Upstream Surface Research Articles

Simulating the Effects of Grain Surface Morphology on Hot Spots in HMX with Surrogate Model Development

AbstractThere have been several numerical studies on the collapse of internal voids in energetic grains but fewer investigations have probed grain‐grain interface effects. In this study, we examine the effects of grain surface morphology and binder conditions on hot spot mechanisms during shock loading using the multi‐physics hydrocode, ALE3D, coupled with the thermochemical code, Cheetah. To improve the accuracy of our grain‐scale simulations, the HMX material models have been updated from previous studies to incorporate new property predictions from molecular dynamics simulations. In our simulations of the interface between two neighboring energetic grains, the upstream grain surface is described by a single sinusoid with amplitude (0.5–2 μm) and wavelength (0.5–2 μm). The effects of grain surface coating, i. e., no binder, partially coated, and fully coated with binder, is also explored. A range of shock loading pressures (10–30 GPa) is considered. Binder coating reduces hot spots at grain‐grain interfaces by limiting plastic deformation and heating of upstream grain surfaces as well as preventing transmission of localized deformation modes (e. g., jetting) to the downstream grain. More plastic work and heating is observed with new HMX material models versus the previous models because the strength does not thermally soften as much as a result of the higher melt temperature; this also reduces vortical flow and jetting mechanisms with the new HMX material models. A surrogate model based on neural networks is developed for the early stage reaction rate. Physics‐based input features improve the performance of the neural networks over basic input features alone with a root mean squared error=1.05 μs−1 and R2=0.98. Accurate and fast‐running surrogate models can effectively serve as structure‐property‐sensitivity relationships.

Investigation of Negative Ion Energy Distribution and Extraction Mechanism With a Compact Retarding Field Energy Analyzer in a Large Filament-Arc Source for Neutral Beam Injectors

In large beam sources for neutral beam injectors (NBIs) operating at high energies, negative hydrogen ions (NI) are extracted from a caesiated plasma discharge. H− ions are generated from volume and surface processes; surface production is enhanced by cesium deposition on the source walls and in particular on the plasma-facing electrode of the accelerator. The mechanisms of negative ion production and of extraction in the magnetic field present at the extraction apertures influence the formation of the single beamlets and their optics. A newly developed compact retarding field energy analyzer (CRFEA) was constructed and installed at the upstream surface of the plasma grid (PG) of a filament-arc source, the research negative ion source (RNIS) at the National Institute of Fusion Science. It was used to characterize the negative ions in the plasma source with and without cesium. The first electrode of the analyzer has a conical shape, resembling the PG apertures from which the beam is extracted. The measured saturation current was analyzed and correlated with the source parameters and the current of the negative-ion beam. The energy distribution of collected ions depends on the origin of the negative ions, and on possible energy exchange processes; but it is found to be also strongly influenced by the curvature of the meniscus (the plasma edge where the beam is formed). This compact retarding field analyzer proved to be effective for the study of the formation of a negative ion beam. The limits of the present design, and possible improvements are discussed, in particular to minimize the dependence of the transmission on perveance and extend the dynamic range of the diagnostic.

Numerical investigations of a 2D bow wedge asymmetric free-falling into still water

The process of asymmetric water entry of a 2D bow is studied using the computational fluid dynamics (CFD) model with STAR-CCM+. The necessity of including the turbulence model in this investigation is discussed. The behaviors of bow slamming pressure, slamming pressure coefficients, slamming velocities with different deflection angles (0–10°) are discussed. The typical bow cross-section is simplified as a wedge with a deadrise angle of 45°. A numerical simulation was conducted and a good agreement was achieved between the numerical results and the experimental data. The results show that the turbulence model should be carefully considered in numerical simulation when the slamming occurs over time scales that are much shorter in duration than the time scales over which viscosity and gravity act on the flow. Additionally, with the increase in deflection angle, the slamming pressure coefficients increase on the upstream surface. And the slamming pressure coefficients decrease on the back stream surface. The jet area increases on the upstream surface and decreases on the back stream surface with the wedge asymmetric water entry.

