http://www.colloquiam.com/public/m.abudari_l.shehadeh_2025a Sun, 13 Apr 2025 16:19:03 +0200 http://www.colloquiam.com/public/m.abudari_l.shehadeh_2025a Aluminum 6061 alloy is the most frequently used aluminum alloy in automobile, aircraft, and aerospace industries. However, poor wear and corrosion resistances, considerably affecting their scaled-up applications. Microarc oxidation (MAO) is ecofriendly, straightforward, efficient, and rapid technique for improving the surface characteristics of aluminum alloys and proves to be a highly effective surface treatment technique to enhance the corrosion and wear resistances of aluminum alloys. This article describes progresses realized in recent years for understanding the effects of electrolyte type, electrolyte composition, and additives on the morphology and  properties of MAO coating film, and  on the hardness of MAO coatings .Usually, applying an electrolyte system and introducing some additives in appropriate concentrations can improve the quality of the MAO coatings and their hardness, whereas some additives have negative effects on the hardness which is related to the corrosive behavior of aluminum. This review article showed that the microhardness values of the MAO coatings which was prepared in Na₂AlO₂ electrolyte was greater than the one which was prepared in Na₂SiO₃ electrolyte with percentage 62 %. As well as found that coatings generated by using pulsed-bipolar mode power source in MAO gives superior characteristics and investigated that provide additives to electrolyte not always enhance hardness and corrosion resistance. The review also highlights that higher hardness often correlates with improved corrosion resistance.

]]> lina mousa http://www.colloquiam.com/public/E._et_al_2024a Mon, 15 Apr 2024 20:25:03 +0200 http://www.colloquiam.com/public/E._et_al_2024a We present a framework to investigate progressive collapse and robustness of 2D framed structures, subjected to multiple column removals. Progressive collapse is first simulated with an algorithm based on the Discrete Elements. The possible collapse mechanisms emerging from the simulations constitute the input for an analytical model. The model takes into account the dynamics of the response to the sudden initial damage and, under the hypotheses of ideally plastic or perfectly brittle ruptures, provides upper and lower bounds for the collapse loads and for the progressive collapse resistance. Closed form expressions are obtained, that can be valuable for robustness-oriented design. A novel concept of hierarchy in robustness capacity design emerges, which partly conflicts with anti-seismic capacity design. Strategies of compartmentalization and the influence of the position of the initial damage within the frame are discussed, also taking into account the impacts between falling rubble and horizontal floor slabs.

]]> Alessandro Calvi http://www.colloquiam.com/public/Calvi_2024f Mon, 15 Apr 2024 23:26:03 +0200 http://www.colloquiam.com/public/Calvi_2024f Structural analysis is conducted by the displacement method for evaluation of the stress-strain state induced by static loads. The analysis is conducted by the modal analysis and acceleration response spectrum method for the evaluation of the stress-strain state induced by dynamic loads (including seismic loads).
Structural analysis is carried out using the finite element method. The above method is based on the schematization of the structure into elements connected only at a set number of points called nodes. The nodes are defined by the three Cartesian coordinates in a global reference system. The unknowns of the problem (within the displacement method) are the displacement components of the nodes referred to the global reference system (translations according to X, Y, Z, rotations around X, Y, Z). The solution of the problem is obtained by a system of linear algebraic equations whose known terms consist of the loads acting on the structure appropriately concentrated at the nodes.

]]> Alessandro Calvi http://www.colloquiam.com/public/Chen_2024a Thu, 08 Feb 2024 06:40:05 +0100 http://www.colloquiam.com/public/Chen_2024a In the manufacturing process of razor blades, the presence of surface defects directly impacts their quality and lifespan. Manual detection of these defects is not only inefficient but also susceptible to external interference. To achieve real-time and stable detection of blade defects, a method based on video analysis was proposed in this paper. Raw surface images of the blades were captured using a computer vision system, and binarization was performed using Otsu's algorithm. Subsequently, contours were identified and preliminarily analyzed using the CCL algorithm to obtain Regions of Interest (ROI). The ROI was then sorted, and subtle defects were filtered out through morphological analysis. A mask was obtained by comparing the ROI with a background model constructed based on frame averaging. Through mask analysis, defect types were determined, achieving efficient detection of surface defects on razor blades. Experimental results demonstrated that the proposed method enabled real-time detection of multiple defect types simultaneously.

