Positive Pressure Coefficient Research Articles

Analysis of Water Film Distribution and Aerodynamic Performances of High-Speed Train Under Rainfall Environment

AbstractThe current research on the aerodynamic performance of the train running in rainy weather is primarily concerned with the trajectory of the raindrops and the aerodynamic variation of trains caused by raindrops. In fact, water film will generate on the train body when raindrops hit the train, which interacts with the flow field around the train, and would probably affect the aerodynamic performance of the train. In this paper, based on shear stress transport (SST) k-w turbulence model and Euler-Lagrange discrete phase model, the aerodynamic calculation model of a high-speed train under rainfall environment is established. The LWF (Lagrangian wall film) is used to simulate the water film distribution of the high-speed train under different rainfall intensities, and the aerodynamic performance of the train are studied. The calculation results show that raindrops will gather on the train surface and form water film under rainfall environment. With the extension of rainfall time, the thickness and coverage range of water film expand, and the maximum thickness of water film can reach 4.95 mm under the working conditions in this paper. The average thickness of water film on the train body increases with the rainfall intensity. When the rainfall intensity increases from 100 mm/h to 500 mm/h, the average water film thickness will increase by 3.26 times. The velocity of water film in the streamlined area of head car is larger than that in other areas, and the maximum velocity is 22.14 m/s. Compared with the rainless environment condition, the skin friction coefficient of the high-speed train increases and the average value will increase by 10.74% for a rainfall intensity of 500 mm/h. The positive pressure and resistance coefficient of the head car increase with the rainfall intensity. This research proposes a methodology to systematically analyze the generation of water film on the train surface and its influence on the train aerodynamic performance; the analysis can provide more practical results and can serve as a reference basis for the design and development of high-speed trains.

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.

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.

First-principles study on electronic, mechanical, and optical properties of pressure-induced vanadium-based perovskite KVO3

Vanadium-based compounds exhibit a variety of excellent characteristics due to their variable oxidation states. In this study, Density Functional Theory (DFT) is performed to investigate the structural, electronic, mechanical, and optical properties of KVO3 under high pressure. The thermodynamical and mechanical stabilities under high pressure are probed by the negative value of formation enthalpy and Born-mechanical stability criteria, respectively. KVO3 displays a nearly metallic nature in both pressurized and unpressurized systems owing to its remarkably narrow band gap. Furthermore, a positive pressure coefficient of the band gap is revealed from electronic properties. A lower effective mass value for charge carriers indicates KVO3's suitability for optoelectronic applications. The mechanical properties indicate that increasing pressure results in a slight increase in elastic constants, elastic moduli, hardness, and machinability index. Additionally, it has been disclosed that it is capable of enduring localized plastic deformation and fracturing under intense pressure in a prospective application. The calculations of the complex dielectric function, absorption, reflectivity, conductivity, refractive index, and loss function for KVO3 with and without pressure reveal a substantial behavior change. The absorption edge exhibits a significant blue shift with the applied pressure. The high peaks in the UV region suggest that it can be used in UV detectors and anti-reflection coatings. The refractive index shows promising application in waveguides.

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.

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.

Numerical Investigations of Wind Loads on Spherical Structures with Various Types of Configurations

Spherical structures with various design styles are encountered in engineering. Most studies have only examined the wind loads on hemispheres or smaller, which leads to a lack of wind-resistant design rules that cover all the styles of a spherical structure. In this study, a validated CFD model was used to systematically examine the wind loads on spherical structures with different apex-height-to-diameter ratios (ARs). The structure types ranged from different truncated spheres to whole spheres located at different distances above the ground. The results indicated that the largest positive mean pressure coefficient (Cp) at the windward surface gradually increased with AR. The structures were subjected to a strong suction effect at the crown of the sphere as well as its two sides and bottom. A polynomial approximation function for area-averaged Cp over the top area was derived to quickly determine the largest suction effect for all types of spherical structures. The drag and lift coefficients increased rapidly with AR and achieved their largest value when the structure was close to a whole sphere, while their changes were small for a whole sphere located far from the ground. Design suggestions were provided based on the results.

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.

