Field Simulation Research Articles

Quantifying the Wind‐Induced Bias of Rainfall Measurements for the Thies CLIMA Optical Disdrometer

AbstractThe wind‐induced bias of rainfall measurements obtained from non‐catching instruments is addressed in this work with reference to the Laser Precipitation Monitor (LPM) optical disdrometer manufactured by Thies CLIMA. A numerical simulation approach is adopted to quantify the expected bias, involving three different models with increasing complexity. Computational Fluid‐Dynamics simulation of the airflow field around the instrument with an embedded Lagrangian particle‐tracking module to obtain raindrop trajectories are performed by solving the Unsteady Reynolds Averaged Navier‐Stokes (URANS) equations and a Large Eddy Simulation (LES) model. URANS‐uncoupled, LES‐uncoupled, and LES‐coupled approaches are tested to assess the impact of modeling the airflow turbulent fluctuations in detail. Due to the non‐radially symmetric external shape of the instrument, various combinations of the wind speed and direction are considered. Catch ratios for monodisperse rain are obtained as a function of the particle Reynolds number and the wind direction and fitted to obtain site‐independent curves to support application of the simulation results. Based on literature expressions to link the drop size distribution of real rainfall events with the rainfall intensity (which instead depend on the local rainfall climatology at the measurement site), sample collection efficiency curves are obtained from the catch ratios of monodisperse rain. The resulting adjustment curves allow rainfall measurements to be corrected using either a real‐time or post‐processing approach. However, at high wind speed and assuming that the wind blows parallel to the instrument sensing area, the instrument may fail to report precipitation altogether.

Numerical study on flow field characteristics and performance of a Mach 10 internal injection kerosene-fueled oblique detonation engine

Oblique detonation engines (ODE) have significant potential for hypersonic propulsion, yet there is a paucity of research investigating internal injection ODEs. In this study, a numerical simulation of the internal flow field of a Mach 10 internal injection kerosene-fueled ODE is conducted. The fuel mixing, pre-combustion, and combustor wave structure in the flow field are analyzed in a situation closer to the real flow field conditions. Further studies have demonstrated that alterations to the upper wall initiation position of nozzle can influence the separation zone, flow field stability and the engine performance. An upper wall initiation position that is too far forward will increase the separation zone area and reduce the engine thrust. Conversely, an upper wall initiation position that is too far back will lead to flow field destabilization and eventually thermal choking. Finally, the effects of increasing the equivalent ratio on the flow field structure and engine performance for a certain configuration are analyzed. The results demonstrate that when the equivalent ratio is elevated, an increase in either the bottom or top incoming flow equivalent ratio results in a transformation of the wave structure within the combustor due to the presence of the incoming boundary layer and the subsonic zone. A large-scale separation zone will form at the bottom of the combustor, resulting in a reduction in nozzle thrust. However, the wedge drag is reduced more, thereby increasing the engine's specific impulse.

Acoustical Analysis of Auditorium in National Educational Museum, West Java

Abstract Besides being the place for evidence of past history and future history, the National Educational Museum in West Java also has audio visual room, for the visitor to learn about the museum more. Visitor ability to understand what is being said in the auditorium depends on the acoustics quality of the room. This study primarily talks about acoustics auditorium and find out if the acoustics in Auditorium of National Educational Museum is optimal for its function. The objective of this analysis is to determine the acoustics quality of the room in Auditorium of National Educational Museum. The simulation results with acoustic standards was carried out after conducting field observations and simulations using Ecotect v.5.50 software. After the simulation conducted it is known that there is some factors that makes this auditorium reverberation time not optimal such as sound-reflecting materials, floor and ceiling shape and elevation, and the number of occupants in the room. Which resulted in the speaker’s voice become less clear to the perceiver. Thus, to respond to the issue some materials can be change to sound-absorbing materials, and the ceiling shape can be made simpler to reduce the reverberation and echoes.

