Frictional Resistance Research Articles

Shear Resistance Evolution of Geogrid-Aggregate Interfaces under Direct Shear: Insights from 3D DEM Simulations

This paper presents a mesoscopic evaluation of the shear resistance evolution of geogrid-aggregate interfaces subjected to direct shear loading. A three-dimensional discrete element method (DEM) model was developed based on experimental data. The tensile response of geogrid were simulated through a series of calibration tests. Aggregate with complex particle shapes were simulated to accurately capture the interlocking effect among aggregates based on the real particle surface. The individual shear resistance components were quantified based on particle displacement field and contact distribution characteristics. The influences of aperture-aggregate size ratio and geogrid stiffness on the shear resistance components are discussed. The results indicate that the peak value of shear resistance component follows a descending order from frictional resistance of aggregate, to passive resistance of transverse rib, and to geogrid-aggregate interface frictional resistance. During the shear process, the frictional resistance of aggregate becomes active first, followed by the geogrid-aggregate interface frictional resistance, and then the development of passive resistance of transverse ribs starts with a certain lag. Optimizing the geogrid-aggregate size ratio and utilizing geogrids with higher rib stiffness could enhance the passive resistance of transverse ribs but would not significantly affect the geogrid-aggregate interface frictional resistance and frictional resistance of aggregate.

Current-carrying tribological behavior of copper alloy matrix and molybdenum alloy coating at high current density

Improving the current-carrying friction and wear resistance of copper alloy current-carrying friction subsets effectively is a hot topic. In this paper, a method of preparing high melting point molybdenum-based coating on copper alloy surfaces by laser cladding technology is presented. A large current (106 A/m2) comparison experiment is carried out with a self-made current-carrying friction device, and the failure mechanism is analyzed. The results show that the molybdenum-based coating significantly improves the adhesion problem between the friction partner and the copper alloy substrate, while the thickness of the stress layer caused by the current-carrying friction is reduced by about 7 times. The molybdenum-based coating significantly reduces the surface arc rate and has a lower friction interface temperature, thus retaining the Al2O3 self-lubricating phase. The research in this paper is expected to provide extended research ideas for the surface protection of current-carrying friction subsets of copper alloys.

Model Tests on Jacked Pile Penetration Characteristics Considering a Static Press-in Piling Machine

This study incorporates a static press-in piling machine into the conventional laboratory model tests for jacked piles. By conducting a comparative analysis between two tests, one involving the static press-in piling machine and the other focusing solely on pile jacking, this study aims to unveil the variations in penetration characteristics with pile sinking depth during the process of pile jacking under the constraint imposed by the static press-in piling machine. When considering the impact of the piling machine, the pile pressing force, pile sinking resistance, pile axial force, and unit side friction resistance of the pile body are higher compared to test results that only focus on pile jacking. There is an acceleration in the total side friction resistance within the depth range of 20 to 30 cm. Additionally, the reduction rate of axial force during the entire pile jacking process is 2% higher, with a general reduction in the “side resistance degradation” phenomenon. The soil pressure around the pile exhibits an initial increase followed by a decrease. The authors believe that the model box test of the jacked pile, considering the pile machine, would be more aligned with engineering practice.

Numerical Simulation of Offshore Suction Bucket Foundation Pullout Characteristics under Undrained Conditions

The suction bucket jacket foundation is widely regarded as a crucial solution for constructing offshore wind farms in water depths ranging from 30 m to 50 m. When subjected to complex loads, the bucket primarily relies on vertical movement to withstand the corresponding loads. This paper investigates the undrained pullout characteristics of the bucket foundation through numerical simulation while keeping its weight constant. This study examined how the pullout capacity of the suction bucket jacket foundation is affected by the aspect ratio and soil conditions. It revealed the changing patterns of bucket–soil frictional resistance and suction during the undrained pullout process, along with their contributions to the pullout capacity of the foundation. The results indicate that the peak pullout load of the bucket increases with decreasing L/D, and the response is more pronounced in soft clay. The frictional resistance changes from upward to downward with increasing displacement, with the maximum frictional resistance occurring at the base of the foundation. The lower part of the footing has a faster response. The suction force increases with displacement, and the proportion of suction force to peak pullout tends to increase as L/D decreases. The soil failure displacement corresponding to the occurrence of the peak pullout load of the foundation lags behind the displacement at which the frictional resistance of the bucket wall stabilizes.

