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The viscous resistance caused by the relative motion of plunger and pump barrel is an important factor in the dynamic analysis of the drainage and production mechanism during coalbed methane exploitation. Existing studies mostly focus on deep well (1000–3000 m) large-displacement pump (usually 80–300 m3/d), and the interstitial medium is mainly crude oil. Regression fitting is mainly carried out based on empirical formula or experimental simulation method, without considering the characteristics of shallower coalbed gas well (400–800 m) small-displacement pump (<10 m3/d). The variation of the clearance between plunger and barrel and the variation of viscous resistance between plunger and barrel are not revealed. Based on the Navier-Stokes equation and Newton's internal friction law, a mathematical model of the annular viscous resistance between the plunger and the pump barrel is established, and an analytical method is used to describe the influence of stroke times, annular clearance, and differential pressure between the upper and lower plungers on the viscous resistance. The results show that the plunger stroke is directly proportional to the variation range of viscous resistance, and low stroke is beneficial to reduce the viscous resistance. The effect of differential pressure between upper and lower plunger of rod pump on viscous resistance of small displacement coalbed gas well is significantly greater than that of plunger running speed. The annular clearance is directly proportional to the differential pressure between the upper and lower parts of the plunger, the inertia force of the plunger, and the shear force of the moving fluid. The annular viscous resistance model between plunger and pump barrel is helpful to improve the calculation accuracy of suspending point load of coalbed gas well pumping unit, analyze the working condition of coalbed gas drainage gas production process, and provide basis for the optimization design of coalbed gas well rod pump clearance. [ABSTRACT FROM AUTHOR]

The rectilinear motion of a chain of identical bodies in a viscous medium with a quadratic law of resistance is considered. Neighboring bodies interact with each other. There are no restrictions on the magnitude of the interaction forces. Motions are constructed in which each of the bodies of the system shifts by the same specified distance, provided that the velocities of each of the bodies of the system coincide at the initial and final moments of time. In particular, the case where the system is at rest at the initial moment of time is considered. In the case where the velocity of the center of mass of the system at the initial moment of time is not equal to zero, a motion is constructed in which the velocity of each of the bodies is piecewise constant and the velocity of the center of mass of the system is constant. This motion is optimized under the condition that the velocity of each of the bodies is bounded. The obtained results can be used to control a locomotion system of several bodies moving in a viscous medium by means of changing its configuration. [ABSTRACT FROM AUTHOR]

Using fluid dynamics finite element simulation analysis method and field test verification method, the effect of treating the inner wall of high-temperature crude oil and natural gas gathering and transportation pipelines at 200-250 °C with high-temperature resistant organic coatings is studied. The results show that after being treated with high-temperature resistant organic coatings, the roughness and damping of the inner wall of natural gas gathering and transportation pipelines can be significantly reduced, further controlling the internal turbulence, reducing the overall resistance of the pipelines, significantly reducing the dynamic pressure inside the pipelines, and achieving higher pipelines transmission efficiency. It provides a good reference for reducing resistance in other natural gas gathering and transportation pipelines. [ABSTRACT FROM AUTHOR]

The Reynolds-averaged Navier–Stokes (RANS)-based computational fluid dynamics (CFD) calculation using a two-equation turbulence model, such as the k–omega shear-stress transport (SST) model, is a mainstream method with sufficient accuracy for the estimation of integral hydrodynamic forces and moment at both the model-scale and full scale. This paper confirmed that the Reynolds stress model (RSM) has sufficient estimation accuracy of viscous resistance and wake distribution at the hull design stage. Herein, the ability of RSMs to estimate the viscous resistance and wake distribution of a JBC ship is evaluated. Specifically, the verification and validation (V&V) method is employed to indicate the numerical and model uncertainties of each turbulence model used to estimate the viscous resistance. The RSMs showed higher numerical uncertainty than the k–omega SST. However, the uncertainty of the experimental measurements is generally smaller than the numerical uncertainty. Moreover, the linear pressure–strain (LPS) and the linear pressure–strain two-layer (LPST) models show less comparison error of the viscous resistance than the k–omega SST. Furthermore, the LPST and k–omega SST models are applied to twenty ships with various full and fine hull forms to calculate the viscous resistance and compare it with the experimental results. The viscous resistance of the LPST model showed a small difference when employed in experimental fluid dynamics (EFD) and CFD calculations. Using the LPST model, the viscous resistance can be estimated with high accuracy in our setting. For industrial use, this study could provide an important insight into the designing of various types of vessels. [ABSTRACT FROM AUTHOR]