Impact of drainage pipe vapor intrusion pathways on sub-slab depressurization system mitigation performance

Sub-slab depressurization (SSD) systems are the most commonly employed technology for mitigating vapor intrusion (VI) impact to indoor air. However, as cases involving preferential VI pathways (e.g. sewers, land drains) are being reported, the efficacy of SSD systems to reduce VI impacts from such pathways is being questioned. In this study, field test and numerical modeling were performed to evaluate the effectiveness of an SSD system for the case of VI involving a drainage pipe preferential pathway. Field tests investigated the SSD performance at the study house under conditions with and without the impact of a drainage pipe pathway. A numerical model was developed to explore the influence of the preferential pathway on SSD mitigation under different scenarios. Both field and simulation results indicated that the sub-slab drainage system inhibits the performance of the SSD, consequently requiring a greater level of flow and depressurization for the system to protect the building. In addition, the SSD caused higher sub-slab vapor concentrations than under natural condition in both field testing and simulation results, which raised concerns for potential VI risk under standard SSD operation. Moreover, simulation results suggested the location of preferential pathways can affect the performance of an SSD system.

Aerodynamic design of two-stage centrifugal compressor for vehicle hydrogen fuel cell

Abstract The on-board hydrogen fuel cell is a power generation device that converts the chemical energy of hydrogen and oxygen directly into electrical energy. The centrifugal compressor mainly provides oxygen for the cathode of the fuel cell system. With the rapid development of the hydrogen fuel cell industry, the key components of the air compressor field are also developing rapidly. In the technical route, most companies launched two-stage compression centrifugal air compressors in response to the increasing power of the product development trend. The newly developed hydrogen fuel cell system power has reached above 120kW to meet the needs of heavy trucks and other applications. Both the flow rate and pressure ratio of the air compressor are required to increase accordingly. Based on the reduction of parasitic power, the optimal efficiency at the working point of the two-stage centrifugal air compressor is taken as the design goal, from one-dimensional aerodynamic calculation to two-dimensional flow channel design. Finally, the feasibility and accuracy of the aerodynamic design are verified based on key parameters such as pressure ratio, flow rate, and efficiency of the final stage through CFD flow field simulation and test data comparison. The results show that the flow rate is consistent with the calculated flow field, and the maximum error of pressure ratio and efficiency is less than 2%, which meets the target requirements. The research results can provide a research and development basis for designing high-performance centrifugal air compressors for fuel cell vehicles.

Application of convolutional neural network for efficient turbulence modeling in urban wind field simulation

Accurate flow field estimation is crucial for the improvement of outdoor environmental quality, but computational fluid dynamics (CFD) based on the widely used Reynolds-averaged Navier–Stokes method has limitations in this regard. This study developed a turbulence modeling framework based on a convolutional neural network (CNN) to model turbulence in urban wind fields. The CNN model was trained by learning the Reynolds stress patterns and spatial correlations with the use of high-fidelity datasets. Next, the model was integrated into the CFD solver to generate accurate and continuous flow fields. The generalization capability of the proposed framework was initially demonstrated on the simplified benchmark configurations. The validated framework was then applied to case studies of urban wind environments to further assess its performance, and it was shown to be capable of delivering accurate predictions of the velocity field around an isolated building. For more complex geometries, the proposed framework performed well in regions where the flow properties were covered by the training dataset. Moreover, the present framework provided a continuous and smooth velocity field distribution in highly complicated applications, underscoring the robustness of the proposed turbulence modeling framework.

Two-dimensional distribution experiment of ‘lattice diffraction’ using ultrasound in an educational laboratory

Abstract A device that can study the two-dimensional distribution of ultrasonic diffraction on lattice structures was developed for educational laboratories, enabling students to design the size, shape and dimension of diffraction obstacles independently. In this experiment, metal balls were used to simulate atomic lattice structures, and the two-dimensional diffraction distribution data of simple cubic, body-centered cubic, and hexagonal close-packed structure were collected. The results were compared with the sound field simulation of COMSOL, and a good consistency was found. By observing the diffraction results of complex structures, students can gain a better understanding of the concept of diffraction.

Certification considerations and sound field simulation of civil aircraft cabin passenger address

Abstract In the design of a civil aircraft cabin passenger address system, it is quite necessary and very important to sufficient consider and demonstrate the system design architecture, equipment selection and arrangement to ensure that the system sound quality complies with the requirements of CCAR25.1423(c). In the design phase, the certification considerations of the passenger address system should be researched in advance to comply with CCAR25.1423(c). The cabin sound field distribution and STI of the civil aircraft cabin passenger address system should be simulated through professional tools to predict, demonstrate and judge the sound quality before the system preliminary design review (PDR). In this paper, the certification considerations of passenger address are developed and elaborated from the system equipment arrangement, automatic gain design, and inhibit method of the Larsen effect. Based on two loudspeaker arrangement options, the cabin sound field distribution and STI of the passenger address are simulated to indicate its compliance with CCAR 25.1423(c) from the proposal design level theoretically.

