Bridge Force Research Articles

Effect of Al content on the agglomeration behavior of inclusions in high Al steel

The product quality problem of high Al steel is closely related to the agglomeration behavior of inclusions. The present study firstly established the stability diagram of inclusion in the Fe–Al–O–N system, thereby evaluating the formation behavior and control condition of various inclusions can be obtained. Based on that, laboratory-scale experiments with different Al contents were designed to obtain the inclusion evolution process. Furthermore, the calculated agglomeration forces were used to explain the difference of evolution of various inclusions. The cavity bridge force increases with the increase of diameter of inclusions and decrease of distance between inclusions, and the van deer Waals force decreases with the increase of diameter and distance. Due to the cavity bridge force is larger than van deer Waals force, the inclusions firstly approached each other by van deer Waals force and then agglomerated by cavity bridge force. In addition, the cavity bridge force of Al2O3 is larger than that of AlN at the same condition because of the larger contact angle. However, the increase of Al content makes this phenomenon converse. When the Al content is > 3 wt. %, the cavity bridge force of AlN is larger than that of Al2O3. When the Al content is > 7 wt. %, the cavity bridge force of Al2O3 disappears. The study can provide theoretical support for inclusion control in high Al steel.

The effect of short-chain fluorocarbon and electrolyte on simultaneous dedusting and explosion prevention performance when applied to coal particle with high oil-content

The fully mechanized mining faces in underground oil-rich coal mines are exposed to the serious dust pollution and the high risk of dust explosion. Traditional materials cannot effectively realize the removal and inerting of coal particles with high oil content. Thus, this paper innovated new materials to eliminate the occupational disasters and explosion accident in underground coal mines by achieving simultaneous dedusting and explosion prevention of coal particles with high oil content. Compare with traditional materials, the presence of short-chain fluorocarbon surfactants and electrolytes achieved 76.30–84.92% improvement on dedusting rate, a maximum 22 times improvement on MIE, 4.20–8.90% improvement on MIT, and 50% improvement of MEC. Mechanism analysis revealed the better performance is attributed to the optimized wetting and agglomerating behaviour. Kinetic analysis showed that the new materials reduced the heat release and inhibit combustion process. The NaCl outperforms NaHCO3 in achieving better dedusting and explosion suppression performance in most cases for its higher TSI and more efficient explosion prevention mechanisms. Studies also demonstrated that the oil content could moderate the dedusting and explosion prevention performance due to the reduction of static liquid bridge force in terms of the increased proportion of saturated hydrocarbons and aromatic hydrocarbons, the reduced concentration of polar functional group, and the corresponding increased contact angle “θ”. The Findings of this paper provide an efficient and environmental-friendly choice for ensuring occupational health and safe production in underground oil-rich coal mines by achieving simultaneous dedusting and explosion prevention. It will also guide the innovation and development of multiple protective materials for coal mine safety protection.

Impact of Stiffness on the Cable Force of Cable-Supported Bridges

Impact of Stiffness on the Cable Force of Cable-Supported Bridges

Damage mechanism and damage evaluation of PC box girder bridge subjected to overheight vehicle impact

AbstractAccidental collisions from overheight vehicles often result in significant damage of bridges. To ensure the safety of the bridge structure, it is essential to develop a method to evaluate the damage caused by these impact loadings. This study aims to investigate the damage mechanism of a prestressed concrete (PC) box girder bridge subjected to overheight vehicle impact using the finite element analysis method. Parametric analyses were performed to study the effects of various factors on the impact force and deformation performance of the bridge. In addition, a damage assessment formula, based on the vertical residual bearing capacity, is proposed to evaluate the damage state of the impacted PC box girder. A mass–velocity (m–v) curve is developed to characterize the damage levels of the impacted PC girder under different vehicle velocity and mass conditions. Then, a theoretical equation for predicting the maximum impact force during the vehicle‐bridge collision is developed. The numerical analysis results show that vehicle‐related parameters have a significant influence on both impact force and local damage of the PC box girder bridge. The proposed mass–velocity (m–v) curve can be used to evaluate the damage state of the PC box girder by relating the performance levels of the girder to each damage index. Moreover, the predicted maximum impact force can be used as an important index to assess the extent of the local damage of the PC box girder.

