By adjusting the signal demodulation architecture and optimizing the control circuit configuration, the phase errors of the Coriolis gyroscope can be substantially mitigated. However, these approaches fail to account for the influence of phase asymmetry error on gyro performance. This article proposes a self-calibration method for phase errors based on virtual precession. First, a dynamic analysis model is established to examine the impact of x / y -channel phase errors and their asymmetry on the gyro control system. Second, the phase errors are decoupled from resonator structural errors via forward-reverse rotation modulation. Building on this, a real-time characterization method for phase errors that utilizes the evolution law of quadrature control voltage is developed. Finally, based on the identification results, a self-calibration method for phase errors is designed to offset the phase delay of the control system from the signal processing perspective. Experimental results demonstrate that after self-calibration, the second and fourth harmonics of the gyro output at different rotational speeds are reduced by 98.85% and 89.58%, respectively. Additionally, the scale factor nonlinearity (SFN) and circumferential drift instability are reduced by 95.40% and 97.52%, respectively. This method is not constrained by the gyro structure and the x / y -channel control strategy, making it broadly applicable to other axisymmetric Coriolis vibratory gyros.

Three-dimensional conjugate simulations were conducted to investigate saturated flow boiling in a rectangular mini-channel, with particular emphasis on the role of inlet Reynolds number on boiling mode selection and transition. A C++ based open-source numerical framework was employed, incorporating a physically informed multi-site nucleation model by coupling a nucleation site density correlation with a Halton-sequence based spatial allocation strategy. Two distinct Re-dependent transition pathways were identified. At low Re, boiling transition is mainly associated with localized dryout development associated with upstream active boiling and progressive downstream liquid starvation. At high Re, the transition is characterized by convective stretching and reorganization of vapor structures, through which elongated vapor slugs evolve into localized vapor films and eventually approach full surface vapor coverage. The global heat transfer characteristics and peak heat transfer capacity are further interpreted in conjunction with boiling mode transition, clarifying the respective roles of wall dryout and volumetric vapor fraction in heat transfer deterioration. Among all cases, Re=2000 provides the most favorable overall thermal response. Overall, within the rectangular mini-channel configuration and operating range considered in this study, Re is closely associated with vapor organization, boiling transition, wall dryout, and global heat transfer performance.

The Hemispherical Resonator Gyroscope (HRG) demands strict symmetry between its orthogonal detection channels to maintain high-precision measurement. While singlechannel closed-loop time-division multiplexing (TDM) circuits effectively eliminate analog gain mismatch and phase delay drift, the inherent asynchronous signal acquisition introduces a fixed time lag between the $X$ and $Y$ channels. Under highly dynamic angular velocity inputs, this time mismatch translates into a significant azimuth-dependent periodic error, severely deteriorating the scale factor linearity. To address this issue without escalating the hardware sampling rate, this paper proposes a high-precision real-time synchronization strategy utilizing a Farrow-structured Fractional-Delay Filter (FDF). By digitally reconstructing and shifting the leading channel sequence using cubic Lagrange interpolation, virtual simultaneous sampling is achieved. The Farrow structure decouples the fractional delay parameter from the filter coefficients, enabling a resource-efficient implementation suitable for embedded FPGA. System-level simulations demonstrate that the proposed FDF compensation effectively suppresses the dynamic tracking error. Specifically, the angular velocity output error under a $500^{\circ} / \mathrm{s}$ dynamic input is significantly reduced from over $\mathbf{4 0 ~ p p m}$ in conventional alternating demodulation to less than 2 ppm. The proposed method substantially enhances the dynamic performance and fullscale linearity of TDM-based HRGs, offering a robust solution for high-bandwidth inertial navigation applications.

The performance of the hemispherical resonator gyro (HRG) in whole-angle (WA) mode is affected by the angle-dependent harmonic drift. Suppressing this drift is essential to improve its temperature stability and operational range. In this article, a novel real-time method for eliminating harmonic drift based on a forward and reverse precession (FRP) control scheme is proposed. First, the sources of harmonic drift in HRG are analyzed. The HRG dynamical equations incorporating multiple error sources are derived and analyzed through numerical simulation. Subsequently, a real-time error identification algorithm is developed and validated through simulation. Finally, a temperature experiment is conducted to validate the method. The experimental results demonstrate that the proposed method can accurately identify and compensate for errors at different temperatures, effectively suppressing the harmonic components in angular velocity by more than 97%. The bias instability (BI) of the HRG remains consistently around 0.024(degrees)/h across various temperatures, indicating strong temperature stability. Additionally, the scale-factor nonlinearity (SFN) is reduced fivefold to 0.84 ppm. Most importantly, this method can be applied to all Coriolis vibratory gyroscopes to effectively eliminate their common angle-dependent harmonic drift.

