Alexey Vasyukov

Virtual blunt injury of human thorax: age-dependent response of vascular system

Abstract This work is the numerical study of the age-dependent responses of the vascular system under low-mass high-speed impact scenario. The grid-characteristic method on the adaptive mesh model of the human thorax is the numerical tool of the study. Due to the lack of valid vascular injury criteria, the numerical model only provides information on injury risk. The numerical simulation demonstrates that an older age changes significantly the vascular response and increases the risk of aorta injury. We focused on the aorta because its rupture is the general consequence of vehicle accidents (great mass impacts at relatively low velocity). Our numerical results are in good agreement with previous studies of great-mass low-speed blunt thorax impact.

Numerical Modeling of Non-destructive Testing of Composites

Low-velocity strikes are considered as one of the most dangerous load types for composites, especially in aviation. They do not lead to an immediate destruction of a whole detail, but inner damage, provoking a delamination between layers or between fiber and matrix, lowers the material strength and may cause a destruction during the flight. This inner damage can only be noticed via complex study, which increases an exploitation cost. Numerical modeling can help to interpret the results obtained from common portable devices, which are currently used for metals. The modification of known methodology can be reliably used for composites. In this research, a hybrid grid-characteristic method of 1-2 order on irregular tetrahedral grid is used. A carbon fiber polymer matrix of unidirectional composite is modeled as a homogeneous orthotropic media with a single distinguished direction along the fiber. As a result, the one-dimensional graphics, which correspond to A-scans in real devices, were obtained. The detailed analysis of received data confirms a rationality of proposed methodoly.

Transcranial ultrasound of cerebral vessels in silico: proof of concept

Abstract Correct diagnostics of vascular pathologies underlies treatment success for patients with cerebrovascular diseases. Transcranial ultrasound is the well-known method for diagnostic of cerebrovascular diseases. Despite high sensitivity and specificity of the method, transcranial ultrasound has some limitations related to the B-mode image quality and accurate insonation of vessels of interest. Overcoming these limitations enables to enhance the quality of the diagnostic procedure. The present work addresses the numerical simulation of ultrasound propagation in a human head by a grid-characteristic method. We used a human tissue-mimicking phantom to verify our numerical model in terms of the accuracy of distance estimation. We obtained pressure distributions within a 3D segmented model of a human head. Our pilot study has some limitations, nevertheless the simulation results demonstrate that mathematical modelling of the transcranial ultrasound can be an effective tool to enhance the ultrasound examination.

Numerical simulation of the failure of composite materials by using the grid-characteristic method

This is an overview of the existing criteria of the failure of the composite materials and of the results of the application of some of them to simulate a low-speed hit on the composition material for the three-dimensional statement of the problem. Simulation is made by means of the grid-characteristic method. Reasons are given for the selection of specific criteria and they are compared with each other.

Combined grid-characteristic method for the numerical solution of three-dimensional dynamical elastoplastic problems

A combined method blending the advantages of smoothed particles hydrodynamics (SPH) and the grid-characteristic method (GCM) is proposed for simulating elastoplastic bodies. Various grid methods, including the GCM, have long been used for the numerical simulation of elastoplastic media. This method applies to the simulation of wave processes in elastic media, including elastic impacts, in which case an advantage is the use of moving tetrahedral meshes. Additionally, fracture processes can be simulated by applying various fracture criteria. However, this is a technically complicated task with the accuracy of the results degrading due to the continual updating of the grid. A more suitable approach to the simulation of processes involving substantial fractures and deformations is based on SPH, which is a meshless method. However, this method also has shortcomings: it produces spurious modes, and the simulation of oscillations requires particle refinement. Thus, two families of methods are available that are optimal as applied to two different groups of problems. However, a realworld problem can frequently be a mixed one, which requires a substantial tradeoff in the numerical methods applied. Aimed at solving such problems, a combined GCM-SPH method is developed that blends the advantages of two constituting techniques and partially eliminates their shortcomings.

Numerical simulation of dynamic processes in biomechanics using the grid-characteristic method

Results of the numerical simulation of mechanical processes occurring in biological tissues under dynamic actions are presented. The grid-characteristic method on unstructured grids is used to solve the system of equations of mechanics of deformable solids; this method takes into account the characteristic properties of the constitutive system of partial differential equations and produces adequate algorithms on interfaces between media and on the boundaries of integration domains.

Numerical modeling of ultrasound beam forming in elastic medium

Abstract Modeling of ultrasonic pulse in a medium is usually based on the system of equations of acoustics. This approximation means that, when a wave pattern is considered, only longitudinal waves are taken into account. This approach works well in many practically meaningful applications. However, for some cases the consideration of only longitudinal waves is not enough, and an analysis of the complete elastic wave pattern is required. This paper is devoted to the modeling of the formation of an ultrasonic pulse in medium using the system of equations of elasticity instead of the system of equations of acoustics. A transducer with phased array is considered. Grid-characteristic numerical method is used for a numerical solution.

Numerical Modelling of Composite Delamination and Non-destructive Testing

Delamination caused by low-velocity strike is considered as one of the most dangerous failure types. The destruction of contact between the plies or composite components significantly lowers the residual strength of the material but cannot be determined by visual inspection. These failures can mostly be determined by ultrasound testing, however, it requires a long time and cannot be carried out on site, which increases the maintenance cost. Both delamination emergence and ultrasound diagnostic results are determined by wave processes in viscoelastic media. The grid-characteristic method used in this chapter shows good results verified on various experimental data. The results of numerical modelling of delamination and its diagnostics are given in this chapter.

Numerical Modeling of Transcranial Ultrasound

Correct diagnostics of vascular pathologies underlies treatment success for patients with cerebrovascular diseases. Generally, ultrasound is a well-known method for diagnostics of vascular diseases among other things, and it can determine the direction of blood flow. Despite the high sensitivity of the method, transcranial ultrasound has some limitations due to complex shape and rheological contrast of the skull bone (Vassilevsky et al., Russ J Numer Anal Math Model 31(5):317–328, 2016). Overcoming these limitations can improve the quality of the diagnostic procedure, and the mathematical modeling of the transcranial ultrasound can be an effective tool to enhance the ultrasound examination. The present work addresses the numerical simulation of ultrasound propagation in a human head. A human tissue-mimicking phantom was used to verify the numerical model and the software package. A model for the signal processing in the ultrasound device was developed. Pressure distributions were obtained within a 3D segmented model of a human head (Danilov et al., Russ J Numer Anal Math Model 27:431–440, 2012; Danilov et al., J Phys Conf Series 407(1):02004, 2012).