Effect of Orientation and Vegetation over the Embankment Crest for Energy Reduction at Downstream

Coastal embankments often collapse due to the tremendous destructive energy of an overtopping tsunami flow due to a deep scour by nappe flow. Hence, to clarify the nappe flow formation condition due to the overtopping, a series of tests were carried out within a laboratory flume with immobile settings by lowering the downstream surface angle of an embankment model while keeping the upstream surface slope constant (1:1) with five non-dimensional overtopping depths and six different crest conditions. The conditions imposed on the embankment crest in the flow direction were without vegetation; horizontal crest, (−)4% descending crest slope, (+)4% ascending crest slope, and adding vegetation model with three different densities across the horizontal crest to improve resistance to the flow. The increased resistance provided by the vegetation models were categorized based on the spacing ratio between cylinders to diameter: sparse, intermediate, and dense. Increased vegetation density above the crest results in a significant reduction of flow energy by approximately 30–50% at the downstream brink edge and 40–60% at the downstream plunge basin. In contrast, the maximum energy reduction was found to be by the dense vegetation model. Additionally, owing to the steep slope of the water surface profile and the increasing vegetation density, the impinging jet’s impact point moved closer to the toe of an embankment. This implies that vegetation covers a smaller area while increasing density to mitigate the destructive intensity of flood/tsunami movement. Meanwhile, the descending crest scenario results in a faster nappe flow formation. In contrast, the ascending crest scenario delays the nappe formation while reducing the downstream slope angle. It maintains the sub-critical flow at the crest, except near the downstream brink edge.

A Bayesian model to solve a two-dimensional inverse heat transfer problem of gas turbine discs

Blade tip clearances in gas turbine engines are strongly affected by heat transfer on rotating disc surfaces as it determines the temperature and in turn the radial growth of rotating discs. In experiments, disc heat transfer is often calculated from disc temperature measurements. This creates a typical ill-posed inverse problem where small uncertainties of temperature measurements can cause large uncertainties of the calculated heat fluxes. In this paper, a Bayesian method is built to calculate heat transfer on both the upstream and downstream surfaces of discs from simulated temperature measurements, reducing the ill-posedness of the problem. A Matérn covariance matrix is employed in the Gaussian prior distribution, and parametric studies are conducted to investigate the accuracy, stability and robustness of the Bayesian method. It is shown that, compared to traditional curve-fitting methods, the Bayesian method offers better accuracy, robustness, and stability. With a temperature uncertainty of 5e-3, the relative errors of the calculated Biot number from the Bayesian method are less than 10%, whereas those from the curve-fitting methods are in the range of 40–90%. Using different initial guesses of the Biot number, the variations of the relative errors are less than 0.8%. The accuracy of the Bayesian method depends on the selection of the standard deviation in the prior distribution, and the best accuracy is obtained when it is twice the maximum Biot number. This study provides guidelines for subsequent experimental research on gas turbine disc heat transfer and data processing.

Experimental observations on turbulent boundary layers subjected to a step change in surface roughness

Based on experimental data acquired with particle image velocimetry, we examine turbulent boundary layers that are subjected to an abrupt change in wall roughness in the streamwise direction. Three different sandpapers (P24, P36 and P60) together with a smooth wall are used to form a number of different surface transition cases, including both R $\rightarrow$ S (where upstream surface is rough and second surface is either smooth or smoother compared with the upstream surface) and S $\rightarrow$ R (where upstream surface is smoother compared with the downstream surface; both surfaces are rough). This enables us to investigate the effect of the surface transition strength ( $M = \ln [y_{02}/y_{01}]$ , where $y_{01}$ and $y_{02}$ are the roughness lengths of the upstream and downstream surfaces, respectively) on the growth of the internal boundary layer (IBL) and the corresponding flow structure. The results show that for each surface transition group (i.e. R $\rightarrow$ S and S $\rightarrow$ R), the thickness of the IBLs is proportional to the strength of the surface transition, and that the IBLs are thicker for the S $\rightarrow$ R cases compared with their R $\rightarrow$ S counterparts for similar $|M|$ , when normalised by the initial boundary layer thickness ( $\delta _0$ ). The results also show that the growth rates of the IBLs could be represented by a power law, consistent with the previous studies. However, despite a wide range of scatter in the literature for the power-law exponent, an average value of $0.75$ (varies between $0.71$ and $0.8$ with no clear trend) is obtained in the present study considering all the surface transition cases. The pre-factor for the power-law fit, on the other hand, is found to be related to the strength of the surface transition. In addition to the variations in the velocity defect and diagnostic plots with the growth of the IBLs, sweep and ejection events appear to differ significantly (depending on the type of the step change). Two-point spatial correlations, moreover, show that the structure is more elongated in the wall-normal and streamwise directions, as the flow accelerates over the downstream surface (i.e. R $\rightarrow$ S cases). For the reverse transition cases (i.e. S $\rightarrow$ R, where the flow decelerates over the downstream rougher surface), however, the correlation coefficients shrink in size in both directions.

