Transient Structures Research Articles

Efficient Structural Optimization under Transient Impact Loads Using Multilayer Perceptron and Genetic Algorithms

Currently, there is a lack of structural optimization methods when a structure is suffering transient impact load, considering nonlinear factors such as material plasticity and strain rate effect. The utilization of derivative-free algorithms also increases computational expenses. Accordingly, this paper presents a novel structure transient optimization approach based on multilayer perceptron combined with a derivative-free optimization method, which can efficiently solve the transient structure dynamics optimization problem with multiple optimization objects. In this approach, the area to be optimized is cut by several closed B-spline curves whose shapes are controlled by several parameters and can be varied and merged at each optimization iteration step. The structure’s transient analysis process is replaced by a machine learning based surrogate model, which is trained by thousands of results from the FEM explicit transient simulation. Additionally, nearly orthogonal Latin hypercube sampling is utilized to simplify parameter dimensionality, reduce the training data set, save calculation time, and give the training data set a more comprehensive range of design parameters. In our optimization process, our design target is to minimize the peak reaction force while with the constrain of ensuring enough stiffness and mass. The results demonstrate our proposed methods could efficiently handle transient optimization problems without sensitivity calculations, exhibiting strong generalization capabilities.

Joint Observation of a Series of Magnetic Holes by Tianwen-1 and MAVEN on Mars

Magnetic holes (MHs) are transient magnetic structures responsible for energy conversion in space plasma. Using single-spacecraft measurements from Mars Atmosphere and Volatile EvolutioN (MAVEN), the existence of MHs on Mars has been confirmed. However, due to the limitations of single-spacecraft observations, significant uncertainty also arises on the identification of the spatial scale and 3D geometry of MHs. In this study, we report a series of MHs successively detected by Tianwen-1 near the high-latitude magnetopause and by the MAVEN spacecraft near the subsolar magnetopause. The large separation between Tianwen-1 and MAVEN (∼4 R M) suggests these MHs are macroscale structures extending along the axial direction. Additionally, we observe whistler waves generated by electron perpendicular anisotropy in one of the macroscale MHs. This study is the first joint observation of Martian MHs, shedding light on the research of transient magnetic structures on Mars.

Asymmetric fluctuation of overlapping dinucleosome studied by cryo-electron microscopy and small-angle X-ray scattering

Abstract Nucleosome remodelers modify the local structure of chromatin to release the region from nucleosome-mediated transcriptional suppression. Overlapping dinucleosomes (OLDNs) are nucleoprotein complexes formed around transcription start sites as a result of remodeling, and they consist of two nucleosome moieties: a histone octamer wrapped by DNA (octasome) and a histone hexamer wrapped by DNA (hexasome). While OLDN formation alters chromatin accessibility to proteins, the structural mechanism behind this process is poorly understood. Thus, this study investigated the characteristics of structural fluctuations in OLDNs. First, multiple structures of the OLDN were visualized through cryo-electron microscopy (cryo-EM), providing an overview of the tilting motion of the hexasome relative to the octasome at the near-atomistic resolution. Second, small-angle X-ray scattering (SAXS) revealed the presence of OLDN conformations with a larger radius of gyration than cryo-EM structures. A more complete description of OLDN fluctuation was proposed by SAXS-based ensemble modeling, which included possible transient structures. The ensemble model supported the tilting motion of the OLDN outlined by the cryo-EM models, further suggesting the presence of more diverse conformations. The amplitude of the relative tilting motion of the hexasome was larger, and the nanoscale fluctuation in distance between the octasome and hexasome was also proposed. The cryo-EM models were found to be mapped in the energetically stable region of the conformational distribution of the ensemble. Exhaustive complex modeling using all conformations that appeared in the structural ensemble suggested that conformational and motional asymmetries of the OLDN result in asymmetries in the accessibility of OLDN-binding proteins.

Nanotubules and Cellular Communication in Trabecular Meshwork Cells.

