Negative Pressure Coefficient Research Articles

Raman spectroscopic insights into the pressure-induced phase transition in natural elbaite

Tourmaline [XY₃Z₆(T₆O₁₈)(BO₃)₃V₃W] is a potential carrier for water and boron cycles in the Earth's interior. Its high-pressure structural behavior has been extensively investigated by single-crystal or powder X-ray diffraction. Here, we collected Raman spectroscopy data of natural elbaite with two different compositions (Fe-poor elbaite and Fe-rich elbaite) up to 35.1 GPa to complementarily characterize the structural modifications proposed by previous studies. Our results reveal two clear discontinuous changes in high-pressure Raman spectra of both samples. The first change occurred at around 15 GPa, characterized by changes in Raman peak intensity, and the pressure dependence of the frequencies of several lattice vibration modes and hydroxyl stretching vibrations. The second change emerged at around 26 GPa and was marked by the systematic appearance of new Raman peaks. Based on previous X-ray diffraction studies, the change at around 26 GPa is likely caused by a phase transition from rhombohedral R3m to rhombohedral R3, whereas the change at around 15 GPa is likely caused by a change in compression mechanism. Furthermore, the WOH stretching vibrations at 3691 cm−1 in Fe-rich elbaite exhibited a negative pressure coefficient, contrasting with the positive pressure coefficient observed in Fe-poor elbaite, suggesting a significant influence of chemical composition on the evolution of stretching vibration in WOH groups under high pressure. After release of pressure, the spectra return to their initial state, indicating the reversibility of all observed changes.

Pressure-Driven Energy Band Gap Narrowing of λ-N2

Probing the energy band gap of solid nitrogen at high pressures is of importance for understanding pressure-driven changes in electronic structures and insulator-to-metal transitions under high pressure. The λ-N2 formed by cold compression is known to be the most stable one in all solid nitrogen phases observed so far. By optimizing the optical system, we successfully measured the high-pressure absorption spectra of λ-N2 covering the polymeric-nitrogen synthetic pressures (124 GPa–165 GPa). The measured optical band gap decreases with increasing pressure, from 2.23 eV at 124 GPa to 1.55 eV at 165 GPa, with a negative pressure coefficient of −18.4 meV/GPa, which is consistent with the result from our ab initio total-energy calculations (−22.6 meV/GPa). The extrapolative metallization pressure for the λ-N2 is around 288(18) GPa, which is close to the metallization pressure (280 GPa) for the η-N2 expected by previous absorption edge and direct electrical measurements. Our results provide a direct spectroscopic evidence for the pressure-driven band gap narrowing of solid nitrogen.

Experimental investigation of wind pressures on photovoltaic (PV) panel installed parallel to residential gable roof

The study was conducted to investigate the wind pressures on PV panels installed parallel to a 30° pitched gable roof, with a special focus on the effects of roof clearance. The wind pressures on the two sides of the scaled panels with four clearances, i.e., ranging from 5 cm to 20 cm with an interval of 5 cm, were tested. The pressure coefficients over taps and zones were examined and discussed. The results show that the most critical positive and negative area-averaged peak net pressure coefficients were comparable in magnitude. With a clearance of 10 cm, the critical positive and negative values were 1.13 and −1.08, respectively, and both occurred at θ = 0°. With effective area of 3.7 m2, the critical positive values increased 26.6 %, 8.3 % and 11.7 % as clearance ranged from 5 cm to 10 cm, 10 cm to 15 cm, and 15 cm to 20 cm, respectively, while the critical negative values changed little when clearance was less than 15 cm, but increased 18.8 % when clearance increased from 15 cm to 20 cm. However, the associated unfavorable wind directions of critical positive and negative values were at θ = 0°, and oblique wind, respectively, remaining nearly unchanged with the increasing of clearance. The tested critical positive and negative area-averaged peak net pressure coefficients were smaller than the values calculated by standards, indicating that the wind resistant designs of roof-mounted PV panels according to the mentioned standards are quite conservation.