The structure and activities of the archaeal transcription termination factor Eta detail vulnerabilities of the transcription elongation complex.

Transcription must be properly regulated to ensure dynamic gene expression underlying growth, development, and response to environmental cues. Regulation is imposed throughout the transcription cycle, and while many efforts have detailed the regulation of transcription initiation and early elongation, the termination phase of transcription also plays critical roles in regulating gene expression. Transcription termination can be driven by only a few proteins in each domain of life. Detailing the mechanism(s) employed provides insight into the vulnerabilities of transcription elongation complexes (TECs) that permit regulated termination to control expression of many genes and operons. Here, we describe the biochemical activities and crystal structure of the superfamily 2 helicase Eta, one of two known factors capable of disrupting archaeal transcription elongation complexes. Eta retains a twin-translocase core domain common to all superfamily 2 helicases and a well-conserved C terminus wherein individual amino acid substitutions can critically abrogate termination activities. Eta variants that perturb ATPase, helicase, single-stranded DNA and double-stranded DNA translocase and termination activities identify key regions of the C terminus of Eta that, when combined with modeling Eta-TEC interactions, provide a structural model of Eta-mediated termination guided in part by structures of Mfd and the bacterial TEC. The susceptibility of TECs to disruption by termination factors that target the upstream surface of RNA polymerase and potentially drive termination through forward translocation and allosteric mechanisms that favor opening of the clamp to release the encapsulated nucleic acids emerges as a common feature of transcription termination mechanisms.

Space Charge Limited Current and Induced Particle Reflection With a Time-Varying Current Injection

Properties of space charge limited current and induced particle reflection with a time-varying current injection are investigated by an efficient grid-free numerical approach. Considering a planar diode with a single-frequency current emitted parallel to the upstream electrode surface, we study the current transmission characteristics between two dc biased electrodes and the influence of current frequency and magnitude on the limiting current first leading to electrons reflection. It is found that on account of the time-varying current injection, the limiting current strongly depends on the current frequency and magnitude, as well as the emission velocity of electrons. For the low-frequency limit, the dc component of the limiting current is approximately equal to half of that obtained from the time-independent model. The limiting current increases monotonically with increasing the frequency, and the dc component has a maximum equal to the limiting current obtained from the time-independent model.

Experimental research on aero-propulsion coupling characteristics of a distributed electric propulsion aircraft

Distributed Electric Propulsion (DEP) aircraft use multiple electric motors to drive the propulsors, which gives potential benefits to aerodynamic-propulsion interaction. To investigate and quantify the aerodynamic-propulsion interaction effect of the wing section, we built a DEP demonstrator with 24 “high-lift” Electric Ducted Fans (EDFs) distributed along the wing’s trailing edge. This paper explores and compares the aero-propulsion coupling characteristics under various upstream speed, throttle, and EDF mounting surface deflection angles using a series of wind tunnel tests. We compare various lift-augmentation power conditions to the clean configuration without propulsion unit under the experiment condition of 15–25 m/s freestream flow and angles of attack from −4° to 16°. The comparison of computational results to the experimental results verifies the effectiveness of the computational fluid dynamic analysis method and the modeling method for the DEP configuration. The results show that the EDFs can produce significant lift increment and drag reduction simultaneously, which is accordant with the potential benefit of Boundary Layer Ingestion (BLI) at low airspeed.

Sunlight-driven nitrate loss records Antarctic surface mass balance

Standard proxies for reconstructing surface mass balance (SMB) in Antarctic ice cores are often inaccurate or coarsely resolved when applied to more complicated environments away from dome summits. Here, we propose an alternative SMB proxy based on photolytic fractionation of nitrogen isotopes in nitrate observed at 114 sites throughout East Antarctica. Applying this proxy approach to nitrate in a shallow core drilled at a moderate SMB site (Aurora Basin North), we reconstruct 700 years of SMB changes that agree well with changes estimated from ice core density and upstream surface topography. For the under-sampled transition zones between dome summits and the coast, we show that this proxy can provide past and present SMB values that reflect the immediate local environment and are derived independently from existing techniques.