Constitutive model for steel fiber reinforced concrete under shear and tension accounting for fiber orientation effect

This paper presents a constitutive model for the behavior of steel fiber reinforced concrete (SFRC) under mixed mode cracking taking into account the fiber orientation effect by using a micromechanical approach. Firstly, the resistant mechanisms of an inclined fiber are modeled by a closed-form analytical function. The bridging force is calculated by integrating on the cracked surface, the product of the fiber extraction force by its orientation probability. A modified model of the aggregate interlock mechanism is combined with the fiber bridging stresses to obtain the cohesive stresses. This mesoscale model is then extended using an elastic damage model and a fixed smeared cracking concept to assess the structural behavior. The model is finally implemented in a Finite Element Analysis (FEA) software, its performance is tested with some experimental results collected in the literature. The model successfully integrates the fiber orientation effect and shows a good prediction of stress transmission.

Investigation on microscopic forces between methane hydrate particles in gas phase dominated system

Hydrate aggregation and deposition on the pipe wall are the main causes of hydrate plugging in pipelines. Microscopic forces between hydrate particles are an important reference for determining the behavior of aggregation or separation from the pipe wall of hydrate particles. Based on a high-pressure visual micro-force measurement system, this study measured the hydrate particle-hydrate particle cohesive force and hydrate particle–wall liquid droplet adhesion force under pure water, as well as hydrate particle–wall liquid droplet adhesion force under anti-agglomerants (AAs). It was found that the magnitude of hydrate particle-hydrate particle cohesive force was ×10 mN/m, and the magnitude of hydrate particle–wall liquid droplet adhesion force was ×103 mN/m. The effects of 4 AAs in the methane gas-dominated system were evaluated from a micro-perspective, revealing that after adding DDBAB, D1021, AEO-9, and CDEA, the maximum reduction of adhesion force was 67%, 64%, 51%, and 53% compared with that under pure water, respectively. The mechanism of AAs reducing adhesion force was further explored, revealing that the adhesion force arose from a liquid bridge and was affected by the gas–water interfacial tension of solutions at low subcoolings. While at high subcoolings, the force was determined by the combined force of the liquid bridge and the hydrate shell. The addition of AAs reduced the gas–water interfacial tension of solutions, and the steric hindrance effect of AA molecules also weakened the tensile strength of the hydrate shell, leading to a decreased adhesion force. These experimental data can help deepen our understanding of the microscopic forces between methane hydrate particles, and provide experimental data and scheme design basis for wellbore flow assurance of deepwater gas wells.

A novel water film enhanced electrostatic agglomeration process to remove fine particles: performance and mechanism

Wet electrostatic agglomeration (WEA) is a very promising method in fine particle removal, however, it is still a challenging problem to avoid short-circuiting of the equipment caused by spraying water during traditional WEA. In this work, a novel WEA process based on a water film was established for the first time, and the fine particle removal and process mechanism were investigated. The influence of discharge and ground electrodes on the particle agglomeration performance was studied, indicating that a much better agglomeration performance was obtained by the spike plate (discharge electrode) thanks to the stronger electric field covering the entire agglomeration area. The corrosion-resistant and low-priced polyvinyl chloride (PVC) plate could significantly improve the water distribution effect after surface grooving modification, and its agglomeration as a grounding electrode under wet conditions was comparable to that of the wet metal plate. The mechanism of the water film enhanced WEA process lay in the fact that the high-voltage electric field greatly promotes the evaporation of the water film, which increased the humidity in the agglomeration space, resulting in liquid bridge force between the water-absorbing particles. In summary, this work provides an alternative novel idea for enhancing the agglomeration performance of the traditional WEA process.

