Search Results (200)

Rectangular box jacking is widely used in densely developed urban areas. However, when conducted with limited clear distance near existing metro tunnels, it introduces considerable structural safety risks. This study investigates a large-section rectangular box jacking project in Suzhou that crosses a double-line metro tunnel with minimal vertical clear distance. Integrated field monitoring and finite element simulations were conducted to analyze the tunnel’s deformation behavior during various jacking phases. The results show that the upline tunnel experienced greater uplift than the downline tunnel, with maximum vertical displacement occurring directly beneath the jacking axis. The affected zone extended approximately 20 m beyond the pipe gallery boundaries. Both the tunnel vault and ballast bed exhibited vertical uplift, while the hance displaced laterally toward the launching shaft. These deformations showed clear stage-dependent patterns strongly influenced by the relative position of the jacking machine. Numerical simulations demonstrated that doubling the pipe–tunnel clearance reduced the vault displacement by 58.87% (upline) and 51.95% (downline). Increasing the pipe–slurry friction coefficient from 0.1 to 0.3 caused the hance displacement difference to rise from 0.12 mm to 0.36 mm. Further sensitivity analysis reveals that when the jacking machine is positioned directly above the tunnel, grouting pressure is the greatest influence on the structural response and must be carefully controlled. The proposed methodology and findings offer valuable insights for future applications in similar tunnelling projects. Full article

This work presents the implementation of a dual-extended Kalman filter (DEKF) in a double pipe counter-current heat exchanger. The DEKF aims to estimate online the heat transfer coefficient (HTC) to monitor the process. Some investigations estimate parameters in heat exchangers to detect fouling. However, there is limited research on online estimation using DEKF. The tests were performed at two operating conditions: in the first condition, the inlet temperatures were without perturbation; meanwhile, in the second operating condition, the cold-water inlet temperature was perturbed by the environmental heat. The experimental tests were carried out at different cold mass flow rates, which impact the temperatures and vary the heat transfer coefficient of the heat exchanger. The results showed adequate agreement between the estimated values of the heat transfer coefficients and those calculated with algebraic equations. This adequate agreement indicates that the DEKF method is conducive to detecting some problems in heat exchanger applications, such as poor heat transfer performance caused by fouling. Full article

Hydrogen-powered aircraft constitute a transformative innovation in aviation, motivated by the imperative for sustainable and environmentally friendly transportation solutions. This paper aims to concentrate on the design of hydrogen powertrains employing a system approach to propose representative design models for distribution and propulsion systems. Initially, the requirements for powertrain design are formalized, and a use-case-driven analysis is conducted to determine the functional and physical architectures. Subsequently, for each component pertinent to preliminary design, an analytical model is proposed for multidisciplinary analysis and optimization for powertrain sizing. A double-wall pipe model, incorporating foam and vacuum multi-layer insulation, was developed. The internal and outer pipes sizing were performed in accordance with standards for hydrogen piping design. Valves sizing is also considered in the present study, following current standards and using data available in the literature. Furthermore, models for booster pumps to compensate pressure drop and high-pressure pumps to elevate pressure at the combustion chamber entrance are proposed. Heat exchanger and evaporator models are also included and connected to a burning hydrogen engine in the sizing process. An optimal liner pipe diameter was identified, which minimizes distribution systems weight. We also expect a reduction in engine length and weight while maintaining equivalent thrust. Full article

In long-distance, large-section rectangular pipe jacking operations, machine deviation is an inevitable factor that poses substantial challenges to the accurate prediction of frictional resistance. To address this issue, a novel methodology is proposed to analyze the dynamic interactions at the pipe–soil–slurry interfaces. This approach integrates real-time alignment monitoring with the Winkler elastic foundation theory to enhance predictive accuracy. A comprehensive predictive framework is developed for excavation profiles and pipeline deflection curves under varying thrust distances, enabling the quantification of complex contact states. By applying Newton’s law of friction and the Navier–Stokes fluid mechanics equations, calculation methods for the frictional resistance of pipe–soil contact and pipe–mud contact are systematically derived. Furthermore, a predictive model for the jacking force in long-distance rectangular pipe jacking, accounting for complex contact conditions, is successfully established. The jacking force monitoring data from the 233.6-m utility tunnel pipe jacking project case is utilized to validate the reliability of the proposed theoretical prediction method. Parametric analyses demonstrate that doubling the subgrade reaction coefficient enhances peak resistance by 80%, while deviation amplitude exerts a 70% greater influence on performance compared to cycle parameters. Slurry viscosity emerges as a critical factor governing pipe–slurry interaction resistance, with each doubling of viscosity causing up to a 56% increase in resistance. The developed methodology proves adaptable across five distinct operational phases—machine advancement, initial jacking, stable jacking, deviation accumulation, and final jacking—establishing a robust theoretical framework for the design and precision control of ultra-long pipe jacking projects. Full article

