Hydrodynamic Calculations Research Articles

DNA supercoiling-induced shapes alter minicircle hydrodynamic properties

DNA in cells is organized in negatively supercoiled loops. The resulting torsional and bending strain allows DNA to adopt a surprisingly wide variety of 3-D shapes. This interplay between negative supercoiling, looping, and shape influences how DNA is stored, replicated, transcribed, repaired, and likely every other aspect of DNA activity. To understand the consequences of negative supercoiling and curvature on the hydrodynamic properties of DNA, we submitted 336bp and 672bp DNA minicircles to analytical ultracentrifugation (AUC). We found that the diffusion coefficient, sedimentation coefficient, and the DNA hydrodynamic radius strongly depended on circularity, loop length, and degree of negative supercoiling. Because AUC cannot ascertain shape beyond degree of non-globularity, we applied linear elasticity theory to predict DNA shapes, and combined these with hydrodynamic calculations to interpret the AUC data, with reasonable agreement between theory and experiment. These complementary approaches, together with earlier electron cryotomography data, provide a framework for understanding and predicting the effects of supercoiling on the shape and hydrodynamic properties of DNA.

Shock cooling emission from explosions of red supergiants – I. A numerically calibrated analytic model

ABSTRACT Supernova light curves are dominated at early time, hours to days, by photons escaping from the expanding shock heated envelope. We provide a simple analytic description of the time-dependent luminosity, L, and colour temperature, Tcol, for explosions of red supergiants (with convective polytropic envelopes), valid up to H recombination (T ≈ 0.7 eV). The analytic description interpolates between existing expressions valid at different (planar then spherical) stages of the expansion, and is calibrated against numerical hydrodynamic diffusion calculations for a wide range of progenitor parameters (mass, radius, core/envelope mass and radius ratios, and metalicity), and explosion energies. The numerically derived L and Tcol are described by the analytic expressions with $10{{\ \rm per\ cent}}$ and $5{{\ \rm per\ cent}}$ accuracy, respectively. Tcol is inferred from the hydrodynamic profiles using frequency independent opacity, based on tables we constructed for this purpose (and will be made publicly available) including bound–bound and bound–free contributions. In an accompanying paper (Paper II) we show − using a large set of multigroup photon diffusion calculations − that the spectral energy distribution is well described by a Planck spectrum with T = Tcol, except at ultraviolet (UV) frequencies, where the flux can be significantly suppressed due to strong line absorption. We defer the full discussion of the multigroup results to paper II, but provide here for completeness an analytic description also of the UV suppression. Our analytic results are a useful tool for inferring progenitor properties, explosion velocity, and also relative extinction based on early multiband shock cooling observations of supernovae.

Modern neuroradiological diagnostic methods for intracranial arterial aneurysms: a review

Aim. Analysis of modern neuroimaging methods of intracranial arterial aneurysms with an emphasis on the possibilities of MR imaging of the vessel wall.Methods. Scientific articles and clinical recommendations from the PubMed from 2012 to 2020 were included into analysis, using keywords: aneurysm, CT, MRI, CFD (computational hydrodynamics), vessel wall imaging. As a result of the search, 137 articles were selected of which 27 articles were used in the review, supplemented by 10 articles from the reference lists 1990–2012.Results. Modern possibilities of intracranial arterial aneurysms imaging were demonstrated, with particular attention to the advantages of the method of MR imaging of the vessel wall. The main technical aspects of MR vessel wall imaging were demonstrated.Conclusion. Modern CT and MR imaging can provide additional information about the processes occurring in the lumen of the aneurysm and its wall. This information can be a key factor in the neurosurgical patient management.

Generalized effective string rope model for the initial stages of ultrarelativistic heavy ion collisions

We present a Generalized Effective String Rope Model (GESRM) for the description of the initial state of relativistic heavy ion collisions. We start from the Effective String Rope Model (ESRM) and take into account fluctuations in the initial state following the Glauber Monte Carlo approach. Results from symmetric Au+Au collisions at different impact parameters and asymmetric A+Au head on collisions are presented at RHIC energies. The produced initial state is used as an initial condition for further hydrodynamical calculations.

