scholarly journals The Benefit of Horizontal Photovoltaic Panels in Reducing Wind Loads on a Membrane Roofing System on a Flat Roof

Wind ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 44-62
Author(s):  
Yasushi Uematsu ◽  
Tetsuo Yambe ◽  
Tomoyuki Watanabe ◽  
Hirokazu Ikeda
Keyword(s):  
Time History ◽  
External Pressure ◽  
Shielding Effect ◽  
Bottom Surface ◽  
Wind Resistance ◽  
Pressure Equalization ◽  
Pv Panel ◽  
Strong Winds ◽  
Flat Roofs ◽  
Roofing System

The present paper proposes a measure for improving the wind-resistant performance of photovoltaic systems and mechanically attached single-ply membrane roofing systems installed on flat roofs by combining them together. Mechanically attached single-ply membrane roofing systems are often used in Japan. These roofing systems are often damaged by strong winds, because they are very sensitive to wind action. Recently, photovoltaic (PV) systems placed on flat roofs have become popular. They are also often damaged by strong winds directed onto the underside, which cause large wind forces onto the PV panels. For improving the wind resistance of these systems, we proposed to install PV panels horizontally with gaps between them. Such an installation may decrease the wind forces on the PV panels due to the pressure equalization effect as well as on the waterproofing membrane due to the shielding effect of the PV panels. This paper discusses the validity of such an idea. The pressure on the bottom surface of a PV panel, called the “layer pressure” here, was evaluated by a numerical simulation based on the unsteady Bernoulli equation. In the simulation, the time history of the external pressure coefficients, measured at many points on the roof in a wind tunnel, was employed. It was found that the wind forces, both on the PV panels and on the roofing system, were significantly reduced. The reduction was large near the roof’s corner, where large suction pressures were induced in oblique winds. Thus, the proposed method improved the wind resistance of both systems significantly.

WIND LOADS ON ROOFING SYSTEM AND PHOTOVOLTAIC SYSTEM INSTALLED PARALLEL TO FLAT ROOF

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Tetsuo Yambe ◽  
Yasushi Uematsu ◽  
Kosuke Sato
Keyword(s):  
Time History ◽  
Photovoltaic System ◽  
Pressure Equalization ◽  
Pv Systems ◽  
External Pressures ◽  
Wind Actions ◽  
Strong Winds ◽  
Wind Pressures ◽  
Flat Roof ◽  
Roofing System

Mechanically-attached waterproofing system has become popular in Japan. Being vulnerable to wind actions, especially to suctions, this roofing system is often damaged by strong winds. Similarly, photovoltaic (PV) systems installed on flat roofs are often damaged by strong winds, because the PV panels are subjected to large wind forces in an adverse wind. In order to reduce such damage to both systems, the authors propose to install the PV panels parallel to the flat roof with gaps between them, which may reduce the net wind forces on the PV panels due to the effect of pressure equalization. In addition, the wind pressures acting on the waterproofing system will decrease significantly. The present paper investigates the validity of the above-mentioned idea. The wind pressures underneath the PV panels, called ‘layer pressures’, are evaluated by a numerical simulation using the unsteady Bernoulli equation together with the time history of external pressures measured at many locations on the rooftop of a flat-roofed building model in a turbulent boundary layer. The results clearly indicate a significant reduction of wind forces acting on the PV panels as well as on the waterproofing system. The use of PV panels for reducing the wind pressures on waterproofing system is quite effective to the corner region of the roof, where very large suctions are induced in a diagonal wind.

scholarly journals Wind-Induced Dynamic Behavior of Mechanically Attached Single-Ply Membrane Roofing Systems Installed on Flat Roofs

2021 ◽  
pp. 1-23
Author(s):  
Yasushi Uematsu ◽  
Shingo Sugiyama ◽  
Takuto Usukura
Keyword(s):  
Dynamic Behavior ◽  
Time History ◽  
Test Method ◽  
Wind Pressure ◽  
Pressure Loading ◽  
Loading Test ◽  
Element Analysis ◽  
Pressure Distributions ◽  
Flat Roofs ◽  
Roofing System