This study investigates the thermal and residual stress development in multi-layer lined pipe welding through numerical simulation and experimental validation. The focus is on the weld overlay/liner transition region, a critical area prone to stress concentrations and fatigue crack initiation. Using finite element analysis (FEA) with the Goldak double-ellipsoidal heat source model, the research examines the temperature evolution, residual stress distribution, and deformation characteristics during the welding process. Key findings reveal that the peak temperature in the weld overlay region reaches 3045.2 °C, ensuring complete metallurgical bonding. Residual stresses are predominantly tensile near the three-phase boundary, with maximum von Mises stress observed in the base pipe at 359.30 MPa. This study also employs Response Surface Methodology (RSM) to optimize welding parameters, achieving a 20.5% reduction in residual axial stress and a 58.1% reduction in residual circumferential stress. These results provide valuable insights for optimizing welding processes, improving quality control, and enhancing the long-term reliability of bimetallic composite pipelines. Full article

Whip restraints based on thin-walled structures are widely used for protection against high-energy pipe breaks in nuclear power plants due to their excellent impact resistance. Recently, biomimetic and hierarchical structures have emerged as focal points in thin-walled structure research, aimed at enhancing energy absorption capacities. Drawing inspiration from the nautilus shell and Fibonacci spiral, based on the nautilus bionic hierarchical multi-cell (NBHMC) structure, this study introduces a novel Nautilus Bionic Double Hierarchical Multi-Cell (NBDHMC) structure. Finite element analysis was employed to evaluate the energy absorption performance of the structure under axial and oblique loads using four crashworthiness parameters. Crashworthiness studies showed that the NBDHMC exhibits superior crashworthiness compared to the NBHMC and hollow circular tube configurations. Finally, the study investigated the influence of combination modes, hierarchical levels, cross-sectional characteristics, and other parameters on the parameterization of the NBDHMC. The results offer innovative insights for the design of highly efficient energy absorbers. Full article

Cracks due to stress corrosion cracking in stainless steels are becoming a problem not only in boiling water reactors but also in pressurized water reactor nuclear plants. Stress improvement measures have been implemented mainly for large-bore welded piping, but in the case of small-bore welded piping, post-welding stress improvement measures are often not possible due to dimensional restrictions, etc. Therefore, knowing the actual welding residual stresses of small-bore welded piping regardless of reactor type is essential for the safe and stable operation of nuclear power stations, but there are only a limited number of examples of measuring the residual stresses. In this study, austenitic stainless steel pipes with an outer diameter of 100 mm and a wall thickness of 11.1 mm were butt-welded. The residual stresses were measured by the strain scanning method using neutrons. Furthermore, to obtain detailed residual stresses near the penetration bead where the maximum stress is generated, the residual stresses near the inner surface of the weld were measured using the double-exposure method (DEM) with hard X-rays of synchrotron radiation. A method using a cross-correlation algorithm was proposed to determine the accurate diffraction angle from the complex diffraction patterns from the coarse grains, dendritic structures, and plastic zones. A quantum beam hybrid method (QBHM) was proposed that uses the circumferential residual stresses obtained by neutrons and the residual stresses obtained by the double-exposure method in a complementary use. The residual stress map of welded piping measured using the QBHM showed an area where the axial tensile residual stress exists from the neighborhood of the penetration bead toward the inside of the welded metal. This result could explain the occurrence of stress corrosion cracking in the butt-welded piping. A finite element analysis of the same butt-welded piping was performed and its results were compared. There is also a difference between the simulation results of residual stress using the finite element method and the measurement results using the QBHM. This difference is because the measured residual stress map also includes the effect of the stress of each crystal grain based on elastic anisotropy, that is, residual micro-stress. Full article

Deep borehole heat exchangers (DBHEs) have been widely used for extracting geothermal energy in China. However, the application of this technology in an open well with high temperature remains unknown. In this paper, the thermal performance of a DBHE installed in a groundwater-filled hot dry rock (HDR) well in the Gonghe Basin of Qinghai Province in China was investigated. A U-shaped pipe subjected to a hydraulic pressure of 30 MPa and a temperature of 180 °C was tested successfully. Severe heat loss was detected during the test, which might have been due to the pipe not being well-insulated. To better understand the performance of DBHEs, a numerical model was developed. The results indicate that the pipe’s thermal performance increased by 247% using insulation with a 15 mm layer thickness and a thermal conductivity of 0.042 W/m·K. Thermal performance was significantly improved by increasing the fluid flow rate and pipe diameter. Among the different pipe configurations, double U-shaped buried pipes can achieve the highest performance. The heat-specific rate can reach up to 341.33 W/m with a double U-shaped pipe with a diameter of 63 mm. The second highest rate can be achieved with a coaxial pipe, while single U-shaped pipes have the lowest one. Full article

