Key Structural Parameters Research Articles

Modelling and analysis of a superconducting magnetic coupler used for cryogenic pump

AbstractIt is difficult to achieve low heat leakage and leak‐free rotary sealing for conventional small‐ and medium‐sized cryogenic liquid pumps (CLPs). This is because the motor in a room‐temperature environment is connected to the pump impeller (in a cryogenic environment) via a long transmission shaft. An axial flux‐concentration superconducting magnetic coupler (AFCSMC) is proposed for CLP to eliminate the transmission shaft. Firstly, the structure and the operation mechanism of AFCSMC are described. Then, a 2D electromagnetic modelling method for AFCSMC is established based on the H‐φ formulation and also validated experimentally in terms of the prediction on the levitation force and the guidance force. Thus, the 2D numerical simulations of AFCSMC are performed in an equivalent static system instead of the actual double rotor motion system in which the moving mesh is quite complicated. It is investigated that dependences of the transmission torque on the key electromagnetic structural parameters, such as permanent magnet arrangement, number of pole‐pairs, ferromagnetic yoke, operating slip, and so on. The results indicate that the average transmitting torque is less affected by the operating slip, and AFCSMC can start asynchronously and operate in steady state with a synchronous speed. With the advantages of low loss, risk‐free of desynchronising, and overload protection, the proposed AFCSMC can provide a competitive candidate for mechanical power transmission technologies in cryogenic engineering.

Symmetries and wave functions of photons confined in three-dimensional photonic band gap superlattices

We perform a computational study of confined photonic states that appear in a three-dimensional (3D) superlattice of coupled cavities, resulting from a superstructure of intentional defects. The states are isolated from the vacuum by a 3D photonic band gap, using a diamondlike inverse woodpile crystal structure, and they exhibit “Cartesian” hopping of photons in high-symmetry directions. We investigate the confinement dimensionality to verify which states are fully 3D-confined, using a recently developed scaling theory to analyze the influence of the structural parameters of the 3D crystal. We create confinement maps that trace the frequencies of 3D-confined bands for select combinations of key structural parameters, namely the pore radii of the underlying regular crystal and of the defect pores. We find that a certain minimum difference between the regular and defect pore radii is necessary for 3D-confined bands to appear, and that an increasing difference between the defect pore radii from the regular radii supports more 3D-confined bands. In our analysis, we find that their symmetries and spatial distributions are more varied than electronic orbitals known from solid-state physics. We surmise that this difference occurs since the confined photonic orbitals derive from global Bloch states governed by the underlying superlattice structure, whereas single-atom orbitals are localized. Based on this realization, we suggest that the extent symmetries of “photonic orbitals” could possibly translate to novel macroscopic behaviors of “photonic solid-state matter,” never before seen in the standard electronic solid-state systems. We also discover pairs of degenerate 3D-confined bands with p-like orbital shapes and mirror symmetries matching the symmetry of the superlattice. Finally, we investigate the enhancement of the local density of optical states for cavity quantum electrodynamics applications. We find that donorlike superlattices, i.e., where the defect pores are smaller than the regular pores, provide greater enhancement in the air region than acceptorlike structures with larger defect pores, and thus offer better prospects for doping with quantum dots and ultimately for 3D networks of single photons steered across strongly coupled cavities. Published by the American Physical Society 2024

A method to rapidly construct 3D canopy scenes for maize and their spectral response evaluation