Enhancing cathode design by considering complex motion and variations of electric field distribution in counter-rotating electrochemical machining

The counter-rotating electrochemical machining (CRECM) shows unique potential in the machining of thin-walled rotating parts with complex convex structures. CREM realizes the shaping of complex convex structures through the relative rotation of the cathode and anode. The complex motion pattern and electric field distribution make it difficult to apply the existing cathode design methods to CRECM. To solve this problem, the matrix equations of cathode motion based on the kinematics and the electric field simulation model are established. The motion trajectories and edge contours at different angles are analyzed. The rotational overlap theory of motion trajectories under the windows at different angles is proved. Besides, the relationship between electric field distribution and the convex structure forming under different angle windows is studied, and the fundamental reason for deviations occurs when the convex profile is rotated to coincide is revealed. Therefore, a prediction model of the sidewall dissolution is established to correct this deviation, thereby deriving a high-precision design formula for the cathode windows of the high convex structures. By designing a cathode with oval-like windows to curry out CRECM experiments, the array-arranged (30×5) circular high convex structure with a maximum roundness error of 0.065 mm is successfully fabricated.

Temperature field simulation analysis for hot blast valve of blast furnace

Temperature field simulation analysis for hot blast valve of blast furnace

Effect of baffles on internal flow characteristics of double-inhalation centrifugal pumps under low flow conditions

In order to investigate the impact of baffles in the inhalation chamber on the external characteristics and operational stability of a double inhalation centrifugal pump under low flow conditions, the flow field simulation software ANSYS CFX and the shear stress transport formulation were employed to numerically simulate the internal flow field of a double inhalation centrifugal pump with and without baffles. Two models were subjected to performance curve simulation and prediction, with the internal flow field, pressure pulsation, and impeller force of the two models being compared and analyzed under three small flow conditions of 0.6Qd (rated flow), 0.5Qd, and 0.4Qd. The velocity and vortex distribution inside the semi-spiral inhalation chamber, as well as their impact on the flow state in front of and inside the impeller, were analyzed. Research has demonstrated that the addition of baffles can enhance the pump head and efficiency in flow conditions of 0.5Qd–0.8Qd. However, there is a tendency for obstruction of flow in conditions below 0.5Qd. Baffles can reduce the amplitude of pressure pulsation within the impeller and the radial force exerted by the impeller as a whole. Consequently, the incorporation of baffles within the inhalation chamber during flow conditions of 0.5Qd–0.8Qd can enhance the operational efficacy of the pump. Nevertheless, within the flow range of <0.5Qd, the pump's performance will decline. This study serves as a foundation for the design of double inhalation centrifugal pumps with semi-spiral inhalation chambers.

Structure optimal design of 500 kV dry-type air-core shunt reactor based on response surface method

The hotspot temperature of the reactor is one of the important indices in reactor design, and the appropriate hotspot value can ensure that the reactor will not overheat failure and threaten the safety of the power system. In this paper, the temperature field simulation model of a 500 kV dry-type air-core shunt reactor is established, and the hotspot temperature of the reactor is obtained by COMSOL software. Then, the radial basis function response surface function is used to construct the response surface function of the hotspot temperature and its related variables, and the applicability of the response surface function is tested to analyze the rationality and accuracy of the response surface function. Finally, the optimal solution of the response surface function under the coordination of variables and related constraints is obtained by using the constrained simulated annealing algorithm. The results show that the hotspot temperature of the reactor envelope winding decreases obviously after optimization.