Study on vertical line source Green's function for hydrodynamic calculations of ocean structures in water with ice cover

The numerical calculation of panel integrals associated with the Green's function satisfying water surface condition with ice cover is the basis for the boundary element method (BEM) to solve hydrodynamic problems of ocean structures in ice regions. In order to simplify the calculation process and reduce the time consuming, the vertical line source representing the analytical integral of ice-covered Green's function over vertical line segment is firstly derived in this paper. Then a semi-analytical quadrature, which accumulates a series of vertical line sources distributing along the horizontal direction, can be derived for the panel integral. In the numerical implementation, the asymptotic analysis method is employed to eliminate the singularity at zero point of the denominator, variable substitution is performed to treat the integral at infinite and approximate polynomials are introduced to evaluate the Bessel functions. Through the calculations of vertical line and panel integrals of Green's function and its derivatives, the analytical expression of vertical line source is proved to be accurate and more efficient than the normal numerical quadrature. Based on this, a BEM program is developed and applied in the hydrodynamic calculations of submerged structures with ice cover. The computed results are found to be in excellent agreement those of the validated BEM based on point source, which further verifies the reliability and practicability of utilization of vertical line source.

RELAP5-CFX COUPLING MODULE: TESTING ON SIMPLE THERMOHYDRAULIC MODELS

The modern direction in the study of the safety of nuclear power plants is to ensure the maximum level of detail in process modeling with a satisfactory level of computational resources. One of the approaches of such task solving is the coupled use of special software with the required levels of detail, for example, systemic thermohydraulic codes with computational hydrodynamics codes.
 This article describes the developed coupling module between the system thermohydraulic code RELAP5/Mod. 3.2 and the CFX computational hydrodynamics code, using an external explicit interfacing scheme without overlap, in which CFX acts as the main code and RELAP5 as the secondary one. The development of this module is part of the work on integrated coupled modeling of severe accidents and makes it possible to model the defining processes and phenomena that occur during a severe accident within the reactor vessel using the CFD model, and the elements of the reactor unit using the RELAP5 model with an acceptable cost of resources and with a high level of detail. To check the coupling technology, the module was tested on simplified models containing serially connected RELAP5- and CFD-models of horizontal pipes, as well as on a closed loop. In view of the further use of the interface module on a full-fledged model of the VVER-1000, testing is performed for three main interface types: "input flow", "output flow" and their combination "input/output flow" on a closed loop. After completion of the testing, the accuracy and credibility of the results of the coupled calculations was evaluated by comparing them with the results of autonomous RELAP5 calculations. Results of the tests calculations support the possibility of using the RELAP5-CFX coupling module on more complex and large-scale RELAP5 and CFD models.

Directed flow and global polarization in Au+Au collisions across energies covered by the beam energy scan at RHIC

We study the directed flow of identified particles in Au+Au collisions at $\sqrt{s_\text{NN}}=7.7$ to 62.4 GeV. The Glauber model is extended to include both a tilted deformation of the QGP fireball with respect to the longitudinal direction and a non-zero longitudinal flow velocity gradient in the initial state. By combining this improved initial condition with a (3+1)-dimensional viscous hydrodynamic model calculation, we obtain a satisfactory description of the transverse momentum spectra and the rapidity dependent directed flow coefficient of different hadron species. Our calculation indicates the sensitivity of the hadron directed flow, especially its splitting between protons and antiprotons, to both the initial geometry and the initial longitudinal flow velocity. Therefore, the combination of directed flow of different hadrons can provide a tight constraint on the initial condition of nuclear matter created in heavy-ion collisions. The initial condition extracted from the directed flow is further tested with the global polarization of $\Lambda$ and $\bar{\Lambda}$ within the same theoretical framework, where we obtain a reasonable description of these hyperon polarization observed at different collision energies at RHIC.

