Bottom Plate Research Articles

Investigation on the Through-Thickness Temperature Gradient and Thermal Stress of Concrete Box Girders

Bridges are generally affected by thermal loads which include the daily cycle, seasonal cycle and annual cycle. Thermal loads mode and thermal effects on bridges, especially for concrete girders, are quite essential but complicated. To investigate the temperature field and thermal stress in the thickness direction of a concrete box girder, the temperature field of a prestressed concrete continuous box girder bridge is monitored, and the temperature distribution in the thickness direction of the concrete box girder is analyzed. Finite element simulation, utilizing air elements specifically designed for concrete box girders, is employed to analyze the temperature field and thermal stress profiles along the thickness of the slab. The findings indicate a variation in temperature along the thickness of the concrete box girder slab. The most significant temperature differential, reaching up to 10.7 °C, is observed along the thickness of the top slab, followed by the bottom plate, with the web exhibiting relatively smaller differentials. Temperature in the full thickness range has a significant impact on the top plate, while the web plate and bottom plate are greatly influenced by temperature ranging from the outer surface to the center of the plate thickness. The temperature difference between the center of the plate thickness and the inner surface is approximately 0. The variation in temperature due to the variation in thickness direction is a temporal factor, wherein the outer layer of the roof is primarily compressed, while the inner layer is subjected to tension. The external surface of the web is mainly compressed. The stress exerted by the internal surface temperature is minimal. The internal and external surface effects of the floor are similar, and as time passes, tensile and compressive stresses appear.

ADVANCING THE FABRICATION OF 3D MINI-TISSUE ENTHESIS CONSTRUCTS: CHARACTERIZATION OF BONE, TENDON, AND BMSC SPHEROIDS

AbstractObjectivesThe enthesis is a specialised structure at the interface between bone and tendon with gradual integration to maintain functionality and integrity. In the process of fabricating an in-vitro model of this complex structure, this study aims to investigate growth and maturation of bone, tendon and BMSC spheroids followed by 3D mini-tissue production.MethodsCell spheroids Spheroids of differentiated rat osteoblasts (dRObs), rat tendon fibroblasts (RTFs) and bone marrow stem cells (BMSC) were generated by culturing in 96 well U bottom cell repellent plates. With dROb spheroids previously analysed [1], RTF spheroids were examined over a duration of up to 28 days at different seeding densities 1×104, 5×104, 1×105, 2×105 in different media conditions with and without FBS (N=3). Spheroid diameter was analysed by imageJ/Fiji; Cell proliferation and viability was assessed by trypan blue staining after dissociating with accutase + type II collagenase mix; necrotic core by H&E staining; and extracellular matrix by picro-sirius red (RTFs) staining to visualise collagen fibres under bright-field and polarised light microscope.3D mini-tissue constructs15 day old mineralised dROb spheroids (∼1.5mm diameter) were deposited in pillar array supports using a customised spheroid deposition system to allow 3D mini-tissue formation via fusion (N=3). Similarly BMSC and RTF spheroids were deposited after determining the seeding density that produced spheroid size equivalent to 15 day old dROb spheroids. Gentle removal of spheroids from supports was performed on day 2, 4 and 6 to assess spheroid fusion. Histological staining was performed to observe cellular arrangement and extracellular matrix.ResultsRTF spheroids diameter reduced over the course of 28 days regardless of the seeding density. A substantial decline in cell numbers over time was observed and suggests lack of cell proliferation due to tenogenic differentiation. Absence of a necrotic core in RTF spheroids, in all seeding densities, reveals their inherent capacity to maintain cell viability in avascular conditions. Picro-sirius red staining demonstrated the presence of collagen type I fibres predominantly in peripheral regions of spheroids maintaining its shape. Small amounts of collagen type III were also noticed. The dROb spheroids fused rapidly within 2 days resulting in the formation of a mini-tissue. 2×105 RTFs and 3×105 BMSCs produced spheroids of ∼1.5mm on day 3 and day 1 respectively. When these spheroids were deposited in pillar array supports, they did not undergo fusion even up to 6 days. This suggests inadequate aggregation of spheroids and insufficient ECM production at this early stage.ConclusionsThis study has demonstrated the ability of RTFs to produce necrotic core-free spheroids with collagen fibres maintaining their structural integrity. For mini-tissue formation, we predict a longer initial culture time of RTF and BMSC spheroids will allow increased cellular interaction and ECM production before deposition, and will facilitate spheroid fusion. These findings will be applied in producing heterogenous mini-tissues, serving as a 3D in-vitro enthesis model.Declaration of Interest(a) fully declare any financial or other potential conflict of interest

