Journal of the Serbian Society for Computational Mechanics最新文献

{"title":"GEOMETRIC OPTIMIZATION OF TRANSITION ZONES BASED ON BIOMIMETICS PRINCIPLES","authors":"I. Atanasovska, D. Momčilović","doi":"10.24874/jsscm.2021.15.02.04","DOIUrl":"https://doi.org/10.24874/jsscm.2021.15.02.04","url":null,"abstract":"The basic definitions and a history of the development of biomimetics as a discipline that considers nature-inspired design are presented in this paper. The discussion and the results of the application of principles of nature-inspired design in machine elements design are given. The fact that transition zones that Nature chose and designed on trees in many cases survived for more than a hundred years, resisting on the various and variable external loads and other external conditions, is considered. Presented case study used the nature-inspired transition shapes in the research of innovative design and geometric optimization of transition zones of high-loaded shafts. The comparative Finite Element Analysis is performed for a particular transition zone with traditional engineering design, as well as with nature-inspired design. The conclusions about the increase of load capacity that is obtained with innovative biomimetics design are discussed.","PeriodicalId":42945,"journal":{"name":"Journal of the Serbian Society for Computational Mechanics","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2021-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45663045","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"FSI ANALYSIS WITH CONTINUOUS FLUID FLOW USING FEM AND SPH METHODS IN LS-DYNA","authors":"M. Topalovic, A. Nikolic, S. Vulovic, Vladimir Milovanović","doi":"10.24874/jsscm.2021.15.02.09","DOIUrl":"https://doi.org/10.24874/jsscm.2021.15.02.09","url":null,"abstract":"The purpose of this research was to investigate the prospect of continuous flow modelling in LS-DYNA using SPH-FEM coupling. The both methods (SPH and FEM) are based on the continuum mechanics, however, SPH implementation uses Lagrangian material framework, while FEM uses an Eulerian formulation for the fluid analysis, and Lagrangian formulation for the solid analysis. The Lagrangian framework of the SPH means that we need to generate particles at one end, and to destroy them on the other, in order to generate a continuous fluid flow. The simplest way to do this is by using activation and deactivation planes, which is a solution implemented in the commercial LS- DYNA solver. Modelling of continuous fluid flow is practical in mechanical (naval) engineering for hydrofoil analysis and in bioengineering for blood vessel simulations. Results show that velocity fields obtained by SPH-FEM coupling are similar to velocity fields obtained by FEM. FEM only solution has a clear advantage in regards to execution time, however, SPH-FEM coupling offers greater insight into fluid structure interaction, that justifies the extra computational cost.","PeriodicalId":42945,"journal":{"name":"Journal of the Serbian Society for Computational Mechanics","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2021-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41858552","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"EXACT AUGMENTED PERPETUAL MANIFOLDS: A COROLLARY FOR THEIR UNIQUENESS","authors":"F. Georgiades","doi":"10.24874/jsscm.2021.15.02.01","DOIUrl":"https://doi.org/10.24874/jsscm.2021.15.02.01","url":null,"abstract":"The perpetual points have been defined recently as characteristic points in a dynamical system. In many unexcited linear and nonlinear mechanical systems, the perpetual points are associated with rigid body motions and form the perpetual manifolds. The mechanical systems that admit rigid body motions as solutions are called perpetual. In the externally forced mechanical system, the definition of perpetual points to the exact augmented perpetual manifolds extended. The exact augmented perpetual manifolds are associated with the rigid body motion of mechanical systems but with externally excited. The definition of the exact augmented perpetual manifolds leads to a theorem that defines the conditions of an externally forced mechanical system to be moving as a rigid body. Therefore, it defines the conditions of excitation of only this specific type of similar modes, the rigid body modes. Herein, as a continuation of the theorem, a corollary is written and proved. It mainly states that the exact augmented perpetual manifolds for each mechanical system are not unique and are infinite. In an example of a