AbstractRotary-wing aerial vehicles offer manoeuvrability and vertical take-off and landing (VTOL) advantages over fixed-wing systems. Rotary-wing systems do however have comparatively higher energy demands and consequently shorter flight times and therefore a greater energy dependence over their fixed-wing counterparts. Advances in photovoltaic technologies have resulted in significant increases in the specific power (power-to-weight-ratio) of solar cells enabling the design of solar-powered rotary-wing aircraft, and now micro-sized variants. The micro aerial vehicle (MAV) presented, the Micro Solarcopter, is a 0.15 m $$\times$$ × 0.15 m $$\times$$ × 0.02 m solar-rechargeable radio-controlled aircraft. The 0.071 kg aircraft can fly for an average time of 3.5 min, recharge in approximately 68 min under 1000 W/m2 irradiance at 25 °C and can hibernate for 38 days without sunlight. The paper explores the use of commercially available photovoltaic cells for the purpose of increasing the energy autonomy of multi-rotor MAVs, by enabling them to stay out in the field without returning to base for charging. A working prototype has been presented which incorporates a battery management system, automatic power on and off, low-power sleep mode, and first-person-view (FPV) camera.

In this paper, a series of incremental dynamic analyses were performed on five masonry towers resting on the base, whose geometry was taken from the literature, in order to determine how the difference in geometric characteristics and deformability of the subsoil affect the global behaviour, failure mechanism and seismic resistance of the towers. Special attention was attributed to determining whether masonry towers experience rocking motion mechanism during seismic excitation, which proved to be suitable in terms of seismic energy dissipation and earthquake resistance. Analyses were carried out using the planar numerical model based on the Combined Finite-Discrete Element Method (FDEM) at the macro level. The conclusions obtained on the basis of the conducted analyses can serve the researchers as guidelines to gain an insight into the expected failure mechanism of masonry towers for the assessment of their seismic resistance, as well as for making decisions about actions during their rehabilitation.

In this paper, numerical analysis of several historical masonry towers located in Italy was conducted. The towers differ in their geometric characteristics in terms of slenderness, thickness of the outer walls, the proportion of openings, while the material properties of all towers are similar. The purpose of this paper was to analyse the influence of various geometries, soil properties and types of earthquakes on the seismic resistance of masonry structures. The geometries of the towers were taken from the available literature. The analysis was carried out with the planar numerical model Y-2D, which is based on the finite-discrete element method (FDEM). The towers were discretized at the macro level using triangular three-node finite elements between which contact elements were implemented that take into account material nonlinearity. The discretization of the towers was carried out at the macro level, taking into account the averaged properties of the mortar and blocks. This is modelled using triangular three-node finite elements between which contact elements are implemented to consider material nonlinearity. In this way, the phenomenon of the initiation and propagation of cracks in the tension and shear was modelled. An incremental dynamic analysis was performed for three real earthquakes until the complete collapse of the structure. In each increment, the appearance of the first cracks, the propagation of the cracks, as well as the failure mode of the structure were monitored. The performed numerical analyses highlight the suitability of the FDEM method in the analysis of the seismic resistance of masonry structures. The conclusions reached in this paper can serve as guidelines for engineers in assessing the seismic resistance of existing masonry structures.

The paper presents a new numerical model for analysis of thin shell structures taking into account geometrical and material nonlinearity, finite displacements, finite rotations and finite strains. The model is based on three-noded rotation-free triangular finite elements and is implemented in the open source Y-FDEM software package based on the Combined finite-discrete element method (FDEM). Material nonlinearity was implemented considering the von Mises flow condition, the Levi-Mises flow rule, and the Johnson-Cook constitutive law. The efficiency of the model was demonstrated on the benchmark problems by comparing numerical results with known analytical or other numerical results.

This article presents the results of a numerical stability analysis of the old stone Protiron structure model in Split exposed to seismic loading. The analysis was performed by open source Y-3D numerical code based on the Combined Finite-Discrete Element Method (FDEM). The FDEM code was extended with a new dissipative contact interaction algorithm in order to overcome the limitation related to energy dissipation under normal contact interaction, which, combined with dry friction, represents a relevant mechanism for energy dissipation in dry-joint masonry structures. The performances of the presented numerical model are demonstrated through the comparison of numerical results with the experimental tests of the Protiron model obtained by the shaking table investigations. The most significant results of the measured displacement vs. time have been numerically reproduced by the presented numerical model which confirms the suitability of the FDEM method for assessing the seismic resistance of dry-joint masonry structures.