Role of gravitational force on mechanical entrainment of nonmagnetic particles in high gradient magnetic separation

Mechanical entrainment is an important mechanism responsible for the low selectivity in high gradient magnetic separation (HGMS). Previous studies on mechanical entrainment mainly focused on particle motion behaviors or interparticle forces, a very important factor attributing entrainment was neglected, namely the effect of gravitational force. In this paper, the role of gravitational force on mechanical entrainment was systematically investigated with varying feeding direction, fluid velocity, size and density of nonmagnetic particles. Results indicated that gravity played a vital role in mechanical entrainment. Nonmagnetic particles were preferentially entrained in deposits of upper surface (relative to gravity direction) rather than upstream surface (relative to flow direction) due to gravity. Mechanical entrainment became more serious with increasing gangue mineral density. Mechanical entrainment of low-density gangue could easily be eliminated with moderate fluid velocity or pulsating frequency, but that caused by large density gangue in upper deposit could hardly be eliminated, even with high fluid velocity or high strength pulsating. Weakening the effect of gravity with nonmagnetic heavy medium (or heavy suspension) should be promising method to enhance selectivity in HGMS, which will be conducted theoretically and experimentally in near future.

Calendering of thermoplastics: models and computations

Abstract John Vlachopoulos (JV) started his polymer processing career with the process of calendering. In two landmark papers with Kiparissides, C. and Vlachopoulos, J. (1976). Finite element analysis of calendering. Polym. Eng. Sci. 16: 712–719; Kiparissides, C. and Vlachopoulos, J. (1978). A study of viscous dissipation in the calendering of power-law fluids. Polym. Eng. Sci. 18: 210–214 he introduced the Finite Element Method (FEM) to solve the governing equations of mass, momentum, and energy based on the Lubrication Approximation Theory (LAT). This early work was followed by the introduction of wall slip (with Vlachopoulos, J. and Hrymak, A.N. (1980). Calendering poly(vinyl chloride): theory and experiments. Polym. Eng. Sci. 20: 725–731). The first 2-D simulations for calendering PVC were carried out with Mitsoulis, E., Vlachopoulos, J., and Mirza, F.A. (1985). Calendering analysis without the lubrication approximation. Polym. Eng. Sci. 25: 6–18. In the intervening 35 years, other works have emerged, however our understanding has not been drastically improved since JV’s early works. Results have also been obtained for pseudoplastic and viscoplastic fluids using the general Herschel-Bulkley constitutive model. The emphasis was on finding possible differences with LAT regarding the attachment and detachment points of the calendered sheet (hence the domain length), and the extent and shape of yielded/unyielded regions. The results showed that while the former is well predicted by LAT, the latter is grossly overpredicted. More results have been obtained for 3-D simulations, showing intricate patterns in the melt bank. Also, the transient problem has been solved using the ALE-FEM formulation for moving free-boundary problems. The results are compared with the previous simulations for the steady-state and show a good agreement. The transient simulations capture the movement of the upstream and downstream free surfaces, and also provide the attachment and detachment points, which are unknown a priori. Finding these still remains the prevailing challenge in the modeling of the calendering process.

Improvement and Verification of One-Dimensional Numerical Algorithm for Reservoir Water Temperature at the Front of Dams

The deep-water temperature of large reservoirs is low, thus easily leads to the appearance and expansion of cracks on the upstream faces of concrete dams. Therefore, in the design phase of a dam, accurately predicting the water temperature distribution at the front of the dam during the operation period of the reservoir takes on a critical significance in the dam simulation analysis of temperature control and crack prevention design. The vertical one-dimensional numerical algorithm of reservoir water temperature was optimized in accordance with the heat transfer equation and considering certain factors (e.g., water temperature transfer, inflow distribution, slag at the bottom of the reservoir, and solar radiation) to solve the above problem. The Nash–Sutcliffe efficiency coefficient (NSE) was adopted to analyze the simulation error qualitatively and quantitatively, and to verify the applicability of the algorithm. The results validated with temperature data measured in four reservoirs illustrate that the proposed algorithm exhibits a higher prediction accuracy than the empirical equation method for water temperature at the front of dams at different scales under different operation modes. The mean deviations of the proposed algorithm are all below 1 °C, and the Nash–Sutcliffe efficiency coefficients (NSE) are all above 0.85. Moreover, compared with the three-dimensional numerical algorithm, the proposed algorithm not only requires a smaller amount of data, but also is simpler to apply and has a higher efficiency. The twelve-month water temperature calculation for a large reservoir takes less than 1 min. This study further reveals that the slag at the bottom of the reservoir is capable of significantly rising the temperature at the dam heel by 5–6 °C. The program compiled by the proposed algorithm can be seamlessly embedded in the simulation program for concrete dam temperature control; thus, the reliability of the simulation of the temperature can be enhanced for temperature field and stress field on the upstream surface of the dam without affecting the total calculation efficiency.