Investigation on preparation and properties of carbon fiber graphite tailings conductive asphalt mixture: A new approach of graphite tailings application

The massive accumulation of graphite tailings (GT) brings huge pressure to environmental engineers. Meanwhile, the conductive asphalt pavement industry is suffering from the high construction cost and the complex acquisition of conductive materials. The application of GT in asphalt mixture as a conductive material may be a win–win solution for the above concerns. This study aims to evaluate the feasibility of preparing carbon fiber graphite tailings (CF-GT) conductive asphalt mixture. The optimum preparation technology and material ratio were explored. The service performance tests of the conductive asphalt mixture were conducted, including conductive characteristics, electrothermal performance and pavement performance. Based on the experimental results, 0.3% (mass fraction) 6 mm-polyacrylonitrile (PAN)-based carbon fiber (CF) and 12% (mass fraction) GT were selected as conductive materials to prepare conductive asphalt mixture with resistivity of 5.75 Ω∙m. The addition of GT reduced the resistance by a maximum of 59.8%. The temperature-sensitive and pressure-sensitive characteristics of the mixture have staged characteristics. Moreover, the resistance and stress of the mixture have an excellent linear correlation in the positive pressure coefficient (PPC) effect stage and negative pressure coefficient (NPC) effect stage respectively, especially NPC. Conductive asphalt mixture has a good heating effect after being powered on. GT combined with CF enhanced the high-&low-temperature performance but deteriorated the moisture damage resistance performance of the asphalt mixture. The feasibility of CF-GT conductive asphalt mixture was demonstrated.

Exploring the impact of vertically separated flows on wind loads of multi-level structures

The complex dynamics of vertically separated flows pose a significant challenge when it comes to assessing the wind loads on multi-level structures, demanding a nuanced understanding of the intricate interplay between atmospheric conditions and architectural designs. Previous studies and wind loading standards provide insufficient guidance for designing wind pressures on multi-level buildings. The behavior of wind around perpendicularly attached surfaces is not quite similar to that of individual flat roofs or walls. When a body is composed of several surfaces with right or oblique angles, the separated flow from surfaces and their interactions will cause complex flow patterns around each surface. A wind tunnel experimental study was carried out on bluff bodies with attached flat plates and other adjacent bluff bodies with different heights to examine the wind-induced pressures on such complex shapes. Mean and peak pressure coefficients were measured to determine the flow interaction patterns and location of localized peak pressures. The results were compared to the Tokyo Polytechnic University Aerodynamic Database of isolated low-rise buildings without eaves. The research findings indicated that there was a noteworthy disparity between the minimum and maximum values and locations of peak pressures on both the wall and roof surfaces of the models used in this study, as compared to the results obtained by the Tokyo Polytechnic University. Moreover, the study conceivably pointed to the difference between the peak negative and positive pressure coefficient locations with the ASCE 7-22 wind loading zones. The peak suction zones were affected by the combined flows at perpendicular faces, and as a result, different wind load zones were obtained dissimilar to those introduced by ASCE 7-22. Wind loading standards may need to be modified to account for the wind pressures on complex building structures with an emphasis on the location of the peak negative pressure zones.

Bandgap Pressure Coefficient of a CH3NH3PbI3 Thin Film Perovskite.

Recent scientific interest in examining the bandgap evolution of a MAPbI3 hybrid perovskite by applying hydrostatic pressure has mostly focused on a room-temperature tetragonal phase. In contrast, the pressure response of a low-temperature orthorhombic phase (OP) of MAPbI3 has not been explored and understood. In this research, we investigate for the first time how hydrostatic pressure alters the electronic landscape of the OP of MAPbI3. Pressure studies using photoluminescence combined with calculations within density functional theory at zero temperature allowed us to identify the main physical factors affecting the bandgap evolution of the OP of MAPbI3. The negative bandgap pressure coefficient was found to be strongly dependent on the temperature (α120K = -13.3 ± 0.1 meV/GPa, α80K = -29.8 ± 0.1 meV/GPa, and α40K = -36.3 ± 0.1 meV/GPa). Such dependence is related to the changes in the Pb-I bond length and geometry in the unit cell as the atomic configuration approaches the phase transition as well as the increasing phonon contribution to octahedral tilting as the temperature increases.

