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Feature Papers in Section "Engineering and Materials" 2025

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A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Engineering and Materials".

Deadline for manuscript submissions: closed (31 December 2025) | Viewed by 4802

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Prof. Dr. Vasilis K. Oikonomou

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Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
Interests: cosmology; inflationary cosmology; modified theories of gravity; physics of the early universe; dark energy; dark matter; supersymmetry; mathematical physics; high energy physics; theoretical physics; epistemic game theory; game theory
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Dear Colleagues,

The multidisciplinary Section “Engineering and Materials" of the Symmetry journal welcomes original research articles with top-level mathematical modeling or experimental outcomes and strongly substantiated conclusions and results, as well as relevant analytical reviews on all aspects of symmetry or asymmetry in engineering, materials, energy sciences, or other interdisciplinary areas.

We aim to provide a virtual forum and database for experts publishing papers with engineering significance, who are dedicated to the most up-to-date issues and mainstream topics. The Section will fill the gap of mathematical modeling in these areas in the scientific literature, emphasizing articles related to cutting-edge technologies and contemporary technology applications. Articles are expected to have original content and demonstrate clear scientific novelty.

Other areas of interest include those associated with engineering and materials science which require a multidisciplinary approach.

Prof. Dr. Vasilis K. Oikonomou
Guest Editor

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

materials engineering
nanotechnology
power systems and thermal engineering
mechanical engineering, mechatronics, and robotics
automation and control engineering
electronic engineering
communication engineering
chemical and molecular engineering
optical engineering and technology
fiber optics technology
mathematical and formal aspects of superconductivity
mechanochemical aspects of aqueous solutions
green chemistry fabrication of materials

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Published Papers (9 papers)

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Research

18 pages, 4791 KB

Open AccessArticle

Research on Structural Design and Plugging Laws of Knot Temporary Plugging Agent

by Jianjun Xue, Qiang Sun, Ran Wei, Weiqing Li, Leilei Yu, Wei Wang and Yongsheng Liu

Symmetry 2026, 18(2), 211; https://doi.org/10.3390/sym18020211 - 23 Jan 2026

Viewed by 188

Abstract

Horizontal wellbore temporary plugging and diversion fracturing serves as a critical technical approach for the economical and efficient development of unconventional oil and gas reservoirs. A degradable knot temporary plugging agent (TPA) offers distinct advantages for perforation plugging in horizontal wellbore; however, existing research remains limited, and the influence of knot TPA parameters on perforation temporary plugging mechanisms has not been clearly elucidated. This study employs a CFD-DBCM coupled model to conduct numerical simulations of temporary plugging with a knot TPA. The simulation is validated through visualized temporary plugging experiments, followed by an optimization analysis focusing on the flank length and structural configurations of the knot TPA. Research indicates that, when the flank is less than 1.6 times the central diameter, its plugging capacity is significantly compromised. Once the flank exceeds 1.6 times the central diameter, the total plugging performance of the knot TPA improves to a certain extent, and the temporary plugging capacity for the upper perforations increases particularly significantly. When flank lengths are identical, a knot TPA with uniformly distributed four flanks exhibits superior plugging performance compared to configurations featuring only single or double flanks. Given formation heterogeneity, a temporary plugging simulation analysis of the combined knot TPA was conducted. The results indicate that employing a combined knot TPA achieves a higher valid plugging rate compared to using only one type of knot TPA, with valid plugging accounting for the majority of cases. Field application of knot TPA was conducted in the fracturing stage of an oil well in Zhejiang, and the changes in on-site data verified the effectiveness of the temporary plugging technique of knot TPA. Full article

(This article belongs to the Special Issue Feature Papers in Section "Engineering and Materials" 2025)

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22 pages, 7119 KB

Open AccessArticle

Optimal Intensity Measures for the Repair Rate Estimation of Buried Cast Iron Pipelines with Lead-Caulked Joints Subjected to Pulse-like Ground Motions

