Spreading Length Research Articles

Analysis of mooring performance and layout parameters of multi-segment mooring system for a 15 MW floating wind turbine

IntroductionFloating wind power is the important path for the development of offshore wind energy, and the performance of the mooring system of floating wind turbines (FOWTs) significantly affects their economic viability, safety, and sustainability.MethodsThis paper systematically analyses the positioning performance, mooring line extreme loads, and fatigue response of a FOWT equipped with both single segment and multi-segment mooring systems, based on the IEA 15 MW large turbine and a floating platform. The hydrodynamic performance of the floating platform is calculated, and the platform’s motion-sensitive directions are analysed through Response Amplitude Operators (RAOs). The natural periods of the platform are validated by free decay tests. The six degrees of freedom (DOFs) motion response and the mooring line peak tensions are analysed under normal and extreme conditions.ResultsThe results show that both mooring systems provide good motion performance and stable tilt angles for the platform. Under ALS (single-line failure) condition, the multi-segment mooring system demonstrates a notable capacity to resist impact loads, with comparatively minor fluctuations in mooring line tension. In the multi-segment system, fatigue damage primarily occurs in the upper mooring chain, with damage approximately 4.5 times greater than that of the bottom chain over a 1-year period. The effects of mooring line spread angles and lengths on performance are also analysed. The results indicate that the mooring line spread angle has slight impact on platform motion response and mooring line tension, while mooring line length significantly affects the extreme tension of the lines.DiscussionThe findings of this study can provide some references in the design of mooring systems for future FOWTs.

Spreading of Dynamically Crosslinked Polydimethylsiloxane Drops

ABSTRACTDynamically crosslinked polymer networks, characterized by non‐permanent bonds, offer unique viscoelastic properties that can be used for various applications such as self‐healing coatings and reusable adhesives. This study investigates the spreading behavior of a silicone polymer network with dynamic imine bonds, focusing on the relationship between material properties and spreading dynamics. We prepare polydimethylsiloxane (PDMS) networks with varied rheological properties by adjusting the ratio of amine and aldehyde groups and curing conditions. The spreading of PDMS spherical drops is investigated on surfaces with different surface energies, with the process quantified by measuring the contact length and height over time. Our findings reveal that higher modulus spheres spread more slowly, and that the spreading length increases more on high energy surfaces. This research could provide insights for developing coatings and adhesives with tunable properties by studying the interaction between transiently‐crosslinked polymers and substrates during spreading.

Accuracy of the preoperative estimation of esophageal invasion length of adenocarcinoma of the esophagogastric junction and its discrepancy with the pathological measurement.

The incidence of esophagogastric junction (EGJ) adenocarcinoma has increased worldwide. As the EGJ is located at the boundary between the thoracic and abdominal cavities, the optimal surgical approach is a subject of debate and estimation of the esophageal invasion length (EIL) is an important factor in its selection. Data from our in-house database were extracted for consecutive patients with Siewert type I, II and III EGJ adenocarcinoma (EIL ≤ 4cm), who underwent transhiatal or transthoracic surgical resection between 2010 and 2016. The clinical records of these patients were reviewed and the accuracy of EIL estimation and its discrepancy with the pathological measurement were analyzed. A total of 82 patients were included in the final analysis. We established that EIL was underestimated in 49 of these patients (59.8%). The mean-distance discrepancy between the preoperative and pathological diagnosis of EIL in the underestimation group was 7.0mm. Multivariate analysis revealed that submucosal cancer spread was an independent risk factor for underestimation (P < 0.01). The mean length of submucosal cancer spread was longer for undifferentiated histologic type EGJ adenocarcinomas. (P < 0.01). The EIL was underestimated in approximately 60% of EGJ adenocarcinomas requiring surgical treatment. Thus, careful management is necessary, especially for EGJ adenocarcinoma of the undifferentiated histologic type.

Hybrid Functional ITO/Silver Nanowire Transparent Conductive Electrodes for Enhanced Output Efficiency of Ultraviolet GaN-Based Light-Emitting Diodes.