mechanical system, the theory is applied by considering different excitation forces in two-time intervals. The numerical simulations with the analytical solutions are in excellent agreement, which is certifying the corollary. Further, due to the different solutions in the two-time intervals, there is a discontinuity in the vector field and the system's overall solution. Therefore, the state space formed by the exact augmented perpetual manifold is nonsmooth. This work is the first step in examining the exact augmented perpetual manifolds of mechanical systems. Further work is needed to understand them, which mathematical space they belong to, considering that nonsmooth functions might form them.","PeriodicalId":42945,"journal":{"name":"Journal of the Serbian Society for Computational Mechanics","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2021-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47250722","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"CONCRETE DAMAGE PLASTICITY MATERIAL MODEL PARAMETERS IDENTIFICATION","authors":"D. Rakić, Aleksandar Bodić, N. Milivojević, V. Dunić, M. Zivkovic","doi":"10.24874/jsscm.2021.15.02.11","DOIUrl":"https://doi.org/10.24874/jsscm.2021.15.02.11","url":null,"abstract":"The procedure for identifying concrete damage plasticity material model parameters is presented in this paper. Concrete damage plasticity material model represents a constitutive model which is based on a combination of theory of plasticity and theory of damage mechanics. This material model is often used in solving geotechnical problems due to its realistic description of mechanical behavior of concrete material. Theoretical basis of concrete damage plasticity material model and material parameters identification procedure are presented in this paper. Proposed identification procedure is applied on experimental data from uniaxial compression and tension load-unload tests taken from literature. By applying experimental data, stress-strain curve is created. Based on stress-strain load-unload curve, stress-plastic strain and stress-degradation dependences are created which are necessary for material parameters identification. Using these dependences material parameters are determined. Verification of estimated parameters is performed in PAK software package using concrete damage plasticity material model. Finite element model is created for numerical simulations of uniaxial compression and tension tests. Numerical simulation results are compared with experimental data. By comparing numerical simulation results and experimental data it can be concluded that this procedure is effective for determining concrete damage plasticity model parameters.","PeriodicalId":42945,"journal":{"name":"Journal of the Serbian Society for Computational Mechanics","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2021-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69034554","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"ON DIFFUSE INSTABILITY OF ORTHOTROPIC VISCOPLASTIC PLATES","authors":"L. Kudrjavceva, M. Mićunović","doi":"10.24874/jsscm.2021.15.02.10","DOIUrl":"https://doi.org/10.24874/jsscm.2021.15.02.10","url":null,"abstract":"Elastic strain is covered by the effective medium homogenization method inside a representative volume element (RVE). It has an incremental quasi rate-independent (QRI) form obtained by the endochronic concept of thermodynamic time. The rate dependence takes place by means of stress rate dependent value of the initial yield stress. Free meso rotations and constrained micro rotations within a representative volume element (RVE) are assumed. A comparison between QRI and J2 diffuse instability equations is presented for orthotropic materials. A new QRI nonlinear evolution equation for orthotropic materials is derived by tensor function representation with Spencer-Boehler structural tensors.","PeriodicalId":42945,"journal":{"name":"Journal of the Serbian Society for Computational Mechanics","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2021-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43912456","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"PHYSICS-INFORMED NEURAL NETWORKS FOR ELASTIC PLATE PROBLEMS WITH BENDING AND WINKLER-TYPE CONTACT EFFECTS","authors":"A. Muradova, G. Stavroulakis","doi":"10.24874/jsscm.2021.15.02.05","DOIUrl":"https://doi.org/10.24874/jsscm.2021.15.02.05","url":null,"abstract":"Kirchhoff plate bending and Winkler-type contact problems with different boundary conditions are solved with the use of