Top Of Wall Research Articles

Three-dimensional numerical modeling, simulation and experimental validation of milling of a thin-wall component

Study on mechanics of milling of thin-wall components using a helical end mill is important in view of its complex nature and prominent applications in aerospace, automobile and electronics areas. This article presents a realistic three-dimensional, thermo-structural, finite-element-based mathematical model for thin-wall milling of aerospace grade aluminum alloy. Lagrangian formulation with explicit solution scheme was employed to simulate the interaction between helical milling cutter and the workpiece. Behavior of the material at high strain, strain rate and temperature was defined by Johnson–Cook material constitutive model. Johnson–Cook damage law and friction law were used to account for chip separation and contact interaction. Experimental work was carried out to validate the results predicted by the mathematical model. The developed model predicted the forces in radial, feed and axial directions with errors of 14%, 26% and 33%, respectively. The prediction errors for deflections at top, middle and bottom portions of thin wall were within 11%–39%. The simulated chip dimensions were in good agreement with experimental results while the computed cutting temperature varied by 17% with respect to the experimental value. Overall, it was found that the developed model predicts the process responses with fair and acceptable prediction accuracy. Using the developed model, a study on the effect of process parameters on the performance parameters, namely cutting and thrust forces, stress distribution, cutting temperature, part deflection and chip morphology was carried out, which is not possible using a two-dimensional orthogonal or oblique cutting model. It was found that the developed three-dimensional mathematical model provided very useful insights into the complex physical interaction of helical cutting tool and workpiece during thin-wall milling of aerospace alloys.

CFD simulation of sand particle erosion under multiphase flow conditions

Although erosion under multiphase flow conditions can be observed frequently, due to its inherent complex nature, it has received much less attention compared to that in single phase flow. In the present study, a Computational Fluid Dynamics (CFD) model was adopted to analyze air-water-sand flow in a Horizontal-Horizontal (H-H) standard elbow with a diameter of 76.2mm (r/D=1.5). For this configuration, erosion was examined under slug/pseudo-slug flow regimes. The CFD model was previously assessed using experimental data obtained using an ultrasonic technique.It was noticed that the passage of slugs was intermittent and only then the particles impacted the pipe elbow at high velocities. Moreover, it was observed that in H-H elbow, maximum erosion occurred at the top of the elbow's outer wall. Qualitative results such as phase distributions, particle concentration, particle velocity and erosion pattern were used to investigate the erosion mechanism under such multiphase flow conditions.

ENHANCEMENT OF A SUNSPOT LIGHT WALL WITH EXTERNAL DISTURBANCES

ABSTRACT Based on the Interface Region Imaging Spectrograph observations, we study the response of a solar sunspot light wall to external disturbances. A flare occurrence near the light wall caused material to erupt from the lower solar atmosphere into the corona. Some material falls back to the solar surface and hits the light bridge (i.e., the base of the light wall), then sudden brightenings appear at the wall base followed by the rise of wall top, leading to an increase of the wall height. Once the brightness of the wall base fades, the height of the light wall begins to decrease. Five hours later, another nearby flare takes place, and a bright channel is formed that extends from the flare toward the light bridge. Although no obvious material flow along the bright channel is found, some ejected material is conjectured to reach the light bridge. Subsequently, the wall base brightens and the wall height begins to increase again. Once more, when the brightness of the wall base decays, the wall top fluctuates to lower heights. We suggest, based on the observed cases, that the interaction of falling material and ejected flare material with the light wall results in the brightenings of wall base and causes the height of the light wall to increase. Our results reveal that the light wall can be not only powered by the linkage of p-mode from below the photosphere, but may also be enhanced by external disturbances, such as falling material.

Treatment of total pelvic organ prolapse using a whole biological patch: A pilot study of 17 patients.

