Direct Coupling Method Research Articles

High efficiency deep ultraviolet micro-LED and optical fiber coupling for low power charge management applications

During space gravitational wave detection missions, it is necessary to manage the charge accumulated on the surface of the test mass. A common method involves using optical fibers to transmit ultraviolet (UV) light, leveraging the photoelectric effect for charge management. An important issue in this process is achieving efficient coupling between the UV light source and the optical fiber. In this paper, for the first time we proposed to use DUV micro-LEDs as light sources for charge management systems, which will have lower power consumption. We conducted simulations to investigate the effect of the size ratio between deep ultraviolet (DUV) micro-LEDs and optical fibers on the coupling efficiency. We further employed a direct coupling method to conduct coupling experiments of DUV micro-LEDs and optical fibers with varying wavelengths and sizes. The simulation and experiment results both indicate that, under the influence of both size and divergence angle, there exists an optimal DUV micro-LED size responsible for maximum coupling efficiency between DUV micro-LEDs and optical fibers which is 80 μm when the optical fiber size is 1000 μm. Applying the 80 μm DUV micro-LED in charge management experiments demonstrated the feasibility of using DUV micro-LEDs as light sources for low power charge management systems, achieving rapid charge–discharge rates and high photoelectric current at lower driving electrical power.

Simulation Analysis and Experimental Investigation on the Fluid–Structure Interaction Vibration Characteristics of Aircraft Liquid-Filled Pipelines under the Superimposed Impact of External Random Vibration and Internal Pulsating Pressure

This paper investigated the fluid–structure interaction vibration response of an aircraft liquid-filled pipeline under external random vibration and internal pulsating pressure. First, the fluid–structure interaction solution is theoretically analyzed, and the advantages and disadvantages of the direct coupling method and the separation coupling method are compared, with the latter chosen as the simulation analysis method in this study. Second, taking the U-shaped oil pipeline of an aircraft engine as an example, simulation modeling was performed to compare and analyze the fluid–structure interaction vibration response of aircraft liquid-filled pipelines under different working conditions, obtaining the vibration response characteristics of stress danger points under various conditions. Finally, a test bench for an aircraft liquid-filling pipeline was built to explore the influence of external random vibrations with different kurtoses, different pipe wall thicknesses and different working conditions on the vibration response danger points of aircraft liquid-filling pipelines, verifying the simulation conclusions and providing a basis for aircraft liquid-filling pipeline design.

Silica-Polymer Heterogeneous Hybrid Integrated Mach-Zehnder Interferometer Optical Waveguide Temperature Sensor.

In this paper, a temperature sensor based on a polymer-silica heterogeneous integrated Mach-Zehnder interferometer (MZI) structure is proposed. The MZI structure consists of a polymer waveguide arm and a doped silica waveguide arm. Due to the opposite thermal optical coefficients of polymers and silica, the hybrid integrated MZI structure enhances the temperature sensing characteristics. The direct coupling method and side coupling method are introduced to reduce the coupling loss of the device. The simulation results show that the side coupling structure has lower coupling loss and greater manufacturing tolerance compared to the direct coupling structure. The side coupling loss for PMMA material-based devices, NOA material-based devices, and SU-8 material-based devices is 0.104 dB, 0.294 dB, and 0.618 dB, respectively. The sensitivity (S) values of the three hybrid devices are -6.85 nm/K, -6.48 nm/K, and -2.30 nm/K, which are an order of magnitude higher than those of an all-polymer waveguide temperature sensor. We calculated the temperature responsivity (RT) (FSR→∞) of the three devices as 13.16 × 10-5 K, 32.20 × 10-5 K, and 20.20 × 10-5 K, suggesting that high thermo-optic coefficient polymer materials and the hybrid integration method have a promising application in the field of on-chip temperature sensing.

Coupling of the best-estimate system code and containment analysis code and its application to TMLB’ accident

With the development of advanced pressurized water reactor technology, the thermal-hydraulic coupling effect between the containment and the primary system becomes increasingly tight. In order to meet the demand for integrated safety analysis between the containment and the primary system, this paper investigates a direct coupling method between the best-estimate system code Advanced Reactor Safety Analysis Code and the containment analysis program ATHROC (Analysis of Thermal Hydraulic Response Of Containment). The feasibility of this direct coupling method and the applicability of the coupled program for overall safety analysis are demonstrated using Marviken two-phase flow release experiments. The ATHROC/ARSAC coupled program is employed to analyze the impact of the pressure relief function of the CPR1000 nuclear power plant pressurizer on the behavior of the primary system and containment during the TMLB’ accident. The calculation results indicate that these measures can reduce the pressure of the primary system to the level acceptable by the low-pressure injection system, but at the same time, they cause the pressure in the containment to rise to nearly 0.4 MPa. Therefore, to ensure the structural integrity of the containment, it is necessary for the non-passive hydrogen recombiner to effectively reduce the hydrogen concentration, thereby avoiding additional pressure increase in the containment due to hydrogen deflagration, which could lead to overpressure failure. The findings of this study are of significant reference value for improving the safety performance of thermal-hydraulic systems in operational Gen-II and advanced Gen-III pressurized water reactor nuclear power plants.