The high quality factor of Hemispherical Resonator Gyroscopes (HRGs) significantly reduces thermoelastic noise but introduces severe challenges for closed-loop startup. Due to the extremely narrow bandwidth, traditional Phase-Locked Loop (PLL) with linear frequency sweeping suffers from the chirp effect, leading to prolonged energy accumulation times or complete capture failures. To address this bottleneck, this paper proposes a rapid startup and robust synchronization control strategy based on nonlinear self-excitation. First, a phase-compensated hard-limiter feedback loop is designed to spontaneously lock onto the mechanical resonance, maximizing energy injection and entirely eliminating the frequency-searching overhead. Second, to prevent transient mechanical shocks during the transition to steady-state operation, a discrete-time bumpless mode-switching logic is formulated. By implementing a dual-criteria evaluation comprising amplitude thresholds and background phase pre-synchronization, the system achieves a mathematically continuous handover to a linear Digital PLL (DPLL) with Automatic Gain Control (AGC). The proposed architecture effectively decouples the startup speed from the steady-state precision, offering a highly robust digital control solution for high-performance vibratory gyroscopes.

The standing wave of the whole angle mode hemispherical resonator gyroscope is in a free precession state. To achieve high accuracy and a wide measurement range, it is necessary to compensate for the drive error to reduce the control force output error and standing wave drift. In this paper, we propose an error parameter identification and compensation method for the drive error, including gain mismatch, electrode angle alignment error, and X/Y channel phase delay. Firstly, we fully elucidate the mechanism of drive error caused by manufacturing and X/Y circuit channel parameter mismatch. Secondly, the drive error is modeled and its impact on the standing wave azimuth and each control loop is analyzed. Thirdly, we present a high-precision error identification method based on the error model that is not affected by the inherent error of the resonator, such as damping anisotropy drift. Finally, a series of experiments are carried out to verify the accuracy of the proposed method for error parameter identification and the effectiveness of the method for HRG performance enhancement. The bias instability of the tested HRG decreases by 4 times from 0.0277 degrees/h to 0.0071 degrees/h, and the scale factor nonlinearity decreases by 5 times from 3.92 ppm to 0.72 ppm.

The vector control method is applied to a whole angle hemispherical resonator gyroscope (HRG). The detection and control of the resonator vibration state are implemented using orthogonal X/Y channels. However, the performance of the HRG is limited by the asymmetry in the gain and phase delay of X/Y channels. To address these issues, a novel detection circuit is proposed. The circuit leverages the closed-loop characteristics to achieve symmetry and stability in the X/Y channel gain while simultaneously eliminating phase delays within the loop. Firstly, a closed-loop single-channel time division multiplexing circuit is designed to overcome the deficiencies of the traditional dual-channel circuit. Secondly, a model is developed to analyze the time division detection errors, and an improved demodulation method is proposed to mitigate detection errors. Lastly, experimental results demonstrate that the designed circuit successfully suppresses drift in both gain and phase delay within the loop, confirming the effectiveness of the proposed solution in enhancing the performance of the HRG.

Variable-stiffness actuators can flexibly adjust the overall or local stiffness of a structure, thus enabling reconstruction, adaptation, and locking capabilities that can meet a wide range of task requirements. However, the programmable design and manufacture of three-dimensional (3D) variable-stiffness actuators has become a challenge. In this paper, we present a method to develop the 3D structure of variable-stiffness actuators that combines variable-stiffness joints with 3D printing technology. The variable-stiffness joints were obtained by arranging steel needles wrapped with enameled copper wire inside the grooves of a polylactic acid (PLA) structure and bonding the three components with silicone glue. First, a variable-stiffness joint was used as a variable-stiffness node and subjected to 3D printing to realize multiple 3D variable-stiffness designs and manufacture a programmable structure. Then, using the repulsive force between paired magnets, we developed a driving actuator for the 3D variable-stiffness structure, enabling the expansion and deployment functions of the structure. In addition, an electromagnetically driven mechanical gripper was designed based on variable-stiffness joints to effectively decrease the driving energy in applications where objects are held for extended periods using variable-stiffness control. Our study provides practical solutions and guidance for the development of 3D variable-stiffness actuators, contributing to the achievement of more innovative and practical actuators.