The paper presents a failure analysis of the bell tower of the church of St. Francis of Assisi on Kaptol in Zagreb subjected to seismic activity using the finite-discrete element method—FDEM. The bell tower is a masonry building, and throughout history it has undergone multiple damages and reconstructions. It was significantly damaged during the earthquake in Zagreb which occurred on 22 March 2020 with a magnitude of 5.5. The analysis was performed on a simplified FDEM 2D numerical model which corresponds to the structure in its current pre-disaster state and the structure after the proposed post-disaster reconstruction. The obtained results showed a good agreement of the crack pattern in the numerical model and the cracks that occurred due to these earthquakes. In addition, the conclusions based on the conducted analysis can provide a better insight into the behaviour and serve as guidelines to engineers for the design of such and similar structures.

Wind phenomena present significant societal risks in many regions of the world due to, among others, economic losses resulting from damages to the built environment, discomfort to people, and disturbances in marine, air, and road traffic. These risks have motivated the development of performance-based design methodologies to support the decision makers in making rational and optimal measures to mitigate those risks. This paper investigates the application of the Performance-Based Wind Engineering (PBWE) methodology to the risk assessment to the critical telecommunication infrastructure subjected to wind hazard. Motivated by failures of telecommunication infrastructure due to wind load, the focus of the study is on the implementation of the PBWE methodology to estimate the expected annual losses to typical lattice frame steel telecommunication towers subjected to the Bora wind along the Croatian coastline. The statistical description of the wind hazards is based on long-term meteorological measurements available at several locations to capture the local variations characteristic for the Bora wind. The uncertainties in the wind hazard and the structural parameters were propagated to the structural response (e.g., displacements, internal forces) through a set of Monte Carlo analyses. The analyses provided a basis to estimate the probabilities of exceeding the serviceability and ultimate limit states. The resulting probabilities were used as an input to the loss function that evaluates risks from the wind hazard. The risk estimates provide valuable information to the stakeholders and decision makers that enable improved strategies for managing risks from wind hazard.

This paper presents a computationally efficient numerical model for the analysis of thin shells based on rotation-free triangular finite elements. The geometry of the structure in the vicinity of the observed triangular element is approximated through a controlled domain consisting of nodes of the observed finite element and nodes of three adjacent finite elements between which a second-order spatial polynomial is defined. The model considers large displacements, large rotations, small strains, and material and geometrical nonlinearity. Material nonlinearity is implemented by considering the von Mises yield criterion and the Levi–Mises flow rule. The model uses an explicit time integration scheme to integrate motion equations but an implicit radial returning algorithm to compute the plastic strain at the end of each time step. The presented numerical model has been embedded in the program Y based on the finite–discrete element method and tested on simple examples. The advantage of the presented numerical model is displayed through a series of analyses where the obtained results are compared with other results presented in the literature.

In this paper, the state of the art in the Combined Finite-Discrete Element Method (FDEM) has been summarized together with the fast emerging hybrid finite discrete element based simulation technology for multiphysics problems ranging from traditional engineering disciplines to biosciences and medical engineering.The key algorithmic aspects of FDEM have been summarized.The relationship between FDEM and virtual experimentation has been explained in more detail.

The Solarcopter proof of concept demonstrated the world's first purely solar-powered rotary-wing aircraft to fly, highlighting the feasibility of powering a rotary-wing unmanned aerial vehicle (UAV) exclusively by solar power. Absolutely no form of energy storage was utilised on this UAV prototype in any way. The novelties of the presented prototype include the exclusion of energy storage, utilising the central surface area of a quadrotor setup to maximise solar panel performance, and employing an ultra-lightweight, rigid, space frame structure. These key factors enabled the thrust-to-weight ratio of the presented prototype to be substantially greater than unity making the concept capable of continuous flight beyond the ground effect, provided sufficient solar energy is available. The presented concept and design was successfully validated with flight tests conducted in real-world conditions. The calculations and conclusions presented in the comments regarding the flight capability of the Solarcopter are premised on use of the Medusa 4000 rather than the Turnigy 800 motor that was implemented on the Solarcopter prototype. It is therefore unsurprising that the authors of the comments were unable to replicate the results presented for the Solarcopter.

