Опір матеріалів і теорія споруд

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A method of determining the coordinates of the stiffness center and the stiffness principal axis of the vibrating system with damping
(КНУБА, 2014) Dang Xuan Truong; Tran Duc Chinh
The report presents a methodology to determine the directions of the stiffness principal axis (in this case subject to the linear displacement and forced rotation angle) of a solid object interact with the surrounding environment by resilient bearing supports. The results also show that determining the coordinates of the stiffness center in the vibrating system with damping factors is necessary in our research.
A methodology of determining of parameter j* in discrete models of finite element method
(КНУБА, 2017) Bazhenov, V. A.; Pyskunov, S. О.; Shkryl, О. О.
Based on the method of reactions, a technique for determining of the parameter J * by the method of subdomain moving in discrete models of finite element method (FEM) has been developed. A number of test problems solved. The obtained results confirm the effectiveness of the technique.
A new approach to the design of suspension roof systems
(КНУБА, 2020) Priadko, I. N.; Rudnieva I. N.; Ribakov, Y.; Bartolo H.
Over the last century, the suspension roofs design has progressed until the advent of the shells theory in the first half of the 20th century, due to a rapid pace in technological advancement. A paradigm shift emerged with the new trend in structural design towards a new design process that cooperatively integrated economy, efficiency, and elegance. Different approaches in computation, design and reliability assessment of roof structures are discussed in this work to identify the key conditions that have significantly contributed to modern suspension roof design principles. A new algorithm to assess the reliability of suspension roofs at the design stage is proposed and a novel method for computational design and reliability evaluation of suspension roofs is presented in this paper. This method enables to solve some topical issues, such as assignment of initial geometric roof parameters and relevant problems, like numerical determination of reliability indices for statistically non-determined systems of suspension roofs with a big cut on elliptical plan.
An analysis of raft thickness in high-rise buildings - case studies
(КНУБА, 2019) Nguyen Anh Tuan; Cao Van Hoa
This study shows that the raft thickness is depended on foundation system, Young modulus of soil right under the raft and number of floors of superstructure, and explains very well the case of thick raft of ICC Tower, thin raft of Dubai Tower and reasonable raft thickness of Incheon Tower.
An estimation of residual lifetime of spatial structural elements under continual fracture condition
(КНУБА, 2014) Bazhenov, V. A.; Gulyar, O. I.; Pyskunov, S. O.
The techniques of modeling of continual fracture process for space circular and prismatic bodies under prolonged load condition and some results of determining of the estimated lifetime (up to local loss of material bearing capacity) and the residual (additional) lifetime (time of continual fracture zone growth) is presented in this paper. The Kachanov-Rabotnov’s scalar damage parameter to describe the continual fracture of the material and the semianalytic finite element method (SFEM) as numerical method of boudary problem solution is used. It‘s shown, that the value of residual lifetime could be differ significantly for different loading condition and object configuration.
An improved gradient-based method to solve parametric optimisation problems of the bar structures
(КНУБА, 2020) Peleshko I. D.; Yurchenko V. V.
The paper considers parametric optimisation problems for the bar structures formulated as nonlinear programming tasks. The method of the objective function gradient projection onto the active constraints surface with simultaneous correction of the constraints violations has been used to solve the parametric optimisation problem. Equivalent Householder transformations of the resolving equations of the method have been proposed. They increase numerical efficiency of the algorithm developed based on the method under consideration. Additionally, proposed improvement for the gradient-based method also consists of equivalent Givens transformations of the resolving equations. They ensure acceleration of the iterative searching process in the specified cases described by the paper due to decreasing the amount of calculations. The comparison of the optimisation results of truss structures presented by the paper confirms the validity of the optimum solutions obtained using proposed improvement of the gradient-based method. The efficiency of the propoced improvement of the gradient-based method has been also confirmed taking into account the number of iterations and absolute value of the maximum violation in the constraints.
Analysis of the effect of the Ho Chi Minh City Tunnel settlement on the adjacent buildings
(КНУБА, 2017) Nguyen Anh Tuan; Tran Duc Chinh; Nguyen Thanh Dat
The paper aims to studying the effect of settlement of the Ho Chi Minh City Tunnel in soft soil condition on the nearby buildings due to tunneling by the Finite Element Method using Plaxis 3D Tunnel.
Analysis of ultimate limit load of spherical shells applying von mises yield criterion
(КНУБА, 2015) Ulitinas, Tomas; Kalanta, Stanislovas; Blaževičius, Gediminas; Atkočiūnas, Juozas
In this paper, the problems of ultimate limit load of spherical shell are formulated and solved. An equilibrium finite element developed by the method of Bubnov-Galerkin is suggested. Equilibrium and geometrical equations are created for this element and, based on these equations, the mathematical models of ultimate limit external load optimization problems for the shell structures are constructed. These are nonlinear mathematical programming problems. The methodology is illustrated by the numerical examples. The solution results are obtained for the finite elements of various sizes and show very high accuracy of the suggested element and convergence of the results.