Centimeter-scale underwater robots have important applications in underwater resource exploration, environmental monitoring, equipment fault diagnosis, and military applications. However, developing small underwater robots remains a challenge because of the limitation of miniaturized structures. In this study, we developed a small underwater robot (JR) with high-speed, inspired by the jellyfish ephyra, composed of a dish-shaped wing, a flexible joint, a rigid support, a semicircular air chamber, with a magnet and a coil integrated as the driving source. Robot JR combines the advantages of electromagnetic drive, flexible structures, miniaturization of the jellyfish robot is realized and high-speed swimming. The size of robot JR was only Φ 5 × 3 cm, which is the smallest besides the jellyfish robot driven by an external magnetic field. Meanwhile, its maximum movement speed reached 4.6 BL/s, which is also considerably faster than that of other jellyfish robots. The design and control strategies of our research will provide a reference for future design and lay a solid foundation for the practical use of small underwater robots.

With the development of science and technology and the continuous exploration of the deep universe, the heat dissipation capacity of space radiant coolant is required to be enhanced accordingly, which leads to the increasing mass of spacecraft and the decline of economy. Heat pipe technology is widely used in aerospace science and technology because it has good thermal conductivity and can realize fluid flow and heat transfer without external power. The alkali metal heat pipe radiator has the advantages of high thermal conductivity, strong anti-collision performance and strong single point failure resistance, which is unparalleled in other radiators. In this paper, finite difference method and iterative method are used to study the influence of fin width, inlet temperature, condensing length of heat pipe and other variables on the radiator weight, and the mechanism is analyzed. Using the analysis method of the combination of the first law and the second law of thermodynamics, the irreversible mechanical energy loss of the coolant in the coolant pipe is related to the entropy production, so as to further analyze the heat transfer characteristics of the two inlet - two outlet radiator.

Compensation for the hemispherical resonator gyroscope (HRG) detection error significantly improves gyroscope performance as well as provides a basis for the implementation of high-precision control algorithms. In this article, an identification method is proposed in which the precession factor and the detection error parameters, including gain error, nonorthogonal angle error, and phase error, can be identified simultaneously in a single test. First, we analyze the detection error caused by gyroscope manufacturing as well as the inconsistency in circuit device parameters. Second, the detection error is modeled, and the impact of the error on the standing wave azimuth detection and the control system is discussed. Third, a method is presented for identifying the error parameters based on the nonlinear least squares. Finally, experiments are conducted to verify the effectiveness of the identification and compensation method. As a result of compensation, the bias instability decreases by 33 times from 5.08°/h to 0.15°/h, and the scale factor nonlinearity decreases by four times from 50.26 to 10.23 ppm.

Silicon thin films have important applications in the electronics and nanotechnology industries, and with the miniaturization of electronic devices, the importance of thermal protection for electronic devices is increasing. The researchers have successfully constructed thermal cloaks based on silicon films through amorphization, perforation, and concave to achieve heat flux regulation. The key to designing a thermal cloak is to use appropriate means to construct a functional region with low thermal conductivity. Our recent research has found that the thermal conductivity of periodically convex silicon films is lower than that of perfect silicon films, and no thermal cloaks have been constructed using this method. Therefore, in this paper, a thermal cloak is constructed using a periodically convex structure and compared with a thermal cloak of the same concave depth. By calculating the ratio of thermal cloaking (RTC), we find that cloaking can be produced using the convex structure, but is less effective compared to the concave structure, mainly because the base film is a perfect silicon film, which does not affect the heat flux transmission. Finally, we use phonon localization theory to explore the underlying mechanism. By calculating the mode participation rate (MPR), we find that phonon localization in the functional region is the main reason for cloaking, and the low-frequency phonon modes contribute more to the cloaking efficiency. Our study can provide experience for the design of nanoscale thermal cloaks.

