A New Blast Absorbing Sandwich Panel with Unconnected Corrugated Layers—Numerical Study

The need for more effective defence systems is of critical importance because of the rising risk of explosive attacks. Sandwich panels are used as plastically deforming sacrificial structures, absorbing blast wave energy. To the authors’ knowledge, the blast behaviour of sandwich panels with connected (welded/bolted/riveted) corrugated layers has been well covered in literature. Hence, the aim of this numerical study was to develop new, easy-to-build, non-expensive, graded sandwich panel with ‘unconnected’ corrugated layers that can be used as a multipurpose sacrificial protective structure against wide range of blast threats. The proposed sandwich panel is composed of six unconnected aluminium (AL6063-T4) core layers encased in a steel (Weldox 460E) frame with 330 × 330 × 150 mm overall dimensions. The numerical analysis was conducted using Abaqus/Explicit solver. First, the performance of four different nongraded layer topologies (trapezoidal, triangular, sinusoidal, and rectangular) was compared, when subjected to ~16 MPa peak reflected over-pressure (M = 0.5 kg of TNT at R = 0.5 m). Results showed that the trapezoidal topology outperformed other topologies, with uniform progressive collapse, lower reaction force, and higher plastic dissipation energy. Then, the trapezoidal topology was further analysed to design a ‘graded’ sandwich panel that can absorb a wide range of blast intensities (~4, 7, 11, 13, and 16 MPa peak reflected over-pressures) by using a (0.4, 0.8, 1.2 mm) stepwise thickness combination for the layers. In conclusion, the superior performance of the proposed sandwich panel with unconnected graded layers can be considered as a novel alternative to the conventional costly laser-welded sandwich panels. Applications of the new solution range from protecting civil structures to military facilities.

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A numerical study of the impact perforation of sandwich panels with graded hollow sphere cores

Advances in Mechanical Engineering ◽

10.1177/16878140211009415 ◽

2021 ◽

Vol 13 (4) ◽

pp. 168781402110094

Author(s):

Ibrahim Elnasri ◽

Han Zhao

Keyword(s):

Boundary Conditions ◽

Hollow Sphere ◽

Sandwich Panel ◽

Numerical Study ◽

Sandwich Panels ◽

Hopkinson Bar ◽

Core Density ◽

The Core ◽

The Impact ◽

Force Displacement

In this study, we numerically investigate the impact perforation of sandwich panels made of 0.8 mm 2024-T3 aluminum alloy skin sheets and graded polymeric hollow sphere cores with four different gradient profiles. A suitable numerical model was conducted using the LS-DYNA code, calibrated with an inverse perforation test, instrumented with a Hopkinson bar, and validated using experimental data from the literature. Moreover, the effects of quasi-static loading, landing rates, and boundary conditions on the perforation resistance of the studied graded core sandwich panels were discussed. The simulation results showed that the piercing force–displacement response of the graded core sandwich panels is affected by the core density gradient profiles. Besides, the energy absorption capability can be effectively enhanced by modifying the arrangement of the core layers with unclumping boundary conditions in the graded core sandwich panel, which is rather too hard to achieve with clumping boundary conditions.

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The Development of a New Shock Absorbing Uniaxial Graded Auxetic Damper (UGAD)

Materials ◽

10.3390/ma12162573 ◽

2019 ◽

Vol 12 (16) ◽

pp. 2573 ◽

Cited By ~ 9

Author(s):

Hasan Al-Rifaie ◽

Wojciech Sumelka

Keyword(s):