Numerical Investigations of Wind Impacts on Chinese Ancient Architectural Roof Surfaces with Ridges and Semi-Cylindrical Tiles

ABSTRACT This study aims to evaluate the impacts of roof ridges and semi-cylindrical tiles on the wind loading on traditional single-eave hip roofs. To the best of the authors’ knowledge, the semi-cylindrical tiles have been considered in the simulation of ancient Chinese architecture for the first time. Several roof models with various ridges and semi-cylindrical tiles are simulated by solving the Reynolds-averaged Navier-Stokes equations (RANS) using the computational fluid dynamics (CFD) technique. The results reveal that the addition of roof ridges and semi-cylindrical tiles has a considerable structural protection effect, which can significantly reduce the suctions, as well as the turbulence fluctuation, on both the windward and leeward sides: the average of negative mean wind pressure coefficients is reduced by 33% on the leeward surface, and approximately 48% on the windward surface one. When the number of protruding ridges and semi-cylindrical tiles increases (decreasing the diameter of them by 40%), the average of area mean wind pressure coefficient for all the wind directions decreases by about 30% on the windward side and about 50% on the leeward side. The average of maximum spatial wind pressure coefficient decreases by about 25% on the windward side and about 40% on the leeward side.

Energy considerations and flow fields over whiffling-inspired wings

Some bird species fly inverted, or whiffle, to lose altitude. Inverted flight twists the primary flight feathers, creating gaps along the wing’s trailing edge and decreasing lift. It is speculated that feather rotation-inspired gaps could be used as control surfaces on uncrewed aerial vehicles (UAVs). When implemented on one semi-span of a UAV wing, the gaps produce roll due to the asymmetric lift distribution. However, the understanding of the fluid mechanics and actuation requirements of this novel gapped wing were rudimentary. Here, we use a commercial computational fluid dynamics solver to model a gapped wing, compare its analytically estimated work requirements to an aileron, and identify the impacts of key aerodynamic mechanisms. An experimental validation shows that the results agree well with previous findings. We also find that the gaps re-energize the boundary layer over the suction side of the trailing edge, delaying stall of the gapped wing. Further, the gaps produce vortices distributed along the wingspan. This vortex behavior creates a beneficial lift distribution that produces comparable roll and less yaw than the aileron. The gap vortices also inform the change in the control surface’s roll effectiveness across angle of attack. Finally, the flow within a gap recirculates and creates negative pressure coefficients on the majority of the gap face. The result is a suction force on the gap face that increases with angle of attack and requires work to hold the gaps open. Overall, the gapped wing requires higher actuation work than the aileron at low rolling moment coefficients. However, above rolling moment coefficients of 0.0182, the gapped wing requires less work and ultimately produces a higher maximum rolling moment coefficient. Despite the variable control effectiveness, the data suggest that the gapped wing could be a useful roll control surface for energy-constrained UAVs at high lift coefficients.

Wind effect on scallop domes with negative amplitude and prominence using Experimental and Numerical Study

