scholarly journals Hydrodynamics of Droplet Impingement on a Thin Horizontal Wire

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Jiayi Zheng ◽  
Jing Wang ◽  
Yanshun Yu ◽  
Taotao Chen
Keyword(s):  
Dynamic Equilibrium ◽  
Flow Regimes ◽  
Droplet Surface ◽  
Droplet Impingement ◽  
Pressure Distributions ◽  
Transient Velocity ◽  
High Pressure Zone ◽  
Hydrodynamic Behaviors ◽  
The Impact ◽  
Horizontal Wire

A model of droplet impacting on a thin horizontal wire is developed and numerically analyzed via level set method (LSM). Through varying the impact velocity, the flow regimes of droplet impacting on the wire are examined and analyzed. The detailed hydrodynamic behaviors including transient velocity and pressure distributions as well as the evolution of the gas-liquid interface during droplet impingement are investigated. The results indicate that the hanging mode, merging mode, and splitting mode appear during the droplet impingement on a thin horizontal wire. In merging mode, the tiny bubbles converge to big bubbles arising from the inertia difference between the liquid and the gas make. Due to the dynamic equilibrium between the friction of the thin wire and the droplet surface tension, the double reflux zone and the high-pressure zone are only observed in hanging mode rather than in merging mode and splitting mode. The flow regimes diagram depending on We and Bo is provided to represent the flow regimes of droplet impacting on a thin horizontal wire. The corresponding exponential correlations are given in form of We = aebBo to distinguish the boundaries between these droplet flow regimes.

A Study on Evolution of Splat Radius and Temperature in Thermal Spray Process

2018 ◽  
Author(s):  
Manpreet Dash ◽  
Sangharsh Kumar ◽  
Partha Pratim Bandyopadhyay ◽  
Anandaroop Bhattacharya
Keyword(s):  
Heat Transfer ◽  
Thermal Spray ◽  
Molten Metal ◽  
Spray Deposition ◽  
Substrate Surface ◽  
Metal Droplet ◽  
Droplet Impingement ◽  
Impact Process ◽  
The Impact ◽  
Maximum Spreading

The impact process of a molten metal droplet impinging on a solid substrate surface is encountered in several technological applications such as ink-jet printing, spray cooling, coating processes, spray deposition of metal alloys, thermal spray coatings, manufacturing processes and fabrication and in industrial applications concerning thermal spray processes. Deposition of a molten material or metal in form of a droplet on a substrate surface by propelling it towards it forms the core of the spraying process. During the impact process, the molten metal droplet spreads radially and simultaneously starts losing heat due to heat transfer to the substrate surface. The associated heat transfer influences impingement behavior. The physics of droplet impingement is not only related to the fluid dynamics, but also to the respective interfacial properties of solid and liquid. For most applications, maximum spreading diameter of the splat is considered to be an important factor for droplet impingement on solid surfaces. In the present study, we have developed a model for droplet impingement based on energy conservation principle to predict the maximum spreading radius and the radius as a function of time. Further, we have used the radius as a function of time in the heat transfer equations and to study the evolution of splat-temperature and predict the spreading factor and the spreading time and mathematically correlate them to the spraying parameters and material properties.

scholarly journals Influence of the Spatial Pressure Distribution of Breaking Wave Loading on the Dynamic Response of Wolf Rock Lighthouse

2021 ◽  
Vol 9 (1) ◽  
pp. 55
Author(s):  
Darshana T. Dassanayake ◽  
Alessandro Antonini ◽  
Athanasios Pappas ◽  
Alison Raby ◽  
James Mark William Brownjohn ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Pressure Distribution ◽  
Distinct Element ◽  
Breaking Waves ◽  
Breaking Wave ◽  
Wave Loading ◽  
Wave Impact ◽  
Pressure Distributions ◽  
Impact Area ◽  
The Impact

