Search Results (916)

Low-altitude wireless networks (LAWNs) require reliable multi-user communication together with accurate range and velocity sensing. Communication and sensing share the same transmit power and spatial degrees of freedom (DoF), and therefore joint beamforming is required to coordinate multi-user spectral efficiency with delay-Doppler estimation accuracy. An adaptive multi-objective beamforming and power allocation framework is developed for a multiple-input multiple-output (MIMO) integrated sensing and communication (ISAC) base station. Communication performance is measured by the achievable multi-user sum spectral efficiency. Sensing performance is characterized by the Cramér–Rao lower bounds (CRLBs) for delay and Doppler frequency. A dimensionless system effectiveness integrated metric (SEIM) combines the three normalized performance components. The beamforming problem is lifted to transmit covariance matrices and treated via semidefinite relaxation (SDR) and alternating successive convex approximation (SCA) under power and per-user signal-to-interference-plus-noise ratio (SINR) constraints. An entropy-regularized weight subproblem provides a closed-form softmax update, and a damping step couples the weight update with the covariance iterations. Numerical results characterize the communication–sensing tradeoff with respect to the transmit power, array size, user loading, SINR requirements, and objective weights. Full article

This paper presents the kinematic design and experimental validation of a two-degree-of-freedom ankle mechanism based on stepper motor actuation and ball-screw transmission. The proposed system employs a hybrid architecture, combining actively controlled motion in the sagittal plane with passively compliant motion in the frontal plane. Experimental evaluation under no-load laboratory conditions demonstrated a strong linear relationship between motor steps and joint angle within an operating range of approximately ±22°, with coefficients of determination exceeding 0.97. The results confirm the predictability and repeatability of the kinematic transformation while revealing minor hysteresis effects associated with mechanical transmission. The proposed mechanism is intended as a validation platform for studying motion transformation in multi-DoF (degree-of-freedom) ankle systems, providing a basis for future work on load analysis, torque modeling, and closed-loop control. Full article

Future gravitational-wave observatories such as Einstein Telescope and Cosmic Explorer will require a substantial evolution of the laser frequency stabilization strategies currently employed in second-generation interferometric detectors. In Advanced Virgo and Advanced LIGO, residual laser frequency noise is strongly suppressed by feedback from the interferometer common-arm degree of freedom, whose long baseline provides an excellent frequency reference over most of the observation band. In third-generation detectors, however, the much longer arm cavities significantly reduce both the free spectral range and the coupled-cavity pole frequency, limiting the achievable bandwidth of the common-arm control loop and degrading the sensing-noise performance at high frequencies. As a consequence, the interferometer itself may no longer provide the broadband frequency stabilization presently achieved in second-generation instruments. This shifts a much larger fraction of the stabilization burden toward the input-optics system. In this review the implications of such a transition are discussed, with particular emphasis on long suspended input mode cleaners, multi-stage stabilization architectures, higher-order optical mode coupling, sensing-noise limitations, and optical layout considerations relevant for future detectors. Full article

Fixed-link manipulators have limited adaptability to changes in task locations and obstacle layouts, while sequential mechanism design and trajectory planning restrict their coordinated performance. This study proposes a surrogate-assisted bilevel optimization method for a four-degree-of-freedom PRRR variable-link-length manipulator. The three link lengths are treated as outer-layer mechanism variables, whereas B-spline control points and trajectory duration are optimized in the inner layer subject to joint, motion, endpoint, and collision constraints. An objective-decoupled surrogate predicts trajectory duration, path length, jerk cost, and minimum clearance, and is embedded in an adaptive reference vector-guided multi-operator multi-objective beluga whale optimization algorithm. The framework combines inverse-kinematics prescreening, surrogate evaluation, high-fidelity trajectory re-optimization, dense constraint verification, and preference-based decision-making. Blind-test, ablation, and high-fidelity verification results show that the method efficiently identifies high-quality, physically feasible mechanism–trajectory candidates. Factorial analysis of an obstacle-constrained handling task indicates that trajectory optimization primarily improves smoothness and clearance, whereas mechanism adaptation redistributes joint motion and further enhances overall trajectory quality. Physical experiments demonstrate the executability of the selected mechanism–trajectory solutions without observed cylinder collision or joint-limit activation in the tested trials. These results demonstrate that the proposed framework provides an effective approach to task-adaptive mechanism–trajectory co-optimization in constrained environments. Full article

