We investigate unsteady hydrodynamics of a shaft-sealed reactor coolant pump (RCP) across cold/hot states (25 degrees C/292 degrees C; 1/15.9 MPa) and tip-clearance variations from the design tip clearance of 0.8 mm (0.5 mm smaller and 1.0 mm and 2.0 mm larger than the design value). Using SST k-omega CFD with rotor-stator coupling, we quantify performance, pressure-pulsation spectra, and radial forces. Dominant components occur at the shaft frequency (1fn approximate to 24.75 Hz) and diffuser blade-passing (5fn approximate to 123.75 Hz), with a leading-peak shift to 5fn near the impeller outlet. Hot conditions intensify pulsations and radial loading and smooth the performance curve; at similar to 1.2Q the hot-state head is similar to 5 % higher. The radial force shows periodic modulation (approximate to 3.22-3.42 kN) and a five-lobe pattern. Clearance changes alter head and spectra: +2 mm reduces head and elevates 5fn, whereas - 0.5 mm improves uniformity and still lowers head. These results provide a spectral-shift-load-coupled basis for clearance tolerance and operating-window selection to enhance RCP stability and safety.

The toroidal propeller, as an emerging propulsor configuration, has shown considerable potential in suppressing tip vortices; however, its cavitation performance has not yet been thoroughly investigated. In this study, a novel toroidal propeller was designed and manufactured, and its cavitation characteristics were systematically examined through a combination of experimental observations and numerical simulations. The hydrodynamic coefficients were measured across a range of advance coefficients, and, for three representative operating conditions, the complete evolution of cavitation-from inception to full development-was documented. The results reveal pronounced differences in both the inception location and the morphology of cavitation under varying advance coefficients, while in the fully developed stage, distinct tip vortex cavitation was consistently observed in the wake. Furthermore, a numerical model for predicting the cavitation performance of the toroidal propeller was established and validated against experimental data, demonstrating high predictive accuracy. Based on this validated model, the influence of vertical angle variations on cavitation performance was further investigated. The computational results indicate that fine adjustments to the vertical angle can effectively mitigate cavitation, thereby improving the overall cavitation performance of the toroidal propeller.

Cavitation generates abnormal excitation force in the internal flow field of the water-jet pump, and then induces the vibration of the pump body, which will directly threaten the navigation safety, stealth performance, and equipment service life of the ship. To accurately reveal the vibration mechanism of water-jet pump under different cavitation stages, the vibration acceleration signals of guide vane bearing foot and elbow bearing foot of water-jet pump are collected through vibration test, and the vibration characteristics of water-jet pump along the X -axis, Y -axis, and Z -axis are systematically analyzed. The findings indicate that the vibration acceleration spectrum characteristics are significantly affected by the cavitation intensity. The amplitude of the dominant frequency in the low frequency band is related to the frequency of the impeller blades, while the broadband signals in the high-frequency band are induced by cavitation. Additionally, the signal intensity of each frequency band increases with the development of cavitation, but the vibration acceleration is partially suppressed during the first critical cavitation stage. According to the analysis of vibration acceleration energy, the vibration energy at different measurement points and in different directions exhibits an upward trend with the cavitation development, but the variation pattern is different. These research outcomes offer critical experimental data and theoretical backing for studying cavitation-induced vibration mechanisms, and hold direct engineering significance for the design of water-jet systems.

Electronic throttle actuators operate under strong nonlinearities, parametric uncertainties, and time-varying disturbances, where discontinuous control actions may introduce chattering and undesired high-frequency oscillations that degrade tracking accuracy and aggravate mechanical excitation. This paper proposes an extended-state-observer-based discrete predictive sliding-mode control strategy (ESO-DPSMC) for sampled-data electronic throttle systems. A discrete-time tracking-error model is established via Euler discretization to support controller synthesis directly in the discrete domain. A discrete-time extended state observer is developed to reconstruct the lumped disturbance online, and boundedness of the observation error is analytically guaranteed. On this basis, an adaptive implicit discrete reaching law with a predictive term is designed to enhance robustness while attenuating chattering-related high-frequency components in the control action. Closed-loop analysis establishes stability and bounded tracking performance in the presence of uncertainties and external disturbances. Comparative experiments on an electronic throttle platform demonstrate improved tracking and disturbance rejection with smoother control action than conventional sliding-mode control, indicating effective suppression of high-frequency oscillations under complex operating conditions.

