Rear Face Research Articles

A Parametrical Study on Hypervelocity Impact of Orbital Debris

A numerical method has been presented to simulate hypervelocity impacts on metal targets. The target is a rectangular prism and is positioned at various inclined angles relative to the impact direction, while four different projectiles such as square prism, triangular prism, truncated cone, and ogival shape are chosen. This numerical model employs an open-source code, MPM3D-F90, which is based on the Material Point Method. In order to enhance flexibility of the code for defining projectiles and target bodies in the material domain, a preprocessor is developed to create a variety of geometrical shapes for a given volume. In addition to supplementing and defining various geometrical bodies, this tool also simplifies the preprocessing process to create the user’s specific preferences for the problem. To demonstrate the utility of the preprocessor tool and investigate the influence of geometry on hypervelocity impacts, simulations are conducted using various projectile and target configurations. The analysis results reveal that the structure of the debris cloud formations, scattering behavior of the ejected particle from both front and rear faces, and penetration depth measures are significantly influenced by the projectile shape and impact angles.

In-plane thermal anisotropy of natural cork and its variability

This study investigates the natural cork thermal anisotropy and its variability using plane slice samples of 1.4 mm thickness, cut along the principal radial, longitudinal, and tangential directions, from bark previously treated for cork stoppers production. Heating was pointwise applied to the rear face using a copper needle coupled to a Peltier element, while an in-plane thermographic technique monitored temperature evolution on the front surfaces using a Flir SC5650 infrared camera. Thermal diffusivity measurements yielded values of 0.172 ± 0.038 mm2/s (radial), 0.161 ± 0.022 mm2/s (longitudinal), and 0.160 ± 0.027 mm2/s (tangential). Additionally, a volumetric heat capacity of 0.25 MJ/(m3·K) was determined using the Hot Disk technique. This information enabled the calculation of thermal conductivity, ranging from 0.033 to 0.048 W/(m·K). Findings align with existing literature, which reports thermal diffusivity between 0.08 and 0.24 mm2/s and thermal conductivity between 0.035 and 0.045 W/(m·K). This study contributes valuable insights into the thermal properties of natural cork and their orientation-dependent variability.

Local structural behaviour of the outer containment of an NPP against hard missile impact

An aircraft crash and missile impact on a nuclear containment structure is currently described as an event beyond design basis; however, soon, it will be qualified as a primary design criterion. In the present study, the structural and dynamic behaviour of the outer containment of a nuclear power plant (NPP) has been studied to substantiate its structural integrity against the rigid missile impact. Scaled experiments (at a 1:4 and 1:3 ratio with respect to shell thickness) have been performed to study the localized behaviour of the containment structure against 10 and 20-kg rigid steel projectiles. The reinforced cement concrete (RCC) targets of thicknesses 150 and 200 mm have been subjected to impact at incidence velocity close to the landing and taking of velocity of the aircraft. The flexural reinforcement ratio was considered 1.25 % for a 150 mm thick target and 1.53 % for a 200 mm thick target. The effect of shear reinforcement on the penetration and perforation resistance has been studied for a 200 mm thick RCC target. A detailed post-test examination was conducted to evaluate the localized physical damage characteristics such as spalling and scabbing of concrete, penetration, perforation, crack propagation, and the damage induced in both flexural and shear reinforcements. The mechanics of deformation and failure modes of the target were investigated under varying incidence velocities, 60–115 m/s. The reinforcement characteristics under dynamic loading, such as strain time histories, strain rate sensitivity, and dynamic material properties, were also investigated. The presence of transverse reinforcement in 200 mm thick targets improved the ballistic performance by 12.50 %. Furthermore, the transverse reinforcement also played a crucial role in restricting the bending of the rear face flexural reinforcement and controlling the rear face damage propagation.