We investigated hybrid functional transparent conductive electrodes (HFTCEs) composed of indium-tin-oxide (ITO) and silver nanowires (AgNWs) for the enhancement of output efficiency in GaN-based ultraviolet light-emitting diodes (UVLEDs). The HFTCEs demonstrated an optical transmittance of 69.5% at a wavelength of 380 nm and a sheet resistance of 16.4 Ω/sq, while the reference ITO TCE exhibited a transmittance of 76.4% and a sheet resistance of 18.7 Ω/sq. Despite the 8.9% lower optical transmittance, the UVLEDs fabricated with HFTCEs achieved a 25% increase in output efficiency compared to reference UVLEDs. This improvement is attributed to the HFTCE's twofold longer current spreading length under operating forward voltages, and more significantly, the enhanced out-coupling of localized surface plasmon (LSP) resonance with the trapped wave-guided light modes.

Dynamics of droplet adsorption by liquid film on a grooved surface

Understanding the dynamics of droplet adsorption by liquid film on a grooved surface is of great significance for the possible manipulation of dropwise condensation on the grooved surface. In this study, an improved phase-field lattice Boltzmann model is proposed to describe the process of droplet adsorption from the ridge to the liquid film within the channel. The results indicate that the leading edge of the droplet undergoes two accelerations during the adsorption process, obeying the power law of and , respectively. The adsorption process between droplets with different sizes and the liquid film exhibits self-similarity characteristics including the same first peak velocity, the similar droplet displacement-time curve and the equal dimensionless spreading length of . Decreasing the contact angle of the droplet from to accelerates the displacement of the leading edge and extends the spreading length. These findings may help reveal the mechanics of droplet adsorption by the liquid film on the grooved surface and thus manipulate the condensation behavior for the heat transfer enhancement.

Numerical analysis of the interaction between a droplet and an air boundary layer

The deformation and movement of droplets are widely utilized in many industrial applications. The present work investigates the evolution of a single droplet interacting with an air boundary layer numerically and validated by wind tunnel experiments. The volume of fluid method is employed to study the interaction from the micro-perspective. The influences of airflow velocity, droplet size, and depression angle on interactions are comprehensively discussed. The outcomes indicate that droplet diameter and airflow velocity significantly influence the interaction. Based on the morphological evolution of the droplets, the regimes of the interaction can be classified into three categories. It is shown that the airflow velocity, depression angle, and droplet diameter influence the droplet maximum streamwise spreading length. Furthermore, only the airflow velocity and droplet diameter influence the maximum height. The scaling law for the maximum streamwise spreading factor is revealed. Finally, the velocity profile of the boundary layer above the droplet maximum height is also analyzed, revealing a power-law relationship in its curve. These results provide valuable insight for further investigation on the droplet–air boundary layer interaction.

Numerical investigation of spreading phenomena of molten corium using EISPH method

Understanding the behavior of molten corium is crucial for effective heat management and ensuring the integrity of reactor containment during severe nuclear incidents. Corium spreading is a complex multi-physics phenomenon influenced by hydrodynamics, heat transfer, and phase change. The Smoothed Particle Hydrodynamics (SPH) method is utilized to study corium flow, leveraging its ability to handle complex fluid dynamics and its compatibility with parallel computing architectures. This research examines two specific corium spreading cases: the VULCANO VE-U7 experiment, which is characterized by a wide mushy zone, and the FARO L26S experiment, noted for its narrow mushy zone. The study compares spreading lengths and temperature profiles over time with experimental data, offering a detailed analysis of the observed spreading behaviors. Variations in physicochemical properties result in distinct spreading patterns between the cases, highlighting the complexity of corium behavior under different scenarios. The findings demonstrate the applicability and capability of the SPH method in capturing various characteristics of corium spreading effectively.

Study on the Influence Mechanism of Hot Flue Gas Injection Pressure on the Wettability of Anthracite Coal: From the Perspective of Molecular Dynamics.

