicking shell) must be ejected from the mortar tube and its flight path must be only few meters. Moreover, the propelling charge can be located only in the warhead and the blast energy must be distributed between the warhead and the ballistic barrel. That turns the problem of internal ballistics into a complex nonlinear dynamical problem. Its solution involves building of the numerical model, optimisation of system parameters and experimental investigations. Presented mortar simulator proved its effectiveness in combat training exercises and is fully adopted in Lithuanian Army training facilitie
Calculation of vibrations of a single degree of freedom system
Get PDFThe three node numerical integration scheme with the displacement and velocity as the nodal variables for integration of the second order differential equation using finite elements in time on the basis of the method of least squares is proposed. The precision of integration is investigated and compared with the corresponding procedure based on the method of Galerkin. The error measure is introduced which shows the higher precision of the least squares techniqu
Changes of the human gait after total hip joint replacement surgery
Get PDFThe aim of this work was to determine the effect of a hip joint replacement on human locomotion-support apparatus and movement functions. 3D biomechanical model of human locomotion-support system was developed for comparative analysis of the healthy state and the state after total hip replacement operation. The effect of shift of hip joint replacement centre position on human movement and muscles activity patterns was determined by using computational and experimental methods. The results of analysis obtained on the basis of this model and method are presented: it is shown that the change of position of hip joint replacement elements (cup and sphere) has substantial effect on human walking patter
Development of smart membrane valve based on geometric moiré interferometry
Get PDFNovel smart membrane valve which functionality is based on optical interference effects caused by moiré interferometry is proposed in this paper. The membrane is comprised from two steel gratings. Geometrical adjustment between adjacent holes in both membranes results in zero flow rate through the valve when no control signal is activated. Rotation of the control membrane generates moiré interference effects which are exploited for flow control. Relationships between the shape and geometric locations of the moiré circles and the control parameters of the second membrane are determined what helps to implement optimal valve control strategie
Modeling and design optimization of butterfly type piezoelectric actuator
Get PDFA study of a novel design miniature butterfly type piezoelectric actuator is proposed and analyzed in the paper. Actuator consists of butterfly type oscillator and two piezoceramic elements. Operating principle of the actuator is based on exciting electrodes of the piezoceramic elements using input voltage of the same frequency but different phases. Elliptic trajectory of the contact point movement is achieving when phases of the voltage differ by ?/2 on different electrodes. Numerical modelling and simulation of the piezoelectric actuator was performed using finite element method. Natural frequencies, modal shapes and actuator response to the different input voltage sets were analyzed. Optimization of actuator boundary conditions was carried out. Experimental prototype of the piezoelectric actuator was built and measurements of driven tip movements were performed. The results of numerical and experimental studies are discusse
Analysis of vibrations of paper in a printing device
Get PDFThe model for the analysis of vibrations of paper in a printing device is presented. It is assumed that paper performs transverse vibrations as a membrane having stiffness due to static tension in its plane. The first eigenmodes are determined. It is shown that the eigenfrequencies of transverse vibrations of the analyzed paper can be controlled by the static tension in the plane of the paper. The model for the analysis of stability of paper in a printing device is presented. It is assumed that paper moves with constant velocity in a given direction. The analysis is performed using a plate-bending element with the contribution of the forces of inertia from the convective accelerations. This results in the eigenproblem determining the critical velocities and stability eigenmodes. The stand was made for obtaining the experimental investigations. Using it the nodal lines of the standing waves were determined and using projection moiré the eigenmodes were determined. The obtained results are used in the process of design of the elements of the printing device
Concept and methods of adaptive vibration protection and stabilization
Get PDFThe concept, the general formulation of problems and the algorithms of adaptive real-time control of multivariate vibration protection and stabilization of multi-axis chassis body position in space, which in the general case provide in general case the solution of the problems of oscillations moderation and motion stability, are considere
Electrovibrostimulation during the training of sportsmen, an experimental set-up
Get PDFIn this study the effects of electrovibrostimulation training are compared with classical powertraining, in a group of 18-24 years old healthy sportsmen, during the spring season of 2007. Former studies showed the effectiveness of electrovibrostimulation on the functional condition of muscles: increase of the strength in the active insufficiency zone and increase of the elasticity in the passive insufficiency zone, consequently improving joint strength and mobility. After four weeks of electrovibrostimulation, applied twice a week, significant increases of isometric strength and explosive strength were observed, whereas the flexibility remained the same. Some hypotheses are discussed concerning the possible working mechanisms of electrovibrostimulatio
Surgical treatment of equinus foot deformity in cerebral palsy patients
Get PDFSince 1997 thirty seven spastic cerebral palsy children (54 feet) with shortening m. triceps surae (soleus and gastocnemius portions) underwent heel cord advancement by simplified technique of Murphy procedure. Good correction of the deformity and gait improvement was obtained in 52 cases (96%). No patient had a recurrence of equines. All patients and his parents are satisfied with results of treatment. It study has documented that heel cord advancement is biomechanicaly- and pathophysiologicaly- grounded procedure for adequate correction and following prevention of equinus deformity. Proposed technique of heel cord advancement is relatively simple minimal invasive and can use for treatment as single or(and) with combination in multilevel operations. Best results of surgical treatment obtained in young child who has non-formed rigid deformation and has no stable pathological gait patterns ye