Study on the effect of tunneling and secondary grouting on the deformation of existing pipelines in bedrock raised strata

Shield crossing the bedrock raised strata easily leads to large deformation of the soil, resulting in deformation and damage of the upper pipelines. To investigate the law of pipeline deformation caused by shield underpassing in bedrock raised strata, the changes in the action range of the additional thrust of the cutter head (p1), the friction resistance of the shield shell (p2), and the additional grouting force (p3) were analysed. A convergence model of the excavation face suitable for bedrock raised strata was proposed. The calculation formula of soil displacement at the axis of the pipeline was derived by using Mindlin’s solution and stochastic medium theory. The solutions of the vertical displacement, bending moment and strain of the pipeline were obtained by the energy variational method and the principle of minimum potential energy. Pipeline deformation analysis and reliability verification were carried out by an engineering case in Hangzhou, China. The influence of bedrock distribution and secondary grouting behind the pipe wall on pipeline deformation was studied. The results show that the calculated results are similar to the measured data with a high degree of coincidence, and the degree of agreement is higher compared to the existing method. When the shield tunneling direction is well controlled, the settlement and bending moment of the pipeline caused by the shield crossing the raised bedrock stratum will be reduced, and the reduction increases with increasing bedrock length and intrusion depth. The secondary grouting behind the pipe wall can reduce the settlement of the pipe line, but it is necessary to reasonably control the three parameters of grouting amount per unit length (Vinj), grouting ring length (Lh), and grouting ring angle (δ). Lh should not be too long and can be controlled below 30 m, δ should be controlled within 60°, and Vinj can be adjusted according to the deformation size of the pipeline to prevent excessive or insufficient correction.

Influence of the Advance Jacked Pipe on the Jacking Force of the Subsequent Pipe Based on Pipe–Soil Full Contact Model

Abstract In pipe jacking engineering, accurate prediction of jacking force is the key to pipe jacking design. Based on a project of the Beijing Daxing Airport Line, the influence of the advance jacked pipes on the jacking force of the subsequent pipe is carried out in the present work. First, the verified numerical model of practical engineering was established, and the jacking force and radial stress of different pipes were analyzed. Then, the two pipes were taken as research object, and the parameters of spacing, angle, buried depth, and pipe diameter were investigated, respectively. The results show that in the actual project, the advance jacked pipes have amplification and superposition effects on friction resistance of the subsequent pipe, and the maximum growth rate is 37.2%. The friction resistance of the subsequent pipe presents a trend of first increasing and then decreasing with the change of the layout angle of advance jacked pipe from 0° to 180°. With the increase of buried depth and pipe diameter, the absolute value of incremental friction resistance of the subsequent pipe increases gradually, but the growth rate remains constant. Finally, the empirical formulas for predicting the friction resistance growth rate of subsequent pipes under different angles are proposed. The research results can provide some reference for the design of pipe jacking.

Enhancing frictional and corrosion resistance performance in aluminum alloy through in situ growth of NiZnAl-LDH membrane and its modification

Anodized aluminum, due to its inherent porous channels and thin protective layer, exhibits poor corrosion resistance and friction performance in severe environments. In this study, an in-situ growth of a NiZnAl-LDH composite coating was developed on the surface of aluminum. Sodium molybdate and ricinoleic acid were used to modify the coating, enhancing both corrosion resistance and friction performance. Various tests, including SEM, infrared, XPS, XRD, and others, were conducted to analyze the structure, composition, and properties of the synthesized coating. The results confirmed the successful synthesis of NiZnAl-LDH with nitrate intercalation, which were subsequently converted to molybdate intercalation through sodium molybdate modification. Electrochemical tests revealed that the corrosion current decreased by a factor of two compared to a plain LDH coating. Friction experiments demonstrated that the co-modified coating exhibited a minimal friction coefficient of 0.23, outperforming the original LDH coating.