by Ning Zhao, Heng Li, Bing Tang, Hongyuan Fang, Qiang Wu and Gang Wang

Symmetry 2026, 18(1), 190; https://doi.org/10.3390/sym18010190 - 20 Jan 2026

Viewed by 204

Abstract

Pulse-like ground motions can cause severe damage to buried cast iron (CI) pipelines, which necessitates the selection of optimal seismic intensity measures (IMs) to estimate pipeline repair rates. Such a selection is essential for mitigating uncertainty in the seismic risk assessment of buried CI pipelines. For the first time, this study systematically screens the optimal scalar and vector IMs for buried cast iron pipelines with lead-caulked joints under pulse-like ground motions by a symmetrical evaluation based on the criteria of efficiency, sufficiency, and proficiency, providing a new method for reducing uncertainty in pipeline seismic risk assessment. We initiate the study by selecting 124 pulse-like ground motions from the NGA-West2 database and identifying 19 scalar and 171 vector IMs as potential candidates. A two-dimensional soil–pipe model is introduced, incorporating variability in the sealing capacity of lead-caulked joints along the axial direction. CI pipeline repair rates are calculated across various scaling factors and apparent wave velocities, yielding 1116 datasets pertinent to CI pipeline damage. The repair rate is adopted as the engineering demand parameter (EDP) to evaluate the efficiency, sufficiency, and proficiency of candidate IMs. Through comprehensive analysis, peak ground velocity (PGV) and the combination of PGV and the time interval between 5% and 75% of normalized Arias intensity ([PGV, Ds_5–75]) are determined as the optimal scalar- and vector-IMs, respectively, for assessing the repair rate of buried CI pipelines under pulse-like ground motions. Full article

(This article belongs to the Special Issue Feature Papers in Section "Engineering and Materials" 2025)

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28 pages, 5227 KB

Open AccessArticle

A BSMOTE-OOA-SuperLearner Hybrid Framework for Interpretable Prediction of Pillar Stability

by Weizhang Liang, Yu Liu, Pengpeng Lu and Zheng Li

Symmetry 2026, 18(1), 49; https://doi.org/10.3390/sym18010049 - 26 Dec 2025

Viewed by 286

Abstract

Pillar stability prediction is essential for underground mining safety, yet it remains challenging due to limited data, class imbalance, and insufficient interpretability. This study proposes an integrated Borderline-SMOTE-Osprey Optimization Algorithm-Super Learner framework (BSMOTE-OOA-SL) for hard-rock pillar stability prediction. The framework combines five heterogeneous base learners (ANN, GBDT, KNN, RF, and SVM), applies Borderline-SMOTE within training folds to alleviate class imbalance, and employs the Osprey Optimization Algorithm (OOA) for systematic hyperparameter optimization. The model is evaluated using a dataset of 241 pillar cases from seven underground mines. Statistical experiments based on multiple random train–test splits show that the proposed framework consistently outperforms individual base learners in terms of Accuracy, Macro-Precision, Macro-Recall, and Macro-F1, demonstrating improved robustness and generalization. Ablation results indicate that the joint use of Borderline-SMOTE and OOA leads to quantitative performance gains of 10.21%, 12.25%, 12.61%, and 12.86% in Accuracy, Macro-Precision, Macro-Recall, and Macro-F1, respectively. Under a representative data split, the model achieves an overall accuracy of 95.92%, with strong class-wise Precision, Recall, and F1-score across all stability categories, and AUC values exceeding 0.9 for all classes (reaching 1.0 for the Failed category). SHAP-based interpretability analysis identifies stress-related indicators—particularly average pillar stress, Stress/UCS ratio, and UCS—as the dominant factors governing pillar stability. Overall, the proposed BSMOTE-OOA-SL framework provides a robust, interpretable, and statistically reliable solution for hard-rock pillar stability prediction. Full article

(This article belongs to the Special Issue Feature Papers in Section "Engineering and Materials" 2025)

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26 pages, 4349 KB

Open AccessArticle

TC-SOM Driven Cluster Partitioning Enables Hierarchical Bi-Level Peak-Shaving for Distributed PV Systems

by Tao Zhou, Yueming Ma, Ziheng Huang and Cheng Wang

Symmetry 2026, 18(1), 21; https://doi.org/10.3390/sym18010021 - 22 Dec 2025

Viewed by 338

Abstract

Given the urgent demand for flexible peak-shaving in power systems and underutilized distributed photovoltaic (PV) regulation potential, this paper proposes a distributed PV peak-shaving control strategy based on the temporal coupling self-organizing map (TC-SOM) neural network and a bi-level model. First, the SOM algorithm is improved for efficient feature extraction and accurate clustering of distributed PV data, realizing rational PV cluster division. On this basis, a bi-level peak-shaving model for distributed PV is constructed, forming a hierarchical peak-shaving mechanism from node demand to PV clusters to individual PVs to ensure inter- and intra-cluster coordination. This hierarchical structure embodies symmetric response logic, enabling balanced interaction between upper-layer node demand guidance and lower-layer PV execution, as well as inter-cluster coordination. Simulations on the IEEE-33 node system confirm its effectiveness: it significantly smooths the load curve, reduces peak–valley differences, and optimizes the flexible utilization of distributed PV through coordinated control, aggregation management, and curtailment regulation, providing strong support for precise PV cluster regulation and stable operation of high-proportion PV-integrated power grids. Full article