High intrinsic thermal conductive polymer films by engineered interchain hydrogen bond interactions

AbstractA series of polyvinyl alcohol (PVA) composite films containing different hydrogen bond acceptors 4,4′‐dihydroxydiphenyl (BP), 1,1′‐biphenyl‐4,4′‐diyl dihexanoate (DHB) and benzene‐1,3,5‐triyl tribenzoate (TBB) were prepared by casting method. Due to the existence of strong intermolecular interaction, the highest in‐plane thermal conductivity of the above films is 1.298 Wm−1 K−1, which is about 65% higher than pure PVA films. Fourier Transform infrared spectroscopy (FT‐IR) and wide‐angle X‐ray diffraction (WXAD) demonstrated that the TBB acts as a thermal bridge to enhance the internal interaction force and make the internal structure more regular. Strong molecular contact forces were demonstrated by mechanical tensile testing. The thermal expansion rate of the system was explored through molecular dynamics. Thermal expansion experiments proved that hydrogen bond can effectively reduce the free volume. Molecular dynamics simulations were also performed in this work. The number and density of hydrogen bonds inside different polymers were calculated, and the phonon thermal transport was quantitatively analyzed. The thermal bridge and intermolecular contact force were discovered to effectively restrict the molecular chain's activity and reduce its free volume. The results of the experiments and molecular dynamics reveal that strong intermolecular interactions and thermal bridges can significantly improve polymer intrinsic thermal conductivity.

CFD-DEM simulations of a gas-solid-liquid fluidization system: Effects on the flow field and particle behavior of semi-dry desulfurization fluidized bed

Gas-solid-liquid multiphase flow systems have been widely applied in energy engineering, petrochemical industries, biochemical industries and food industries, etc., which usually involve multi-physical processes and multi-reaction stages. As a typical gas-solid-liquid multiphase flow system, the semi-dry flue gas desulfurization fluidized bed has been widely applied by small and medium-scale thermal power plants for its advantages of excellent mixing effect, relatively high efficiency and low cost. This study focused on the fluid hydrodynamics, wet particle motions and the transfer efficiency (SO2 removal efficiency) in a fluidized bed via two-way coupled CFD-DEM numerical simulations with the implementation of different semi-dry desulfurization stages (“constant-rate” absorption stage, “falling-rate” absorption stage and solid absorption stage) as well as the liquid bridge force. To avoid the fast evaporation of small droplets, simulations based on larger particles (Geldart group D) were also conducted to clarify the influence of varying liquid volume contents. Results revealed that the existence of liquid layers would partly enhance the desulfurization efficiency, while in this case the bed exhibits poor fluidization characteristics. Adding humification water in the solid absorption stage would transform the reaction stage from solid absorption stage to “constant-rate” absorption stage, which improves the desulfurization efficiency significantly. It could also be summarized that the increase of Ca/S molar ratio would enhance the desulfurization efficiency partly, but the improvement would not be obvious when the Ca/S molar ratio is greater than a certain range.

CFD-DEM investigation on the agglomeration behavior of micron-sized combusted iron fines

The occurrence of agglomeration due to particle sintering is one of the most significant technical issues hindering the direct reduction process of iron oxide fines (DRI) in a high-temperature fluidized bed. To get a better understanding of the agglomeration mechanism, the (de-)fluidization behavior of micron-sized iron oxide particles in a 3-D fluidized bed is investigated using Computational Fluid Dynamics coupled with a coarse-grained Discrete Element Method (CFD-cgDEM). The inter-particle cohesive force is considered as a temperature-dependent solid bridge force. The coarse-grained method is first verified by comparing results for different scaling factors. Subsequently, the effects of temperature on the bed pressure drop, void fraction distribution, particle velocity distribution, and agglomerate size are investigated. In conclusion, the developed model shows the capacity for reliable prediction of particle agglomeration behavior, which can shed light on the design of the DRI process in high-temperature fluidized beds.

