Simulation Experimental Results Research Articles

Efficient estimation of true fixed-effects stochastic frontier models

AbstractFixed-effects modeling has become the method of choice in several panel data settings, including models for stochastic frontier analysis. A notable instance of stochastic frontier panel data models is the true fixed-effects model, which allows disentangling unit heterogeneity from efficiency evaluations. While such a model is theoretically appealing, its estimation is hampered by incidental parameters. This note proposes a simple and rather general estimation approach where the unit-specific intercepts are integrated out of the likelihood function. We apply the theory of composite group families to the model of interest and demonstrate that the resulting integrated likelihood is a marginal likelihood with desirable inferential properties. The derivation of the result is provided in full, along with some connections with the existing literature and computational details. The method is illustrated for three notable models, given by the normal-half normal model, the heteroscedastic exponential model, and the normal-gamma model. The results of simulation experiments highlight the properties of the methodology.

Background-oriented schlieren experimental and simulation study of the effect of sidewalls on optical turbulence anisotropy in a thermal convection turbulence simulator

The anisotropic optical structure characteristics within the Rayleigh-Bénard (RB) turbulence simulator have been investigated through experiment and simulation. We collected data using background-oriented schlieren technology and extracted displacements using optical flow algorithms. The wavefront phase can be recovered using the conjugate gradient iterative algorithm. We analyzed the optical structural characteristics within the turbulence simulator under different temperature differences. It is observed that with an increased temperature difference, the spatial correlation of the refractive index field decreases at an accelerated rate as the separation distance increases, and the degree of anisotropy characterized by the phase structure function increases. Large eddy simulation and split-step beam propagation method complement experimental results. Numerical simulations demonstrate consistency with experimental data. The results show that the von Karman power spectral density fits the simulation and experimental phase structure function very well relative to the Kolmogorov power spectral density, which demonstrates that the simulation system combining dynamics simulation and optical simulation can achieve power spectral characteristics that are consistent with reality. The experimental and simulation results are crucial for understanding the flow field's optical structural properties inside the turbulence simulator. They will help to construct a suitable turbulence simulator for optical engineering applications and establish a rational scheme for analyzing its internal optical structural properties.

ASYMMETRICAL 7 LEVEL MULTILEVEL INVERTER FOR DYNAMIC LOADS

Asymmetric multilevel inverters (AMLIs) have received great attention in the power industry due to their ability to solve problems caused by power supply in various applications. This report explores the design, analysis and performance of AMLI's heavy-duty equipment. Dynamic loads are characterized by rapid and unpredictable changes in power demand, causing significant outages due to the limitations of traditional inverters in providing efficient power delivery and stability. The AMLI concept takes advantage of the ability to produce multiple voltage levels, providing greater flexibility to adapt to the needs of the load. This study investigates the optimization of modulation techniques to improve the efficiency and response time of the inverter in dynamically changing scenarios. In addition, factors such as harmonic distortion and power quality were also taken into account in the study, and the effect of asymmetric voltage levels on the overall system performance was examined. Simulation results and experimental results show that the effectiveness of AMLI in dynamic switching is good. The results of this study provide great insights into the use of AMLI with electronic devices, showing promise in improving power conversion and safety in real-world applications. Keywords: Asymmetric multilevel inverters (AMLIs), Power industry, Design, Analysis, Performance, Heavy-duty equipment.

Super-resolution imaging of telescopic systems based on optical-neural network joint optimization

Abstract Optical telescopes are an important tool for acquiring optical information about
distant objects, and resolution is an important indicator that measures the ability to observe
object details. However, due to the effects of system aberration, atmospheric vortex, and
other factors, the observation image of ground-based telescopes is often degraded, resulting in
reduced resolution. This paper proposes an optical-neural network joint optimization method
to improve the resolution of the observed image by co-optimizing the point spread function
(PSF) of the telescopic system and the image super-resolution network. To improve the speed
of image reconstruction, we designed a generative adversarial net (LCR-GAN) with light
parameters, which is much faster than the latest unsupervised networks. To reconstruct the
PSF trained by the network in the optical path, a phase mask is introduced. It improves the
image reconstruction effect of LCR-GAN by reconstructing the point spread function that
best matches the network. The results of simulation and verification experiments show that
compared with the pure deep learning method, the super-resolution image reconstructed by
this method is rich in detail and easier to distinguish stars or stripes.