Experimental Investigation of Frictional Resistance in Sliding Contact between Undulating Surfaces and Third-Body Particles

The third-body particle-involved sliding contact between two rough rubbers with wavy surfaces is experimentally studied. The experiment is designed to isolate the direct contact between the first bodies so that friction resistance is induced completely by the interactions between the third-body particle and the surfaces of the rubbers. In dry contact of a single particle, it is found that the particle exhibits pure rolling during the sliding of the first bodies, and the macroscopic friction resistance for overcoming sliding does not depend on the particle size, but it is significantly influenced by the initial position of the surface waviness relative to the particle’s position. The behavior of the particle under lubricated conditions exhibited significant differences. Due to the low local friction at the interface, the particle rapidly glided down to the valley of the waviness during compression. This abrupt motion of the particle resulted in it coming to rest in a stable position, awaiting a substantial force to push it forward. The friction resistance in the case with lubrication was found to be independent of the initial position of the waviness, and its value consistently remained at the maximum found in dry contact. Therefore, lubrication actually increases the macroscopic friction resistance. An approximate solution for the specific case of dry contact is proposed to understand the friction behavior.

The Influence of Q & T Heat Treatment on the Change of Tribological Properties of Powder Tool Steels ASP2017, ASP2055 and Their Comparison with Steel X153CrMoV12.

In connection with the growing importance of the efficiency and reliability of tools in industrial sectors, our research represents a key step in the effort to optimize production processes and increase their service life in real conditions. The study deals with the comparison of the tribological properties of three tool steels, two of which were produced by the powder metallurgy method-ASP2017 and ASP2055-and the last tool steel underwent the conventional production method-X153CrMoV12. The samples were mechanically machined with the finishing technology of turning and, finally, heat treated (Q + T). The study focused on the evaluation of hardness, resulting microstructure, wear resistance, and coefficient of friction (COF). The ball-on-disc method was chosen as part of the COF and wear resistance test. The tribological test took place at room temperature with dry friction to accelerate surface wear. The pressing material was a hardened steel ball G40 (DIN 100Cr6). Measurements were performed at loads of 10 N, 6 N, and 2 N and turning radii of 13 mm, 18 mm, and 23 mm, which represents a peripheral speed of 0.34, 0.47, and 0.60 m/s. The duration of the measurement for each sample was 20 min. The results showed that the COF of powder steels showed almost the same values, while a significant difference occurred with the increase of the radius rotation in the case of conventional steel. The results within the friction mechanism showed two types of wear, namely, adhesive and abrasive wear, depending on the Q + T process. From a tribological point of view in terms of wear, it was possible to state that the material ASP2055 after Q + T showed the lowest rate of wear of all the tested steels.

Tribological Properties of a Sliding Joint with an a-C:H:W Coating under Lubrication Conditions with PAO8 Oil and the Addition of 2% MoS2 Nanoparticles.

One of the promising methods for improving the durability and reliability of friction joints in combustion engines is the use of thin and hard coatings, including coatings based on amorphous DLC. The a-C:H:W coating was produced using the commercial PVD method. The tested tribological joints were made of AISI 4337 steel and SAE-48 bearing alloy (conformal contact) and AISI 4337 steel and valve shims (non-conformal contact). The contact area was lubricated with SAE 5W40 engine oil and PAO8 oil + 2 wt.% MoS2 nanoparticles. The objective of this work is to explore the influence of PAO8 + MoS2 on the tribological properties of a sliding joint with an a-C:H:W coating and the change in the properties of the oils. In the conformal contact, the lubrication of the a-C:H:W coating with PAO8 + MoS2 caused a significant increase in the friction resistance (than in) as compared to the joints with a quenching and tempering surface layer and lubricated SAE 5W40, while in the non-conformal contact, the lubrication of the a-C:H:W coating with PAO8 + MoS2 caused a decrease in the friction resistance and temperature of the contact area. The joints with the a-C:H:W coating were characterized by higher wear of the SAE-48 bearing alloy, as compared to the joints with the surface layer without coating (lubricated with SAE 5W40 oil-11-fold increase, PAO8 + MoS2-46-fold increase). The wear of valve shims with the a-C:H:W coating was significantly lower as compared to the wear of the commercial version of the valve shims (the difference between joints lubricated with SAE 5W40 oil and PAO8 + MoS2 was 12%, 36% and 29% for unit pressures of 10, 15 and 20 MPa). Lubrication of the a-C:H:W coating with PAO8 oil + MoS2 protected the sliding joints against seizing in non-conformal contact.