Glaucoma causes dysfunction to tissues located in the anterior and posterior eye. In the anterior eye, the trabecular meshwork (TM) is the site of pathogenesis, where decreased TM cell numbers and alterations to the amount and composition of extracellular matrix hinder outflow of aqueous humor fluid from the anterior chamber. This causes intraocular pressure (IOP) elevation. Elevated IOP, a main risk factor for primary open-angle glaucoma, damages the axons of retinal ganglion cells in the posterior eye, which ultimately leads to blindness. Thus, clinical treatment paradigms for glaucoma are focused on reducing IOP. Normotensive IOPs are established by balancing the production of aqueous fluid from the ciliary body with drainage through the TM to Schlemm's canal. When IOP becomes elevated, TM cells coordinate a homeostatic response to lower IOP, which requires effective and efficient cellular communication. Tunneling nanotubes (TNTs) are transient specialized structures that allow cells to communicate with one another. Actin-rich tubes allow direct transmission of signals and cargoes between cells. This is important to overcome limitations of diffusion-based signaling in aqueous environments such as the anterior eye. Here, we describe a live-cell imaging method for monitoring TNTs in primary TM cells.

Bouncing behaviour of a particle settling through a density transition layer

The present work focuses on a specific bouncing behaviour as a spherical particle settles through a density interface in the absence of a neutral buoyant position. This behaviour was initially discovered by Abaid et al. (Phys. Fluids, vol. 16, issue 5, 2004, pp. 1567–1580) in salinity-induced stratification. Both experimental and numerical investigations are conducted to understand this phenomenon. In our experiments, we employ particle image velocimetry (PIV) to measure the velocity distribution around the particle and to capture the transient wake structure. Our findings reveal that the bouncing process begins after the wake detaches from the particle. The PIV results indicate that an upward jet forms at the central axis behind the particle following wake detachment. By performing a force decomposition procedure, we quantify the contributions from the buoyancy of the wake ( $F_{sb}$ ) and the flow structure ( $F_{sj}$ ) to the enhanced drag. It is observed that $F_{sb}$ contributes primarily to the enhanced drag at the early stage, whereas $F_{sj}$ plays a critical role in reversing the particle's motion. Furthermore, our results indicate that the jet is a necessary condition for the occurrence of the bouncing motion. We also explore the minimum velocities (where negative values denote the occurrence of bouncing) of the particle, while varying the lower Reynolds number $Re_l$ , the Froude number $Fr$ , and the upper Reynolds number $Re_u$ , within the ranges $1 \leqslant Re_l\leqslant 125$ , $115 \leqslant Re_u\leqslant 356$ and $2 \leqslant Fr\leqslant 7$ . Our findings suggest that the bouncing behaviour is influenced primarily by $Re_l$ . Specifically, we observe that the bouncing motion occurs below a critical lower Reynolds number $Re^\ast _{l}=30$ in our experiments. In the numerical simulations, the highest value for this critical number is $Re^\ast _{l}=46.2$ , which is limited to the parametric ranges studied in this work.

Magnetic Hole and Its Resultant Electron Pitch‐Angle Distribution at Jupiter

AbstractMagnetic hole (MH), sometimes referred to as magnetic bottle, exhibits strong magnetic fields at its neck but weak magnetic fields at its belly. Such structure has been widely reported in the solar wind and the Earth's magnetosphere, but has not been reported at Jupiter. Here, for the first time, we report two MHs in the Jupiter's magnetosphere by utilizing measurements of the Juno mission, with one existing in the dawn side and the other existing in the dusk side. We find that the electron pitch‐angle distribution inside the MHs can be either cigar‐type or pancake‐type. The cigar‐type distribution probably appears at the belly of the MH, whereas the pancake‐type distribution probably appears at the neck. Our analyses of the depression of magnetic fields inside the MHs support such a conjunction. These results have advanced our understanding of the transient structure and its related electron dynamics in the giant planets' magnetosphere.

Atypical Exon 2/3 Mutants G48C, Q43K, and E37K Present Oncogenic Phenotypes Distinct from Characterized NRAS Variants.

NRAS belongs to the RAS family of GTPases. In colorectal cancer (CRC), NRAS mutations are rare compared to KRAS, but may lead to worse outcomes. We report the functional characterization of the novel NRAS mutants-G48C, Q43K, and E37K-identified in Filipino young-onset CRC patients. Unlike previously characterized NRAS mutants with no apparent effects on cell proliferation, these mutants enhanced proliferation of both HCT116 and NIH3T3 cells. This was confirmed in 3D spheroid assays to mimic the spatial organization of cells. G48C and E37K showed apoptosis resistance in both cell lines, and Q43K showed resistance in HCT116 cells. All three showed no effect on cellular migration in NIH3T3, but G48C enhanced the migration rate of HCT116 cells. Actin staining of NIH3T3 cells expressing the mutants showed a shrunken cytoplasm and transient structures associated with motility and invasiveness. Docking simulations show that GDP is only able to bind fully within the binding pocket of wild-type NRAS, but not in the mutants. Further, G48C, Q43K, and E37K all have less negative ΔG values, indicating a weaker GDP-binding affinity compared to wild-type NRAS. Taken together, the results suggest that oncogenic readouts of NRAS mutants are codon- and mutation-specific, with potential repercussions on the aggressiveness, resistance, and therapeutic response.

