Current Issue : April-June Volume : 2026 Issue Number : 2 Articles : 5 Articles
The growing interest in high-power amplifiers for the teraherz (THz) radar system leads to significant performance improvements of THz wave traveling-wave tubes (TWT). This article presents a detailed development of a G-band pulsed wave TWT with 120·W output power. Three approaches have been combined to improve the tube’s output power including proposing the modied folded waveguide (MFWG) slow wave structure (SWS), using large beam current, and adopting phase velocity tapering (PVT). Firstly, the MFWG SWS circuit has an additional degree of freedom that can be used to achieve approximately 36% higher interaction impedance than that in the conventional folded waveguide (CFWG). Subsequently, the electron beam current was increased to approximately 100 mA to boost the DC power of the electron beam. Finally, the PVT technology dramatically enhanced the output power from 98 W to 143 W, concomitant with a notable increase in electronic eciency from 4.75% to 7.03%. Hot experimental results show that the measured output power can be over 100 W at 20% duty cycle within a bandwidth of 5 GHz when the operation voltage and the current are 22.48 kV and 103.5 mA, respectively. In addition, the maximum power is 121 W with the corresponding electronic eciency of 5.1%. The proposed G-band 100 W TWT will have broad applications in far-distance highresolution imaging....
This work presents an experimental and theoretical study of a pitching point-absorber wave energy converter (WEC) equipped with a nonlinear stiffness mechanism (NSM) based on a pre-compressed spring. The mechanism is designed to reduce the equivalent restoring stiffness and enhance the device response without external control. A 1:13 scale prototype of the Lafkenewen WEC, deployed off Lebu (Chile), was tested in regular waves within a wave tank for two configurations: with and without the NSM. The rotational response amplitude operator (RAO) was obtained from experiments and compared against a linear hydrodynamic model formulated via Newtonian mechanics and frequency domain radiation/excitation coefficients. Dry friction at the hinge was represented as an equivalent viscous damping term identified iteratively. Unlike narrow-resonance WECs, both configurations exhibited a broadband response without a sharp resonance peak in the 0.7–1.2 Hz range, due to significant radiation damping and hinge friction. The NSM produced a moderate amplification of the rotational RAO (up to ∼32%) while preserving the broadband character. Theoretical predictions agreed with the measurements when dry friction was included. These results demonstrate that passive stiffness reduction via an NSM enhances wave–structure energy transfer even in systems dominated by effective damping and provides a consistent basis for future nonlinear time domain modeling and control-oriented studies....
Floating offshore wind–wave hybrid systems, as a novel structural form integrating floating wind turbine foundations and WECs, can effectively enhance the efficiency of renewable energy utilization when properly designed. A numerical model is established to investigate the dynamic responses of a wind–wave hybrid system comprising a semi-submersible FOWT and PA wave energy converters. The optimal damping values of the PTO system for the wind–wave hybrid system are determined based on an NSGA-II. Subsequently, a comparative analysis of dynamic responses is carried out for the PTO system with different states: latching, fully released, and optimal damping. Under the same extreme irregular wave conditions, the pitch motion of the FOWT with optimal damping is reduced to 71% and 50% compared to the latching and fully released states, respectively. The maximum mooring line tension in the optimal damping state is similar to that in the fully released state, but nearly 40% lower than in the latching state. This optimal control strategy not only sustains power generation but also enhances structural stability and efficiency compared to traditional survival strategies, offering a promising approach for cost-effective offshore wind and wave energy utilization....
The small waterplane area twin hull (SWATH) is a type of high-performance vessel known for its excellent seakeeping performance, remarkable maneuverability, and high lateral stability. These advantages have led to its growing application in scientific research ships. Since many research operations require a vessel to maintain a fixed position, Dynamic Positioning Systems (DPSs) are essential. To better support diverse scientific tasks, the R/V SHIYAN 1 was upgraded with an enhanced dynamic positioning system. A ship motion model was established after comprehensively accounting for environmental factors such as wind, waves, and currents. By automatically controlling three actuators, the system successfully achieved effective dynamic positioning. In comparative tests conducted under conditions of wind speed at 13.4 m/s, wave height at 3.2 m, and current at 0.2 m/s, the power system was able to maintain a positioning radius within 5 m. Analysis of data from three dynamic positioning experiments revealed that wave loads had the most significant impact on positioning accuracy, followed by wind loads, while ocean current loads had the least influence. This upgrade not only improves the vessel’s operational capability but also enhances its effectiveness in marine scientific exploration....
The growing demand for wind energy necessitates efficient health monitoring strategies to ensure the long- term reliability of wind turbines. Monitoring critical loads, such as flapwise blade root moments and tower base fore- aft moments, is crucial for preventing turbine fatigue and failure. However, direct measurements through physical sensors are costly, time- consuming, and limited to specific locations. This study introduces a probabilistic data- driven virtual sensing framework that uses multi- hidden Gauss- Markov model (Multi- HGMM) to estimate these loads by capturing the relationship between measurable quantities and key structural metrics, without requiring extensive physical sensors. An expectation–maximization algorithm is used to determine the HGMM parameters from a comprehensive dataset. This dataset includes routinely recorded SCADA data, such as wind speed, rotor speed, and pitch angles, along with additional key features that were carefully selected for their relevance to load estimation. In a subsequent stage that includes operational measurement data, the probabilistic HGMM can be used to estimate loads. We validate our approach on a 5- MW wind turbine model developed by the National Renewable Energy Laboratory (NREL), for above- rated wind speeds where turbines face heightened loads due to increased aerodynamic forces, critical for structural integrity. The results demonstrated that the multi- HGMM approach achieved a mean absolute error of approximately 6% for estimating both the tower base moment and flapwise moment when incorporating tower top accelerations and shaft bending moments alongside baseline features. By reducing reliance on physical sensors, this virtual sensing methodology offers a scalable, cost- effective solution for wind turbine monitoring....
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