Viscous Resistance Coefficient Research Articles

Research on dynamic response of centrifugal pendulum vibration absorber based on hybrid damping model

The application of the centrifugal pendulum vibration absorber (CPVA) has expanded from the aerospace sector to the automotive sector. To date, in most previous studies, viscous damping has been assumed to be present between the absorber and rotor, and damping has been neglected in other studies. To reflect and control the dynamic behaviour of the CPVA in vehicular applications realistically, a hybrid damping model incorporating viscous damping and rolling resistance was developed in this study and validated by conducting tests. Under the combined action of the centrifugal force, gravity, viscous resistance, and rolling resistance, an equation of motion of the CPVA was established using the Lagrangian function equation of the second type. The wear state of the kinematic pair between the absorber and rotor, which is common in practical applications, was included into a mathematical model in which the rolling resistance coefficient changes with the travel of the absorber, whereas the viscous resistance coefficient remains unchanged. A model was established to simulate the response of the absorber under a wide range of working conditions, and corresponding tests were performed. Compared with the results obtained using only viscous damping as reported in other studies, those of the proposed hybrid damping model are more consistent with the experimental results. This work fills the existing research gap and lays a foundation for further control of the dynamic behaviour of CPVAs in the gravitational field, particularly at low rotational speeds.

Effect of permeable spacer structure on energy loss and mass transfer in reverse osmosis membrane modules

This study used numerical simulation to investigate the effects of a novel permeable cylindrical-flow distributor on energy loss and mass transfer in reverse osmosis (RO) membrane modules. The analysis focused on variables, such as Reynolds number, inlet concentration and flow incidence angle, influencing the improvement of water production efficiency in RO membranes and the reduction of concentration polarisation on the membrane surface. The membrane surface shear stress, vorticity, permeate flux and concentration polarisation factor were used to describe these effects. To better explain the performance of the permeable flow distributor, the viscous resistance coefficient (Du) in the porous media model was used to measure the permeability of the flow distributor. Furthermore, a produced water energy consumption factor (JCP) was defined to represent the energy required for unit water production. The results indicate that the permeable flow distributor significantly reduces pressure loss in the membrane channels, avoiding the high energy consumption associated with traditional flow distributors in RO processes. The Du exhibits an optimal value in the range of 1e8 to 1e10, which maximises the JCP, leading to a 32.9 % improvement compared to traditional impermeable flow distributors. This achievement enables energy-efficient and effective desalination of seawater.

Transfer Learning with Deep Neural Network toward the Prediction of Wake Flow Characteristics of Containerships

In this study, deep neural network (DNN) and transfer learning (TL) techniques were employed to predict the viscous resistance and wake distribution based on the positions of flow control fins (FCFs) applied to containerships of various sizes. Both methods utilized data collected through computational fluid dynamics (CFD) analysis. The position of the flow control fin (FCF) and hull form information were utilized as input data, and the output data included viscous resistance coefficients and components of propeller axial velocity. The base DNN model was trained and validated using a source dataset from a 1000 TEU containership. The grid search cross-validation technique was employed to optimize the hyperparameters of the base DNN model. Then, transfer learning was applied to predict the viscous resistance and wake distribution for containerships of varying sizes. To enhance the accuracy of feature prediction with a limited amount of data, learning rate optimization was conducted. Transfer learning involves retraining and reconfiguring the base DNN model, and the accuracy was verified based on the fine-tuning method of the learning model. The results of this study can provide hull designers for containerships with performance evaluation information by predicting wake distribution, without relying on CFD analysis.

A new method to estimate the resistance coefficients of net panels modeled as porous media

Modeling net panels as thin porous media is an effective approach to carry out computational fluid dynamics (CFD) simulations of fishing nets and aquaculture cages. Existing methods to estimate the resistance coefficients for these porous media are based on simplified analytical models that relate these coefficients to the drag and lift coefficients of the panel. We propose a new method that uses a CFD model of the flow through a layer of porous media to estimate the resistance coefficients from regression analysis with experimental data. To increase the computational performance, the CFD model response is pre-calculated and interpolated in the regression analysis. The proposed method is applied to different net panels compared with existing methods. Results show that it provides better results than previous methods. Estimating both the inertial and the viscous resistance coefficients always provides better results than estimating just the inertial coefficients and it does not complicate the regression analysis with the proposed method. The method is easy to implement, fast and it could be used to estimate the resistance coefficients of materials other than net panels, since it does not make any assumption about the geometric characteristics of the actual material.

