Full-scale Numerical Simulation Research Articles

Numerical study of hydrodynamic drag effects of streamwise riblet structures on SUBOFF bare hull model

This study performs a full-scale numerical simulation on meter-scale underwater vehicles (UWVs) with micrometer-scale V-type streamwise riblet structures, focusing on hydrodynamic drag using the SUBOFF model. The periodic simulation along the azimuthal direction enables the full-scale analysis. Two main scenarios are discussed: (1) effect of riblet structure size on drag at a constant maneuvering speed and (2) effect of maneuvering speed on drag for representative riblet cases. In scenario (1), the average wall shear stress at the central region of the body exhibited significant reduction of approximately 50%. However, owing to larger effective area at the central surface of the body fixed with riblets, the friction drag may either decrease or increase depending on the riblet size. Consequently, R100 case showed maximum total drag reduction of ∼3%, whereas R500 case showed maximum increase in drag of ∼3%, where R100 and R500 indicate riblet-applied SUBOFF models with riblet heights of 100 and 500 μm, respectively. In scenario (2), friction drag in riblet-applied region exhibited smaller variations in R100 case, showing universal drag reduction effect at all speeds. In contrast, R500 case showed significant variations, with drag increments ranging from minimum of 1% to maximum of 12% at all speeds.

Research on Resistance Characteristics of Fire Zone of Mine Tunnel Fire and Construction of Calculation Model

To investigate resistance change in the fire area of a roadway caused by roadway fires, a mathematical calculation model for thermal resistance is developed. Theoretical research is conducted to analyze the factors influencing resistance change through theoretical derivation, revealing that temperature is a key factor contributing to the change in thermal resistance. By leveraging the correlation between changes in CO concentration and temperature on the downwind side of the roadway within the fire zone, researchers developed mathematical models to predict temperature increases at various points downwind of the fire source. These models were then used to determine the mathematical relationship governing the change in thermal resistance. The accuracy of the numerical simulation software was validated using Fluent numerical simulation software and scaled-down model experiments. Full-scale numerical simulation experiments were conducted to investigate the fire characteristics of roadway fires and validate the thermal resistance mathematical model. The results indicate that the thermal resistance in the numerical simulation is 7.55 Pa at 20m from the fire source and 5.54 Pa at the end of the roadway. The decrease in resistance is linear. The minimum error between the thermal resistance calculated by the mathematical model and the gradient of the pressure drop in the numerical simulation is 0.03 Pa, approximately 2.3%. Furthermore, the fitting degree of the pressure drop in each section is as high as 97.7%. The calculation model demonstrates high accuracy and offers a theoretical foundation for investigating fire resistance in tunnel fire.

Axial mechanical response of concrete pipe jacking considering the deflection of the bell-and-spigot joint: Full-scale test and numerical simulation

The bell-and-spigot joints play a vital role in the axial mechanical response of pipe jacking. This paper investigates the influence of joint deflection on the axial stress distribution and jacking load transfer of concrete pipe jacking via full-scale tests and numerical simulation. The joint deflection contributes to the single-side eccentricity or diagonal eccentricity of the pipe segments. The increase in joint deflection influences the extension of axial stress concentration in the vertical direction near the joint, while the increase in jacking load enhances the maximum compressive stress of the pipe wall in the alignment direction. In addition, the nonlinear axial strain–stress property of the cushioning plank among the segments resulted in the nonlinear transfer of the jacking load. Moreover, the joint deflection also induces the visible tensile stress or inelastic stress of the pipe under diagonal loading mode, indicating a risk of structural damage.