Simulation study on effect of flame cutting speed on temperature field and residual stress distribution

Due to the advantages of flame cutting in thick plate cutting and cutting cost, it is widely used in the metal cutting process of shipbuilding and machinery manufacturing. But at the same time, the local heating of flame cutting will cause residual stress inside the steel plate. Residual stress is an important reason for deformation and cracking of components. The change of temperature field is the premise of affecting the distribution of residual stress. Cutting speed has an important effect on the distribution of temperature field and residual stress field. In this paper, ABAQUS is used to create a finite element model for flat flame cutting of Q345D low-alloy steel. Based on the working principle of flame cutting, the model of flame cutting composite heat source is established and the subprogram of composite heat source is written. The thermal-mechanical direct coupling method is used to simulate and analyze the effect of different cutting speeds on the temperature and residual stress field distribution of the flat flame cutting process, to provide a reference for the subsequent processing.

A coupled computational framework for the transient heat transfer in the typical pyrotechnic device

Propellant combustion in pyrotechnic devices produces high-temperature, high-pressure gas. The component is moved by high-pressure gas, which subsequently impacts the energy absorber and causes it to compress and deform. The temperature difference between the high-temperature gas and the wall causes transient heat transfer. Propellant combustion, transient heat transfer, and structural response are coupled, but previous studies had to independently analyze them. Therefore, a multi-physical field numerical model is developed based on the commercial software ABAQUS in this paper, which couples energetic material combustion, transient heat transfer, and structural response. In the user subroutine VUAMP, a lumped-parameter model is used to predict the parameter distribution of combustion products. This determines the load applied on the thin-walled tube and the boundary conditions of transient heat transfer. In ABAQUS, the transient heat transfer and structural response are investigated by the direct thermo-dynamic coupling method. The coupling effect between multiple physical fields is realized by real-time parameter exchange. The rationality and accuracy of the coupling model are verified by comparison with the experiment. The results show that the coupling model can effectively simulate the complex coupling process after considering the transient heat transfer and the interaction between multiple physical fields. Taking a pyrotechnic device as the research object, the pressure load accuracy obtained by the coupled model is improved by 5.1%, and the structure response obtained is also closer to the experiment result. At the same time, more characteristic parameters of the structure field and temperature field are obtained.

Thermal–Mechanical Coupling Analysis of Wheel–Rail Sliding Friction under Two-Point Contact Conditions

The generation of wheel–rail-sliding frictional heat is often accompanied by transverse displacement of a wheel. To study the thermal problem of wheel–rail sliding friction at two-point contact, this paper uses an LM tread wheel and a 60 kg·m−1 rail as examples. A thermal–mechanical-coupled finite-element model of equal proportion wheel–rail sliding is established. A direct-coupling method is used to analyze the thermal–mechanical coupling of the wheel–rail interface under sliding contact. This model considers the temperature-dependent material properties and boundary conditions, such as thermal convection and thermal dissipation, in the process of nonstationary frictional-heat conduction. Firstly, the effects of different sliding speeds, axle loads, and contact modes on the temperature and stress fields of the contact area are analyzed. Then, the lubrication and cooling effects of friction modifiers on the rail top and rail gauge angle are compared. The results show that, at a sliding speed of 2 m/s and an axle load of 30 t under a sliding condition of 200 mm, on the top and side of the rail, the temperatures at the contact patch centers are 813 °C and 547.7 °C, respectively. Under different operating conditions, the rail-side temperature is 55–75% of that of the temperature at the rail top, and the rail-side contact and friction stress values are 76–96% of those at the rail top. This indicates that frictional thermal damage on the rail side cannot be ignored. With a lower sliding speed, the thermal response of the two contact patches is closer. The impact of axle load on the frictional temperature and stress on the rail side is more critical than the sliding speed. The optimal lubrication choice is overall lubrication, which can decrease the rail top temperature by 47.2% and frictional stress by 56.2%, as well as decreasing the rail side temperature by 70.3% and frictional stress by 77.4%.

