Search Results (2,888)

To address the limited endurance of unmanned underwater vehicles (UUVs) during long-duration missions, this study proposes a foldable and retractable wave energy converter (WEC) conformally integrated with the UUV hull. A two-degrees-of-freedom heave-coupled dynamic model of the float–UUV system is established, and parameter-matching relationships are derived using complex dynamic stiffness and impedance-matching theory. A bidirectionally coupled STAR-CCM+-AMESim co-simulation framework resolves the nonlinear viscous flow field, relative motion, and PTO dynamic response in closed loop. Under regular wave conditions defined based on a representative Bohai Sea state, the effects of the transmission ratio and spring stiffness on the coupled motion and equivalent resistive load power output are systematically investigated. Under the specified wave condition, average electrical power varies unimodally with both parameters, reaching 70.8 W at a transmission ratio of 15 and a spring stiffness of 4642 N/m; the corresponding peak power is 161.2 W. The system is more sensitive to increases than decreases in transmission ratio, suggesting a value slightly below the theoretical optimum for engineering design. The instantaneous power shows an asymmetric double-peak pattern, indicating a shift in dominance between direct float-driven generation and spring-mediated energy release. Agreement between theory and co-simulation provides numerical cross-validation and offers a theoretical basis and numerical methodology for designing and optimizing WECs on mobile UUV platforms. Full article

Thermodynamic concepts are increasingly used in nonlinear photonics to describe Rayleigh–Jeans thermalization, optical wave turbulence, condensation, negative-temperature states, and statistical mode locking. We ask how far this reasoning can be extended to localized structures maintained far from equilibrium by gain, loss, dispersion, and nonlinearity, using strongly chirped dissipative solitons (DSs) of the complex cubic–quintic Ginzburg–Landau equation as a model system. Their internal energy flows and separation of correlation scales connect coherent solitary waves with semi-incoherent wave kinetics, driven-open systems, and Bose–Einstein-condensation analogies. We review thermodynamic-like indicators based on spectral entropy, internal energy, effective temperature, and spectral condensation, and we relate them to dissipative-soliton resonance (DSR), stochastic mode-locking self-start, and redistribution between single- and multipulse attractors. Normal and anomalous group-delay dispersion provide complementary cases. In normal dispersion, DSR is accompanied by spectral localization, increasing scale separation, and growing multipulse accessibility; the statistical degree-count interpretation becomes meaningful only after the two scales separate and still requires ensemble calibration. In anomalous dispersion, the spectrum has extended wings, and noisy calculations reveal finite robust regions inside a larger existence domain, without an analogous thermodynamic turnover along the continuation tested. Thus, the unification is strongest at the level of the adiabatic solution and state-selection diagnostics, not an equilibrium thermodynamics. DSs thereby provide a photonic platform linking nonequilibrium thermodynamics, wave turbulence, driven condensates, and statistical phase-transition concepts. Full article

Metal–Insulator–Metal (MIM) tunneling diodes are among the most promising rectifying devices for long-wave infrared (LWIR) rectenna systems due to their ultrafast response and zero-bias operation. However, their performance is strongly dependent on the choice of electrode and dielectric materials, making the identification of optimal material combinations a key challenge. To address this issue, this theoretical study presents a numerical investigation of a new class of MIM diodes based on a quantum-mechanical tunneling framework. Novel combinations of transition-metal dichalcogenides (NbS₂, VSe₂, and TaS₂) as anode materials (M1), conductive carbides and nitrides (Mo₂C, VN, and V) as cathode materials (M2), and rare-earth oxide and oxyhalide compounds (Sc₂O₃, LaOF, and LaOBr) as tunnel barriers (I) were selected through an extensive literature survey. These materials were combined to design previously unexplored MIM architectures for LWIR rectification. The electrical transport and rectification properties were evaluated using the Simmons tunneling model by calculating the current density–voltage (J–V) and current–voltage (I–V) characteristics, together with key figures of merit (FOMs), including zero-bias resistance, asymmetry factor, nonlinearity, and responsivity, at room temperature (300 K). The effects of tunnel barrier height and dielectric properties on device performance were systematically investigated. Among all the investigated architectures, the TaS₂/LaOBr/V MIM diode exhibited the most promising overall performance, achieving an asymmetry factor exceeding 2.5 × 10⁵, a nonlinearity factor of 1, and a zero-bias responsivity of 10 V⁻¹ at 300 K. Furthermore, this structure demonstrated the highest current density and the most favorable I–V characteristics among the proposed material combinations. These results identify the TaS₂/LaOBr/V material system as a promising candidate for high-performance LWIR energy harvesting applications, owing to its optimized tunnel barrier height, which promotes efficient electron tunneling while maintaining excellent rectification properties. Full article