This study investigates the wind effect on hexa-sectored scallop domes using Computational Fluid Dynamics (CFD) and wind tunnel tests. Similar to the shape of a seashell, the scallop dome is one of the most common domes used to cover large spans. The scallop dome has an additional curvature equal to its sectors compared to a base dome (spherical). Hence, it has better structural efficiency compared to a spherical dome under the same condition. The curvatures on the scallop dome create alternate “ridges” and “grooves” on it. According to the computations of the article, the grooves created on this dome in the sector, as well as their position angle to the wind direction significantly affect pressure coefficient value. Due to these differences, wind pressure on scallop domes significantly differs from wind pressure on spherical domes. The results indicate that the ridges cause negative wind pressure coefficients whose magnitude reaches a maximum of −2.0 for an angle of alignment of 30°. The analyses have been conducted through Ansys-Fluent. This study presents the equation of wind pressure coefficient in the most critical of dome groove positions. The arch created between the grooves of a scallop dome is another effective parameter on maximum negative pressure. In the case study scallop dome, if the wind effect angle is considered α = 15, the maximum deformation in the structure will be created, which is 20% higher than that of α = 0.

Wind Tunnel Experiments on Interference Effects of a High-Rise Building on the Surrounding Low-Rise Buildings in an Urban Block

High-rise buildings cause accelerated winds around them. However, the interference effects of high-rise buildings on the surrounding low-rise buildings in urban blocks have not been evaluated. This study investigated the wind pressure coefficients on the roofs and walls of low-rise buildings surrounding a high-rise building through wind tunnel experiments. Seventy-two wind directions were considered from 0° to 355° in 5° increments, and the influence of the wind direction on the wind pressure coefficients of surrounding buildings was evaluated. At a 30° wind direction angle, the positive and negative peak wind pressure coefficients occurred in a low-rise building at the leeward side of the high-rise building. The positive peak pressure, approximately 1.4 times that without a nearby high-rise building, occurred at the windward corner on the front wall of a low-rise building. The negative peak value, approximately three times that without a nearby high-rise building, was observed at the windward edge on the roof of a low-rise building. Thus, accelerated winds caused by high-rise buildings may result in unexpected damage to the surrounding low-rise buildings.

Experimental Study on Aerodynamic Forces of a Suspended Arch Roof

With the development of building materials, construction technology, and design concepts, suspended arched roofs (SARs) are becoming increasingly popular. The wind loads of arched roofs springing from ground level (ARSGL) and vaulted roofs on side walls (VRSW) have already been studied; however, the wind loads of SARs, which are very different from those of ARSGL or VRSW, have not received adequate attention. Based on the wind tunnel tests of a rigid model of an actual SAR design scheme, the mean value, root mean square (RMS) value, and most unfavorable value of the wind pressure coefficient and overall lift coefficient of this type of roof are analyzed. Furthermore, the influence of the buildings below or surrounding it is investigated and discussed. The test results indicate that the net wind pressure of the SAR is affected by the upper- and lower-surface wind pressures. Both the most unfavorable wind pressure (positive pressure) and suction (negative pressure) coefficients of the SAR are larger near the edge (arch foot) and smaller in the internal area. The maximum values of the most unfavorable pressure and suction coefficients of the tested SAR are 4.5 and 8.0, respectively, and these values are larger than those of ARSGL and VRSW. The buildings below cause airflow congestion under the SAR and eventually increase the net pressure coefficients near the windward edge of the SAR. The shielding effects of the surrounding buildings of the tested SAR reduce the wind pressure coefficient; however, the wind pressure in some areas of the tested SAR increases because of the narrow tube effects between surrounding buildings. The lift coefficient of the tested SAR significantly increases because of the presence of buildings below in some cases.

Aerodynamic effect of an alula-like vortex generator using pressure sensitive paint technique

Herein, the pressure-sensitive paint (PSP) was used to quantitatively investigate the aerodynamic effect of an alula-like vortex generator, which is a bio-inspired passive flow control structure. The global pressure distributions on the upper surface at different angles of attack were measured to determine the strength of sectional suction forces on the wing. An alula-like vortex generator equipped at the leading edge of the wing enlarged the area of the suction region (negative pressure coefficient) on the upper surface in both the streamwise and spanwise directions under near-stall and deep-stall conditions, which is related to the generation of lift and avoiding the stall of wing. A wing model equipped with a vortex generator of an 11% height/chord length ratio exhibited the greatest performance at all angles of attack. In this study, the use of PSP technique not only helps to understand the aerodynamic effect of the alula-like vortex generator but also shows a perspective tool for bio-inspired MAVs design.