Calculation of the Flow Hydrodynamics in Reverse-Flow Cyclones Using the Flow Vision Software Package

Calculation of the Flow Hydrodynamics in Reverse-Flow Cyclones Using the Flow Vision Software Package

Motion Response of Floating Platform Hoisting Impeller Based on Fully Coupled Model

Given the construction efficiency and operation safety of offshore wind turbine hoisting, it is necessary to study the motion response characteristics of a floating platform-hoist coupling system. Using SESAM hydrodynamic calculation software, a fully coupled model of a floating crane ship and fan impeller is established. The accuracy of the calculation model is verified by comparing the numerical simulation results with the pool experimental results. Based on this research, the sensitivity factors of floating crane ship motion are analyzed. The results show that the floating crane should choose the bow-top wave operation to minimize the rolling motion of the hull. The wind speed and the elevation angle of the boom have a great influence on the motion of the floating crane. The larger the wind speed, the greater the motion response of the hull, the smaller the elevation angle of the boom, and the larger the roll value of the hull. The higher the impeller height, the greater the motion displacement of the floating crane, but the influence is different on the hull motion under different working conditions. The results of the simulation analysis can provide a reference and basis for offshore wind turbine hoisting.

Experimental study and numerical simulation of hydrodynamics for fish-like underwater vehicle

This article presents the results of experimental and computational modeling of the movement of a fish-like underwater robot. The experimental 3D model is constructed from photographs of Pacific bluefin tuna. This model allows us to study biomorphic swimming with various motion parameters, namely: the amplitude and frequency of strokes is set by the servo control signal, the angle between the tail fin and the elastic plate is set by the number and stiffness of springs in the hinge. The calculation method involves the joint solution of the equations of dynamics of the robot and the equations of hydrodynamics of the fluid flowing around it. For this task, an original mesh deformation algorithm was developed that allows hydrodynamic calculations to be performed near the tail of the model performing transverse oscillations. The use of deformable mesh technology allows you to reproduce the shape of the tail vibrations as accurately as possible. In addition, the calculation scheme has the property of conservativeness, which makes it possible to obtain high quality calculations, confirmed by comparison with experimental data.

Prediction of energy and cavitation characteristics of high specific speed Francis hydraulic turbines

BACKGROUND: Cavitation is a phenomenon that occurs in vane hydraulic machines: pumps, hydraulic turbines, when the pressure in a certain area of the flow reaches the level of saturated steam pressure. Its occurrence depends on the design and mode of operation of the hydraulic turbine. In order to design a hydraulic turbine with high cavitation qualities, it is necessary to be able to reliably predict this phenomenon.
 AIMS: The article describes approaches to modeling the operation of Francis hydraulic turbines based on the ANSYS software package.
 METHODS: Using quasi-3D methods was modeled turbine blade system with 75 meters head. Hydrodynamic computation carried out in single-phase and two-phase formulations using the ANSYS CFX package.
 RESULTS: The design of a flow path Francis turbine 3D solid model with a specific speed coefficient ns =283 has been completed. The flow part of the hydraulic turbine includes a spiral case, a stator, a guide vane, an impeller and a draft tube. Computational modeling of the flow of a single-phase viscous fluid in a hydraulic turbine in different modes was carried out to construct a universal characteristic. The optimal efficiency is found and the flow characteristics are calculated. The losses in the elements of the flow part of the hydroturbine under various operating modes are determined, the zone of optimal operation is found. The cavitation flow is calculated using a two-phase flow model (water-steam). For both sides of the impeller blade, a pressure distribution was obtained, which can be used to judge the possibility of cavitation in areas where the pressure of the water column is less than the vaporization pressure. The value of the critical cavitation coefficient for the three most unfavorable modes was determined, and the dependence of the efficiency on the cavitation coefficient was constructed. The area occupied by steam on the blade during cavitation flow is visualized, its area is determined relative to the surface area of the blade.
 CONCLUSIONS: The designed hydraulic turbine has good energy and cavitation qualities, confirmed by the calculation. This version of the hydroturbine can be used as the initial one with further optimization of the blade system and elements of the flow path, to improve the energy and cavitation qualities.