Optimization and control of cable forces in a hybrid beam cable-stayed bridge based on a distributed algorithm

Based on the existing permanent load equilibrium method, influence matrix method and adaptive control method, a distributed algorithm and control method for the cable forces of hybrid laminated girder cable-stayed bridges is proposed. The method uses the permanent load equilibrium approach to initially determine the permanent load cable forces, then adjusts it based on the influence matrix of the main girder displacement, and finally combines the calculation of finite element software to determine the cable forces that satisfy the internal force requirements of each member of the hybrid laminated girder cable-stayed bridge under the joint action of permanent load and live load. Through adjusting the cable force of an actual bridge, it can be found that this method is highly efficient in calculation, and the efficiency and accuracy of control of the cable forces are high, ensuring that the cable forces and alignment of the bridge structure after completion are in line with the design expectations.

Determining the hanger force of the suspension bridge with short extended spans: An analytical algorithm

Single-main-span suspension bridges with short extended spans usually combine significant stiffness with high economic efficiency, making them lucrative as railway bridges. However, short extended spans induce negative side hanger forces according to the conventional continuous multiple-rigid-support beam method (CMRSBM). Therefore, the support reaction of the rigid support cannot be directly used as a hanger force, thus necessitating a new solving method for hanger force assessment. This study proposes a calculation method for hanger force optimization considering the live load effect for a single-main-span suspension bridge with short extended spans. Under the combined action of dead and live loads, we optimize the hanger force to utilize the main beam material economically. It is noteworthy that the optimized hanger forces are not equal to those obtained by the CMRSBM. Therefore, the bending strain energy of the main beam is no longer the minimal, and the corresponding geometry of the main beam under the dead load differs from that at the completed bridge state. We incorporate specified hanger forces into the finite element method (FEM) to facilitate further calculation of the suspension bridge after hanger force optimization. Thus, the main beam deformation and the processing geometry of the main beam during manufacture are then estimated. The proposed method is verified by applying it to an exemplary suspension bridge. It is found that the optimized hanger forces are uniform. Under the action of dead and live loads, there are two flat bending moment envelopes for the entire main beam: one in the upper and one in the bottom. This indicates an efficient use of the material, which agrees with the initial goal. The main beam displacement manifests itself as the downwarping of the extended spans and arching of the main span. Therefore, the main beam should be pre-arched or pre-deflected during manufacturee.

A Predictive Model of Capillary Forces and Contact Diameters between Two Plates Based on Artificial Neural Network.

Many efforts have been devoted to the forecasting of the capillary force generated by capillary adsorption between solids, which is fundamental and essential in the fields of micro-object manipulation and particle wetting. In this paper, an artificial neural network (ANN) model optimized by a genetic algorithm (GA-ANN) was proposed to predict the capillary force and contact diameter of the liquid bridge between two plates. The mean square error (MSE) and correlation coefficient (R2) were employed to evaluate the prediction accuracy of the GA-ANN model, theoretical solution method of the Young-Laplace equation and simulation approach based on the minimum energy method. The results showed that the values of MSE of capillary force and contact diameter using GA-ANN were 10.3 and 0.0001, respectively. The values of R2 were 0.9989 and 0.9977 for capillary force and contact diameter in regression analysis, respectively, demonstrating the accuracy of the proposed predictive model. The sensitivity analysis was conducted to investigate the influence of input parameters, including liquid volume and separation distance, on the capillary force and contact diameter. The liquid volume and separation distance played dominant roles in affecting the capillary force and contact diameter.