Tracking shock movement on the surface of an oscillating, straked delta wing

Limit cycle oscillations (LCO), a mechanical nonlinearity similar to flutter, have affected high performance aircraft, like the F-16 and F-18, for years. The phenomena causes a lateral motion of the cockpit that makes performance of typical pilot tasks difficult. To better understand the nature of LCO and why high performance aircraft are typically afflicted, a computational model was developed to compare to wind tunnel tests and investigate the flow field around a straked, semispan delta wing and monitor the changes as the wing was pitched in an oscillatory fashion. The oscillations were intended to mimic LCO. By understanding the flow field around an oscillating wing, the fluid force that acts as the source of the motion could be discerned. The computational investigation focused on tracking shock movement along the top surface of the wing to confirm the presence of shock-induced trailing edge separation, one possible driver of LCO. The surface pressure was shown to be sensitive to the starting trim angle, oscillation frequency and oscillation amplitude. A separation bubble aft of the shock was observed as the source of sharp, localized negative surface pressure coefficient. The large change in surface pressure caused by the separation bubble could be an important phenomena contributing to the onset of LCO.

Experimental investigation of surface pressures, velocities, and dynamic structural analysis of tornadic winds on a luminary pole

Several engineering and media reports have demonstrated that luminary and lighting poles are susceptible to tornadic wind actions. This paper provides the first dynamic structural analysis of a 1:50 geometrically scaled model of a generic luminary pole of a circular cross-section tested under transient wind loads caused by translating tornado-like vortices (TLVs). The physical experiments were performed in the WindEEE Dome tornado simulator at Western University (Canada). The tornadic wind actions on the pole are also compared against the reference atmospheric boundary layer (ABL) wind gust with the mean recurrent period of 50 years. Three different positions of the luminary pole in respect to the TLV path were considered: (1) TLV center passing over the pole; (2) TLV core radius passing over the pole; and (3) an intermediate case in which the pole was positioned between the TLV center and the core radius. In all cases two circular cylinders of different diameters were used to simulate two different cross-sections of an actual luminary pole. Our study demonstrates that luminary poles are more susceptible to tornadic wind actions compared to ABL winds. The tip displacements of the pole were larger in the TLVs and the direction and magnitude of the displacements were dependent on the relative positions of the TLVs and the luminary pole. The highest wind forces were observed in the regions characterized by strong tangential wind speeds. The entire luminary pole was subjected to negative pressure coefficients during the TLV passage. However, our structural analysis showed that the pole always stayed in the elastic region of deformation and there was no permanent bending or collapse of the structure.

Large-Scale Wind Testing on Roof Overhangs for a Low-Rise Building

Roof overhangs are prone to wind damage because they are subject to wind load at both the upper and bottom surfaces. Wind standards assume that the pressure at the bottom covering of a roof overhang will be the same as the external pressure coefficient on the adjacent wall surface. A large-scale experimental campaign was carried out at the Wall of Wind (WOW) Research Experimental Facility to investigate the validity and possible limitations of such assumptions. The experimental setup considered two 1:10 scaled models [0.61 m (2 ft) and 1.83 m (6 ft) inclined overhangs with a soffit] of a low-rise hip roof building with roof slope 4:12, eave height of 7.5 m (24 ft), and horizontal dimensions of 12.2 m (40 ft)× 15.24 m (50 ft). The two models were tested for open terrain for 40 wind directions (WDs). The study provided information on pressure variations at the top and bottom surfaces of overhangs, adjacent roof areas, and underneath walls. Pressure and correlation coefficients were generated between soffits and underneath walls to quantify the effect of overhang width. The research showed that the 0.61 m (2 ft) overhang experienced higher suction coefficients at the edges compared to the 1.83 m (6 ft) overhang. In addition, the results confirmed that, for both configurations, soffit positive pressure coefficients may be assumed to be equal to the adjacent wall external pressure, as stated by a common standard, while this might not be applicable for negative pressure coefficients. Correlation and regression analyses between soffit pressure taps and wall upper taps show that the 1.83 m (6 ft) soffit appeared to be less correlated with the wall upper taps, compared to the 0.61 m (2 ft) soffit. Finally, area-averaged pressure coefficients for overhangs and adjacent roof areas were compared to the provisions in one standard for each specified zone, and differences were found.