Thermoplastic composite pipes (TCP) consist of three distinct layers—liner, reinforcement, and coating—offering superior advantages over traditional industrial pipes, including flexibility, lightweight construction, and corrosion resistance. This study systematically characterises the thermal properties of TCP layers and their compositions using a multi-method approach. Thermal analysis was conducted through differential scanning calorimetry (DSC) for isothermal and non-isothermal crystallisation, thermogravimetric analysis (TGA) for thermal stability, and Fourier transform infrared spectroscopy (FTIR) for material identification. FTIR confirmed polyethylene as the primary component of TCP, with compositional variations across the layers. TGA results indicated that thermal degradation begins at approximately 200 °C, with complete decomposition at 500 °C. DSC analysis revealed a double melting peak, prompting further investigation into its mechanisms. On-isothermal crystallisation kinetics, analysed at cooling rates of 10 °C/min and 50 °C/min, revealed an anisotropic crystalline growth pattern. Although nucleation occurs uniformly, the subsequent three-dimensional crystalline growth is governed more by the degree of supercooling than by the crystallography of the glass fibres. This underscores the importance of precisely controlling the cooling rate during manufacturing to optimise the anisotropic properties of the reinforced layer. This study also demonstrates the value of FTIR, TGA, and DSC techniques in characterising the thermo-physical behaviour of TCP, offering critical insights into thermal expansion, shrinkage phenomena, and overall material stability. Given the limited body of research on this specific TCP formulation, the findings presented here lay a foundation for both quality enhancement and process optimisation. Moreover, the paper offers a distinctive perspective on the dynamic behaviour, thermal expansion, and long-term performance of TCP in demanding oil and gas environments. Full article

In this study, we propose a novel device, the coaxial cross double-twisted tape and vortex generator (CV), to significantly enhance the heat transfer performance of high-viscosity lubricating oil. Based on numerical simulation results, we thoroughly analyze the thermal–hydraulic behavior of the lubricating oil within the enhanced pipe. We explore four distinct geometrical configurations of the CV. Among them, a particular variant, the CVCP, achieves the most remarkable enhancement in heat transfer performance. To further understand the heat transfer characteristics of CVCPs, we examine the effects of twist ratios (y = 2.0, 3.0, 4.0, and ∞) and angles (α = 0°, 30°, and 60°). The results reveal that, across a wide Reynolds number range (40 ≤ Re ≤ 840), the heat transfer performance of CVCP is closely related to the twist ratio and angle. Notably, the performance evaluation criterion (PEC) of a tube with CVCP inserted is 1.14–1.54 times higher than that of conventional twisted tapes. Overall, these findings provide valuable insights into optimizing heat transfer in high-viscosity fluids and serve as a meaningful reference for future research and engineering applications aimed at enhancing lubricating oil heat transfer within tubes. Full article

This study investigates the effects of novel pipe cross-section designs on the thermal, hydraulic, and exergetic performance of a double-pipe heat exchanger, aiming to identify the most efficient design for industrial applications. Four novel cross-sections are proposed: Case 1 (rounded square), Case 2 (hexagonal), Case 3 (triangular), and Case 4 (star-like), all maintaining the same inlet area as the base model (circular). A 3D CFD model using the Finite Volume Method and realizable k-ε turbulence model is employed to analyze performance under turbulent flow conditions (Re = 3000–20,000). Key metrics, including the Nusselt number, overall heat transfer coefficient, pressure drop, and exergy destruction, are evaluated. The results show that Case 2 achieves a 7% increase in the Nusselt number at Re = 3000 and a 2% increase at Re = 20,000, while Case 4 exhibits a 180% improvement in the overall heat transfer coefficient at Re = 13,100. However, Case 4’s higher pressure drop reduces its performance compared to the base model. Case 2 demonstrates the best thermal characteristics, making it the most suitable for industrial applications. Full article

Double-layer pipelines are widely used in deep-sea energy transport because of their strong thermal insulation and enhanced structural safety. The stress distribution and the interaction mechanism between inter-pipes of double-layer pipelines are elucidated. A mechanical model is developed to characterize the thermal deformation difference between the two layers. The mechanical response of the pipeline can be divided into two distinct modes based on the initial deformation stages: (1) an inner-pipe-dominated elongation that creates compressive stress in the inner pipe and tensile stress in the outer pipe, and (2) an outer-pipe-dominated elongation that reverses this stress distribution. Sagging deformation (bowl-shaped deformation), primarily caused by the self-weight of the inner pipe, is identified as the critical factor that drives the stress concentration and bending moment at the inner–outer pipe connection. Engineering approaches, such as inserting spacers or additional supports in the annular cavity, effectively reduce peak stresses in both layers under extreme conditions. Full article