Genome-Wide Identification of Stable RNA Secondary Structures Across Multiple Organisms Using Chemical Probing Data: Insights into Short Structural Motifs and RNA-Targeting Therapeutics.

Small molecules targeting specific RNA binding sites, including stable and transient RNA structures, are emerging as effective pharmacological approaches for modulating gene expression. However, little is understood about how stable RNA secondary structures are shared across organisms, an important factor in controlling drug selectivity. In this study, I provide an analytical pipeline named RNA Secondary Structure Finder (R2S-Finder) to discover short, stable RNA structural motifs for humans, Escherichia coli ( E. coli ), SARS-CoV-2, and Zika virus by leveraging existing in vivo and in vitro genome-wide chemical RNA-probing datasets. I found several common features across organisms. For example, apart from the well-documented tetraloops, AU-rich tetraloops are widely present in different organisms. I also found that the 5' untranslated region (UTR) contains a higher proportion of stable structures than the coding sequences in humans, SARS-CoV-2, and Zika virus. In general, stable structures predicted from in vitro (protein-free) and in vivo datasets are consistent in humans, E. coli , and SARS-CoV-2, indicating that most stable structure formation were driven by RNA folding alone, while a larger variation was found between in vitro and in vivo data with certain RNA types, such as human long intergenic non-coding RNAs (lincRNAs). Finally, I predicted stable three- and four-way RNA junctions that exist both in vivo and in vitro conditions, which can potentially serve as drug targets. All results of stable sequences, stem-loops, internal loops, bulges, and three- and four-way junctions have been collated in the R2S-Finder database ( https://github.com/JingxinWangLab/R2S-Finder ), which is coded in hyperlinked HTML pages and tabulated in CSV files.

Numerical investigation of the effect of the structure and number of spiral baffles on the vibration and heat transfer coefficient of spiral tubes within spiral tube heat exchangers

In response to the advantages of compactness and high efficiency of spiral elastic tube heat exchanger and its easy-to-vibrate characteristics, this study aims to further improve its heat transfer efficiency by utilizing fluid-induced vibration-enhanced heat transfer technology, so a design scheme of reverse baffle spiral tube heat exchanger (RB-STHE) is proposed to enhance the turbulence characteristics of the shell-side fluid by installing spiral baffles, thus promoting the vibration of the spiral tube. In this study, four new types of the RB-STHE (Model A, B, C, and D) were used as research objects, and the two-way fluid–structure coupling calculation method (using CFX and Transient Structure software) was adopted to systematically investigate the effect of fluid-induced spiral tube vibration on the comprehensive heat transfer coefficient (HTC) of the RB-STHE under different flow velocities and structure schemes, and based on the research data, the objective of no reduction in the comprehensive HTC and savings in the use of materials is taken as the goal, so as to put forward the improved Model C-1. The results show that: although the fluid-induced spiral tube vibration can effectively improve the HTC of the spiral tube, it also increases the pressure drop in the RB-STHE, and the larger the amplitude, the higher the degree of influence; among them, Model C is most affected by the spiral tube vibration, and its HTC and pressure drop are maximally enhanced by 6.33% and 5.85%, respectively. The change in the number of baffles has a significant effect on the comprehensive HTC of the RB-STHE. Compared to the Model D without a spiral baffle, the maximum improvement in the comprehensive HTC of Model C with one spiral baffle installed in the RB-STHE is 14%, while the Model A with four spiral baffles and the Model B with two spiral baffles have a maximum reduction in the comprehensive HTC of 20% and 3%, respectively. In addition, compared to Model C, the structure improved Model C-1 significantly reduces the size of the spiral baffle while effectively maintaining the comprehensive HTC of the RB-STHE, making the structure more reasonable, which provides a reference for heat exchanger design.

