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Volume 8, Number 4, October 2023

This study evaluated the acoustic performance of two configurations of serial HR arrays and lined HR arrays in the presence of grazing flow using a 3D numerical simulation. The dual, triple, and quad HR arrays were compared to the conventional HR array. The simulation results showed that the number of resonant frequencies increased with the number of serial HR arrays. The CTL did not significantly change with the number of serial HR arrays. The acoustic performance of the two, three, and four-lined HR arrays was compared to the conventional HR array. The results showed that the resonant frequency and TLmax increased with the number of lined HR arrays. The CTL also increased with the number of lined HR arrays. The effect of the grazing flow Mach number (Ma) was investigated on the four-lined HR array configuration and compared to the conventional HR configuration. TLmax and CTL decreased for both configurations with increasing Ma. The four-lined HR array configuration had significantly better acoustic performance than the conventional HR configuration. The TLmax and CTL increased by more than 300% when the configuration was changed from the conventional HR to the four-lined HR array at Ma = 0. The increment percentage decreased with increasing Ma.

Key Words
acoustic liner design; aeroacoustics; flow noise; Helmholtz resonator; lined HR array

Hadi Dastourani and Iman Bahman-Jahromi: Department of Aeronautical Science & Technology, Khayyam Research Institute, 14665-834, Tehran, Iran

This paper presents an optimization of the reinforced concrete ribbed slab in terms of minimum CO2 emissions and an economic justification of the final optimal design. The design variables are six geometry variables including the slab thickness, the ribs spacing, the rib width at the lower and toper end, the depth of the rib and the bar diameter of the reinforcement, and the seventh variable defines the concrete strength. The objective function is considered to be the minimum amount of carbon dioxide gas (CO2) emission and at the same time, the optimal design is economical. Seven significant design constraints of American Concrete Institute's Standard were considered. A robust metaheuristic optimization method called improved dolphin echolocation and ant colony optimization (IDEACO) has been used to obtain the best possible answer. At optimal design, the three most important sources of CO2 emissions include concrete, steel reinforcement, and formwork that the contribution of them are 63.72, 32.17, and 4.11 percent respectively. Formwork, concrete, steel reinforcement, and CO2 are the four most important sources of cost with contributions of 67.56, 19.49, 12.44, and 0.51 percent respectively. Results obtained by IDEACO show that cost and CO2 emissions are closely related, so the presented method is a practical solution that was able to reduce the cost and CO2 emissions simultaneously.

Key Words
CO2 emissions; economic justification; hybrid metaheuristic optimization algorithm; optimal design; reinforced concrete ribbed slab

Shima Bijari: Department of Civil Engineering, University of Birjand, Birjand, Iran

Mojtaba Sheikhi Azqandi: Department of Mechanical Engineering, University of Birjand, Birjand, Iran

An innovative inertial reactive armor is being developed through a multi-discipline project. Unlike the well-known explosive or non-explosive reactive armour that uses high-energy explosives or bulging effect, the proposed inertial reactive armour uses active disc elements that is set to rotate rapidly upon impact to effectively deflect and disrupt shaped charges and kinetic energy penetrators. The effectiveness of the proposed armour highly depends on the tangential velocity of the impact point on the rotating disc. However, for a single layer armour with an array of high-speed rotating discs, the tangential velocity is relatively low near the center of the disc and is not available between the gap of the discs. Therefore, it is necessary to configure the armor with double layers to increase the tangential velocity at the point of impact. This paper explores a multi-objective geometry design optimization for the double-layered armor using Nelder-Mead optimization algorithm and integration tools of the python programming language. The optimization objectives include maximizing both average tangential velocity and high tangential velocity areas and minimizing low tangential velocity area. The design parameters include the relative position (translation and rotation) of the disc element between two armor layers. The optimized design results in a significant increase of the average tangential velocity (38%), increase of the high tangential velocity area (71.3%), and decrease of the low tangential velocity area (86.2%) as comparing to the single layer armor.

Key Words
double-layered armor; geometry design; inertial reactive armor; multi-objective optimization

Bekzat Ajan, Christos Spitas and Elias Abou Fakhr: Department of Mechanical and Aerospace Engineering, School of Engineering and Digital Sciences, Nazarbayev University, Astana 010000, Kazakhstan

Dichuan Zhang: Department of Civil and Environmental Engineering, School of Engineering and Digital Sciences, Nazarbayev University, Astana 010000, Kazakhstan

Dongming Wei: Department of Mathematics, School of Sciences and Humanities, Nazarbayev University, Astana 010000, Kazakhstan

This article explores how multi-objective optimization techniques can be used to design cost-effective and structurally optimal spatial steel structures, highlighting that optimizing performance can be as important as minimizing costs in real-world engineering problems. The study includes the minimization of maximum horizontal displacement, the maximization of the first natural frequency of vibration, the maximization of the critical load factor concerning the first global buckling mode of the structure, and weight minimization as the objectives. Additionally, it outlines a systematic approach to selecting the best design by employing four different evolutionary algorithms based on differential evolution and a multi-criteria decision-making methodology. The paper's contribution lies in its comprehensive consideration of multiple conflicting objectives and its novel approach to simultaneous consideration of bracing system, column orientation, and commercial profiles as design variables.

Key Words
conceptual and feature based design; design optimization; simulation based design; steel structure; structural optimization

Cláudio H. B. de Resende: Postgraduate Program of Civil and Environmental Engineering, Pontifical Catholic University of Rio de Janeiro

Luiz F. Martha: Department of Civil and Environmental Engineering, Pontifical Catholic University of Rio de Janeiro

Afonso C. C. Lemonge and Patricia H. Hallak: Department of Applied and Computational Mechanics - Federal University of Juiz de Fora

José P. G. Carvalho: Postgraduate Program of Civil Engineering - Federal University of Rio de Janeiro

Júlia C. Motta: Postgraduate Program of Civil Engineering - Federal University of Juiz de Fora

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