Plane Wall Research Articles

Numerical Study on Plane and Radial Wall Jets to Validate the 2D Assumption for an Idealized Downburst Outflow

Turbulent radial and plane wall jets have been extensively investigated both experimentally and numerically over the past few decades. Previous studies mostly focused on the heat and mass transfers involved in jet flows. In this study, a comprehensive investigation was conducted on turbulent radial and plane wall jets, considering both jet spread and velocity decay for different parameters. The numerical results were compared with existing experimental measurements. The comparison focused on the velocity profile, jet spread, and velocity decay, and revealed that the Reynolds stress model (RSM) performs well in the simulation of both radial and plane wall jets. The results show that with a typical ratio of cloud base height to diameter for most downburst events, the effects of nozzle height and Reynolds number on the evolution of the radial wall jet are not significant. Both the jet spread and velocity decay exhibit a clear dependence on the Reynolds number below a critical value. Above this critical value, the plane wall jet becomes asymptotically independent of the Reynolds number. The co-flow was found to have a significant influence on the evolution of the plane wall jet. Comparatively, the jet spread and velocity of the radial wall jet were faster than those of the plane jet. For applications in civil engineering, it is valid to approximate the downburst outflow with a two-dimensional (2D) assumption from the perspective of longitudinal evolution of the flows.

Evaluation of a Textile PIFA for Wearable IoT Application and its Challenges

The ever increasing use of body-worn systems in the Internet of Things application such as needs better antenna subsystem designs compatible with its requirements. Several challenges limiting the performance of a body-worn system, from materials, and environmental conditions to the effects of on body application and its hazards are discussed. As a test case, a flexible textile planar inverted-F antenna is presented and discussed. The choice of this topology is due to its simplicity in design and fabrication, relatively broad bandwidth and the presence of a rear ground plane, which minimizes the impacts of the human body on the antenna performance. It is designed on a felt substrate, whereas Aaronia-shield conductive textile is utilized as its conductive parts (radiator, shorting wall and ground plane). The antenna performance are studied in two cases, first in free space and then in bent conditions in the close proximity to the human body. The influence of the relative humidity on the textile antenna performance is also investigated numerically. Simulated and measured results indicated good agreements. Finally, the proposed antenna is integrated with a transceiver module and evaluated on the body in practice. Its wireless link quality is assessed in an indoor laboratory.

Comparison reinforcement design shear wall modelling planar and assembly in elevator shaft

Shear walls modelling as planar or assembly have different assumption in behaviour that will give different responses in forces. Shear wall planar modelling as individual walls which each wall was modelled as a vertical beam. Shear Wall assembly modelling as a combined unit to be represented by one beam element. The application of shear wall assembly is placed in elevator shafts in buildings or stairwell. [1]. In ETABS program, there are two types modelling shear wall are planar walls and wall assemblies. The analysis is based on three types of design section that are Simplified Compression (C) and Tension (T), Uniform Reinforcing and General Reinforcing. The purpose of this study is comparing the planar walls Simplified C and T with planar walls Uniform Reinforcing and wall assemblies Uniform Reinforcing. The conclusion for longitudinal reinforcement are, first, planar walls Simplified C and T is 40 to 96 % larger than wall assemblies, except pier P6 is 28 % smaller, second, planar walls Uniform Reinforcing is larger than 7 to 33 % wall assemblies Uniform Reinforcing, except pier P6 is 39 % smaller, third, the planar walls Simplified C and T, planar walls Uniform Reinforcing transversal reinforcement are 1 to 8 % larger than wall assemblies Uniform Reinforcing, except pier P6 is 51 % smaller.

