Rigid Panels Research Articles

Experimental study of flow and mass transport in the near-wake region of a rigid planar metal net panel

Aquaculture cages constructed from rigid material have become increasingly popular in recent years due in part to the continuous expansion of the aquaculture industry offshore, where cages need to withstand much harsher ocean conditions. Most previous studies of hydrodynamic interactions with aquaculture cages have explored the impacts of more traditional flexible cage net panels on wake flow fields and mass transport properties. In the current experimental study, Particle Image Velocimetry and Planar Laser Induced Fluorescence techniques were used to measure flow and concentration fields in the near wake region of a steady current through a rigid metal net panel to analyze both the flow patterns and mass transport processes. The results indicated that, similar to a flexible polyethylene net panel, the time-average velocities and turbulence characteristics in the near wake region were highly inhomogeneous and anisotropic, with the turbulent intensity following a short-range, power-law decay downstream of the panel. In direct comparison with a flexible net panel of similar net solidity, the rigid net panel was found to slightly enhance the lateral spreading of the plume, with cross-sectional profiles of the mean concentration and concentration fluctuation shown to exhibit self-similar Gaussian distributions. The rigid net panel also resulted in a lower flow blockage, as measured by a velocity reduction coefficient, with the corresponding turbulent intensity also reduced compared to the flexible panel due to an overall reduction in the drag force. In addition, the rigid panel tended to create larger wake eddies than the flexible panel, leading to enhanced scalar mixing and, hence, faster rates of concentration decay in the near-wake region. These experimental findings have potential implications for cage-based aquaculture operations, where rigid fish cages are comparatively more likely to generate favorable environments for fish growth, as well as helping to reduce negative impacts on the surrounding aquatic environment.

Modelling Open Ocean Aquaculture Structures Using CFD and a Simulation-Based Screen Force Model

The numerical framework of the open source CFD solver REEF3D is utilised to study the fluid–structure interaction of an open ocean aquaculture system and waves. The presence of the net is considered in the momentum equations of the fluid using a forcing term based on Lagrangian–Eulerian coupling and the hydrodynamic loads on the net. They are defined semi-empirically using a screen force model. Here, the hydrodynamic force coefficients are calculated from the net geometry and fluid velocity. The necessary force coefficients are predicted from a new simulation-based screen force model. Here, CFD simulations are performed to obtain the hydrodynamic loads on net panels for varying net geometries, angles of attack and velocities. Then, a Kriging metamodel is applied to fit a polynomial to the data. The proposed net model is validated against measurements for waves and current through rigid net panels and applied to simulate the dynamics of an open ocean aquaculture cage in waves. In current, the model predicts the drag forces and velocity reduction within a 10% error band, whereas it tends to under-predict the lift forces by up to 20%. In waves, the model tends to over-predict the crests with increasing wave height, but the deviations are also within a 10% error band.

Shrinkable Self-Similar Structure Design

Abstract Origami techniques, as folding and unfolding, can be utilized in shrinkable structures. Especially when the crease pattern is rigid foldable, it can be treated as a mechanical linkage of rigid panels connected by hinges. Since rigid foldable crease patterns have the strong geometrical constraint of the facets not being able to stretch or bend, it is difficult to design new crease patterns, and variations of existing patterns are limited. However, it is known that there are cases where crease patterns can be made rigid foldable by adding some slits. This paper proposes a mechanical linkage that folds into a similar flat shape by adding slits. A method is presented of generating rigid foldable crease patterns in arbitrary polygons that fold smaller, and it is confirmed that structures that have a mechanism for shrinking can be generated from these crease patterns using rigid thick panels and hinges.

On local kirigami mechanics II: Stretchable creased solutions

Following on Part I of this work series on local kirigami mechanics, we present a study of a discretely creased mechanism as a model to investigate the mechanics of the basic geometric building block of kirigami—the e-cone. We consider an annular disk with a single radial slit discretised by a series of radial creases connecting kinematically flat rigid panels. The creases allow both relative rotation and separation between panels, capturing both bending and stretching deformations. Admissible equilibrium configurations are obtained by penalising these deformations using elastic springs with stiffnesses derived from compatible continuum plate deformations. This provides a tool to study both inextensible and extensible e-cone configurations due to opening of the slit and rotation of its lips. This creased model hence offers the possibility to study the e-cone away from its isometric limit, i.e., for plates with finite thickness, and explore the full range of post-buckling (far-from-threshold) behaviour as well as initial buckling (near-threshold) instability. Our local approach provides a fundamental understanding of kirigami phenomenology, underpinned by a proper theoretical approach to geometry and mechanics.