A physics‐based medical image segmentation method is developed. Specifically, the image greyscale intensity is used to infer the voxel partial volumes and subsequently formulate a porous medium analogy. The method involves first translating the medical image volumetric data into a three‐dimensional computational domain of a porous material. A velocity field is then obtained from numerical simulations of incompressible fluid flow in the porous material, and finally a velocity iso‐surface provides the surface description of the target object. The approach is tested on CT images of eight patient‐specific cases, where cerebral aneurysms, nasal cavities (NC), and an aortic arch (AA) are the objects of interest. In the aneurysm cases, the results are compared against constant greyscale thresholding and manual segmentation. The manual segmentations of the aneurysms are validated by a clinical practitioner. Only a qualitative comparison is available for the NC, and the AA geometries. The results show that the proposed method is effective and capable of extracting the target object in a noisy domain. A sensitivity study is carried out to verify the method's performance with respect to modelling or user choices. The segmentation by the proposed method is also evaluated by performing computational fluid dynamics simulation, including a near‐wall flow analysis, to ensure that the segmented geometry and the resulting computed solution are representative and meaningful. [ABSTRACT FROM AUTHOR]

The terminal settling velocity (TSV) calculation of drops and other spherical objects in fluid medium is a classical problem, which has important application values in many fields such as the study of cloud and precipitation processes, the evaluation of soil erosion, and the determination of fluid viscosity coefficient etc. In this paper, a new explicit approximation model of TSV is established, which combines the theoretical solution of N-S equation about fluid motion around spherical objects and the statistical regression of solution dimensionless coefficients with measurement data. This new model can adapt to different values of drop parameters and medium parameters in a large range of Re. By this model, the relative and absolute calculation errors of TSV are in range of −3.42%−+ 4.34% and −0.271 m/s−+ 0.128 m/s respectively for drop radius 0.005−2.9 mm. Their corresponding root mean square values are 1.77% and 0.084 m/s respectively, which are much smaller than that of past theoretical and empirical models. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Prediction of the total resistance of a pusher-barge system has become enormous complexity involving nonlinear-hydrodynamic flow behaviour around their hull forms. Both empirical and simplified numerical solutions may still lead to inaccurate results due to the presence of nonlinear characteristics of the pressure and viscous resistances. The use of a more sophisticated method would obviously necessitate solving the above problem. This paper presents a Computational Fluid Dynamics (CFD) approach to predict the total resistance of a pusher-barge system at various barge configurations. To achieve such an objective, four different configurations of the barge models incorporated with various Froude numbers have been taken into account in the computational simulation. In general, the results revealed that the increase of Froude number (Fr = 0.182 to 0.312) was proportional to the magnitude of RT, RP, and RV. Regardless of the various Froude number, the pusher-barge system with a 13BP configuration provides the highest resistance compared to the 12BP and 11BP. In addition, the arrangement of barges in the longitudinal (12BP) and lateral (21BP) configurations produced a significant effect with increases in RT, RP, and RV values of 110%, 167.5%, and 77.6%, respectively. The possible reason for this is that the increase of the total wetted surface area for 21BP has produced a proportionally higher amount of pressure and viscous resistance. Finally, the numerical results were presented and analyzed based on some aspects involving the total resistance and resistance coefficient in terms of pressure and viscous resistance of the pusher-barge system. This analysis provides very valuable information on selecting a proper arrangement of the pusher-barge system, which results in less total resistance. [ABSTRACT FROM AUTHOR]

Object and purpose of research. This paper studies towing resistance assessment method in deep open water for icebreakers, supply vessels, and cargo vessels with high ice class. Materials and methods. The method suggested in this paper is based on the regression analysis of model test data obtained as per the form-factor scheme. The paper also suggests full-scale extrapolation formulae for wave resistance coefficient