Dynamic inductive charging (DIC) combined with hybrid energy storage systems (HESSs) and vehicle-to-grid (V2G) capabilities offers a promising pathway toward extended-range electric vehicles with grid integration benefits. However, real-time optimal energy management remains challenging due to multi-axis coil misalignment, component aging, and bidirectional power flow uncertainty. This paper proposes an adaptive digital twin driven artificial intelligence (AI) energy management framework integrating physics-informed neural networks (PINNs), soft actor critic (SAC) deep reinforcement learning, and model predictive control (MPC) for optimal power distribution among a proton exchange membrane fuel cell (PEMFC), lithium-ion battery, supercapacitor, dynamic wireless charging, and grid interface in four-wheel drive electric vehicles (4WD-EVs). The framework features: (1) a self-evolving digital twin with online learning via Elastic Weight Consolidation (EWC) updating every 50 cycles; (2) a PINN-based state estimator for battery-state estimation, with an average inference time of 1.1 ms and a worst-case latency of 2.8 ms; (3) a hierarchical SAC–MPC strategy with high-level mode selection and low-level power optimization; (4) real-time five-degree-of-freedom WPT misalignment compensation, achieving a mean efficiency of 91.5% under the evaluated dynamic lateral misalignment conditions, with a 50 mm displacement amplitude; (5) degradation-aware V2G optimization generating €582.50/year in revenue while reducing battery aging by 31.8%; and (6) comprehensive techno-economic analysis yielding a discounted payback period of approximately 5.57 years and a net present value of approximately €3777 over a 10-year horizon. Validated through 200+ hours of hardware-in-the-loop (HIL) simulation on the dSPACE/NVIDIA Jetson platform, the proposed approach achieves a 24.3% cost reduction and 31.8% lower battery degradation. The MPC controller exhibits an average execution time of 32.1 ms, a 95th-percentile latency of 44.8 ms, and a worst-case latency of 62.4 ms, while remaining within the 100-ms real-time control deadline. Results demonstrate the viability of adaptive digital twins for next-generation EVs with autonomous charging and multi-source architectures. Full article

This paper develops a distributed control framework for leader–follower formation tracking in multi-agent unmanned aerial vehicle (UAV) systems. Feedforward compensation converts the networked tracking task into local error stabilization problems, and an L_p zero-sum game is used to construct a finite-time robust feedback law. The disturbance-free closed loop is proven to converge in finite time, whereas under nonzero disturbances, the result is a certified L_p attenuation bound rather than exact finite-time convergence. A single-critic adaptive dynamic programming architecture approximates the value function, and an offline sampled data training procedure avoids injecting probing noise into the physical plant. In the reported planar outer-loop simulation, the local errors settle within 4.3 s, compared with 8.2 s for the quadratic L₂ baseline, and the reported cumulative disturbance attenuation indicator decreases from 2.74 to 0.48. The current validation uses a fully actuated translational outer-loop abstraction; extensions to underactuated six-degree-of-freedom dynamics, saturation, and hardware experiments are left for future work L_p. Full article

In the contemporary landscape of spacecraft engineering, reaction wheels, control moment gyros, and momentum wheels are standard tools for precise attitude control, functioning by exchanging angular momentum through the rotation of a solid mass around its major axis. The VEKTOR-FDA (Vector Fluid Dynamic Actuator) proposed in this paper offers an alternative by utilizing the principle of rotating liquid to generate angular momentum instead of relying on a solid body. Electromagnetic pumps drive and circulate the fluid, connecting to a hollow sphere via inlet and outlet channels. The fluid within the sphere is drawn into the pump through the outlet channel and reintroduced through the inlet channel. This circulation, combined with the spherical shape, generates a rotational fluid flow inside the hollow sphere, creating a rotating fluid volume and an angular momentum vector aligned with the rotation axis. By utilizing at least three pumps arranged orthogonally, simultaneous operation allows flow mixing, which can be precisely controlled by adjusting the individual flow velocities of each pump. This setup enables the rotation axis of the fluid flow to be directed in any desired orientation, allowing the rotating fluid volume and its angular momentum vector to be spatially aligned as needed. As a result, a single VEKTOR-FDA can manage attitude control across all three axes of the spacecraft, effectively functioning as a multiple-degree-of-freedom (MDOF) actuator. The electromagnetic pump drive in the VEKTOR-FDA actuator provides self-lubrication and eliminates the need for moving mechanical parts, minimizing potential damage from mechanical loads like shocks during launch. Its simple design also enables the use of commercial off-the-shelf components, ensuring cost-effective implementation. This paper provides a comprehensive overview of the motivation and concept behind the VEKTOR-FDA actuator. Additionally, this paper presents analyses and experimental results that investigate how rotating fluid flow can be generated within the sphere and examines its behavior. The study evaluates various factors influencing fluid flow inside the sphere, including configurations with variable cross-sectional shapes of the inlet and outlet channels. Furthermore, it determines the optimal positioning and arrangement of these channels to achieve efficient fluid flow volume, which is essential for maximizing angular momentum output. Full article