Three-dimensional (3D) scenes of a maize canopy can be utilized to depict its vertical structure and serve as the foundation for a 3D radiative transfer model. Given the inherent heterogeneity of canopy structures, evaluating their spectral response is crucial for remote-sensing inversion algorithms. Yet existing methods to model 3D canopy scenes of crops lack the high efficiency required for large-scale breeding applications. Hence, this study aims to develop a method to rapidly construct 3D canopy scenes of maize based on key structural parameters—namely, leaf area, base angle, and inclination angle—across multiple cultivars and growth stages. The accuracy of this canopy scenes modeling method was validated by comparison with a fine-scale 3D model and a multi-growth stage reflectance dataset. The root mean square error (RMSE) and normalized root mean square error (NRMSE) between the fine-scale 3D model and the constructed 3D model were less than 0.021 and 6.4%, respectively. Moreover, the RMSE and NRMSE between the simulated reflectance and measured reflectance were less than 0.042 and 11.1%, respectively. Next, we integrated the 3D radiative transfer model with 3D scenes to analyze the spectral response of maize canopy structure. The findings revealed that the near-infrared band was affected more by leaf area than leaf base angle, while the opposite is observed for the red-edge band. Furthermore, the middle layer contributed more to the canopy reflectance than either the upper or lower layers. Notably, two maize scenes where two structural parameters simultaneously change could elicit the same canopy spectra. The proposed method thus offers the dual advantages of rapid modeling and high efficiency, making it highly applicable for maize and other similar crops.

A simplified numerical method based on anisotropic porous media model for the precooler of the hypersonic precooled engine

The precooler is a key component of hypersonic precooled engine, and its actual structural have a high anisotropy in the axial, circumferential, and radial direction. Considering the non-uniform flow inside the precooler is crucial to study the flow and heat transfer characteristics of the precooler. The previous simplified method for the precooler has not fully considered the flow non-uniformity of the axial, radial and circumferential direction. In this paper, a simplified numerical method based on anisotropic porous media model for the precooler was proposed. The unique aspect of this method is the integration of anisotropic surface porosity of porous media model with the zero-dimensional heat transfer model. In addition, the influence of key structural parameters on the flow and heat transfer characteristics of precooler was studied. It is found that as the tube transverse pitch increases from 2 to 3.5, the total flow rate increases by 11%, and the heat exchange rate decreases by 25%. As the number of tube rows increases from 7 to 13, the heat exchange rate increases by 22%, but the total pressure loss coefficient increases from 0.046 to 0.082. In addition, the decrease of inner diameter of the precooler improves the heat exchange rate, but reduces the flow capacity of the precooler. These results indicate that the simplified numerical method is capable of simulating the behavior of precooler and provides some guidance on the design of precooler.

Energy absorption performance of woven metallic lattices with orthogonal spiral wires under quasi-static compression

Woven metallic lattice (WML) structures are gaining attention for their beneficial mechanical properties, such as low weight and special energy absorption capability. They hold potential for diverse applications, including energy absorption components in aerospace. Drawing inspiration from the traditional double-arrow lattice, this study proposes a novel WML design featuring multi-plateau stresses. The deformation behavior of this structure under compression was investigated using finite element analysis and experimental methods. Three gradient structures defined by the different layer arrangements along load direction associated with specific structure variables, namely positive gradient (PG), negative gradient (NG), and hybrid gradient (HG), were introduced, along with an examination of their mechanical properties. The study explored the influence of key parameters of the cell structure on compression characteristics. Findings suggest that enhancing cell vertex angle and wire diameter can improve energy absorption, while the opposite holds true for cell base angle. Among the gradient structures analyzed, the PG WML structure demonstrates optimal energy absorption due to its dual-plateau stress characteristics. The NG WML structure is noteworthy for its uniform lattice deformation during initial compression stages, which is crucial for precision engineering with subtle deformation control strategies. Lastly, the deformation pattern of the HG WML structure during compression progresses from low to high strength.

Effect of side chain ionizability of polycarboxylate superplasticizer on cement hydration

Although the side chain ionizability (the adsorption group density and adsorption space are changed) of polycarboxylate superplasticizer (PCE) serve as the key structural parameter in affecting the cement hydration, its effect on cement hydration is unclear. Based on PCE with nonionizable side chain (NSC-PCE) and the PCE with ionizable side chain (ISC-PCE), the influence of the side chain ionizability of PCE on the hydration behavior of cement was studied. Compared with NSC-PCE, ISC-PCE has a stronger ability to change the migration of water and ions, thus delaying the crystal nucleation and growth of cement hydration (better morphology and distribution, the crystal size was reduced by more than 20 %), increasing the crystal growth index (tendency toward spherical growth), prolonging the phase boundary reaction (reduce micro-cracks), which was conducive to the formation of more uniform and dense crystals (good strength, ISC-PCE: 50.0 MPa > NSC-PCE: 49.2 MPa > Blank: 48.7 MPa). These findings provide the design basis and theoretical guidance for the innovative development of PCE.