A complete and non-splice porcine small-intestine submucosa (SIS) patch was used for total pelvic anatomical repair of organ prolapse. This study included a total of 17 patients with severe total pelvic organ prolapse, including five patients with combined stress urinary incontinence (SUI). Panhysterectomy was performed, and then a porcine SIS patch was placed on the anterior (posterior) vaginal wall. The top of the vaginal wall was moved to the corresponding side of the vaginal wall, and the patch was sutured to bilateral uterosacral ligaments, the sacrospinous ligament, and arcus tendineus fasciae pelvis. SUI was addressed at the same time. 'Failure' was defined as anterior or posterior wall prolapse beyond the hymen. The mean follow-up duration was 11.6 ± 7.45 months (2-24 months). No symptom recurrence was observed in the five patients with combined SUI. One patient who underwent porcine SIS patch placement on the posterior wall experienced stage II anterior vaginal wall prolapse after surgery. The vaginal wall and fornix of the remaining patients with patches were restored to stable anatomical positions (92.85%). No organ damage, infection, erosion, or rejection was observed, and no blood transfusion was necessary. This study is the first to implement total pelvic anatomical repair using a complete and non-splice SIS. Our results suggest that this new surgical method is safe and can achieve satisfactory therapeutic effects, especially for patients with combined SUI.

Experimental evaluation of the interaction between strength concrete block walls under vertical loads

Abstract This paper aims to evaluate the interaction between structural masonry walls made of high performance concrete blocks, under vertical loads. Two H-shaped flanged wall series, all full scale and using direct bond, have been analyzed experimentally. In one series, three flanged-walls were built with the central wall (web) supported and, in the other one, three specimens were built without any support at the central web. The load was applied on the central wall and vertical displacements were measured by means of displacement transducers located at eighteen points in the wall-assemblages. The results showed that the estimated load values for the flanges were close to those supported by the walls without central support, where 100% of the load transfer to the flanges occur. The average transfer load rate calculated based on the deformation ratio in the upper and lower section of the flanged-walls, with the central web support, were 37.65% and 77.30%, respectively, showing that there is load transfer from the central wall (web) toward the flanges, particularly in the lower part of the flanged walls. Thus, there is indication that the distribution of vertical loads may be considered for projects of buildings for service load, such as in the method of isolated walls group. For estimation of the failure load, the method that considers the walls acting independently showed better results, due to the fact that failure started at the top of the central wall, where there is no effect of load distribution from the adjacent walls.

A SOLAR FLARE DISTURBING A LIGHT WALL ABOVE A SUNSPOT LIGHT BRIDGE

ABSTRACT With the high-resolution data from the Interface Region Imaging Spectrograph, we detect a light wall above a sunspot light bridge in the NOAA active region (AR) 12403. In the 1330 Å slit-jaw images, the light wall is brighter than the ambient areas while the wall top and base are much brighter than the wall body, and it keeps oscillating above the light bridge. A C8.0 flare caused by a filament activation occurred in this AR with the peak at 02:52 UT on 2015 August 28, and the flare’s one ribbon overlapped the light bridge, which was the observational base of the light wall. Consequently, the oscillation of the light wall was evidently disturbed. The mean projective oscillation amplitude of the light wall increased from 0.5 to 1.6 Mm before the flare and decreased to 0.6 Mm after the flare. We suggest that the light wall shares a group of magnetic field lines with the flare loops, which undergo a magnetic reconnection process, and they constitute a coupled system. When the magnetic field lines are pushed upward at the pre-flare stage, the light wall turns to the vertical direction, resulting in the increase of the light wall’s projective oscillation amplitude. After the magnetic reconnection takes place, a group of new field lines with smaller scales are formed underneath the reconnection site, and the light wall inclines. Thus, the projective amplitude notably decrease at the post-flare stage.