A multicomponent wetting model of coal-water-methane-hot flue gas was hereby constructed to investigate the influence of complex components of hot flue gas on coal wettability. Besides, whether it is feasible to use the NIST method to capture the system pressure was verified from a microscopic perspective. Moreover, how the interaction energy and hydrogen bonds between water and coal, the spreading length of water nanodroplets in the X-direction, and the three-phase contact angle vary with the hot flue gas injection pressure were discussed. Here are the findings: (1) The absolute value of interaction energy between water and coal is negatively correlated with the pressure. In addition, the gradient of decrease shrinks continuously when the pressure rises. (2) As the pressure rises, a decline is monitored in both the number of hydrogen bonds and the spreading length of water nanodroplets in the X-direction, and a critical pressure value exists around 32.64 MPa, which divides the variation into two stages, i.e., rapid decrease and slow decrease. (3) The three-phase contact angle grows with the rise of pressure, and its critical pressure value is similar to that of number of hydrogen bonds and spreading length. In addition, it is found that the density of the gas adsorption layer augments as the pressure rises, which can be seen that a higher injection pressure is favorable for gas wetting. These research observations brought to light that appropriately raising the hot flue gas injection pressure can promote the transition of wetting mode from water wetting to gas wetting, which is of great benefit for relieving the water lock effect and effectively improving the transportation environment of gas.

Investigation on droplet spreading and energy conversion process on solid surface with low impinging velocity

Accurately and quantitatively tracking the droplet impinging and spreading process in theory is of paramount importance for informing and advancing engineering application. However, the existing models have problems such as large energy calculation deviations and imprecise shape hypotheses, which lead to significant theoretical errors and require in-depth correction. In this paper, a numerical model based on the laminar flow equation coupled phase field method and the dynamic contact angle model involved in the droplet impinging and spreading process is first developed and validated. The morphology and parameters of droplet spreading at various conditions and the role and influence of gravitational potential energy are further investigated. Subsequently, a semi-empirical modified spoon-like model grounded in numerical outcomes and attempting to overcome traditional assumptions limitations is advanced, with its practical applicability rigorously discussed. Results show that the droplet spreading process basically undergoes “round sphere”, “round cap”, and “pancake-like /cylinder-like” to “shallow bottomed round tray”. Changes in Weber number (We) and equilibrium contact angle (θe) marginally alter the duration, spreading size, and droplet morphology characteristics in each process. The impact of gravitational potential energy is notably modulated by process parameters, exhibiting an increase with escalating droplet diameter and density, while decreasing in response to heightened initial droplet velocity and surface tension coefficients. Conversely, it remains largely invariant to changes in droplet viscosity and equilibrium contact angle. The consideration of shape factor and viscosity modification factor allows the surface energy and viscous dissipation energy to be accurately defined, making the proposed semi-empirical modified spoon-like model exhibit good performance, for all 65 studied cases the relative errors of droplet maximum spreading length factor (βmax) and center thickness (h) fall essentially within the 5% and 10% interval respectively.

Study of the effect of pore properties of microporous layer on water transport process in proton exchange membrane fuel cell

Aiming at the “water flooding” phenomenon inside the Gas Diffusion Layer (GDL) of the Proton Exchange Membrane Fuel Cell (PEMFC), this paper visualizes the effects of the pore properties and gradient structure of the microporous layer (MPL) on water transport. Specifically, we visualize the impact of pore properties and gradient structure on water transport. For this purpose, a liquid water capillary finger advancement visualization test platform is constructed to analyze the evolution of liquid water in the porous medium and reveal the effects of single porosity, single pore diameter, gradient porosity, and gradient pore diameter of the MPL on the liquid water transport. Moreover, the time of the non-wetting liquid touching the top, the maximum spreading length, and the residual volume in the MPL are analyzed to evaluate the drainage capacity. The results highlight that the microporous layer's smaller porosity and pore size could limit the interface's extended width between the microporous and gas diffusion layers. Additionally, the residual volume of non-wetting liquid is 21.6 % less in the case of φ = 0.3 than for φ = 0.45, and the residual volume of non-wetting liquid is 11.8 % less in the case of d = 0.82 mm compared to d = 2.45 mm. Furthermore, the residual volume of the microporous layer in the Catalyst layer (CL) side of the microporous layer is 11.8 % less than that in the case of d = 2.45 mm. Finally, we conclude that when the pore gradient law is opposite, it is unfavorable for liquid water discharge.