Layered structure of turbulent plane wall jet

This paper investigates the layered structure of a turbulent plane wall jet at a distance from the nozzle exit. Based on the force balances in the mean momentum equation, the turbulent plane wall jet is divided into three regions: a boundary layer-like region (BLR) adjacent to the wall, a half free jet-like region (HJR) away from the wall, and a plug flow-like region (PFR) in between. In the PFR, the mean streamwise velocity is essentially the maximum velocity, and the simplified mean continuity and mean momentum equations result in a linear variation of the mean wall-normal velocity and Reynolds shear stress. In the HJR, as in a turbulent free jet, a proper scale for the mean wall-normal flow is the mean wall-normal velocity far from the wall and a proper scale for the Reynolds shear stress is the product of the maximum mean streamwise velocity and the velocity scale for the mean wall-normal flow. The BLR region can be divided into four sub-layers, similar to those in a canonical pressure-driven turbulent channel flow or shear-driven turbulent boundary layer flow. Building on the log-law for the mean streamwise velocity in the BLR, a new skin friction law is proposed for a turbulent wall jet. The new prediction agrees well with the correlation of Bradshaw and Gee (1960) over moderate Reynolds numbers, but gives larger skin frictions at higher Reynolds numbers.

Numerical analysis to study enhancement in heat transfer using wavy surface in turbulent dual jet

Enhancement in the heat transfer rate is an essential research area in the present time. Therefore, to achieve this goal in the present case, a sinusoidal wavy wall surface is used in a turbulent dual jet. The changes in amplitude (A) and number of cycle (N) of the sinusoidal wavy surface, not only affect the turbulent characteristics but also improve the heat transfer rate. In comparison to the plane wall surface in a dual jet, it is found that nearly 20.70% of improvement in heat transfer is achieved when N = 7 and A = 0.7. The A and N of the sinusoidal wavy surface are varied from 0.1 to 0.7 and 4 to 12 with an interval of 0.1 and 1, respectively. The Reynolds number (Re), offset ratio, and Prandtl number (Pr) are set to 15 × 103, 5 and 0.71, respectively, for all the computational simulations. The average Nusselt number (Nuavg) increases almost linearly when the amplitude changes from 0.1 − 0.7 up to N = 7. A new scaled self-similarity solution for the crest and trough positions is performed to neglect the effect of bottom wall variation. The similarity solution of the crest for various number of cycles in the combined region for different amplitudes suggests that when A ≥ 0.5, the profiles of all the number of cycles spread close to the wall region and in the outer region. Whereas, the self-similarity behaviour of trough shows that when A ≥ 0.3, the profiles of all the number of cycles spread only close to the wall region and almost coincide in the outer region and inflection point rises in the crosswise distance as amplitude increases. It is also noticed that the decay in bottom wall temperature increases with increasing A when N = 10, thereafter, the decrease in bottom wall temperature is nearly same beyond N > 9.

Reflection of Irregular Waves from Perforated-wall Structures when the Chamber is Filled with Rocks

Kim, Y.-T. and Lee, J.-I., 2021. Reflection of irregular waves from perforated-wall structures when the chamber is filled with rocks. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 151–155. Coconut Creek (Florida), ISSN 0749-0208. The perforated-wall is normally applied to the quay walls and breakwaters such as vertical structures to improve the hydraulic characteristics. The perforated-wall could reduce the wave reflection, wave pressure, and wave overtopping comparing with the plane wall. The chamber of perforated-wall was generally designed empty, that is, the chambers were filled with only seawater. In this study, the hydraulic characteristics of perforated-wall were investigated with hydraulic model experiments when the chambers were filled with the armor rocks. The perforated-wall with vertical slits was applied in the tests. The numbers of the chamber and the sizes of the armor rock were changed. The reflection from the perforated wall was measured and compared for the various test conditions.

Two dimensional unsteady flow past a square cylinder: Influence of proximal plane wall and power-law index

A numerical analysis using Ansys Fluent has been done to investigate the flow physics involved in both Newtonian and Power-law (shear-thinning) fluid flow over a square cylinder, placed near a wall with altered gap-to-side (G/a) ratios (where G represents the gap between the cylinder and the plane wall and a represents side of the square cylinder). At a constant Reynolds number, Re = 150, numerical calculations for unsteady, incompressible Navier-Stroke (N-S) equation with varying viscosity is carried out by using second-order upwind momentum and least square cell based pressure solver. It is found that for small G/a ratio shear-thinning fluid exhibits vortex shedding which was absent for Newtonian fluid. G/a ratio and power-law index have a strong influence on the coefficient of lift and coefficient of drag (CL and CD respectively). With the increase in gap-ratio, CD decreases and CL increases at a constant value of power-law (n) index. Also, CL increases and CD reduces with a decrease in n at a constant value of G/a. Detailed observation of instantaneous and mean vorticity and streamlines, coefficient of lift and drag, mean pressure distribution over the cylinder and the plane wall and recirculation length have been presented.