The Experience in Drone Use to Evaluate the Coefficients of Turbulent Diffusion in Small Water Bodies

Small lakes and reservoirs located in the zone of active technogenesis are subject to the risk of various emergency situations. The present-day computer technologies, including hydrodynamic computation modules, can be used to effectively estimate and forecast their consequences with the aim to minimize the adverse effect. These models require evaluating the coefficients of horizontal diffusion. The theoretical analysis of such processes is very difficult because of their specifics. Studies aimed at evaluating these coefficients in Russia and other countries are very few, even under the assumption of their homogeneity and isotropy. The modern measurement technologies involving the use of pilotless vehicles, make such studies much simpler. The article discusses the significance of such studies, the technology of their performance, and the results obtained for the Verkhne-Zyryansk Reservoir. A field experiment with the use of eight floats yielded an average estimate of the coefficient of horizontal turbulent diffusion equal to 0.012 m2/s. The specific features of the obtained results are discussed.

Beyond the US-SOMO-AF database: a new website for hydrodynamic, structural, and circular dichroism calculations on user-supplied structures.

At the 25th International Analytical Ultracentrifugation Workshop and Symposium, we described the recent implementation of the UltraScan SOlution MOdeler AlphaFold (US-SOMO-AF) database, containing hydrodynamic, structural, CD calculations, and other ancillary information, performed on the entire AF v2 database of predicted protein structures, containing more than 1,000,000 entries. The scope of the US-SOMO-AF database was that of providing direct access to pre-calculated physicochemical parameters for rapid assessment against their experimentally determined counterparts to test the compatibility in solution of predicted AlphaFold structures. In the meantime, the AlphaFold consortium has extended its database of predicted structures to an astonishing > 200 million entries, making it quite impractical for their coverage in the US-SOMO-AF database. Therefore, we have created the US-SOMO-Web site, allowing the rapid calculations of all the properties, as present in the US-SOMO-AF database, on user-supplied PDB and mmCIF structures, as well as allowing direct processing of the latest AlphaFold models. Major features on the website are described, along with current limitations and potential future developments.

High-Order Mixed Finite Element Variable Eddington Factor Methods

We apply high-order mixed finite element discretization techniques and their associated preconditioned iterative solvers to the Variable Eddington Factor (VEF) equations in two spatial dimensions. The mixed finite element VEF discretizations are coupled to a high-order Discontinuous Galerkin (DG) discretization of the discrete ordinates transport equation to form effective linear transport algorithms that are compatible with high-order (curved) meshes. This combination of VEF and transport discretizations is motivated by the use of high-order mixed finite element methods in hydrodynamics calculations at the Lawrence Livermore National Laboratory (LLNL). Due to the mathematical structure of the VEF equations, the standard Raviart Thomas (RT) mixed finite elements cannot be used to approximate the vector variable in the VEF equations. Instead, we investigate three alternatives based on the use of continuous finite elements for each vector component, a non-conforming RT approach where DG-like techniques are used, and a hybridized RT method. We present numerical results that demonstrate high-order accuracy, compatibility with curved meshes, and robust and efficient convergence in iteratively solving the coupled transport-VEF system and in the preconditioned linear solvers used to invert the discretized VEF equations.

