Fankai Meng

Small catamaran unmanned surface vessels (USVs) under wave action experience continuous roll and pitch, causing the solar irradiance on deck-mounted photovoltaic (PV) panels to vary and thereby affecting power output. The quantitative effect of wave-induced hull motion on PV power fluctuation and daily energy yield remains insufficiently quantified, and the separate contributions of roll and pitch remain unquantified. We developed a coupled PV power simulation model for a catamaran USV and applied it to six scenarios combining three sea states (Hs = 0.6, 1.0, and 1.5 m) with two wave directions (0°and 90°). Under the simulated clear-sky conditions, the attitude-induced daily energy loss rate did not exceed 1.3% across all scenarios and remained below 0.2% in following seas. Wave direction strongly controlled the power output characteristics: at a given sea state, the coefficient of variation of power under beam seas was 2.3–2.8 times that under following seas, and the maximum loss rate was 6.5 times the corresponding following-sea value. The realized motion contribution was wave--dependent, with roll dominating under beam seas and pitch dominating under following seas. Under the prescribed equal-amplitude motions, roll exhibited approximately five times the fluctuation sensitivity of pitch, whereas the dominant contribution under irregular waves depended on wave direction. Power fluctuation followed a diurnal pattern, stronger in the early morning and late afternoon and weaker around midday. These results suggest that roll mitigation may be prioritized in PV system design for catamaran USVs, while reducing beam-sea exposure may be considered in route planning to improve power stability.

An improved availability–dependability–capability (ADC) assessment framework is proposed for evaluating the mission effectiveness of solar-powered unmanned surface vehicles (USVs) under the coupled effects of hardware state transitions and stochastic energy supply. Within the availability and dependability dimensions, a joint state space is constructed that couples hardware condition states with battery state of charge (SOC). A Monte Carlo simulation driven by real solar irradiance data is used to derive the initial probability distribution and the dynamic state transition matrix. In the capability dimension, a hierarchical index system is established, and a hierarchical Criteria Importance Through Intercriteria Correlation (CRITIC) method is introduced to achieve objective weighting that accounts for inter-index correlations across multiple levels. Case-study calculations for a typical task profile yield a baseline mission effectiveness of approximately 0.661934. Comparative analysis reveals that neglecting the dynamic evolution of the energy state overestimates effectiveness by 38.94%, whereas ignoring random hardware failures produces a deviation of roughly 9.48%. These findings indicate that, while energy-state dynamics impose the dominant constraint on mission performance, the contribution of hardware degradation remains substantial. The concurrent influence of both limiting factors confirms the necessity of an assessment framework that explicitly integrates hardware and energy states, as developed in this work.

A heat pipes-cooled thermoelectric cooling channel structure is proposed and the thermodynamic model is established based on the finite-time thermodynamics theory. With refrigeration flux and the coefficient of performance (COP) as the performance indexes, the influence of key operating parameters such as working current and inlet temperature and design parameters such as thermoelectric module parameters and heat pipe parameters on the cooling performance of the device is analyzed by numerical simulation. In addition, this paper also compares the refrigeration performance of the heat pipe-cooled thermoelectric cooling channel and the air-cooled thermoelectric cooling channel under the same working conditions. The results show that the maximum refrigeration flux and maximum COP of the heat pipe-cooled thermoelectric cooling channel are 0.517 “W∙” 〖“cm” 〗^“-2” and 1.245, respectively. The results are 154.60 % and 42.30 % higher than those of the air-cooled thermoelectric cooling channel.

A detailed model of heat pipe-cooled two-stage thermoelectric (TE) air conditioner is established. The performance is analysed comprehensively including the cooling power, coefficient of performance (COP), thermodynamic perfectibility and extreme temperature difference. The influences of key parameters including working current, distribution ratio of TE elements and heat pipe parameters are analysed by numerical simulation. The working current and the TE element number ratio are optimized for the maximum cooling power and the maximum COP respectively. The influences of the cross-sectional area, the length of the TE element and the temperature difference on the optimal variables and optimal performance is obtained. The results show the refrigeration performance of the TE air conditioner can be effectively improved by heat pipe cooling. The two-stage mode can effectively improve the refrigeration temperature difference. The extreme temperature difference can be improved from 60 K to 110 K.

A model for the quantum Brayton refrigerator that takes the harmonic oscillator system as the working substance is established. Expressions of cooling load, COP and ecological function are derived. With numerical illustrations, the optimal ecological performance is investigated. At the same time, effects of heat leakage and quantum friction are also studied. For the case with the classical approximation, the optimal ecological performance, and effects of heat leakage and quantum friction are also investigated. For both general cases and the case with classical approximation, the results indicate that the ecological function has a maximum. The irreversible losses decrease the ecological performance, while have different effects on the optimal ecological performance. For the case with classical approximation, numerical calculation with friction coefficient and heat leakage coefficient shows that the cooling load (R_E) at the maximum ecological function is 6.23% smaller than the maximum cooling load (R_max). The COP is also increased by 12.1% and exergy loss rate is decreased by 27.6%. Compared with the maximum COP state, the COP (ε_E) at the maximum ecological function is 0.55% smaller than the maximum COP (ε_max) and that makes 7.63% increase in exergy loss rate, but also makes 6.17% increases in cooling load and 6.20% increases in exergy output rate.