Application of parameter continuation method for investigation of vibroimpact systems dynamic behaviour. problem state. short survey of world scientific literature
(КНУБА, 2014) Bazhenov, V. A.; Pogorelova, O. S.; Postnikova, T. G.
Authors in their works study vibroimpact system dynamic behaviour by numerical parametric continuation technique combined with shooting and Newton-Raphson’s methods. The technique is adapted to two-mass two-degree-of-freedom vibroimpact system under periodic excitation. Impact is simulated by nonlinear contact interaction force based on Hertz’s contact theory. Stability or instability of obtained periodic solutions is determined by monodromy matrix eigenvalues (multipliers) based on Floquet’s theory. In the present paper we describe the state of problem of parameter continuation method using for nonlinear tasks solution. Also we give the short survey of numerous contemporary literature in English and Russian about parameter continuation method application for nonlinear problems. This method is applied for vibroimpact problem solving more rarely because of the difficulties connected with repeated impacts.
Application of stiffness rings for improvement of operating reliability of the tank with shape imperfections
(КНУБА, 2020) Lukianchenko, O. O.
An efficiency of using of two stiffness rings for improvement of operating reliability of the tank with real shape imperfection at the action of combination load was evaluated. The computer model of the tank was constructed in the form of the thin cylindrical shell by of the program complex of finite element analysis. The tank stability problem under separate and joint action of surface pressure and axial compression was solved by the Lancosh method in linear formulation and as a nonlinear static problem by the Newton-Raphson method. The region of the tank failure-free work, which has the graphical presentation, confirmed the improvement of the tank wall stability due to the use of stiffness rings, especially in the area of surface pressure action.
Applied problems of dynamics of pipelines, conveying liquid
(КНУБА, 2015) Limarchenko, O. S.; Limarchenko, V. O.; Majid, M.; Timokhin, A. P.
Nonlinear applied problems dynamics of pipelines with flowing liquid were considered on the basis of complex approach, which includes variational statement of the problem with automatic derivation of dynamical boundary conditions, mixed Euler-Lagrange description of fluid-structure interaction, method of modal decomposition, qualitative and numerical research of system behavior.We investigate system behavior of pipeline on moving foundation, for liquid flow with velocities, which are in a vicinity of critical velocities of liquid flow or exceed them, Different variants of foundation motion includes vibrations, rotation. Investigation showed the presence of alternative equilibrium state, near which pipeline oscillations occur for certain ranges of velocities of liquid flow.
Basic relationships for physically and geometrically nonlinear problems of deformation of primatic bodies
(КНУБА, 2020) Maksimyuk, Yu. V.; Pyskunov, S. O.; Shkril, A. A.; Maksimyuk, O. V.
The initial relations of thermo elastic-plastic deformation of prismatic bodies are given in the paper. The basic concepts, indifference of deformation tensors, with the condition of energy conjunction in description of the shaping process are laid out on the basis of classical works.
Boundary element approaches to the problem of 2-d non-stationary elastic vibrations
(КНУБА, 2020) Vorona, Yu. V.; Kozak, A. A.
Two boundary element approaches are used to solve the problem on non-stationary vibrations of elastic solids. The first approach is based on the transition to the frequency domain by means of a Fourier series expansion. The second approach is associated with the direct solution of a system of time-dependent boundary integral equations, with a piecewise constant approximation of the dependence of the unknowns on time. In both cases, a collocation scheme is used to algebraize the integral equations, and the difficulties associated with the calculation of singular integrals are overcome by replacing the kernels with the initial segment of the Maclaurin series. After such a replacement, the kernels take the form of a sum, the first term of which is the corresponding fundamental solution of the statics problem while other terms are regular. Since integration of static kernels is not difficult the problem of calculating the diagonal coefficients of the SLAE turns out to be solved. The developed techniques are compared in the process of dynamics analysis solving of elastic media with two cylindrical cavities. The boundary of one of the cavities is subjected to a radial impulse load, which varies according to the parabolic law. Both approaches have shown the similar effectiveness and qualitative consistency.
Buckling and vibrations of the shell with the hole under the action of thermomechanical loads
(КНУБА, 2020) Bazhenov, V. A.; Krivenko, O. P.
The paper outlines the fundamentals of the method of solving static problems of geometrically nonlinear deformation, buckling, and vibrations of thin thermoelastic inhomogeneous shells with complex-shaped midsurface, geometrical features throughout the thickness, under complex thermomechanical loading. The technique is based on the geometrically nonlinear equations of three-dimensional thermoelasticity, the finite element formulation of the problem in increments, and the use of the moment finite-element scheme. A thin shell is considered by this method as a threedimensional body. We approximate a shell by one spatial universal finite element (FE) throughout the thickness. The universal FE is based on an isoparametric spatial FE with polylinear shape functions for coordinates and displacements. The universal element has additional variable parameters introduced to expand its capabilities. The method of modal analysis of the shell is based on an approach that at each current stage of thermomechanical loading takes into account the stresses accumulated at the previous stages. The developed algorithm allows one to study geometric nonlinear deformation and buckling of elastic shells of an inhomogeneous structure with a thin and medium thickness, as well as to study small vibrations of the shells relative to the reference deformed state caused by static loading, taking into account large displacements and a prestressed state. An analysis of the stability and vibration of the spherical panel with the hole is carried out. The effect on the frequencies and mode shapes of the shell of the sequential action of thermal and mechanical loads is investigated.