A Study of the Mechanical Properties of Polyester Fiber Concrete Continuous Rigid Frame Bridge during Construction

This study investigates the mechanical performance of a polyester fiber concrete continuous rigid frame bridge during construction and the spatial stress distribution of the 0# block box girder, with a focus on the backdrop of the bridge in Pipa Zhou, Jiangxi Province. Stress monitoring at critical cross-sections during bridge construction was combined with FE simulations to analyze the stress and alignment deviation variations along the cantilevered construction process of the bridges. Subsequently, after validating the accuracy of the whole bridge model, the actual internal force of the box girder cross-section was extracted to act on the 0# block box girder solid model, and the spatial force of the 0# block box girder under the state of maximal cantilever and the completed bridge was further investigated. The results indicate that during cantilever construction, the top, and bottom plates of the box girder were subjected to compression, with the bottom plates having relatively low compression stress close to the critical values for compression and tension. Attention should be paid to controlling tensile stress application. After reaching a quarter of the bridge’s span in construction, the alignment deviation of the main beam increases, necessitating enhanced monitoring and adjustments of the main beam elevation. Furthermore, FE analysis shows that under maximum cantilever and the completed bridge states, the stress variations of the top and bottom plates of the 0# block box girder remain consistent, with the top plate stress varying by no more than 2.5 MPa and the bottom plate stress varying by approximately 1 MPa. Moreover, the 0# block box girder shrinkage cracks were mainly located in the bottom and web plate, and the number of cracks in the 0# block box girder with polyester fibers was reduced compared to the cracks in the ordinary concrete box girder.

Mechanical properties of coal-rock combined bodies under the action of ScCO2: A study of damage and failure mechanism

Injecting CO2 into deep unrecoverable coal seams can help achieve carbon sequestration targets and improve the coalbed methane output rate. However, CO2 reaches a supercritical in situ storage state that impacts the coal storage structure. Based on the independently developed ScCO2 soak system, RFPA3D numerical simulation, and theoretical calculations, the mechanical damage characteristics and failure mechanism of RCR samples with three types of coal seam thicknesses and three types of top and bottom plate lithologies under the action of ScCO2 are investigated. The study reveals that (1) under the action of ScCO2, with the increase in the coal thickness, the deterioration degree of compressive strength and modulus of elasticity of the RCR combined body gradually increases and decreases, respectively, (2) ScCO2 will promote the plastic failure of the coal mass and exacerbate the tendency of the RCR combined body to change from tensile splitting failure to shear plastic failure, and the degree of plastic failure of the RCR combined body has a positive correlation with the coal thickness and the rock-coal strength ratio, and (3) ScCO2 accelerates the failure of the RCR combined body, and the coal mass enters the plastic failure stage earlier, while the rock mass ends the elastic strain energy accumulation and unloads and releases energy earlier, reducing the accumulation and release of energy in the combined body. The research results can provide a theoretical reference for the geological storage of CO2 deep inaccessible coal seams.

Effects of vapor duct thickness on the thermal performance of ultra-thin vapor chambers under forced-convection cooling