The Reynolds-averaged Navier–Stokes (RANS)-based computational fluid dynamics (CFD) calculation using a two-equation turbulence model, such as the k–omega shear-stress transport (SST) model, is a mainstream method with sufficient accuracy for the estimation of integral hydrodynamic forces and moment at both the model-scale and full scale. This paper confirmed that the Reynolds stress model (RSM) has sufficient estimation accuracy of viscous resistance and wake distribution at the hull design stage. Herein, the ability of RSMs to estimate the viscous resistance and wake distribution of a JBC ship is evaluated. Specifically, the verification and validation (V&V) method is employed to indicate the numerical and model uncertainties of each turbulence model used to estimate the viscous resistance. The RSMs showed higher numerical uncertainty than the k–omega SST. However, the uncertainty of the experimental measurements is generally smaller than the numerical uncertainty. Moreover, the linear pressure–strain (LPS) and the linear pressure–strain two-layer (LPST) models show less comparison error of the viscous resistance than the k–omega SST. Furthermore, the LPST and k–omega SST models are applied to twenty ships with various full and fine hull forms to calculate the viscous resistance and compare it with the experimental results. The viscous resistance of the LPST model showed a small difference when employed in experimental fluid dynamics (EFD) and CFD calculations. Using the LPST model, the viscous resistance can be estimated with high accuracy in our setting. For industrial use, this study could provide an important insight into the designing of various types of vessels.

• Determine permeability equation of permeable asphalt mixture. • Develop the program to calculate multi-directional connective void content. • Propose a pore throat model to reveal the variation of flow resistance. • Explore the impacting parameters of inertia and viscous resistance distribution. Flow resistance distribution of fluid is the basis of comprehensively grasping the permeability of permeable asphalt mixture. This study aimed to investigate the flow resistance of fluid in permeable asphalt mixture. Considering the influence of anisotropy of permeable asphalt mixture, the vertical and transverse permeability tests of five types of permeable asphalt mixture were carried out using multidirectional permeability test instrument developed by our research group. The fitting equation of permeability was determined by comparing Darcy's law with Forchheimer equation. Moreover, the flow resistance is usually considered as an effective parameter to reveal the structural permeability. The connective void content of permeable asphalt mixture is important to calculate flow resistance. Accordingly, it is necessary to obtain the transverse and vertical connective voids of the asphalt mixture considering the influence of anisotropy. Therefore, a program for calculating the multi-directional connective void content was developed based on the theory of projection reconstruction. On this basis, a pore throat model was applied to reveal the variation of flow resistance of asphalt mixture. The results show that the weight of inertia resistance and viscous resistance is different in various seepage velocities. The viscous resistance is dominant when the fluid flow velocity is less than 0.0087 m/s under experimental conditions, and the inertial resistance is dominant when the fluid flow velocity is greater than 0.0087 m/s. The viscous resistance and inertia resistance of fluid are affected by the anisotropy and structure type of permeable asphalt mixture. When the vertical void content decreases by 3.3%, the corresponding viscous and inertial resistance increase by 7.92 kPa/m and 0.84 kPa/m, respectively. For the transverse void, the viscous and inertial resistance increase by 3.19 kPa/m and 2.02 kPa/m respectively as the content decreases by 3.5%. The influence of void structure of permeable asphalt mixtures on fluid flow is revealed from a microscopic perspective, which can be used to guide the optimization design of gradation of permeable asphalt mixtures. [ABSTRACT FROM AUTHOR]

The ability of a blood clot to modulate blood flow is determined by the clot's resistance, which depends on its structural features. For a flow with arterial shear, we investigated the characteristic patterns relating to clot shape, size, and composition on the one hand, and its viscous resistance, intraclot axial flow velocity, and shear distributions on the other. We used microfluidic technology to measure the kinetics of platelet, thrombin, and fibrin accumulation at a thrombogenic surface coated with collagen and tissue factor (TF), the key clot-formation trigger. We subsequently utilized the obtained data to perform additional calibration and validation of a detailed computational fluid dynamics model of spatial clot growth under flow. We then ran model simulations to gain insights into the resistance of clots formed under our experimental conditions. We found that increased thrombogenic surface length and TF surface density enhanced the bulk thrombin and fibrin generation in a nonadditive, synergistic way. The height of the platelet deposition domain—and, therefore, clot occlusivity—was rather robust to thrombogenic surface length and TF density variations, but consistently increased with time. Clot viscous resistance was non-uniform and tended to be higher in the fibrin-rich, inner "core" region of the clot. Interestingly, despite intraclot structure and viscous resistance variations, intraclot flow velocity variations were minor compared to the abrupt decrease in flow velocity around the platelet deposition region. Our results shed new light on the connection between the structure of clots under arterial shear and spatiotemporal variations in their resistance to flow. [ABSTRACT FROM AUTHOR]