PVSails: Harnessing Innovation With Vertical Bifacial PV Modules in Floating Photovoltaic Systems

AbstractIn the context of offshore floating photovoltaic systems (FPVs), this paper explores the use of bifacial photovoltaic modules installed in the vertical position. The energy harvested from the rear face of vertically configured bifacial PV modules compensates for the reduced production at the front face of the module, and this demonstrates the potential of bifacial technology for offshore applications. By comparison, most existing horizontally tilted bifacial FPV systems gain only a small benefit in production from the rear face of the module due to the minimum radiation received, and what also must be taken into consideration is the negative effect of significant soiling owing to the low tilt angle of the PV modules. Hence, to overcome these drawbacks, we have developed the innovative “PVSail” concept, which explores the deployment of vertical FPV systems on floats, buoys, or poles/minipiles. Floating vertical bifacial PV systems (VBPVs) have huge potential to harness all the energy generation capabilities enhance by reflected light, especially from snow‐covered surfaces in northern regions. Our analysis considers a patented mooring and vertical PV system that allows the VBPV structure to align with the prevailing wind direction to shed wind loads, and our numerical analysis explores the potential of VBPV applied to Catania in Italy and Nigg Bay in the United Kingdom. Our analysis study has revealed that across an azimuth angle range (0°–180°), vertical bifacial modules experience roughly a 9% decrease in energy yield at Catania and about a 5% energy yield gain in higher latitude regions like Nigg Bay. Additionally, increasing the latitude of the installation location of VBPV reduces the energy yield sensitivity to the orientation, that is, azimuth angle. The PVSail concept opens the door to novel deployment possibilities in offshore renewable energy projects.

Blast Performance of Polyurea-Coated Modular Structure Composed of Fiber-Reinforced Polymer and Foam Sandwich Panels

Lightweight modular structures have become a requirement in today’s world, especially for areas that are prone to occurrence of extreme events, such as earthquakes and blasts, and are situated in difficult terrains with challenging accessibility. Sandwiched composites can be one of the most suitable building units for construction of these structures due to their engineered mechanical and physical properties. Therefore, in this numerical study, performance assessment of a sandwich modular structure in the shape of a truncated cylinder is conducted under blast load. The sandwich modular structure is composed of flat and curved carbon fiber-reinforced polymer (CFRP) and extruded polystyrene (XPS) foam sandwich panels. A three-dimensional (3D) finite element (FE) model of the sandwich modular structure is developed considering the orthotropic behavior of CFRP facesheets and the crushing foam behavior is accounted for the XPS foam core in the FE modeling. The damage assessment in the CFRP facesheet is performed using Hashin’s damage criterion. Furthermore, the effect of polyurea with varying thicknesses on the blast-resistance of the structure is investigated. The polyurea is modeled as hyperelastic material using the Mooney-Rivlin model. The influence of polyurea positioning is studied when (a) applied externally to flat and curved walls of the structure directly exposed to the blast and (b) applied internally to flat and curved walls of the structure opposite to the exposure of the blast (rear face). It is observed that the flat walls of the structure are more vulnerable to the blast load than the curved walls of the structure. Moreover, a quadratic and linear reduction in the deflection of flat and curved walls with increasing thickness of polyurea coating is obtained, respectively. In addition, with increasing thickness of the additional polyurea coating, a logarithmic reduction in the kinetic energy of the sandwich modular structure is reported.

Ballistic response mechanism and resistance-driven evaluation method of UHMWPE composite

The use of ultra-high molecular weight polyethylene (UHMWPE) composite in the design of lightweight protective equipment, has gained a lot of interest. However, there is an urgent need to understand the ballistic response mechanism and theoretical prediction model of performance. This paper explores the ballistic response mechanism of UHMWPE composite through experimental and simulation analyses. Then, a resistance-driven modeling method was proposed to establish a theoretical model for predicting the bulletproof performance. The ballistic response mechanism of UHMWPE composite encompassed three fundamental modes: local response, structural response, and coupled response. The occurrence ratio of these fundamental response modes during impact was dependent on the projectile velocity and laminate thickness. The bulletproof performance of laminate under different response modes was assessed based on the penetration depth of the projectile, the bulging height on the rear face of the laminate, the thickness of remaining sub-laminate, and residual velocity of the projectile. The absolute deviations of bulletproof performance indicator between theoretical value and experimental value were well within 11.13%, demonstrating that the established evaluation model possessed high degree of prediction accuracy.