This study discusses the (2+1)-dimensional Kadomtsev–Petviashvili–Benjamin–Bona– Mahony equation, which emerges in weakly nonlinear dispersive plasma waves and shallow water dynamics in ocean engineering. Logarithmic dependent-variable transformations are applied to reconstruct a one-exponential tau function as a common one-soliton profile and derive its dispersion relation. This is a standard transformed solution listed as three normalized logarithmic maps, but not a new family of solutions. Only a one-exponential soliton is claimed, no two-soliton family and no arbitrary-N soliton family. The explicit rational rogue-wave families of the first, second, and third orders are derived using a modified version of a well-known center-shifted polynomial tau-function method that is applied to the KPBBM bilinear form, with both center parameters $\beta$ and $\gamma$ independent. The novelty is thus limited to the specific model and is not based on a new KPBBM equation or a fundamentally novel symbolic algorithm. The rogue-wave center translates in the longitudinal and transverse directions through $\beta$ and $\gamma$, respectively, for a fixed order N and fixed model parameters. They leave the pattern, localization width, background, and the arrangement of inner patterns unchanged. Lump solutions and lump–soliton interaction structures are also obtained and investigated. The auxiliary Hirota bilinear constraint and its reduced bilinear representation are explicitly given. The higher-degree equations found in the directional logarithmic maps are not new multilinear equations, but rather the denominator-cleared differential polynomial residuals. The validity of each solution family retained is guaranteed by means of analytical substitution or vanishing of symbolically identical-to-zero residual in the original KP–BBM equation. The two- and three-dimensional plots are used only to demonstrate the amplitude profile, localization, and propagation of the solutions, as verified by the analysis. In the weakly nonlinear, long-wave and weakly transverse regime where the KPBBM reduction is valid, these solutions give idealized mathematical representations of localization and interaction mechanisms. They are not predictive of coastal instability or offshore hydrodynamic loading, for which dimensional calibration and experimental/field validation would be necessary. Full article

It is well known that meshless methods are effective for solving fractional differential equations on both regular and irregular domains. However, many commonly used basis functions such as Legendre wavelets and B-splines are naturally defined on rectangular domains, which limits their applicability in certain meshless frameworks. In this paper, we are motivated to develop a new meshless method for solving the time-fractional mixed nonlinear diffusion and diffusion-wave equation on arbitrary domains, by employing a skillful extension technique. The proposed method utilizes the well-known Legendre multiwavelets to obtain the best approximate solution by seeking the minimum of approximate solutions within a reproducing kernel space. This approach avoids the need to compute complicated shape functions or other local basis functions. Moreover, the construction of the reproducing kernel Legendre multiwavelet bases presented in this paper is straightforward. Numerical examples on both rectangular domains and domains with curved boundaries confirm that the method is efficient and achieves high accuracy. Full article

This study examines the Gardner equation, a fundamental nonlinear partial differential equation (PDE) used in modeling various physical phenomena, and wave motions. Hyperbolic and trigonometric analytical solutions are derived using the Sardar sub-equation method. Additionally, an artificial neural network (ANN) in combination with the Sardar sub-equation method, an analytical solution approach for the Gardner equation, is proposed. The results demonstrate that the ANN-based hybrid model predicted the Gardner equation solutions with accuracy. This study can be useful in the integration of classical analytical methods and the ANN-based approaches to solutions of nonlinear partial equations. Full article

