Pub Date : 2021-12-30DOI: 10.24874/jsscm.2021.15.02.09
M. Topalovic, A. Nikolic, S. Vulovic, Vladimir Milovanović
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.
{"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":"1 1","pages":""},"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}
Pub Date : 2021-12-30DOI: 10.24874/jsscm.2021.15.02.11
D. Rakić, Aleksandar Bodić, N. Milivojević, V. Dunić, M. Zivkovic
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.
{"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":"42 1","pages":""},"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}
Pub Date : 2021-12-30DOI: 10.24874/jsscm.2021.15.02.01
F. Georgiades
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.
{"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":" ","pages":""},"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}
Pub Date : 2021-12-30DOI: 10.24874/jsscm.2021.15.02.04
I. Atanasovska, D. Momčilović
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.
{"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":" ","pages":""},"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}
Pub Date : 2021-12-30DOI: 10.24874/jsscm.2021.15.02.10
L. Kudrjavceva, M. Mićunović
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.
{"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":" ","pages":""},"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}
Pub Date : 2021-12-30DOI: 10.24874/jsscm.2021.15.02.05
A. Muradova, G. Stavroulakis
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.
{"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":" ","pages":""},"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}
Pub Date : 2021-12-30DOI: 10.24874/jsscm.2021.15.02.07
Panagiotis Koutsianitis, Georgios K. Tairidis, Alexandros Kougkoulos, G. Stavroulakis
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.
{"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":" ","pages":""},"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}
Pub Date : 2021-12-30DOI: 10.24874/jsscm.2021.15.02.03
P. Siogkas, G. Kalykakis, C. Anagnostopoulos, T. Exarchos
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.
本工作的目的是研究和比较用于内皮剪切应力计算的两种不同的流动动力学技术（稳态-脉动流），比较病变特异性smartFFR和ESS值，以及总血管smartFFR和ESS值，并研究smartFFR和ESS与应力MBF（心肌血流量）和MFR（心肌流量储备）的关系。本研究共纳入了6名冠状动脉疾病测试前可能性中等的患者的10条冠状动脉，这些患者用15O水或13N氨同时接受了CTCA和PET-MPI治疗。7例应力MBF和MFR值正常，3例应力异常。当>1个连续片段显示应力MBF≤2.3mL/g/min和MFR≤2.5（对于15O水）或1.79mL/g/min和≤2.0（对于13N氨）时，PET被认为是异常的。动脉管腔表面的ESS计算为血管壁附近的粘度和血流速度梯度的乘积。为了计算smartFFR，我们对每种情况进行了瞬态模拟。我们使用100毫米汞柱的压力作为入口的边界条件（即平均人主动脉压）。在出口处，使用4个时间步长的流动剖面，时间步长持续时间为0.25秒。在每个时间步长中，应用1、2、3和4ml/s的体积流速作为出口边界条件。病理智能血流储备分数的临界值为0.83。与病变特异性smartFFR的相应值相比，总血管计算的smartFFR结果存在差异（0.88 vs 0.97，p=0.01）。对于ESS，病变特异性和总血管值之间的差异可以忽略不计（2.22 vs 2.74，p=0.9）。病变特异性（r=-0.543）与总血管smartFFR＆ESS之间存在中度负相关（r=-0.915）在血管smartFFR被认为异常的血管中，ESS值更高（1.97 vs 5.52，p=0.01）。与正常血管相比，PET-MPI异常的血管的总血管长度smartFFR更低（0.75 vs 0.93，p=01）。在具有病理应力MBF和CFR的血管中ESS更高（5.5 vs 2.0，p=0.02）与PET-MPI测量值相比，血管井的功能意义。
{"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":" ","pages":""},"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}
Pub Date : 2021-11-01DOI: 10.24874/jsscm.2021.15.01.10
S. Savin
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.
{"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":" ","pages":""},"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}
Pub Date : 2021-11-01DOI: 10.24874/jsscm.2021.15.01.01
M. Kojic, M. Milošević, B. Milićević, Vladimir Geroski, V. Simić, D. Trifunović, G. Stanković, N. Filipovic
Heart wall tissue plays a crucial role in living organisms by generating the mechanical force for blood flow. This tissue has a complex internal structure comprised mostly of muscle cells, in which biochemical energy is transformed into mechanical active stress under rhythmical electrical excitation. The overall heart functioning depends, among other physiological conditions, on the mechanical properties of the tissue. Over the past centuries, experimental and theoretical investigations have been conducted in order to establish the constitutive laws governing wall tissue behavior. Regarding computational modeling, many material models have been introduced, from simple elastic anisotropic to more sophisticated ones, based on various formulations of strain potentials. We here present a novel computational model that directly employs experimental constitutive relationships. Therefore, we avoid any fitting of material parameters for a selected analytical form of the constitutive law. Hysteretic characteristics of the tissue are included, as well as either incompressibility or compressibility according to experimentally determined curves. Deformation is split into deviatoric and volumetric parts in order to handle compressibility. The correctness and accuracy of the model is demonstrated through simple cases for loading and unloading conditions. Furthermore, the model was implemented for left ventricle (LV) deformation, where the FE mesh was generated from echocardiography recordings. Here, a specific algorithm, which accounts for LV torsion, was introduced to determine trajectories of material points on the internal LV surface. Hysteresis of the constitutive curves was used to calculate mechanical energy of LV wall tissue deformation. For completeness, the fluid flow within the LV was computed as well.
{"title":"COMPUTATIONAL MODEL FOR HEART TISSUE WITH DIRECT USE OF EXPERIMENTAL CONSTITUTIVE RELATIONSHIPS","authors":"M. Kojic, M. Milošević, B. Milićević, Vladimir Geroski, V. Simić, D. Trifunović, G. Stanković, N. Filipovic","doi":"10.24874/jsscm.2021.15.01.01","DOIUrl":"https://doi.org/10.24874/jsscm.2021.15.01.01","url":null,"abstract":"Heart wall tissue plays a crucial role in living organisms by generating the mechanical force for blood flow. This tissue has a complex internal structure comprised mostly of muscle cells, in which biochemical energy is transformed into mechanical active stress under rhythmical electrical excitation. The overall heart functioning depends, among other physiological conditions, on the mechanical properties of the tissue. Over the past centuries, experimental and theoretical investigations have been conducted in order to establish the constitutive laws governing wall tissue behavior. Regarding computational modeling, many material models have been introduced, from simple elastic anisotropic to more sophisticated ones, based on various formulations of strain potentials. We here present a novel computational model that directly employs experimental constitutive relationships. Therefore, we avoid any fitting of material parameters for a selected analytical form of the constitutive law. Hysteretic characteristics of the tissue are included, as well as either incompressibility or compressibility according to experimentally determined curves. Deformation is split into deviatoric and volumetric parts in order to handle compressibility. The correctness and accuracy of the model is demonstrated through simple cases for loading and unloading conditions. Furthermore, the model was implemented for left ventricle (LV) deformation, where the FE mesh was generated from echocardiography recordings. Here, a specific algorithm, which accounts for LV torsion, was introduced to determine trajectories of material points on the internal LV surface. Hysteresis of the constitutive curves was used to calculate mechanical energy of LV wall tissue deformation. For completeness, the fluid flow within the LV was computed as well.","PeriodicalId":42945,"journal":{"name":"Journal of the Serbian Society for Computational Mechanics","volume":" ","pages":""},"PeriodicalIF":0.4,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48297417","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}
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