Flexural Performance of Steel–Normal Concrete–Ultra-High-Performance Concrete Composite Slabs with Steel Ribs

For steel–concrete composite bridges, the cracking of concrete in the tensile zone influences the serviceability of bridges and decreases their durability. UHPC, as a high-tensile and -durability material, is used to replace a part of the concrete to enhance the tensile performance. Thus, the steel–normal concrete–UHPC composite slab, as a new composite structure, is formed. This paper investigates the flexural behaviours of steel–normal concrete–UHPC composite slabs through a full-scale experiment, numerical simulation, and theoretical analysis. The research results indicate that (1) UHPC enhances the flexural performance of the tensile zone and delays the development of cracks. The initial cracking force of concrete increases from 44 kN to 91 kN. (2) UHPC effectively enhances the carrying capacity of composite slabs. A 50 mm UHPC layer makes the flexural bearing capacity of steel–concrete composite slabs increase by 13.51%. (3) The construction methods influence the initial cracking force of composite slabs. For full-span scaffolding construction, the initial cracking force decreases from 91 kN to 69 kN compared with construction without brackets. (4) The theoretical model considering the tensile contribution of cracking UHPC can accurately predict the bearing capacity of the composite slabs. And the theoretical values of the bearing capacity are lower than the experimental values, which makes the composite slabs safer in service.

Effect of different particle sizes on combustion characteristics of DCR engines

The ramjet engine has undergone rapid development in recent decades, and the dual combustion chamber ramjet (DCR) engine was proposed in the last century. Boron, with its high volumetric and gravimetric heating values, is one of the most attractive fuel additives for ramjet engines. However, due to the problem of low combustion efficiency, boron is difficult to achieve high efficiency combustion in practical applications. In order to investigate the combustion characteristics of boron-containing gas solid phase components in DCR engines, the Realizable k-ε model, finite rate/vortex dissipation model and boron particle King model ignition combustion calculation program were written. A three-dimensional full-scale two-phase flow numerical simulation was carried out in the combustion chamber of the DCR engine to calculate the effects of different particle sizes on the combustion characteristics. Through the analysis of the simulation results, the particle size affects the ignition time of boron particles and is positively correlated with the combustion efficiency, but with a non-linear growth. A smaller particle size can promote the ignition of boron particles, improve the solid phase combustion efficiency and achieve efficient combustion.

Finite-Element Performance Degradation Behavior of a Suspension Prestressed Concrete Arch Bridge with Grouting Defects

In response to the difficulty in effectively dealing with grouting defects in corrugated pipes within a suspension prestressed concrete arch bridge, a method for assessing the deterioration in the performance of prestressed concrete girders afflicted with grouting defects was established in the present study. Specifically, a time-varying model of steel strand corrosion within grouting defects was constructed by investigating the corrosion theory of steel strands. In addition, a full-scale numerical simulation model of the long-span prestressed concrete bridge was established based on a practical project. Through the described means, the long-term impact of steel strand corrosion at various locations, lengths, and quantities on the vertical displacement and axial stress of girders was elucidated. The results reveal that in the presence of corrosion affecting 16 steel strands located in the midspan bottom plate, a vertical displacement alteration of 17.55 mm was observed in the midpoint region of the girder over a 30-year period following the bridge’s construction. Further, when considering the combined effects of concrete shrinkage, creep, and the corrosion of 16 steel strands in the midspan bottom plate, the axial compressive stress within the midpoint region of the girder decreased from an initial 6.30 MPa to 0.79 MPa over the same 30-year timeframe post-construction. It was observed that two indicators of vertical displacement and axial stress can be employed to evaluate the performance degradation of prestressed concrete bridge girders with grouting defects. The present findings may provide a reference for the operation and management of bridges with grouting defects.

Study on seismic response of a novel prefabricated box culvert with split components based on shaking table test

The prefabricated structure of municipal engineering may face the challenges of shared load-bearing and coordinated deformation under complex geological conditions, earth pressure and groundwater under earthquake action. This study investigated the seismic performance of a novel prefabricated box culvert with split components (PBC-SC) to be constructed in the class Ⅱ site. A 1:10 test model fully considering all connection details was prepared, and shaking table tests were conducted using El Centro seismic waves with peak accelerations ranging from 0.1 g to 0.3 g. The full-scale numerical simulation of the soil-structure model of PBC-SC was prefabricated with ABAQUS to truly account for soil-structure interaction effect. The results of shaking table tests and numerical simulations on PBC-SC were analyzed and compared according to the similarity ratio. Even under the excitation peak acceleration of 0.3 g El Centro seismic wave, the measured acceleration and Fourier spectrum of each segment had only a small difference, thus usage of PBC-SC as a global structure could offer relatively continuous deformability and good seismic performance. To decompose the box culvert into simple assembled components, the connection techniques such as cylindrical pin connection, tongue-and-groove connection and mortise-tenon connection were adopted to ensure the seismic performance of PBC-SC. The research results provided a new idea for the design of PBC-SC and assembly connections for prefabricated structure, as well as further techniques and referable data for seismic response analysis.