The article considers regularities of the influence of forces of viscous resistance generated by the damper device in the cylindrical hinges of the nodes connect the links of the crane-manipulator units mobile transport-technological ma-chines. The specified effect is considered on the efficiency of the damping of oscillations of the metal in the process of operation, due to the presence of increased clearances due to wear of the holes of the hinge eyes. It is shown that the force of viscous resistance should be considered in addition to the generated damping devices forces of elastic resis-tance, as the latter determine the effectiveness of damping in general. The main role of forces of viscous resistance is the dissipation of energy of an oscillatory turning movement of the mating parts of the metal structures due to oscilla-tory displacement of the hinge pin within the hinge gap until the complete decay of oscillations. Considered in relation to the crane-manipulator installing mobile transport-technological machines AST-4-A the effect of the action of forces of viscous resistance is almost not observed when the coefficient of viscous damping less than 0.01 MN∙s/m, in the range 0,01...0,05 MN∙s/m this influence begins to manifest itself more and more noticeable, in the range of 0,05...0,4 MN∙s/m has a lot of damping vibrational displacement of the hinge pin within the gap, while the coefficient of viscous damping more than 0.4 MN∙s/m oscillatory process becomes aperiodic with an almost complete attenuation in the range of one oscillation of the hinged finger.

This research aims the influence analysis of the resistance forces created by viscoelastic dampers in the cylindrical hinges of the manipulators of the transport and technological machines, as well as to the effectiveness of oscillation damping of the metal structure during operation. The construction of the hinged dampers that has been designed by the authors is original. The mathematical model of joint operation of the cylindrical hinge with an excessive backlash and viscoelastic damper has been formed in the article. It is shown that the determinative role of viscous resistance forces involves irreversible energy dissipation of the oscillating rotary movement of the neighboring manipulator links due to oscillating displacement of the hinge pin within the backlash limits in the hinge until the oscillations fade completely. The quantitative analysis of the effectiveness of reducing impact load of the metal structure is performed; moreover the dependence correlations of dynamic process characteristics and engineering factors of the hinged dampers have been determined. Depending on the correlation between stiffness and viscosity of the damper, the effect of viscous resistance forces may not practically occur; it may lead to intensive damping of oscillatory displacement of the hinge pin within the clearance limits. In the latter case, the oscillation process becomes aperiodic with practically complete fading within one oscillation of the hinge pin. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: The manipulation of a nanoconfined fluid flow is a great challenge and is critical in both fundamental research and practical applications. Compared with chemical or biochemical stimulation, the use of temperature as controllable, physical stimulation possesses huge advantages, such as low cost, easy operation, reversibility, and no contamination. We demonstrate an elegant, simple strategy by which temperature stimulation can readily manipulate the nanoconfined water flow by tuning interfacial and viscous resistances. We show that with an increase in temperature, the water fluidity is decreased in hydrophilic nanopores, whereas it is enhanced by at least four orders of magnitude in hydrophobic nanopores, especially in carbon nanotubes with a controlled size and atomically smooth walls. We attribute these opposing trends to a dramatic difference in varying surface wettability that results from a small temperature variation. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Dalian University of Technology / Dalian Ligong Daxue Xuebao is the property of Journal of Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Basing on the equations of three-dimensional problem of elasticity theory, asymptotic solutions of non-classical boundary value problems of natural vibrations of orthotropic shells in the presence of viscous internal resistance are obtained, when the top front surface of the shell is given with two choices of spatial boundary conditions, and a displacement vector is given at the bottom surface. The characteristic equations for the determination of natural frequencies are derived. Functions of boundary layer type and characteristic equations for detecting the speed of boundary layer vibrations damping from the edge surface into the shell are obtained.