A novel BEM-DEM coupling in the time domain for simulating dynamic problems in continuous and discontinuous media

This work presents a novel scheme to couple the Boundary Element Method (BEM) and the Discrete Element Method (DEM) in the time domain. The DEM captures discontinuous material behaviour, such as fractured and granular media. However, applying the method to real-life applications embedded into infinite domains is challenging. The authors propose a solution to this challenge by coupling the DEM with the BEM. The capability of the BEM to model infinite domains accurately and efficiently, without the need for numerical artifices, makes it the perfect complement to the DEM. This study proposes a direct monolithic interface-based coupling method that resolves any incompatibilities between the two methods in two dimensions. The benchmark results show that the proposed methodology consistently produces results that align with analytical solutions. The final example in the paper showcases the full potential of this innovative methodology, where the DEM models a fracturing process, and the BEM evaluates its far-field effect.

The Direct-Coupling Method for Analyzing the Performance of Aerostatic Bearings Considering the Fluid–Structure Interaction Effect

In the interest of analyzing the effect of the structural deformation root caused by gas pressure on the static features of aerostatic bearings, a fluid–structure interaction (FSI) model based on orifice-type aerostatic bearings is proposed that can predict the characteristics of aerostatic bearings more accurately by using the direct-coupling method (DCM). By using COMSOL Multiphysics, the governing equation matrix of the finite element model of structural deformation and gas film pressure was solved with the integral solution method, and the orifice boundary conditions were calculated with the root iteration method. At the same time, the static performance of I-shaped orifice-type aerostatic bearing with various supply pressures was analyzed theoretically and tested experimentally. The results show that in comparison with the calculation results without taking account of structural deformation, the theoretical values from the model derived in this paper considering the FSI effect are closer to the experimental values. Finally, by using the orthogonal design method, FSI simulation was carried out to analyze how the key dimension factors influence the structural stiffness of the spindle, and it is concluded that the thrust bearing’s stiffness is strongly influenced by the thickness of the thrust plate.

Efficient time-domain approach for hydroelastic-structural analysis including hydrodynamic pressure distribution on a moored SFT

This study investigates the hydroelastic analysis of a moored SFT (submerged floating tunnel) and the corresponding hydrodynamic pressure distribution under wave excitations. Time-domain discrete-module-beam (DMB) method, in which an elastic structure is modeled by multiple sub-bodies with beam elements, is employed to express the deformable tunnel with multiple mooring lines. Moreover, the top-down scheme is also adopted for detailed structure analyses with less computational cost, which applies the calculated hydrodynamic pressure distribution over SFT's surface to the three-dimensional finite element model. The hydrodynamic pressure includes both wave-induced diffraction pressure and motion-induced radiation pressure. For the validation of the developed numerical approach, comparisons are made with computationally intensive hydroelastic-structural direct-coupled method, two-dimensional wave flume experiment, and independently developed inhouse moored-SFT-simulation program. Furthermore, the influences of flexural motions with buoyancy-weight ratio (BWR) (or bending stiffness) and regular/irregular wave conditions on the dynamic pressure distribution and the resulting local stresses are investigated.

Application of direct coupling method to design problems of hydrostatic guideways accounting for fluid-structure interactions

The deformation of slide carriages caused by oil pressure produces a substantial effect on the performance of hydrostatic guideways. This paper is aimed to propose a practical fluid-structure interaction (FSI) model adopting the direct coupling method to predict the performance more efficiently. To this end, the full-size model containing elastic deformation and thin film pressure fields is solved simultaneously, and the specific boundary conditions caused by the orifice are considered and enforced via the root iterative method. The model is confirmed to be mesh-independent by meshing with three different densities. Furthermore, the vertical stiffness, deformation, and flow rate of the hydrostatic guideway are evaluated and tested with various oil supply pressures. Compared with the theoretical values without considering deformation, the simulation results take the structural deformation into account and thereby exhibit good agreement with those of the experiment. Based on the proposed FSI model, the orthogonal design method is also employed to analyze the influence of structure geometry, and the carriage slide thickness is introduced as the key influential factor of stiffness.