The present paper investigates the wind-induced dynamic behavior of a mechanically attached single-ply membrane roofing system installed on flat roofs of middle-rise and high-rise buildings with or without parapets. First, the wind pressure distributions on the roof were measured in a turbulent boundary layer. The results indicate that the parapets affect the wind pressure distributions significantly. Very large peak suctions are induced near the windward corner of the roof in an oblique wind in the case of a building without parapets. Then, we have developed a test method for evaluating the wind-resistant performance of the roofing system using three Pressure Loading Actuators (PLAs) and a chamber to which a full-scale specimen is attached. In the experiments, the chamber was divided into three spaces by using thin silicon sheets. The PLAs generated different fluctuating pressures in these spaces using the time history of wind pressure coefficients measured at three points near the windward corner of the roof in an oblique wind. We measured the membrane deformations and the wind forces acting on the fasteners connecting the membrane with the structural substrate. The results indicate that horizontal forces nearly equal to or larger than the vertical ones are generated on the fasteners, which may cause pulling out of fasters more easily. The failure mode was found to be different from that obtained from a ramped pressure loading test. We have also developed a model of finite element analysis, which was validated by an experiment. The results of analysis for a wide area of roofing system indicate that relatively large horizontal forces may be generated on the fasteners in the field region of the roof for buildings with parapets.

An Innovative Structural Health Monitoring System for Large Transmission Towers Based on GPS

2019 ◽  
Vol 19 (04) ◽  
pp. 1971002 ◽  
Author(s):  
X. X. Cheng ◽  
Y. J. Ge
Keyword(s):  
Structural Health Monitoring ◽  
Real Time ◽  
Health Monitoring ◽  
Time History ◽  
Time Behavior ◽  
Structural Health ◽  
Transmission Towers ◽  
Strong Winds ◽  
Force Equilibrium

In this paper, we propose an innovative structural health monitoring (SHM) system for large transmission towers that are frequently subjected to strong winds. The system is based on the strategy of using a static force equilibrium equation to calculate the whole structure’s real-time stress distribution according to its real-time behavior, as captured by the global positioning system (GPS). The reason for adopting this approach is that large transmission towers are fundamentally quasi-static structures and they are not prone to resonance under wind excitations. A case study is used to present the SHM system, then its effectiveness is validated by comparing the simulated SHM results with the exact solution obtained by a realistic time-history dynamic analysis. Additionally, we discuss the use of a new reliability analysis method based on the Ditlevsen’s bounds to assess the real-time structural conditions.

scholarly journals Analysis of Wind-Induced Vibration of a Spoke-Wise Cable–Membrane Structure

2020 ◽  
Vol 8 (8) ◽  
pp. 603
Author(s):  
Hua Huang ◽  
Yaoqiang Xian ◽  
Wei Zhang ◽  
Mengxue Guo ◽  
Kun Yang ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Dynamic Behavior ◽  
Damage Assessment ◽  
Membrane Structure ◽  
Aerospace Industry ◽  
Time History ◽  
Wind Load ◽  
Membrane Structures ◽  
Wind Resistance ◽  
Wind Induced Vibration

Lightweight cable–membrane structures can span large distances and undertake aesthetically pleasing shapes. They are widely used for roofs and modern structural canopies and in the aerospace industry for large on-board antenna reflectors that are to be deployed in space. This paper studies a wind-induced vibration under different cable stress relaxation conditions based on the wind load time-history to obtain the dynamic behavior of such a structure. Particularly, the focus is put upon its wind resistance in the event of stress relaxation. This research can provide an important reference for the design of wind resistance, damage assessment, and emergency maintenance for the spoke-wise cable–membrane structure (SCMS).

scholarly journals Photovoltaic Panels Temperature Regulation Using Evaporative Cooling Principle: Detailed Theoretical and Real Operating Conditions Experimental Approaches

Energies ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 145
Author(s):  
Zeyad A. Haidar ◽  
Jamel Orfi ◽  
Zakariya Kaneesamkandi
Keyword(s):  
Electrical Power ◽  
Evaporative Cooling ◽  
Operating Conditions ◽  
Bottom Surface ◽  
Transfer Model ◽  
Solar Pv ◽  
Pv Panel ◽  
Better Regulation ◽  
Steady State Heat ◽  
Electrical Power Output