In this paper, the nonlinear Nurshuak–Tolkunay–Myrkakulov (NTM-III) equation is analyzed using the methods of dynamical systems theory and exact solution techniques. The NTM-III model is reduced to a second-order nonlinear ordinary differential equation by using appropriate reductions, then written as a planar Hamiltonian dynamical system. Analytical study of the equilibrium points, bifurcation structures, and stability properties is conducted using Jacobian matrices and eigenvalue theory. Different parameter combinations are shown in various phase portraits, with the saddle and center equilibrium states present and their stability indicated. An external periodic perturbation is added to the system to study complex nonlinear dynamics. Using phase portraits, time-series analysis, return maps, Lyapunov exponents, sensitivity analysis, and multistability diagnostics, the resulting forced dynamical model is investigated. Chaotic behavior, strong dependence on initial conditions, and multiple coexisting attractors for the same set of parameters are illustrated through numerical simulation. In addition, a set of exact analytical solutions, including trigonometric, hyperbolic, and exponential wave structures, is obtained using the Multivariate Generalized Exponential Rational Integral Function (MGERIF) method. The solutions obtained display interesting nonlinear wave interactions, multi-peakon formations, and localized propagation patterns. The findings show the complex relationship among bifurcation, chaos, multistability, and nonlinear wave propagation in the NTM-III equation and provide new insight into the equation’s mathematical and physical properties. Full article

This paper proposes a data-driven model predictive control (MPC) framework for high-precision speed control of rotary traveling wave ultrasonic motors (RTWUSMs) under temperature drift. To address the strong nonlinearity and time-varying thermal characteristics of RTWUSMs, a Koopman–convolutional neural network–long short-term memory (Koopman–CNN–LSTM) prediction model with radial basis function (RBF) observable features is constructed. The model maps the nonlinear electromechanical coupling and friction-driven dynamics of the motor into a linear invariant subspace, achieving high prediction accuracy while maintaining low computational complexity. On this basis, a data-driven MPC scheme is designed, which eliminates the dependence on accurate analytical plant models and compensates for thermal-induced speed drift through online driving frequency adjustment. The experimental results show that under 900 s of continuous operation, the proposed scheme achieves a relative steady-state speed error of 0.37%, which is significantly better than typical temperature drift compensation methods. This scheme can also provide stable tracking performance under load torques of 0.5 N·m and 1.0 N·m, providing a practical solution for the long-term stable speed regulation of RTWUSM in precision drive applications. Full article

Static rotor eccentricity distorts the air-gap magnetic field of permanent-magnet (PM) traction motors and may aggravate electromagnetic vibration and noise in electric vehicles. The equivalent remanence method (ERM) is an established eccentric-field modeling strategy; this study does not claim ERM itself as new. Instead, it extends the framework to link a prescribed static-eccentricity ratio to equivalent-remanence harmonics and low-order radial electromagnetic-force waves. Fourier decomposition is used to obtain the radial air-gap flux density, and the Maxwell stress tensor is used to calculate and decompose the radial electromagnetic-force density. The analytical magnetic field is evaluated against finite element method (FEM) results over relative eccentricity ratios from 0.16 to 0.80, and the first-order resultant force is further compared with measurements from a 4-pole, 24-slot prototype operating at 2000 r/min under open-circuit no-load conditions. Static eccentricity introduces first-, second-, and third-order force waves in addition to the fourth-order component under a uniform air gap; the first-order component is the dominant additional low-order force. The measured first-order force increases from approximately 300 to 675 N as eccentricity increases, while FEM and analytical predictions reproduce the same nonlinear trend. The FEM and analytical mean absolute percentage errors relative to experiment are 3.78% and 8.55%, respectively. The analytical overprediction is attributed mainly to idealized assumptions such as neglected local saturation, end leakage, and manufacturing deviations. The formulation is therefore suitable for harmonic interpretation and preliminary force prediction under no-load or weakly saturated conditions. Full article