Numerical Study of Heat Transfer in a Two-Dimensional Rarefied Hydrogen Gas Moved Jet Impingement Using Direct Simulation Monte Carlo-Finite Difference Coupled Method

Temperature control is an important indicator for the lithography. However, the factors causing temperature fluctuation in lithography remain unclear under a low-pressure environment. In this work, in order to study the jet impingement heat transfer of hydrogen under rarefied conditions, the direct simulation Monte Carlo (DSMC) method and the finite difference method (FDM) are coupled. The heat exchange capacity in the jet impingement obtained using DSMC method is treated as a boundary condition for substrate. The difference of impingement heat transfer of rarefied hydrogen jet under different conditions of inlet absolute pressure, impingement distance and jet aperture are studied. The temperature of substrate is calculated by FDM. Results show that heat exchange capacity of the jet impingement rises with an increasing the inlet absolute pressure and pipe diameter, drops with reducing impact distance. The temperature control requirements can be met when the heat exchange capacity exceeds 380 W/(m2·K), the structural parameters satisfying the temperature control requirement are demarcated. The aforementioned findings can provide design ideas for high-precision temperature control devices.

Bio-Based Degradable Poly(ether-ester)s from Melt-Polymerization of Aromatic Ester and Ether Diols.

Vanillin, as a promising aromatic aldehyde, possesses worthy structural and bioactive properties useful in the design of novel sustainable polymeric materials. Its versatility and structural similarity to terephthalic acid (TPA) can lead to materials with properties similar to conventional poly(ethylene terephthalate) (PET). In this perspective, a symmetrical dimethylated dialkoxydivanillic diester monomer (DEMV) derived from vanillin was synthesized via a direct-coupling method. Then, a series of poly(ether-ester)s were synthesized via melt-polymerization incorporating mixtures of phenyl/phenyloxy diols (with hydroxyl side-chains in the 1,2-, 1,3- and 1,4-positions) and a cyclic diol, 1,4-cyclohexanedimethanol (CHDM). The polymers obtained had high molecular weights (Mw = 5.3–7.9 × 104 g.mol−1) and polydispersity index (Đ) values of 1.54–2.88. Thermal analysis showed the polymers are semi-crystalline materials with melting temperatures of 204–240 °C, and tunable glass transition temperatures (Tg) of 98–120 °C. Their 5% decomposition temperature (Td,5%) varied from 430–315 °C, which endows the polymers with a broad processing window, owing to their rigid phenyl rings and trans-CHDM groups. These poly(ether-ester)s displayed remarkable impact strength and satisfactory gas barrier properties, due to the insertion of the cyclic alkyl chain moieties. Ultimately, the synergistic influence of the ester and ether bonds provided better control over the behavior and mechanism of in vitro degradation under passive and enzymatic incubation for 90 days. Regarding the morphology, scanning electron microscopy (SEM) imaging confirmed considerable surface degradation in the polymer matrices of both polymer series, with weight losses reaching up to 35% in enzymatic degradation, which demonstrates the significant influence of ether bonds for biodegradation.

Simulation Analysis and Verification of Temperature and Stress of Wheel-Mounted Brake Disc of a High-Speed Train

During the braking process, a large amount of heat energy is generated at the friction surfaces between the brake disc and pads and rapidly dissipates into the disc volume. In this paper, a three-dimensional thermo-mechanical coupling model of high-speed wheel-mounted brake discs containing bolted joints and contact relationships is established. The direct coupling method is used to analyze the temperature and stress of the brake discs during an emergency braking event with an initial speed of 300 km/h. A full-scale bench test is also conducted to monitor the temperatures of the friction ring and bolted joints. The simulation result shows that the surface temperature of the friction ring reaches its peak value of 414 °C after 102 s of braking, which agrees well with the bench test result. The maximum alternating thermal stress occurs in the bolt hole where the maximum circumferential compressive stress is − 658 MPa and the maximum circumferential tensile stress is 134 MPa. During the braking process, the out-of-plane deformation of the middle part of the friction ring is larger than that of the edge, which increases the axial tensile load of the connecting bolt. This work provides support for the design of brake discs and connecting bolts.

A simpler and greener alternative route for anchoring carbohydrates with structural integrity on silica and glass supports

A novel, straightforward, and environmentally friendly direct coupling procedure to immobilize carbohydrates on solid supports is presented. A characterization study showed that all amino groups on solid supports participated in the linkage with a carbohydrate unit, implicating that the surface load can be easily adjusted by tuning the amination coverage of the surface. Most importantly, the integrity of the cyclic conformation of the linked sugar unit was demonstrated, a feature that is critical for most of the possible applications of carbohydrate-functionalized surfaces. Furthermore, carbohydrate-immobilized submicron particles synthesized by the direct coupling method, on which lectin profiling experiments were conducted, validated the successfulness of our simplistic approach.

