Maximum Reduction Rate Research Articles

Effect of double cracks merge on fatigue crack propagation life of engine heat shield

To prevent overheating of the airframe, an aero-engine is often designed to play a role in shielding heat radiation heat shield. Since the thermal protection system used in this paper is active, it is subject to a cold gas pressure load on the outside and a thermal radiation load from the combustion chamber on the inside. Therefore, the working environment of the heat shield is very harsh. Taking the heat shield of an aero-engine as the research object, the finite element method (FEM) is used to analyze the thermal-mechanical coupling (TMC) of the actual working process of the heat shield, and the mechanical quantities such as the thermal stresses and mechanical stresses are comprehensively analyzed. According to the finite element simulation results, two stress concentrations are obtained near the connecting lug, and the stress concentrations are set as the initial crack insertion locations. Using the theory related to linear elastic fracture mechanics (LEFM) and the Forman-Newman-de Koning (FNK) model, the fatigue crack propagation life (FCPL) and its law of the merged double cracks of the engine heat shield are calculated. The results show that the FCPL of the heat shield decreases nonlinearly and the critical crack length decreases linearly under different working conditions. This law applies not only to single cracks but also to merged double cracks. In terms of FCPL, the merged double cracks are lower than the single crack with a maximum life reduction rate of 70.9%.

Effects of incorporated silicone oils on the antifouling and drag reduction of Fe2O3/PDMS coatings

To develop an environmentally friendly fouling release coating, the effects of different silicone oils on the antifouling and drag reduction of the coating based polydimethylsiloxane (PDMS) reinforced iron oxide (Fe2O3) were investigated. The Fe2O3/PDMS coatings incorporated phenylmethyl silicone oil (PSO), methyl silicone oil (MSO), and a mixture of PSO and MSO were prepared. The surface morphology of the coating and the leaching rate of silicone oil were characterized by CLSM. The mechanical properties, anticorrosion, antifouling, and drag reduction performance of the coating were tested through the stress-strain curves, pull-out test, EIS, bacterial and diatom adhesion experiment, and single turntable torque experiment. Results revealed the leaching rate of PSO was the highest in the air. The hydrophobicity, the surface free energy, the multiple interlayer adhesion strength, the anticorrosion, the resistance to bacterial biofilms and Navicula tenera adhesion, and the drag reduction of the coating with PSO (IO-PSO) were better than those of the coating with MSO (IO-MSO). |Z|1 Hz for the coating IO-PSO immersed for 720 h can still reach the order of 1011 Ω cm2. The maximum drag reduction rate of the coating IO-PSO at 1600 rpm was 3.52 % compared to the epoxy coating.

Combined conventional ultrasonography with clinicopathological features to predict axillary status after neoadjuvant therapy for breast cancer: A case-control study.

This study aimed to evaluate the value of a model combining conventional ultrasonography and clinicopathologic features for predicting axillary status after neoadjuvant therapy in breast cancer. This retrospective study included 329 patients with lymph node-positive who underwent neoadjuvant systemic treatment (NST) from June 2019 to March 2022. Ultrasound and clinicopathological characteristics of breast lesions and axillary lymph nodes were analyzed before and after NST. The diagnostic efficacy of ultrasound, clinicopathological characteristics, and combined model were evaluated using multivariate logistic regression and receiver operator characteristic curve (ROC) analyses. The area under ROC (AUC) for the ability of the combined model to predict the axillary pathological complete response (pCR) after NST was 0.882, that diagnostic effectiveness was significantly better than that of the clinicopathological model (AUC of 0.807) and the ultrasound feature model (AUC of 0.795). In addition, eight features were screened as independent predictors of axillary pCR, including clinical N stage, ERBB2 status, Ki-67, and after NST the maximum diameter reduction rate and margins of breast lesions, the short diameter, cortical thickness, and fatty hilum of lymph nodes. The combined model constructed from ultrasound and clinicopathological features for predicting axillary pCR has favorable diagnostic results, which allowed more accurate identification of BC patients who had received axillary pCR after NST. A combined model incorporated ultrasound and clinicopathological characteristics of breast lesions and axillary lymph nodes demonstrated favorable performance in evaluating axillary pCR preoperatively and non-invasively.