Azimuthal anisotropy measurement of (multi)strange hadrons in Au+Au collisions at sNN=54.4 GeV

Azimuthal anisotropy of produced particles is one of the most important observables used to access the collective properties of the expanding medium created in relativistic heavy-ion collisions. In this paper, we present second ($v_{2}$) and third ($v_{3}$) order azimuthal anisotropies of $K_{S}^{0}$, $\phi$, $\Lambda$, $\Xi$ and $\Omega$ at mid-rapidity ($|y|<$1) in Au+Au collisions at $\sqrt{s_{\text{NN}}}$ = 54.4 GeV measured by the STAR detector. The $v_{2}$ and $v_{3}$ are measured as a function of transverse momentum and centrality. Their energy dependence is also studied. $v_{3}$ is found to be more sensitive to the change in the center-of-mass energy than $v_{2}$. Scaling by constituent quark number is found to hold for $v_{2}$ within 10%. This observation could be evidence for the development of partonic collectivity in 54.4 GeV Au+Au collisions. Differences in $v_{2}$ and $v_{3}$ between baryons and anti-baryons are presented, and ratios of $v_{3}$/$v_{2}^{3/2}$ are studied and motivated by hydrodynamical calculations. The ratio of $v_{2}$ of $\phi$ mesons to that of anti-protons ($v_{2}(\phi)/v_{2}(\bar{p})$) shows centrality dependence at low transverse momentum, presumably resulting from the larger effects from hadronic interactions on anti-proton $v_{2}$.

Research on hydrodynamic performance calculation of buoy-chain-sprocket wave energy collection device

Buoy-chain-sprocket wave energy collection device is a new type of oscillating buoy wave energy collection device, which has a good application prospect. The calculation method of the hydrodynamic performance of wave energy device (e.g. the first-level average collection efficiency of wave energy) is the core scientific problem of wave energy device, and it is also the theoretical basis for the optimization and control of wave energy device prototype. In this paper, on basis of linear potential flow theory, after the velocity potentials are calculated with eigenfunction expansion method and matching asymptotic expansion method, the frequency-domain wave loads in the heave, surge and pitch directions of the floating body are obtained. And then the motion coordination relationship of the floating body of buoy-chain-sprocket wave energy collection device is used to establish time-domain hydrodynamic motion response equations of the floating body of the device based on the Cummins method. After these equations are solved via the fourth-order Runge-Kutta method, the first-level average collection efficiency of the wave energy device is acquired. In order to further improve the calculation accuracy, the frequency-domain wave-exciting force is calculated by using variable draft depth when the hydrodynamic response of buoy-chain-sprocket wave energy collection device is calculated in this paper. Finally, the reliability of the above calculation method for the hydrodynamic performance of buoy-chain-sprocket wave energy collection device is verified through physical model experiment.

Research on dynamic behavior vibration control of semi-submersible Marine platform based on ARID control system

As the development and infrastructure of deepwater oil and gas resources, the performance of the deepwater offshore platform is directly related to personnel safety, equipment safety, normal production and drilling process. Therefore, hydrodynamic calculation[1] and flow response-based control and optimization are current hot research topics. Semi-submersible marine platforms are widely used in the industry due to their large deck area, strong wind and wave resistance, and excellent mining ability. However, their complex and diverse lines in the marine environment result in a series of dynamic responses due to wave loads, particularly in the rotating dynamic behavior, which cannot be efficiently controlled using traditional vibration control methods.Many research studies have focused on developing efficient control systems to suppress the dynamic behavior of semi-submersible marine platforms. For instance, active mass dampers (AMD) and tuning rotational inertia dampers (TRID) devices have been used to control the translation dynamic behavior of the platform. However, their performance in controlling the rotating dynamic behavior of the platform is unsatisfactory.To address this challenge, this paper proposes a new type of active control system called the Active Rotary Inertia Driver (ARID), which utilizes an active torque control system to suppress the rotating dynamic behavior of the semi-submersible marine platform. The ARID system is developed based on AMD and TRID devices and aims to enhance personnel and equipment safety, as well as the normal production and drilling process of the platform.Therefore, this study presents a comprehensive review of the research status on hydrodynamic calculation and flow response-based control and optimization of deepwater offshore platforms, particularly the semi-submersible marine platform. The proposed ARID system is expected to contribute to this research area by offering an efficient solution to the rotating dynamic behavior of the platform.