Experimental investigation of OH* emission spectrum characteristics and transient ignition dynamics in methane and coal dust mixtures explosions

Combustible gases, dusts and their mixtures are widely present in human production and life，and the fire and explosion disasters caused by them pose a serious threat to the field of energy security applications. Studying the ignition process of mixtures is essential for disaster risk assessment and safety protection. In this work, the explosion characteristics and OH* emission spectra of the mixtures were experimentally tested by varying the fuel equivalence ratio ( ER ≈ 0.79 ~ 1.71), and the evolution of the transient flow field structure during the ignition process was quantitatively analyzed using the schlieren image velocimetry method. The results indicate that the emission spectrum of OH* is closely correlated with the maximum explosion pressure, and the spectral intensity of OH* at 306.4nm is consistent with the maximum rate of explosion pressure rise. The flow field during the ignition process of the mixtures shows that a small amount of coal dust (concentration≤30g/m3) can significantly promote flame acceleration and instability as the methane concentration is in lean combustion or stoichiometric ratio. However, when the concentration of coal dust increases (concentration≥40g/m3), coal dust will suppress flame acceleration and instability. For methane concentration in fuel-rich combustion state, coal dust always suppresses flame acceleration and instability. The experimental results contribute to a further understanding of gas and coal dust mixed explosions and provide a verification database for the construction of chemical kinetic mechanisms.

Hydrogen Peroxide Heterolytic Cleavage Induced Gas Phase Photo-Fenton Oxidation of Nitric Oxide.

Nitric oxide (NO) is one of the major air pollutants that may cause ecological imbalance and severe human disease. However, the removal of NO faces challenges of low efficiency, high energy consumption, and production of toxic NO2 byproducts. Herein, we report an efficient *OOH intermediate-involved NO oxidation route with high NO3- selectivity via a gas phase photo-Fenton system. Fe single atoms (Fe SAs)-anchored NH2-UiO-66(Zr) (Fe SAs@NU) was synthesized. The five-coordinated Fe SAs undergo a transient structure reconstitution during the photo-Fenton process, which enables a novel heterolytic cleavage pathway of H2O2 to derive specific ·OOH/·O2- radicals as reactive oxygen species. Therefore, a high NO (550 parts per billion) removal rate of 81% (NO3- selectivity up to 99%) is achieved under visible-light irradiation (>420 nm). This study provides new insight for the high-performance photo-Fenton process via a transient structure reconstitution pathway for the removal of gas phase NOx pollutants.

Neuregulin 1 Signaling Attenuates Tumor Necrosis Factor α-Induced Female Rat Luteal Cell Death.

The corpus luteum (CL) is a transient ovarian endocrine structure that maintains pregnancy in primates during the first trimester and in rodents during the entire pregnancy by producing steroid hormone progesterone (P4). CL lifespan, growth, and differentiation are tightly regulated by survival and cell death signals through luteotrophic and luteolytic factors, including the epidermal growth factor (EGF)-like factor family. Neuregulin 1 (NRG1), a member of the EGF family, mediates its effect through ErbB2/3 receptors. However, the functional role of NRG1 in luteal cells (LCs) is unknown. Thus, this study investigated the role of NRG1 and its molecular mechanism of action in rat LC. Our experimental results suggest a strong positive correlation between steroidogenic acute regulatory protein (StAR) and NRG1 expression in mid-CL and serum P4 and estrogen (E2) production. In contrast, there was a decrease in StAR and NRG1 expression and P4 and E2 production with an increase in tumor necrosis factor α (TNFα) expression in regressing CL. Further in vitro studies in LCs showed that the knockdown of endogenous Nrg1 promoted the expression of proinflammatory and proapoptotic factors and decreased prosurvival factor expression. Subsequently, treatment with exogenous TNFα under these experimental conditions profoundly elevated proinflammatory and proapoptotic factors. Further analysis demonstrated that the phosphorylation status of ErbB2/3, PI3K, Ak strain transforming or protein kinase B (Akt), and ErK1/2 was significantly inhibited under these experimental conditions, whereas the treatment of TNFα further inhibited the phosphorylation of ErbB2/3, PI3K, Akt, and ErK1/2. Collectively, these studies provide new insights into the NRG1-mediated immunomodulatory and prosurvival role in LCs, which may maintain the function of CL.

Extraction of Molecular-Frame Electron-Ion Differential Scattering Cross Sections Based on Elliptical Laser-Induced Electron Diffraction.