Comparative analysis of CO2 reduction by soluble Escherichia coli formate dehydrogenase H and its selenocysteine-to-cysteine substitution variant

Metal-dependent formate dehydrogenases (Me-FDHs) are highly active CO2-reducing enzymes operating at low redox potentials and employ either molybdenum or tungsten to reduce the bound substrate. This makes them suitable for electrochemical applications such as fossil-free production of commodity chemicals utilizing renewable energy. Electrocatalytic CO2 reduction by cathode-immobilized Me-FDHs has been recently demonstrated and rational protein engineering can be used to optimize Me-FDHs for various carbon reduction reactions. In the present study, CO2 reduction by soluble monomeric Escherichia coli formate dehydrogenase H (EcFDH-H) was demonstrated and the function of its nucleophilic selenocysteine residue as a transient ligand of a centrally bound molybdenum atom was investigated. Kinetic analysis of the wildtype enzyme revealed maximum CO2 reduction rates of 44 ± 6 s−1 at pH 5.8 that was decreased to 19% and 0% in the case of selenocysteine substitution with the structural homologues cysteine and serine, respectively. Further selenocysteine-to-cysteine substitution effects included an increased acid tolerance as well as stronger inhibition by nitrate and azide indicating a shift of the Mo oxidation state from IV to VI. Conversely, a destabilizing effect on the oxidized Mo(VI) center could be assigned to the native selenocysteine residue that may facilitate the observed efficient CO2 reduction by rapid transition between Mo oxidation states. Taken together, the performed characterization of EcFDH-H as a catalyst for CO2 reduction and the selenocysteine substitution analysis furthers the understanding of the active-site structure of Me-FDHs and thereby supports the development of more efficient biocatalysts for CO2 reduction.

Enhancing energy efficiency in rural CCHP systems with optimal gas engine size selection and Improved Coyote Optimizer

This study introduces a novel tactic to efficiently size the selection of gas engines for Combined Cooling, Heating, and Power (CCHP) systems in rural areas. This method is based on an adapted bio-inspired method, called Improved Coyote Optimizer (ICO). The proposed ICO technique uses a combination of metaheuristic optimization techniques and the system model to determine an optimal overall engine size while satisfying given operating constraints and minimizing the total cost. The analysis revealed that the fuel consumption of the gas engine and boiler in the proposed system is dependent on the power level. At 40 kW, the engine consumed 1558 units of fuel, while the boiler consumed 1430 units, with this difference increasing to 411 units at 110 kW. These findings emphasize the importance of improving the fuel efficiency of the engine, particularly at higher power levels. Furthermore, the study assessed the system’s CO2 emissions, finding that the minimum yearly emissions of 220,600 kg occurred at an engine power of 1 kW, while the maximum CO2 reduction rate of 40% was achieved at 120 kW. This suggests that larger engines are more efficient, resulting in lower CO2 emissions due to reduced fuel consumption. In terms of financial considerations, the engine power dimension of 118.9 kW yielded the highest cash flow value of 49,840 $. However, variations in engine power between 60 and 100 kW indicate a wider range of production costs and output quantities. To accurately evaluate the return on investment, more detailed information on production costs and output within this range is necessary. Lastly, the study compared different optimization methods and found that the Improved Coyote Optimizer (ICO) demonstrated the fastest convergence, reaching its ideal values in 3000 iterations. Both the ICO-based method and the ABC-based technique successfully minimized the cost function, with the ICO-based method achieving the best value of 0.20. Furthermore, the proposed algorithm is practical to a wide variety of CCHP system configurations, making it a valuable tool for practitioners.

Influence of a groove-structured vortex generator on the drag reduction characteristics of a multiphase pump

The oil–gas mixture pump significantly contributes to marginal oil field extraction and remote transportation of deep-sea oil. Nevertheless, during the operation of the mixture pump, it is inevitable to encounter problems like the separation of the mixed media from the hydraulic components as well as the gas phase from the liquid phase, which leads to enhancing the flow resistance of the mixed media. Therefore, this study investigates the influence of a groove-structure vortex generator on the drag reduction characteristics of a helical axial-flow gas–liquid multiphase pump under the design flow rate condition and various inlet gas content rates. The findings show that the vortex generator with diverse groove depths can prevent the separation of the mixed media from the blade suction surface effectively and minimize the flow resistance of the media in the 1/10 of the blade inlet. In particular, excellent drag reduction results were gained with a maximum drag reduction rate of 36.7% when the relative depth was 3/40. In addition, the efficiency of the mixture pump increased by a maximum of 2.1%, and the head increased by a maximum of 4.3%. The significance of this study lies in its potential to further optimize the design and performance of gas–liquid multiphase pumps. It provides new insights into the design and application of vortex generators. It offers robust support for the optimization and enhancement of gas–liquid multiphase pumps.