Wind-structure interaction analysis of empty cylindrical silos for various slenderness ratio

Wind is the flow of air within the earth’s atmosphere, which affects any structure greatly. Studies on the effect of wind loading on shell structures is an important field of structural research. Many shell structures, such as, chimneys, silos, tanks etc. are an integral part of the advancement of the industry and agriculture. Such shell structures are vulnerable against aerodynamic excitation and can be subjected to structural failure due to vortex-induced vibration, ovalling, buckling, rupture, over-turning etc. The present study focuses on the static fluid–structure interaction analysis to assess the wind pressure and wind-induced deformation of cylindrical silo shells. Cylindrical silos are a type of shell structure for storing granular materials, such as grains, wheat, cement, coal, fly-ash etc. Cylindrical silos very much susceptible to radial deformation and buckling failure under wind loading in empty state. In the present study the authors have conducted the wind-structure interaction studies on intermediate to tall (slenderness ratio range: 1.5 to 4.0) cylindrical silo shells for terrain category 2, as per IS-875: part 3, 2015. The silos are flat topped with uniform thickness and fixed at the base, free at the top. The logarithmic law is used to simulate wind velocity profile. The circumferential mean wind pressure coefficient distribution for each silo, is calculated and compared with Indian standard. This study is conducted for smooth flow with very low turbulence intensity for simplicity. This study exhibits that, with the increase in slenderness ratio from 1.5 to 4.0, the magnitude of negative pressure coefficients decreases, however no significant increase can be seen for positive pressure coefficients. The sway of the silos increases with the increment in slenderness ratio. The radial deformation is dominant in the intermediate portion and the nature of deformation is typical for each silo. Based on the nature of radial deformation the critical locations can be identified, which need to be strengthened to resist wind-induced deformation. It is also seen that the presence of flat roof provides significant strengthening at the top of the silos against wind-induced radial deformation.

Wind flow on and around U-shaped buildings

PurposeThis paper presents the numerical examination of wind pressure distributions on U-plan shaped buildings having four different depth ratios (DR) as 0.5, 1, 2 and 4 over wind incidence angle (WIA) of 0°. The purpose of this study is to investigate the effect of irregular building form, DRs, distances from the reentrant corner, wind velocity values on and around wind pressure distributions of the buildings. With this aim, ANSYS Fluent 20.0 Computational Fluid Dynamics (CFD) program is used for the analysis.Design/methodology/approachFour U-shaped buildings having the same height, width and wing length but having different DR in plan were analyzed by the application of CFD package of ANSYS 20. With this purpose, wind pressure distributions on and around U-plan shaped buildings were analyzed for the wind velocity values of 2 and 5 m/s over WIA of 0°. Comprehensive results were obtained from the analyses.FindingsWhile the change in the DR values did not create a significant change in positive pressure coefficients on A and E surfaces, negative pressure values increased as the DR decreased. The negative pressure coefficients observed on the A and E surfaces become higher than the positive pressure coefficients with the decrease in the DR. On contrary to that condition, with the decrease in the DR, G surfaces take higher positive pressure coefficients than the negative pressure coefficients. The reason for this is that the DR decreases and negative pressure values on G surface significantly decrease. The effect of the DR on the pressure coefficients is remarkable on B and D surfaces. The negative pressure coefficients on the B and D surfaces tend to increase as the DR decreases.Research limitations/implicationsThis study focused on DRs and wind velocity values effect on pressure coefficients to limit variables. Different building wing dimensions did not take into account.Originality/valueAlthough there are a number of studies related to wind behavior of irregular plan shaped buildings, irregular building forms have not been extensively investigated parametrically, especially in terms of the effect of DR on wind pressures. This study is therefore designed to fill this gap by analyzing impacts of various parameters like building shape with various DRs, WIA and wind velocity values on wind pressure distributions and velocity distributions on and around the building.

Wind pressure characteristics of elliptical retractable dome roofs

This study investigated the wind pressure characteristics of an elliptical plan retractable dome roof. Wind tunnel experiments were performed on elliptical dome roofs with varying wall height-to-span ratios (0.1–0.5) and opening ratios (0, 10, 30, and 50 %), where the opening ratio was defined as the ratio of the open area of the roof to the total area of the roof. The resulting peak pressure coefficients of the closed dome roof were then compared with those of the Japanese wind load code (AIJ-RLB (2015)) as there are no current peak pressure coefficients for the cladding design code of elliptical dome roofs. The resulting peak pressure coefficients for each elliptical retractable dome roof opening ratio were also compared with those for the cladding design of spherical retractable domes proposed in previous research. Finally, based on the results of the comparative analysis, negative and positive peak pressure coefficients were proposed for the cladding design of elliptical retractable dome roofs.