Ultra-thin vapor chambers (UTVCs) have drawn considerable attention for the growing need of thermal management for thin portable electronic devices. In fact, our novel UTVC design has the potential for high-power applications. This work presents the performance test results under forced convective cooling for our novel UTVCs with thicknesses t = 0.40, 0.50 or 0.58 mm, having vapor duct thickness h = 0.15, 0.25, or 0.35 mm, respectively. The vapor duct thickness is shown to exert great effect on the maximum heat transfer rate (Qmax) and mild effect on the values of thermal resistance (Rvc) of the UTVC. These novel copper–water UTVCs simply comprise a top plate etched with arrayed pillars as the condenser and a mesh-wicked bottom plate as the evaporator and liquid path. The inner surface of the top plate contains cross parallel vapor ducts configured by aligned pillars for vapor spreading all over the vapor chamber. The pillars provide strong structural support, an enlarged condensation area, and a direct shortcut for liquid return. The condenser, with a footprint of 140 × 80 mm2, is cooled by a cold plate with running water of 50 °C. The UTVCs having h = 0.35 or 0.25 mm display values of Qmax of about 140 W or 90 W, respectively, with similar values of Rvc of 0.036–0.055 K/W. The UTVCs with h = 0.15 mm display greatly degraded values of Qmax of about 55 W with higher values of Rvc of 0.053–0.078 K/W. With a shorter return distance for the condensed water directly through the arrayed pillars, this UTVC design demonstrates a rather high Qmax of 140 W using only a single layer of #200 copper mesh wick at h = 0.35 mm.

Study on the Spatiotemporal Dynamic Evolution Law of a Deep Thick Hard Roof and Coal Seam

Underground mining in coal mines causes strong disturbance to geological structures and releases a large amount of elastic strain energy. When the roof is a hard and thick rock layer, it is easy to cause dynamic disasters such as rock burst. To analyze the impact of a deep thick and hard roof fracture on the safe mining of thick coal seams, this paper studied the dynamic evolution process of the stress field, displacement field, energy field, and plastic zone of the coal seam and overlying strata during the mining process using FLAC3D numerical simulation. The results show that as the working face continues to be mined, the concentrated stress in the overlying strata first increases and then decreases, and the support pressure in front of the working face continues to increase. When it advances to 100 m, collapse occurs, and the stress increases sharply; the bottom plate undergoes plastic failure, resulting in floor heave. The overlying strata mass in the top plate exhibits downward vertical displacement, while the rock mass in the bottom plate exhibits upward vertical displacement, with a maximum subsidence of 4.51 m; energy concentration areas are generated around the working face roadway, forming an inverted “U” shape. When collapse occurs, the energy density decreases slightly; the direction of the plastic zone changes from “saddle shaped” to complete failure of the upper rock layer, and the overlying strata is mainly shear failure, which expands with the increase in mining distance. The research results have important practical significance for guiding the safe mining of deep thick and hard roof working faces.

Optimization methods for the distortion of thin-walled box girders and investigation of distortion effects

To investigate the distortion process of thin-walled box girders, three commonly used methods based on energy variational calculus and static balance analysis are optimized. A generalized analytical formula for box-girder distortion research is derived, and a fourth-order distortion control differential equation is obtained. Typical numerical examples are used to verify and compare the three methods. The results show that the value of distortional warping normal stress calculated by the optimized methods is slightly different from the literature values and that the maximum error between methods does not exceed 5.39%. The calculation results of Method 2 and Method 3 are similar. The values of the geometric distortion characteristics calculated by the three methods are related to the cross-sectional form of the box girder and the distortion analysis process, and the calculated values are not unique. The absolute value of the peak normal stress of distortion on the top plate of a thin-walled box girder with a cantilever plate is smaller than that on the bottom plate. Under a concentrated distortion load, the distribution of the distortion deformation along the length of a simply supported box girder with only end diaphragm is not consistent, and there is reverse deformation near the beam end.

Ultrasonic guided wave defect detection method for tank bottom plate based on SH0 mode multichannel magnetostrictive sensor

To address the challenge of ultrasonic detection of multiple defects in large-scale tank bottom plates, a multi-channel magnetostrictive sensor was designed and developed to effectively excite SH (Shear Horizontal) mode guided waves. The optimal overall scheme of the sensor was obtained by considering the sensor excitation energy, coupling efficiency, and fabrication process. Through experimental tests, the consistency of each channel of the sensor is evaluated, and the center frequency and detection range of the sensor are measured. To detect defects of varying sizes and depths in steel plates, a rotating total focus imaging method is proposed. And we conducted experiments using a multi-channel magnetostrictive sensor to achieve SH0 guided wave imaging of multiple defects across the full domain. Our experimental results demonstrate that, across 8 rotations, we achieved a minimum relative position error of 4.32% and a minimum absolute angle error of 2.16°. Our research provides an effective solution for ultrasonic detection of tank bottom plates, and the proposed method is also applicable for defect detection in other large plate-like structures.