Study on the shear properties of masonry pagoda mortar and its influencing factors

Mortar stands as one of the fundamental components in masonry construction, significantly enriching the global cultural heritage, particularly evident in ancient masonry structures. In this paper, the improvements of shear strength of mortar were studied, based on the original formulation material of sticky-rice lime mortar. The study considered the effect of different aggregates and additives on the shear strength of mortar, the shear tests and scanning electron microscopy were employed to analyze the shear strength index and microscopic shear basis of the mortar. The results showed that 2 wt% Na-SiO2 significantly enhanced the shear strength of the mortar. Furthermore, the adhesion and frictional resistance between fiber and lime played a crucial role in enhancing the mortar's shear resistance. Incorporating a 0.5 wt% fiber additive not only effectively improved the mortar's brittleness but also acted as a deterrent to crack formation. Compared to pure lime mortar, the mixture of sand and clay aggregate exhibited a larger capacity at the same volume. This mortar also showcased better plasticity and ductility, making it more suitable for structures with significant shear deformation. These analytical findings provide valuable insights for modifying mortars in the restoration of historical buildings.

Reynolds number dependence of turbulent flows over a highly permeable wall

Direct numerical simulations of turbulent flows over highly permeable porous walls were performed at various Reynolds numbers to examine the effects of the Reynolds number on permeable wall turbulence. The porous medium consisted of Kelvin cell arrays with porosity $0.95$ , and the permeability Reynolds number $Re_K$ ranged from approximately 7 to 50. Simulations with thin and thick porous walls were performed to investigate the effects of spanwise roller vortices associated with the Kelvin–Helmholtz instability. The results show that the effect of the Kelvin–Helmholtz instability becomes more significant with increasing the permeability Reynolds number, and spanwise rollers, for which length scale is an order of channel height, dominate turbulence when $Re_K \gtrsim 30$ . Spanwise rollers reinforce the negative correlation between the wall-normal and streamwise velocity fluctuations close to the porous/fluid interface, and intensify the turbulent velocity fluctuations away from the porous walls, leading to increased frictional resistance. An investigation of the Reynolds number dependence of the modified logarithmic law indicates that the zero-plane displacement and equivalent roughness height are proportional to the square root of permeability, whereas the von Kármán constant increases with the permeability Reynolds number because of the increased mixing length resulting from the relatively large-scale velocity fluctuations induced by spanwise rollers. We developed a model for the modified log law for permeable wall turbulence based on permeability, and confirmed that the skin friction coefficient obtained from the model reasonably predicts the skin friction coefficient for several types of high-porosity porous media. Hence, permeability is a key parameter that characterizes the logarithmic mean velocity profiles over a variety of porous media with high porosity.

Comparative research on the pipe-soil frictional resistances of circular and rectangular pipe sections during trenchless pipe jacking.