Characterization of bifacial technology Pv systems

Bifacial solar technology has experienced exponential growth in recent years and its trend is increasing for the coming years. Considering the advantages that it offers over monofacial technology such as its current price equivalence, the increase in performance thanks to the production of the rear face and the consecutive reduction of the LCOE, it is logical that more and more photovoltaic plants with this technology are been installed. Nowadays, there are some regulatory gaps regarding bifacial technology and, due to this growing trend, it is necessary to study, research and implement the optimal way to evaluate these systems. This article has experimented with a 3.3 kW bifacial photovoltaic system, divided into two strings with different configurations, whose monitoring system has all the instrumentation included in the IEC 61,724 standard, with the addition that it has several rear irradiance sensors arranged in different locations of the system to evaluate the variability of this parameter. After an experimental campaign of 9 months, a power estimation analysis and the calculation of the PR and PR25°C have been carried out using the different rear irradiance sensors. The variability of this parameter depending on the location of the sensor has affected the results in such a way that the RMSE committed in the power estimation has varied between 10.22% and 2.63%, while the PR and PR25°C of the system has oscillated between 0.84 for the most unfavorable case and 0.95 in the most favorable case. Assumed the great variability between performance ratios, it is necessary to establish a specific normative standard for the evaluation of Bifacial PV systems.

Evaluation and Characterization of Ultrasonic Cutting of Monofilament Nylon

Nylon (polyamide) is a typical composite base material, but its low hardness, poor rigidity, and low dimensional stability easily lead to burrs, fractures, curling, and other problems after nylon end faces are processed by conventional techniques. To prevent these problems, this article conducted experimental research comparing ultrasonic and conventional cutting of monofilament nylon and used the controlled variable method to analyze the micromorphology after cutting at different speeds and tensions. A novel ratio was also derived to characterize the topographic quality, and the feasibility and advantages of ultrasonic cutting of nylon were verified by evaluating the nylon surface quality under different cutting conditions. Test results showed layering on the rear face of nylon with ultrasonic cutting as well as a morphology quality directly proportional to the feed speed of the tool and inversely proportional to the tensile force exerted on the material. The end face of nylon after ultrasonic cutting provided a ratio 2.9% lower than that obtained from conventional cutting as well as a roughness reduction of 31.3%. Compared with conventional cutting, the end face was preserved, and no large-area breakage or edge curling occurred when using ultrasonic cutting. Moreover, a force analysis theoretically confirmed the advantages of ultrasonic cutting.

Heat transfer improvement and drag force reduction around three heated square cylinders controlled by partitions

Investigating the subject offers a pioneering approach to enhancing thermal performance and aerodynamic efficiency, unlocking novel strategies for optimizing energy utilization and air dynamics in engineering applications. In this research, a numerical study of airflow control coupled to heat transfer around several heated square cylinders is carried out at a fixed Reynolds number (Re=100). The effect of the positioning and length of the control partitions is examined. Numerical simulations are carried out using the lattice Boltzmann method with multiple relaxation times model. The obtained results reveal the existence of a critical position g=0 where a significant improvement in the Nusselt number is observed. This improvement amounts to 31.1% for the rear face of the top obstacle, 30.2% for the rear face of the central obstacle, and 36.65% for the rear face of the bottom obstacle compared to the uncontrolled case. Thus, a complete suppression of the vortex shedding is observed when the length of the partitions reaches a critical value (Lp=4D). Furthermore, a maximum percentage of drag reduction is achieved by around 6.03% for the central block and 16.67% for the two end blocks when the length of the control partitions reaches this critical value.

Numerical Modeling and Nonlinear Finite Element Analysis of Conventional and 3D-Printed Spinal Braces

This study aims to describe the numerical modeling and nonlinear finite element analysis of typical spinal braces as a first step towards optimizing their topology for 3D printing. Numerical simulation was carried out in Abaqus CAE software Version 2021, utilizing a CAD (Meshmixer Version 3.5.474) scan of an actual spinal brace. Boundary conditions were defined by means of contact surfaces between the human body and the supporting pads located in the interior of the brace. The process of tightening the straps on the rear face of the brace was simulated via appropriate imposed displacements. The response is described through the deformations and developing stresses of the brace and the contact pressures in the areas of interaction with the human body. Parametric analysis indicated that increasing the cross-sectional thickness or elastic modulus of the brace material results in higher maximum von Mises stresses and lower displacements. The comparison between 3D-printed and conventional braces highlighted the potential of 3D-printing technology to achieve comparable performance with customized designs, leveraging the constitutive properties of 3D-printed material obtained from tension tests. The tension tests demonstrated that the 3D-printed material achieved higher values of modulus of elasticity compared to traditional brace materials. Finally, the topology optimization criteria to be applied for the design of spinal braces in the next step of this ongoing research are briefly described.