Dynamic modeling and vibration suppression evaluation of composite honeycomb hemispherical shell with functional gradient protective coating

The vibration reduction performance of composite honeycomb hemispherical shells (CHHSs) coated with functional gradient protection coating (FGPC) are investigated in this work. Using the first-order shear deformation theory and the power-law distribution rule, the virtual spring technique, the regional decomposition method, and the Newmark-Beta approach, etc., a dynamic model of the FGPCCHHSs under base excitation is formulated to solve the inherent characteristics and displacement responses in time and frequency domains. After a set of convergence analyses are completed to ascertain an appropriate segment number and the stiffness values of virtual springs employed in the predictive model, the forecasted vibration parameters are verified using the literature and experimental results that are performed on uncoated and coated shells. The maximal natural frequency errors of the current model compared to the experimental results are 3.8% and 4.8%, and the displacement response errors under different excitation amplitudes are less than 10.3% and 12.7%, respectively, which demonstrate the correctness of such a model. Finally, the impact of key structural and material parameters on the vibration behaviors of the FPGCCHHSs is evaluated. To improve their vibration suppression capability, it is recommended to choose a high gradient index of coating material and a large thickness ratio of the FGPC to the overall shell with a reasonable moduli ratio of Material A to Material B of the FGPC to improve vibration reduction capability. This study offers a practical model tool and several important design recommendations for vibration prediction and dynamic attenuation of honeycomb sandwich hemispherical shell structures in aerospace engineering.

Неразрушающая оценка механических характеристик металла ответственных конструкций на основании анализа его ключевых структурно-химических и деформационных параметров

Большое количество и значительная протяженность ответственных металлических конструкций, разнообразие условий их производства и эксплуатации, примененных марок сталей, используемых технологий сварки не позволяют получить исчерпывающие и достоверные данные о механических характеристиках (или хотя бы их возможной вариации) конструктивных элементов путем проведения выборочных разрушающих испытаний. Отсутствие этих сведений приводит в одних случаях к снижению надежности конструкций, в других – к чрезмерному расходованию средств при их обслуживании. Проблема повышения эффективности прогнозирования работоспособности металлических конструкций может быть решена с использованием методов неразрушающей оценки механических свойств металла. Теоретический анализ показал, что наиболее эффективным является метод, позволяющий выполнить оценку ключевых групп факторов, ответственных за формирование механических свойств металла: химических, структурных, деформационных. В ходе проведения экспериментальных исследований установлено, что основные структурно-химические параметры металла с достаточной точностью и достоверностью могут быть определены непосредственно на анализируемой конструкции с применением портативного приборного оборудования. Для оценки деформационной способности металла подтверждена возможность использования методики, предусматривающей выполнение поверхностного микроиндентирования и определение показателя хрупкости металла. В целом, подход, основанный на установлении корреляции между структурными, химическими, деформационными параметрами металла и его основными механическими свойствами, с последующим сбором соответствующих данных в процессе эксплуатации ответственных металлических конструкций позволит выйти на качественно новый уровень эффективности оценки их технического состояния, а также управления надежностью и безопасностью. A large number and considerable length of critical metal structures, variety of their production and operation conditions, used steel grades, used welding processes make it impossible to obtain comprehensive and reliable data on structural element mechanical properties (or at least possible variation thereof) by means of random destructive tests. The lack of this information results in the structure reliability degradation in some cases, and in other cases – to excessive maintenance expenses. The problem of enhancing the efficiency of predicting metal structure serviceability can be solved by using methods of non-destructive evaluation of the mechanical properties of metal. Theoretical analysis has shown that the most effective method is the one allowing the evaluation of key groups of factors responsible for the formation of mechanical properties of metal: chemical, structural, stress-strain factors. In the course of experimental studies, it was found that the main structural and chemical parameters of metal can be determined with reasonable accuracy and reliability directly on the structure being analyzed using portable instrumentation equipment. To assess the deformation capacity of the metal, the suitability of technique involving the surface micro-indentation and determination of the metal brittleness index was confirmed. In general, the approach based on the establishment of correlation between metal structural, chemical, deformation parameters and its main mechanical properties followed by relevant data acquisition during the critical metal structures operation will allow reaching a totally new level of efficiency in assessing their technical condition, as well as reliability and safety management.