This paper introduced a novel adaptive continuous predefined-time sliding mode control method for fast and accurate tracking control of high-order nonlinear systems, addressing unknown uncertainties and disturbances. First, we proposed a continuous predefined-time disturbance observer, designed through the differentiation of the estimated value. Then, a hierarchical predefined-time sliding surface structure is presented, which consists of a recursive sliding surface and an additional integral sliding surface. Based on the proposed sliding surface, we presented a continuous sliding mode control law, which ensures chattering-free operation and enables tracking errors to converge within a predefined time. This is achieved through the use of observer information and the introduction of integrator component. To mitigate the impact of observer errors, we incorporated a bidirectional adaptive law. This law updates the switching control gain, ensuring practical predefined-time stability. The stability of the closed-loop tracking control system, guaranteed under predefined-time constraints, was demonstrated and analyzed using the Lyapunov theory. We applied this universal control method to an electronic throttle system, achieving fast and accurate robust trajectory tracking. Comparative experimental and simulation studies with existing sliding mode control methods validated the effectiveness and superiority of the proposed approach.

As the key equipment of the nuclear power plant, the performance of the reactor coolant pump (RCP) are directly related to the safe operation of the nuclear power plant. However, the non-uniform inflow affects the stable operation of RCP. In this article, the transient flow characteristics of the RCP under non-uniform inflow conditions are investigated by establishing a steam generator simulation equipment-reactor coolant pump (SGSERCP) coupling model for numerical simulation. The transient flow field inside the RCP under non-uniform inflow conditions is extracted. The Q criterion is used to extract and analyze the vortex structure distribution of the RCP under non-uniform inflow conditions. The influence mechanism of non-uniform inflow on the vortex structure inside the RCP is revealed. The research in this article deeply reveals the influence of non-uniform inflow on the flow of RCP, and provides support for further exploring the influence mechanism of non-uniform inflow on RCP.

Environmental concerns have made the development of non-flammable, high-specific heat capacity, and high-performance lubricants an urgent priority, driving an increased demand for aqueous-based formulations. A key challenge for their widespread application is achieving low friction across a broad range of speeds. A low-viscosity system composed of polyalkylene glycol (PAG), water, and diethylene glycol offers superlubricity (i.e., friction coefficient <= 0.01) at rolling speeds above 150 mm/s; however, significant friction remains at lower rolling or sliding speeds. This limitation can be addressed by introducing eco-friendly and non-toxic gallate molecules. For example, adding 1 % lauryl gallate stabilizes the friction coefficient at approximately 0.04 with no measurable wear. To activate the anti-friction and anti-wear properties of gallates, the molecules must have alkyl chains with eight or more carbon atoms. Large-scale molecular dynamics simulations have been conducted to explore the key mechanisms by which gallate molecules achieve such superior lubricity. This is made possible through innovative machine learning techniques that enable simulations with Density Functional Theory (DFT) accuracy, allowing the modeling of large systems over extended timescales. Simulations reveal that the superior lubricity of gallates results from the strong anchoring of molecular patches that chemisorb onto the iron surface in specific orientations, enabling the alkyl chains to form an inert cushion at the steel/steel interface. Lubrication occurs thanks to this chemical inert buffer region, which effectively separates the metal surfaces realizing a beneficial friction and wear reducing tribofilm, with a clear dependence on the chain length. These findings by a combined experimental-computational approach provide valuable insights for the development of sustainable lubricants, advancing the field of green tribology.

In order to realize the accurate tracking control of air-fuel ratio with time delay for natural gas engine, a novel sliding mode control strategy based on predefined-time stability and smith predictor is proposed in this paper. First, a delayed dynamic model of the AFR is established according to the operating principles of natural gas engines. To address the large time-delay characteristics of AFR control, an adaptive Smith predictor is employed to estimate and compensate for the delayed dynamics of the AFR. Based on the compensated output, a predefined-time sliding mode controller is designed to ensure tracking performance. Robust stability is analyzed using the Lyapunov function. Finally, multiple test conditions are designed according to practical requirements to validate the AFR control strategy.