Enhancing the Heat Transfer Rate Through Surface Manipulation

In the present paper, the flow characteristics and the heat transfer rate of turbulent dual jet impinging on a sinusoidal wavy surface are numerically studied. Finite-volume-based two-dimensional Reynolds-averaged Navier–Stokes equations are used to handle the complex behavior of the turbulent dual. The offset ratio is varied from 3 to 15 with an interval of 2. To evaluate the role of sinusoidal wavy surface on flow and heat transfer characteristics, the amplitude and number of cycle are varied from 0.1 to 0.7 m and from 4 to 12 with an interval of 0.1 m and 1, respectively. In the present numerical work, the Reynolds number and Prandtl number are set to 15,000 and 0.71, respectively. The bottom wall is maintained at a constant temperature. The results show that the sinusoidal wavy surface affects both the flow characteristics and heat transfer rate, and that it also enhances the heat transfer rate significantly. Approximately, a maximum of 23.27% enhancement in heat transfer rate is achieved with respect to the plane wall surface. It is also found that the average Nusselt number depends on both amplitude and number of cycle of the sinusoidal wavy surface.

The role of hydrodissection in native tissue repair of anterior vaginal wall defects

A variety of surgical techniques are available for vaginal prolapse repair, indicating a lack of consensus. A debate regarding the utility of hydrodissection for splitting the surgical plane of the vaginal wall exists. The aim of this study is to evaluate the impact of hydrodissection in anterior colporrhaphy (AC). Patients undergoing primary AC were randomly assigned to an approach with (study group) versus without (control group) hydrodissection. Five surgeons performed both techniques, and the trimmed vaginal tissue was retrieved for histological analysis. Two pathologists, blinded to the surgical approach, evaluated the presence of a loose connective tissue at the surgical dissection plane (controversially deemed 'fascia', as explained in this article). In addition, we compared the operative time, pain score and haemoglobin levels. After statistical analysis, data were presented using percentile, and statistical significance was tested using the χ2 and Fisher's exact tests. Forty-six patients underwent primary elective AC, with 23 patients in each, the study and control groups. The groups were comparable regarding age (study group 60.33 ± 11.95 years and control group 59.86 ± 12.04, P = 0.90), menopausal status (study group 17 (73.9%) and control group 15 (68.2%), P = 0.67) and other characteristics. We found no difference in sample characteristics between the two groups. Connective tissue was found in only 13.6% (n = 3) of patients after hydrodissection and in 27.3% (n = 6) of patients without hydrodissection (P = 0.46). The hydrodissection group had significantly less bleeding than the control group (ΔHB 0.66 ± 0.66 vs 1.21 ± 0.84, P = 0.05). After hydrodissection, less bleeding was noted without compromise the surgical planes.

Re-entrant transition as a bridge of broken ergodicity in confined monolayers of hexagonal prisms and cylinders

The entropy-driven monolayer assembly of hexagonal prisms and cylinders was studied under hard slit confinement. At the conditions investigated, the particles have two distinct and dynamically disconnected rotational states: unflipped and flipped, depending on whether their circular/hexagonal face is parallel or perpendicular to the wall plane. Importantly, these two rotational states cast distinct projection areas over the wall plane that favor either hexagonal or tetragonal packing. Monte Carlo simulations revealed a re-entrant melting transition where an intervening disordered Flipped-Unflipped (FUN) phase is sandwiched between a fourfold tetratic phase at high concentrations and a sixfold triangular solid at intermediate concentrations. The FUN phase contains a mixture of flipped and unflipped particles and is translationally and orientationally disordered. Complementary experiments were conducted with photolithographically fabricated cylindrical microparticles confined in a wedge cell. Both simulations and experiments show the formation of phases with comparable fraction of flipped particles and structure, i.e., the FUN phase, triangular solid, and tetratic phase, indicating that both approaches sample analogous basins of particle-orientation phase-space. The phase behavior of hexagonal prisms in a soft-repulsive wall model was also investigated to exemplify how tunable particle–wall interactions can provide an experimentally viable strategy to dynamically bridge the flipped and unflipped states.