Numerical Analysis of Deformation of AZ31 Magnesium Alloy in Backward Extrusion with Counter Pressure

A numerical simulation on the deformation behavior of AZ31 magnesium alloy during backward extrusion with counter pressure was investigated by FE software DEFORM. The results show that the steady load increases nonlinearly with the increment of counter pressure. The equivalent strain gradient decreases significantly results from the counter pressure and the unevenness in the top of wall disappeared approximately when the counter pressure is 10~15MPa. Furthermore, there are obviously shear band along the inner fillet to outer fillet of workpiece. Higher hydrostatic pressure generated with counter pressure compared that of no counter pressure leads to improve the plastic deformation limit. The damage factor is reduced significantly in the backward extrusion with counter pressure, which is beneficial to the improvement of crack.

Predicting the behaviour of storage cells in early Condeep structures

RASP, also now called VecTor6, is a nonlinear finite element program for the analysis of reinforced concrete structures that uses 3-dimensional stress–strain relation of cracked concrete based on the modified compression field theory. RASP was used to predict the behavior of a 3-dimensional 1:13 scale model of a typical upper dome-cell wall junction of a storage cell in an early Condeep structure. It predicted a flexure-shear failure at the top of the cell wall when it was subjected to a pressure differential equivalent to 129–134 m head of water. Yet, there was deviation between the theoretical and the observed response of the model since the analysis ignored the detrimental effect of water pressure in the cracks. Before applying the results of the pressure test on the scale model to the prototype structure the size effect in shear was examined. It was concluded that because the failure was triggered by flexural yielding the size effect in shear was not significant for this case.

Modal analysis for kinematic response of flexible cantilever retaining wall

Seismic response of flexible cantilever wall retaining a semi-infinite viscoelastic soil under plane strain condition is investigated in this study. A novel modal analysis is derived based on the assumption of vanishing vertical displacements of the soil-wall system. The horizontal displacements of the soil-wall system are expressed by a series of modes in terms of the separate variable method. The boundary value problem is solved by considering the soil-wall interaction. Good agreement of the proposed solution results with those by the available methods confirms its accuracy. Closed-form solutions are derived for the following: (i) the displacement and stress field of the soil-wall system; (ii) the stiffness in the mth mode and dynamic Winkler modulus of the soil; (iii) translational and rotational response factors of the wall; (iv) the displacement amplification factor at the wall top. Kinematic response of the soil-wall system is evaluated in order to assess dynamic behavior of the wall.

The effect of using a high-albedo material on the Universal Temperature Climate Index within a street canyon

This study investigates the effect of different high-albedo adaptation strategies on air temperature, mean radiant temperature and the Universal Temperature Climate Index (UTCI) for an idealized 2D street canyon. The used numerical model computes the heat transport in the canyon, and specifically takes into account the effect of multiple scattering of radiation. In general the mean radiant temperature has a much larger impact on the UTCI than the air temperature. Moreover, the mean radiant temperature exhibits strong spatial variations in the canyon due to its sensitivity to shading. The impact of albedo-differences on the UTCI is thus relatively small compared to the large shading effects. The best strategy to minimize the UTCI for the outdoor environment with building height to width ratio H/W=0.5 is found to be a uniform albedo of 0.2. For H/W=1.0, an albedo gradient from high at the bottom part to low at the top of the vertical walls showed the lowest UTCI. Although using high-albedo materials can mitigate the atmospheric urban heat island effect, it is very likely to increase pedestrian heat stress.

High-rise Reinforced-concrete Building Incorporating an Oil Damper in an Outrigger Frame and Its Vibration Analysis

The reinforced-concrete multi-story shear-wall structure, which can free a building from beams and columns to allow the planning of a vast room, has increasingly been used in Japan as a high-rise reinforced-concrete structure. Since this structural system concentrates the seismic force onto multi-story shear walls inside, the bending deformation of the walls may cause excessive deformation on the upper floors during an earthquake. However, it is possible to control the bending deformation to within a certain level by setting high-strength and rigid beams (outriggers) at the top of the multi-story shear walls; these outriggers restrain the bending behavior of the walls. Moreover, it is possible to achieve high energy dissipation by placing vibration control devices on the outriggers and thus restrain the bending behavior. This paper outlines the earthquake response analysis of a high-rise residential tower to demonstrate the effectiveness of the outrigger frame incorporating vibration control devices.