Hypericin (C30H16O8) is a naturally occurring substance, an anthraquinone derived from St. John’s wort, possessing outstanding antiviral, antitumor, antibacterial, and antioxidant properties. Today, hypericin is primarily used in medicinal applications. It is a small, flat organic molecule with a graphene-like core surrounded by oxidized functions, suggesting it could act as a graphene precursor in tribological contacts. Therefore, we investigated the lubrication properties of hypericin as an additive in glycerol, used as a base oil. It is well established that glycerol is superlubricious under full and thin film elastohydrodynamic (EHD) lubrication regimes but generally fails with steel under more severe conditions (mixed and boundary regimes). We studied the effect of hypericin added to glycerol for steel-on-steel and steel-on-silicon friction pairs. For the steel-on-steel configuration, results show that hypericin is a strong anti-wear additive due to its antioxidant properties that scavenge OH radicals. Moreover, hypericin is also an efficient friction-reducing agent, providing a steady state and robust ultralow friction coefficient (0.02–0.03). Thus, it outperforms most traditional additive formulations under the same conditions, although it does not achieve superlubricity (coefficient of friction (CoF) < 0.01) under more severe conditions. For steel-on-silicon, hypericin significantly extends the superlubricity regime of glycerol to lambda ratios well below unity (low sliding speeds). The mechanism of superlubricity is attributed to the friction-induced formation of graphene layers from hypericin molecules, smoothing friction surfaces, and operating a hybrid liquid–solid superlubricious system.

The operational performance of the reactor coolant pump is crucial to the safety and reliability of nuclear power plants, However, in practical applications, non-uniform inflow at the inlet can significantly affect the pump’s stability and efficiency. This study focuses on the nuclear reactor coolant pump, conducting refined numerical simulations of its internal flow. The internal flow field distributions of the reactor coolant pump’s overflow components are analyzed under both uniform and non-uniform inflow conditions, and the Q-criterion is applied to capture vortex structures inside the pump. Results show that the scale and intensity of vortex structures increase under non-uniform inflow, especially in the outlet section of the pressurized water chamber casing. This study aims to gain a deeper understanding of the reactor coolant pump’s performance under complex conditions, providing theoretical support for its efficient operation and optimal design.

During the hydraulic performance experiment, significant vibration and noise were observed in the mixed-flow pump operating in the hump region. Cavitation occurrence in the impeller flow channels was confirmed through the transparent chamber. To analyze cavitation flow structure evolution in the mixed-flow pump, this paper integrates numerical and experimental approaches, capturing cavitation flow structures under the valley condition through high-speed photography technology. During the various stages of cavitation development, the cavitation forms are mostly vortex cavitation, cloud cavitation, and perpendicular vortex cavitation. Impeller rotation induces downstream transport of shedding cloud cavitation shedding structures. Flow blockage occurs when cavitation vortexes obstruct specific passages, accelerating cavitation growth that culminates in head reduction through energy dissipation mechanisms. Vortex evolution analysis revealed enhanced density of small-scale vortex structures with stronger localized core intensity in the impeller and diffuser. Despite larger individual vortex scales, reduced core intensity persists throughout the full flow domain. Concurrently, velocity profile characteristics across flow rates and blade sections (spanwise from tip to root) indicate heightened predisposition to flow separation, recirculation zones, and low-velocity regions during off-design operation. This study provides scientific guidance for enhancing anti-cavitation performance in the hump region.

In this paper, proper orthogonal decomposition (POD) technique is used to analyze the internal flow excitation characteristics of the reactor coolant pump. The stable operation of the reactor coolant pump (RCP), a critical component of nuclear power plants, is essential for maintaining reactor core cooling. The influence of the lower chamber of the steam generator on the pump inlet conditions is considered. Through numerical simulation and feature extraction techniques, the flow patterns and dynamic behaviors of key components such as impeller, diffuser and casing are analyzed in depth, and the multi-transient data of RCP are successfully processed. The POD analysis identifies the dominant energy structures within the flow field, offering insights into the primary flow characteristics. Studies have shown that POD technology can not only identify and explain complex flow phenomena under non-uniform inflow conditions, but also significantly improve the performance improvement and fault prevention capabilities of reactor coolant pumps.