Optimization of offshore wind farm inspection paths based on K-means-GA.

As global demand for offshore wind energy continues to rise, the imperative to enhance the profitability of wind power projects and reduce their operational costs becomes increasingly urgent. This study proposes an innovative approach to optimize the inspection routes of offshore wind farms, which integrates the K-means clustering algorithm and genetic algorithm (GA). In this paper, the inspection route planning problem is formulated as a multiple traveling salesman problem (mTSP), and the advantages of the K-means clustering algorithm in distance similarity are utilized to effectively group the positions of wind turbines, thereby optimizing the inspection schedule for vessels. Subsequently, by harnessing the powerful optimization capability and robustness of genetic algorithms, further refinement is conducted to search for the optimal inspection routes, aiming to achieve cost reduction objectives. The results of simulation experiments demonstrate the effectiveness of this integrated approach. Compared to traditional genetic algorithms, the inspection route length has been significantly reduced, from 93 kilometers to 79.36 kilometers. Simultaneously, operational costs have also experienced a notable decrease, dropping from 141,500 Chinese Yuan to 125,600 Chinese Yuan.

Experimental and theoretical studies on the compatibility of DNTF and typical hydrocarbon polymer binders.

3,4-bis(3-nitrofurazan-4-yl) furoxan (DNTF) is one of the third-generation energetic compounds with excellent comprehensive properties, which can be added to polymer bonded explosive (PBX) to improve energy levels and regulate sensitivity, so the compatibility of DNTF with other components in PBX, especially the binder, is the first question. Herein, two typical hydrocarbon polymers commonly used in PBX, which are hydroxyl-terminated polybutadiene (HTPB) and polyisobutylene (PIB), were selected as the binder, and the compatibility of HTPB and PIB with DNTF was investigated by differential scanning calorimetry (DSC), the vacuum stability test (VST), and in situ infrared spectroscopy (in situ IR). The results of compatibility experiments were verified by using the binding energy and solubility parameter criteria in molecular dynamics (MD). Experimental and MD simulation results showed that DNTF could be compatible with PIB but incompatible with HTPB. The frontier molecular orbital theory in quantum chemistry (QC) was adopted to explore the frontier orbital electron distribution and energy levels of DNTF/HTPB and DNTF/PIB composite systems to better understand the microscopic compatibility mechanism. The compatibility results of the two composite systems were explained from the perspective of electron transfer. All these can deduce that a hydrocarbon polymer binder with a saturated carbon-hydrogen bond at the end of the molecular chain has good compatibility with DNTF, compared with a hydroxyl group, which has bad compatibility with DNTF.

A hybrid wave vibration energy harvester with electromagnetic double-speed and piezoelectric up-frequency driven by a rotating ball

The energy crisis and environmental pollution have driven the development of ambient energy harvesting technologies, and ocean waves usually contain abundant vibration energy, making the study of wave energy harvesting technology of profound value. This paper proposes a hybrid wave vibration energy harvester with electromagnetic double-speed and piezoelectric up-frequency driven by a rotating ball. For the electromagnetic generator (EMG), the excitation magnet and coil move simultaneously, resulting in double the flux variation rate compared with traditional structures, enhancing the output voltage. For the piezoelectric transducer (PZT), four piezoelectric cantilever beams are magnetically coupled with the EMG, generating power through bistable motion and broadening the working frequency band of the cantilever beam structure. The harvester is modeled and simulated, and its performance is tested on a simulated vibration platform, with simulation and experimental results in good agreement. Under external excitation at 0.8 Hz, the optimal load and maximum power for each EMG are 8.2 Ω and 207.2 mW, respectively, and the optimal load and maximum power for each PZT are 100 kΩ and 1.52 mW, respectively. The harvester can produce a maximum output power of 420.48 mW, demonstrating high efficiency in energy capture under low-frequency and multidirectional wave excitation.

Performance evaluation of coupled-inductor DC-DC converter for wind energy conversion system

ABSTRACT This paper studies the performance of single-switch-coupled inductor-based quadratic DC-DC converter employed in the machine side converter of wind energy conversion system. The performance of the converter is evaluated in terms of voltage conversion ratio, voltage and current stress on the switch of the converter. The detailed circuit analysis, power loss analysis, modelling and integration issues have been elaborated in this work. The DC-link voltage regulation of wind energy conversion system is carried out using closed-loop control scheme including maximum power point tracking scheme and dual-loop control scheme. Simulation results and experimental results have been provided in this work.