When water waves encounter marine structures, significant scattering is produced, which affects the stability and safety of marine equipment. The cloaking of marine structures in water waves, achieved by water-wave transformation metamaterials, provides a new approach to solving this problem. However, in the anisotropic water depth required for perfect cloaking, the radial water depth tends to infinity, and the circumferential water depth tends to zero at the edge of the structure, leading to a singularity problem. This results in extreme parameters of the metamaterial near the structure, making fabrication difficult. To address the above issue, a comb-type metamaterial for weak scattering of water waves is designed in this paper based on space-transformation metamaterials, by which optimized control over the scattering characteristics of water waves is achieved. First, a general nonlinear spatial transformation is designed for both weak scattering and perfect cloaking. Then, the anisotropic water depths and equivalent gravitational acceleration parameters for the two cases are calculated and analyzed. Subsequently, the Helmholtz equation is solved using the finite element method, and the distributions of wave fields under anisotropic water depths and metamaterials for weak scattering and perfect cloaking are compared and analyzed. The results show that for weak scattering, the radial and circumferential water depths tend to constant values at the edge of the structure, thus resolving the singularity problem in perfect cloaking, while the control performance over water waves is comparable. Compared with perfect-cloaking metamaterials, the designed weak-scattering metamaterial significantly reduces the water depth parameters near the structure while maintaining water-wave control performance, making it easier to fabricate. Full article

In order to investigate the soliton solutions of the third-order nonlinear modified Benjamin–Bona–Mahony equation, this research presents a hybrid analytical and machine-learning methodology. A novel combination of symbolic computation and data-driven modeling is introduced to strengthen the theoretical analysis and improve the simulation capabilities. Next, we propose a Riccati sub-equation neural network (RSENN) framework in which the traveling-wave transformation and Riccati sub-equation structure are incorporated into the neural network model. The proposed RSENN framework accurately approximates the soliton solutions and predicts their spatiotemporal evolution governed by the modified Benjamin–Bona–Mahony equation. The data-driven discovery of the model equation is also performed by estimating the unknown parameters under different noise intensities. The RSENN model is trained using the Levenberg–Marquardt algorithm, and its accuracy and predictive capability are evaluated by comparing its numerical outputs with the exact analytical solutions. The results demonstrate the robustness of the proposed RSENN approach under different levels of noise contamination. Full article

To achieve the optimal balance between structural safety and stripping economy for the rock slopes of a specific open-pit iron mine, a rigorous mathematical modeling and computational framework was established. In contrast to traditional simplified pseudo-static evaluations, authentic monitored seismic and blasting waveforms were integrated within an explicit dynamic strength reduction model to ensure that transient stress wave propagation and progressive failure paths of rock slopes were accurately captured. Furthermore, a constrained multi-objective optimization model was established so that the nonlinear trade-off between dynamic safety margins and stripping volumes could be quantitatively resolved. Based on the application to the studied open-pit slopes, it was revealed that severe deep plastic yielding and topological shear band coalescence were caused by transient dynamic stress waves when the slope angle was steepened to 45°. Consequently, the factor of safety (FS) was abruptly reduced to an unsafe range of 1.01 to 1.20. Through the effective exclusion of this high-risk 45° configuration, a global optimal mining slope angle of 42° was rigorously established. At this optimal angle, a robust factor of safety ranging from 1.45 to 1.98 was consistently maintained across all extreme multi-field coupled conditions. Ultimately, from an engineering perspective, dynamic shear failure paths were successfully interrupted, and the need for expensive structural reinforcement was eliminated. Economically, waste rock stripping volumes were significantly minimized, whereby the overall stripping ratio was optimized, and life-cycle excavation efficiency was maximized. Full article

Urban green space supply (UGSS) is a core component of territorial spatial planning, and the advancement of the park city initiative has been temporally associated with a systematic transformation. Differentiation in UGSS is a comprehensive issue concerning ecological environment, public welfare, and high-quality urban development, and it is closely related to the achievement of United Nations Sustainable Development Goal (SDG) 11.7. This study employs a comprehensive approach combining spatiotemporal dynamic analysis (Mann–Kendall trend test and Theil–Sen slope estimation), differentiation measures (Gini coefficient and Theil index), and the explainable machine learning SHAP model to conduct a large-sample empirical analysis of 1760 towns in China from 2015 to 2024. The findings show the following: First, park city construction corresponds to notable spatiotemporal evolution of UGSS in China’s towns, with approximately 85% of towns showing a significant rise. Second, park city construction coincides with a reduction in differentiation in both the outcomes and processes of UGSS in China’s towns, with both the Gini coefficient and Theil index declining to varying degrees. An analysis of the Theil index further confirms that the observed changes in the Theil index are more pronounced in disadvantaged towns, and the differentiation in UGSS originates more from intra-regional disparities than from inter-regional gaps. Third, the differentiation in UGSS shows deep structural correlates, with the associations of socio-economic and natural ecological factors exhibiting various complex nonlinear associations such as inverted U-shape, arc shape, U-shape, and wave shape. These associations are specifically manifested as mixed directionality of associations, hierarchical intensity of associations, threshold-based evolutionary pathways, geographic spatial heterogeneity, and interactive relationships among factors. This study recommends that the policy design of park city construction and green space system planning should promptly establish a new model combining situational response, threshold management, and collaborative governance. The nonlinear and interpretable analytical paradigm constructed in this study holds significant value for achieving precise supply and equitable sharing of green space resources. Full article