SIMPLE PRESS TOOL DESIGN AS A SUPPORTING TOOL FOR FORMING PLATES WITH A THICKNESS OF 3 MM

The press tool is one of the combined Jig and Fixture tools that can be used to form and cut metal by means of emphasis. The working process of this tool is based on the compressive force passed on by Punch to cut or shape the workpiece according to the desired geometric and size. This research aims to design a cutting machine for sheet metal forming processes that are able to improve the production process in industry. In this study, the author designed the components of a progressive type presstool machine in the process of making clamps with a thickness of 3mm with software inventor design media. Includes components shanks (St.60), top plate (St.60), bearing locator (St.40), bottom plate (St.60), punch (SKD-11), dies (SKD-11), pillar shaft (St.40), spring (St.40). Analysis of calculations carried out in this study produces a cross-sectional area of the shear field (132mm2), shear voltage (32 kg/mm2), Formation style (4,224kg), presstool engine power (1267.2 watts/168.9688 HP). Press tools are designed to make clamps made of steel plates with a thickness of 3 mm. From the design results obtained the dimensions of the tool as follows the length of 450 x 400 x 542 mm. The results of press tool type of precision equipment used to form or cut workpiece materials according to needs and to increase production in industry

Ship grounding model tests in a water tank: An experimental study

Ship grounding experiments are important benchmarks used to validate numerical analysis, analytical and empirical formulation. They are key to the understanding of damage mechanism. A set of small-scale ship model grounding tests over a sharp rock are conducted in a water tank considering the influence of surrounding water. Two damage modes are observed in the grounding tests, Mode I for discontinuous fracture/tear and Mode II for continuous fracture/tear. The horizontal grounding resistance forces, damage extents of ship bottom plates, and ship motions are recorded and discussed in detail. Moreover, the energy dissipation process of ship model during grounding process is analyzed based on the test results. The influence of the initial velocity, the initial relative height between the upper surface of the horizontal ship bottom plate and the rock tip, and the rock eccentricity on the ship motion response and structural damage are studied.

Mitigation of wave force on a tunnel in the presence of submerged porous plate over trench-type bottom topography

Abstract Thin porous plates serve as an effective model for the construction of breakwater. Thus, the problem involving oblique wave interaction with a tunnel in the presence of a submerged horizontal porous plate over a trench-type bottom is investigated. In this paper, for the mathematical formulation of the physical model, water wave potentials are defined using Havelock's expansions and flow past over porous structure is modelled based on Darcy's law. The advantage of the trench type of bottom and horizontal plate are studied through the numerical results of forces on the tunnel. The study reveals that more energy loss and less force on the tunnel are obtained if the porous effect parameter of the plate or the length of the plate is increased up to a moderated value of these parameters. Compared to the case without porous plate and trench-type bottom topography, there are significant changes in forces due to this porous breakwater and trench-type bottom topography. In addition, from the present results, it may be noted that the load on the submerged tunnel is reduced by adding a submerged horizontal porous plate and asymmetric trench, which is helpful in understanding the role of porous breakwaters and trenches in applications to Ocean and Coastal Engineering.

Stiffened Plate Analysis by Considering the Effect of Uniaxial Load on FPSO Vessels

Abstract: Plates are a very important part of shipbuilding and offshore structures. The reinforced plate is used to withstand loads acting in the axial and bending directions. The structure of the deck or bottom plate exhibits buckling or yielding behavior. Thus, it is very important to analyze the ultimate bearing capacity of a plate structure subjected to compressive loads for safe ship structure design. The material configuration used is the most important aspect in the FPSO structure design criteria. Plates and stiffened plates experience local buckling due to the external load when the hull girder collapsed. The objective of the present study is to analyze the effect of flange and web thickness to the ultimate strength on the FPSO in terms of plate deformation located of the bottom and deck area under compression stages. In this study, the attached plate thickness is varied according to FPSO data and BKI Rule. The stiffened plates element located at the bottom and deck area are modelled by Tee-Bar and Angle-Bar element. The simply supported condition is applied to the model and the anon-liniear Finite Element Method is used for the analysis. The result obtained by NLFEM shows that under tension and compression, the stiffened plate of Tee-Bar model, the deformations are 1,75 mm and 1,8 mm respectively. While for Angle-Bar model the deformation are 12,4 mm and 13 mm under compressing respectively.
 