Fluid–structural coupling of an impinging shock–turbulent boundary layer interaction at Mach 3 over a flexible panel

We present high-fidelity numerical simulations of the interaction of an oblique shock impinging on the turbulent boundary layer developed over a rectangular flexible panel, replicating wind tunnel experiments by Daub et al. (AIAA Journal, vol. 54, 2016, pp. 670–678). The incoming free-stream Mach and unit Reynolds numbers are $M_{\infty } = 3$ and $Re_{\infty }=49.4\times 10^6 {\rm m}^{-1}$ , respectively. The reference boundary layer thickness upstream of the interaction with the shock is $\delta _0 = 4$ mm. The oblique shock is generated with a rotating wedge initially parallel to the flow that increases the deflection angle up to $\theta _{{max}} = 17.5^{\circ }$ within approximately $15$ ms. A loosely coupled partitioned flow–structure interaction simulation methodology is used, combining a finite-volume flow solver of the compressible wall-modelled large-eddy simulation equations, an isoparametric finite-element solid mechanics solver and a spring-system-based mesh deformation solver. Simulations are conducted with rigid and flexible panels, and the results compared to elucidate the effects of panel flexibility on the interaction. Three-dimensional effects are evaluated by conducting simulations with both full ( $50 \delta _0$ ) and reduced ( $5\delta _0$ ) spanwise panel width, the latter enforcing spanwise periodicity. Panel flexibility is found to increase the separation bubble size and modify its spectral dynamics. Time- and spanwise-averaged streamwise profiles of the wall pressure exhibit a drop over the flexible panel prior to the interaction and a reduced peak pressure in comparison with the rigid case. Spectral analyses of wall pressure data indicate that the low-frequency motions have a similar spectral distribution for the rigid and flexible cases, but the flexible case shows a wider region dominated by low-frequency motions and traces of the panel vibration on the wall pressure signal. The sensitivity of the interaction to small variations in the wedge extent and incoming boundary layer thickness is evaluated. Predictions obtained from lower-fidelity modelling simplifications are also assessed.

A review of the bird impact process and validation of the SPH impact model for aircraft structures

The aim of this paper is to study the phenomenon of bird strike during each phase of the impact and to present a numerical model for its prediction in order to develop the best practices to make a structural component resistant to bird strike. To this end, the Smooth Particle Hydrodynamics (SPH) bird model is developed and validated based on experiments by Barber and Wilbeck and two papers by Guida et al. The experiments considered the impact of small birds on rigid flat panels. Guida et al. developed a 8 lb bird model to predict the impact on a deformable small leading-edge bay and on a full-scale leading edge. The hydrodynamic theory is applied to determine the shock pressure, the shock equation of state, the stagnation pressure and the steady-state equation for water with different porosities. Subsequently, the bird structure is analyzed for different bird geometries and target models. This analysis allowed to design critical components of an aircraft structure, such as the leading edge of the C27J aircraft tail cone in compliance with current aviation airworthiness requirements.

A Numerical Study of the Hydrodynamics of an Offshore Fish Farm Using REEF3D

Abstract In this article, the hydrodynamics of and nonlinear interaction between the large offshore fish farm “ShenLan 1” and regular waves are investigated using the open-source computational fluid dynamics (CFD) toolbox REEF3D. The framework consists of a rigid body dynamics solver for the frame structure coupled to a fluid solver including the shielding effects of the nets. The solver and grid independence are validated using a 2D numerical wave tank, a free decay test, and a study of the wave loads on a rigid net panel. Then, the effects of regular wave parameters, the thickness of the vertical outer columns of the structure, and the variations of the aspect ratios on the loads, responses, and maximum mooring tension forces are studied. It is concluded that the response motion is sensitive to the wave period rather than the wave height due to the longer duration of unidirectional wave loads acting on the frame. The frequent events of partial submersions and wave overtopping in rather steep waves are confirmed through the capturing of the free surface. The net system accounts for about 30% of the total drag but does not influence the structural response to a larger extend. The effect of the aspect ratio on the hydrodynamics is more distinct than that of the frame thickness. As a result of the study, the first step toward a systemic evaluation of the importance of different structural parts of an offshore fish cage for the expected responses is provided.