Pipe jacking is a trenchless construction method to achieve forward tunneling and efficient construction of underground structure simultaneously without extensive surface excavation. In the process of pipe jacking construction, the jacking force provided by the hydraulic jacking equipment must overcome the frontal resistance of the cutter head and the frictional resistance between the pipe sections and formation at the same time. In particular, the pipe-soil frictional resistance increases with the increases of jacking distance, buried depth, pipe diameter and the complexity of jacking trajectory. Therefore, it is very important to correctly estimate jacking force in trenchless jacking engineering practice for the smooth implementation of pipe jacking, operation risk and comprehensive cost control. Firstly, the stress states of jacking circular and rectangular pipe sections in the soil are analyzed, and the key influencing factors of their pipe-soil frictional resistance are obtained respectively. Then, the pipe-soil frictional resistance of jacking the circular and rectangular pipe sections with the same external surface area in the dry sandy soil and coal granular layer are tested separately by using the self-developed multifunctional experimental apparatus during trenchless pipe jacking. The results show that the pipe-soil frictional resistances of jacking circular and rectangular pipe sections in the coal granular layer are always smaller than that in the sandy soil under the same experimental conditions, and the corresponding fitting calculation equation of pipe-soil frictional resistances are obtained respectively. Meanwhile, the modified calculation methods of the above pipe-soil frictional resistances are proposed respectively based on the relationship between the lateral pressure coefficient K and the buried depth of pipe section H. Moreover, the disturbed area of soil in the upper part of jacking circular pipe section presents an arc distribution, while the disturbed area of soil in the upper part of jacking rectangular pipe section presents a slightly concave distribution. Due to the different disturbance conditions of soil around the pipe section, the lateral pressure coefficient K should be corrected in the calculation equations of pipe-soil frictional resistance of jacking circular and rectangular pipe sections based on the discrete element numerical simulation analysis by EDEM software. Finally, the pipe-soil frictional resistances obtained by different methods in the sandy soil are compared and analyzed. The calculated values of the modified theoretical calculation method are very close to the experimental test values, while the other methods are smaller than the experimental test values, which makes the rationality of the modified theoretical calculation method of pipe-soil frictional resistance is verified, and some suggestions are also put forward for the value of some coefficients in the relevant empirical estimation equations. The above research achievements systematically compared the states of pipe-soil frictional resistances of jacking circular and rectangular pipe sections based on different research methods, especially for the correct evaluation of jacking force during trenchless pipe jacking, they could provide some valuable references and effective guidance for the subsequent research, engineering practice and further development of trenchless pipe jacking technology.

Advancing Shallow Tunnel Construction in Soft Ground: The Pipe-Umbrella Box Jacking Method

The development of modern cities has often led to increased traffic congestion and limited usable space. One effective solution to these problems is to construct roadway tunnels, which can expand urban space and alleviate traffic congestion. However, building large underpass tunnels in urban areas, especially in soft ground, presents technical challenges owing to its extensive environmental disturbance. The pipe-umbrella box jacking method offers a promising solution to these challenges as this method does not require breaking the ground from the surface or disrupting surface traffic. This study reviews the key techniques of the pipe-umbrella box jacking method for constructing large rectangular tunnels with small burial depths in soft ground. The study focuses on three main technical issues: pipe umbrella installation, soil face excavation, and box jacking control. Furthermore, two tunnel projects in Shanghai, China, are presented as case studies to showcase the construction challenges and countermeasures during box jacking tunneling with pipe-umbrella. Practical construction experience has revealed that the installation of the pipe umbrella before box jacking serves as an effective method of ground pre-support. However, its performance can be influenced by factors such as pipe installation deviation and inter-pipe connection design. Both open-face steel grid extrusion (SGE) shields and closed-face earth pressure balanced (EPB) shields can be used for soil excavation during box jacking, with different work modes resulting in distinct ground deformation patterns. Additionally, lubrication grouting has been found to effectively reduce friction resistance and affect vertical ground deformation. The study also examines the lessons learned from case studies and proposes optimization measures. This study can serve as a valuable reference for the tunneling industry, providing insights into the pipe-umbrella box jacking method and its application in constructing large rectangular tunnels in soft ground.

A Theoretical Method for Calculating the Internal Contact Pressure of Parallel Wire Cable during Fretting Wear