On the wall-bounded model of fingering double diffusive convection

The present work aims at clarifying the effects of a solid boundary on the salt fingers in the wall-bounded double diffusive convection turbulence driven by the salinity and temperature differences between the top and bottom plates. The fluid properties are the same as the seawater, and two-dimensional direct numerical simulations are conducted over a wide range of the thermal and salinity Rayleigh numbers which measure the strength of driving salinity difference and stabilising temperature difference. We find that the bulk density ratio $\varLambda _b$ , defined by the mean temperature and salinity gradients at the bulk, controls the flow morphology. As $\varLambda _b$ exceeds unity, the bulk flow shifts from wide convection rolls to slender salt fingers. Two different regimes are further identified for the cases of salt-finger type. One is the confined salt-finger regime where the characteristic height of salt fingers is comparable to the bulk height and the influences of the solid boundary are noticeable. The other is the free salt-finger regime where the salt fingers are much shorter than the bulk height. In this latter regime, the transport properties versus $\varLambda _b$ are in quantitative agreement with those obtained in the fully periodic domain (e.g. Traxler et al., J. Fluid Mech., vol. 677, 2011, pp. 530–553). For a limited range of density ratio at the highest salinity Rayleigh number considered here, multiple states can be obtained from different initial conditions. The large-scale secondary instability and spontaneous formation of staircase from finger layers are not observed in the current study.

Couette-Poiseuille flow in a fluid overlying an anisotropic porous layer

In this study, Couette-Poiseuille flow inside a channel partially filled with a porous medium is treated. Considering the applicability to the practical scenarios, we assume that the porous medium is anisotropic in nature. More precisely, the model under steady-state assumption is described by the coupling of Brinkman-Forchheimer and Stokes equations. We develop the existence and uniqueness results corresponding to this two-dimensional Stokes-Brinkman-Forchheimer coupled system using the Browder-Minty theorem. For this we restrict the permeability to a diagonal matrix. The coupled system involves a non-linear term due to the Brinkman-Forchheimer equation. We propose an algorithm based on shooting and searching techniques to develop a numerical solution for this system, however, for an arbitrary anisotropic permeability matrix. The robustness of the presented numerical solution is established by comparing it with asymptotic solutions corresponding to small and large Darcy numbers. For the case of a large Darcy number, the problem of interest is a regular perturbation while the same is a singular perturbation problem for the case of a small Darcy number, which is dealt with using Prandtl's matching principle. With the velocity distribution determined, we have presented a comparative analysis of the shear stress distribution at the liquid-porous interface and at the bottom plate, which is of interest to analyze the stress distribution on the arterial wall. The asymptotic results are found to be in good agreement with those obtained numerically.

Research on the Stability and Support Effect of Earth Section of Hydraulic Tunnel Based on FLAC 3D

The stress of the surrounding rock of hydraulic tunnel can produce a stress load on the lining body, which may cause the crack failure of the lining. The distribution and deformation characteristics play a key role in ensuring the long-term stability of tunnels. Therefore, an analysis of the distribution characteristic is of great significance. This paper takes the branch tunnel in the Yellow River Diversion Project of central Shanxi as an entity for modeling, and uses the finite difference program FLAC3D for analysis and calculation. The research results show that before the support is strengthened, the compressive stress of feet-lock bolts has exceeded the compressive strength of the bolts, with obvious stress concentration at the arch feet; the deformation mainly occurs on the vault and the bottom plate; after strengthening the support, the deformation of the steel arch prop, the axial force of the steel arch prop, and the maximum tensile stress of the anchor rods are all reduced. The stable support effect can meet the requirements of construction and later operation.