]]> Lilong Chen http://www.colloquiam.com/public/Carbonell_arqueologo_2022a Sat, 05 Feb 2022 18:07:02 +0100 http://www.colloquiam.com/public/Carbonell_arqueologo_2022a José Manuel Torres-Carbonell http://www.colloquiam.com/public/Flores_Burhani_2021a Wed, 31 Mar 2021 17:34:02 +0200 http://www.colloquiam.com/public/Flores_Burhani_2021a Fast and precise propagation of satellite orbits is required for mission design, orbit determination and payload data analysis. We present a method to improve the computational performance of numerical propagators and simultaneously maintain the accuracy level required by any particular application. This is achieved by determining the positional accuracy needed and the corresponding acceptable error in acceleration on the basis of the mission requirements, removing those perturbation forces whose effect is negligible compared to the accuracy requirement, implementing an efficient and precise algorithm for the harmonic synthesis of the geopotential gradient (i.e., the gravitational acceleration) and adjusting the tolerance of the numerical propagator to achieve the prescribed accuracy level with minimum cost. In particular, to achieve the optimum balance between accuracy and computational performance, the number of geopotential spherical harmonics to retain is adjusted during the integration on the basis of the accuracy requirement. The contribution of high-order harmonics decays rapidly with altitude, so the minimum expansion degree meeting the target accuracy decreases with height. The optimum degree for each altitude is determined by making the truncation error of the harmonic synthesis equal to the admissible acceleration error. This paper presents a detailed description of the technique and test cases highlighting its accuracy and efficiency.

]]> Roberto Flores http://www.colloquiam.com/public/Proietti_et_al_2020a Sat, 02 Jan 2021 19:58:02 +0100 http://www.colloquiam.com/public/Proietti_et_al_2020a In nominal mission scenarios, geostationary satellites perform end-of-life orbit maneuvers to reach suitable disposal orbits, where they do not interfere with operational satellites. This research investigates the long-term orbit evolution of decommissioned geostationary satellite under the assumption that the disposal maneuver does not occur and the orbit evolves with no control. The dynamical model accounts for all the relevant harmonics of the terrestrial gravity field at the typical altitude of geostationary orbits, as well as solar radiation pressure and third-body perturbations caused by the Moon and the Sun. Orbit propagations are performed using two algorithms based on different equations of motion and numerical integration methods: (i) Gauss planetary equations for modified equinoctial elements with a Runge-Kutta numerical integration scheme based on 8-7^th-order Dorman and Prince formulas; (ii) Cartesian state equations of motion in an Earth-fixed frame with a Runge-Kutta Fehlberg 7/8 integration scheme. The numerical results exhibit excellent agreement over integration times of decades. Some well-known phenomena emerge, such as the longitudinal drift due to the resonance between the orbital motion and Earth’s rotation, attributable to the J2 term of the geopotential. In addition, the third-body perturbation due to Sun and Moon causes two major effects: (a) a precession of the orbital plane, and (b) complex longitudinal dynamics. This study proposes an analytical approach for the prediction of the precessional motion and show its agreement with the (more accurate) orbit evolution obtained numerically. Moreover, long-term orbit propagations show that the above mentioned complex longitudinal dynamics persists over time scales of several decades. Frequent and unpredictable migrations toward different longitude regions occur, in contrast with the known effects due only to the perturbative action of J2

]]> Roberto Flores http://www.colloquiam.com/public/Sangra`_Flores_2020a Wed, 04 Nov 2020 12:23:02 +0100 http://www.colloquiam.com/public/Sangra`_Flores_2020a The Tisserand graph (TG) is a graphical tool commonly employed in the preliminary design of gravity-assisted trajectories. The TG is a two-dimensional map showing essential orbital information regarding the Keplerian orbits resulting from the close passage by one or more  massive bodies, given the magnitude of the hyperbolic excess speed and the minimum allowed pericenter height for each passage. Contours of constant populate the TG. Intersections between contours allow to link consecutive flybys and build sequences of encounters en route to a selected destination.