Focusing on the complex aerodynamic interference and attitude response during multibody separation in the low-pressure and low-density environment of near space, a numerical investigation of the effects of different initial separation conditions on submunition motion is conducted. A three-dimensional unsteady flow model is established by coupling the six-degree-of-freedom rigid-body equations with the overset mesh technique. The effects of the free stream Mach number, initial angle of attack, initial separation velocity, and separation altitude on the motion characteristics of the submunition are systematically analyzed. The results show that, compared with conventional low-altitude conditions, aerodynamic forces have a weaker corrective effect on the separation motion and attitude in near space, making the initial separation parameters more influential. Increasing the free stream Mach number and initial angle of attack enhances the radial separation capability but intensifies the attitude response. As the separation altitude increases, the aerodynamic forces weaken, and the displacement and attitude variations in the submunition decrease accordingly. The initial axial separation velocity V_x0 has relatively little influence on the radial separation distance and pitching response. Increasing the initial radial separation velocity V_y0 increases the radial separation distance and reduces pitch oscillations, whereas increasing the magnitude of the initial lateral separation velocity $\left|V_{z0}\right|$ significantly amplifies the roll and yaw responses. The results provide a reference for the design of initial parameters for multi-body separation systems operating in near space. Full article

Improving the conversion of incident wave energy into useful pneumatic power requires a clear understanding of the coupling among floating body motions, internal water column oscillation, air compression, and pneumatic damping in oscillating water column (OWC) systems. In this study, a coupled multi degree of freedom (MDOF) analytical framework is developed by incorporating the surge, heave, and pitch motions of the floating body together with internal water column oscillation and compressible chamber air dynamics. A distinctive feature of the framework is the direct comparison between a simplified single degree of freedom (SDOF) configuration and the coupled MDOF configuration, which enables the contribution of body motion coupling to pneumatic energy conversion to be explicitly identified. Based on potential flow theory, frequency-domain hydrodynamic characteristics are coupled with the pneumatic response to evaluate added mass, radiation damping, hydrodynamic impedance, chamber pressure, pneumatic power, and capture width ratio (CWR). The MDOF results exhibit two distinct pneumatic power peaks. The dominant peak reaches a non-dimensional pneumatic power coefficient P* of approximately 0.88 at ω ≈ 0.4 (kh ≈ 0.13), whereas a secondary peak of approximately 0.06 appears in the higher frequency regime (kh ≈ 2.2), reflecting the primary water column resonance and the contribution of coupled structural responses, respectively. Comparison with wave-basin measurements reproduces the principal CWR trend and resonance peak location, although the peak magnitude is overpredicted near resonance. The results clarify how body motion coupling and pneumatic damping jointly govern the transfer of incident wave energy into pneumatic power and provide a practical framework for resonance tuning and preliminary performance optimization of OWC systems. Full article

Pedestrian-induced vibration is a critical serviceability concern for flexible structures such as footbridges and long-span floors. Existing human–structure interaction models commonly rely on single-degree-of-freedom simplifications and time-domain simulations, making them less suitable for frequency-domain analysis. This paper proposes a spectral analysis model for crowd-structure interaction vibration under unrestricted pedestrian traffic. The structure was formulated as a multi-degree-of-freedom modal system, whereas each pedestrian is represented by an independent spring–mass–damper system. To address the time-varying nature of moving crowds, a piecewise stationary assumption was introduced: the continuous walking path was discretized into fixed position groups, within each of which a time-invariant coupled equation of motion was established. The response spectra obtained for different position groups were combined using residence-time weighting, thereby allowing nonuniform walking speeds to be considered. The corresponding frequency response function was derived using the state–space method, and the structural acceleration power spectral density and root mean square responses were obtained by incorporating an unrestricted crowd walking load spectral model. Comparisons with field measurements from two footbridges demonstrated reasonable agreement. The resulting framework offers an efficient frequency-domain approach for vibration serviceability assessment under unrestricted pedestrian traffic. Full article