High-accuracy fiber Bragg grating inclinometer

Inclination monitoring plays a significant role in research on deformation monitoring of slopes, inclination monitoring of bridges, earthquake monitoring, and other areas of monitoring. Existing electromagnetic signal-based inclinometers face practical issues such as difficulty adapting to harsh environments, poor large-scale networking capabilities, and unstable signal transmission. Hence, what we believe to be a novel inclinometer based on fiber sensing principles is proposed. The sensor employs suspension sensing based on the plumb principle, using bearings to overcome mechanical friction caused by rigid fixation between the mass block and the cantilever, thereby improving sensitivity and accuracy of the sensor. Key structural parameters of the sensor were optimized and simulated, followed by fabrication of the sensor and performance test on an inclination test platform. Experimental results indicate that, within a measurement range of ±9∘, the sensor exhibited a sensitivity of 305.2 pm/°, a resolution of approximately 3.3×10−4∘, an accuracy of 2%, a repeatability error of 1.9%, and favorable creep resistance stability for long-term measurement, thus addressing the requirements for slope deformation monitoring.

Impact Performance of 3D Orthogonal Woven Composites: A Finite Element Study on Structural Parameters

This study uses the finite element method (FEM) to investigate the effect of key structural parameters on the impact resistance of E-glass 3D orthogonal woven (3DOW) composites subjected to low-velocity impact. These structural parameters include the number of y-yarn layers, the path of the binder yarn (z-yarn), and the density of the x-yarn. Using ABAQUS, yarn-level finite element (FE) models are created based on the measured geometrical parameters and validated for energy absorption and damage behavior from experimental data gathered from the previous study. The results from finite element analysis (FEA) indicate that the x-yarn density and the binder path substantially influenced the composites’ damage behavior and impact performance. Increasing x-yarn density in 3DOW leads to a 15% increase in energy absorption compared to models with reduced x-yarn densities. Moreover, as the x-yarn density increases, crack lengths at the back face of the resin matrix decrease in the y-yarn direction but increase in the x-yarn direction. The basket weave structure absorbs less energy than plain and 2 × 1 twill structures due to the less constrained weft primary yarns. These results underscore the importance of these structural parameters in optimizing 3DOW composite for better impact performance, providing valuable insights for the design of advanced composite structures.

Key structure design and vibration reduction performance analysis of four-tooth unequal pitch end mill based on spectral characteristics

The unequal pitch end mill can effectively suppress the vibration in the cutting process, and it is widely used in the processing of key parts. In this article, the four-tooth unequal pitch end mill is taken as the research object. Combined with the actual working conditions, the key structural parameters and process parameters are optimized from the perspective of spectrum energy distribution and processing efficiency, and the vibration reduction performance of the tool is analyzed and verified. First, the influence of process parameters, inter-tooth angle and helix angle of unequal pitch milling cutter on spectrum amplitude is analyzed. Second, for the milling aluminum alloy AL7075-T6, the most significant parameters affecting the vibration reduction performance of the milling cutter-tooth angle and helix angle and the matching process parameters were optimized. Finally, in order to explore the milling performance of unequal pitch end mills, experiments were carried out on equal pitch and unequal pitch end mills under the same process parameters. The gap between the two tools in milling force and milling vibration was analyzed, and the superiority of unequal pitch end mills in improving milling stability was verified.