Solar photovoltaic (PV) applications are gaining a great interest worldwide and dominating the renewable energy sector. However, the solar PV panels’ performance is reduced significantly with the increase in their operating temperature, resulting in a substantial loss of energy production and poor economic scenarios. This research contributes to overcoming the PV performance degradation due to the temperature rise. This work involves experimental and theoretical studies on cooling of PV panels using the evaporative cooling (EC) principle. A new EC design to cool the bottom surface of a PV panel was proposed, fabricated, tested, and modeled. A series of experimentation readings under real conditions showed the effectiveness of the method. A steady state heat and mass transfer model was implemented and compared with the experimental data. Fair agreement between the results of the modelling and experimental work was observed. It was found that the temperature of the PV panel can be decreased by 10 °C and the power improvement achieved was 5%. Moreover, the EC helps to stabilize the panels’ temperature fluctuation, which results in a better regulation of electrical power output and reduces the uncertainty associated with solar PV systems.

Wind Resistance Correlation of Adhesive Applied Roofing System

2011 ◽  
Vol 39 (6) ◽  
pp. 103805
Author(s):  
M. R. Mitchell ◽  
R. E. Link ◽  
H. Tanaka ◽  
W. Li ◽  
A. Baskaran ◽  
...  
Keyword(s):  
Wind Resistance ◽  
Roofing System

Active Modulated Reflectance Roofing System to Tailor Building Solar Loads for Increased HVAC Efficiency

2014 ◽  
Author(s):  
Daniel M. Wolfe ◽  
Keith Goossen
Keyword(s):  
Space Heating ◽  
Cooling Load ◽  
Energy Usage ◽  
Modified Bitumen ◽  
Alternative Technologies ◽  
Heating And Cooling ◽  
Heating And Cooling Load ◽  
Roofing Materials ◽  
Flat Roofs ◽  
Roofing System

Space heating and cooling contributes a significant percentage of a building’s overall energy usage profile. The construction of a building’s envelope is an essential component that impacts the overall heating and cooling load. For many years, flat roofs were covered with low albedo materials such as asphalt or modified bitumen, which can reach temperatures of 150°F to 180°F during summer months. More recently, alternative technologies, such as “white roofs”, have been put forth to mitigate the problem of unwanted thermal gain. However, these traditional roofing materials and recent innovations are passive structures and only promote seasonal benefits. This paper proposes and demonstrates the concept of an active variable reflectance roofing system that can tailor solar loads to desired heating or cooling, significantly reducing overall space heating and cooling energy requirements and costs.

scholarly journals Enhancement of energy transfer efficiency for photovoltaic (PV) systems by cooling the panel surfaces

2021 ◽  
Vol 4 (8(112)) ◽  
pp. 83-89
Author(s):  
Hasan Shakir Majdi ◽  
Mahmoud A. Mashkour ◽  
Laith Jaafer Habeeb ◽  
Ahmad H. Sabry
Keyword(s):  
Energy Transfer ◽  
Energy Transfer Efficiency ◽  
Transfer Efficiency ◽  
Bottom Surface ◽  
Thermal Coefficient ◽  
Solar Photovoltaic ◽  
Solar Pv ◽  
Pv Systems ◽  
Pv Panel ◽  
Storage Batteries

The thermal coefficient of a solar photovoltaic (PV) panel is a value that is provided with its specification sheet and tells us precisely the drop in panel performance with rising temperature. In desert climates, the PV panel temperatures are known to reach above 70 degrees centigrade. Exploring effective methods of increasing energy transfer efficiency is the issue that attracts researchers nowadays, which also contributes to reducing the cost of using solar photovoltaic (PV) systems with storage batteries. Temperature handling of solar PV modules is one of the techniques that improve the performance of such systems by cooling the bottom surface of the PV panels. This study initially reviews the effective methods of cooling the solar modules to select a proper, cost-effective, and easy to implement one. An active fan-based cooling method is considered in this research to make ventilation underneath the solar module. A portion of the output power at a prespecified high level of battery state-of-charge (SOC) is used to feed the fans. The developed comparator circuit is used to control the power ON/OFF of the fans. A Matlab-based simulation is employed to demonstrate the power rate improvements and that consumed by the fans. The results of simulations show that the presented approach can achieve significant improvements in the efficiency of PV systems that have storage batteries. The proposed method is demonstrated and evaluated for a 1.62 kW PV system. It is found from a simultaneous practical experiment on two identical PV panels of 180 W over a full day that the energy with the cooling system was 823.4 Wh, while that without cooling was 676 Wh. The adopted approach can play a role in enhancing energy sustainability.