Full-Scale Numerical Simulation of the Local Scour Under Combined Current and Wave Conditions Based on Field Data

Full-Scale Numerical Simulation of the Local Scour Under Combined Current and Wave Conditions Based on Field Data

Numerical Modelling and Investigation of the Impact Behaviour of Single Guardrail Posts

Vehicle restraint systems are vital hardware elements in road safety engineering. The certification process of a vehicle restraint system includes full-scale crash tests, component testing and numerical simulation of these tests. To achieve reliable crash test simulation results, the soil–post interaction must be modelled to capture the behaviour realistically. There is no standardised approach for modelling the soil–post interaction in the praxis. In this study, the finite element method is utilised to investigate the soil–post response under quasi-static and dynamic impact loading. Two different modelling techniques are applied for this purpose. The first technique is the finite element continuum method, with the soil modelled using the advanced hypoplastic constitutive relation and calibrated using laboratory test data. The second technique is a lumped-parameter model, for which a systematic parameters calibration routine using basic soil properties is introduced. The numerical models are validated using a series of full-scale field tests performed by the authors on single posts in standard road shoulder materials. The performance comparison of the investigated modelling techniques shows that the hypoplastic constitutive relation can capture the post behaviour realistically under different loading conditions using the same parameter set. The introduced lumped-parameter model adequately simulates the post behaviour with high computational efficiency, which is very important when simulating several posts. The conducted parametric study elucidates that the soil’s relative density, the post’s embedment length, and the post-section modulus govern the single post’s lateral load-bearing behaviour and energy dissipation capacity.

Estimating longitudinal maximum smoke temperature attenuation due to large-angle bifurcation in UTLT-like tunnels under longitudinal ventilation condition

Extensive studies have focused on single-straight tunnels or subway bifurcation tunnel fire. However, the effect of large angle bifurcation on longitudinal maximum temperature rise attenuation in Urban Traffic Link Tunnel（UTLT）needs to be further studied. In this study, based on the theoretical analysis, a double exponential prediction model for longitudinal temperature rise attenuation in bifurcation tunnels is established. To obtain the correlation coefficients, a series of full-scale numerical fire simulation experiments were carried out in an UTLT-like tunnels using Fire Dynamics Simulator. The results revealed that the bifurcation structure of the large-angle bifurcation angle tunnels impeded the longitudinal movement of the fire smoke and hot smoke diversion. Without longitudinal ventilation conditions, the longitudinal decay of the temperature rise in each region can be expressed as the sum of double exponential expressions with different coefficients. The law governing the effect of the bifurcation angle on the longitudinal decay of the temperature rise is the quadratic equation of the angle sin α. A prediction model for the longitudinal decay of the temperature rise in the tunnel downstream of the fire source under longitudinal ventilation is proposed. The findings of the numerical simulation corresponded to those of the model prediction.

High frequency attenuation of elastic waves transmitted at an angle through a randomly-fluctuating horizontally-layered slab

This paper is concerned with the modeling of elastic waves traveling at small incidence angles through a randomly-fluctuating horizontally-layered slab, in regimes where the wavelength is small compared to the thickness of the slab. The wave propagation problem is reset in a frame following the coherent front, which propagates in a homogenized medium. This homogenized medium is anisotropic because of the layering, and the equations obtained account explicitly for the coupling of quasi-P and quasi-S waves. The resulting model is governed by a set of coupled stochastic ordinary differential equations that can be approximated numerically very efficiently, and yields in particular estimates of the transmission and reflections coefficients of the slab. The latter compare favorably to the coefficients obtained in a full scale numerical simulation of the (micro-scale) wave equation, for a fraction of the cost.