A 2.4-7GHz Dual Band Microstrip Patch Antenna (DBMPA)

We designed a 2.4-7GHz dual-band microstrip patch antenna DB-MPA using electromagnetic field simulation and transmission characteristic (S21) measurements. Optimizing the slot length of the patch surface increased the directional antenna gain at 7 GHz by 3.5 dB compared to 2.48 GHz, reducing the effect of the higher spatial propagation loss of 9 dB at 7 GHz. A transmission system simulation with an antenna component model incorporating S21 data measured with the 2.4-7GHz DB-MPA from 1 to 8 GHz was conducted at a spatial propagation distance of 5 to 40 m to verify the practicality of the 2.4-7GHz DB-MPA

Numerical simulation of temperature field and stress field of laser cladding Stellite6

To comprehensively investigate the evolution of the stress field, a three-dimensional thermodynamic model of laser cladding was developed in this paper. By analyzing the physical process and constructing a mathematical model, the temperature transfer and stress distribution were calculated. The simulation examined the evolution and distribution of stress at various scanning speeds, discussing the interplay between the temperature field and the stress field during rapid heating and cooling. Residual stress was measured through X-ray diffraction in experiments, and the crack distribution within the cladding layer was observed. The findings indicated that the stress values calculated from the simulation model aligned well with the experimental results. By combining experimental data, we conducted a qualitative analysis of the distribution of residual stresses and the trends of crack initiation, leading to the proposal of an optimized processing scheme that significantly enhances the quality and reliability of the cladding layer.

A microstructural thermo‐elastoplastic analysis of the mushy zone during laser beam welding

AbstractAs a modern method of contact free fusion, laser beam welding has gained importance in recent years. This is due to both the possibiliy of a high advance speed of the laser and low thermal distortion of the components compared to other welding processes, see Dal and Fabbro. These beneficial process properties follow from a focused laser, which thus results in a precise energy input. In addition, laser beam welding processes can be automated which makes the process attractive for a wide range of applications, cf. Dilthey. Nevertheless, various influences, like the temperature gradient, the chemical composition or process parameters, may have an effect on the occurrence of so‐called solidification cracks. Solidification cracks arise during solidification and occur in the area of the mushy zone, which is located behind the melt pool. The material behavior in the mushy zone is governed by a dendritic morphology. Due to this, liquid phase inclusions may occur in some parts of the mushy zone, see Hills et al.. When these trapped areas solidify, no further liquid phase can follow and a negative pressure is created. The resulting stresses can then lead to solidification cracks. In further studies, the geometry of the dendritic morphology will be generated on the basis of previous phase field simulations. These describe the dendrite growth controlled by the chemical concentration. The resulting geometry will then be simulated using the possibilities of a thermo‐elastoplastic material model, which will enable temperature‐driven imitation of growth. This contribution addresses the evolving state of the dendritic microstructure in a simplified manner. Therefore, for the first study, a simplified morphology is used, that is, no secondary arms and an elliptical geometry of the dendrites is assumed. Thermal as well as elastoplastic effects are already taken into account, in order to represent the inherent stress and strain states in the microstructure. These may be related to critical states leading to failure in the future.

Elimination of cracks in Al–Zn–Mg–Cu alloy by addition of TiO2 in selective laser melting

7050 aluminium alloy is widely used in aerospace industry due to its excellent mechanical properties. 7050 aluminium alloy belongs to Al–Zn–Mg–Cu alloy. Due to the formation of cracks in selective laser melting (SLM) forming of Al–Zn–Mg–Cu alloys, 7050 aluminium alloy is difficult to be applied to forming and manufacturing in this technological field. In order to solve this critical problem, in this paper, titanium dioxide (TiO2) powder was mixed with 7050 aluminium alloy using ball milling method to achieve the effect of eliminating cracks. The cracks in the specimens completely disappeared when the TiO2 additions were 1.5 wt% and 2 wt%. With the addition of TiO2, the grains gradually changed from coarse columnar crystals to fine equiaxed crystals. Combined with the temperature field simulation, the grain refinement and crack elimination mechanism of TiO2 in SLM forming were analysed. The grain refinement is attributed to the formation of Al3Ti. The crack elimination was attributed to the reduction of the intergranular solid-liquid channel length. The maximum values of tensile strength and elongation of 7050 aluminium alloy formed by SLM are achieved at 2 wt% of TiO2. The values are 389 MPa and 8.8 %. The better mechanical properties were attributed to the synergistic effect of crack elimination, Hall-Petch, and Orowan strengthening. This study provides experimental guidance for the preparation of crack-free 7050 aluminium alloy.