Simulation of the mixing component of a horizontal air-assisted centralised wheat metering device

A horizontal air-assisted centralised metering device involves the use of conveying airflow for mixing and conveying during the seeding process, making it suitable for high-speed precision seeding. This study identified key structural parameters for the mixing component. Computational fluid dynamics (CFD) simulations were used to analyse the influence of the key structural parameters on airflow distribution and airflow velocity. The results suggested selecting a contraction section conical angle of 40° with maximal conveying airflow velocity and minimal airflow pressure loss. A mixing chamber length of 25 mm prevented the retention and blockage. An expansion section conical angle of 20° achieved higher airflow velocity within the expansion section. CFD-DEM (Discrete Element Modelling) coupled simulation were used to analyse the influence of mixing chamber height, seeding rate, and conveying airflow velocity on seed conveying performance. The results indicated that a mixing chamber height of 16 mm ensured stable seed acceleration, reduced the probability of seed-wall collisions. Seed collisions within the mixing chamber and expansion section increased noticeably along with the rising seeding rates. While airflow velocity in the range of 16–25 m s−1 facilitated timely seed conveyance and reduced seed-wall collisions. Verification experiments for the optimal parameter combination of the mixing component indicated that a conveying airflow velocity of 22 m s−1 resulted in the stability coefficient of variation of total seeding mass not exceeding 1.04 %, the uniformity coefficient of variation of seeding mass in each row not exceeding 3.61 %. This research offers valuable insights for structural improvements in the mixing component of the horizontal air-assisted metering device.

Seismic performance of self-centering steel column base with buckling-restrained bars

Self-centering structures, emerging as a vital innovation in earthquake-resilient design, offer notable advantages in structural integrity, rapid functional recovery post-earthquake, and economic efficiency over the building's life cycle. This paper introduces a self-centering steel column base, employing buckling-restrained bars for energy dissipation. Through an analysis of its force mechanism, it conducts low-cycle reciprocating load test on four set of specimens with varying buckling-restrained bars and axial compression ratios. The results demonstrate the column base's superior seismic performance, characterized by its ability to rapidly restore seismic functionality after unloading and replacing the buckling-restrained bars. The force-displacement hysteresis curves exhibit a distinctive double-flag shape, with a minimal residual story drift of 0.001 rad, underscoring the structure's exceptional self-centering capability. The displacement ductility coefficients and equivalent viscous damping coefficients confirm the column base's excellent deformation and energy dissipation capabilities. Furthermore, a refined ABAQUS finite element model is developed and validated against the load test results, further analyzing the seismic performance relative to key structural parameters.

Effect of key structure parameters of passive pre-chamber on in-cylinder combustion processes and emissions within a gasoline engine

Due to increasingly strict global emission regulations and energy conservation policies, gasoline engines are facing significant challenges. Achieving high efficiency and ultra-low emissions in gasoline engines has become a critical technical challenge that requires attention. Pre-chamber (PC) Turbulent Jet Ignition (TJI) is a highly promising technology for improving thermal efficiency and reducing emissions in gasoline engines. This study employs a three-dimensional flow simulation analysis combined with a detailed chemical reaction mechanism. The investigation is based on eight distinct passive PC structural configurations. The effects of various structural parameters, including the orifice number (ON), orifice axis angle (OAA), orifice diameter (OD), and volume ratio (VR), on the in-cylinder combustion process and emission characteristics are investigated, in which the formation of the fire nucleus and the propagation of the flame are intensively involved. The investigation is conducted under equivalence ratio working condition. Among these, the ITE of the best configuration is relatively 5.46% higher than the baseline engine. The combustion duration decreased by 55.95% to 7.4 °CA compared to the baseline engine, while particulate soot emissions also decreased by 51.22%.

Design and experimental validation of a broadband multi-modal coupled capsule-shaped transducer for underwater acoustics