Capillary forces and capillary bridges between a three-finger microgripper and a plate

ABSTRACT The presence of surface tension in liquids, which induces a strong capillary force between wetting particles in micro/nano scale, has aroused extensive attention. In present study, a fundamental investigation on capillary forces and rupture behaviors of capillary bridges between a three-finger microgripper and a plate is conducted in quasi-static state. Theoretical analysis is performed for solutions of the capillary force. The capillary bridges between a three-finger microgripper and a plate are established based on the principle of energy minimization. An analytical approach for computing the capillary force for the three-finger/plate geometry is proposed by means of variables obtained from the simulation models. The comparison of the single-finger capillary bridge and three-finger capillary bridge is investigated based on the developed models. The effects of separation distance, capillary bridge volume, radial distance and contact angle on the capillary force of three-finger capillary bridges are analyzed in detail. The results demonstrate that the variation of capillary force with separation distance and volume changing is not monotonic, which is caused by the edge effect of the three-finger microgripper. Capillary force measurements were experimentally characterized to demonstrate the reliability of the simulation models and the capillary force solution method based on an established experimental platform.

Minimum fluidization velocity and reduction behavior of combusted iron powder in a fluidized bed

The fluidization and reduction behavior of micron-sized iron oxide powder, produced by iron combustion, is studied in a lab-scale cylindrical fluidized bed. The minimum fluidization velocity umf is found to stabilize above normalized static bed heights of 0.5 H/D (static bed height divided by the bed diameter). umf is measured as a function of temperature between 280 and 860 K for both H2 and N2 as fluidizing gas. The experimental results start to deviate from the Ergun correlation at temperatures above 560 K, both for N2 and H2. A new correlation, taking the cohesive inter-particle solid bridge force into account, is proposed in this work to predict the minimum fluidization velocity at high temperature. Reduction experiments are carried out for a total time of 5 h at constant excess velocity with 50, 75 and 100 vol% of H2 and temperatures between 623 and 823 K. Gradual defluidization occurs when the operating temperature exceeds 800 K. A maximum reduction degree of 61% is obtained at 807 K and 100 vol% H2.

Comprehensive screening strategy coupled with structure-guided engineering of l-threonine aldolase from Pseudomonas putida for enhanced catalytic efficiency towards l-threo-4-methylsulfonylphenylserine.

l-Threonine aldolases (TAs) can catalyze aldol condensation reactions to form β-hydroxy-α-amino acids, but afford unsatisfactory conversion and poor stereoselectivity at the Cβ position. In this study, a directed evolution coupling high-throughput screening method was developed to screen more efficient l-TA mutants based on their aldol condensation activity. A mutant library with over 4000l-TA mutants from Pseudomonas putida were obtained by random mutagenesis. About 10% of mutants retained activity toward 4-methylsulfonylbenzaldehyde, with five site mutations (A9L, Y13K, H133N, E147D, and Y312E) showing higher activity. Iterative combinatorial mutant A9V/Y13K/Y312R catalyzed l-threo-4-methylsulfonylphenylserine with a 72% conversion and 86% diastereoselectivity, representing 2.3-fold and 5.1-fold improvements relative to the wild-type. Molecular dynamics simulations illustrated that additional hydrogen bonds, water bridge force, hydrophobic interactions, and π-cation interactions were present in the A9V/Y13K/Y312R mutant compared with the wild-type to reshape the substrate-binding pocket, resulting in a higher conversion and Cβ stereoselectivity. This study provides a useful strategy for engineering TAs to resolve the low Cβ stereoselectivity problem and contributes to the industrial application of TAs.

Development of a High-Function Fiber Stylus for Microstructure Measurement with Water-Repellent and Antistatic Coatings

The precise measurement of microstructures and other micron-sized materials has garnered considerable interest in recent years. We have developed a measurement system that uses an etched small diameter optical fiber as a stylus to measure microstructures with low contact force. However, when the diameter of the stylus tip is less than a few tens of micrometers, the surface forces between the measured surface and the stylus tip become larger than the gravity of the stylus tip, causing the stylus tip to stick to the measured surface. This adhesion leads to an increase in measurement time and a decrease in measurement accuracy. In this study, we fabricated a high-function stylus with water-repellent and antistatic coatings applied to the stylus tip to reduce the adhesion between the stylus tip and measured surface due to surface forces, and conducted performance evaluation tests. As a result, the average separation distance was 13.8 µm when a fluorinated resin coating with a contact angle of 105° was used, confirming that the influence of liquid bridge forces could be reduced by approximately 78%. Additionally, when static elimination experiments were conducted by scanning the charged surface at a pitch of 0.5 µm using an antistatic coating stylus with a gold on the stylus surface, the average adsorption distance was 3.6 µm, confirming that the effect of electrostatic force could be reduced by 71%.