Constitutive Relations ◽

Reaction Force ◽

Superior Performance ◽

Dissipation Energy ◽

Specific Strength ◽

Optimum Parameters ◽

Plastic Dissipation ◽

Structural Applications ◽

Auxetic Structures ◽

3D Printed

Auxetic structures are efficient cellular materials that can absorb blast/impact energy through plastic deformation, thus protecting the structure. They are developing sacrificial solutions with light weight, high specific strength, high specific toughness and excellent energy dissipating properties, due to its negative Poison’s ratio nature. The use of auxetic and non-auxetic panels in blast resistant structures had been relatively perceived by researchers. Nonetheless, implementation of those energy dissipaters, explicitly as a uni-axial passive damper is restrained to limited studies, which highlight the potential need for further explorations. The aim of this paper is the design of a new uniaxial graded auxetic damper (UGAD) that can be used as a blast/impact/shock absorber in different scales for different structural applications. First, the geometry, material, numerical model and loading are introduced. Then, a detailed parametric study is conducted to achieve the most efficient graded auxetic system. Moreover, the designed auxetic damper is numerically tested and its static and dynamic constitutive relations are derived and validated analytically. The selection of optimum parameters was based on the ratio of the reaction force to the applied load (RFd/P) and plastic dissipation energy (PDE). The final designed UGAD contains three auxetic cores that have the same geometry, material grade (6063-T4), size and number of layers equal to eight. The cell-wall thickness t of the three auxetic cores is 1.4 mm, 1.8 mm and 2.2 mm, respectively; composing a graded auxetic system. The performance of the three auxetic cores together have led to a wide plateau region (80% of total crushing strain) and variant strength range (1–10 MPa), which in return, can justify the superior performance of the UGAD under different blast levels. Finally, the 3D printed prototype of the UGAD is presented and the possible applications are covered.

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Ultralight micro-perforated sandwich panel with hierarchical honeycomb core for sound absorption

Journal of Sandwich Structures & Materials ◽

10.1177/1099636221993880 ◽

2021 ◽

pp. 109963622199388

Author(s):

Wei He ◽

Xiangjun Peng ◽

Fengxian Xin ◽

Tian Jian Lu

Keyword(s):

Theoretical Model ◽

Sound Absorption ◽

Sandwich Panel ◽

Structural Parameters ◽

Sandwich Panels ◽

Honeycomb Core ◽

Physical Mechanisms ◽

Wide Range ◽

Model Predictions ◽

Absorption Performance

A theoretical model is developed to study the superior sound absorption performance of ultralight mirco-perforated sandwich panels with double-layer hierarchical honeycomb core. Numerical simulations are performed to validate theoretical model predictions and explore physical mechanisms underlying the sound absorption. Systematic parametric study is implemented to investigate the influence of specific structural parameters on sound absorption. To maximize sound absorption, optimal structural parameters of the hierarchical sandwich are obtained using the method of simulated annealing. It is demonstrated that viscous dissipation of the air inside micro-perforations and around inlet/outlet regions dominates sound absorption. Compared to micro-perforated sandwich panels with regular honeycomb core, not only the proposed hierarchical construction has much improved load-bearing capacity, but also significantly enhanced sound absorption covers a wide range of frequency.

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A relationship between the incremental values of area under the ROC curve and of area under the precision-recall curve

Diagnostic and Prognostic Research ◽

10.1186/s41512-021-00102-w ◽

2021 ◽

Vol 5 (1) ◽

Author(s):

Qian M. Zhou ◽

Lu Zhe ◽

Russell J. Brooke ◽

Melissa M. Hudson ◽

Yan Yuan

Keyword(s):