Thermal diffusivity and thermal conductivity of alkali feldspar at 0.8–3 GPa and 300–873 K

The heat transport properties of feldspar, one of the major minerals of the crust, are important for constraining the thermal state of the Earth’s crust. The thermal diffusivity (D) and thermal conductivity (κ) of two natural alkali feldspars, namely, perthite and albite (Ab), were simultaneously measured at high temperatures (300–873 K) and high pressures (0.8–3 GPa) using a transient plane-source method. The present results show that the D and κ of these alkali feldspars decreased with the increase in temperature, whereas the κ of perthite remained almost constant at above 450 K. The D and κ of these samples decreased by 24–35% and 8–21% when the temperature increased from 300 to 873 K, respectively, suggesting that phonon conduction may be the dominant mechanism. The D and κ of these samples also exhibited a positive pressure dependence as indicated by their positive pressure coefficients: 0.052–0.098 mm2s−1GPa−1 for D and 0.189–0.325 Wm−1K−1GPa−1 for κ. Combining previous data with the results of this study, the D and κ of an intermediate albite-orthoclase solid solution can be reasonably estimated by an empirical model. Furthermore, the average κ of the crust was recalculated to accurately constrain the thermal thickness and temperature of the lithosphere. The present estimate suggests that partial melting can occur at shallow depths of the middle and lower crust, which may provide a new understanding of the low-velocity and high-conductivity anomalies revealed by geophysical observations in the crust.

Study on wind flow around a pentagon plan shape tall building using CFD

Multi-storey buildings are emerging because of the lack in land availability within urban areas. Mostly, tall buildings are irregular in plan and more complex to wind action. In the present scenario, it is important to study the wind structure interaction for irregular plan shape tall buildings. This paper is focused on understanding the behaviour of pentagon plan shape building under wind load at different wind incident angles 0°, 45°, 90°, 135° and 180°. The wind behaviour is studied using Computational Fluid Dynamics (CFD) and turbulence model k- is used for external flow simulation around the tall buildings. The building models are scaled in the ratio 1:300 and wind velocity at inlet is scaled in the ratio 1:5 respectively. From the results, external pressure coefficient on various faces of the buildings, drag coefficient and lift coefficients are determined for pentagon shape building. The maximum positive external pressure coefficient (Cp) is 0.446 had occurred in Face A at 180° wind incident angle and the maximum value of the negative external pressure coefficient (Cp) is 0.388 had occurred in Face D at 135° wind incident angle.

Estimation of Wind Load on Stepped Tall Building Using CFD Simulation

The behavior of wind around stepped tall building is quite different comparing with the symmetric plan shape tall building. Setback roof of stepped buildings is widely responsible for the turbulence around the building. The purpose of this work is to understand the behavior of wind load on stepped tall building model. Four different models having the same dimensions and same aspect ratios but different setback distances, namely Models A, B, C and D, are considered. The setback distances are 0.2L, 0.3L, 0.4L and 0.5L (L = length) and are located at H/2 level (H = height) from the base of domain. Computational fluid dynamics simulations are taken out of terrain category 2 with the model scale 1:300. The foreground of this study is the external pressure and force variation around the building face and roof at 0° and 90° wind incidence angles. Maximum positive pressure coefficient develops at 90% of building height from the base of all models and for setback case it goes to 80%. Negative pressure develops at the building roof top, whereas positive pressure develops in the setback roof for the same model and wind angle. This type of pressure variable will be considered in roof design of stepped building.

Internal and External Pressure Effects on Superconductivity in FeTexSe1-x (x = 0.46, 0.54) Single Crystals

We have synthesized and studied the transport properties of FeTexSe1-x (x = 0.4, 0.46, 0.5, 0.54, and 0.58) single crystals grown by slow cooling method and found a sharp increase of Tc up to x = 0.46 followed by a moderate decrease of Tc up to x = 0.58. We present the temperature dependence of electrical resistivity under various pressures up to ~ 2.5 GPa, and the pressure dependence of Tc shows positive pressure coefficients of ~ 2.7 K/GPa and ~ 3.33 K/GPa for x = 0.46 and x = 0.54, respectively, up to 2 GPa followed by a decreasing trend with marginal variation of Tc with negative pressure coefficients of − 0.602 K GPa−1 (x = 0.46) and − 0.7 K GPa−1 (x = 0.54) at maximum pressure of 2.5 GPa. Furthermore, both normal state resistivity and activation energy decrease sharply, and it suggests that the reduction of net electron-phonon scattering and densities of states (DOS) at the Fermi surface with application of pressure leads to enhancement of metallic behavior in FeSe systems.