Fluid resonance in the narrow gap of a box-wall system under cnoidal wave action

Fluid resonance within a narrow gap formed by a box in close proximity to a plane wall under cnoidal wave action is investigated using the Computational Fluid Dynamics (CFD) package OpenFOAM®. Fluid resonance behavior excited by the second-order harmonic component of the incident cnoidal waves is concerned. Numerical simulations show the large second-order induced wave height in the gap which increases as the incident wave height gets larger or the water depth gets shallower. The large double-frequency component of the cnodial waves is the major reason for the phenomenon. Harmonic analysis indicates that the CFD results can be represented well by a second-order approximation, and the free surface nonlinearity is an indispensable factor in the action of the cnoidal incident wave. Similar phenomenon is also found in the horizontal wave force. However, the second-order induced resonance within the gap has insignificant effect on the vertical wave force.

Adsorption of Binary Mixtures of the Lennard-Jones Truncated and Shifted Fluid on Planar Walls

Gas phase adsorption of binary mixtures on planar walls in dispersive systems was studied by molecular dynamics simulations, extending a previous study on the adsorption of pure components. The interactions between all particles, fluid as well as solid, were described by the Lennard-Jones truncated and shifted potential with a cutoff radius of 2.5 σ. Two classes of fluid mixtures were studied: (a) symmetric mixtures, in which the pure components and also their interactions with the wall particles are the same but the unlike fluid–fluid interaction parameter is varied; (b) an asymmetric mixture, in which the dispersive energy of one fluid component was lowered, such that it becomes light-boiling. For the asymmetric mixture, both nonselective walls as well as walls with different selectivity for the two fluid components were investigated. Data on the surface excess, the thickness, and the structure of the adsorbate layer as well as on the selectivity were measured. The results give insight into how adsorption of binary mixtures is influenced by the different dispersive interactions between the fluids and between the fluids and the wall.

The Influence of Variable Density on Turbulent Wall Jet: A Numerical Comparative Study

The first objective of this numerical research is to help understand the influence of variable density on the structure of turbulence, through the study of a wall jet, and to validate our results with those of the experimental study of A. Soudani. The source of density variation is the mixture between two different non-reactive fluids, with a fixed temperature and pressure. A mass weighted averaging for different variables is applied to the calculation, using ANSYS FLUENT 15.0 commercial software. The principal experience consists of injecting tangentially and alternatively near the wall a gas (air-helium) different from the external flow, through a slot of height 3mm between two plane walls. Such a process permits to provoke an important density difference. The study reaches the conclusion that turbulence is strong, with a slight increase of velocity near the wall and an evident diminution of skin friction, in the case of light fluid injection. The second aim is to estimate the Kolmogorov and large eddies’ scales to construct LES grid to access instant variables in experience.

MHD mixed convection of hybrid nanofluid in a wavy porous cavity employing local thermal non-equilibrium condition

The current study treats the magnetic field impacts on the mixed convection flow within an undulating cavity filled by hybrid nanofluids and porous media. The local thermal non-equilibrium condition below the implications of heat generation and thermal radiation is conducted. The corrugated vertical walls of an involved cavity have {T}_{c} and the plane walls are adiabatic. The heated part is put in the bottom wall and the left-top walls have lid velocities. The controlling dimensionless equations are numerically solved by the finite volume method through the SIMPLE technique. The varied parameters are scaled as a partial heat length (B: 0.2 to 0.8), heat generation/absorption coefficient (Q: − 2 to 2), thermal radiation parameter (Rd: 0–5), Hartmann number (Ha: 0–50), the porosity parameter (ε: 0.4–0.9), inter-phase heat transfer coefficient (H*: 0–5000), the volume fraction of a hybrid nanofluid (ϕ: 0–0.1), modified conductivity ratio (kr: 0.01–100), Darcy parameter left(Da: 1{0}^{-1},mathrm{ to },1{0}^{-5}right), and the position of a heat source (D: 0.3–0.7). The major findings reveal that the length and position of the heater are effective in improving the nanofluid movements and heat transfer within a wavy cavity. The isotherms of a solid part are significantly altered by the variations on Q, {R}_{d}, {H}^{*} and {k}_{r}. Increasing the heat generation/absorption coefficient and thermal radiation parameter is improving the isotherms of a solid phase. Expanding in the porous parameter varepsilon enhances the heat transfer of the fluid/solid phases.