In the presented paper a simple method was applied to calculate a viscous and inertial resistant coefficient of a porous material substituting a flared fin heat sink geometry. Based on the performed calculations plots showing the variation of the resistant coefficients with heat sink height and distance between fins were made. In addition, empirical relations that can be applied for a calculation of required resistant coefficients were proposed. Finally a comparison of a flow characteristic both for the real heat sink and its porous representation for selected cases was shown. In the analysis an air flow in room temperature was investigated. Analyses were performed for a range of Reynolds number: 8.3·10 3 – 1.7 10 4 . All the necessary numerical calculations were made in ANSYS Fluent commercial code, Microsoft Excel and Matlab. [ABSTRACT FROM AUTHOR]

The prediction of wave resistance in naval architecture is an important aspect especially at high Froude numbers where a great percentage of total resistance of ships and submerged bodies is caused by waves. In addition, during hull form optimization, wave resistance characteristics of a ship must closely be observed. There are potential, viscous and experimental methods to determine the wave resistance of a ship. Reynolds-averaged Navier–Stokes equation–based methods usually follow the experimental method that determines the form factor first. However, it is proven in recent studies that the form factor changes with the Reynolds number. As the Reynolds number increases, this change in the form factor is being neglected. In this study, a Reynolds-averaged Navier–Stokes equation–based prediction of wave resistance is presented that overcomes this flaw. The methodology is validated with the benchmark problems of submerged and surface-piercing bodies to determine the effectiveness of the proposed method. The method is also validated by experiments carried out at the Ata Nutku Ship Model Testing Laboratory of Istanbul Technical University for a totally submerged ellipsoid and the benchmark KRISO Containership. Results reveal the robustness of the present methodology. [ABSTRACT FROM AUTHOR]

The viscous resistance of a tourist submarine suitable for working in the Red Sea area has been calculated at different speeds using Computational Fluid Dynamics (CFD). The finite volume RANSE code CFX has been used to study the resistance and the hydrodynamic characteristics of the flow around the tourist submarine at different speeds. The Omega Reynolds Stress turbulent model has been used in different numerical simulations. Half of the computational domain was used in this research work due the symmetry of the tourist submarine hull. The mesh generation software of the CFD code has been used for generating the required unstructured tetrahedral grid for the numerical simulations. The numerical results for the tourist submarine viscous resistance are comparable with the available results from other sources. [ABSTRACT FROM AUTHOR]

To examine debris flow mobility with respect to the runout distance and velocity, strength parameters (e.g., the Bingham and Herschel-Bulkley yield stresses, undrained shear strength, flow behavior index) are needed. In modeling debris flow, the Bingham and Herschel-Bulkley yield stresses are often used, but they lead to large differences in the runout distance and velocity of the failed masses. It is very difficult to determine the true yield stress. In this study, we propose using the viscous resistance, obtained from the normalized flow curve resulting when the shear stress and shear rate are divided by reference shear stress and shear rate values (i.e., $\log \tau /\tau _0 - \log \gamma /\gamma _0 $). The viscous resistance and strength parameters are compared from the viewpoint of geotechnology and rheology. The shear strength and flow characteristics of marine sediments can be characterized in terms of the viscous resistance and the viscous resistance is linearly related to other strength parameters (e.g., viscosity, yield stress and undrained shear strength). Thus, the viscous resistance provides a simple and easy approach for approximating strength and flow parameters in debris flow dynamics. [ABSTRACT FROM AUTHOR]

The paper investigates the performance of the ball packed-bed regenerator from the study of inertial, viscous resistance and thermal characteristics of the packed bed regenerator. In the first part of the paper the inertial resistance and viscous resistance characteristics of the regenerator based on previous experimental data are studied. The Ergun's equation has been accepted widely to calculate the pressure drop in the thermal regenerator with its two coefficients, 150 and 1.75. Revised Ergun's equation is achieved for ball packed regenerator. The values of coefficients of Ergun's equation calculated by simulation are compared with the experimental results. In the second part of the paper the thermal characteristics of the regenerator are studied by using 3-D transient model. The variation of pressure drop, temperature, effectiveness, velocity along the regenerator bed is studied and presented. [ABSTRACT FROM AUTHOR]