Towards an accurate CFD prediction of airflow and dispersion through face mask

Given the difficulty of experimental measurement of respiratory airflow and dispersion through a face mask, accurate numerical simulation is an important method to increase the understanding of the health effect of face masks and to develop high-performance ones. The objective of this study is to develop such an accurate modeling framework based on computational fluid dynamics (CFD) theory and method. For model validation, the flow characteristics through the face mask were tested experimentally, and the air speed and exhaled pollutant concentration in the breathing zone were measured with human subjects. The influence of gird division, time step size, and turbulence model on simulation accuracy were investigated. The result shows that the viscous resistance coefficient and inertial resistance coefficient of face masks (surgical masks) were 3.65 × 109 and 1.69 × 106, respectively. The cell size on the surface of face masks should not be larger than 1.0 mm; the height of the first layer cells near the face masks should not be larger than 0.1 mm; and the time step sizes discretizing the breathing and coughing periods should not be more than 0.01 s and 0.001 s, respectively. The results given by LES model show closer agreement with the experimental data than RANS models, with approximately 10% relative deviation for the air speed near the face mask. Overall, the SST k-ω model performs the best among the RANS models, especially for the air speed. The findings obtained form a CFD modeling framework for an accurate prediction of airflow and dispersion problems involving face masks.

Numerical Investigations about Flow Resistance Values for Stirling Type Pulse Tube Cryocooler

Pulse tube cryocoolers are extensively used for space application because of simplicity and reliability in operation. Many researchers have attempted the numerical analysis of the oscillatory flow inside the cryocooler, however, the precise predictions of the exact behavior of the gas inside the cryocooler using CFD has not yet been reported. While performing the CFD analysis of cryocooler, the values of inertial and viscous resistance coefficients play vital role and highly contributes to the pressure drop taking place in porous media. The prime objective of present work is to analyze the effect of these resistance values on performance of cryocooler. A single stage Stirling type pulse tube cryocooler model from literature is employed to perform the CFD analysis and the results obtained from the analysis are validated to ensure that methodology used for analysis is correct. The resistance values mentioned in the literature are applicable for steady and unidirectional flows. The model is further modified for the values of resistances for oscillating flow at room temperature and oscillating flow at cryogenic temperature. It is observed that performance predictions for oscillating flow at cryogenic temperature resistance values yields substantially lower temperature than all other cases. As experimental validation of this model is still not reported in literature, the reliability of accurate resistance values is not confirmed. Hence, another model of single stage Stirling type pulse tube cryocooler from literature is numerically analyzed for various operating conditions and is compared with its experimental performance, and found to be in fair agreement.

Face shield intensifies inhaled exposure to self-generated bio-effluents

The presence of a face shield may block the forward and upward dilution of bio-effluents, generated from one's own exhalations and skin, through the breathing zone, which might thus intensify the user's inhaled exposure, especially for long-term use. The objective of this study is to quantify this exposure risk. The flow characteristics of the porous region at the top of a typical face shield were tested experimentally. The viscous resistance coefficient and inertial resistance coefficient of the porous region were 4.9 × 107 and −402, respectively. The influence of breathing mode (via mouth and nose), pulmonary ventilation rate (6–8 L/min), and bio-effluents generation location (i.e., exhalation, groin, and armpit) on the exposure risk of bio-effluents were then studied by computational fluid dynamics (CFD) technology in combination with the species transport model. The inhaled fraction (iF) index was used to assess the exposure risk. A face shield can considerably increase the exposure risk, the inhaled fraction index being increased from 0.28% to 2.97% for skin pollutants, and from 2.25% to 6.96% for exhaled pollutants. It means that the fraction of oxygen (O2) in the inhaled air of face shield wearers is 20.58%, being 2% less than that without face shield. For face shield wearers, a higher pulmonary ventilation rate and breathing through nose would further increase the exposure risk. This information would be important boundary conditions for accurate simulation and design of face shield as well as the design of protective clothing.