Solar Radiation Transmittance Characteristics of Textile Woven Fabrics suitable for Greenhouse covering Materials

Nowadays, greenhouse covering materials have a vital role in terms of a protective cultivation process. Many farmers use polyfilms, rigid or semi-rigid plastic panels, and glazing materials as greenhouse covering materials in the present scenario. However, these plastic covering materials are known for their high cost, short service life, and cause of harmful environment. Solar transmittance property is one of the main criteria for choosing any greenhouse covering materials. This study prepares various woven fabrics made of polyester, cotton, and polyester–cotton blend yarns. Their solar transmittance characteristic is analyzed to develop fabric and compare it with a polyethylene film already used as a greenhouse cladding material to substitute for plastic materials. The solar transmission of polyester fabric is achieved as high as 70% in the photosynthesis active radiation, suitable for a commercial greenhouse material. In addition, the polyester fabric has tensile strength and extension much higher than that of commercial plastic greenhouse material.

Analysis of design of spacecraft solar arrays

Solar arrays supply electrical power to spacecraft equipment and also provide charging of electrochemical batteries used in the shadow sections of the orbit. Photovoltaic converters of light energy of solar radiation form the basis of the solar battery. Their principle of operation is based on the phenomenon of the photoelectric effect. The article provides an overview of the development of solar cells and the classification of modern designs of solar cells for spacecraft. The review considers stationary and deployable solar batteries used both on the first spacecraft and on space stations. The classification of solar cell designs is made taking into account their characteristic features. These features are the rigidity of the supporting structure, the method of placement in the starting position and the method of orientation towards the light source. The classification covered rigid panel solar arrays, flexible substrate solar panels, inflatable solar arrays, self-expanding solar arrays, and solar concentrator panels. In each design group of this classification, corresponding examples of solar cells are presented. The presented review and classification makes it possible to track trends in the development of solar array designs for spacecraft.

Design of deployable curved-surface rigid origami flashers

This paper proposes an approach to designing rigid origami flashers that can be deployed onto curved-surface configurations. The method of designing planar origami flashers that can be wrapped around regular polygonal central hubs is presented. Based on the principle of parallel projection, planar origami flashers are projected onto target spherical surfaces to obtain the vertices on the boundary creases between sections of adjacent origami flashers. The geometric relationships of thin-panel curved origami flashers are established in terms of foldability, and other vertices in each section are calculated using numerical methods. Flexible and elastic hinges modify the thin-panel curved origami flashers into thick-panel rigid flashers. The thick rigid panels maintain the shape of flashers, and the flexible creases treated using thickness-accommodating methodologies are used to maintain the foldability of the thick panels. Additionally, we analysed the parameters that affect the accuracy of the surface fitting. The feasibility of the proposed approach is verified using numerical simulations and physical prototypes. The novel designing of deployable curved-surface rigid origami flashers facilitates their potential applicability in solid surface antennas, surface reflectors, and other space engineering applications.

Effect of torsional spring and shape on the performance of bioinspired caudal fin

The swimming ability of fish is greatly influenced by the hydrodynamics of their caudal fins. In this paper, the effects of flexibility and shape on the performance of a bioinspired panel are numerically studied. The flexibility is simplified as a torsional spring, and three typical shapes (i.e., square, convex, and concave shapes) are considered. The results are obtained based on three-dimensional numerical simulations of flapping panels at Re = 1000 and St = 0.5. It is shown that the flexibility can significantly affect the performance of pitching panels, by changing the phase lag between the motions of the fore and hind parts. When the phase lag is in the range of 0.1π–0.6π, the performance improvement can be obtained by the flexible panels, as compared with the rigid panel. Moreover, the maximum thrust (or efficiency) can be achieved by a flexible panel when the phase lag is approximately 0.35π (or 0.24π). On the other hand, it is found that the convex shape is optimal for thrust generation, but the square shape is optimal for propulsive efficiency. Moreover, the mechanism by which flexibility and shape can influence the performance of the pitching panel is analyzed. The results obtained here may provide some light on designing the efficient propulsor for microunderwater robots.