Full-scale numerical simulation and experimental validation of the thermal environment under the heating mode in an air-conditioned room

The numerical simulation of the air flow of the room equipped with the crossflow fan air conditioners has been conducted a lot. However, the simulation of the air flow distribution under the heating mode has always been difficult to match the experimental data well, due to the fact that both the air temperature and the flow are affected by the buoyancy. In addition, very few full-scale simulations were conducted. To precisely predict the air flow and temperature distribution of the room with the crossflow fan air conditioner, a full-scale steady numerical simulation was conducted with the Computational Fluid Dynamics (CFD) package. The full-scale physical model was constructed strictly according to the real settings, including the detailed components of the air-conditioner, such as the crossflow fan and the heat exchangers. The Shear-Stress Transport (SST) k-ω turbulent model was selected to simulate the low Reynold flow near the inner surface of the room, and to simulate the high Reynold and transitional flow near the fan blades of the air-conditioner. The porous medium model was used to simulate the heat exchange fins in the air-conditioner. Furthermore, an experiment under the same condition was also conducted to verify the accuracy of the simulation. Results showed that the simulated supply air flow rate was 537.48 m3/h, producing a 4.97% deviation from the experiment result. Meanwhile, the upward movement of the supply air from the outlet of the air-conditioner was observed, leading to higher air temperatures in the upper region of the room. Furthermore, among all 210 measured temperature data points in the room, 149 data points had the deviation within ±5%, and 194 data points had the deviation within ±10%. 9 abnormal data points with greater deviation near the door were detected, which might be resulted from the outdoor cold air leakage through the crack between the door and the floor in the experiment. Conclusively, the full-scale numerical simulation in this study produced an accurate and reliable solution to predict the air temperature distribution in buildings, thus providing a potential method for the design or optimization of the air-conditioners.

Failure mechanism of a Q690 steel tubular transmission Tower: Full-Scale experiment and numerical simulation

The failure mechanism of a Q690 steel tubular transmission tower is investigated through full-scale experiment. The tower is mainly subject to the influence of the wind and the loads from the transmission lines. The displacements and the strains of the key positions as well as the ultimate bearing capacity of the tower are thus obtained. The final collapse is induced by the buckling instability of the compressed main member of a tower leg. A finite element model is established, whose validity is verified by the experimental data. Then, the numerical model is used for further analysis on the structural responses of the tower. It is found that once plasticity occurs at a certain point on the main member, its lateral displacement would be much accelerated, thus amplifying the second-order effect thereof. The horizontal auxiliary members, connected to the bottom of the compressed main member, are initially under tension. While the deformation of the main member is aggravated, they gradually undergo the transition from tension to compression, constituting a lateral support to the main member. This support then enforces the plasticity to develop towards the middle section of the main member, resulting in the final failure at the same location as observed in the full-scale experiment. These findings are crucial for a progressive understanding of the failure mechanism of this type of high-strength steel tubular towers, and they have contributed to the optimization of the design method to prevent the collapse of transmission tower under similar circumstances.

Numerical Simulation Analysis and Full-Scale Experimental Validation of a Lower Wall-Mounted Solar Chimney with Different Radiation Models

As a type of passive architectural structure, wall-mounted solar chimneys enhance the natural ventilation volume of a building’s interior, and maximize reductions in the building’s operational energy consumption. They are indispensable in the building’s energy conservation and emission reduction. Therefore, measuring the wall-mounted solar chimney’s flow characteristics and relevant index parameters is particularly important. This paper uses a combination of full-scale experiments and numerical simulation to conduct a detailed analysis of the wall-mounted solar chimney. Four different radiation models, namely DO (discrete ordinates), S2S (surface-to-surface), MC (Monte Carlo), and Rosseland are used for comparison, and the results of the numerical simulation are compared with the experimental data. The results show that the maximum turbulent viscosity of the fluid predicted by the S2S radiation model is higher than that of the MC and DO models by 16.87% and 8.44%, respectively. The errors of the DO radiation model in the midline and glass cover plate direction concerning the experimental results are only 0.33% and 0.15%, respectively. The mistakes of the MC radiation model in these two directions are 0.51% and 0.47%, respectively. The DO radiation model is more suitable in numerical simulation predictions related to the wall-mounted solar chimney.