We extracted the molecular-frame elastic differential cross sections (MFDCSs) for electrons scattering from N_{2}^{+} based on elliptical laser-induced electron diffraction (ELIED), wherein the structural evolution is initialized by the same tunneling ionization and probed by incident angle-resolved laser-induced electron diffraction imaging. To establish ELIED, an intuitive interpretation of the ellipticity-dependent rescattering electron momentum distributions was first provided by analyzing the transverse momentum distribution. It was shown that the incident angle of the laser-induced returning electrons could be tuned within 20° by varying the ellipticity and handedness of the driving laser pulses. Accordingly, the incident angle-resolved DCSs of returning electrons for spherically symmetric targets (Xe^{+} and Ar^{+}) were successfully extracted as a proof-of-principle for ELIED. The MFDCSs for N_{2}^{+} were experimentally obtained at incident angles of 4° and 7°, which were well reproduced by the simulations. The ELIED approach is the only successful method so far for obtaining incident angle-resolved ionic MFDCS, which provides a new sensitive observable for the transient structure retrieval of N_{2}^{+}. Our results suggest that the ELIED has the potential to extract the structural tomographic information of polyatomic molecules with femtosecond and subangstrom spatiotemporal resolutions that can enable the visualization of the nuclear motions in complex chemical reactions as well as chiral recognition.

Early Events in G-quadruplex Folding Captured by Time-Resolved Small-Angle X-Ray Scattering.

Time-resolved small-angle X-ray experiments (TR-SAXS) are reported here that capture and quantify a previously unknown rapid collapse of the unfolded oligonucleotide as an early step in G4 folding of hybrid 1 and hybrid 2 telomeric G-quadruplex structures. The rapid collapse, initiated by a pH jump, is characterized by an exponential decrease in the radius of gyration from 20.6 to 12.6 Å. The collapse is monophasic and is complete in less than 600 ms. Additional hand-mixing pH-jump kinetic studies show that slower kinetic steps follow the collapse. The folded and unfolded states at equilibrium were further characterized by SAXS studies and other biophysical tools, to show that G4 unfolding was complete at alkaline pH, but not in LiCl solution as is often claimed. The SAXS Ensemble Optimization Method (EOM) analysis reveals models of the unfolded state as a dynamic ensemble of flexible oligonucleotide chains with a variety of transient hairpin structures. These results suggest a G4 folding pathway in which a rapid collapse, analogous to molten globule formation seen in proteins, is followed by a confined conformational search within the collapsed particle to form the native contacts ultimately found in the stable folded form.

Neural Tube Organoids: A Novel System to Study Developmental Timing.

The neural tube (NT) is a transient structure formed during embryogenesis which develops into the brain and spinal cord. While mouse models have been commonly used in place of human embryos to study NT development, species-specific differences limit their applicability. One major difference is developmental timing, with NT formation from the neural plate in 16 days in humans compared to 4 days in mice, as well as differences in the time taken to form neuronal subtypes and complete neurogenesis. Neural tube organoids (NTOs) represent a new way to study NT development in vitro. While mouse and human NTOs have been shown to recapitulate the major developmental events of NT formation; it is unknown whether species-specific developmental timing, also termed allochrony, is also recapitulated. This review summarises current research using both mouse and human NTOs and compares developmental timing events in order to assess if allochrony is maintained in organoids.

Observations of Compressional Structures Driven by Interaction Between Foreshock Ions and Discontinuities

AbstractThe ion foreshock is very dynamic, characterized by various transient structures that can perturb the bow shock and influence the magnetosphere‐ionosphere system. One important driver of foreshock transients is solar wind directional discontinuities (DDs) that demagnetize foreshock ions leading to a local current. If this current decreases the field strength at the DD, a hot flow anomaly (HFA) can form. Recent hybrid simulations found that when the current increases the field strength at the DD, a compressional structure forms with enhanced density and field strength opposite to HFAs. Using MMS and THEMIS observations, we confirm this situation. We demonstrate that the current geometry driven by the foreshock ions plays a critical role in the formation. The initial gyrophase of foreshock ions, due to their specular reflection, determines whether they can cross the DD. When many of the foreshock ions cannot cross the DD and the local current they drive increases the field strength at the DD, the enhanced field strength inhibits more foreshock ions from crossing the DD, further enhancing the local current. This feedback loop promotes the growth of the compressional structure. Such foreshock ion‐driven compressional structures can result in dynamic pressure enhancements in the magnetosheath, leading to magnetosheath jets. Our study enables prediction of the location and formation probability of such compressional structures and their potential geoeffectiveness.