Vertical force generation of a vectorial thruster that employs a rigid flapping panel

The vertical force generation and flow features of a flapping panel that employs combined motion of horizontal oscillation, longitudinal rotation, and leading-edge-based pitching motion were investigated numerically. The sole vertical force generation is realized by combining the horizontal oscillation and longitudinal rotation, while the vertical force and forward thrust are obtained simultaneously by employing the combined motion of the horizontal oscillation, longitudinal rotation, and pitching motion about the leading edge of the panel. The effects of the phase shift (Ψ) of the longitudinal rotation and the amplitudes of the longitudinal rotation and pitching motion are investigated and discussed, respectively. Results show that the phase shift determines the instantaneous attitude of the panel and influences the directions of the instantaneous generated forces and thus plays an important role in the vertical force generation. The panel could generate stable forward thrust while maintaining the pitching motion constant and adjusting the longitudinal rotation amplitude, and in the meantime, the vertical force increases linearly with the rotation amplitude. On the other hand, the vertical force may change to the opposite direction when the longitudinal rotation is kept constant and the pitching amplitude is adjusted. The results of the current research show the potential of employing these kinds of combined motions to fish-tail-mimic propulsors of robotic fishes that pursue high maneuverability.

Making insulation more climate friendly

Insulating and air sealing are effective ways to reduce the carbon footprints of homes and other buildings, and rigid foam panels are a popular material for doing that work. But many of the panels have a little-known climate cost: the global warming potential (GWP) of the gas, or blowing agent, used to puff the foam. In the case of panels made of extruded polystyrene (XPS)—a closed-cell foam suitable for wet or dry conditions—that gas has been hydrofluorocarbon-134a (HFC-134a). HFC-134a is a good blowing agent , but it has a GWP of 1,430, meaning it traps 1,430 times as much heat as carbon dioxide does over 100 years. As regulations seeking to eliminate HFC-134a take effect this year in Canada and the US, panel makers including Owens Corning and DuPont are switching their blowing agents to blends containing hydrofluoroolefins (HFOs). Refrigeration is the largest use for HFCs and other fluorocarbon gases,

High-Stability Flexible X-ray Detectors Based on Lead-Free Halide Perovskite Cs2TeI6 Films.

Normal flat panel X-ray detectors are confined in imaging of curved surfaces and three-dimensional objects. Except that, their rigid panels provide uncomfortable user experience in medical diagnosis. Here, we report a flexible X-ray detector fabricated by the combination of a lead-free Cs2TeI6 perovskite film and a polyimide (PI) substrate. High-quality Cs2TeI6 polycrystalline films are prepared by a low-temperature electrospraying method. The resistivity even remained at the level of 1011 Ω·cm after 100 cycles of bending tests with a low bending radius of 10 mm. The resulting flexible Cs2TeI6 detectors exhibit better response stability than those based on rigid SnO2:F glass (FTO), which is attributed to the superior crystallization of films and the growth stress relief of flexible substrates. Furthermore, an X-ray sensitivity of 76.27 μC·Gyair-1·cm-2 and a detection limit of 0.17 μGyair·s-1 are achieved. A series of distortion-free clear X-ray images are obtained for objects with different materials and densities. These findings provide insights into flexible X-ray detectors based on perovskite films and motivate research in wearable X-ray detectors for medical radiography and dose monitoring.

A programmable origami-inspired webbed gripper

Origami-inspired design is becoming an innovative approach to create functional mechanisms with a variety of attractive features including scalability, programmability and simplicity. This paper presents the design of a webbed-foot-inspired gripper by employing a novel origami webbing structure, which is generated by strategically integrating several elementary Miura-ori and waterbomb-ori modules. The grasping behaviour of the proposed webbed gripper can be accustomed through rearranging the 2D crease pattern of the origami webbing by taking advantage of shape and kinematic programmability for each elementary module. And based on the rigid panels and joints, a comprehensive quantitative approach to achieve specific grasping performance is performed in terms of closed extendable configuration and enclose input angle. The origami webbing can be fabricated from a single flat paper sheet and deploy along a straight path symmetrically together with supporting skeletons. A sample webbed gripper activated with cables is designed to exhibit potential applications, and primary experimental work focusing on object grasping capability is carried out. The results demonstrate the feasibility and practicability of the origami-inspired webbed gripper design, and numerous novel origami webbing structures can be developed based on this construction strategy.

Lattice model for self-folding at the microscale.