Motion and coalescence of sessile drops driven by substrate wetting gradient and external flow

2014 ◽  
Vol 746 ◽  
pp. 214-235 ◽  
Author(s):  
Majid Ahmadlouydarab ◽  
James J. Feng
Keyword(s):  
External Pressure ◽  
External Flow ◽  
Shielding Effect ◽  
Hydrodynamic Drag ◽  
Single Drop ◽  
Initial Shape ◽  
Moving Contact Line ◽  
Drop Dynamics ◽  
Moving Contact ◽  
Asymmetric Shape

AbstractWe report two-dimensional simulations of drop dynamics on a substrate subject to a wetting gradient and an external pressure gradient along the substrate. A phase-field formulation is used to represent the drop interface, and the moving contact line is modelled by Cahn–Hilliard diffusion. The Navier–Stokes–Cahn–Hilliard equations are solved by finite elements on an adaptively refined unstructured grid. For a single drop and a pair of drops, we consider three scenarios of drop motion driven by the wetting gradient only, by the external flow only, and by a combination of the two. Both the capillary force and the hydrodynamic drag depend strongly on the shape of the drop. Since the drop adapts its shape to the local wetting angles and to the external flow on a finite time scale, hysteresis is a prominent feature of the drop dynamics under opposing forces. For each wetting gradient, there is a narrow range of the magnitude of the external flow within which a single drop can achieve a stationary state. The equilibrium drop shape and position depend on its initial shape and the history of forcing. For a pair of drops, the wetting gradient or external flow alone tends to produce catch-up and coalescence. The flow-driven coalescence arises from a viscous shielding effect that relies on the asymmetric shape of the trailing drop once it is deformed by flow. This mechanism operates at zero Reynolds number, but is much enhanced by inertia. With the two forces opposing each other, the external flow favours separation while the wetting gradient favours coalescence. The outcome depends on their competition.

scholarly journals Molecular globules in the Veil bubble of Orion

2020 ◽  
Vol 639 ◽  
pp. A1 ◽  
Author(s):  
J. R. Goicoechea ◽  
C. H. M. Pabst ◽  
S. Kabanovic ◽  
M. G. Santa-Maria ◽  
N. Marcelino ◽  
...  
Keyword(s):  
Star Formation ◽  
Uv Radiation ◽  
Formation Rate ◽  
External Pressure ◽  
Molecular Structures ◽  
Molecular Core ◽  
Local Standard ◽  
Strong Winds ◽  
The Veil ◽  
Molecular Abundances

Strong winds and ultraviolet (UV) radiation from O-type stars disrupt and ionize their molecular core birthplaces, sweeping up material into parsec-size shells. Owing to dissociation by starlight, the thinnest shells are expected to host low molecular abundances and therefore little star formation. Here, we expand previous maps made with observations using the IRAM 30 m telescope (at 11″ ≃ 4500 AU resolution) and present square-degree 12CO and 13CO (J = 2–1) maps of the wind-driven “Veil bubble” that surrounds the Trapezium cluster and its natal Orion molecular core (OMC). Although widespread and extended CO emission is largely absent from the Veil, we show that several CO “globules” exist that are blueshifted in velocity with respect to OMC and are embedded in the [C II] 158 μm-bright shell that confines the bubble. This includes the first detection of quiescent CO at negative local standard of rest velocities in Orion. Given the harsh UV irradiation conditions in this translucent material, the detection of CO globules is surprising. These globules are small (Rg = 7100 AU), not massive (Mg = 0.3 M⊙), and are moderately dense: nH = 4 × 104 cm−3 (median values). They are confined by the external pressure of the shell, Pext∕k ≳ 107 cm−3 K, and are likely magnetically supported. They are either transient objects formed by instabilities or have detached from pre-existing molecular structures, sculpted by the passing shock associated with the expanding shell and by UV radiation from the Trapezium. Some represent the first stages in the formation of small pillars, others of isolated small globules. Although their masses (Mg <MJeans) do not suggest they will form stars, one globule matches the position of a known young stellar object. The lack of extended CO in the “Veil shell” demonstrates that feedback from massive stars expels, agitates, and reprocesses most of the disrupted molecular cloud gas, thereby limiting the star-formation rate in the region. The presence of molecular globules is a result of this feedback.

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