Real scenario analysis of buried natural gas pipeline leakage based on soil-atmosphere coupling

Buried pipeline is the most common mode of natural gas transportation. The analysis of methane diffusion characteristics in leakage accident is of great significance for accident detection and secondary explosion accident prevention. The existing numerical simulation and experimental studies focused on the diffusion of methane in the soil from the leakage of buried natural gas pipeline, and the coupling process of methane passing through the soil and entering the atmosphere was rarely mentioned. However, the surface atmosphere is the main area of human activities, which increases the possibility of fire and other risk factors. In this paper, the coupling process of methane leakage passing through soil and entering the atmosphere was studied by numerical simulation, and the effects of various factors on the methane concentration in the first danger zone (FDZ) and the second danger zone (SDZ) were analyzed. Based on the least square method and multiple regression theory, combined with MATLAB mathematical calculation software, a methane concentration prediction model on the high-risk side of the FDZ was established. The results showed that after methane entered the atmosphere, the diffusion velocity increased significantly. The downstream building surface of the FDZ was the high-risk side of methane distribution, and the upstream building surface of the SDZ was the high-risk side. The average calculation error of the methane concentration prediction equation on the high-risk side of the FDZ was 9.97%, which can effectively evaluate the methane concentration under any leakage working condition. When the buildings floors were different, the high building surface between high building and low building was the high-risk side of methane distribution. This study provides guidance for the design of buried natural gas pipelines in residential buildings, and supplies basis for improving detector installation and gas leakage maintenance specifications.

Research on the life-limiting sputtering mechanism of 30 cm ion thruster

“Pits-and-grooves” patterns on the downstream accelerator grid surface had a severe effect on the thruster life; however, the sputtering patterns on the decelerator grid upstream surface were also observed after the thruster worked for over 3000 h. Reduction of the thruster diameter was adapted to prevent the erosion rate at the decelerator grid, but it decreased the thruster performance. Therefore, balancing the lifetime and performance was so critical for the optimization design of ion thruster. A three-dimension numerical model was established, and a Particle-In Cell-Monte-Carlo-Collision method was applied to investigating the hitting process and sputtering mechanism of a 30 cm ion thruster. Based on the experimental beam ion density profile in the plume, ion optics was divided into three regions, where the center region accounted for 73.3% of the effective extraction diameter of 30 cm. Beam ions in the center and the center-edge region were focused very well, and no ions striked directly on any grid surface, whereas ions at the edge were under-focused and had a cross-over interception. Decreasing the screen grid diameter from 13 to 12 could reduce the maximum erosion depth of the decelerator grid from 1.0 × 10−3 to 9.0 × 10−4, which only resulted in a 0.03% decrease of thruster performance. The maximum erosion depth of the accelerator grid caused by charge exchange xenon ion bombardment was 1.0 × 10−3 locating in the center region, which was twice that of 9.0 × 10−4. Improving the flatness was the way to extend the thruster lifetime. The maximum error of simulation was about 4.38%. The simulation results can provide technical reference for the optimization design of the ion thruster.

Numerical analysis of cavitation and impact load characteristics of supercavitating vehicle entering water at high speed

In order to obtain the influence of water entry angle and speed on the cavitation and impact load characteristics of supercavitating vehicle, a high-speed water entry numerical model of supercavitating vehicle based on VOF model is established, and the accuracy of the model is verified by relative experiments. Through simulation, the cavitation evolution process, cavitation size, impact load change and surface pressure distribution of supercavitating vehicle entering water at different angles and velocities are obtained and compared. The results show that with the increase of water entry velocity, the depth of cavitation closing position increases, the cavitation size increases, the peak value of axial load increases and the surface pressure of vehicle increases; With the increase of water entry angle, the bubble closing time remains unchanged, the bubble size decreases, the axial load peak increases, and the asymmetry of pressure distribution decreases. The pressure on the upstream surface of the cavitator increases along the radius to the center of the circle, but the asymmetry decreases when it enters the water obliquely.