This study investigates coolant pump performance under high-temp & pressure conditions versus standard, focusing on nuclear reactors. Our comprehensive analysis includes 3D modeling, numerical simulations, and experimental validation. We compared internal flow patterns of coolant pumps using boric acid water vs. clean water. Results show significant changes in pumps’ characteristic curves, head, and efficiency under extreme conditions. Minor differences impact flow phenomena crucially. We observed alterations in streamline smoothness, vortex intensity, and pressure distribution, enhancing our understanding of fluid-pump-environment interactions. This paper offers insights and guidance for optimizing coolant pump design and maintenance in nuclear reactors.

In the third-generation nuclear power technologies, the non-uniform inflow at the pump inlet caused by the direct connection structure between the reactor coolant pump and the steam generator significantly impacts the pump's performance and internal flow, and may also induce additional vibration and noise, which in turn affects the pump's performance and structural integrity. In this paper, the flow complexity inside the reactor coolant pump under non-uniform inflow is analyzed by numerical simulation. The wavelet analysis method is used to compare the pressure pulsation characteristics and flow stability of reactor coolant pumps in both time and frequency domains. It is found that under non-uniform inflow conditions, the main characteristic signal waveforms tend to be chaotic and energy migrates to the main detail signals. Increased flow instability and pressure pulsations between the main flow path components were observed. Furthermore, the study reveals the main excitation frequency and harmonic components of the pressure pulsation. This study provides theoretical foundations and technical support for the design and optimization of reactor coolant pumps.

Nuclear energy, classified as a clean energy source, enjoys extensive application in numerous countries worldwide. In recent years, the growth rate of marine organisms has accelerated, resulting in the formation of large aggregations of marine organisms and other large congregations that have the potential to obstruct the cold source water intake system of nuclear power plants. The safety situation about the cold source is of significant concern. This paper presents a summary of water intake safety events at nuclear power plants around the world in recent years. It also analyzes the current status of comprehensive prevention and control technology for disaster-causing floating bodies at nuclear power plants’ water intakes. The analysis is based on the latest developments in global nuclear power technology. This study provides a comprehensive overview of the advancements in fine offshore monitoring and early warning systems, passive interception techniques for open channel dredging, the evolution of active defense measures, the development of composite water intake open channel structures, bubble curtain interception methods, cutting and grinding techniques, and the subsequent transportation of marine organisms. Nevertheless, shortcomings remain in the water intake safety of nuclear power plants. These include an inadequate design basis for water intake open channels and sewage interception networks, as well as deficiencies in marine organism early warning and monitoring equipment and layout. Furthermore, the issue of sea ice represents a novel challenge confronting the nuclear power industry in coastal regions situated at high latitudes. Therefore, it is essential to undertake research and implement improvements to the comprehensive technology used to prevent and control water intake safety in nuclear power plants. It is imperative to provide robust backing for the long-term advancement of nuclear power technology.

High-speed mixed-flow and axial-flow pumps often exhibit hump or double-hump patterns in flow–head curves. Operating in the hump region can cause flow disturbances, increased vibration, and noise in pumps and systems. Variable-speed ship navigation requires waterjet propulsion pumps to adjust speeds. Speed transitions can lead pumps into the hump region, impacting efficient and quiet operation. This paper focuses on mixed-flow waterjet propulsion pumps with guide vanes. Energy, entropy production, and flow characteristic analyses investigate hump formation and internal flow properties. High-speed photography in cavitation experiments focuses on increased vibration and noise in the hump region. This study shows that in hump formation, impeller work capacity decreases less than internal fluid loss in the pump. These factors lead to an abnormal increase in the energy curve. The impeller blades show higher pressure at peak conditions than in valley conditions. Valley conditions show more pressure and velocity distribution variance in impeller flow passages, with notable low-pressure areas. This research aids in understanding pump hump phenomena, addressing flow disturbances, vibration, noise, and supporting design optimization.