Stormwater and flood simulation of sponge city and LID mitigation benefit assessment.

In the context of global climate change and the influence of human activities, the concept of "sponge city" is put forward to realize the purification, collection, and reuse of rainwater. The effective evaluation of LID facilities in sponge cities is of great guiding significance for the promotion and construction of sponge cities. IFMS (Integrated Flood Modeling System) Urban was selected to construct the rainstorm simulation. LID parameters were added to simulate the improvement of urban waterlogging after the construction of sponge city. A reasonable disaster loss assessment method was used to calculate the disaster mitigation benefit brought by the construction of sponge city. Through the comparison of the inundation situation before and after LID facilities' construction, it can be concluded that the mitigation effect of LID facilities on the overall inundation area of the city decreases with the increase of rainfall recurrence period, with the maximum reduction rate reaching 13.63% in the 5-year recurrence period and the minimum reduction rate of 11.06% in the 50-year recurrence period. LID facilities have a better disaster reduction effect for rainfall events with a small recurrence period than for rainfall events with a large recurrence period.

Anti-wear properties of multi-bioinspired textures with hierarchical and superhydrophobic structures under water lubrication

Surface texturing is a promising way to reduce wear, but further improvements in wear resistance via single textures remain challenging. Inspired by multiple biological surfaces, we design and prepare two microtextures (MTs) on AISI 440C steel by femtosecond laser and then construct superhydrophobic micro/nanostructures in the MTs to obtain two multi-bioinspired hierarchical textures (MHTs). The MHTs show significant wear resistance under relatively low loads and high frequencies. Remarkably, compared with polished surfaces, the wear rates of the dimple-shaped MHTs (DMHTs) and the groove-shaped MHTs decrease by 64.6% and 50.0%, respectively. The introduction of the superhydrophobic micro/nanostructures enables the maximum wear reduction rate of the DMHTs 121.2% higher than that of the corresponding single textures. The wear resistance of the MHTs originates from the synergetic effects (manifested by the increases in surface hardness and hydro-dynamic pressure) of the laser-ablated MTs and superhydrophobic micro/nanostructures. We envision that this work will inspire the design and fabrication of more multi-bioinspired textures to achieve further improvements in wear resistance of mechanical parts under water lubrication.

Study on probability model and length effect of tensile strength of unidirectional CFRP plate

This manuscript investigates the probability model and the length effect of tensile strength for unidirectional plates of carbon fiber reinforced polymers (CFRP). Firstly, 30 unidirectional CFRP plates with length of 250 mm are investigated by tensile strength tests and statistical analysis of strength probability characteristics with Normal, Lognormal, traditional Weibull and couple-Weibull distribution. While the test results show that the probability density curve of tensile strength exhibits double peaks, a couple-Weibull model is proposed to describe the probability characteristics of tensile strength, which exhibits good accuracy and applicability with comparison to the experimental results. On this basis, the tensile strength of ten groups of unidirectional CFRP plates with different lengths is tested. The results show that the influence of length effect on tensile strength is significant, and the maximum strength reduction rate is 17.11%. Finally, a probability model of tensile strength considering length effect is established based on couple-Weibull model. With comparison to the test results, it is validated to properly consider the variation of tensile strength with different lengths for unidirectional CFRP plate and give accurate prediction results.

Research on drag reduction performance of sliding plate of rice direct seeding machine based on non-smooth structure of loach surface

Sliding plate has the problems of large sliding resistance and serious soil adhesion. Loach moves freely and flexibly in mud, has highly efficient lubrication and drag reduction effects. The sliding plate of rice direct seeding machine was selected as the research object and loach as the bionic prototype. The macroscopic and microscopic structure characteristics of loach were observed, the body surface of loach was covered by scales, which had a ridged non-smooth structure. The simulation analysis of the drag reduction performance of the non-smooth structure was carried out, the maximum drag reduction rate was 2.55% at the speed of 1 m/s. A bionic sliding plate of rice direct-seeding machine was constructed based on the non-smooth structure of loach body surface, and its working performance was simulated and analyzed. The results of orthogonal test show that the order of primary and secondary factors of bionic structure parameters affecting drag reduction rate was ribbed spacing > ribbed width > ribbed height. The optimal parameter combination was ribbing height 4 mm, ribbing width 4.5 mm, ribbing spacing, and the optimal drag reduction rate was 4.21%. The results of this study can provide theoretical support for bionic design of soil-engaging components in wet and soft paddy field.