Fretting wear of the stay cable is an important factor affecting the service life of the cable. To accurately calculate the extent of fretting wear, it is necessary to calculate the internal contact pressure in the cable. Although there are many theories and experiments on the contact behavior between wires, there are still no theoretical formulations for calculating the distribution of contact pressure in stay cables. In this paper, by studying the transfer effect of contact pressure in the cable, the PIC (parallel wire cable internal point contact pressure) model for calculating the contact pressure in the parallel wire cable is proposed, considering the effects of wire twisting, sheath compression, and cable bending on the contact pressure. A finite element model corresponding to the contact mode between steel wires is established, and the effectiveness of the PIC model is verified through numerical simulation analysis and a comparison of the existing contact models. The results indicate that contact pressure caused by wire twisting (CWT) is superimposed layer by layer inwards, with the contact pressure increasing closer to the inner layers, and its magnitude is mainly related to the axial tension and twist angle. Simultaneously, on the same layer, contact points along the diagonal experience the greatest contact pressure. Contact pressure caused by sheath compression (CSC) is assumed to conform to the Boussinesq distribution, with the outer layers exhibiting greater contact pressure compared to the inner layers. Contact pressure caused by cable bending (CCB) conforms to the two-dimensional closely arranged contact force transmission model, has a clear layering phenomenon, and the contact pressure within the same layer does not change significantly. The magnitude of the contact pressure is exponentially related to the curvature of the cable and proportional to the tension of the cable, which explains the reason why the slip occurs later for the cables with high tensile forces. Among these three types of contact pressure, CWT is the greatest, followed by CCB, while CSC is the smallest. The theoretical analysis results show that factors such as wire radius, tension, torsion angle, and wire position have an impact on contact pressure. Contact pressure is transmitted along force chains within the cable, following the superposition law between layers. It is uncertain whether slip occurs in the neutral axis or in the outermost layer because of the different distributions of tangential force and interlayer frictional resistance between the layers of wires. Fretting wear simulations of two wires demonstrate that contact pressure has a significant influence on wear patterns, and the “averaging” of contact pressure is a major reason for achieving uniform interface wear. While the contact width increases proportionally with the contact pressure, excessive contact pressure can complicate the problem by changing the contact mode from gross slip to partial slip. This study provides a theoretical method for calculating contact pressures at any contact point within the cables in engineering practice.

Development and evaluation of CrAlAgN self-lubricating coatings for high temperature metal forming dies

Conventional lubricants are widely used for die release as well as for cooling assistance on the die surface. However, lubrication is difficult at high temperatures. Oxidation and scaling occur on the work pieces that lead to poor surface finish and a possible warping of the material during cooling. The aim of this research is to develop self-lubricating CrAlAgN nanocomposite coatings for metal forming dies and evaluate their thermal fatigue resistance and wear behavior at elevated temperatures. The CrAlAgN coatings with different Ag contents have been deposited by plasma-enhanced magnetron sputtering. The structure and properties of the coatings were systematically studied to determine the optimal Ag content for achieving a combination of good adhesion, thermal fatigue resistance, and surface lubricity at elevated temperatures. The thermal fatigue resistance of the coatings was evaluated using thermal cyclic testing by cycling the coatings from room temperature to 800 °C up to 1200 cycles. The high temperature wear behavior of the coatings was evaluated using a tribometer up to 900 °C. Good thermal fatigue resistance and low coefficient of friction (COF) were observed in the CrAlAgN coatings with an Ag content in the range of 5–10 at. % at 800 °C. The CrAlAgN coating with 10 at. % Ag exhibited the lowest average COF of 0.05 at 800 °C. The COF of thick CrAlAgN coatings (8 at. % Ag) decreased from 0.5 to 0.2 from 500 to 900 °C, accompanied by an increase in the wear rate under more aggressive wear test conditions. The lubricity of the CrAlAgN coatings at high temperatures was attributed to the lubrication effects from the mixed oxides and encapsulated Ag diffused toward the surface. To further evaluate the coating performance, a hydraulic hot forging punch was coated with a thick CrAlAgN (8 at. % Ag) coating and evaluated in the industrial forging process. The preliminary in-plant trials demonstrated that the coating significantly reduced the dimensional distortion and wear for the forging punch.

DIFFERENCE IN FRICTIONAL RESISTANCE BETWEEN LIGATURE WIRE AND ELASTIC MODULE” (AN IN VITRO STUDY)

Introduction: The purpose of this in-vitro study was to compare the frictional resistance forces generated by slid low friction elastomeric ligatures and stainless steel ligatures wire during leveling and alignment phase. Methods: The testing metal plates consisted of three stainless steel 0.022-in slot size preadjusted brackets of lateral incisor, canine and first premolar. First comparison were the bracket position vertically adhered to the plates. The second one were the canine bracket was adhered as a high canine in 2 mm. The forces generated by wires (0.014-in superelastic nickel-titanium) with the 2 types of ligatures at different bracket position were recorded. Results and Conclusions: The results of the present study revealed that there was a statistically significant difference in the frictional force between group A and group B with a p-value of 0.047 which is less than 0.05 level of significance, while there was no statistically significant difference in the frictional force between group C and group D with a p-value of 0.56 which is greater than 0.05 level of significance.