CFD analysis and calculation models establishment of leakage of natural gas pipeline considering real buried environment

Different from the above ground pipeline, the soil characteristics and ground conditions have a great impact on the risk of leakage accident for buried natural gas pipeline. In this paper, the effects of ground conditions and soil characteristics on methane leakage and diffusion were studied by using numerical simulation. The two processes of methane leakage and diffusion, the methane leakage rate and the methane diffusion Early Warning Boundary (EWB) were investigated. Finally, based on the least square method and multiple regression theory, the calculation models of methane leakage rate and EWB were established. The results showed that: Compared with Unhardened Surface Ground (UHSG) condition, Hardened Surface Ground (HSG) increased the distribution of pressure, velocity and methane concentration in soil. The viscous resistance coefficient and inertial resistance coefficient of soil had a great influence on the methane leakage rate, while the ground conditions did not. Both ground conditions and soil characteristics had a certain impact on the EWB of methane diffusion. The average error of methane leakage rate direct calculation model was 4.48%, and the average error of EWB calculation model under HSG and UHSG condition was 3.59% and 7.77% respectively. The methane leakage rate and the EWB calculation models suggest the soil characteristics as independent variables and can provide the rapid calculation of leakage rate and EWB under any soil characteristics without the help of computer iterative solution. The methane leakage rate direct calculation model makes up for the vacancy of calculation method of leakage rate of buried pipeline under different soil characteristics.

Measurement and Numerical Simulation of Coal Spontaneous Combustion in Goaf under Y-type Ventilation Mode.

In the process of advancing the working face, the temperature rise and oxidation characteristics of residual coal in goaf and the prediction of index gas are of great significance to mine fire prevention and safety production. Based on the coal spontaneous combustion test, the oxygen consumption and heat release characteristics of coal spontaneous combustion were analyzed by taking coal samples at the working face and carrying out temperature-programmed experiments in the laboratory. The characteristic temperature and index gas of coal spontaneous combustion were determined as the judgment bases of “three zones” of spontaneous combustion in goaf, and the influencing factors of coal spontaneous combustion in goaf under Y-type ventilation were analyzed. Based on the test results, the changes of gas composition in goaf during the advancing of the W1310 working face were monitored. According to the actual situation of the W1310 working face in the Gaohe energy mine of Lu’an group, the multifield three-dimensional numerical simulation calculation and analysis of gas composition in goaf were carried out, and the distribution of oxygen concentration field in goaf under different air volume ratios of machine roadway and air roadway was studied. Through the analysis of the parameters of porous media in the goaf, combined with the actual situation, the user-defined function was compiled for the key parameters such as porosity, viscous resistance coefficient, and inertial resistance coefficient of porous media in the goaf. The three-dimensional seepage field, gas concentration field, oxygen concentration field, and pressure field of the gas components in goaf during the advancement of the goaf working face were simulated. The comparison of the numerical simulation results with the field-measured results shows good agreement. In order to consider safety, the numerical simulation results with a wide oxidation temperature rise zone are used for linear regression, and the regression equation is used to dynamically determine the O2 concentration at a point away from the goaf and to determine the “three-zone” state of the point, which is of great significance to guide the progress of the working face and safe production.

Numerical study on the naturally captured air volume of outside cabin heat exchanger for wind power generation

In this paper, the outside cabin heat exchanger based on the porous media approach was established. The effects of altitude, viscous resistance coefficient, inertial resistance coefficient, and core thickness on the naturally captured air volume of the heat exchanger were investigated by numerical simulation. Results showed that the naturally captured air volume of the heat exchanger tends to be larger on both sides and smaller in the middle, and there is a quasi-linear increase proportional to the incoming wind velocity. With the increment of altitude, viscous resistance coefficient, and inertial resistance coefficient, the average naturally captured air volume of the heat exchangers shows a downward trend. The trend would be clear with the increment of the incoming wind velocity, nevertheless, the effect of core thickness is weak. In addition, the design values of the viscous resistance coefficient and the inertial resistance coefficient should be restricted in the order of 106 and below 500, respectively. Based on the weak effect of the naturally captured air volume of the heat exchanger, the thickness of the core can be appropriately increased to ensure the heat transfer area of the heat exchanger.