Addressing the challenge of acquiring depth information in aero-engine assembly scenes using monocular vision, which complicates mixed reality (MR) virtual and real occlusion processing, we propose an ORB-SLAM3-based monocular vision assembly scene virtual and real occlusion processing method. The method proposes optimizing ORB-SLAM3 for matching and depth point reconstruction using the MNSTF algorithm. MNSTF can solve the problems of feature point extraction and matching in weakly textured and texture-less scenes by expressing the structure and texture information of the local images. It is then proposed to densify the sparse depth map using the double-three interpolation method, and the complete depth map of the real scene is created by combining the 3D model depth information in the process model. Finally, by comparing the depth values of each pixel point in the real and virtual scene depth maps, the virtual occlusion relationship of the assembly scene is correctly displayed. Experimental validation was performed with an aero-engine piping connector assembly scenario and by comparing it with Holynski’s and Kinect’s methods. The results showed that in terms of virtual and real occlusion accuracy, the average improvement was 2.2 and 3.4 pixel points, respectively. In terms of real-time performance, the real-time frame rate of this paper’s method can reach 42.4 FPS, an improvement of 77.4% and 87.6%, respectively. This shows that the method in this paper has good performance in terms of the accuracy and timeliness of virtual and real occlusion. This study further demonstrates that the proposed method can effectively address the challenges of virtual and real occlusion processing in monocular vision within the context of mixed reality-assisted assembly processes. Full article

With ambitious targets set by the EU for the reduction of emissions from the energy sector by 2030, there is a need to design and develop more building projects using renewable energy sources. Even though in Europe, heating and cooling share from renewable resources is increasing, and in 2021, the total share in this sector in Croatia was at 38%, the share of heat production by heat pumps is rather low. One possibility to increase this share is to install energy piles when constructing a building, which is becoming an increasingly common practice. This case study focuses on such a system designed for a large, non-residential building in Zagreb, Croatia. The complex was designed as 13 separate dilatations, with central heating and cooling of all facilities, covered by 260 energy piles (130 pairs in serial connection), with a length of the polyethylene pipe of 20 m in a double loop inserted within the pile. The thermo-technical system was designed as a bivalent parallel system, with natural gas covering peak heating loads and a dry cooler covering cooling peak loads when the loads cannot be covered only by ground-source heat pumps. In the parallel bivalent system, the geothermal source will work with a much higher number of working hours at full load than is the case for geothermal systems that are dimensioned to peak consumption. Therefore, the thermal response test was conducted on two energy piles, connected in series, to obtain thermogeological parameters and determine the heat extraction and rejection rates. The established steady-state heat rate defines the long-term ability to extract heat energy during constant thermal load, with the inlet water temperature from the pile completely stabilized, i.e., no significant further sub-cooling is achieved in the function of the geothermal field operation time. Considering the heating and cooling loads of the building, modeling of the system was performed in such a manner that it utilized renewable energy as much as possible by finding a bivalent point where the geothermal system works efficiently. It was concluded that the optimal use of the geothermal field covers total heating needs and 70% for cooling, with dry coolers covering the remaining 30%. Additionally, based on the measured thermogeological parameters, simulations of the thermal response test were conducted to determine heat extraction and rejection rates for energy piles with various geometrical parameters of the heat exchanger pipe and fluid flow variations. Full article

This study aims to identify the most suitable pre-reinforcement support measures to prevent TBM jamming when passing through the fractured zone of a gully fault. Given the high likelihood of jamming in such areas, the research focuses on selecting the most effective support system by considering factors such as surrounding rock stability, strata displacement, support structure stress, and cost-effectiveness. Theoretical analysis is employed to predict TBM jamming risks, based on design data, a 10 m gully unit and fractured rock mass were established at 75 m in the excavation direction with assigned parameters. Support effects of pipe curtains, grouting, anchors, and arch supports were analyzed under four conditions: chemical grouting, conduit installation, advanced pipe grouting, and double-layer pipe grouting. On-site verification reveals that TBM jamming occurs when the resisting torque on the cutter exceeds the maximum torque the cutter can generate. For the gully fault, pre-reinforcement measures are essential to stabilize the surrounding rock. Among the different methods, surface drilling reinforcement is the most effective. It significantly improves the surrounding rock’s stability, reducing the plastic zone’s depth by approximately 52.3% compared to the advanced pipe shed method. The axial force on the anchors decreases by 77.9–83.8%, arch stress is reduced by 68.9–90.8%, and tunnel deformation is minimized by 2.13–50.78%, all of which contribute to enhancing the safety of the initial support structure. On-site coring results, TBM boring parameters, and deformation monitoring data confirm that the surface drilling pre-reinforcement method outperforms the grouting pre-reinforcement for the pipe shed, ensuring the safe excavation of TBM in the gully fault conditions. These findings provide valuable insights for TBM tunnel construction in similar geological environments. Full article