physics-informed neural networks (PINN). The PINN is built on the base of mechanics laws and deep learning. The idea of the technique includes fitting the governing partial differential equations at collocation points and then training the neural network with the use of optimization techniques. Training of the neural network is performed by numerical optimization using Adam’s method and the L-BFGS (Limited- Broyden–Fletcher–Goldfarb–Shanno) algorithm. The error loss function and the computational error of the approximate solution (output of the neural network) of the bending problem and contact problem with Winkler type elastic foundation are shown on examples. The predictions of the NN are investigated for different values of the foundation’s constants. The effectiveness of the proposed framework is demonstrated through numerical experiments with different numbers of epochs, hidden layers, neurons and numbers of collocation points. The Tensorflow deep learning and scientific computing package of Python is used through a Jupyter Notebook.","PeriodicalId":42945,"journal":{"name":"Journal of the Serbian Society for Computational Mechanics","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2021-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43660968","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"CORONARY ATHEROSCLEROSIS ASSESSMENT: A NEW ANATOMICAL, FUNCTIONAL, MORPHOLOGICAL AND BIO-MECHANICAL APPROACH","authors":"P. Siogkas, G. Kalykakis, C. Anagnostopoulos, T. Exarchos","doi":"10.24874/jsscm.2021.15.02.03","DOIUrl":"https://doi.org/10.24874/jsscm.2021.15.02.03","url":null,"abstract":"The aims of this work are to investigate and compare two different flow dynamics techniques (steady state - pulsatile flow) for endothelial shear stress calculation, compare lesion specific smartFFR and ESS values, as well as total vessel smartFFR and ESS values, and investigate the relationship between smartFFR and ESS to stress MBF (myocardial blood flow) and MFR (myocardial flow reserve). A total of 10 coronary vessels of 6 patients with intermediate pre-test likelihood for coronary artery disease, who have undergone both CTCA and PET-MPI with 15O-water or 13N-ammonia, were included in the study. Seven (7) cases had normal stress MBF and MFR values and three (3) had abnormal ones. PET was considered abnormal when > 1 contiguous segments showed both stress MBF ≤2.3mL/g/min and MFR ≤2.5 for 15O-water or 1.79 mL/g/min and ≤2.0 for 13N-ammonia, respectively. The ESS at the luminal surface of the artery was calculated as the product of viscosity and the gradient of blood velocity near the vessel wall. To calculate the smartFFR, we performed a transient simulation for each case. We used a pressure of 100 mmHg as a boundary condition at the inlet (i.e. mean human aortic pressure). At the outlet, a flow profile of 4 timesteps with a timestep duration of 0.25 sec was used. In each timestep, a volumetric flow rate of 1, 2, 3 and 4 ml/s are applied as outlet boundary conditions. The cut-off value for a pathological smartFFR is 0.83. There is a difference in total vessel calculated smartFFR results compared to the corresponding values of lesion specific smartFFR (0.88 vs 0.97, p=0.01). For ESS there is a negligible difference between lesion specific and total vessel values (2.22 vs 2.74, p = 0.9). There is a moderate negative correlation between both lesions specific (r = -0.543) and total vessel smartFFR and ESS (r = -0.915). ESS values were higher in vessels where vessel smartFFR was considered abnormal (1.97 vs 5.52, p = 0.01). Total vessel length smartFFR was lower in vessels with abnormal PET-MPI compared to the normal vessels (0.75 vs 0.93, p = 0.01). ESS is higher in vessels with pathological stress MBF and CFR (5.5 vs 2.0, p = 0.02). The total vessel length smartFFR and lesion ESS appear to assess the functional significance of the vessel well, when compared to the PET-MPI measurements.","PeriodicalId":42945,"journal":{"name":"Journal of the Serbian Society for Computational Mechanics","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2021-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49198315","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"PARAMETRIC INVESTIGATION OF BAND GAP EFFECTS IN CHIRAL MICROSTRUCTURES","authors":"Panagiotis Koutsianitis, Georgios K. Tairidis, Alexandros Kougkoulos, G. Stavroulakis","doi":"10.24874/jsscm.2021.15.02.07","DOIUrl":"https://doi.org/10.24874/jsscm.2021.15.02.07","url":null,"abstract":"Vibration suppression has been thoroughly studied