High-speed airborne platforms impose stringent aerodynamic constraints that restrict traditional planar antenna designs. Concurrently, multi-component echoes from extended targets and complex propagation environments induce strong signal coherence, severely degrading spatial angle estimation. To address these dual challenges, this paper proposes a straight-curved hybrid L-shaped asymmetric conformal array hardware topology tailored for cylindrical radomes. Building upon this, a millimeter-wave radar 3D point cloud imaging framework is developed for coherent targets. An orthogonal virtual manifold transformation is first devised to effectively compensate for the non-linear phase distortion induced by the conformal topology. Subsequently, a cascaded Forward-Backward Spatial Smoothing (FBSS) and Root-MUSIC framework is used for efficient signal decoherence. To resolve angle mismatches, a global cost function based on the cross-covariance Frobenius norm is formulated, which pairs independent angles and significantly suppresses spatial ghost targets. Systematic evaluations using 3D computer vision metrics demonstrate that the proposed method achieves accurate geometric restoration of aircraft targets with coherent signals. In the representative simulation, the method obtains a median point-wise localization error of 0.3986 m, a Chamfer Distance (CD) of 0.9695 m², an Earth Mover’s Distance (EMD) of 1.9504 m, and a spatial angular resolution of 1.0° under the stated test conditions. Under the stated simulation assumptions, boundary analyses indicate stable reconstruction around a post-pulse-compression SNR of −8.0 dB and a conformal curvature of 12.50 m⁻¹ ($r=0.08$ m), providing simulation-based design references for conformal radar 3D imaging. Full article

This study focuses on the Significant Wave Height (SWH) retrieval from the Ka-band radar interferometer (KaRIn) on the Surface Water and Ocean Topography (SWOT) satellite by combining backscattering and interference characteristics. To this end, the backscattering-related and interference-related parameters were jointly used as inputs to develop a machine learning model. Here, the backscattering-related data include normalized radar cross-section (NRCS), incidence angle, and the image spectra parameters extracted from KaRIn Level 1B (L1B) data, while the interference-related data correspond to the Level 2 (L2) volumetric correlation, which characterizes the influence of ocean wave scattering on interferometric coherence. The machine learning model is built upon a Multi-Layer Perceptron (MLP), which serves as a nonlinear fitting tool. SWH retrievals from the proposed method and the existing L2 SWH product as a reference were validated by the collocated European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis data, Haiyang2C (HY2C) and Haiyang2D (HY2D) altimeter data, and National Data Buoy Center (NDBC) buoy data. Validations show that both KaRIn SWH have a good agreement with collocations in terms of correlation coefficient (COR), BIAS and root mean square error (RMSE). Moreover, the retrieval accuracy from the proposed method (with an RMSE of about 0.29 m) is better than that of the L2 product (with an RMSE of about 0.46 m) when validated against the collocated ECMWF datasets. Ablation analysis further confirms that image spectra parameters and volumetric correlation are the dominant factors driving the retrieval accuracy improvement, with notable contribution differences among the sub-parameters of spectral features. This performance gain arises from the complementary physical mechanisms of backscattering and interferometric observables, which describe sea state information from independent dimensions. These accurate SWH retrievals can help correct sea state biases for collocated KaRIn sea surface height products and complement wave products from other satellite sensors. Full article