Blast effect on layered polyurethane foam

The shock wave interaction with solids has been a classical problem of interest for a long time in various domains due to its diverse applications. One such application is energy dissipation using polymeric foam. Since the mechanical compression of polymeric foam exhibits an extended plateau region, it is a primary choice of interest in any form of energy dissipation, particularly blast wave energy. Density-based layered foam has a higher chance of more blast energy absorption compared to a single layer of the same density. Hence, in this study, the response of the blast-induced compression of three different polyurethane (PU) foam densities such as 29.201 kg/m3, 59.692 kg/m3, and 107.720 kg/m3, say D1, D2, and D3, respectively, are carried as single layer and bilayer of the same thickness using a Blast Wave Simulator (BWS). Here, we experimentally record the incident and reflected blast pressure near the blast-hitting face and the reaction force at the rear face of the foam. The full-field displacement of PU foam because of the blast wave is measured using a 2D DIC method. In the bilayer PU foam B2 (D2/D1←, the arrow represents the blast direction), the peak displacement of 10.478 mm, the reaction force, FT of 3.75 kN, reflection coefficient, Cr of 1.99, and energy absorption Eabs of 18.68 J was observed. The increase in energy absorption of the bilayer B3 (D2/D1←) compared to a single layer D1 is 83.03 %, and for the bilayer B1 (D1/D2←) it is 18.90 %. This observation helps to utilize the foam for the blast and shock-prone zone more effectively. The force exerted on the reaction wall of the PU foam helps in deciding the type of material to be used as the blast barrier wall. Also, this study proposes an outline to examine the material’s response in a uni-directional compression because of blast wave impact.

Simulink model of a bifacial PV module based on the manufacturer datasheet

The paper proposes an update of a mathematical model of a Photo-Voltaic (PV) module, considering the possibility that also the rear face of the PV module produces energy. The proposed approach allows to write a new descriptive equation, whose terms are function of the information always available in the modern datasheet of the PV module’s manufacturers. This implies that no pre-processing of the datasheet’s parameters is needed to use the proposed model, whichever are the solar irradiance and the cell/module temperature. The model considers the total solar radiation (front and back side), such that the produced energy increases. Simulink environment is used to calculate the total solar radiation.

Практическая реализация инженерной методики определения напряженного состояния в горизонтальных сечениях железобетонных подпорных стен

Retaining walls made of reinforced concrete are widely used in hydraulic engineering and transport construction. Since their rear faces are covered with ground filling, it seems difficult to control the stressed state of the rear working fittings, which in some cases led to deviations in the work of structures from the project. In this article, corner type retaining walls are considered. The purpose of the work was to develop and test an engineering technique for determining the stress state in horizontal sections of retaining walls made of reinforced concrete. In the framework of this work, studies were conducted on the structures of reinforced concrete retaining walls that interact with the soils of the base and backfill. At the same time, using the provisions of structural mechanics and the theory of reinforced concrete, an engineering technique was developed that allows calculating the stress state of reinforced concrete retaining walls along horizontal sections. To test the proposed calculation methodology, the in-situ data of instrumental surveys of the operated lower retaining walls of the PSPP water intake (pumped storage power plant) were used on the basis of the “reinforcement unloading” method in relation to the facing structural reinforcement of the walls. The developed method was practically implemented to assess the effective tensile stresses in the rear working reinforcement, as well as the compressive stresses in the concrete of retaining walls.