Effect of current spreading layer on Internal Quantum efficiency and optical power of flip chip gallium nitride LEDs with circular contacts

The unique properties of the Indium Tin Oxide (ITO) make it an excellent choice as a current spreading layer in Flip Chip Light Emitting Diodes (FCLEDs) and other optoelectronic devices. Herein, the performance of FCLEDs is analyzed by a precise mathematical model for the current spreading length (Ls) produced by the ITO layer under circular-shaped contacts. The expressions are formulated without approximations using ABC-model for extracting the Internal Quantum Efficiency (IQE, ηint), optical power (Pint) and Emission Intensity (EI). The thickness (tITO) and resistivity (ρITO) of the ITO layer are varied for different current densities, and their adverse effects on IQE are determined. At lower current densities, IQE increases with thickness and decreases for high resistivity of the ITO layer. At higher current densities, there is a gradual decrease in IQE irrespective of the ITO layer presence due to “Efficiency Droop”. The IQE in the proposed work is 82 % at a thickness of 50–200 nm and current density of 8 A/cm2, and the optical power is around 40 mW, showing good agreement with the experimental data, making it feasible for future high-performance FCLEDs.

Oblique impingement of an ice particle on a water film

In the present study, we experimentally investigated the oblique impinging process of an ice particle on a water film. A parameter study of the impact velocity, impact angle, and water film thickness was carefully carried out. The results showed that three impact categories occurred, namely uprising liquid sheet, crown with a notch, and complete crown. The uprising liquid sheet only occurred in the case when the dimensionless water film thickness was 0.1, which appeared to be independent of the impact velocity and the impact angle. The crown with a notch only occurred in the case when the impact velocity was 23.0 m/s. The left tilt angles of uprising liquid sheet, crown with a notch, and complete crown all increased first and then decreased with the dimensionless time. Among the three experimental parameters investigated in the present study, the dimensionless water film thickness had the most significant effect on the evolutions of the left tilt angles. The dimensionless spreading lengths in x- and y-direction all increased with the increase in dimensionless water film thickness. In addition, the correlations of dimensionless spreading lengths in x- and y-direction were proposed. In addition, the lifetime of complete crown generally increased with the increase in the impact velocity and the dimensionless water film thickness. Within the scope of the present study, the dimensionless maximum height of uprising liquid sheet generally ranged from 3.0 to 3.5. When the impact angle was 30.0°, the dimensionless maximum height of the crown with a notch increased with the increasing dimensionless water film thickness. The present work not only provides a new insight into the study of the ice crystal icing but also offers effective support for the development of efficient anti/de-icing methods.

Impact and spread dynamics of a viscoelastic droplet on an inclined hydrophilic surface

In this work, the impact of a three-dimensional viscoelastic droplet on an inclined hydrophilic surface is investigated by means of direct numerical simulations. The volume-of-fluid method is adopted to capture the interface, and the Oldroyd-B model is used to describe the rheological behavior of the viscoelastic droplet. The effects of the Weissenberg number (Wi) and the Weber number (We) on the impacting and spreading processes are studied, including the viscoelastic droplet shape, velocity, energy transformation, and stress distribution. Our results are in good agreement with the experimental data in the literature. In particular, the elastic force markedly influences droplet deformation at intermediate Wi values, although this trend diminishes at higher or lower Wi values. With increasing We, the impacting viscoelastic droplet reaches its maximum deformation more rapidly, while the nonmonotonic peak of kinetic energy indicates that the droplet elasticity plays significant role at moderate We. Additionally, the inclination of the surface has a pronounced effect on the droplet spreading process, and the elongated viscoelastic droplet at larger inclination angle is likely to experience a stronger oscillation. According to further analyses, We exerts a modest influence on the change rates of the droplet potential energy and spreading length in the flow direction. However, a larger inclination angle reduces stress concentration and accelerates the change rates. Due to the oscillation dynamics, Wi exhibits a non-monotonic effect on the spreading process and induces a monotonous increase in potential energy of viscoelastic droplets. The above analyses provide insights into the impact mechanism of droplets on an inclined hydrophilic wall and, therefore, will guide the applications in the future.