Prediction Accuracy ◽

Risk Model ◽

Event Rate ◽

Numerical Study ◽

Superior Performance ◽

New Model ◽

Wide Range ◽

Precision Recall Curve ◽

Dose Model ◽

Recall Curve

Abstract Background Incremental value (IncV) evaluates the performance change between an existing risk model and a new model. Different IncV metrics do not always agree with each other. For example, compared with a prescribed-dose model, an ovarian-dose model for predicting acute ovarian failure has a slightly lower area under the receiver operating characteristic curve (AUC) but increases the area under the precision-recall curve (AP) by 48%. This phenomenon of disagreement is not uncommon, and can create confusion when assessing whether the added information improves the model prediction accuracy. Methods In this article, we examine the analytical connections and differences between the AUC IncV (ΔAUC) and AP IncV (ΔAP). We also compare the true values of these two IncV metrics in a numerical study. Additionally, as both are semi-proper scoring rules, we compare them with a strictly proper scoring rule: the IncV of the scaled Brier score (ΔsBrS) in the numerical study. Results We demonstrate that ΔAUC and ΔAP are both weighted averages of the changes (from the existing model to the new one) in separating the risk score distributions between events and non-events. However, ΔAP assigns heavier weights to the changes in higher-risk regions, whereas ΔAUC weights the changes equally. Due to this difference, the two IncV metrics can disagree, and the numerical study shows that their disagreement becomes more pronounced as the event rate decreases. In the numerical study, we also find that ΔAP has a wide range, from negative to positive, but the range of ΔAUC is much smaller. In addition, ΔAP and ΔsBrS are highly consistent, but ΔAUC is negatively correlated with ΔsBrS and ΔAP when the event rate is low. Conclusions ΔAUC treats the wins and losses of a new risk model equally across different risk regions. When neither the existing or new model is the true model, this equality could attenuate a superior performance of the new model for a sub-region. In contrast, ΔAP accentuates the change in the prediction accuracy for higher-risk regions.

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NUMERICAL STUDY OF BLAST-RESISTANT SANDWICH PANELS WITH ROTATIONAL FRICTION DAMPERS

International Journal of Structural Stability and Dynamics ◽

10.1142/s0219455413500144 ◽

2013 ◽

Vol 13 (06) ◽

pp. 1350014 ◽

Cited By ~ 16

Author(s):

WENSU CHEN ◽

HONG HAO

Keyword(s):

Energy Absorption ◽

Sandwich Panel ◽

Numerical Study ◽

Blast Resistance ◽

Sandwich Panels ◽

Blast Loading ◽

Blast Loads ◽

Friction Damper ◽

Energy Absorber ◽

Blast Energy

Blast-resistant structures are traditionally designed with solid materials of huge weight to resist blast loads. This not only increases the construction costs, but also undermines the operational performance. To overcome these problems, many researchers develop new designs with either new materials or new structural forms, or both to resist the blast loads. Friction damper, as a passive energy absorber, has been used in earthquake-resistant design to absorb vibration energy from cyclic loading. The use of friction damper in blast-resistant design to absorb high-rate impact and blast energy, however, has not been well explored. This study introduces a new sandwich panel equipped with rotational friction hinge device with spring (RFHDS) between the outer and inner plates to resist the blast loading. This device RFHDS, as a special sandwich core and energy absorber, consists of rotational friction hinge device (RFHD) and spring. The RFHD is used to absorb blast energy while the spring is used to restore the original shape of the panel. This paper studies the mechanism of RFHD by using theoretical derivation and numerical simulations to derive its equivalent force–displacement relation and study its energy absorption capacity. In addition, the energy absorption and blast loading resistance capacities of the sandwich panel equipped with RFHDS are numerically investigated by using Ls-Dyna. It is found that the proposed sandwich panel can recover, at least partially its original configuration after the loading and thus maintain its operational and blast-resistance capability after a blasting event. In order to maximize the performance of the proposed sandwich panel, parametric calculations are carried out to study the performance of RFHDS and the sandwich panels with RFHDS. The best performing sandwich panel with RFHDS in resisting blast loadings is identified. This sandwich panel configuration might be employed to mitigate blast loading effects in structural sandwich panel design.

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Strain Sensor via Wood Anomalies in 2D Dielectric Array

Nanomaterials ◽

10.3390/nano11041022 ◽

2021 ◽

Vol 11 (4) ◽

pp. 1022

Author(s):

Rashid G. Bikbaev ◽

Ivan V. Timofeev ◽

Vasiliy F. Shabanov

Keyword(s):