Out-of-plane buckling of boundary regions in planar RC structural walls: an approach to prevent instability

Despite the slenderness that usually characterizes planar RC structural walls, these structural elements effectively resist significant in-plane earthquake demands. However, during the 2010 Chile and 2011 New Zealand earthquakes, some medium to high-rise buildings exhibited out-of-plane buckling instability, a failure mode that had only been observed in experiments. This failure mode was first studied in the 1980s; however, it was just after the recent earthquakes that several studies arose to improve design procedures to avoid future damage. Parameters as the height-to-thickness ratio, reinforcement content, material properties, and the hysteretic behavior of the longitudinal steel have been identified as critical for the onset of buckling instability. In this paper, the influence of the concrete cover was studied through a fiber-based element parametric analysis conducted on 120 RC prisms that simulate boundary elements of special RC walls. The prisms were subjected to incremental axial cyclic loading that mimics the effects of in-plane lateral displacements. As a result, a new approach is presented to limit tensile strains developed in the longitudinal reinforcement of boundary zones to prevent the onset of out-of-plane buckling instability.

Out-of-plane buckling of boundary regions in planar RC structural walls: an approach to prevent instability

Despite the slenderness that usually characterizes planar RC structural walls, these structural elements effectively resist significant in-plane earthquake demands. However, during the 2010 Chile and 2011 New Zealand earthquakes, some medium to high-rise buildings exhibited out-of-plane buckling instability, a failure mode that had only been observed in experiments. This failure mode was first studied in the 1980s; however, it was just after the recent earthquakes that several studies arose to improve design procedures to avoid future damage. Parameters as the height-to-thickness ratio, reinforcement content, material properties, and the hysteretic behavior of the longitudinal steel have been identified as critical for the onset of buckling instability. In this paper, the influence of the concrete cover was studied through a fiber-based element parametric analysis conducted on 120 RC prisms that simulate boundary elements of special RC walls. The prisms were subjected to incremental axial cyclic loading that mimics the effects of in-plane lateral displacements. As a result, a new approach is presented to limit tensile strains developed in the longitudinal reinforcement of boundary zones to prevent the onset of out-of-plane buckling instability.

Experimental and numerical study on planar multi-column walls behaviours with boundary supports

The continuous-supported multi-column walls have already been used in modular steel buildings (MSB). Therefore, using two full-scale specimens, the current study evaluated the axial behaviour of planar multi-column walls with structural hollow sections (SHS). Then, a 3D finite element model (FEM) was created and validated to study the individual column and boundary support effects on each column. Prediction equations in EC3, AISC360, and GB50017 were then used to predict the ultimate compressive resistance of columns in walls. Because of the elastic buckling, the current slenderness limit for Class 3 steel cross-sections becomes less conservative. The boundary support effect enhances external columns rigidity and capacity than other columns, leading to instability. FEM provides reasonable estimates of the compressive behaviour of walls and each column. Each column exhibits distinct load distribution, confirming that the assumption of uniform load distribution among columns is unacceptable for multi-column modular walls. The prediction equations showed that GB50017 was safer than the EC3 and AISC, while EC3 was the least secure. Hence, the current study concluded experimental, numerical, and analytical findings to evaluate the axial behaviour of multi-column walls in multi-storey MSBs.