Analysing the shape memory behaviour of GnP-enhanced nanocomposites: A comparative study between experimental and finite element analysis

Abstract Shape memory polymers (SMPs) are capable of enduring significant deformations and returning to their original form upon activation by certain external stimuli. However, their restricted mechanical and thermal capabilities have limited their broader application in engineering fields. To address this, the integration of graphene nanoplatelets (GnPs) with SMPs has proven effective in enhancing their mechanical and thermal properties while maintaining inherent shape memory functions. The study evaluated shape memory nanocomposites (SMNCs) using dynamic mechanical, thermogravimetric, and static tensile, flexural, and shape memory tests, along with scanning electron microscopy to analyse tensile fractures. The results indicate that the optimal content of GnP is 0.6 wt%, resulting in excellent shape memory, thermal, and mechanical properties. Specifically, this composition demonstrates a shape recovery ratio of 94.02%, a storage modulus of 4580.07 MPa, a tensile strength of 61.42 MPa, and a flexural strength of 116.37 MPa. Additionally, the incorporation of GnPs into epoxy reduces recovery times by up to 52% at the 0.6 wt% concentration. While there is a slight decrease in the shape fixity ratio from 98.77% to 93.02%, the shape recoverability remains consistently high across all samples. Current finite element (FE) models often necessitate complex, problem-specific user subroutines, which can impede the straightforward application of research findings in real-world settings. To address this, the current study introduces an innovative finite element simulation method using the widely used ABAQUS software to model the thermomechanical behaviour of SMNCs, importantly incorporating the time-dependent viscoelastic behaviour of the material. The effectiveness of this new approach was tested by comparing experimental results from bending test of SMNCs cantilever beam with outcomes derived from FE simulations. The strong agreement between the experimental data and simulation results confirmed the precision and reliability of this novel technique.

Location strategy for logistics distribution centers utilizing improved whale optimization algorithm

Abstract An enhanced whale optimization algorithm is introduced to address the challenges associated with the logistics distribution center location problem, aiming to overcome the traditional heuristic algorithm’s susceptibility to local optima and enhance the overall efficiency of the logistics system. This improvement involves the integration of stochastic sinusoidal inertia weights and a variational strategy to augment the global search capability and convergence accuracy of the conventional algorithm. The results of experimental simulations indicate that the upgraded whale algorithm exhibits superior computational performance compared to other heuristic algorithms. Furthermore, it demonstrates the ability to effectively compute optimal distribution center locations, thereby enhancing the delivery efficiency of the logistics distribution system.

Self-tuning speed and flow control of micro turbojet engines based on an improved evolutionary strategy

At present, the controllable parameters of micro turbojet engines in engineering applications are mainly speed-fuel flow (hereinafter referred to as flow) control, in which closed-loop proportional–integral–derivative (PID) control is mostly used to achieve a stable control of engine speed under slow engine conditions. For the optimal adjustment of PID parameters, this paper designs an improved evolutionary strategy for the self-tuning of control parameters in the engine speed and flow control system and formulates an improved PI controller based on a neural network. The simulation experimental results show that the method can realistically achieve stable and fast control of the engine under above slow conditions.

Coulomb-induced emission time shifts in high-order harmonic generation from H2+

Accurate emission times of high-order harmonic generation (HHG) are vital for high-precision ultrafast detection in attosecond science, but a quantitative analysis of Coulomb effects on this time is absent in the molecular HHG. Here, we investigate the Coulomb-induced emission-time shift in HHG of H2+ with two different internuclear distances R, where the times obtained via the Gabor transform of numerical data from solving the time-dependent Schrödinger equation are used as simulation experiment results. Based on the molecular strong-field approximation, we develop a trajectory-resolved classical model that takes into account the molecular two-center structure. By selecting appropriate electron trajectories and including Coulomb interactions, the classical trajectory method can reproduce Gabor emission times well. This consistence reveals that Coulomb tails cause an emission-time shift of ∼35 as at the R = 2.0 a.u. case and of ∼40-60 as at the R = 2.6 a.u. case under the present laser parameters when compared to the Coulomb-free quantum-orbit model. Our results are of significance to probe the attosecond dynamics via two-center interference.

