In this paper the model of a elastic composite medium which consists of a matrix containing a set... more In this paper the model of a elastic composite medium which consists of a matrix containing a set of orthotropic crystals with the random orientation of the anisotropy axes is presented. The axes orientation is described by the Gauss distribution. The numerical investigation is proposed for rectangular plate, when the normal strains are given in the one side. Other sides are free of strain. The finite - difference technique is used for model discretization.
Urban change detection is an important part of sustainable urban planning, regional development, ... more Urban change detection is an important part of sustainable urban planning, regional development, and socio-economic analysis, especially in regions with limited access to economic and demographic statistical data. The goal of this research is to create a strategy that enables the extraction of indicators from large-scale orthoimages of different resolution with practically acceptable accuracy after a short training process. Remote sensing data can be used to detect changes in number of buildings, forest areas, and other landscape objects. In this paper, aerial images of a digital raster orthophoto map at scale 1:10,000 of the Republic of Lithuania (ORT10LT) of three periods (2009–2010, 2012–2013, 2015–2017) were analyzed. Because of the developing technologies, the quality of the images differs significantly and should be taken into account while preparing the dataset for training the semantic segmentation model DeepLabv3 with a ResNet50 backbone. In the data preparation step, norma...
An efficient finite element model of the ballistic impact and perforation of the woven fabrics st... more An efficient finite element model of the ballistic impact and perforation of the woven fabrics structures has been developed in LS-DYNA. The bullet has been considered as a deformable body in contact with the fabric package presented by interwoven yarn structure. The model of the weave has been created by presenting the multifilament yarns by thin shell elements the thickness of which represents the real thickness of yarns. The total model of the fabric has been developed by employing the multi-scale approach. The “woven” zone in the vicinity of the bullet impact has been joined with the uniform surrounding areas of textile presented by membrane elements. The junction between the two types of zones of the fabric has been performed by means of the tie constraint and by proper adjustment of material parameters ensuring the minimum cumulative wave propagation speed error along selected directions. The model has been verified by comparing the response of the structure with the reference...
The finite element model of transient pressure pulse propagation in a pipeline is presented in th... more The finite element model of transient pressure pulse propagation in a pipeline is presented in the form of the standard structural dynamic equation, which combines steady flow analysis for obtaining the initial conditions of the flow in the form of pressures and flow rates and non-linear dynamic analysis by using explicit numerical integration techniques. Three options of simplification of governing equation set have been analyzed. At low values of steady flow speed many non-linear and convection terms could be omitted, while at the flow speeds comparable with the wave propagation speed the full equation system has been analyzed. The full equation system analysis involves the techniques ensuring corrections of the initial conditions and of the nodal flow rate balance. The investigated pipelines may contain large number of branches and loops. Parts of large pipelines are analyzed as separate sub-models by employing non-reflecting boundary conditions at the cut boundaries. Properties ...
Abstract- The paper presents the finite element (FE) modelling of operation of a rotational motio... more Abstract- The paper presents the finite element (FE) modelling of operation of a rotational motion sensor that uses a balanced oscillator (tuning fork) to sense the angular rate. The 3D FE model has been employed to examining the sensor’s modal properties. The sensitivity functions have been obtained for adjusting the geometric parameters of the quartz element in order to achieve the desired values of natural frequencies. The performance of computations during the dynamic analysis has been enhanced by introducing a dynamically reduced model based on truncation of dynamic contributions of higher modes of the vibrating structure. Results are presented in terms of sensor performance characteristics for various design parameters and modes of operation. The modelling assumptions adopted are tested experimentally on the vibrating quartz resonator.
Summary. The aim of this study was to establish a mathematical model of the infiltration of sodiu... more Summary. The aim of this study was to establish a mathematical model of the infiltration of sodium chloride solution into cadaveric liver tissue. Methods. The time law of the flow of the infiltrated fluid at every node of the finite element model was obtained in terms of Darcy s velocity, ...