Higher Plants ◽

Numerical Study ◽

Reciprocal Lattice ◽

Strain Sensing ◽

Photonic Materials ◽

Sensing Applications ◽

Wide Range ◽

Sensor Structure ◽

Optical Behavior ◽

Chlorophyll Absorption

Optical sensing is one of many promising applications for all-dielectric photonic materials. Herein, we present an analytical and numerical study on the strain-responsive spectral properties of a bioinspired sensor. The sensor structure contains a two-dimensional periodic array of dielectric nanodisks to mimic the optical behavior of grana lamellae inside chloroplasts. To accumulate a noticeable response, we exploit the collective optical mode in grana ensemble. In higher plants, such a mode appears as Wood’s anomaly near the chlorophyll absorption line to control the photosynthesis rate. The resonance is shown persistent against moderate biological disorder and deformation. Under the stretching or compression of a symmetric structure, the mode splits into a couple of polarized modes. The frequency difference is accurately detected. It depends on the stretch coefficient almost linearly providing easy calibration of the strain-sensing device. The sensitivity of the considered structure remains at 5 nm/% in a wide range of strain. The influence of the stretching coefficient on the length of the reciprocal lattice vectors, as well as on the angle between them, is taken into account. This adaptive phenomenon is suggested for sensing applications in biomimetic optical nanomaterials.

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Numerical study of geometric morphing wings of the 1303 UCAV

The Aeronautical Journal ◽

10.1017/aer.2021.15 ◽

2021 ◽

pp. 1-17

Author(s):

B. Nugroho ◽

J. Brett ◽

B.T. Bleckly ◽

R.C. Chin

Keyword(s):

Flight Control ◽

Numerical Study ◽

Aerodynamic Characteristics ◽

Morphing Wing ◽

Rolling Moment ◽

Wide Range ◽

Morphing Wings ◽

Wing Geometry ◽

Lift And Drag ◽

Wing Morphing

ABSTRACT Unmanned Combat Aerial Vehicles (UCAVs) are believed by many to be the future of aerial strike/reconnaissance capability. This belief led to the design of the UCAV 1303 by Boeing Phantom Works and the US Airforce Lab in the late 1990s. Because UCAV 1303 is expected to take on a wide range of mission roles that are risky for human pilots, it needs to be highly adaptable. Geometric morphing can provide such adaptability and allow the UCAV 1303 to optimise its physical feature mid-flight to increase the lift-to-drag ratio, manoeuvrability, cruise distance, flight control, etc. This capability is extremely beneficial since it will enable the UCAV to reconcile conflicting mission requirements (e.g. loiter and dash within the same mission). In this study, we conduct several modifications to the wing geometry of UCAV 1303 via Computational Fluid Dynamics (CFD) to analyse its aerodynamic characteristics produced by a range of different wing geometric morphs. Here we look into two specific geometric morphing wings: linear twists on one of the wings and linear twists at both wings (wash-in and washout). A baseline CFD of the UCAV 1303 without any wing morphing is validated against published wind tunnel data, before proceeding to simulate morphing wing configurations. The results show that geometric morphing wing influences the UCAV-1303 aerodynamic characteristics significantly, improving the coefficient of lift and drag, pitching moment and rolling moment.

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A Computational Study on the Role of Parameters for Identification of Thyroid Nodules by Infrared Images (and Comparison with Real Data)

Sensors ◽

10.3390/s21134459 ◽

2021 ◽

Vol 21 (13) ◽

pp. 4459

Author(s):

José R. González ◽

Charbel Damião ◽

Maira Moran ◽

Cristina A. Pantaleão ◽

Rubens A. Cruz ◽

...

Keyword(s):