Study on Wind Load Characteristics and Wind-Induced Response of Supertall Buildings with Single-Sided Large-Span Straight Platforms

The presence of large-span straight platforms can complicate the airflow around buildings and alter surface wind pressure, gas bypass and wind response in supertall buildings. The article uses the Reynolds-averaged Navier–Stokes (RANS) method in Computational Fluid Dynamics (CFD) to investigate the differences in surface mean wind pressure, gas bypass, wind coefficients, displacement and acceleration responses between the models with and without platforms, and the wind load on the platforms themselves at different wind directions. The results show that: the presence of platforms generally reduces the maximum negative pressure coefficient on the building surface, reaching a maximum reduction of 31.56% at 30°, and causes a small increase in the maximum positive pressure coefficient, reaching a maximum increase of 5.30% at 0°. The mean wind pressure on the lower surface of the platform is greater than the upper surface. The target building has a lower frequency of vortex shedding than the reference model, with a maximum reduction of 5.68%. The presence of platforms increases the vertex displacement of the building by up to 22.85% and decreases the vertex acceleration by up to 9.14%. These results can be used as references for the ventilation, comfort and safety assessment of similar supertall buildings.

Stress-Tuned Optical Transitions in Layered 1T-MX2 (M=Hf, Zr, Sn; X=S, Se) Crystals.

Optical measurements under externally applied stresses allow us to study the materials’ electronic structure by comparing the pressure evolution of optical peaks obtained from experiments and theoretical calculations. We examine the stress-induced changes in electronic structure for the thermodynamically stable 1T polytype of selected MX compounds (M=Hf, Zr, Sn; X=S, Se), using the density functional theory. We demonstrate that considered 1T-MX materials are semiconducting with indirect character of the band gap, irrespective to the employed pressure as predicted using modified Becke–Johnson potential. We determine energies of direct interband transitions between bands extrema and in band-nesting regions close to Fermi level. Generally, the studied transitions are optically active, exhibiting in-plane polarization of light. Finally, we quantify their energy trends under external hydrostatic, uniaxial, and biaxial stresses by determining the linear pressure coefficients. Generally, negative pressure coefficients are obtained implying the narrowing of the band gap. The semiconducting-to-metal transition are predicted under hydrostatic pressure. We discuss these trends in terms of orbital composition of involved electronic bands. In addition, we demonstrate that the measured pressure coefficients of HfS and HfSe absorption edges are in perfect agreement with our predictions. Comprehensive and easy-to-interpret tables containing the optical features are provided to form the basis for assignation of optical peaks in future measurements.

Numerical investigation of flow around two cylinders in tandem above a scoured bed