The matrices of a substructure ensuring minimum modal errors of the whole structure are obtained ... more The matrices of a substructure ensuring minimum modal errors of the whole structure are obtained by using optimization approach. The mass and stiffness matrices of a small component domain of selected dimension are obtained by applying the modal synthesis of a limited number of closeto-exact modes such that after assembling a larger joined domain model the modal convergence rate of the latter should be as high as possible. The goal is achieved by formulating the minimization problem for the penaltytype target function representing the cumulative relative modal error of the joined domain and by applying the gradient descent minimization method. After the optimum matrices of a component domain are obtained, they can be used in any structure as higher-order elements or super-elements. The “combined” mass matrices can be treated as a special case of the presented approach. The performance of the obtained dynamic models is demonstrated by solving short wave pulse propagation problems by ...
Conventional finite element method (FEM) is capable of obtaining wave solutions, but large discret... more Conventional finite element method (FEM) is capable of obtaining wave solutions, but large discretized structures at high frequency require high computational resources, the computational domain can be reduced by combining FEM with analytical assumption for guided wave. Semi Analytical Finite Element (SAFE) formulation for immersed waveguide in perfect fluid is used for acquiring propagating wave modes as dynamic equilibrium states. Modes are solutions to eigenvalue problem and provide with important characteristic features of the guided waves – phase velocity, attenuation, wave structure, etc. The effect of surrounding leaky medium is modeled via traction boundary condition, which is based on assumption of the continuity of stresses at solid-fluid interface. The boundary condition causes wave attenuation due to energy leakage into outer medium. The derivation of the eigen-problem takes into account complex wavenumbers of leaky wave in fluid and guided wave in a three-dimensional wavegui...
A time law of small vibrations of the center of pressure (COP) of humans in standing position (hu... more A time law of small vibrations of the center of pressure (COP) of humans in standing position (human posture) provides a useful information about the physical and health condition of an individual. In this work controlled inverted pendulum (CIP) model with a single degree of freedom (DOF) is used in order to simulate the vibration of COP of a human body in anterio‐posteriori (forward‐backward) direction during still standing. A method for identification of the CIP model parameters is based on numerical computation of the sensitivities of the penalty‐type error function to small variations of model parameters. The approach is applicable to structural models with any number of DOF and any structural complexity. Numerical example demonstrates the model parameter identification results providing nearly the best match of the model behaviour to the real experimental record of COP position.
Purpose The purpose of this paper is to investigate the influence of geometrical microstructure o... more Purpose The purpose of this paper is to investigate the influence of geometrical microstructure of items obtained by applying a three-dimensional (3D) printing technology on their mechanical strength. Design/methodology/approach Three-dimensional printed items (3DPI) are composite structures of complex internal constitution. The buildup of the finite element (FE) computational models of 3DPI is based on a multi-scale approach. At the micro-scale, the FE models of representative volume elements corresponding to different additive layer heights and different thicknesses of extruded fibers are investigated to obtain the equivalent non-linear nominal stress–strain curves. The obtained results are used for the creation of macro-scale FE models, which enable to simulate the overall structural response of 3D printed samples subjected to tensile and bending loads. Findings The validation of the models was performed by comparing the computed results against the experimental ones, where satis...
The heat resistance of fabric enhanced by bio-ceramic additives (BCAs) is investigated theoretica... more The heat resistance of fabric enhanced by bio-ceramic additives (BCAs) is investigated theoretically and experimentally in order to determine the influence of modification of the infrared (IR) absorption property of the fabric. The enhanced IR sensitivity of textiles improves the thermoregulatory processes when worn in cold environments. The finite element model has been developed by taking into account the coupled phenomena of heat conduction, surface convection and the interaction of the fabric with IR power flux by employing heat transfer differential equations and the Stefan–Boltzmann law. Evaluations of IR absorptivity, reflectivity and transmissivity, the temperature transients during the hot plate chamber test and heat retaining properties of the fabric heated by an IR lamp have been obtained experimentally and simulated by means of the developed finite element model. The values of model parameters have been found, which provided a satisfactory match between the computation a...