The survivability analysis of offshore rock lighthouses requires several assumptions of the pressure distribution due to the breaking wave loading (Raby et al. (2019), Antonini et al. (2019). Due to the peculiar bathymetries and topographies of rock pinnacles, there is no dedicated formula to properly quantify the loads induced by the breaking waves on offshore rock lighthouses. Wienke’s formula (Wienke and Oumeraci (2005) was used in this study to estimate the loads, even though it was not derived for breaking waves on offshore rock lighthouses, but rather for the breaking wave loading on offshore monopiles. However, a thorough sensitivity analysis of the effects of the assumed pressure distribution has never been performed. In this paper, by means of the Wolf Rock lighthouse distinct element model, we quantified the influence of the pressure distributions on the dynamic response of the lighthouse structure. Different pressure distributions were tested, while keeping the initial wave impact area and pressure integrated force unchanged, in order to quantify the effect of different pressure distribution patterns. The pressure distributions considered in this paper showed subtle differences in the overall dynamic structure responses; however, pressure distribution #3, based on published experimental data such as Tanimoto et al. (1986) and Zhou et al. (1991) gave the largest displacements. This scenario has a triangular pressure distribution with a peak at the centroid of the impact area, which then linearly decreases to zero at the top and bottom boundaries of the impact area. The azimuthal horizontal distribution was adopted from Wienke and Oumeraci’s work (2005). The main findings of this study will be of interest not only for the assessment of rock lighthouses but also for all the cylindrical structures built on rock pinnacles or rocky coastlines (with steep foreshore slopes) and exposed to harsh breaking wave loading.

Simulation on the Physical Process of Neural Electromagnetic Signal Generation Based on a Simple but Functional Bionic Na+ Channel

2021 ◽  
Author(s):  
Fan Wang ◽  
Jingjing Xu ◽  
Yanbin Ge ◽  
Shengyong Xu ◽  
Yanjun Fu ◽  
...  
Keyword(s):  
Dynamic Equilibrium ◽  
Electromagnetic Signal ◽  
Na Channel ◽  
Physical Processes ◽  
Flux Transport ◽  
Ionic Flux ◽  
Concentration Difference ◽  
Voltage Gated ◽  
Electromagnetic Signals ◽  
The Impact

Abstract The physical processes occurring at open Na+ channels in neural fibers are essential for understanding the nature of neural signals and the mechanism by which the signals are generated and transmitted along nerves. However, there is less generally accepted description of these physical processes. We studied changes in the transmembrane ionic flux and the resulting two types of electromagnetic signals by simulating the Na+ transport across a bionic nanochannel model simplified from voltage-gated Na+ channels. Results show that the Na+ flux can reach a steady state in approximately 10 ns owing to the dynamic equilibrium of Na+ ions concentration difference between the both sides of membrane. After characterizing the spectrum and transmission of these two electromagnetic signals, the low-frequency transmembrane electric field is regarded as the physical quantity transmitting in waveguide-like lipid dielectric layer and triggering the neighboring voltage-gated channels. Factors influencing the Na+ flux transport are also studied. The impact of the Na+ concentration gradient is found higher than that of the initial transmembrane potential on the Na+ transport rate, and introducing the surface-negative charge in the upper third channel could increase the transmembrane Na+ current. This work can be further studied by improving the simulation model; however, the current work helps to better understand the electrical functions of voltage-gated ion channels in neural systems.

Surface Roughness Impact on Secondary Flow and Losses in a Turbine Exhaust Casing

2018 ◽  
Author(s):  
Isak Jonsson ◽  
Valery Chernoray ◽  
Borja Rojo
Keyword(s):  
Surface Roughness ◽  
Secondary Flow ◽  
Suction Side ◽  
Pressure Probe ◽  
Time Resolved ◽  
Pressure Distributions ◽  
Turbulence Decay ◽  
Inlet Swirl ◽  
High Level ◽  
The Impact

This paper experimentally addresses the impact of surface roughness on losses and secondary flow in a Turbine Rear Structure (TRS). Experiments were performed in the Chalmers LPT-OGV facility, at an engine representative Reynolds number with a realistic shrouded rotating low-pressure turbine (LPT). Outlet Guide Vanes (OGV) were manufactured to achieve three different surface roughnesses tested at two Reynolds numbers, Re = 235000 and Re = 465000. The experiments were performed at on-design inlet swirl conditions. The inlet and outlet flow of the TRS were measured in 2D planes with a 5-hole probe and 7-hole probe accordingly. The static pressure distributions on the OGVs were measured and boundary layer studies were performed at the OGV midspan on the suction side with a time-resolved total pressure probe. Turbulence decay was measured within the TRS with a single hot-wire. The results showed a surprisingly significant increase in the losses for the high level of surface roughness (25–30 Ra) of the OGVs and Re = 465000. The increased losses were primary revealed as a result of the flow separation on the OGV suction side near the hub. The loss increase was seen but was less substantial for the intermediate roughness case (4–8 Ra). Experimental results presented in this work provide support for the further development of more advanced TRS and data for the validation of new CFD prediction methods for TRS.