A one-dimensional Thue–Morse graphene photonic crystal (1D TMGPC) composed of alternating identical dielectric layers and graphene sheets is proposed, in which two distinct graphene chemical potentials are arranged according to a Thue–Morse quasi-periodic sequence. Using the transfer matrix method, we demonstrate that this structure effectively modulates terahertz waves and generates multiple abundant photonic bandgaps at both 20 K and 300 K. Notably, a novel splitting of low-frequency bandgaps produces two additional omnidirectional and polarization-insensitive bandgaps centered at approximately 1.45 THz and 1.95 THz. By analyzing the dispersion relations, reflection phase, photonic density of states, and electric field distributions, the boundary-driven modulation mechanism associated with the quasi-periodic chemical potential is elucidated. Furthermore, the proposed structure exhibits excellent multi-dimensional tunability. The bandgap properties can be dynamically tuned via the electrical control of graphene chemical potentials without altering the physical geometry. Structural tailoring provides an additional degree of freedom, as increasing the Thue–Morse sequence order induces passband splitting. Additionally, increasing the number of repeating periods yields comb-like multi-channel narrowband filtering responses. At a cryogenic temperature of 20 K, two distinct multi-channel narrowband comb filtering responses appear in the frequency ranges of 1.20–1.33 THz and 4.10–4.80 THz, with a minimum full width at half maximum (FWHM) of 1.10 GHz. At a room temperature of 300 K, the higher-frequency comb filtering response remains in the range of 4.10–4.80 THz, with a minimum FWHM of 5.70 GHz. Moreover, we evaluate the performance and stability of the structure when employed as filters and electro-optic switches, thereby providing useful insights for terahertz applications. With its simple geometry, abundant bandgaps, and flexible electro-structural tunability, the proposed 1D TMGPC is highly promising for broadband and electrically tunable terahertz devices. Full article

This work presents the first complete system for automated six degrees of freedom (6DOF) satellite pose estimation from spatially resolved, ground-based, adaptive optics (AO)-corrected imagery, addressing a key challenge in Space Domain Awareness (SDA). The approach mitigates the need for human labeling by directly regressing satellite orientation and position from blurry, noisy, and deeply shadowed imagery. A multi-stage deep neural network pipeline localizes the satellite, predicts pose, and optionally applies temporal filtering. Networks are trained exclusively on fully synthetic imagery generated from a CAD model, yet generalize effectively to real data, bridging the Sim2Real domain gap. On 137 real, human-labeled test images of Seasat, the model achieved a mean rotation error of $5^{°}$ and a mean image-plane translation error of 21 cm. Slant range error was quantitatively evaluated on synthetic data due to unknown real-sensor parameters. Qualitative evaluation of additional real Seasat imagery rated 177 of 199 predicted poses as “ground truth equivalent” or “high-confidence match,” with zero catastrophic failures. The system was extended to seven degrees of freedom (7DOF) for satellites with articulating components and demonstrated on real Hubble Space Telescope (HST) imagery, achieving ${5.5}^{°}$ rotation error, 51 cm image-plane translation error, and $8^{°}$ symmetry-adjusted solar array error on a 249-frame pass with causal temporal filtering. Across 586 real test images from Seasat and HST (captured over multiple decades under diverse conditions) the system consistently performed well. Full 6DOF performance was quantified on a high-fidelity wave optics (HFWO) synthetic test set of Seasat, where the model achieved ${8.4}^{°}$ mean rotation error, 34 cm image-plane translation error, and 1.4% line-of-sight range error at $r_0=6$ cm and 1031 km range. In a limited 200-image benchmark, the model demonstrated 48% lower mean rotation error than a single human labeler while operating ∼800× faster. It required <40 h and a single A100 GPU to generate data and train. The approach was also demonstrated for ARGOS, a smaller satellite with highly symmetric geometry. An exploratory General Image-Quality Equation-based image quality metric (AO-IQ) was introduced as an empirical correlate for pose accuracy. General-purpose models like GPT-4o and Depth Anything V2 failed across most SDA tasks, but rapid gains in vision-language models warrant continued monitoring. These results establish a new operational baseline for practical, real-time satellite pose estimation from AO SDA imagery. Full article