Energy-efficient equipment for disintegration of extremely strong materials

This research aims to reduce the power input of strong material disintegration and to improve the final product quality. The energy-efficient method of disintegration is proposed for extremely strong materials and industrial waste using vibropercussion crushers composed of two mobile crushing bodies free from stiff kinematic links and operating in strictly synchronous phase opposition. The crushers implement the phenomenon of self-synchronization of drive unbalance-mass vibration generators, which greatly simplifies the design and lowers the dynamic loads imposed on the machine components. The influence exerted by the material under treatment on the dynamics of vibropercussion crushers is studied. In particular, the procedure is developed for the while-in-operation calculation of the viscous resistance coefficient and, as a consequence, average vibration amplitudes of effectors of the machine with regard to the loading. The common method of taking the influence of the process material on the vibration machine dynamics in the form of a linear viscous damper is inapplicable in case of vibropercussion systems and needs amendment. The conditions of steady-state synchronous co-phase rotation of vibration generators are determined. Alternatively, performance of the crushers drops down to total failure of crushing. The recommendations on selecting science-based geometrical and inertia parameters for the vibropercussion crushers are given. The recommendations should be taken into account in the machine design and engineering to ensure efficient and reliable steady-state operation. The study is implemented using the approach of vibration engineering and theory of synchronization of mechanical vibration generators. The theoretical results are compared with the experimental data.

Study on the pressure drop of crude oil-water with surfactant flow in porous media

An experimental study which aimed to analyze the pressure drop when the oil-water two-phase flow mixed with surfactant flows through porous medias was introduced. Porous media with the quartz sands mainly ranging from 0.2–1.2 mm and the oil-water two-phase system with Liaohe crude oil and water were prepared. Surfactant compounded with petroleum sulfonate (PS-30) and dodecyl dimethyl Betaine (BS-12) was used to improve the fluidity of oil-water mixture. The interfacial tension, viscosity and contact angle of the oil-water-surfactant mixture were tested. Then the pressure drop experiments were conducted, which considered three influence factors including the standard deviation of the granularity, the concentration of the surfactant and the ratio of oil to water. Forchheimer resistance model was used to fit the results, and the influence of three factors on the viscous resistance coefficient α −1 and inertial resistance coefficient C2 were discussed. The results indicated that the compound mixture PS-30/BS-12 is significantly better than other surfactants in terms of pressure drop, and the appropriate concentration of the surfactant is 0.3%. Pressure drop of the mixture can be well fitted by Forchheimer resistance model but α−1 and C2 still needed to be adjusted by test.

Dynamic Loading Research of the Gondola car Supporting Structure with an Elastic-Viscous Filler in a Center Sill

Purpose. The work aims to investigate dynamic loading of the supporting structure of a gondola car with an elastic-viscous filler in the center sill by means of mathematical modeling. Methodology. Mathematical modeling of the dynamic loading of the supporting structure of a gondola car with a closed center sill filled with a filler with elastic-viscous properties has been carried out. The case of the highest load on the supporting structure of the gondola car in operation is taken into account – a shunting collision, taking into account the action of a load of 3.5 MN on the rear stop of the automatic coupler. To determine the dynamic loading of a gondola car, a mathematical model formed by prof. G. I. Bohomaz was used. However, within the framework of this study, the model was refined by adapting it to the determination of the dynamic loading of a gondola car. It also takes into account the friction forces arising between the center plates of the body and the center pivots of the bogies, as well as the properties of the energy-absorbing material. The solution of the mathematical model was carried out in the MathCad software package. In this case, the differential equations of motion were reduced to the Cauchy normal form, and then integrated using the Runge-Kutta method. Initial displacements and speeds are taken equal to zero. The calculation was carried out on the example of a universal gondola car model 12-757 built by Kriukivskyi Carriage Works PJSC (Kremenchug) on standard bogies 18-100. Findings. Accelerations are obtained as components of a dynamic load acting on a gondola car with a closed center sill structure filled with an elastic-viscous filler. It was found that with the stiffness of the center sill filler of 82 kN/m, as well as the viscous resistance coefficient of -120 kN∙s/m, the maximum accelerations of the gondola car supporting structure is about 37 m/s2 (0.37g). Originality. A mathematical model is proposed for determining the dynamic loading of a gondola car with a closed structure of a center sill filled with an elastic-viscous filler. The model makes it possible to obtain accelerations as the components of the dynamic loading acting on the supporting structure of the gondola car, taking into account the improvement measures during a shunting collision. Practical value. The results of the research will help to reduce the damage to the supporting structures of gondola cars in operation, reduce the cost of their maintenance, create developments in the design of innovative structures of rolling stock, as well as increase the efficiency of its operation.