Оценка технической возможности достижения одинакового хода поршней в кривошипно-шатунном механизме с прицепными шатунами

The article presents the technical capabilities for achieving the specified operating characteristics of engine components and parts taking into account the geometric characteristics of the crank mechanism (crank mechanism). It also presents the assessment and achievements of the required level of strength parameters of some structural elements of the main connecting rod and the entire mechanism as a whole. Making changes to a proven design and established production is a complex and multifactorial task. It is necessary to make changes that would minimize production and technological losses. Besides, they must fit harmoniously into existing technology and production capabilities ensuring the fulfillment of new technical requirements and characteristics. When solving the problem of ensuring the same piston stroke for a V-2 engine, the analysis of the design documentation showed that in addition to making changes to the design of the crank mechanism, it is necessary to make changes to other engine parts. The need for these changes was determined by the method of “scrolling” the assembly of crankshaft parts in the volume of the engine crankcase using 3D modeling programs for parts and checking their performance. The results of assessing the kinematics of the crankshaft engine of V-2 type engines proved that in addition to changing the design of the main connecting rod, it is necessary to perform additional processing of the axial stiffener rib of the upper half of the crankcase, as well as to make changes to the design of the trailing connecting rod in order to eliminate contact with the cylinder liner and, possibly, the liner itself. However, changes in the engine design will entail significant changes in the technological process of its manufacture. Obviously, these changes should be minimal. In order to preserve the engine design, it is necessary to make some significant changes. They can affect significant production and technological changes, which in conditions of mass production require fairly strong theoretical and practical justification. Therefore, when implementing these technical solutions, it was necessary to perform calculation and kinematic analysis based on 3D modeling and logical analysis, excluding disruption of engine operation. In addition, to assess the load on the lower head of the connecting rod, a hydrodynamic calculation was performed. The results also include the hydromechanical characteristics of a complexly loaded bearing and a diagram of the hydrodynamic pressures acting in a thin lubricant layer

Impact of separately located obstacles on air flow movement calculation

In hydrodynamic calculations, the confederation of the right set of coordinates of a continuous medium (gas, liquid) becomes complicated because it makes the calculation mechanismspecific and tied only to a specific object. The paper is devoted to an improved method to calculate the small-scale circulation of the surface layer of the atmosphere in urban areas with many isolated buildings from each other. The proposed method will work for explicit and implicit schemes for calculating the transport equations and conservation of momentum of motion. It is designed to calculate the small-scale circulation of the surface layer of the atmosphere in urban areas with many isolated buildings from each other. The method allows for consideration of the interaction of a continuous medium flow with impenetrable obstacles discretely and randomly located inside the calculation area. This method will be helpful when calculating microcirculation in urban development.

Numerical modeling of wind turbine with vertical axis using turbulence model k − ω in ANSYS FLUENT

The paper considers a variant of the problem of modeling the flow around a developed wind turbine. Since the task is reduced to modeling a flat task, the 2D design mode was chosen. The k – ω turbulent model was used to model the vertical axis wind turbine. In the research process, experimental methods for measuring wind speed and torque, methods of mathematical modeling, and computational fluid dynamics were used. The object of research is a wind turbine designed to generate electricity from wind energy. The research aims to develop a wind turbine with a vertical axis and radial frames, equipped with flat blades and stoppers, operating at low wind speeds. Research methods: in the research process, experimental methods for measuring wind speed and torque, methods of mathematical modeling, and computational hydrodynamics were used. A computational experiment HTBO with four sections based on the ANSYS environment was carried out. Scope of the results: the results will be used in designing and manufacturing wind turbines operating at low wind speeds. Ultimately, low-power wind turbines will be developed. Economic efficiency and significance of the work: the wind turbine being developed is made with available purchased materials and will have a short payback period. It is used for domestic and other purposes where access to electricity is limited.