scholarly journals Changes in Dynamic Plantar Pressure During Loaded Gait

2013 ◽  
Vol 93 (9) ◽  
pp. 1175-1184 ◽  
Author(s):  
Stephen L. Goffar ◽  
Rett J. Reber ◽  
Bryan C. Christiansen ◽  
Robert B. Miller ◽  
Jacob A. Naylor ◽  
...  
Keyword(s):  
Plantar Pressure ◽  
Repeated Measures ◽  
Load Carriage ◽  
Relative Distribution ◽  
Arch Height ◽  
Great Toe ◽  
Pressure Distributions ◽  
Increased Risk ◽  
The Impact ◽  
Load Conditions

Background Lower extremity overuse injuries are detrimental to military readiness. Extremes of arch height and heavy loads carried by military personnel are associated with increased risk for overuse injury. Little is known regarding the impact of load carriage on plantar pressure distributions during gait. Objective The objective of this study was to determine how load carriage affects plantar pressure distributions during gait in individuals with varying arch types. Design A cross-sectional, repeated-measures design was used for the study. Methods The study was performed at a research laboratory at Fort Sam Houston, Texas. Service members who were healthy and weighing ≥70 kg were enrolled in the study. The participants (97 men, 18 women; mean age=31.3 years, SD=5.6; mean weight=86.0 kg, SD=11.0) were categorized as having high-, normal-, or low-arched feet on the basis of published cutoff values for the arch height index. Plantar pressure measurements were obtained with the use of an in-shoe pressure measurement system while participants wore combat boots and walked on a treadmill under 3 loaded conditions (uniform, 20-kg load, and 40-kg load). Maximal force (MaxF) and force-time integral (FTI) were assessed with the use of a 9-sector mask to represent regions of the foot. A 3 × 3 repeated-measures analysis of variance was used for analysis across the levels of load and arch type. Results A significant interaction existed between arch type and load for MaxF and FTI in the medial midfoot, with greater force in low-arched feet. In the medial forefoot, MaxF and FTI were greatest in high-arched feet across all load conditions. In the great toe region, low-arched and normally arched feet had greater MaxF and FTI. The relative distribution of FTI increased proportionately in all regions of the foot regardless of arch type for all load conditions. Limitations The influence of fatigue, greater loads, and different walking speeds was not assessed. Conclusions Regardless of arch type, increases in load did not alter the relative distribution of force over the plantar foot during gait. Participants with high-arched feet had greater force in the medial forefoot region, whereas those with normally arched or low-arched feet had greater force in the great toe region, regardless of load. These differences in force distribution may demonstrate different strategies to generate a rigid lever during toe-off.

On Transition From Supersonic to Subsonic Flow at Low Reynolds Numbers in a Tube

1969 ◽  
Vol 36 (2) ◽  
pp. 146-150 ◽  
Author(s):  
R. Y. Chen ◽  
J. C. Williams
Keyword(s):  
Mach Number ◽  
Static Pressure ◽  
Subsonic Flow ◽  
Supersonic Nozzle ◽  
Reynolds Numbers ◽  
Impact Pressure ◽  
Low Reynolds Numbers ◽  
Pressure Distributions ◽  
Low Reynolds ◽  
The Impact

A supersonic low-density gas stream produced in a supersonic nozzle was passed through a circular tube in which the transition from supersonic to subsonic flow took place. Static pressure distributions along the tube (and nozzle) and impact pressure distributions across the tube at several stations were measured to determine the nature of this transition. The impact pressure distributions were used, together with the local static pressure, to infer Mach number and velocity profiles in the tube. When the pressure distributions and center-line Mach number distributions are considered together, one obtains a fairly clear picture of the processes involved in the transition from supersonic to subsonic flow at low Reynolds numbers.

scholarly journals Optimal Combination of Currency Assets and Algorithm Simulation under Exchange Rate Risk

Complexity ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Jun Wei
Keyword(s):  
Money Demand ◽  
Dynamic Equilibrium ◽  
Money Market ◽  
Demand Model ◽  
Demand For Money ◽  
Virtual Economy ◽  
The Interest Rate ◽  
Economic Assets ◽  
Social Wealth ◽  
The Impact