Comparison of Friction Produced at Backet-Wire Interface in Monocrystalline Ceramic Brackets of 8 Different Brands: An In Vitro Study

ABSTRACT Introduction: The esthetic during the various orthodontic treatments has led to the invention of the brackets. When different ceramic brackets and archwires are used, the different frictional forces may result in the different outputs. Hence, in the present study, we evaluated and compared the frictional resistance between eight standard monocrystalline ceramic bracket models and each of the archwires of four different alloys. Materials and Methods: Frictional force was tested using Instron testing machine, in vitro, for eight types of monocrystalline ceramic bracket, and four types of archwires beta-titanium, NiTi, copper-nickel-titanium, and stainless steel statistical analysis were done using various tools, and significance value of <0.05 was considered. Results: Ormco and AO (Radiance) monocrystalline ceramic brackets created lesser frictional resistance than other monocrystalline ceramic brackets. Stainless steel archwire generates lesser static friction. Beta-titanium archwire created higher static friction. A 0.017 × 0.025 inch stainless steel archwire generates lesser static friction to 0.019 × 0.025 inch TMA. Conclusion: It can be concluded that Ormco and AO (Radiance) monocrystalline ceramic brackets, with stainless steel archwires and of size 0.017 × 0.025 inch, can generate better forces when used for the orthodontic tooth movements.

Isolated slug traveling in a voided line and impacting at an end orifice

Driven by upstream high-pressure steam, liquid slugs in nuclear power plant pipelines impact the end orifice at high speed, leading to bursting pipelines and threatening the plant's safety. This research aimed to accurately and efficiently assess the dynamic behavior of an isolated slug driven by pressurized air in a voided line with an end orifice. An improved one-dimensional (1D) model for the slug motion and impact was established. The dynamic variation of the pressure at both the slug's tail and front, the variation of the slug length, and the frictional resistance coefficient in the model was obtained by three-dimensional (3D) computational fluid dynamics (CFD). Based on 27 cases with different pipeline diameters and tank pressures, it was observed that the driving air pressure had a quadratic relationship and that the slug length had a constant rate of decrease vs the slug tail displacement. Finally, the decrease in the driving air pressure behind the slug, the increase in the air pressure ahead of the slug, the holdup coefficient, and the friction factor obtained from the 3D CFD results were interpreted in the 1D model, and the velocity histories of the liquid slug were found to be in excellent agreement with the 3D CFD solutions.

Understanding the Role of Sharp Edges in the Propagation of Surface Gravity Waves

AbstractUltra‐rough oceanic surfaces, such as oyster reefs, are characterized by densely‐packed, sharp‐edged roughness elements that induce high frictional resistance on the ambient flows. To effectively employ, for example, oyster reefs as a nature‐based solution in coastal protection, a detailed understanding of the frictional wave energy dissipation processes is necessary. This work reports on an experimental study in which six surrogates of very to ultra‐rough oceanic bed surfaces were subjected to regular waves. The influences of different sharpness' of roughness elements (bluntly‐shaped, sharp‐edged, and a combination thereof) and relative spacing between elements compared to the near‐bed horizontal excursion amplitude, λ/ab, on the wave attenuation have been investigated. Turbulence is 2–27 times larger for sharp‐edged surfaces and 1 to 18 times larger for mix surfaces than those of bluntly‐shaped surfaces. Maximum bed shear stresses, hydraulic roughness lengths, and wave friction factors are likewise significantly larger for sharp‐edged compared to bluntly‐shaped surfaces. These observations indicate that the sharp edges are crucial for frictional energy dissipation. Comparing the maximum bed shear stresses determined from wave height reductions to those determined from velocity measurements indicates that in addition to turbulent kinetic energy (TKE), periodic form‐induced stresses significantly contribute to the overall bed shear stresses. This study provides new insight into the frictional dissipation processes of oscillating flows encountering ultra‐rough surfaces.