Sloshing effect analysis of liquid storage tank under seismic excitation

Sloshing wave height is a main parameter in the seismic design of liquid storage tanks, and severe sloshing may lead to the liquid leakage or buckling of the steel tank wall. To accurately evaluate the sloshing wave height of the tank under earthquake action, a total of three shaking table tests were conducted on the liquid storage tanks, and numerical simulation methods based on the direct coupling method as well as the bidirectional coupling method were implemented. The sloshing height results from tests and simulations were compared with the values obtained from the theoretical formula, and the applicability of various calculation methods was analyzed. Thereafter, the theoretical formula of the simplified mechanical model and the bidirectional coupling method were adopted to predict the sloshing wave height of tanks with various dimensions, and the theoretical formula was further modified. Simultaneously, the influence of pulse-like ground motion on sloshing effect and hydrodynamic pressure of large-scale liquefied natural gas (LNG) storage tanks was examined. Additionally, the GB 50341–2014, API 650–2013, and Eurocode 8–2006 were utilized to assess the sloshing wave height of large storage tanks subjected to seismic ground motion, and the applicability of the computed results has been further discussed. Based on the above research, practical design recommendations were proposed in this work, which can provide a guidance for the seismic design of storage tanks.

Numerical Simulation of Ultrasonic Spot Welding of Superelastic NiTi Alloys: Temperature Distribution and Deformation Behavior

Abstract Ultrasonic spot welding (USW) has attracted increasing attention due to its high-throughput solid-state bonding mechanism, which shows great potential in the semiconductor and automotive industries for joining of metal sheets. However, the short welding cycle makes it challenging to effectively monitor the temperature history and deformation of the workpieces during the process. In this study, a three-dimensional (3D) finite element analysis model for USW of superelastic NiTi shape memory alloy (SMA) with Cu interlayer was developed using ansysworkbench. The thermal-stress coupled phenomena including the heat generation and stress distribution during the welding process were simulated and analyzed. First, a superelastic constitutive model for NiTi SMAs was constructed. The distribution of temperature and stress fields was then obtained by thermal-stress analysis using the direct coupling method, and the superelasticity of SMAs was observed. The simulation results showed that the highest temperature occurred in the center of the welding area during USW, which is proportional to the welding time and inversely proportional to the clamping pressure. In addition, the maximum stress occurred at the center of the contact surface between upper NiTi and Cu interlayer. After that, the validity of the simulation results was verified by setting up a thermocouple temperature measurement platform to collect the temperature data, which exhibited a good agreement with the simulated results. The simulation procedure demonstrates its potential to predict temperature and stress distributions during the USW process.

Thermo elasto-plastic contact analyzis for high temperature applications

This study presents the development of a thermo-mechanical simulation model for an elastic-plastic contact problem between a half cylinder and a plane plate. The set of equations was solved using direct coupling method by ANSYS mechanical. The results obtained from the present numerical model of the structural contact without heat transfer are compared with those of analytical, experimental and other numerical models. Then, the contact problem was solved using a coupled thermo-mechanical model. Computational results showed significant effects of thermal consideration in the elastic-plastic contact problem. Large deformations of structure due to high temperature are predicted using the thermo-mechanical model with elastic-plastic deformations. This model is useful to predict deformations on the structural components due to contact at high temperature situation.

3-D sloshing of liquid filled laminated composite cylindrical tank under external excitation

A new three dimensional finite element formulation is developed for the analysis of sloshing of liquid inside a partially filled laminated composite cylindrical tank under external excitations. Direct coupling method is adopted for efficient fluid–structure interaction between tank and liquid. The tank structure is modelled using 8 noded 3-D degenerated shell elements and the liquid inside tank is modelled using 20 noded brick elements. Experiments were conducted to validate the developed formulation. The results generated from developed formulation are in close agreement with the results available in open literature and the results obtained from experiment. Parametric studies are conducted by varying the tank thickness, ply orientation, and water level inside the tank to understand their effect on slosh height. Composite tanks are subjected to harmonic and seismic (Koyna earthquake 1967) loading for the parametric study.

Optimal voltage of direct current coupling for a fuel cell–battery hybrid energy storage system based on solar energy

A hybrid energy storage system based on a polymer electrolyte membrane fuel cell and a battery is designed and applied using solar energy in this study. The fuel cell and batteries are connected using a direct coupling method. The optimal DC coupling voltage is examined by turning the fuel cell operation on and off. The voltage difference is first evaluated and it is found that a 2 V difference yields the optimal condition with the longest operating time and transition period without system failure. Various on–off couples are then determined. It is found that an on–off​ couple of 49–51 V presents the best transition period, indicating the good harmonized operation between the fuel cell and batteries. Therefore, an on–off couple at 49–51 V for fuel cell operation is the optimal and suitable DC coupling voltage according to this work system.