Online Crack Detection of Highly Curved Cylindrical Coils

Many vision-based methods for defect detection have been proposed to replace inefficient manual inspection. However, due to the complex shape and high degree of freedom required to manipulate individual coils, an automatic optical inspection (AOI) method for cylindrical coils remains unsuccessful due to the difficulty of automatically scanning the front, rear, outer, and inner faces of complex spiral-shaped cylindrical coils. This paper presents a turnkey integrated system that can be operated in real time for real coil manufacturers. First, a novel 1-degree-of-freedom rotational progressive system is designed to automatically transport and sort individual spiral coils. Second, a multisensor imaging system is designed to capture images of 360° panoramic views of a cylindrical coil. Then, a robust automatic defect detection algorithm consisting of crack detection and geometric measurement is developed to detect defects in cylindrical coils during manufacturing procedures. The results of a large-scale validation experiment indicate that the proposed AOI system is robust and is practically immune to variations in surface normal vectors, occlusion, and defocus blur, and it has a high sensitivity and specificity of 99.75% and 94.2%, respectively. This validation experiment proved that the software and hardware designed in this study can implement defect detection of spiral coils.

Numerical study of gas–surface interface effects due to transpiration in a hypersonic flow over a blunt body

This paper investigates the impact of transpiration on a hypersonic flow over a cylinder, considering different degrees of rarefaction. The study analyzes the interaction between freestream argon gas flow at Mach 5 and transpiring argon gas at the fluid–solid interface at a velocity of 10 m/s. Freestream Knudsen numbers considered are 0.002, 0.01, 0.05, and 0.25, spanning from a continuum to rarefied regime. Flow simulations utilize the open-source direct simulation Monte Carlo solver, Stochastic PArallel Rarefied-gas Time-accurate Analyzer. The influence of transpiration on flow and surface properties is examined by comparing non-transpiration and transpiration cases. At all regimes, transpiration increases the normal shock stand-off distance, while a comparison of flow properties along the stagnation line reveals a reduction in the velocity and an increase in the post-shock temperature with transpiration. Surface heat flux comparison indicates that transpiring gas reduces heat flux on the cylinder's upstream-facing front surface at all Knudsen numbers. However, at Kn∞ = 0.25, a shift occurs, and surface heat flux starts increasing locally from the top/bottom point on the cylinder surface through the rear face of the cylinder. Furthermore, a test for the validity of the continuum-based blowing correction correlation function reveals the failure of the empirical model, even in the continuum regime at Kn∞ = 0.002, casting doubt on its applicability to vehicles with curvilinear blunt-body shapes. Additionally, a sensitivity analysis demonstrates that transpiring gas with a number density an order of magnitude higher than the freestream reduces stagnation peak heat flux by nearly 30%, while transpiring gas with a temperature two times higher than the freestream shows a ∼13% reduction.

High‐velocity ballistic response of AA 1100‐H14 based carbon‐fiber metal laminates: An experimental investigation

AbstractA detailed experimental investigation was carried out for the high‐velocity ballistic response of AA 1100‐H14 based carbon‐fiber metal laminates (FMLs). FMLs with different metal volume fractions and the same thickness of carbon‐epoxy fiber laminates were tested to examine the surface and internal damage. The ballistic performance parameters, namely % escalation in absorbed energy, specific energy absorbed, ballistic limit, specific perforation energy, first cracking energy, and global deformation profile, were studied and a comparison was drawn with pure carbons fiber reinforced epoxy composite laminates. Despite having greater thickness, pure carbon fiber‐reinforced epoxy composite laminates absorbed less impact energy than FMLs and failed catastrophically. For FMLs, the % escalation in the absorbed energy and the specific energy absorption kept increasing with the increasing impact velocity until the onset of perforation. Once the perforation started, both these parameters showed a decreasing trend. Thick FMLs absorbed a good amount of energy, leading to projectile recoil suffering minimal damage. The ballistic velocity, specific perforation energy, and first cracking energy on the front and rear face of FMLs layers showed an increasing trend. The minimum for the thinner and maximum for the thicker FMLs attributed to the large thickness and more metal volume fraction. Contrary to the large deformation of the impacting points, pure carbon fiber‐reinforced epoxy composite laminates showed very minimal deformation as compared to FMLs. The brittle nature of the epoxy resin resisted the deformation to a large extent leading to less energy absorption.Highlights High‐velocity ballistic response of AA 1100‐H14 based carbon‐FMLs was investigated. Ballistic performance parameters of FMLs were studied and was compared with carbons fiber reinforced composite laminates. The ballistic limit of FMLs showed a direct dependence its thickness and metal volume fraction. In the absence of any metallic layer, pure carbons fiber reinforced composite laminates absorbed less impact energy.