Acute changes of superior mesenteric artery pressure after intraarterial bolus injection of prostaglandin-E1.

Background: A bolus injection of prostaglandin-E1 (PGE1) into the superior mesenteric artery (SMA) immediately before SMA-portography can effectively visualize the portal vein. Objective: The purpose of this study was to obtain basic pharmacoangiographical data and evaluate the hemodynamic changes following intra-arterial bolus injection of PGE1. Materials and Methods: Forty-four consecutive patients undergoing transcatheter arterial chemoembolization (TACE) for liver cancer were retrospectively evaluated. SMA-portography was performed prior to TACE. An intra-arterial bolus injection of PGE1 was performed immediately before SMA-portography. Both SMA pressure and left brachial artery pressure were measured before, 1, 2, 3, 4, and 5 minutes after SMA-portography. Results: Systolic pressure in the SMA decreased significantly 3 minutes after SMA-portography and remained low for 5 minutes. The maximum reduction rates in systolic and diastolic blood pressure in the SMA were 4.8% (4 minutes after SMA-portography) and 6.8% (5 minutes after SMA-portography), respectively. The left brachial artery pressure decreased similarly to the SMA. There were no significant changes in pulse pressure before or after PGE1 injection in either the SMA or brachial arteries. Conclusion: A bolus injection of PGE1 into the SMA was shown to decrease blood pressure in the SMA and brachial arteries, but the pulse pressure remained constant.

Numerical study on the performance of mixed flow blood pump with superhydrophobic surface.

To meet the clinical status of the wide application of percutaneous mechanical circulatory support, this paper selects the mixed flow blood pump applied with superhydrophobic surface as the research object. The Navier slip model was used to simulate the slip characteristics of superhydrophobic surface, and the effects of the blade wrap angle and the superhydrophobic surface on the performance of the mixed flow blood pump are studied by numerical simulation. The results show that (1) considering the head, hydraulic efficiency, and hemolysis index of the blood pump, the optimal value of the blade wrap angle of the mixed flow blood pump in this paper is 60°. (2) The hydraulic efficiency of the blood pump with superhydrophobic surface is improved, and the maximum growth rate is about 13.9%; superhydrophobic surface can reduce the hemolysis index of blood pump under various working conditions, and the maximum reduction rate of hemolysis index of blood pump is 22.9%. (3) The variation trends of blood pump head, hydraulic efficiency, and hemolysis index with the increased rotating speed before and after setting superhydrophobic slip boundary conditions are the same as their original variation trends.

Performance and unsteady flow characteristic of forward-curved impeller with different blade inlet swept angles in a pump as turbine

As an economical energy recovery device, a pump as turbine (PAT) is widely used in micro hydropower and energy recovery fields. Compared with an original impeller, a special impeller with forward-curved blades can dramatically enhance a PAT's efficiency and broaden its high-efficiency range because the blade angles created by the latter more effectively match the PAT's operating mode. The shape of blade curve and sweep has obvious influence on the performance of a PAT. To investigate how the inlet swept angle of forward-curved blade influences the performance of PAT, five different forward-curved impellers with different inlet swept angle blades were designed and numerically investigated based on a verified computational fluid dynamics (CFD) method. The effects of blade inlet swept angles on the external characteristics, energy loss and unsteady characteristics of PAT are analyzed. Compared with the blade whose inlet swept angle is 0°, the maximum efficiency of back-swept PAT with swept angle of −8° increases by 0.58% while the head decreases by 0.49 m. However, the efficiency of forward-swept PAT of 8° reduces by 0.9%, and the head increases by 0.68 m. The maximum reduction rates of the main frequency amplitude of pressure pulsation in the volute, impeller and draft tube of back-swept PAT are 35.2%, 45.47% and 67.24%, respectively, indicating that the back-swept blade can contribute to improve the operation stability of PAT. Moreover, the vortex in PAT with back-swept blade is greatly improved under partial and design flow rate, which can improve the unsteady flow characteristics of PAT.