Thermogravitational Convection in a Controlled Rotating Darcy-Brinkman Nanofluids Layer Saturated in an Anisotropic Porous Medium Subjected to Internal Heat Source

Thermogravitational convection in a controlled rotating Darcy-Brinkman nanofluids layer saturated in an anisotropic porous medium heated from below is Thermogravitational convection in a controlled rotating Darcy-Brinkman nanofluids layer saturated in an anisotropic porous medium heated from below is investigated. The presence of a uniformly distributed internal heat source and considers the Brinkman model for different boundary conditions: rigid-rigid, free-free, and lower-rigid and upper-free are considered. The effect of a control strategy involving sensors located at the top plate and actuators positioned at the bottom plate of the nanofluids layer is analysed. Linear stability analysis based on normal mode technique is employed. The resulting eigenvalue problem is solved numerically using the Galerkin method implemented with Maple software. The model used for the nanofluids associates with the mechanisms of Brownian motion and thermophoresis. The influences of the internal heat source strength, mechanical anisotropy parameter, modified diffusivity ratio, nanoparticles concentration Darcy-Rayleigh number and nanofluids Lewis number are found to advance the onset of convection. Conversely, the Darcy number, thermal anisotropy parameter, porosity, rotation, and controller effects are observed to slow down the process of convective instability.investigated. The presence of a uniformly distributed internal heat source and considers the Brinkman model for different boundary conditions: rigid-rigid, free-free, and lower-rigid and upper-free are considered. The effect of a control strategy involving sensors located at the top plate and actuators positioned at the bottom plate of the nanofluids layer is analysed. Linear stability analysis based on normal mode technique is employed. The resulting eigenvalue problem is solved numerically using the Galerkin method implemented with Maple software. The model used for the nanofluids associates with the mechanisms of Brownian motion and thermophoresis. The influences of the internal heat source strength, mechanical anisotropy parameter, modified diffusivity ratio, nanoparticles concentration Darcy-Rayleigh number and nanofluids Lewis number are found to advance the onset of convection. Conversely, the Darcy number, thermal anisotropy parameter, porosity, rotation, and controller effects are observed to slow down the process of convective instability.

Bioinspired Collagen/Hyaluronic Acid/Fibrin-Based Hydrogels for Soft Tissue Engineering: Design, Synthesis, and In Vitro Characterization.

A major challenge for future drug development comprises finding alternative models for drug screening. The use of animal models in research is highly controversial, with an ongoing debate on their ethical acceptability. Also, animal models are often poorly predictive of therapeutic outcomes due to the differences between animal and human physiological environments. In this study, we aimed to develop a biomimetic hydrogel that replicates the composition of skin for potential use in in vitro modeling within tissue engineering. The hydrogel was fabricated through the crosslinking of collagen type I, hyaluronic acid, four-arm PEG succinimidyl glutarate (4S-StarPEG), and fibrinogen. Various ratios of these components were systematically optimized to achieve a well-interconnected porosity and desirable rheological properties. To evaluate the hydrogel's cytocompatibility, fibroblasts were embedded within the matrix. The resulting hydrogel exhibited promising properties as a scaffold, also facilitating the growth of and proliferation of the cells. This biomimetic hydrogel holds great potential for tissue engineering applications, particularly in skin regeneration and cancer research. The study used melanoma spheroids fabricated using the 96-round bottom well plate method as a potential application. The results demonstrate that the developed hydrogels allowed the maintenance of spheroid integrity and viability, meaning it has a promising use as a three-dimensional in vitro model of melanoma for both tissue engineering and drug screening applications.