Local impact resistance of curved sandwich panel with Miura-ori foldcore

Curved sandwich structures have demonstrated great potential for engineering applications. However, little study on the impact resistance of the curved Miura-ori sandwich structure is found. In this study, the curved sandwich panel with a curved Miura-ori foldcore (CPCM) is proposed and its impact resistance is numerically investigated. The force displacement history, energy absorption, specific energy absorption, residual velocity of the projectile and the displacement of the rear face sheet are used to evaluate the performances of the CPCM. Various loading scenarios including different impact velocities and positions, different projectile sizes and geometries are considered. Moreover, the curved sandwich panel with a curved honeycomb core (CPCH) that have similar specifications and the same relative density as the CPCM is simulated as well for comparison. It is found that the CPCM shows excellent impact resistance with a ballistic limit around 61 % higher than that of the CPCH. Its energy absorption capacities and impact resistance are improved under blunt projectile impact. However, when the impact velocity is above the ballistic limit, the energy absorption EA of the CPCM remains at a constant level, irrespective of the impact velocity.

Cherenkov-Type Terahertz Generation by Long-Wavelength Ultrafast Laser Excitation of a GaP Crystal

We explore, both theoretically and experimentally, the potential of semiconductor materials for the Cherenkov scheme of terahertz generation on the example of GaP crystal pumped by femtosecond laser pulses of 1.54 μm wavelength. We use a convenient scheme with a focused-to-a-line laser beam which is introduced into the crystal by oblique incidence at the Brewster angle on the crystal front face and propagates in the crystal at the Cherenkov angle to its normal. A half of the generated Cherenkov wedge impinges normally the rear face of the crystal and generates an output terahertz beam with a plane wavefront. The whole generation process is simulated by FDTD method. In experiments, the laser pulses of 140 fs duration and 10 μJ energy were converted to wideband (~2.5 THz bandwidth) terahertz radiation with the efficiency of ~3 × 10−5, which exceeds the efficiency of the standard collinear scheme by at least an order of magnitude.

3D digital image correlation analysis of medium velocity soft impacts on laminated composite

In aerospace acamedic and industrial world, soft impacts are commonly used to replace bird strike tests for the validation of materials and structures as well as the calibration of numerical models. However in general, the analysis reported show only a few part of the experimental information available. In this paper, three laminate composites made of epoxy resin reinforced by glass or carbon fibres are tested under gelatin impact at several velocities up to complete failure. A detailed analysis based on 3D Digital Image Correlation (3D DIC) and visual inspection of the three laminates is provided for a total of 21 tests with impact velocities in the range 60–112 m/s. DIC extraction provides accurate quantitative displacement fields of the rear face in both time and space. Moreover, specific failure scenarios are identified for each laminate. The results obtained provide a suitable database for the development of numerical models. In addition, all experimental data from DIC extractions are opened to the readers on the Recherche Data Gouv website for comparisons with their own tests or numerical models.

Detection of surface moving heat source using experimental temperature measurements on the opposite surface and inverse techniques

The identification of mobile sources is a widely researched area in multiple scientific and technical domains. Detecting mobile heat sources is an essential task in different fields, including fire safety, environmental monitoring, material science, and energy systems. In this investigation, we present an innovative solution to solve the inverse problem of detecting mobile heat sources, utilizing a three-dimensional transient inverse heat conduction problem (IHCP) formulation. The goal is to identify a moving heat source from thermographic infrared measurements of the rear face. The proposed method includes a finite volume approach with model reduction techniques to improve computational efficiency. Additionally, we use the conjugate gradient method to solve the inverse problem. We verified the proposed approach by conducting experiments on a metal plate with a moving heat source from a laser and comparing recalculated temperature of the front face with thermocouple measurements. Our results indicate that our method can detect the location and trajectory of the mobile heat source with high accuracy and efficiency. This study also highlighted the limits of source speed that can be detected by this method. This technique could be considered as an excellent option for real-time monitoring of mobile heat sources in practical applications.