Full-scale test and numerical simulation of three-ring staggered-joint shield segment reinforcement under ultimate load conditions

Using the self-developed multiring shield segment prototype test loading system, the three-ring staggered full-scale segments under ultimate loading are tested to investigate the mechanical characteristics of the segments before and after reinforcement. Then, a numerical simulation is carried out based on the MIDAS GTS NX to study the stiffness change before and after segment reinforcement. The test results show that the maximum bending moment at the waist of the reinforced segment moves down, and the maximum offset and bolt stress are greatly reduced. The maximum offset occurs at the waist and top of the reinforced segment, and joint 5 bears the maximum shear stress and principal stress, which decreased by 29.5% and 28.6%, respectively. Compared with the single-ring shield segment after reinforcement, the three-ring segment enters the plastic state earlier, and the overall stiffness of the segment is greatly improved, which can weaken the intermediate stage of plastic deformation and delay the process of the segment entering the plastic state. In addition, the stiffness of the unreinforced segment decreases sharply when its lateral convergence deformation is greater than 25.03 mm, but the stiffness of the reinforced segment is still in a stable state. The plastic deformation of the concrete starts from the bolt hole and goes along the bolt hole to the two ends of the bolt. Lateral expansion occurred, and the bolts of the reinforced segment did not break during the whole loading process.

Experimental and numerical investigation on the shear behavior and damage mechanism of segmental joint under compression-shear load

The segment dislocation at circumferential joints severely impacts on the structural safety of shield tunnels during construction and operation. Especially for the underwater tunnel with a super-large cross-section, the circumferential joint usually consists of oblique bolts and distributed mortises and tenons to control the dislocation. Given this, a series of full-scale loading tests of the circumferential joint is carried out based on Jinan Yellow River Tunnel, and a three-dimensional refined numerical model with concrete damage plastic (CDP) constitutive is also established to reveal the condition of stress and damage. The deformation process of joints, the stress of bolts, and the damage characteristics of mortises and tenons are investigated through the full-scale tests and numerical simulation. Moreover, the mechanical behavior and damage evolution of circumferential joint has been revealed under compression-shear loads. Besides, the influence of mortises and tenons, bolts on the shear resistance of joints is unraveled. The results show that the deformation process of the circumferential joint can be divided into three stages under the ordinal shearing loading scenario (OSLS) and reverse shearing loading scenario (RSLS). The bolt plays an important bearing role under OSLS and the bolt is in an unstressed state under RSLS, which makes the shear stiffness and shear capacity of the joint under OSLS larger than that under RSLS. The tenon and bolt hole damage presents local concrete crushing, while the damage of mortise occurred with concrete spalling. Compared with bolts, the mortises and tenons can significantly improve the shear stiffness and the ultimate bearing capacity of circumferential joints.

Damage Zone of the Reinforced Concrete Beam under Rectangular Explosive Contact Explosions

This paper investigates the damaged area of a reinforced concrete beam under rectangular explosive contact explosion, through full-scale beam tests and numerical simulation. The calculation equation of beam surface load distribution based on equivalent impulse is established, with a consideration of the effect of the length and height of rectangular explosive on the load distribution, and the calculation equation of beam damage area is further proposed. Through changing the mass of the rectangular TNT explosive (1~6 kg) and the shape of the 1 kg rectangular explosive, 5 cases of the test were carried out on a full-scale reinforced concrete beam. The damaged area of the beam is divided into three parts: blasting crater, damage span of the front face, and damage span of the bottom face. The RHT (Riedel–Hiermaier–Thoma) material model is used to simulate concrete for numerical simulation. Curve fitting was performed based on the numerical simulation results. With the prediction of the load distribution on the beam surface, the size of the surface crushing area and the span of the damaged area are calculated; the section resistance function of the beam is introduced to calculate the depth of the blasting crater; and the correlation curve between the damaged span of the front face, the depth of the blasting crater, and the mass of the block TNT is established. The local damage to the beam under the contact explosion load can be evaluated more accurately when the mass of the rectangular TNT is 1~6 kg.