(This article belongs to the Special Issue Feature Papers in Section "Engineering and Materials" 2025)

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14 pages, 3043 KB

Open AccessArticle

First-Principles Study of AlCrFeMoTi High-Entropy Alloys

by Xiao Hu, Yilong Liu, Yunyun Wu, Shuliang Zou, Weiwei Xiao and Jinghao Huang

Symmetry 2025, 17(11), 1965; https://doi.org/10.3390/sym17111965 - 14 Nov 2025

Viewed by 693

Abstract

The AlCrFeMoTi high-entropy alloy exhibits promising application potential as a corrosion-resistant structural material in advanced nuclear energy systems, particularly in lead–bismuth fast reactors. In this present study, first-principles calculation based on the density functional theory was employed to investigate the phase and electronic structure of AlCrFeMoTi HEA. The Gibbs free energy calculation results and XRD experimental results both indicate that the BCC phase is more stable for AlCrFeMoTi HEA. The atom distribution model was constructed according to the site preference of atoms occupying sublattices. The results indicate that alloying atoms have an obvious site preference. For example, Fe, Mo, and Cr atoms always prefer the 1a sublattice, while Al and Ti atoms tend to favor the 1b sublattice. And the atom site preference is temperature-sensitive. At 973 K, the site occupancy configuration is (Al₅Cr₁₆Fe₂₆Mo₁₇Ti₀)_1a(Al₂₁Cr₉Fe₀Mo₉Ti₂₅)_1b. Based on the steady-state phase structure, the band structure, density of states, and charge density were calculated. The electronic structure results show that metal bonds are formed between alloying elements in AlCrFeMoTi HEA, exhibiting strong metallic properties. Full article

(This article belongs to the Special Issue Feature Papers in Section "Engineering and Materials" 2025)

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26 pages, 1030 KB

Open AccessArticle

Symmetry Optimized Water Flooding Characteristic Curves: A Framework for Balanced Prediction and Economic Decision Making in Heterogeneous Reservoirs

by Xiao Guo, Honglin Ren, Lingfeng Du, Yiting Guan and Youbin He

Symmetry 2025, 17(11), 1924; https://doi.org/10.3390/sym17111924 - 10 Nov 2025

Viewed by 507

Abstract

As a cornerstone of recoverable reserve prediction in water flooding projects, characteristic curve analysis has proven to be critical for reservoir management in the G Oilfield. This study introduces an enhanced methodology that significantly improves prediction accuracy through three key innovations: (1) development of a modified Type A curve with correction factor c to address early-stage nonlinear deviations, reducing prediction errors from 12.7% to 4.3% across 35 wells; (2) establishment of phase-specific model selection criteria demonstrating Type C curve superiority (>80% water cut) versus Zhang/Yu-type curves’ effectiveness in heterogeneous reservoirs (water cut ≥ 50%, errors < 5%); and (3) implementation of an integrated workflow incorporating linear segment optimization and economic threshold standardization. Field validation through 15-year production data (2008–2023) confirms <6% error in recovery factor predictions, significantly enhancing development strategy formulation. The technical framework provides novel insights into the water flooding curve theory while offering practical solutions for mature field management, particularly in complex continental reservoirs. Full article

(This article belongs to the Special Issue Feature Papers in Section "Engineering and Materials" 2025)

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20 pages, 3881 KB

Open AccessArticle

Symmetry–Asymmetry Framework for Rubberized Concrete: Correlations Between Mixture Design and Rubber Properties and Concrete Flowability and Mechanical Characteristics, and Three-Stage Transition of Compressive Strength

by Tetsuya Kouno, Yu Qiu and Rui Tang

Symmetry 2025, 17(11), 1917; https://doi.org/10.3390/sym17111917 - 8 Nov 2025

Viewed by 515

Abstract

This study systematically investigated the effects of mix design conditions (water–cement ratio) and rubber properties (particle size, surface area, and mixing ratio) on the flowability and mechanical characteristics of rubberized concrete, in which rubber particles were incorporated as part of the fine aggregate. The fresh properties (slump and air content) and hardened properties (compressive strength and Young’s modulus) were measured, and their correlations with rubber surface area and mixing ratio were analyzed. The results showed that slump and air content converged to constant values with increasing rubber surface area, exhibiting symmetric behavior. These characteristics were accurately approximated using logistic and exponential functions. In contrast, compressive strength did not decrease monotonically with increasing rubber content but could be divided into three distinct regions: a low-substitution region (Region I), an intermediate transition region (Region II), and a high-substitution region (Region III). Particularly in Region II, where the rate of strength reduction increased sharply, the logistic function was found to describe the asymmetric behavior more appropriately than the conventional exponential function. Furthermore, an estimation formula incorporating a correction term into the logistic function was proposed to account for the influence of the W/C ratio on compressive strength. This two-stage estimation model achieved higher predictive accuracy than conventional equations, eliminating the 0.88 bias observed in previous models. Finally, a practical design methodology based on this two-stage model was presented, demonstrating its applicability to concrete with various mixture ratios and water–cement ratios. Full article