CFD-DEM study of reactive gas-solid flows with cohesive particles in a high temperature polymerization fluidized bed

The cohesive particles are commonly encountered in high temperature polymerization fluidized bed reactors. However, detailed studies on the effect of cohesiveness on the hydrodynamics, heat transfer, and reaction characteristics in such reactors have been rarely reported. In this work, a CFD-DEM approach coupled with solid bridge force model and polymerization reaction kinetics model is established to simulate the reactive gas–solid flows with cohesive particles. The results demonstrate that cohesive particle agglomeration significantly increases the inhomogeneity of concentration and velocity fields, and hinders particle circulation. The hindered particle circulation further results in pronounced temperature inhomogeneity. Moreover, the local hot spots are readily formed in the agglomerates, which expand and deteriorate rapidly if not controlled promptly. Besides, how the cohesion model parameters, namely contact time and maximum cohesive force limitation, affect the onset temperature and the severity of particle agglomeration is revealed. The established model extends the particle-scale study of cohesive gas–solid flows to reactive systems.

A coarse grain model with parameter scaling of adhesion forces from liquid bridge forces and JKR theory in the discrete element method

The discrete element method (DEM) is a reliable tool for analyzing powder processes. However, the DEM is problematic for fine particle simulations owing to its huge computational cost. Coarse grain models, where multiple original particles are replaced with one large particle, are a promising solution. In such a model, scaling laws for forces acting on a coarse-grained particle are used to make its behaviors match the behaviors of the original particles. While various scaling laws have been proposed, there is not enough insight into combining several scaling laws and the relationship between scaled parameters. This study newly proposes a coarse grain model with a systematic parameter scaling law for adhesion forces, especially liquid bridge forces. Simulation results are compared with experimental results. Good agreements are achieved for macroscopic particle behaviors such as cascading angles and lifted heights. The adequacy of the proposed coarse grain model is also verified. The behaviors of the coarse-grained particles well match the corresponding behaviors of the original particles. Consequently, this study demonstrates the superiority of the coarse grain model by comparing its results with those obtained without the model.

Experimental and numerical study on the consequence of seismic-induced transversal poundings for a simply-supported bridge

Shear keys bolted at the underside of bridge girders are expected to act as restrainers to prevent girder dislocation in the transversal direction when experiencing a strong earthquake. However, the impact forces generated at the restrainers will be transferred to adjacent structures and may cause damage to the bridge. Previous research on this topic was scarce as shear keys are usually regarded as secondary structures due to their relatively small dimensions compared to the main components, e.g., girders and piers. This study investigates the pounding effect on the transmission of seismic force in a simply-supported bridge with spherical steel bearings. Shake table tests are carried out on 1:6 scaled models with and without shear keys. To incorporate the effect of excitation characteristics, three ground motions with different peak accelerations are considered. The result indicates that in the absence of shear keys (i.e., no pounding), the bearings can partially isolate the girder from piers. Consequently, the table acceleration transferred to the girder is much smaller than to the pier top. In the case of installing shear keys, the seismic behavior of bearings would significantly influence the pounding occurrence and thus the subsequent bridge response. When involving poundings, the generated impact loads will dramatically increase the acceleration of the girder and the bending moment at the pier base compared to the counterpart without shear keys. Based on the experimental result, a numerical model is established and validated. The model is then used to determine a proper gap size between the participating impact components for obtaining a good overall bridge performance.