The Structural Design and Optimization of Top-Stiffened Double-Layer Steel Truss Bridges Based on the Response Surface Method and Particle Swarm Optimization

A lightweight design optimization algorithm is proposed to optimize the design parameters of stiffened double-layer steel girder bridges, the aim of which is to improve structural safety and reduce superstructure works. Taking a top-stiffened double-layer steel truss bridge as the reference project, a multiscale mixed-element model of the initial design parameters is established, and its computational accuracy is verified. Considering the structural configuration and loading characteristics of the bridge, the elastic modulus of steel, the deck plate thickness, the stiffening vertical bar height, and the relative distance between the double-layer main girders are selected as the design parameters for optimization. The mid-span vertical deflection, the axial forces in the stiffeners, the bottom plate of the deck, the compressed web tube at the pier top, and the quantity of superstructure works are chosen as the objective functions to be minimized. A lightweight calculation equation reflecting the relationship between the optimization parameters and the objective functions is established using the response surface method (RSM). Subsequently, an improved weighted particle swarm optimization (WPSO) model is employed to perform the multi-objective optimization of the design parameters for the bridge, and the results are compared with those obtained from the multi-objective genetic algorithm NSGA-II. The results show that the RSM accurately fits the numerical relationship between the optimization parameters and the objective response functions. When minimizing the quantity of superstructure works as the primary control objective and minimizing the mid-span vertical deflection and the axial forces in the compressed web tube at the pier top as secondary control objectives, the optimization results achieved by WPSO outperform those obtained by NSGA-II. The optimized results lead to reductions of 11.09%, 3.92%, 7.56%, 4.45%, and 8.38% in the respective objective function values of the structure. This method has important theoretical significance for the optimization of structural design parameters.

Experimental study on the influence of maintenance track position on vortex-induced vibration performance of a box girder suspension bridge

To study the influence of maintenance track on the vortex-induced vibration (VIV) performance of main girder, the VIV response and time history of surface pressure data of a section model were obtained by wind tunnel vibration and pressure measurements for a large-span steel box girder suspension bridge. The VIV performance of the main girder was tested at ±5° attack angles of various maintenance track positions, including 1, 2.5, and 5 m away from the outer edge of the girder bottom plate. The mean values, root variances and amplitude spectra of vortex-induced force and the correlation and contribution coefficients of local aerodynamic force to overall aerodynamic force were analyzed. The results show that when the maintenance track is 1 m away from the outer edge of the bottom plate, the main girder exhibits the worst VIV performance with a maximum amplitude of 0.457 m, far beyond the allowable value of the specification. The VIV performance of the main girder was greatly improved by moving the maintenance track inward. The pressure analysis indicates that the large pressure fluctuation at the front and rear parts of the upper surface is attributed to the strong VIV of the main girder. In this sense, the improved VIV performance is mainly contributed by the weakening of pressure fluctuation in these two areas and the reduced local aerodynamic force. When the distance between the maintenance track and bottom plate is adjusted to 2.5 m, a 3.5 m wind barrier with a ventilation rate of 30% effectively inhibits the VIV of the box girder. The main reason for the suppression is that the elimination of pressure fluctuation on the upper surface of the girder disturbs the correlation between local aerodynamic force and overall aerodynamic force, consequently diminishing the contribution of local aerodynamic force to the vortex-induced force.

Exploration and Application of Acoustic Emission Detection Technology in Leakage Detection of the Bottom Plate of Crude Oil Metal Storage Tanks

The use of acoustic emission detection technology can conduct online and non-stop detection and evaluation of crude oil metal storage tanks, achieving the integrity detection and evaluation of storage tanks. In order to explore the applicability of acoustic emission detection technology in the leakage detection of the bottom plate of crude oil metal storage tanks, this project carried out online acoustic emission detection of crude oil metal storage tanks, magnetic flux leakage detection after tank opening and cleaning, and compared and analyzed the results of two detection technologies. The adaptability of online acoustic emission detection technology was analyzed and explored. It was found that acoustic emission technology can qualitatively evaluate the corrosion of tank bottom plates, but cannot accurately locate corrosion defects. For tanks with severe corrosion that require maintenance, it is still necessary to open the tank and use magnetic flux leakage and other detection techniques to determine the location of defects. Through comparative analysis of acoustic emission testing technology and magnetic flux leakage testing technology, the results obtained from acoustic emission testing technology are conservative compared to the actual results. It is recommended to upgrade the evaluation of corrosion degree for the acoustic emission evaluation results of crude oil metal storage tanks.