Retaining walls with relief shelves

Cantilever retaining wall with pressure relief shelves is considered as a special type of retaining wall. The concept of providing pressure relief shelves on the backfill side of a retaining wall reduces the total earth pressure on the wall, which results in a reduced thickness of the wall and ultimately in an economic design of a cantilever wall. A limited number of solutions and measurements can be found for this type of wall in the literature. The shapes of the measured earth pressure distributions differ among studies because the model scales were different; for example, the wall during one measurement was permitted to move but was not permitted to move in the other measurements. This paper presents a Finite Element analysis of this type of wall using PLAXIS2D-AE.01. The reduced total active earth pressure due to the provisioning of shelves is depicted. It was found that the shelves had a significant effect on the resulting earth pressure distribution. The distribution approximately followed the distribution of the solution by Klein (Calculation of retaining walls (in Russian). Vysshaya Shkola, Moscow, 2014). It also followed the shape of the measurements of Yakovlev (Experimental investigation of earth pressure on walls with two platforms in the case of breaking loads relieving on the backfill. Odessa Institute of Naval Engineers, pp 7–9, 1974). A parametric study was conducted to enable a discussion of the effects of the number of shelves, shelf rigidity, and shelf position on the resulting distribution of the lateral earth pressure, wall top movement, and acting maximum flexural moment of the wall. For high retaining walls and for some repair systems for constructed walls that have problems with stability, it is recommended to provide the cantilever wall with a shelf at a third of the wall height from the top of the wall or more shelves at different levels. Suggested updates are provided to enhance the manual solution of Klein in the calculation of the acting maximum bending moment of the wall.

Finite Element Modeling and Mechanical Behavior of Masonry-Infilled RC Frame

During the analysis of reinforced concrete structures, the infill wall is usually simplified as a diagonal inclined strut to facilitate finite element modeling calculations. However, the actual seismic damage and single frame-filled wall pushover experimental results show that when the earthquake shear force is huge, the top of the infill wall and the beam–column connections are usually, thus the path of the force transfer will be changed. Based on this actual failure phenomenon, a new calculation model which has different contact position between the equivalent bracing walls and the frame columns is generated. Thus, the force analysis is given based on this model, the formulae for calculating the equivalent width of bracing walls, the shear bearing capacity of the wall-filled frame, and the infill wall’s actual participation in the stiffness. A finite element simulation method by ABAQUS is used to determine an empirical formula for calculating the reasonable contact position between the equivalent bracing walls and the frame columns. The verification results show that the finite element model presented in this paper is more reasonable, and the stiffness and shear resistance of infill wall should not be neglected. The calculation formula of stiffness of infill wall presented in this paper is coincided with seismic code. But the calculation formula of shear resistance of infill wall presented in seismic code is higher than the actual value, so it is suggested that calculation formula presented in this paper should be accepted.

Thermosolutal Mixed Convection in an Air Filled Ventilated Enclosure With Slot Wise Embedded Heat and Contaminant Sources

Airflow, heat, and contaminant transfer in a mechanically ventilated two-dimensional rectangular enclosure by discrete heat and contaminant sources as well as external forced convection at various inlet and outlet locations is numerically simulated. Two different enclosure configurations are considered. In configuration A, the cold air is injected at the top of the left vertical wall and exited at the bottom of the right vertical wall. In configuration B, the cold air is injected at the lower edge of the left vertical wall and exited at the top of the right vertical wall. The objective of the study is to find the relative locations of inlet and outlet in order to obtain more effective cooling in the core of the enclosure by maximizing the heat and contaminant removal rate and reducing the overall temperature. The developed mathematical model is governed by the two-dimensional continuity, momentum, energy, and concentration equations. The governing equations in Cartesian co-ordinates are solved by finite volume based semi-implicit method for pressure linked-equations (SIMPLE) algorithm based on a staggered grid system. Results are presented for different values of the Reynolds number, Grashof number, Sherwood number, and Buoyancy ratio in the laminar regime. A convective transport visualization technique is used to study the behavior of physical phenomena due to stream function, thermal, and solutal functions. The results indicate that cooling inside the core of the enclosure is most effective when the inlet is kept at the bottom of the left vertical wall.