Full-scale numerical simulation of hemodynamics based on left ventricular assist device.

Ventricular assist devices have been widely used and accepted to treat patients with end-stage heart failure. The role of VAD is to improve circulatory dysfunction or temporarily maintain the circulatory status of patients. In order to be closer to the medical practice, a multi-Domain model of the left ventricular coupled axial flow artificial heart was considered to study the effect of its hemodynamics on the aorta. Because whether LVAD itself was connected between the left ventricular apex and the ascending aorta by catheter in the loop was not very important for the analysis of simulation results, on the premise of ensuring the multi-Domain simulation, the simulation data of the import and export ends of LVAD were imported to simplify the model. In this paper, the hemodynamic parameters in the ascending aorta, such as blood flow velocity vector, wall shear stress distribution, vorticity current intensity, vorticity flow generation, etc., have been calculated. The numerical conclusion of this study showed the vorticity intensity under LVAD was significantly higher than that under patients' conditions and the overall condition is similar to that of a healthy ventricular spin, which can improve heart failure patients' condition while minimizing other pitfalls. In addition, high velocity blood flow during left ventricular assist surgery is mainly concentrated near the lining of the ascending aorta lumen. What's more, the paper proposes to use Q criterion to determine the generation of vorticity flow. The Q criterion of LVAD is much higher than that of patients with heart failure, and the closer the LVAD is to the wall of the ascending aorta, the greater the Q criterion is. All these are beneficial to the effectiveness of LVAD in the treatment of heart failure patients and provide clinical suggestions for the LVAD implantation in clinical practice.

Numerical Simulation of Heat Transfer Characteristics of Petroleum Hydrocarbon-Contaminated Soil During Ex-Situ Indirect Thermal Desorption

ABSTRACT Indirect thermal desorption process of petroleum hydrocarbon contaminated soil is very complex and difficult to be analyzed by engineering full-scale numerical simulation considering multi-phase flow and interphase heat as well as mass transfer. Therefore, it is urgent to develop a simple and rapid calculation method to guide technology development and engineering applications. In this paper, the method of equivalent specific heat approximation was proposed to simplify the mass transfer process on the material side to the heat transfer process under variable specific heat conditions, and the numerical simulation of engineering scale indirect thermal desorption equipment was studied by coupling the diffusion flame combustion model, weighted-sum-of-gray-gases model, and discrete ordinates model. The heating process of soil in thermal desorption chamber was simulated, and the influence of soil residence time and designed feed rate on process parameters was obtained. The research results showed that soil residence time should be extended appropriately under the condition of less than 1.75 hours and designed feed rate be limited within 4 t/h to ensure reasonable soil discharge temperature that was directly related to the removal efficiency of petroleum hydrocarbons in contaminated soil. Meanwhile, the modification scheme of power distribution of combustion system was further studied to improve the heating uniformity of tubes.

Static and Dynamic Response Characteristics of a Full-Scale Long-Cantilever Tower under Various Loading Conditions

Long-cantilever transmission towers are drawing more and more attention in ultrahigh-voltage (UHV) transmission projects. To meet the requirements of high-voltage safety clearance, the structural characteristics of long-cantilever transmission towers are significantly different from traditional ones. Aiming to ensure the safety of long-cantilever transmission towers during service, this paper investigates their static and dynamic characteristics under various extreme loading conditions based on full-scale tests and numerical simulation. With the strain data tested in seven typical cases, the bending moments and axial forces of the main members were back-calculated and the initial imperfections were calculated based on these results. Using a stochastic subspace identification algorithm, the evolution of the modal parameters during the full-scale test was revealed. The damage position of the main members was identified according to the mode shape changes, and the dynamic collapse process was analyzed via the measured dynamic responses and recorded videos. Numerical simulation was conducted in ANSYS using the calculated initial imperfections, and the results were in good agreement with the full-scale test. The results show that torsion action was not dominant for this tower and the failure mode was still the bending failure at the tower body. The proposed imperfection quantification method makes up for the deficiency of the empirical values, and using experimental results to guide numerical simulation proves practical. The modal parameters vary greatly under different loading conditions, which can be attributed to the damage after each loading case.