Numerical investigation on fluid dynamic characteristics around shoulder ventilation of submarine-launched vehicle

In order to study the influence of the ventilating cavitation flow at the shoulder of a submerged-launched vehicle on the surface hydrodynamic characteristics, a three-dimensional potential model for the shoulder ventilation of the vehicle was established based on the homogeneous multiphase flow theory, standard RNG k-ε model, Singhal cavitation model and overlapping grid technology, and the numerical simulation of the unsteady evolution process of the ventilated cavitation flow was carried out, and the cavitation flow morphology evolution, surface pressure distribution and resistance characteristics under different ventilation rates were compared. The results showed that the thickness and length of the ventilated cavitation flow in the early stage of fusion continue increased with the increasing of ventilation volume, and its thickness and length changed slightly in the later stage; when the exhaust position did not change and the ventilation volume was within a certain range, the differential pressure resistance coefficient and viscous resistance coefficient decreased with the increasing of internal pressure of the ventilated cavity.

An approach based on the porous media model for numerical simulation of 3D finned-tubes heat exchanger

Developing efficient and compact heat exchangers is of important significance to improve the energy utilization efficiency of entire society. 3D finned-tubes, as a kind of passive enhanced heat exchange technology, are widely used for improving the thermal-hydraulic performance of the heat exchanger. In the numerical study of 3D finned-tube heat exchanger, on account of the limit by computing capacity, it is very hard to carry out the full-size numerical simulation, so the method based on porous media model becomes a common approach for numerical simulation of the heat exchanger. In the present study with the discrete 3D finned-tube heat exchanger as the study object, a kind of approach based on the porous media model under the cylindrical coordinate system is proposed. In this approach, only the fin region on the surface of base tube is simplified to the annular porous media zone while the region beyond the fin tips is still regarded as the pure gas flow region. The resistance coefficients of annular porous media, which are used to represent the retardation effects of the fin on the fluid motion, are given under the cylindrical coordinate system. Based on serialized numerical simulations of the fin configuration model seen by the air when it flows in the circumferential, axial and radial direction, the viscous resistance coefficients and inertial resistance coefficients of the annular porous media zone in each direction are obtained through fitting. Through comparison of simulated values between the porous media model and 3D finned-tube practical physical model, it is found that the pressure drop calculated by the method based on porous media model proposed in this study agree well with that based on the real physical model. The pressure drop predicted by the porous media model also agree well with the experimental results. In the approach based on porous media model, the grid number and calculation cost are smaller than those in practical physical model. Especially in case of tube bundles, number of grids applied in the simulation based on porous media model is far less than the grid quantity in the practical physical model simulation, but the pressure drop obtained by the porous media model is almost equal to the result obtained from the practical physical model. Besides, in the present method, only the fin zone is deemed as the porous media, so the flow field in the region beyond the fin tips will still be solved as same as that in the full-size simulation. Thus more flow details within the heat exchanger can be captured. The approach based on porous media model under the cylindrical coordinate system proposed can be used in the simulation study of the internal flow field of 3D finned-tube heat exchangers in actual scale. On this basis, this approach can contribute to optimization design of the 3D finned-tube heat exchanger.