Dynamic interactions of tram-turnout coupling system in embedded turnout area

Embedded turnout is one of the key facilities in the embedded track network of modern tram systems. In this study, the damping performance and track stiffness of an embedded turnout are tested on site. A multi-rigid body dynamics model of the tram and a finite-element dynamics model of the embedded turnout are established, and the two models are coupled based on the wheel-rail contact theory for the turnout area. Next, the dynamic responses of the tram passing through the embedded turnout are analyzed. The results show that the embedded turnout has favorable damping performance. The high stiffness of variable section rails at the switch and frog would lead to an increase in the wheel-rail dynamic force. When the tram passes through the embedded turnout, the wheel-rail vertical force reaches maximum values of 106.3 and 35.2 kN at the frog and switch, respectively; the maximum wheel derailment coefficient and wheel weight reduction rate are 0.49 and 0.57, respectively, which are within the safety limit specified in the Standards; the maximum lateral and vertical vibration accelerations of the tram body are 0.38 and 0.71 m/s2, respectively, satisfying the comfort requirements; the wheel–rail wear work at the switch is greater than that at the frog.

Investigation of drag reduction mechanism for blunt bodies with plasma spikes

The two main problems in hypersonic vehicles are wave drag and aerodynamic heating. This work proposes a novel method for drag reduction by combining spikes with the plasma synthetic jet actuator (PSJA). Numerical simulations are performed to better understand the drag reduction mechanism with an incoming flow at Mach 6. The results suggest that the flow field is affected primarily by the diffracted wave and synthetic jet. The maximum drag reduction reaches 47.7% with the plasma spike compared with the opposing jet. A better drag reduction effect is achieved when increasing the energy density of the PSJA, while the propagation velocity of the diffracted wave remains constant. A wider and faster jet is obtained with a larger PSJA orifice diameter. However, the control time of the jet shortens. A mode conversion occurs when the orifice diameter is 1 mm. Furthermore, the maximum drag reduction rate increases from 37.6% to 49.0% when the length diameter ratio (L/D) increases from 0.5 to 1.5. The effect of spike length on drag reduction decreases gradually at greater lengths.

Reduce the magnetic damping of Pt/ferromagnet heterostructures by inserting a Hf spacer layer

We investigated the effect of the Hf spacer layer on the magnetic damping of Pt/ferromagnet (FM) heterostructures by using broadband ferromagnetic resonance. The magnetic damping of Pt/Co is reduced greatly and then enhanced slightly as the thickness of the Hf spacer layer increases, which is ascribed to the competition of the magnetic proximity effect, the anti-damping behavior, and the spin-pumping effect occurring at the interface. The 3-nm-thick Hf spacer layer results in a maximum reduction rate as high as 48.8% for the magnetic damping of the Pt/Co samples. The reduction of magnetic damping by the Hf spacer layer was additionally demonstrated in the heterostructures of Pt/NiFe and Pt/CoFeB, which suggests the universal tuning effect of the Hf spacer layer on the magnetic damping of Pt/FM systems.

Study on the Synthesis and Properties of a New Salt-Resistant Drag Reducer

Summary To solve the problem of poor salt resistance of conventional drag reducers, a hydrophobic associative polymer drag reducer was prepared by inverse emulsion polymerization with acrylamide (AM), methacrylic acid (MAA), 2-acrylamide-2-methylpropane sulfonic acid (AMPS), and hexadecyl dimethyl allyl ammonium chloride (C16DMAAC) as the main monomers. The synthetic product was confirmed as the target product by infrared (IR), nuclear magnetic resonance (NMR), and mass spectrometry (MS). The viscosity-average molecular weight of the prepared drag reducer is 1100×104 g/mol. The pipeline friction results show that the drag reducer has good friction reduction and salt resistance. When the concentration in clean water is 0.06%, the maximum friction reduction rate is 71.1%. When the salinity is 5×104 mg/L, the calcium ion concentration is 2000 mg/L, and the suspended solid content is 500 mg/L, the maximum friction reduction rate is 68.9% when the concentration of the drag reducer is 0.06%. Salt water will not significantly lower the friction reduction rate. If the concentration of the drag reducer is increased to 0.08%, the maximum drag reduction rate will reach 73.8%. The microrheological test results of the friction reducer solution show that, at 0.2% concentration, there is no network structure between friction reducer molecules, which is consistent with Newtonian fluids possessing a certain viscosity. The elasticity index (EI) of the drag reducer solution is basically unchanged over time, maintaining good friction reduction and sand-carrying performance during the shearing process of large displacement pumping.