(This article belongs to the Special Issue Feature Papers in Section "Engineering and Materials" 2025)

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26 pages, 8666 KB

Open AccessArticle

A Robust Lagrangian Implicit Material Point Method for Accurate Large-Deformation Analysis

by Qin-Yang Sang, Zhi-Gang Liu, Yong-Lin Xiong, Rong-Xing Wu and Jiang-Hua Yan

Symmetry 2025, 17(11), 1876; https://doi.org/10.3390/sym17111876 - 5 Nov 2025

Viewed by 796

Abstract

The material point method (MPM) has shown significant potential for simulating problems involving large deformations. However, many implicit MPM formulations based on the traditional Updated Lagrangian (UL) scheme still face challenges in terms of computational stability. In this study, we propose a novel Lagrangian equilibrium formulation for an implicit MPM that is tailored to large-deformation problems. (1) The previously converged state is utilized to simplify stiffness matrix computations, thereby improving the stability of the algorithm. (2) The framework supports a variety of high-order interpolation functions, which effectively mitigate numerical artifacts such as cell-crossing errors. (3) The B-bar technique is further incorporated to suppress spurious stress oscillations in the incompressible limit. The proposed method is validated through two classical benchmark tests, the simple shear of a single element and the cantilever beam problem, by comparing the simulation results with analytical solutions and alternative numerical approaches. Finally, its capability is demonstrated in slope stability and strip footing analyses, confirming the superior accuracy, stability, and robustness of the method for large-deformation elastoplastic problems. Full article

(This article belongs to the Special Issue Feature Papers in Section "Engineering and Materials" 2025)

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23 pages, 3161 KB

Open AccessArticle

Characterizing Hydraulic Fracture Morphology and Propagation Patterns in Horizontal Well Stimulation via Micro-Seismic Monitoring Analysis

by Longbo Lin, Xiaojun Xiong, Zhiyuan Xu, Xiaohua Yan and Yifan Wang

Symmetry 2025, 17(10), 1732; https://doi.org/10.3390/sym17101732 - 14 Oct 2025

Viewed by 679

Abstract

In horizontal well technology, hydraulic fracturing has been established as an essential technique for enhancing hydrocarbon production. However, the complex architecture of fracture networks challenges conventional monitoring methods. Micro-seismic monitoring, recognized for its superior resolution and sensitivity, enables precise fracture morphology characterization. This study advances diagnostic capabilities through integrated field–laboratory investigations and multi-domain signal processing. Hydraulic fracturing experiments under varied geological conditions generated critical micro-seismic datasets, with quantitative analyses revealing asymmetric propagation patterns (total length 312 ± 15 m, east wing 117 m/west wing 194 m) forming a 13.37 × 10⁴ m³ stimulated reservoir volume. Spatial event distribution exhibited density disparities correlating with geophone offsets (west wing 3.8 events/m vs. east 1.2 events/m at 420–794 m distances). Advanced time–frequency analyses and inversion algorithms differentiated signal characteristics demonstrating logarithmic SNR (Signal-to-Noise Ratio)–magnitude relationships (SNR 0.49–4.82, R² = 0.87), with near-field events (<500 m) showing 68% reduced magnitude variance compared to far-field counterparts. Coupled numerical simulations confirmed stress field interactions where fracture trajectories deviated 5–15° from principal stress directions due to prior-stage stress shadows. Branch fracture networks identified in Stages 4/7/9/10 with orthogonal/oblique intersections (45–65° dip angles) enhanced stimulation reservoir volume (SRV) by 37–42% versus planar fractures. These geometric parameters—including height (20 ± 3 m), width (44 ± 5 m), spacing, and complexity—were quantitatively linked to micro-seismic response patterns. The developed diagnostic framework provides operational guidelines for optimizing fracture geometry control, demonstrating how heterogeneity-driven signal variations inform stimulation strategy adjustments to improve reservoir recovery and economic returns. Full article

(This article belongs to the Special Issue Feature Papers in Section "Engineering and Materials" 2025)

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