This paper introduces a novel approach to expand the working frequency band of underwater acoustic transducers through multi-modal coupling. We designed a broadband multi-modal coupled piezoelectric capsule-shaped transducer structure by leveraging the advantages of conventional piezoelectric spherical-shell and piezoelectric cylindrical-tube transducers. First, the finite element method (FEM) was employed to scrutinize the influence of key structural parameters on the acoustic performance of the capsule-shaped transducer, thereby establishing the foundation for the final transducer design. Subsequently, the designed transducer was characterized through modal analysis and harmonic response analysis of electrical-mechanical-acoustical multiphysics field coupling. Finally, a prototype of the capsule-shaped transducer was fabricated and measured, with the results compared with those of a spherical-shell transducer. A comparative analysis of the measured outcomes revealed that the capsule-shaped transducer exhibits coupling among three modes within the frequency range of 10 kHz to 30 kHz. The transmitting voltage response (TVR) values exceeded 143.5 dB, reaching a maximum of 151.9 dB, and the working frequency bandwidth achieved 18 kHz. Compared with the spherical-shell transducer, the average TVR value demonstrates a 3.7 dB improvement, and the bandwidth exhibited an 8.4 % increase. According to the experimental findings, the proposed capsule-shaped piezoelectric transducer offers advantages such as high voltage response, a broad working frequency band, compact size, low weight, and easy installation. This technology can be further applied to small underwater platforms, enhancing their acoustic detection range and spatial coverage performance.

水稻穴播器取种装置设计与试验

The core equipment of rice dry direct-seeding with film mulching devices shows poor adaptability to rice varieties, struggling to accommodate diverse seeding quantity for both hybrid and conventional rice varieties. A seed-filling component with unilateral and bilateral seed-filling function was designed to solve this challenge. Through theoretical analysis the key structural parameters of the seed-filling component were determined. Then Discrete Element Method (DEM) simulations were conducted to analyze the seeding performance, leading to the identification of optimal parameters for orifice width and orifice deflection angle of the seed-filling component, which are 7.7 to 8.5 mm and 1.71 to 2.41 degrees, respectively. Bench experiments using the central composite design indicates that the optimal parameters for the seed-filling component's orifice width and orifice deflection angle are 8.1 mm and 1.99 degrees, respectively. In the optimal combination of orifice parameters, for unilateral seed-filling in hybrid rice, the miss-seeding rate is 4%, the qualified rate is 84.8%, and the reseeding rate is 11.2%. For bilateral seed-filling in conventional rice, the miss-seeding rate is 4.2%, the qualified rate is 85.2%, and the reseeding rate is 10.6%. The result of field hole-seeding with film mulching is consistent with the result of indoor bench experiments, demonstrating that the seed-filling component of the hole seeder can meet the seeding requirements for rice precision direct-seeding with film mulching. This paper provides theoretical reference for the design and optimization of the seed-filling component for rice hole-seeding equipment.

Design and Parameter Optimization of a Dual-Disc Trenching Device for Ecological Tea Plantations

This paper addresses challenges in the application of existing colters in Chinese ecological tea plantations due to abundant straw roots and insufficient tillage depth. Aligned with the agronomic requirements of hilly eco-tea plantations, our study optimizes the structural advantages of the joint use of rotary tillage blades and double-disc colters to design an efficient trenching device. Our investigation explores the motion characteristics of a double-disc colter during deep trenching operations, in conjunction with rotary tillage blades. Employing discrete element method (DEM) simulations, this paper aims to minimize the working resistance and enhance the tillage depth stability. Single-factor experiments are conducted to determine the impact of key structural parameters on the tillage depth stability and working resistance. The optimal parameters are determined as a relative height of 80 mm to 120 mm, a 280 mm to 320 mm diameter for the double-disc colter, and a 10° to 14° angle between the two discs. The central composite design method is used to optimize the structural parameters of the double-disc colter. The results indicate that when the relative height is 82 mm, the diameter of the double-disc colter is 297 mm, and the angle between the two discs is 14°, the tillage depth stability performance reaches 91.64%. With a working resistance of merely 93.93 N, the trenching device achieves optimal operational performance under these conditions. Field validation testing shows a tillage depth stability coefficient of 92.37% and a working resistance of 104.2 N. These values deviate by 0.73% and 10.93%, respectively, from the simulation results, confirming the reliability of the simulation model. A field validation test further confirms that the operational performance of the colter aligns with the agronomic requirements of ecological tea plantations, offering valuable insights for research on trenching devices in such environments.

Dynamic Simulation of the Leaf Mass per Area (LMA) in Multilayer Crowns of Young Larix principis-rupprechtii.