The excess money supply did not lead to a rapid rise in the price index, which in turn triggered inflation. In this case, the redetermination of the demand for money is particularly important. At the same time, with the continuous expansion of the capital market and the rapid development of the virtual economy, the virtual economy is gradually deviating from the real economy. When selecting assets, microentities often incorporate virtual economic assets into investment considerations. Therefore, it is necessary to establish a money demand model that considers the impact of virtual economic assets. This paper uses the asset selection of microentities as the microfoundation to establish a money demand model to explain its economic significance. And based on the money demand model established, a dynamic equilibrium model of the money market was established, and the stability of the dynamic equilibrium point of the money market was verified through mathematical deduction. Based on the dynamic equilibrium model of the money market, the impact of money supply was analyzed. In order to verify the correctness of the aforementioned theory, this paper conducts an empirical analysis. Through cointegration analysis and the vector error correction model (VECM model), the correctness and applicability of the established money demand model are verified, and money demand, total social wealth, spreads between expected stock returns and interest rates, and real estate expectations are found. There is a long-term equilibrium relationship between the rate of return and the interest rate. The total amount of social wealth, the expected rate of return on stocks, and the interest rate spread will have an impact on the demand for money in the short term.

scholarly journals Droplet Impact on Suspended Metallic Meshes: Effects of Wettability, Reynolds and Weber Numbers

Fluids ◽  
2020 ◽  
Vol 5 (2) ◽  
pp. 81 ◽  
Author(s):  
Konstantinos Vontas ◽  
Cristina Boscariol ◽  
Manolia Andredaki ◽  
Anastasios Georgoulas ◽  
Cyril Crua ◽  
...  
Keyword(s):  
General Context ◽  
Liquid Penetration ◽  
Droplet Impingement ◽  
Textile Design ◽  
Lower Viscosity ◽  
Wide Range ◽  
Jet Printing ◽  
Break Up ◽  
Metallic Meshes ◽  
The Impact

Liquid penetration analysis in porous media is of great importance in a wide range of applications such as ink jet printing technology, painting and textile design. This article presents an investigation of droplet impingement onto metallic meshes, aiming to provide insights by identifying and quantifying impact characteristics that are difficult to measure experimentally. For this purpose, an enhanced Volume-Of-Fluid (VOF) numerical simulation framework is utilised, previously developed in the general context of the OpenFOAM CFD Toolbox. Droplet impacts on metallic meshes are performed both experimentally and numerically with satisfactory degree of agreement. From the experimental investigation three main outcomes are observed—deposition, partial imbibition, and penetration. The penetration into suspended meshes leads to spectacular multiple jetting below the mesh. A higher amount of liquid penetration is linked to higher impact velocity, lower viscosity and larger pore size dimension. An estimation of the liquid penetration is given in order to evaluate the impregnation properties of the meshes. From the parametric analysis it is shown that liquid viscosity affects the adhesion characteristics of the drops significantly, whereas droplet break-up after the impact is mostly controlled by surface tension. Additionally, wettability characteristics are found to play an important role in both liquid penetration and droplet break-up below the mesh.

Multiphase Flow Under Heterogeneous Wettability Conditions Studied by Special Core Analysis and Pore-Scale Imaging

SPE Journal ◽  
2019 ◽  
Vol 24 (03) ◽  
pp. 1234-1247 ◽  
Author(s):  
Shuangmei Zou ◽  
Ryan T. Armstrong
Keyword(s):  
Multiphase Flow ◽  
Relative Permeability ◽  
Flow Regimes ◽  
Wettability Alteration ◽  
Core Analysis ◽  
Pore Scale ◽  
End Effect ◽  
The Impact ◽  
Capillary End Effect ◽  
Special Core Analysis

Summary Wettability is a major factor that influences multiphase flow in porous media. Numerous experimental studies have reported wettability effects on relative permeability. Laboratory determination for the impact of wettability on relative permeability continues to be a challenge because of difficulties with quantifying wettability alteration, correcting for capillary-end effect, and observing pore-scale flow regimes during core-scale experiments. Herein, we studied the impact of wettability alteration on relative permeability by integrating laboratory steady-state experiments with in-situ high-resolution imaging. We characterized wettability alteration at the core scale by conventional laboratory methods and used history matching for relative permeability determination to account for capillary-end effect. We found that because of wettability alteration from water-wet to mixed-wet conditions, oil relative permeability decreased while water relative permeability slightly increased. For the mixed-wet condition, the pore-scale data demonstrated that the interaction of viscous and capillary forces resulted in viscous-dominated flow, whereby nonwetting phase was able to flow through the smaller regions of the pore space. Overall, this study demonstrates how special-core-analysis (SCAL) techniques can be coupled with pore-scale imaging to provide further insights on pore-scale flow regimes during dynamic coreflooding experiments.

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