Research and empirical Analysis of Traffic flow Modeling based on fluid Mechanics

In this paper, the overtaking lane change flow is introduced, and the corresponding traffic flow continuity equation is established. Through the differential analysis of traffic flow parameters, the motion differential equation of road traffic flow is established. Compared with fluid mechanics, according to Newton’s second law, the simple calculation of traffic pressure, viscous resistance coefficient and viscous resistance is put forward, and the interference from downstream traffic wave is defined as the viscosity of traffic flow, and the difference between wave velocity and maximum wave speed is the coefficient of viscous resistance along the way. the viscous resistance along the route is proportional to the length of the lane, the rate of change of flow along the direction of traffic flow and the coefficient of viscous resistance along the route. The model can obtain the relationship between traffic flow parameters. The simulation example shows that the model can reflect the basic characteristics of traffic flow.

Determination of the viscous resistance of a plane damper with a newtonian fluid using the equation similarity with the shaft torsion problem

This paper describes the similarity between the Reynolds equation for a thin viscous layer of liquid in a plane damper and the commonly known equations of membrane deflections and equations of free torsion of a shaft. Based on the similarity of equations, a viscous resistance coefficient of a plane damper in the normal direction was determined. An approximate formula of the viscous friction coefficient in tangential direction was derived using the Couette flow assumption. The paper shows that acquiring the same viscous friction coefficients in the normal and tangential direction for a plane damper with a thin lubricating layer is not possible.

A mechanical model for spherical fragments penetrating gelatine

The behaviour and effects of a spherical fragment penetrating a simulant and those of biological tissue are similar. To accurately describe the interaction between spherical fragments and muscle tissue, this study first discusses the wounding mechanism and establishes a mechanical model considering the effects of strain rate based on the properties of gelatine, which is a widely used representative simulant in physical surrogates for muscle tissue. Subsequently, experiments wherein gelatine was penetrated by spherical fragments with diameters of 3, 4, and 4.8 mm were conducted. The inertial and viscous resistance coefficients were identified using the least squares method and the experimental results obtained for the 4-mm spherical fragment. Numerical calculations show that the mechanical model agrees well with the experimental values. Further, the mechanical model's ability to adequately describe the motion of spherical fragments penetrating gelatine with good generality is proved. The proposed model can therefore provide a scientific basis for small arms ammunition design and protection evaluation.

Flow dynamic in a packed bed filled with Ni‐Al2O3 porous catalyst: Experimental and numerical approach

AbstractNumerical simulations and experiments have been carried out to explore the effect of particle shapes on the pressure drop and the loss factor in a packed fixed bed filled with a porous catalyst. The packed bed is presented by the Ni‐Al2O3 catalyst of the different shapes. The commercial program ANSYS Fluent is used for the analysis; more than 20 mln cells are used for computational fluid dynamics (CFD) modeling. The catalyst particles were set as a porous medium with the viscous resistance coefficients and the inertial resistance coefficients. The comparison of the pressure drops between the experimental and simulation results show a good correlation with the divergence of results <8%. To determine the effect of the porosity properties of the medium on the numerical results, two cases of CFD modeling were realized (with taking into account the porous medium properties and without it). The discrepancy between results increases with an increasing gas flow rate.

Time-dependent deformation of artificial muscles based on Nylon 6

Considering the potential applications of the Nylon 6 with thermal-induced deformation, we studied the creep deformation of non-twisted Nylon 6 wires and Nylon 6 artificial muscles as functions of annealing temperature. For comparison, we also studied the creep deformation of chicken muscle fibers in a temperature range of 20 to 35 °C. The experimental results showed that we could use the standard linear viscoelastic model to describe the creep deformation of the chicken muscle fibers, the non-twisted Nylon 6 wires, and the Nylon 6 artificial muscles. A simple method was developed to calculate the mechanical (elastic) constants and viscous resistance coefficient (viscosity) of the three different materials. The activation energy for the creep deformation of the chicken muscle fibers in the temperature of 20 to 35 °C was 18.79 kJ/mol. For the non-twisted Nylon 6 wires, the activation energy for the creep deformation was generally larger than that of the chicken muscle fibers, and was dependent on the annealing temperature. For the Nylon 6 artificial muscles, the activation energy for the creep deformation was smaller than that of the chicken muscle fibers.