Multi-objective optimization of loading path for sheet hydroforming of tank bottom

As a critical component of the propellant tank, the tank bottom is subjected to complex loads such as internal pressure and vibration and has high requirements for structural load-bearing capacity. Hydroforming deep drawing is one of the techniques for the integral forming of the tank bottom. As the tank bottom is a large-size thin-walled structure, defects such as cracks and wrinkles are prone to occur during the hydroforming deep drawing process. Aiming at reducing these defects, the hydraulic pressure loading path and blank holder force loading path of the hydroforming deep drawing process are studied, and a multi-objective optimization method is proposed to improve the surface accuracy and thickness distribution uniformity of the tank bottom. The complex loading path curve optimization problem is transformed into a functional relationship between hydraulic pressure and blank holder force with time. The hydraulic pressure and blank holder force at each time node are used as design variables, and the maximum wall thickness reduction rate, rupture trend factor, wrinkle height, and wrinkle trend factor are used as optimization targets. The radial basis function (RBF) neural network is used to establish the approximate model between the loading path and the optimization target, and the multi-objective particle swarm optimization (MOPSO) algorithm is used to optimize the solution. Taking the hemispherical tank bottom as an example, the optimal hydraulic pressure loading path and blank holder force loading path are obtained, and the quality of the formed part is improved.

Misalignment effect on the ultimate strength of welded stiffened panels under uniaxial compression

Longitudinal stiffener misalignment (LSM) is inevitable in the manufacturing process of stiffened hull panels, affecting the geometric appearance and bearing capacity. However, the knowledge of the effect of LSM on the ultimate strength of stiffened panels is limited. In this paper, continuous numerical simulations are first conducted regarding forced alignment, welding process and ultimate strength analysis by using the nonlinear finite element method. A simplified model is then derived considering LSM and initial deflection based on a comparative study of the ultimate strength and collapse patterns. Influences of various combinations of LSM and initial deflection on the strength characteristics and failure behaviors are documented and discussed. According to the parametric analysis, it is found that the LSM imperfection decreases the ultimate strength, but the degree of reduction depends on the shape and amplitude of the panel initial deflection. The maximum reduction rate is 8.71% occurring in the case where the deflection shape with slight amplitude is symmetric. On the basis of 120 numerical results, an empirical formula is proposed for predicting the residual strength as a function of the dimensionless misalignment degree together with panel and column slenderness.

Study on the influences of the fractal dimension of the root system and slope degree on the slope stability

The problem of quantifying the effect of the alfalfa root morphology on the stability of the shallow surface layer of the slope of the Haizhou open-pit coal mine and the optimal slope degree in terms of the reinforcement of the shallow surface layer by the alfalfa root system was addressed. In this study, the mechanical parameters of plain soil and alfalfa root–soil composite samples were measured by indoor soil tests and triaxial compression tests, and a calculation model for the slope of the Haizhou open-pit coal mine was established in FLAC3D numerical simulation software to analyze the influence of the alfalfa root system on the maximum displacement of the shallow surface layer of the slope and the relationship with the fractal dimension of the alfalfa root system. The fractal dimension was applied to quantify the influence of the alfalfa root morphology to further investigate the relationship between the fractal dimension of the root system and the optimal slope of the shallow surface layer. The analysis showed that the fractal dimension of the alfalfa root system varied at different slope degrees, i.e., 40° > flat > 30° > 50°; the maximum soil displacement of the shallow surface layer of the slope increased with slope in nonlinear increments. Analysis of the fractal dimension of the alfalfa root system and the maximum displacement reduction rate at the different slope degrees revealed that the optimal slope degree of the shallow surface layer reinforced by alfalfa varied between 30° and 40°. The study results could provide a basis for further explaining the nature of the role of the alfalfa root morphology in reinforcing shallow surface soil and the optimal slope degree of the slope of the Haizhou open-pit coal mine reinforced by alfalfa roots.