Heat Transfer ◽

Thyroid Nodules ◽

Numerical Study ◽

Computational Study ◽

Internal Heat ◽

Heat Transfer Process ◽

The Body ◽

Physical Parameters ◽

Infrared Sensors ◽

Wide Range

According to experts and medical literature, healthy thyroids and thyroids containing benign nodules tend to be less inflamed and less active than those with malignant nodules. It seems to be a consensus that malignant nodules have more blood veins and more blood circulation. This may be related to the maintenance of the nodule’s heat at a higher level compared with neighboring tissues. If the internal heat modifies the skin radiation, then it could be detected by infrared sensors. The goal of this work is the investigation of the factors that allow this detection, and the possible relation with any pattern referent to nodule malignancy. We aim to consider a wide range of factors, so a great number of numerical simulations of the heat transfer in the region under analysis, based on the Finite Element method, are performed to study the influence of each nodule and patient characteristics on the infrared sensor acquisition. To do so, the protocol for infrared thyroid examination used in our university’s hospital is simulated in the numerical study. This protocol presents two phases. In the first one, the body under observation is in steady state. In the second one, it is submitted to thermal stress (transient state). Both are simulated in order to verify if it is possible (by infrared sensors) to identify different behavior referent to malignant nodules. Moreover, when the simulation indicates possible important aspects, patients with and without similar characteristics are examined to confirm such influences. The results show that the tissues between skin and thyroid, as well as the nodule size, have an influence on superficial temperatures. Other thermal parameters of thyroid nodules show little influence on surface infrared emissions, for instance, those related to the vascularization of the nodule. All details of the physical parameters used in the simulations, characteristics of the real nodules and thermal examinations are publicly available, allowing these simulations to be compared with other types of heat transfer solutions and infrared examination protocols. Among the main contributions of this work, we highlight the simulation of the possible range of parameters, and definition of the simulation approach for mapping the used infrared protocol, promoting the investigation of a possible relation between the heat transfer process and the data obtained by infrared acquisitions.

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Heat transfer characteristics of nanofluids from a sinusoidal corrugated cylinder placed in a square cavity

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/09544062211027208 ◽

2021 ◽

pp. 095440622110272

Author(s):

Salaika Parvin ◽

Nepal Chandra Roy ◽

Litan Kumar Saha ◽

Sadia Siddiqa

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Rayleigh Number ◽

Aspect Ratio ◽

Average Nusselt Number ◽

Numerical Study ◽

Heat Transfer Characteristics ◽

Number Range ◽

Transfer Characteristics ◽

Wide Range

A numerical study is performed to investigate nanofluids' flow field and heat transfer characteristics between the domain bounded by a square and a wavy cylinder. The left and right walls of the cavity are at constant low temperature while its other adjacent walls are insulated. The convective phenomena take place due to the higher temperature of the inner corrugated surface. Super elliptic functions are used to transform the governing equations of the classical rectangular enclosure into a system of equations valid for concentric cylinders. The resulting equations are solved iteratively with the implicit finite difference method. Parametric results are presented in terms of streamlines, isotherms, local and average Nusselt numbers for a wide range of scaled parameters such as nanoparticles concentration, Rayleigh number, and aspect ratio. Several correlations have been deduced at the inner and outer surface of the cylinders for the average Nusselt number, which gives a good agreement when compared against the numerical results. The strength of the streamlines increases significantly due to an increase in the aspect ratio of the inner cylinder and the Rayleigh number. As the concentration of nanoparticles increases, the average Nusselt number at the internal and external cylinders becomes stronger. In addition, the average Nusselt number for the entire Rayleigh number range gets enhanced when plotted against the volume fraction of the nanofluid.

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Automated simulation techniques for uncovering high-performance bioinspired cellular structures under blast loads

Journal of Sandwich Structures & Materials ◽

10.1177/10996362211020458 ◽

2021 ◽

pp. 109963622110204

Author(s):

Abdallah Ghazlan ◽

Tuan Ngo ◽

Tay Son Le ◽

Tu Van Le

Keyword(s):

Energy Dissipation ◽

Trabecular Bone ◽

Reaction Force ◽

Blast Loading ◽

Performance Criteria ◽

Superior Performance ◽

Cellular Structures ◽

Design Parameters ◽

Engineering Practice ◽

Automated Simulation

Trabecular bone possesses a complex hierarchical structure of plate- and strut-like elements, which is analogous to structural systems encountered in engineering practice. In this work, key structural features of trabecular bone are mimicked to uncover effective energy dissipation mechanisms under blast loading. To this end, several key design parameters were identified to develop a bone-like unit cell. A computer script was then developed to automatically generate bone-like finite element models with many combinations of these design parameters, which were simulated under blast loading. The optimal structure was identified and its performance was benchmarked against traditional engineered cellular structures, including those with hexagonal, re-entrant and square cellular geometries. The bone-like structure showed superior performance over its engineered counterparts using the peak transmitted reaction force and energy dissipation as the key performance criteria.

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