Performance of rubble mound breakwaters under tsunami attack, a case study: Haydarpasa Port, Istanbul, Turkey

Ports are one of the most vulnerable coastal utilities in case of marine natural hazards such as tsunamis and need to be protected against their devastating effects. Thus, studying the effects of tsunamis on protective structures such as breakwaters is critical. The Sea of Marmara is a part of an active earthquake zone that has generated tsunamis in the history. In terms of population density, coastal utilization, and economic potential, Marmara coastline seems most vulnerable to marine hazards. The availability of natural stones allows for wide use of rubble mound breakwaters as coastal protective structures in Turkey. The stability of these types of structures under the attack of storm waves has already been studied. However, their stability and performance under the effect of long waves and tsunami attacks have not yet been studied experimentally. The present study is a case study focusing on Haydarpasa Port, located at the southern entrance of Istanbul Bosphorus Strait (North coast of the Sea of Marmara). It aims to investigate the performance level of the port in case of tsunami attack.Physical model experiments were conducted in the 105-m long wave flume in the Port and Airport Research Institute (PARI), Japan, with a Froude-type length scale of 1/30. The experiments conducted to test the stability of rubble mound breakwater were twofold: (i) solitary wave experiments and (ii) tsunami overflow experiments. The heights of incoming tsunami waves were selected from results of simulations were conducted in the same region (Oyo Int. Co., 2007; Ayca, 2012; Yalciner et al., 2014; Guler et al., 2014; Aytore, 2015). First, the incoming solitary wave heights were selected as 5, 7.5, and 10cm. Using the overflow heights obtained from solitary wave experiments, i.e., wave height at the top of crown wall when the solitary waves are overtopping the crown wall, tsunami overflow experiments were conducted ranging from an overflow height of 1.1cm to 4.6cm. Results of these experiments showed that Haydarpasa Breakwater, especially the crown wall of the breakwater, is not stable under a moderate tsunami attack. Therefore, an improved cross section was also tested under the same conditions, and the improvement proved successful.

The minimally invasive treatment of cyst simplex of sublingual gland by the mucosal bridge-tunnel surgery

To explore the clinical effectiveness of minimally invasive treatment of cyst simplex of sublingual gland by the mucosal bridge-tunnel surgery. A total of 35 patients were enrolled. Minimally invasive treatment of cyst simplex of sublingual gland was performed by mucosa bridge-tunnel surgery. Two parallel incisions were initially made at the apex of cyst of sublingual gland with about 2 mm wide, and then free mucosa flap was obtained from the top of the cyst wall along the incisions. The mucosal tunnel was made by suturing the base of the mucosal stripe at the deepest part of the cyst wall, and the mucosal bridge was formed by suturing two external edges of the incisions. The follow-up period was 6-48 months. 30 cases (85.7%) were cured and 4 cases (11.4%) were improved with no recurrence except for one loss of follow-up. Totally, patients were satisfied with the treatment. Mucosal bridge-tunnel surgery is a safe, effective, simple and easy-operating method to the cyst simplex of sublingual gland patients who are undergoing a relapse after treatment with drug injection or palliative care, young, worn with age, with bilateral problem, intolerant to a major surgery, or having a higer expectation to the treatment.

Conjugate free convection with surface radiation in open top cavity

This paper reports the numerical study of two-dimensional, steady, incompressible, conjugate, laminar, natural convection with surface radiation in open top cavity having air as the intervening medium for different locations of uniform volumetric heat generating source at the left wall. For surface radiation calculations, radiosity–irradiation formulation has been used, while the view factors required therein, are calculated using the Hottel’s Crossed-string method. The analysis has been done for a constant property of fluid, with the Boussinesq approximation assumed to be valid. The effects of the magnitude of heat source, location, the material and surface properties of the heat source on both heat transfer and fluid flow have been studied and discussed. An important contribution from the present work is to find the location of heat source for efficient cooling and it is found at the top of the left wall. Based on a large set of numerical data, correlations have been developed for maximum non-dimensional temperature of heat source for three different locations at the left wall.