Observations and Simulations of a Double‐Core Hot Flow Anomaly

AbstractHot Flow anomalies (HFAs), one of the most well‐analyzed transient phenomena in the Earth's foreshock, are known as kinetic structures driven by tangential discontinuities (TDs). Recently, a 2‐dimensional (2D) magnetohydrodynamics (MHD) model reproduced HFAs with either a high‐ or low‐density core. Further investigation of an HFA with two cores observed by the Magnetospheric Multiscale (MMS) mission is reported. The observation via the Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission suggests this MHD HFA is associated with a foreshock density hole‐like structure. The trailing flux tube in simulation may propagate with a TD in the foreshock. Our work suggests that HFAs with two low‐density cores can also be achieved in MHD process. Results show the total ram pressure can be an excellent diagnostic for the presence of transient structures, such as HFAs, at the bow shock.

CD28 hinge used in chimeric antigen receptor (CAR) T-cells exhibits local structure and conformational exchange amidst global disorder

T-cell therapies based on chimeric antigen receptor (CAR) targeting of a tumor-specific antigen offer hope for patients with relapsed or refractory cancers. CAR hinge and transmembrane regions link antigen recognition domains to intracellular signal transduction domains. Here, we apply biophysical methods to characterize the structure and dynamic properties of the CD28 CAR hinge (CD28H) used in an FDA-approved CD19 CAR for the treatment of B-lineage leukemia/lymphoma. By using nuclear Overhauser effect spectroscopy (NOESY), which detects even transiently occupied structural motifs, we observed otherwise elusive local structural elements amidst overall disorder in CD28H, including a conformational switch from a native β-strand to a 310-helix and polyproline II helix-like structure. These local structural motifs contribute to an overall loosely formed extended geometry that could be captured by NOESY data. All FDA-approved CARs use prolines in the hinge region, which we find in CD28, and previously in CD8α, isomerize to promote structural plasticity and dynamics. These local structural elements may function in recognition and signaling events and constrain the spacing between the transmembrane and antigen recognition domains. Our study thus demonstrates a method for detecting local and transient structure within intrinsically disordered systems and moreover, our CD28H findings may inform future CAR design.

A 99.99% current efficiency fast transient response capacitor-less LDO with feedforward compensation technique based on small-signal gain stage

An ultra-low power capacitor-less LDO with feedforward compensation technique based on the small-signal gain stage and composite transient enhancement structure is proposed. The feedforward compensation technique based on the small-signal gain stage reaches a low frequency zero ,by utilizing the compensating effect of the zero to relieve the adverse effects of the pole, thereby enhancing the stability and performance of the circuit. Furthermore, the small gain stage can adjust the quiescent current consumption,contributing to a significant reduction in system energy consumption. The proposed composite transient enhancement structure can reduce the transition time of the circuit, adjust the gain of the circuit under different operating conditions to achieve precise gain control and improve the transient performance of the system. The proposed LDO is designed using SMIC 0.18um CMOS process. The simulation results show the total quiescent current is 0.94uA and the current efficiency is up to 99.99%. The extremely low FoM value of 0.04 represents a good transient performance. Synthesizing the comparison of various parameters, the superiority of this design can be clearly concluded.

Influence of gate cutoff effect on flow mode conversion and energy dissipation during power-off of prototype tubular pump system

Understanding the cutoff effect of gates is essential for enhancing the overall quality of the pump system's power-off process, minimizing energy losses, and reducing potential risks associated with hydraulic transients. In this study, both numerical simulations and experimental investigations were conducted on the power-off process of a tubular pump system, considering scenarios with and without gate functionality. The simulations utilized a dynamic mesh method to model gate movement, incorporated the torque balance equation to determine the real-time impeller speed, and applied the 3D-VOF method for free surface modeling in reservoirs. Power-off experiments were performed on a model pump system and a prototype pump system to validate the numerical simulation results. To elucidate the mechanism of the gate's cutoff effect, flow modes during the power-off process were categorized based on the four-quadrant static test results of the pump, revealing the deviations between transient and static characteristics. By comparing the transient flow structures of the pump system under different gate operating states, specific energy dissipation behaviors during gate cutoff were analyzed. The research findings enhance the understanding of hydraulic transients, which is essential for developing more sustainable and resilient energy systems.