Leaf mass per area (LMA) is a key structural parameter that reflects the functional traits of leaves and plays a vital role in simulating the material and energy cycles of plant ecosystems. In this study, vertical whorl-by-whorl sampling of LMA was conducted in a young Larix principis-rupprechtii plantation during the growing season at the Saihanba Forest Farm. The vertical and seasonal variations in LMA were analysed. Subsequently, a predictive model of LMA was constructed. The results revealed that the LMA varied significantly between different crown whorls and growing periods. In the vertical direction of the crown, the LMA decreased with increasing crown depth, but the range of LMA values from the tree top to the bottom was, on average, 30.4 g/m2, which was approximately 2.5 times greater in the fully expanded phase than in the early leaf-expanding phase. During different growing periods, the LMA exhibited an allometric growth trend that increased during the leaf-expanding phase and then tended to stabilize. However, the range of LMA values throughout the growing period was, on average, 40.4 g/m2. Among the univariate models, the leaf dry matter content (LDMC) performed well (adjusted determination coefficient (Ra2) = 0.45, root mean square error (RMSE) = 13.48 g/m2) in estimating the LMA. The correlation between LMA and LDMC significantly differed at different growth stages and at different vertical crown whorls. The dynamic predictive model of LMA constructed with the relative depth in the crown (RDINC) and date of the year (DOY) as independent variables was reliable in both the assessments (Ra2 = 0.68, RMSE = 10.25 g/m2) and the validation (absolute mean error (MAE) = 8.05 g/m2, fit index (FI) = 0.682). Dynamic simulations of crown LMA provide a basis for elucidating the mechanism of crown development and laying the foundation for the construction of an ecological process model.

Reduced order model for flow distribution in tapered headers of U-type heat exchangers

Flow maldistribution in the channels of plate heat exchangers (PHEs) results in uneven temperature distribution leading to thermal distortion of the plates, increased pressure drop, and reduced thermal efficiency. Ensuring a uniform flow distribution is paramount for the efficiency and reliability of these systems. Using a modified header shape has the potential to improve flow conditions. To date, there is no mathematical model to predict flow distribution for tapered headers in PHEs. In this context, a reduced-order model has been developed to rapidly assess the potential impact of tapered headers on flow distribution. This model marks a pioneering effort in developing a comprehensive model for estimating flow distribution and pressure drop applicable to both uniform and tapered headers of U-type PHEs, providing valuable insights without necessitating significant computational resources. Key structural parameters, such as header diameter, number of channels, channel area, and taper ratio, that influence flow distribution have been identified by solving the differential equations numerically. For tapered headers, a more uniform flow distribution occurs with fewer plates for the same flow resistance, i.e., the average total head loss coefficient (ζ). Beyond a critical header diameter, the flow remains nearly uniform, regardless of the ζ value. For higher ζ values, there is a channel area range where flow uniformity either increases or remains nearly uniform. One of the most significant findings is the identification of the conditions where tapered headers provide more flow uniformity compared to straight headers. Validated by existing literature, this model shows promising practical applications in the rapid design and optimization of plate heat exchangers.

Fast relaxation of interlayer excitons from the free to self-trapped states in lead halide perovskite van der Waals heterostructures

We study the thermal relaxation of interlayer excitons from the free to momentary self-trapped states in lead halide perovskite van der Waals heterostructures based on the well-known Huang-Rhys model. We find that these relaxation processes (self-trapped processes) are very fast ranging from nanoseconds to picoseconds. Moreover, the self-trapped time displays different variational trends by regulating three key structural parameters of the heterostructure, which could be intrinsically attributed to the modulation of exciton–phonon coupling by these structural parameters, resulting in the variation of the self-trapping depth. The underlying physical pictures that the changing of intersection points of two adiabatic potential between the free and momentary self-trapped states in the configuration coordinates are proposed to explain these relaxation processes. These results not only provide the significant enlightenments for analyzing the abnormal features of excitonic spectra in experiments but also present the practical ways to modulate the dynamical processes of excitons in two-dimensional structures.