Impact of ENVI-met-Based Road Greening Design on Thermal Comfort and PM2.5 Concentration in Hot–Humid Areas

Road greening markedly impacts road thermal comfort and air quality. However, previous studies have primarily focused on thermal comfort or PM2.5 individually, with relatively few addressing both aspects comprehensively, particularly in humid regions. This study combined field measurements and simulations. It employed physiological equivalent temperature (PET) and quantified the horizontal distribution of particulate matter 2.5 (PM2.5). The research examines the effects of planting spacing, tree species, and tree–shrub combinations on pedestrian walkways in humid climates during both summer and winter. Using measured tree data and road PM2.5, a plant model was established and pollution emission parameters were set to validate the effectiveness of the ENVI-met through fitting simulations under various scenarios. The results indicated that (1) plant spacing for trees influenced both the road thermal environment and PM2.5 levels. Smaller spacing improved thermal conditions but increased PM2.5. (2) trees with large canopies and high leaf area indices (LAIs) notably enhanced thermal comfort, while those with smaller canopies and dense understories facilitated PM2.5 dispersion. The 3 m spacing resulted in a maximum absolute PM2.5 concentration difference (C) of 5.05 μg/m3 in summer and a maximum mean absolute PM2.5 concentration difference (M) in the downwind region of 2.13 μg/m3 in winter. (3) Combining trees with shrubs moderately improved pedestrian thermal comfort. However, taller shrubs elevated PM2.5 concentrations on walkways; heights ranging from 1.5 m to 2 m in summer showed higher C values of 5.38 μg/m3 and 5.37 μg/m3. This study provides references and new perspectives for the optimization of roadway greening design in humid areas in China.

Optimization Method for Allocating Peak-Period Parking Demand in Hub Parking Lot Clusters

With the expansion of urban scale and the popularization of multi-modal transportation, transportation hubs, as the link of multi-modal travel, are becoming increasingly important in urban development and residents’ lives. In situations of high parking demand, the increase in road traffic volume and parking search delays exacerbates the service pressure on hub parking lots and the traffic congestion on surrounding roads. Therefore, reasonable parking demand allocation is one of the key solutions to this problem. Based on the analysis of the vehicle parking search process, this paper constructs a model for estimating parking search delay on roads outside hub parking lots and proposes an optimization model for parking demand allocation aimed at minimizing the total parking search delay of vehicles. Finally, taking a major transportation hub in Nanjing as a case study, data were obtained through field investigations and simulation experiments to identify peak parking demand periods and calibrate the model parameters. The results show that the average vehicle delay was reduced by 4.5%, with a total reduction of 13,860 s in vehicle delay for parking demands at the hub within one hour. Therefore, by optimizing the allocation of parking demand, the average delay for vehicles searching for parking can be reduced to a certain extent.

Efficient Fourth-Order PSTD Algorithm with Moving Window for Long-Distance EMP Propagation.

Satellite-borne electromagnetic pulse (EMP) detection technology plays an important role in military reconnaissance, space environment monitoring, and early warning of natural disasters. However, the complex ionosphere greatly distorts the waveform during propagation and poses a challenge to EMP detection. Therefore, it is necessary to conduct theoretical research on EMP propagation in the ionosphere. Conventional second-order pseudo-spectral time-domain (PSTD-2) algorithm has difficulties in keeping the stability and accuracy of waveforms in calculations over hundreds of kilometers of propagation. To overcome the difficulties, a fourth-order PSTD algorithm incorporating the moving window technique (MWPSTD-4) is proposed. In the numerical examples, the performance of MWPSTD-4 is compared with PSTD-4 and PSTD-2 in the long-distance propagation of EMP. The results show that the MWPSTD-4 improves efficiency while guaranteeing accuracy and is suitable for large-scale electromagnetic field simulation. The proposed method provides a basic algorithm to eliminate the numerical dispersion interference for calculating the long-distance propagation of EMP in complex spaces and is helpful for the design and calibration of satellite-borne EMP detectors.

Numerical Simulation of Flow Field, Distribution of Bubbles, and Inclusions in Slab Continuous Casting Mold under Electromagnetic Braking Assisted with High‐Temperature Quantitative Velocity Measurement

Numerical Simulation of Flow Field, Distribution of Bubbles, and Inclusions in Slab Continuous Casting Mold under Electromagnetic Braking Assisted with High‐Temperature Quantitative Velocity Measurement