Understanding the dynamic interaction between pressure pulsations and vibrations in reactor coolant pumps is crucial for enhancing the operational safety and stability of nuclear power plants. This study investigates the characteristics of pressure pulsation and vibration signals at multiple monitoring points of a reactor coolant pump under varying rotational speeds. A comprehensive analysis combining time-frequency domain techniques and wavelet-based methods-specifically Cross Wavelet Transform (XWT) and Wavelet Transform Coherence (WTC)-was conducted to explore the evolution of energy distribution and signal intensity across different operating conditions. The results reveal that both the amplitude and energy of pressure pulsation and vibration signals increase significantly with rotational speed. In the frequency domain, a trend of spectral energy concentration toward the blade passing frequency (BPF) and its harmonics is observed, with some monitoring points exhibiting dominant frequencies corresponding to the sum of the impeller and guide vane passing frequencies. Moreover, strong coherence in the primary frequency bands indicates a pronounced dynamic synchronization between pressure pulsations and vibrations. The findings provide theoretical insights into the dynamic response mechanisms of reactor coolant pumps under complex conditions, and provide valuable references for vibration monitoring, fault diagnosis, and structural optimization.

This paper presents a study on the internal flow characteristics of reactor coolant pumps using Dynamic Mode Decomposition (DMD) technology. As a core component of nuclear power plants, the internal flow characteristics of reactor coolant pumps play a crucial role in the performance and stability of the pumps. This paper initially introduces the application of DMD and Proper Orthogonal Decomposition (POD) methods in fluid mechanics, emphasizing the effectiveness of DMD in analyzing the dynamic characteristics of flow fields. A computational model of the reactor coolant pump was constructed, and numerical simulation of the internal flow field under non-uniform inflow conditions was conducted. The impact of the lower chamber of the steam generator on the pump’s inlet conditions was evaluated. The numerical simulation results were analyzed using DMD technology, extracting flow characteristics and revealing the main flow modes and dynamic behaviors in the flow field. The results demonstrate that the DMD technology can accurately capture the time-dynamic characteristics within the flow field, providing crucial insights for optimizing performance and preventing faults in the reactor coolant pump.

This study explored the complexity of internal flow patterns in a reactor coolant pump (RCP) facing non-uniform inflow conditions. Utilizing CFD simulations, we analyzed the flow behavior under non-uniform inlet conditions simulated by a steam generator and compared it with flows under standard straight pipe inlets. The examination covered five main computational areas: the inlet, the rotating impeller, the stationary diffuser, the casing, and the outlet extension. By examining the transient evolution of the pump's primary flow components under varying inflow conditions, the study exposed the impact of non-uniform inflow on the pump's internal flow field. It was observed that non-uniform inflow, particularly under the simulated conditions of the steam generator, significantly influences the velocity and pressure distributions within the impeller and diffuser, consequently affecting the pump's performance by reducing flow stability and energy conversion efficiency. Additionally, the study established grid independence, ensuring the accuracy and reliability of the numerical simulation results. These findings offer vital scientific insights for the design and operation of RCPs and enhance the prediction and optimization of real pump performance through precise flow field simulations that reflect actual inflow conditions.

In order to achieve precise and robust tracking control of electronic throttle (ET) systems subject to external disturbances and uncertainties, a novel 2-order discrete-time fast terminal sliding mode control (2-DFTSMC) approach is presented in the paper. Specifically, a novel recursive nonlinear discrete-time sliding surface is developed by utilizing the fast terminal sliding surfaces and principles of high-order sliding mode (HOSM). Compared with previous methods, the proposed hierarchical two-layer discrete-time sliding surface has the capability to suppress the chattering and reduce the tracking error. Then, in order to further improve the system convergence dynamics, the improved exponential reaching law and disturbance estimator are also employed. Rigorous theoretical analysis proves that the quasi-sliding mode (QSM) exists and the tracking error is reduced. Finally, through experimental comparisons, it is verified that the proposed 2-DFTSMC approach is superior to traditional DLSMC and DFTSMC, which demonstrates the advantages and effectiveness of the 2-DFTSMC scheme with the recursive discrete-time sliding surface.