Three-dimensional shell-like structures can be obtained spontaneously at the microscale from the self-folding of 2D templates of rigid panels. At least for simple structures, the motion of each panel is consistent with a Brownian process and folding occurs through a sequence of binding events, where pairs of panels meet at a specific closing angle. Here, we propose a lattice model to describe the dynamics of self-folding. As an example, we study the folding of a pyramid of N lateral faces. We combine analytical and numerical Monte Carlo simulations to find how the folding time depends on the number of faces, closing angle, and initial configuration. Implications for the study of more complex structures are discussed.

Design and Dynamic Analysis of Rigid Foldable Aeroshells for Atmospheric Entry

A novel rigid deployable aeroshell architecture has been developed, where rigid panels with a thermal protection system layer are connected between retractable ribs. Following origami principles, an optimal fold pattern is selected and imposed on the panels to ensure efficient flat stowage during launch and repeatable deployment. The design process includes minimizing the number of folds to reduce stacking height and maximizing the angles between each fold line to avoid an unfavorable aerothermodynamic response. The dynamic behavior of the optimal design is analyzed with the aid of a dynamic multibody analysis model. Results from the dynamic model show that the process of deployment is highly sensitive to panel geometry (especially panel thickness and hinge design). Robust, repeatable, and controllable deployment is most readily achieved with a small (but nonzero) panel thickness and selection of interpanel hinges, which allow a degree of over-rotation, avoiding a premature hard stop, which would otherwise prevent full deployment. Modeled results have been verified through experimental testing of a 0.4-m-diam scale model.

Reprogrammable Kinematic Branches in Tessellated Origami Structures

Abstract We analyze the folding kinematics of a recently proposed origami-based tessellated structure called the Morph pattern, using thin, rigid panel assumptions. We discuss the geometry of the Morph unit cell that can exist in two characteristic modes differing in the mountain/valley assignment of a degree-four vertex and explain how a single tessellation of the Morph structure can undergo morphing through rigid origami kinematics resulting in multiple hybrid states. We describe the kinematics of the tessellated Morph pattern through multiple branches, each path leading to different sets of hybrid states. We study the kinematics of the tessellated structure through local and global Poisson’s ratios and derive an analytical condition for which the global ratio switches between negative and positive values. We show that the interplay between the local and global kinematics results in folding deformations in which the hybrid states are either locked in their current modes or are transformable to other modes of the kinematic branches, leading to a reprogrammable morphing behavior of the system. Finally, using a bar-and-hinge model-based numerical framework, we simulate the nonlinear folding behavior of the hybrid systems and verify the deformation characteristics that are predicted analytically.

Internal Force on and Deformation of Steel Assembled Supporting Structure of Foundation Pit under Thermal Stress

The steel assembled support structure of a foundation pit can be assembled easily with high strength and recycling value. Steel’s performance is significantly affected by the surrounding temperature due to its temperature sensitivity. Here, a full-scale experiment was conducted to study the influence of temperature on the internal force and deformation of supporting structures, and a three-dimensional finite element model was established for comparative analysis. The test results showed that under the temperature effect, the deformation of the central retaining pile was composed of rigid rotation and flexural deformation, while the adjacent pile of central retaining pile only experienced flexural deformation. The stress on the retaining pile crown changed little, while more stress accumulated at the bottom. Compared with the crown beam and waist beam 2, the stress on waist beam 1 was significantly affected by the temperature and increased by about 0.70 MPa/°C. Meanwhile, the stress of the rigid panel was greatly affected by the temperature, increasing 78% and 82% when the temperature increased by 15 °C on rigid panel 1 and rigid panel 2, respectively. The comparative simulation results indicated that the bending moment and shear strength of pile 1 were markedly affected by the temperature, but pile 2 and pile 3 were basically stable. Lastly, as the temperature varied, waist beam 2 had the largest change in the deflection, followed by waist beam 1; the crown beam experienced the smallest change in the deflection.

Recent advances in flexible alternating current electroluminescent devices

Since its first discovery by Destriau in oil dispersion of ZnS:Cu phosphors, alternating current electroluminescence (ACEL) has found enormous applications in lighting, full-color displays, and optoelectronics. ACEL materials are particularly useful for constructing flexible light-emitting devices owing to their low cost and easy integration with flexible electrodes and polymer substrates. ACEL devices utilizing the phosphor-elastomer composite as the emissive layer are intrinsically stretchable/deformable, in contrast to direct current light-emitting diodes that are often built on rigid panels. In this Research Update, we summarize recent advances in the design and preparation of various flexible-panel ACEL devices. Emerging applications enabled by these flexible ACEL devices are also highlighted.