Temperature-pressure-composition model for melt viscosity in the Di-An-Ab system

A model for the viscosity (η) of melts in the system CaMgSi2O6-CaAl2Si2O8-NaAlSi3O8 (Di-An-Ab) based on data compiled from the literature is presented. The model is calibrated on 560 measurements of melt viscosity at 1 atm pressure on 40 individual melt compositions and 303 measurements obtained at high pressure on 18 melt compositions. The model is continuous and accounts for variations in melt composition (X), temperature (T) and pressure (P). At ambient pressure, the model spans 15 orders of magnitude of η, a T range of 933–2450 K, and reproduces the dataset well (RMSE = 0.26 log units). The high-P model is calibrated over a T range of 970–2470 K and pressures of 50 MPa to 13 GPa for viscosities of 10−1 to 1014.5 Pa s and reproduces the high-pressure dataset to within (larger) experimental uncertainties (RMSE = 0.35 log units). Used in conjunction with chemical proxies for melt structural organization (i.e. SM and NBO/T), the model illustrates the strong coupling between viscosity and changes in melt polymerization as a function of X and P. Di-An-Ab melts with SM values >25.34 have positive pressure coefficients and show a minimal to strong increase in viscosity with pressure. Model values of glass transition temperatures (Tg) (i.e. η ~ 1012 Pa s) range between 930 K and 1130 K at 1 atm; Tg values for highly polymerized melts are depressed by as much as 150 K at 5 GPa at elevated pressures but are higher for more depolymerized melts and higher P. Melt fragility (m) is only weakly affected by increased P as expressed by a slight decrease in m for the most fragile melts versus a slight increase for the least fragile melts. Activation energies (Ea) increase with rising P for depolymerized melts and decrease with rising P for polymerized melts with the crossover at SM = 25.34. Ea values increase at low T for all P conditions and the effects of P are most pronounced at lower T. Lastly, a comparison of the liquidus surface topology for the ternary system to the corresponding isokoms of viscosity shows the relative effects of composition and temperature on melt viscosity at liquidus conditions to be highly varied.

Investigation on wind tunnel experiment of oval-shaped arch-supported membrane structures

This paper presents wind pressure distribution characteristics of oval-shaped arch-supported membrane structures based on the wind tunnel experiments. Distribution of mean and fluctuating wind pressure coefficient is presented meticulously using pressure maps. Influence of different factors including rise-span ratio, wind direction, and terrain category, on the distribution of mean, fluctuating and peak wind pressure coefficient is discussed. Both enclosed and open structures are considered. Results show that structure experiences critical suction pressure at immediate downslope of arch axis under oblique wind direction. The significant influence of rise-span ratio and wind direction on the distribution of mean and peak wind pressure coefficient is observed. Variations of wind pressure coefficient, due to change in key parameters, are distinct in windward area but changes are insignificant in leeward area. Relatively larger area of roof of open structure is loaded with positive wind pressure coefficient, as compared to an enclosed roof. Moreover, clustering analysis is performed to divide the roof surface into different zones, then mean and peak wind pressure coefficient are proposed for corresponding zones of roof surface considering different rise-span ratios under different wind directions. The outcomes are expected to be useful to engineers and researchers to understand similar type of structures.

Efficacy Analysis of Thickness and Camber Size of Cross Section of the Stator on Hydrodynamic Parameters in Linear Jet Propulsion System

The linear jet propulsion system, unlike pump-jets which are widely used in underwater bodies, is installed inside a tunnel under the vessel and can be used for high-speed crafts, tugs, and service boats. However, this system has not received adequate attention by researchers, which is the subject of the current study. In the present paper, hydrodynamic performance of the linear jet propulsion system is numerically investigated. Accordingly, the Ansys-CFX software is utilized and RANS equations are solved using the SST turbulent model. The results of the proposed numerical model, in the form of thrust and torque coefficient as well as efficiency, are compared with available experimental data for a ducted propeller, and good compliance is achieved. Considering the importance of stator cross section on the performance of the linear jet propulsion system, the influence of thickness and camber size of the stator on linear jet propulsion systems are examined. Based on the numerical findings, it is determined that at constant advance ratio, with increasing thickness of stator, the efficiency increases. It is also observed that as the span length increases, the maximum and minimum of the pressure coefficient increase for different thicknesses. Furthermore, it is seen that positive and negative pressure coefficients decrease with an increase in foil thickness.