In this paper the model of a elastic composite medium which consists of a matrix containing a set... more In this paper the model of a elastic composite medium which consists of a matrix containing a set of orthotropic crystals with the random orientation of the anisotropy axes is presented. The axes orientation is described by the Gauss distribution. The numerical investigation is proposed for rectangular plate, when the normal strains are given in the one side. Other sides are free of strain. The finite - difference technique is used for model discretization.
Urban change detection is an important part of sustainable urban planning, regional development, ... more Urban change detection is an important part of sustainable urban planning, regional development, and socio-economic analysis, especially in regions with limited access to economic and demographic statistical data. The goal of this research is to create a strategy that enables the extraction of indicators from large-scale orthoimages of different resolution with practically acceptable accuracy after a short training process. Remote sensing data can be used to detect changes in number of buildings, forest areas, and other landscape objects. In this paper, aerial images of a digital raster orthophoto map at scale 1:10,000 of the Republic of Lithuania (ORT10LT) of three periods (2009–2010, 2012–2013, 2015–2017) were analyzed. Because of the developing technologies, the quality of the images differs significantly and should be taken into account while preparing the dataset for training the semantic segmentation model DeepLabv3 with a ResNet50 backbone. In the data preparation step, norma...
An efficient finite element model of the ballistic impact and perforation of the woven fabrics st... more An efficient finite element model of the ballistic impact and perforation of the woven fabrics structures has been developed in LS-DYNA. The bullet has been considered as a deformable body in contact with the fabric package presented by interwoven yarn structure. The model of the weave has been created by presenting the multifilament yarns by thin shell elements the thickness of which represents the real thickness of yarns. The total model of the fabric has been developed by employing the multi-scale approach. The “woven” zone in the vicinity of the bullet impact has been joined with the uniform surrounding areas of textile presented by membrane elements. The junction between the two types of zones of the fabric has been performed by means of the tie constraint and by proper adjustment of material parameters ensuring the minimum cumulative wave propagation speed error along selected directions. The model has been verified by comparing the response of the structure with the reference...
The finite element model of transient pressure pulse propagation in a pipeline is presented in th... more The finite element model of transient pressure pulse propagation in a pipeline is presented in the form of the standard structural dynamic equation, which combines steady flow analysis for obtaining the initial conditions of the flow in the form of pressures and flow rates and non-linear dynamic analysis by using explicit numerical integration techniques. Three options of simplification of governing equation set have been analyzed. At low values of steady flow speed many non-linear and convection terms could be omitted, while at the flow speeds comparable with the wave propagation speed the full equation system has been analyzed. The full equation system analysis involves the techniques ensuring corrections of the initial conditions and of the nodal flow rate balance. The investigated pipelines may contain large number of branches and loops. Parts of large pipelines are analyzed as separate sub-models by employing non-reflecting boundary conditions at the cut boundaries. Properties ...
Abstract- The paper presents the finite element (FE) modelling of operation of a rotational motio... more Abstract- The paper presents the finite element (FE) modelling of operation of a rotational motion sensor that uses a balanced oscillator (tuning fork) to sense the angular rate. The 3D FE model has been employed to examining the sensor’s modal properties. The sensitivity functions have been obtained for adjusting the geometric parameters of the quartz element in order to achieve the desired values of natural frequencies. The performance of computations during the dynamic analysis has been enhanced by introducing a dynamically reduced model based on truncation of dynamic contributions of higher modes of the vibrating structure. Results are presented in terms of sensor performance characteristics for various design parameters and modes of operation. The modelling assumptions adopted are tested experimentally on the vibrating quartz resonator.
Summary. The aim of this study was to establish a mathematical model of the infiltration of sodiu... more Summary. The aim of this study was to establish a mathematical model of the infiltration of sodium chloride solution into cadaveric liver tissue. Methods. The time law of the flow of the infiltrated fluid at every node of the finite element model was obtained in terms of Darcy s velocity, ...