in the last few years. A number of methods has been proposed for this purpose. An evolving method lies in the search of band gap regions, that is, certain frequency ranges where vibrations are isolated. In the present investigation, a periodic unit cell of a chiral metamaterial has been created in order to study its dynamic behavior and how this affects the wave propagation into a lattice structure consisting of repeated chiral microstructures. Each cell represents a composite structure consisted by a soft matrix with hard connector wings and a circular core. The system is studied by plane stress finite elements. The design parameters of the structure that define the shape and the material are modified in order to study the changes at the appearance of the band gap areas. In addition, results of the dynamic response of the structure in the frequency domain will be presented in order to show the magnitude of the vibration reduction that can be achieved in a specific frequency range.","PeriodicalId":42945,"journal":{"name":"Journal of the Serbian Society for Computational Mechanics","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2021-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45299299","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"FORCED CONVECTION IN A LID-DRIVEN NON-NEWTONIAN BLOOD FLOW THROUGH A STENOTIC ARTERY","authors":"Ignatius Fernandes, N. Bodke","doi":"10.24874/jsscm.2021.15.01.05","DOIUrl":"https://doi.org/10.24874/jsscm.2021.15.01.05","url":null,"abstract":"Cardiovascular diseases are one of the major health concerns globally, mainly caused by inadequate blood flow in different body parts. The lack of blood flow is often due to abnormal narrowing of blood vessels, and a systematic technique to boost blood flow in these areas can help cure the disease. One such method uses elevated temperatures to influence blood flow in the concerned areas. This paper investigates this process, i.e. the forced convection, through blood flow in a stenotic region of a human artery. A part of the stenotic region is considered a porous medium and the top wall is subjected to a higher temperature with a lid moving from left to right. Blood is considered as a non-Newtonian fluid with the power law index varying from 0.5 to 1.5. The geometric properties are considered to match the problem of blood flow in the artery affected by stenosis. The Carreau-Yasuda model is used to represent the non-Newtonian fluid flow in porous media and the numerical analysis is carried out using the Lattice Boltzmann method. This problem is investigated to study the influence of the moving lid and other geometric properties on convection and flow properties such as velocity profiles, streamlines, isotherms and heat transfer.","PeriodicalId":42945,"journal":{"name":"Journal of the Serbian Society for Computational Mechanics","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42620038","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"NUMERICAL ANALYSIS OF REINFORCED CONCRETE BEAM-COLUMN JOINT UNDER ACCIDENTAL IMPACT","authors":"S. Savin","doi":"10.24874/jsscm.2021.15.01.10","DOIUrl":"https://doi.org/10.24874/jsscm.2021.15.01.10","url":null,"abstract":"The purpose of this study is to create a universal computational model of a plane-stressed joint element, which could be implemented as a special finite element of the beam-column subassembly integrated into the FEA procedure to improve its accuracy. The combination both of the finite element method and the finite difference method has been accepted to simulate the structural behavior of monolithic reinforced concrete joints of building frames. The finite difference method is used directly for analysis the stress-strain state of a 2D stressed member of a monolithic joint, and the FEM is used for preliminary obtaining the conditions on the contour of this plane stressed member. The proposed model allows considering the discrete reinforcement, as well as the disruption of the adhesion of the reinforcing bars to concrete matrix along the contact surface. For the purposes of implementing the model, an algorithm for the stress-strain state analysis of the beam-column joint is proposed. An example of calculating an experimental frame unit based on the proposed approach is considered.","PeriodicalId":42945,"journal":{"name":"Journal of the Serbian Society for Computational Mechanics","volume":null,"pages":null},"PeriodicalIF":0.4,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47684575","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}