Interstory Drifts from Shear Strains at Base of High-Rise Concrete Shear Walls

Shear strains may have negligible influence on maximum displacements at the top of slender shear walls, but may significantly increase interstory drift ratios at lower levels where gravity-load columns are often less flexible. A nonlinear finite-element (FE) model calibrated with experimental results confirmed that large shear strains occur in flexural tension regions of concrete walls due to vertical tension strains in the presence of diagonal cracks and in the absence of demand on the horizontal shear reinforcement. A fan of diagonal cracks will form at the base of flexurally hinging walls independent of the shear stress level. A parametric study confirmed that a principal strain angle of 75° can be used to estimate shear strains from vertical tension strains. Thus interstory drift ratios due to shear strains can be estimated from the easily calculated flexural demands. A simple and safe estimate of interstory drift ratio due to shear strains is 60% of the global drift ratio. Interstory drift ratios from shear strains up to 0.8% have been measured in slender wall tests.

OSCILLATING LIGHT WALL ABOVE A SUNSPOT LIGHT BRIDGE

With the high tempo-spatial \emph{Interface Region Imaging Spectrograph} 1330 {\AA} images, we find that many bright structures are rooted in the light bridge of NOAA 12192, forming a \emph{light wall}. The light wall is brighter than the surrounding areas, and the wall top is much brighter than the wall body. The New Vacuum Solar Telescope H$\alpha$ and the \emph{Solar Dynamics Observatory} 171 {\AA} and 131 {\AA} images are also used to study the light wall properties. In 1330 {\AA}, 171 {\AA}, and 131 {\AA}, the top of the wall has a higher emission, while in the H$\alpha$ line, the wall top emission is very low. The wall body corresponds to bright areas in 1330 {\AA} and dark areas in the other lines. The top of the light wall moves upward and downward successively, performing oscillations in height. The deprojected mean height, amplitude, oscillation velocity, and the dominant period are determined to be 3.6 Mm, 0.9 Mm, 15.4 km s$^{-1}$, and 3.9 min, respectively. We interpret the oscillations of the light wall as the leakage of \emph{p}-modes from below the photosphere. The constant brightness enhancement of the wall top implies the existence of some kind of atmospheric heating, e.g., via the persistent small-scale reconnection or the magneto-acoustic waves. In another series of 1330 {\AA} images, we find that the wall top in the upward motion phase is significantly brighter than in the downward phase. This kind of oscillations may be powered by the energy released due to intermittent impulsive magnetic reconnection.

Microstructure and mechanical properties of the rheoformed cylindrical part of 7075 aluminum matrix composite reinforced with nano-sized SiC particles

Abstract The microstructure and mechanical properties of the rheoformed parts of 7075 aluminum matrix composite were investigated. The results show that more liquid phase and spheroidal solid grains were found in the microstructures in the top and medium regions of the side wall of the rheoformed parts due to dependence of the deformation on liquid flow and flow of liquid incorporating solid grains. Yield strength and ultimate tensile strength of the rheoformed composite parts are enhanced as compared with the as-extruded and the rheoformed parts of 7075 matrix alloy. The yield strength, ultimate tensile strength and elongation of the rheoformed composite parts with T6 reach 399 MPa, 492 MPa and 9.6%, respectively. When stirring time increases from 5 min to 20 min, the mechanical properties increased due to fine-grained strengthening and a further increase more than 20 min led to a slight change. Pressure led to a significant increase of the mechanical properties due to some reduction of defects and dislocations strengthening. An increase of SiC volume fraction from 0.5% to 1% led to an improvement of yield strength and ultimate tensile strength and a further increase led to a decrease.