Effects of in situ leaching on the origin and migration of rare earth elements in aqueous systems of South China: Insights based on REE patterns, and Ce and Eu anomalies

In situ leaching of ion-adsorption rare earth element (REE) deposits has released large amounts of REE-containing wastewater. However, the origin, speciation, distribution and migration of REEs in aqueous systems of the mining catchment are poorly understood. Groundwater, surface water, in situ leachates and weathered granite soil samples were collected from a catchment affected by mining activities in South China. The REE concentrations in groundwater (6.18 × 10–3–0.49 μmol L–1) and surface water (2.54–44.05 μmol L–1) decreased from upstream to downstream. REEs in groundwater were detected in organic matter associated (FA-REE) colloids, while the REE3+ and REE(SO4)+ were converted to REE(CO3)+ and FA-REE colloids from leachates and upstream surface water to downstream. The REE patterns of leachates and upstream groundwater (light and middle REE enrichment) resembled those of soil, but showed heavy REE enrichment due to FA-REE colloids in the downstream. REE in surface water were derived from middle REE enriched leachate. The Ce and Eu anomalies in the water samples indicated the REE origin (i.e., mining activities) and the hydrological variations (e.g., oxidation environment and water-rock interaction). Our results reveal the origin and fate of REE in aqueous systems of ion-adsorption REE mining catchments.

Evaluating the effects of dams and meteorological variables on riparian vegetation NDVI in the Tibetan Plateau

As the third pole of the world, the Qinghai-Tibet Plateau (QTP) has a very special climate and geographical environment. In the past 20 years, with the increasing demand for clean energy, more than ten hydropower stations have been built. The impacts of these hydropower stations on riparian vegetation (RV) have only been described qualitatively in previous studies, while the contribution of dams and meteorological variables to riparian vegetation has not been quantitatively assessed. This study selected eight representative large-scale hydropower stations in the QTP, calculated and analyzed the dynamics of the standardized difference vegetation index (NDVI) of the RV pre-and post the dams construction, combined with the measured temperature and precipitation data to explore the driving factors of RV changes. The results show that the dams promoted the growth of RV and they were the main contributor (>50%) while precipitation and temperature had relatively small impacts. The effect of dams varies for different regions, compared with the sub-cold regions, it was more significant in humid and semi-humid regions of temperate zone. The dams affected RV in an indirect way through regulating the microclimate, promoting precipitation and slowing down the rate of temperature rise and these effects may come from the increase of the upstream water surface area.

Experimental study on local scour depth around pile groups

An accurate prediction of local scour depth at piles is essential for bridge safety. In order to obtain the prediction formula of local scour around pile groups, a series of local scour experiments of pile groups were carried out. The results show that the scouring depth decreases along the flow direction and the deepest scouring occurs in the first row of the upstream surface. The local scour depth of the front row is greater than that of the single pile. According to the test data and previous data, a calculation coefficient of pile group scour depth with reasonable forms is introduced. The scour depth calculated by this coefficient is in good agreement with the measured value, which proves the rationality of the proposed coefficient.

Release and transformation of phosphorus in sediment following seasonal freezing-thawing cycles

River ice in the upper Yarlung Zangbo River is characterized by seasonal freezing-thawing cycles (SFTC). It is important to explore the effects of SFTC on phosphorus release and transformation from upstream surface sediments to protect the ecosystem of the Yarlung Zangbo River. The process and mechanism of phosphorus release and transformation in sediments following SFTC were investigated in a laboratory simulation experiment. The results showed that after freezing, sediment particles were broken, the specific surface area was increased by 14%, and the particle size was decreased by 43%, which resulted in weakened adsorption of phosphorus by sediments. Moreover, the destruction of organic matter (OM) on the sediment surface will release more ion adsorption sites and promote the release of phosphorus. The bioavailabilities of exchangeable phosphorus (Ex-P), aluminum phosphorus (Al-P) and iron phosphorus (Fe-P) increased by 60.09%, 86.86% and 31.86%, respectively, after freezing. Organic phosphorus (O-P) is used indirectly by organisms, and O-P content showed a significant correlation with OM content. Water affected the oxygen content in sediments during the freezing period, and continuous hypoxia promoted the release and transformation of Fe-P and Al-P.