Stretch-Controlled Branch Shape Microstructures for Switchable Unidirectional Self-Driven Spreading of Oil Droplets.

Unidirectional transport of liquids has attracted the attention of researchers in recent years for its wide application foreground. However, it is still a challenge to control the spreading of liquid, especially for oils with relatively high viscosity. In this paper, a flexible surface textured with branch-shaped microstructures is proposed. These asymmetric microstructures exhibit excellent unidirectional spreading behaviors for various oils. By suitably stretching the flexible surface to different stretch ratios, the spreading length of the oil droplets can be controlled. Moreover, the ongoing forward spreading of oil droplets can be suspended dynamically when the surface is stretched to 40%. Corresponding mechanism analysis demonstrates that surface stretching can narrow and close the microvalves between adjacent branches, which restrain the flow of the precursor film and the primary droplet. The switchable unidirectional spreading behavior enables the surface with such microstructures to be used for oil transportation, oil-water separation, and controllable lubrication.

Numerical simulation of solidification of molten slag impacting inclined wall in boiler based on smoothed particle hydrodynamics method

In order to study the process of high temperature liquid slag impinging on the wall, the slagging phase change is produced by combustion of high alkali coal in a boiler chamber. In this paper, based on the smoothed particle hydrodynamics (SPH) method, the flow spreading and solidification model of slag particles hitting the inclined wall are established, and the dynamic process of flow spreading and the phase change of slag particles hitting the wall are analyzed by simulating the deposition process of the phase change of slag particles hitting the wall. The effects of different inclination angles of the wall on its deformation and solidification heat transfer are further discussed. It is shown that the change of inclination angle during the impact of single slag on the wall has a greater influence on the spreading flow process. During the impact of single/double slag on the wall with different inclination angles, the time taken by the double slag to reach the final spreading length and complete phase transition is nearly five times longer than that of the single slag. The direction of slag impact also has an effect on the spreading and phase transition. This SPH method provides a novel numerical simulation idea to study the kinetic behavior of molten slag hitting the wall and the problems related to phase change deposition in boilers.

Experimental investigation of interactions between a water droplet and an airflow boundary layer

The deformation and movement of droplets is widely relevant in many fields of research. The present work experimentally investigates the evolution of a single droplet interacting with an air boundary layer. A series of experiments are carried out using a high-speed photography technique to determine the effects of the airflow velocity, drop height, and droplet size. The morphological characteristics can be classified into three types according to the experiments. The outcomes indicate that both the drop height and the airflow velocity significantly influence the maximum streamwise spreading length, but only the drop height has an impact on the maximum lateral spreading width. The maximum streamwise spreading factor follows a power function relationship with WeRe−0.5. In addition, the crater maximum streamwise and lateral spreading diameters are mainly influenced by the drop height. An energy conversion model is established by considering the effects of the aerodynamic drag force, surface tension, and viscous force. This study provides experimental reference data for the scenario of a droplet interacting with an air boundary layer.

Numerical study on the thermodynamic behavior of de-icing liquid droplets impacting walls

Spraying de-icing fluid is a key method to ensure the safe operation of aircraft in icy and snowy weather. The film aggregation and internal mixing of de-icing fluid droplets on the aircraft skin during a collision are crucial. Considering the rheological properties of the molecular viscosity change of the de-icing fluid droplets during the collision and the heat transfer model of the heat loss after the impact, the phase field method is used to capture the gas–liquid interface, and a thermal pressure/viscous coupling model is constructed. The thermodynamic behavior of different axial distances is calculated. The results show that, as the dimensionless axial distance of the droplet increases, the spreading length of the fused droplet decreases instead, and the heat transfer rate of the droplet increases with the increase in spreading length. After stabilizing, the increase or decrease in the heat transfer rate depends on the strength of the heat transfer between the liquid layers. As the dimensionless axial distance increases, the internal flow of the droplet weakens and, between the droplet and the wall, the heat flux density gradually decreases and the average temperature drop of the droplet becomes gradual.