Buckling of the steel frames with the I-shaped cross-section columns of variable web height
(КНУБА, 2018) Bilyk, S. I.; Bilyk, А.S.; Nilova, T.O.; Shpynda, V. Z.; Tsyupyn, E. I.
Presented is the research of the stability of portal frames made of variable I cross-sections, depending on supports fastening factors and frames elements unfastening. In the process of mathematical research examined were five different cases of fixing columns nodes of portal frames resiliently mounted in each case, the stability criteria having been defined. In addition, conducted were studies to determine the coefficients of the portal frames elements effective length calculation in finding critical load on the column. Coefficients of the effective length factor of the welded variable I cross-section columns have been obtained. The influence of brace systems on stiffening of the whole structure, stability of the unit frames as well as the overall stability of the building with computer simulation and calculation have been studied, the coefficients of the influence of the frame structure on the stability of the unit frames having been obtained.
Calculation of random wave parameters using regression method
(КНУБА, 2015) Dang Xuan Truong
This research introduces a new method to calculate the parameters of random waves. Here we calculate the wave height and period. The process observation data from multiple waves of different conditions is a complex problem for the designers of offshore structures. The regression method is proposed as a new method with high reliability to solve this problem.
Control of the strength properties of welded connections in the manufacture of building steel structures
(КНУБА, 2019) Datsenko, I. P.; Kotsiuruba, V. I.; Mirnenko, V. I.; Tkach, I. M.; Tryhubenko, S. S.; Shyshanov, M. O.
As is well known in construction, mechanized welding with self-shielded cored wire has found wide application. In this case, welding methods that are used do not always allow to realize the potential that is laid in this group of welding materials. In addition, modern welding methods are characterized by a large heat input in parts and welded joints. In this regard, in the article ways to improve the technological capabilities of mechanized welding with flux-cored wire by introducing modulated current into the production of building steel structures are discussed.
Creation of mathematical model of platformvibrator with shock, designed for concrete products compaction and molding
(КНУБА, 2020) Bazhenov, V. A.; Pogorelova, O. S.; Postnikova, T. G.
Platform-vibrators are the main molding equipment in the production of precast concrete elements. Shock-vibration technology for the precast concrete production on low-frequency resonant platform-vibrators significantly improves the quality of the products front surfaces and the degree of their factory readiness. This technology is used to produce large elements. We describe the creation of a mathematical model for platform-vibrator that uses shock to produce asymmetric oscillations. The values of the upper and lower accelerations of the mold with concrete have different values with shock-vibration technology. The created mathematical model corresponds to the two-body 2-DOF vibro-impact system. It is strongly nonlinear non-smooth discontinuous system. It has some peculiar properties, namely: the upper body with very large mass breaks away from the lower body during vibrational motion; both bodies move separately; the upper body falls down onto the soft constraint; the impact that occurs is soft one due to the softness and flexibility of the constraint. The soft impact simulation requires special discussion. In this paper, we simulate a soft impact by a nonlinear contact force in accordance with the Hertz quasistatic contact law. The numerical parameters for this system were chosen in such a way that: firstly they provide the fulfillment of requirements for real machine, and secondly they allow analyzing its dynamic behavior by nonlinear dynamics tools. The created model is well enough to fulfill a number of requirements, namely: T-periodic steady-state movement after passing the transient process; the appropriate value of mold oscillations amplitude; the satisfactory value of the asymmetry coefficient that is the ratio of lower acceleration to the upper acceleration. We believe that the created model meets all the necessary requirements.
Definition of the failure region of the oil tank with wall imperfections in combined loading
(КНУБА, 2018) Bazhenov, V. А.; Lukianchenko, O. O.; Kostina, О. V.
The stability of an oil reservoir with real imperfections of a wall under the joint action of axial compression and surface pressure is studied using a program complex of finite element analysis. To determine the permissible range of fail-safe operation of the reservoir, irregular imperfections of the middle wall surface are simulated as ratios of the buckling forms with different maximum amplitudes obtained in solving the problem of loss of stability by the Lanczos method. The stability of the shell with real and simulated imperfections of the wall is investigated using the nonlinear static problem by the Newton-Raphson method. Critical ratios of axial compression and surface pressure are determined to ensure overall stability of the reservoir wall. The region of failure on the stability of the oil reservoir with real imperfections is obtained.
Design solutions of optimal systems under action of dead and live mobile load
(КНУБА, 2018) Kitov, Yu. P.; Verevicheva, M. A.; Vatulia, G. L.; Deryzemlia, S. V.
The authors have considered the design of a three-span beam bridge of a given length under live load. The purpose of this study is obtaining an equally strong system, in which the maximum stresses in all elements are equal to the estimated ones. A few statically determinate and statically indeterminate systems have been considered to determine the optimal one. It has been proved that optimal solutions exist both in the set of statically determinate and indeterminate systems.