Due to high output power, long lifetime, high efficiency, and compact structure, the space nuclear power (SNP) system is considered an ideal choice for future large-scale and deep space missions. The system's mass, volume, and thermoelectric conversion efficiency directly affect and determine the system's performance compared with ground nuclear devices. The mass of the space nuclear power system is a vital parameter due to the limitation of cost, volume, and transportation. This study designed and optimized the recompression supercritical with nitrous oxide and helium (N2O-He) Brayton cycle with a small modular reactor for mass. Each Brayton cycle component model was developed to estimate the cycle performance systematically. The mass estimation model of the Brayton system includes a nuclear reactor, radiation shadow shield, Brayton cycle unit, recuperator, and radiator. A small modular reactor was designed to predict the minimum mass reactor suited to the given cycle conditions. The system mass optimization explored the trade-offs between the reactor, radiation shield, Brayton cycle unit, recuperator, and radiator to obtain the minimum mass of the space nuclear energy system to satisfy the operating requirements. Sensitivity parametric investigations are considered to evaluate the effects of crucial decision variables on the whole Brayton cycle mass. Furthermore, multi-objective optimization is performed to find optimum operating parameters to minimize the system mass. The results illustrate that the specific mass of the system is less than 20 kg/kW. The total mass of the whole system is 5605.93 kg using near-term materials, of which the Baryton Rotating Unit, radiator, and shadow shield mass dominate the total mass. The Brayton Rotating Unit, radiator, and radiation shield account for 44.64%, 32.53%, and 14.29%, respectively. It is concluded that after the dual-objective optimization analysis, the mass of the cycle decreased by 18.44%, which used the existing technical materials.

The impact of wind power integration on power system voltage stability has received extensive attention recently. A new voltage stability H-index based on the Norton’s current distribution law is established, which could be quickly calculated by phasor measurement unit (PMU) data. For steady-state analysis, the voltage stability margin could be directly assessed by computing the difference between H-index and 1. Applicability of the proposed H-index is validated in the case of reverse power flow, i.e. the active power is transmitted from wind farms to the point of common coupling (PCC). Then, the characteristics of H-index with increased wind power are analyzed. Based on the relationship between H-index and wind farm current injection, an online voltage stability monitoring method is presented. In this monitoring process, three important currents are proposed to be mainly monitored along with the H-index, namely the ‘worry current’, ‘transition current’ and ‘limit current’. Therefore, the voltage stability analysis and control strategies can be implemented according to the monitored currents and H-index. Effectiveness of the proposed online voltage stability analysis method is further verified by simulation results performed in an improved 39-bus system.

Nanoscale thermal cloaks have great potential in the thermal protection of microelectronic devices, for example, thermal shielding of thermal components close to the heat source. Researchers have used graphene, crystalline silicon film, and silicon carbide to design a variety of thermal cloaks in different ways. In our previous research, we found that the porous structure has lower thermal conductivity compared to bulk silicon; thus, so we tried to use the porous structure to construct the functional region to control the heat flux. We first calculated the thermal conductivity of crystalline silicon and porous silicon films by means of nonequilibrium molecular dynamics, proving that the porous structure satisfied the conditions for building a thermal cloak. A rectangular cloak with a porous structure was constructed, and a crystalline silicon film was used as a reference to evaluate its performance by the index of the ratio of thermal cloaking. We found that the thermal cloak built with a porous structure could produce an excellent cloaking effect. Lastly, we explain the mechanism of the cloaking phenomenon produced by a porous structure with the help of phonon localization theory. Porous structures have increased porosity compared to bulk silicon and are not conducive to phonon transport, thus producing strong phonon localization and reducing thermal conductivity. Our research expands the construction methods of nanocloaks, expands the application of porous structure materials, and provides a reference for the design of other nanodevices.

The fuel assembly of sodium-cooled fast reactor (SFR) is considered a compact heat interchanger with the intricate flow. The wire-wrapped make a great difference on the secondary flow and transverse momentum mixing. The investigations on fully developed convective heat transfer in a 7-pin fuel bundle with wrapped-wire are conducted for particular Reynolds number from 2 x 10(4) to 2 x 10(5), and heat flux at 500 to 1500 kW/m(2) employing commercial computational fluid dynamic (CFD) code based on the finite volume method (FVM). The SST k-omega turbulent model and periodic boundary conditions are adopted at the inlet and outlet to obtain the fully developed fluid field and capture the detailed information in the near-wall region. The model validation and mesh independence verification are conducted, and the maximum error is 10.3%. The results are analyzed in view of sensitivities of secondary flow and thermodynamic irreversibility to mass flow rate and heat flux from the local and systemic scales by means of the entropy generation analysis approach. The axial profiles of secondary flow and entropy generation rate under different working conditions are studied. The results indicate that due to the helical structure of the wrapped-wire, the secondary flow, and entropy generation present similar periodical fluctuation and symmetric distributions in axial direction. Also, the secondary flow enhance has an impact on the heat transfer. The thermal irreversibility is also analyzed, and the result shows that heat conduction is the leading cause of the irreversible losses. Ep decreases with the Reynolds number, and increases with heat flux, which means the better thermal economic performance occurs at lower velocity and higher heat flux.