Flow mechanisms around two cylinders in tandem arrangement above a scoured bed have been investigated using the three-dimensional unsteady Navier–Stokes equations with the Spalart–Allmaras improved delayed detached-eddy simulation model. A turbulent inlet boundary layer generation method is adopted to obtain more realistic inlet boundary conditions. First, uniform flow over a single cylinder at Re = 3900 and flow over a single cylinder above scoured beds at Re = 6000 were simulated to validate the numerical model, boundary layer generation method, and mesh density effect. Second, two cylinders in the tandem arrangement above scoured beds with six different pitch ratios L/D are investigated numerically in terms of instantaneous vortex characteristics, the hydrodynamic force, and time-averaged flow fields. The simulation results in scoured beds are compared with simulations under the near flat wall and wall-free conditions. The major findings can be summarized as follows. (1) When L/D≤2.0, the wake of two tandem cylinders is dominated by the intermittent shedding, and the downstream sand dune in the scoured bed hinders the Kármán vortex formation at the rear of the downstream cylinder. Lift force fluctuations of the two cylinders have small amplitudes, and their spectra show a multi-peak distribution and no dominant peak frequency in the spectrum of the upstream cylinder. A squarish cavity-like recirculation zone is formed between two cylinders at L/D=2.0. (2) When L/D≥3.0, the periodic vortex shedding is evident in the wake of the upstream cylinder, and the small sand berm between two cylinders has an impact on the bottom shear layer of the upstream cylinder. The downstream cylinder is periodically impacted by the vortices shed from the upstream cylinder. Lift force spectra of the upstream and downstream cylinders have the same peak frequency. (3) Due to the influence of scoured bed and the inlet boundary layer, the time-averaged lift coefficient of the upstream cylinder remains negative when L/D≥1.5, and the critical spacing for drag inversion is relatively smaller compared with under wall-free conditions. The negative pressure coefficient values of the upstream cylinder are smaller than the values in near flat wall and wall-free conditions.

Piezoresistive Properties of 3D-Printed Polylactic Acid (PLA) Nanocomposites.

An increasing interest is focused on the application of 3D printing for sensor manufacturing. Using 3D printing technology offers a new approach to the fabrication of sensors that are both geometrically and functionally complex. This work presents the analysis of the 3D-printed thermoplastic nanocomposites compress under the applied force. The response for the corresponding resistance changes versus applied load is obtained to evaluate the effectiveness of the printed layer as a pressure/force sensor. Multi-walled carbon nanotubes (MWNT) and high-structured carbon black (Ketjenblack) (KB) in the polylactic acid (PLA) matrix were extruded to develop 3D-printable filaments. The electrical and piezoresistive behaviors of the created 3D-printed layers were investigated. The percolation threshold of MWNT and KB 3D-printed layers are 1 wt.% and 4 wt.%, respectively. The PLA/1 wt.% MWNT 3D-printed layers with 1 mm thickness exhibit a negative pressure coefficient (NPC) characterized by a decrease of about one decade in resistance with increasing compressive loadings up to 18 N with a maximum strain up to about 16%. In the cyclic mode with a 1 N/min force rate, the PLA/1 wt.% MWNT 3D-printed layers showed good performance with the piezoresistive coefficient or gauge factor (G) of 7.6 obtained with the amplitude of the piezoresistive response (Ar) of about -0.8. KB composites could not show stable piezoresistive responses in a cyclic mode. However, under high force rate compression, the PLA/4 wt.% KB 3D-printed layers led to responses of large sensitivity (Ar = −0.90) and were exempt from noise with a high value of G = 47.6 in the first cycle, which is a highly efficient piezoresistive behavior.

Wind tunnel experiment on rectangular-shaped arch-supported membrane structures

This paper highlights the investigation of wind tunnel experiment on rectangular-shaped arch-supported membrane structures. Series of wind tunnel experiments are carried out to record the time history of pressure under different wind directions for both enclosed and open structures. In order to present the comparative analysis, contours and graphs for mean and peak wind pressure coefficients are plotted considering different parameters such as rise-span ratio, wind direction, and boundary wall. Study shows that under oblique wind direction, strong flow separation occurs in the windward arch edge which creates larger suction pressure coefficient on the immediate downside of windward arch. Based on area and intensity of negative pressure coefficient, 45⁰ is the most critical wind direction. Influence of rise-span ratio is noticeable. When rise-span ratio increases from 0.2 to 0.35, pressure coefficient increases significantly, however when rise-span ratio further increases to 0.5, increase in pressure coefficient is marginal. Moreover, in order to ease the engineering design application, roof surface is divided into different zones and assigned with mean and peak wind pressure coefficient.