This paper presents two numerical models (Model L and Model N) and its application in the analysis of dynamic stability of beam-type structures. Both numerical models use two-noded rotation-free finite elements and take into account the exact formulation for finite displacement, finite rotations, and finite strains. Model L was previously developed and is intended for linear elastic material behavior, whereas Model N is newly developed, considers laminar cross sections, and takes into account the nonlinear material behavior. Both models have been implemented into the open-source finite discrete element package Y-FDEM. Performance and conditions under which both numerical models can be used for the analysis of dynamic stability are presented by numerical examples which show good agreement in comparison with the analytical solutions.

Fracture coalescence is a critical phenomenon for creating large, inter-connected fractures from smaller cracks, affecting fracture network flow and seismic energy release potential. In this paper, simulations are performed to model fracture coalescence processes in granite specimens with pre-existing flaws. These simulations utilize an in-house implementation of the combined finite–discrete element method (FDEM) known as the hybrid optimization software suite (HOSS). The pre-existing flaws within the specimens follow two geometric patterns: (1) a single-flaw oriented at different angles with respect to the loading direction, and (2) two flaws, where the primary flaw is oriented perpendicular to the loading direction and the secondary flaw is oriented at different angles. The simulations provide insight into the evolution of tensile and shear fracture behavior as a function of time. The single-flaw simulations accurately reproduce experimentally measured peak stresses as a function of flaw inclination angle. Both the single- and double-flaw simulations exhibit a linear increase in strength with increasing flaw angle while the double-flaw specimens are systematically weaker than the single-flaw specimens.

This study presents the performance of a combined finite-discrete element method for prediction of the structural response of reinforced concrete beams under impact loading. A combination of finite and discrete element methods enables the modelling of the concrete and the reinforcement before the concrete cracking, as well as a discontinuous nature of the concrete caused by fracture and fragmentation under high impact loading. Discretization of the concrete with triangular finite elements is coupled with one-dimensional reinforcing bars embedded inside the concrete finite elements. The cracking in the concrete activates the joint elements used to simulate the non-linear behavior of both concrete and reinforcement. Numerical analysis based on experimental test data has been carried out to simulate the main features of the reinforced concrete beams impacted by free-falling drop-weights. A high level of accuracy was demonstrated in various comparisons between the experimental tests and the analysis results, including peak displacement, crack pattern, damage level and failure modes of reinforced concrete beams.

Numerical simulations are performed to examine the packing behavior of human red blood cells (RBCs). A combined finite-discrete element method (FDEM) is utilized, in which the RBCs are modeled as no-friction and no-adhesion solid bodies. The volume-to-void ratio of a large number of randomly packed RBCs is clarified, and the effects of the RBC shape, the mesh size, the cell number, and the container size are investigated. The results show that the packed human RBCs with normal shape have a void ratio of 28.45%, which is slightly higher than that of the flat or thick cells used in this study. Such information is beneficial to the further understanding on the geometric features of human RBCs and the research on RBC simulations.

This aim of this paper is to present the application of the combined finite–discrete element method (FDEM) in structural mechanics. FDEM is an innovative numerical technique, which has been intensively used in the past several decades in various engineering simulations. FDEM combines the advantages of both the finite and the discrete elements and enables the simulation of initiation and propagation of cracks, as well as interaction of a large number of discrete elements. The examples presented in this paper show the advantages of FDEM in the analysis of structural mechanics issues including dry-joint masonry structures, concrete and reinforced concrete structures, masonry structures with mortar joints and confined masonry structures, cable and truss structures, membrane structures, and plate and shell structures.

A combined finite-discrete element method, adapted for the analysis of a parallel cable element model using graphic cards, is presented in the paper. The basic objective is to speed up sequential computation time by one or two orders of magnitude. The developed solution is implemented in the open-source FDEM Y code. Performance measurements for this solution are conducted on simple examples, and relevant discussions are made.