Recently, microgrid (MG) structures include a mix of renewable energy sources (RES) and conventional sources. At high levels of RES penetration, reduced inertia and frequency stability have been confirmed in several studies. Properly designed and structured load frequency control (LFC) and virtual inertia control (VIC) are feasible solutions to these problems. In this paper, a new hybridized two-degree-of-freedom (2DOF) non-integer controller is proposed for multi-generation, multi-area MGs’ frequency regulation. The proposed new LFC is based on a 2DOF tilt-integral/tilt-derivative-double-derivative controller with a filter (TI-TD²F²). Meanwhile, the proposed design process considers coordinating capacitive energy storage (CES) to help regulate frequency deviation, as well as the high penetration of RESs (wind and PV). The incorporation of CES participation in frequency regulation helps provide fast VIC for the studied multi-MG system. Furthermore, an Enhanced Escape Algorithm (EESC) optimization algorithm is proposed to simultaneously optimize the control parameter set of the two-area MG system. The proposed EESC optimization algorithm identifies appropriate parameters for controller design, yielding better overall dynamic performance. An enhanced Escape Algorithm (EESC) is based on boosting the searching mechanism of the conventional Escape Algorithm by the integration of three modifications, including the Chaos map logistic mutation mechanism, the Fitness distance balance mechanism, and the Sorted Quasi-oppositional based learning (SQOBL). The proposed 2DOF TI-TD²F² controller demonstrates improved frequency stability and sustainable operation under load changes, variation in RESs, and other uncertainties of system parameters. The obtained results showed that the proposed EESC optimization algorithm adjusts the parameters of the TI-TD²F² controller, which significantly improves the dynamic performance in load frequency and tie-line power control. Compared to traditional TID and FOPID controllers, TI-TD²F² achieves up to a 70–80% reduction in tie-line power deviation and up to 60% faster settling time in many scenarios, demonstrating better robustness, faster response, and better overall system stability. Full article

Conventional integer-order parameter designs of grid-forming inverters provide limited degrees of freedom for impedance adjustment, motivating the exploration of additional approaches for flexible impedance reshaping across different frequency ranges. This paper establishes a full fractional-order grid-forming inverter (FFO-GFMI) by incorporating fractional-order inductor-capacitor (LC) filters, corresponding decoupling control, and fractional-order multi-loop controllers into a conventional grid-forming inverter. Based on the harmonic linearization method, positive- and negative-sequence impedance models of the FFO-GFMI are developed to characterize its broadband impedance characteristics. The developed models are validated through impedance scanning, and the effects of fractional-order parameters on broadband impedance characteristics are systematically investigated. The results reveal that fractional-order LC filters mainly regulate medium- and high-frequency resonance characteristics, while fractional-order control loops provide effective low- and medium-frequency impedance reshaping. Furthermore, load-step simulations demonstrate that the selected fractional-order configuration improves dynamic performance, reducing the active power settling time from 0.3121 s to 0.1974 s and the active power overshoot from 19.75% to 4.51%. Full article

In response to issues such as axial vibration, attenuation of drilling pressure transmission and increased impact loads on components near the drill bit that frequently occur during long-distance drilling in near-horizontal directional boreholes in underground coal mines, a multi-degree-of-freedom axial vibration model for directional long-hole drill-string systems has been established based on structural and stress analysis of the drill-string system. The model accounts for borehole-wall friction, buoyancy correction, self-weight, Rayleigh damping, drilling pressure input, and the velocity interaction between the drill bit and the coal–rock formation, and employs numerical integration to solve for the displacement, velocity, and spectral response of the drill bit and the pulse probe. The results indicate that an increase in the friction coefficient widens the vibration envelope, whilst the principal frequencies remain concentrated at approximately 5 Hz and its harmonics. When the drilling pressure is increased from 80 kN to 110 kN, the response increases gradually, and under high-pressure (120 kN) and heavy-duty drilling tool combinations, the displacement and velocity are significantly amplified; when the drill-string length was increased from 400 m to 550 m, the system’s response shifted from a relatively regular periodic response to a low-frequency, multi-peak response with amplitude modulation. The velocity response of the pulse probe was generally higher than that of the drill bit, indicating that it is a component sensitive to axial impacts near the drill bit. The research findings provide a theoretical basis for optimising drilling pressure, controlling frictional resistance and designing vibration-damping drill-string configurations for long directional boreholes in coal mines. Full article