Study on the Effect of Natural Wind on the Smoke Spread Law of Extra-Long Tunnel Fires with Inclined Shafts for Air Supply and Exhaust

High-temperature smoke generated by tunnel fires is the most important factor causing casualties. To explore the influence of natural wind on fire smoke movement in an extra-long highway tunnel based on the Taihang Mountain Tunnel, the distribution law of natural wind in the tunnel was obtained by on-site monitoring of the meteorological conditions at the tunnel site. A three-dimensional fire dynamics tunnel model considering an inclined shaft smoke exhaust was established, and the influence of natural wind on tunnel temperature distribution, smoke spread and smoke exhaust efficiency was studied. The results show that the natural wind speed of the Taihang Mountain Tunnel is mainly concentrated at 0~3 m/s. The main wind direction of the natural wind on the left tunnel is opposite to the driving direction, and the distribution probability of the main wind direction in each section is 81.27% and 72.15%, respectively. The main wind direction of the right tunnel is the same as the driving direction, and the distribution probability of the main wind direction in each section is 56.78%, 69.73%, 67.32% and 64.65%, respectively. The negative natural wind can inhibit the smoke spread downstream of the smoke exhaust port, but it is not conducive to the smoke exhaust. The positive natural wind promotes the smoke spread to the downstream of the smoke exhaust port, and the larger the natural wind speed, the longer the spread length. Natural wind reduces the smoke exhaust efficiency. For positive or negative natural wind with a guaranteed rate of 70%, the smoke exhaust efficiency is reduced by 27.76% and 15.59%, respectively, compared with the condition without natural wind. The research results can provide a useful reference for the design of fire smoke exhausts and smoke control schemes in extra-long highway tunnels.

Sub-pixel target fine spatial feature extraction method based on aperture coding and micro-scanning imaging mechanism

The small imaging size of targets over long distances results in the loss of geometry and spatial features. Current methods are subject to sampling limitations and cannot accurately capture the spatial features of sub-pixel targets. This paper proposes a method to accurately locate and extract the fine spatial features of sub-pixel targets through aperture coding and micro-scanning imaging. First, the formation mechanism of imaging features for sub-pixel targets is analyzed. Second, the optical aperture is anisotropically coded in different directions to modulate the spreading spots of the target. The primary spreading direction and the center of the anisotropic spreading spots are extracted. The contour and the location of the target are determined from the spreading length and the intersections of the primary spreading directions. Then, the target is sampled by different detector units through various micro-scanning offsets. The pixel units containing different sub-pixel components of the target after offset are determined based on the location results. The fine spatial distribution of the sub-pixel target is reconstructed based on the intensity variations in the pixel units containing the target. Finally, the accuracy of the sub-pixel target fine spatial feature extraction method is validated. The results show a sub-pixel localization error of less than 0.02 and an effective improvement of the sub-pixel target spatial resolution. This paper provides significant potential for improving the ability to capture spatial features of targets over long distances.

Slump-flow channel test for evaluating the relations between spreading and rheological parameters of sediment mixtures

Understanding debris flow phenomena and modeling them effectively requires accurate estimation of their rheological parameters. This study introduces a simple approach defined as the “slump-flow channel test”, which employs a horizontal rectangular channel to evaluate these parameters. The results of slump-flow channel tests indicate that the spreading parameters (spread length, angle of reach, and time to final spread) of sediment mixtures are strongly influenced by their sediment fractions and rheological properties. An empirical analysis of the temporal evolution of the spread length and spread velocity was carried out employing both experimental and simulation results. The numerical simulation of the slump-flow channel tests was performed using the Flow-3D software. Both experimental and simulation results demonstrate that the spreading and the rheological parameters of sediment mixtures exhibit strong correlations and this implies that the rheological parameters of sediment mixtures can be evaluated indirectly using a simple slump-flow channel test.