The hemispherical resonator and the electrode base are prone to tilt and eccentricity during the assembly process, which greatly restricts the working accuracy of gyro. In order to reduce this impact, the influence of the resonator assembly error on gyro drift under different electrode configuration schemes is analyzed. Secondly, an error parameters identification method based on nonlinear optimization is proposed, which can realize the synchronous identification of the two channels' gain ratio and misalignment angle. Finally, a signal demodulation compensation scheme is designed to compensate the error parameters. The experimental results show that after the feedforward compensation, the angular rate oscillation amplitude under dynamic conditions is reduced by two orders of magnitude, and the bias stability of gyro output is improved by 5 times.

Future space exploration is now focused on new field-deep space planets. Deep space exploration and the development and utilization of resources are inestimable strategic significance for the country to seize the initiative and command heights of deep space exploration. Nuclear electric propulsion (NEP) systems convert heat from the fission reactor to electrical power and then use the electrical power to produce thrust. Compared with traditional propulsion technology, the NEP system with variable Isp can be used for several applications. The NEP spacecraft is more suitable for deep space exploration missions due to the advantages of high specific impulse, high power, and long life. This paper analyzes the relationship between the transfer travel time, specific mass, power, and payload ratio of the NEP spacecraft through simple performance models. Use the mass optimization and specific mass optimization models based on the NEP system composition and small thrust orbit theory to maximize the payload ratio for a given transfer time and technological characteristics. Finally, applied this NEP model to discuss the feasibility of Mars, Jupiter, and Saturn transfer missions and compared it with the Tianwen-1, Juno, and Cassini-Huygens Cassini–Huygens spacecraft, respectively. Results show that when the NEP spacecraft specific mass reaches 4.77 kg/kW, the Earth–Mars transfer time can be changed to 331.31 days, the payload increases to 1650 kg, the transfer time for Jupiter and Saturn mission would be shorted to 661.31 days and 1131.31 days, the corresponding payload significantly increases which achieved to 1270 kg and 2981 kg. The nuclear electric propulsion spacecraft dramatically improves the detection capability of the spacecraft and provides a reference for the feasibility demonstration and subsequent design of the deep space and the extrasolar planet exploration.

Long life, high energy density, high efficiency, and compact power system is necessary for space exploration to achieve a future goal. Recompression supercritical Brayton cycle has excellent potential for application of space nuclear power generation systems. However, it faces the choice of cycle working fluid which limits the cycle thermal efficiency and quality. In order to improve the thermal efficiency of the nuclear power system, a new composition of the working fluid, nitrous oxide and helium (N2O-He) mixture is used in the system. Comprehensive studies and optimization are performed for the significant parameters, including the split ratio, pressure ratio, minimum operating temperature, maximum operating temperature, and minimum operating pressure. Optimum values have been obtained at which the maximum thermal efficiency and minimum Brayton rotating unit (BRU) mass of the cycle occur. Results show that the thermal efficiency improves with an increase in the split ratio, main compressor pressure ratio, and maximum operating temperature, and decreasing minimum operating temperature and minimum operating pressure. The proposed novel working fluid cycle has superior performance compared with N2O (deviation of 5.1%) and CO2 (deviation of 6.5%). The optimized thermal efficiency and BRU mass are calculated as 42.67% and 3584.80 kg at optimum conditions. (c) 2021 Published by Elsevier Ltd.

The weight of radiator affects the launch weight of spacecraft and the feasibility of engineering development. Heat pipe radiator is widely used in space heat emission because of its strong resistance to single point failure and excellent heat transfer performance. This paper analyzed the sensitivity of fin width, inlet temperature, condensing section length and coolant mass flow of a direct contact heat pipe radiator are analyzed on four types of heat pipe radiators. The optimal design parameters of two inlet - two outlet radiator are obtained by double objective optimization, and the optimal design parameters are L-f = 0.0893 m, Tf11 = 697.8371 K, l(hpc) = 0.7736 m, q(m) = 8.9184 kg/s. ANSYS fluent 19.0, a CFD code is used to simulate the flow and the heat transfer characteristics of radiator with the best design parameters. Which indicates the intersection of coolant pipe and annular pipe of the radiator should be thickened, and the fin shape should be optimized along the direction of the fin isotherm.