English

BACKGROUND Incisional hernias are a common occurrence following midline laparotomy. Numerous techniques have been employed in the management of this common condition. Randomized trials and evidence based medicine help us in deciding what the optimal treatment is in a particular condition. This is often not possible in case of hernia due to the heterogeneity of population. Laparoscopy is gaining popularity in the management of this condition as results are comparable to open surgery with lesser post-operative pain. The placement of mesh intraperitoneally as in laparoscopic intraperitoneal onlay mesh repair has its own disadvantage such as mesh erosion into viscera. Placement of mesh endoscopically as an onlay repair seems to be a good option, more so in the developing world, considering the prohibitive cost of composite mesh. The purpose of this study was to analyze the technical ease, reproducibility, outcome, postoperative pain and complications of laparoendoscopic hybrid technique in the management of abdominal wall hernia. METHODS This technique combines the benefits of minimal invasive surgery and ease of onlay mesh repair, while reducing wound related problems associated with open surgery. It involves first a laparoscopic approach in entry, reducing the contents, visualizing the sac followed by endoscopic dissection using the same trocar anterior to abdominal wall in the subcutaneous plane. This is followed by sac dissection, suturing the abdominal wall and placing an onlay mesh RESULTS Fifteen patients have been operated; no subcutaneous drains were placed. A polypropylene onlay mesh was used and fixation done with suturing. No major complications were seen. There was no subcutaneous emphysema. CONCLUSIONS The laparoendoscopic hybrid technique offers advantage of being minimally invasive and having lower wound related complications, with early ambulation and decreased hospital stay. It is also technically easier to suture the defect and allow complete excision of the sac. However a randomized trial is necessary and larger series are required to compare the results with other established techniques. KEY WORDS Incisional Hernia, Laparo - Endoscopic - Onlay Mesh, Surgical Techniques, SCOLA

Modeling of Thermal Conductivity in a Medium with Phase Transition with a Moving Boundary of Phase Change

This work is devoted to the theoretical study of the effect of the phase interface motion on thermal conductivity in a liquid-solid nonlinear medium with a phase transition. The problem under consideration deals with the Stefan problems. Its most significant feature is the jump in the phase properties at separation of their moving boundaries. The objective was achieved by solving the following tasks: the construction of the process mathematical model based on its cell representation and with the use of the Markov chain theory mathematical apparatus, performing numerical experiments with the developed model, demonstrating its operability and the possibility to achieve the set goal. The most significant scientific results were as follows. First was an algorithm for the construction of a cell mathematical model of nonlinear thermal conductivity in a phase transitions medium with a moving phase interface for domains of a canonical shape (plane wall, cylinder, ball). Second, the results of the numerical experiments, showing that the jump of properties affected greatly the kinetics of the process. The significance of the results obtained consisted in the development of a simple but informative mathematical model of the media heat treatment kinetics with phase transformations, available for a direct use in the engineering practice. The proposed algorithm for constructing the model can be effectively used in prediction the open water pipes freezing in cold regions, in modeling the heat treatment of metals, in choosing the freezing modes of food products for a long-term storage, and other thermo-physical processes.

Position-Tracking Control of Dual-Rope Winch Robot With Rope Slip Compensation

This article presents the design and position-tracking control of a novel two-degree-of-freedom dual-rope winch robot. It is designed to be facilely installed at both corners of a building using two synthetic ropes and to move freely on the wall plane using the ropes to perform building maintenance work. This robot consists of a dual-rope winch system responsible for its movement on a plane and a thrust module that allows the robot to remain close to the wall through the force of the propeller. In the dual-rope winch system, ascending modules driven by two pulleys and connected by differential gears are arranged symmetrically; the position and posture on the plane can be determined by controlling the ropes. The robot winds a synthetic rope around the pulley to support the load with frictional force. Precise position control is difficult to implement because of the elasticity of the rope and the slip around the pulley. Therefore, in this article, a feedforward control to predict and compensate for the slip length of the rope and a proportional-integral controller to regulate the position error owing to the dynamic characteristics of the rope are proposed. Experiments to verify the performance of the controller for various trajectories were performed on the test bench. It was confirmed that the actual trajectory deviation is within 0.5% of the target trajectory.