The matrices of a substructure ensuring minimum modal errors of the whole structure are obtained ... more The matrices of a substructure ensuring minimum modal errors of the whole structure are obtained by using optimization approach. The mass and stiffness matrices of a small component domain of selected dimension are obtained by applying the modal synthesis of a limited number of closeto-exact modes such that after assembling a larger joined domain model the modal convergence rate of the latter should be as high as possible. The goal is achieved by formulating the minimization problem for the penaltytype target function representing the cumulative relative modal error of the joined domain and by applying the gradient descent minimization method. After the optimum matrices of a component domain are obtained, they can be used in any structure as higher-order elements or super-elements. The “combined” mass matrices can be treated as a special case of the presented approach. The performance of the obtained dynamic models is demonstrated by solving short wave pulse propagation problems by ...
Conventional finite element method (FEM) is capable of obtaining wave solutions, but large discret... more Conventional finite element method (FEM) is capable of obtaining wave solutions, but large discretized structures at high frequency require high computational resources, the computational domain can be reduced by combining FEM with analytical assumption for guided wave. Semi Analytical Finite Element (SAFE) formulation for immersed waveguide in perfect fluid is used for acquiring propagating wave modes as dynamic equilibrium states. Modes are solutions to eigenvalue problem and provide with important characteristic features of the guided waves – phase velocity, attenuation, wave structure, etc. The effect of surrounding leaky medium is modeled via traction boundary condition, which is based on assumption of the continuity of stresses at solid-fluid interface. The boundary condition causes wave attenuation due to energy leakage into outer medium. The derivation of the eigen-problem takes into account complex wavenumbers of leaky wave in fluid and guided wave in a three-dimensional wavegui...
A time law of small vibrations of the center of pressure (COP) of humans in standing position (hu... more A time law of small vibrations of the center of pressure (COP) of humans in standing position (human posture) provides a useful information about the physical and health condition of an individual. In this work controlled inverted pendulum (CIP) model with a single degree of freedom (DOF) is used in order to simulate the vibration of COP of a human body in anterio‐posteriori (forward‐backward) direction during still standing. A method for identification of the CIP model parameters is based on numerical computation of the sensitivities of the penalty‐type error function to small variations of model parameters. The approach is applicable to structural models with any number of DOF and any structural complexity. Numerical example demonstrates the model parameter identification results providing nearly the best match of the model behaviour to the real experimental record of COP position.
Purpose The purpose of this paper is to investigate the influence of geometrical microstructure o... more Purpose The purpose of this paper is to investigate the influence of geometrical microstructure of items obtained by applying a three-dimensional (3D) printing technology on their mechanical strength. Design/methodology/approach Three-dimensional printed items (3DPI) are composite structures of complex internal constitution. The buildup of the finite element (FE) computational models of 3DPI is based on a multi-scale approach. At the micro-scale, the FE models of representative volume elements corresponding to different additive layer heights and different thicknesses of extruded fibers are investigated to obtain the equivalent non-linear nominal stress–strain curves. The obtained results are used for the creation of macro-scale FE models, which enable to simulate the overall structural response of 3D printed samples subjected to tensile and bending loads. Findings The validation of the models was performed by comparing the computed results against the experimental ones, where satis...
The heat resistance of fabric enhanced by bio-ceramic additives (BCAs) is investigated theoretica... more The heat resistance of fabric enhanced by bio-ceramic additives (BCAs) is investigated theoretically and experimentally in order to determine the influence of modification of the infrared (IR) absorption property of the fabric. The enhanced IR sensitivity of textiles improves the thermoregulatory processes when worn in cold environments. The finite element model has been developed by taking into account the coupled phenomena of heat conduction, surface convection and the interaction of the fabric with IR power flux by employing heat transfer differential equations and the Stefan–Boltzmann law. Evaluations of IR absorptivity, reflectivity and transmissivity, the temperature transients during the hot plate chamber test and heat retaining properties of the fabric heated by an IR lamp have been obtained experimentally and simulated by means of the developed finite element model. The values of model parameters have been found, which provided a satisfactory match between the computation a...
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