Partial hard occluded target reconstruction of Fourier single pixel imaging guided through range slice

Fourier single pixel imaging utilizes pre-programmed patterns for laser spatial distribution modulation to reconstruct intensity image of the target through reconstruction algorithms. The approach features non-locality and high anti-interference performance. However, Poor image quality is induced when the target of interest is occluded in Fourier single pixel imaging. To address the problem, a deep learning-based image inpainting algorithm is employed within Fourier single pixel imaging to reconstruct partially obscured targets with high quality. It applies a distance-based segmentation method to segment obscured regions and the target of interest. Additionally, it utilizes an image inpainting network that combines multi-scale sparse convolution and transformer architecture, along with a reconstruction network that integrates Channel Attention Mechanism and Attention Gate modules to reconstruct complete and clear intensity images of the target of interest. The proposed method significantly expands the application scenarios and improves the imaging quality of Fourier single pixel imaging. Simulation and real-world experimental results demonstrate that the proposed method exhibits the high inpainting and reconstruction capacity in the conditions of hard occlusion and down-sampling.

Adaptive backstepping sliding mode compensation control for electro‐hydraulic load simulator with backlash links

AbstractWhen a mechanical backlash between the loading piston rod and the steering gear piston rod connection of the electro‐hydraulic load simulator (EHLS), it will lead to poor loading accuracy. To solve this problem, an adaptive backstepping sliding mode controller based on the backlash feedforward compensation and state observer is proposed. First, the mechanism of surplus force generation in the EHLS is analyzed, and a mathematical model containing position disturbance and backlash nonlinearity is established based on the analysis results. Second, a state observer is designed to estimate the system state and the parameter adaptive law is designed to estimate the system parameters. Third, the adaptive backstepping method is combined with the non‐singular terminal sliding mode control (NTSMC) strategy to deal with the position disturbance and parameter uncertainty and to enhance the system's dynamic performance. Finally, a backlash feed‐forward compensator is engineered to restrain the detrimental effects caused by the backlash nonlinearity, and the simulation experimental results show that the designed new method can realize the precise loading of the EHLS under different working conditions, and the surplus force is suppressed better at the same time.

Cost-effective 3D-printed rotatable reflectors for two-dimensional beam steering

In this paper, we have developed a 2D optical scanning module comprising cascaded 3D-printed one-axis rotating mirrors with large areas (30×30mm2 for the X-direction scan and 60×25mm2 for the Y-direction scan). Each mirror device contains a square or rectangular silicon substrate coated with aluminum, serving as the mirror. A 3D-printed structure, including the mirror frame (with four embedded mini permanent magnets on the backside), torsion springs, and base, is combined with the mirror; two electromagnets are situated under the mirror as the actuation mechanism. We apply DC voltage to the electromagnets to create magnetic force. The electromagnets can interact with the permanent magnets to make the mirror rotate. The X scan of the 2D scanning module can achieve a static optical scan angle of ∼11.8deg at the -X corners, and the corresponding Y-scan angle is ∼4.5deg, both with 12 VDC. Moreover, we have observed a fan-shaped distortion, a phenomenon not thoroughly studied previously for combining two single-axis scan mirrors. Therefore, we also perform a simulation to establish and demonstrate a correlation between the simulation prediction and experimental results. The 2D scanning module can be a low-cost alternative to the expensive conventional galvanometer scanners, and it can be used to upgrade a rangefinder to a simplified LiDAR.

Emergency Evacuation Path Planning Method for the Large Ships

When an emergency occurs in a large ship, it is necessary to provide a scientific and reasonable evacuation strategy for the passengers in the ship, so as to avoid the loss of life and property caused by untimely evacuation. For the traditional Dijkstra’s algorithm, which only selects the optimal path based on the single index of path length, this paper takes into account the influence of path length, congestion and safety, and selects the optimal path in real time according to the dynamically changing external environment, which is more suitable for the application of emergency evacuation in large ship. The results of simulation experiments also prove the effectiveness of the algorithm proposed in this paper.

Studying the factor limitations of AC corrosion on pipelines

This paper systematically summarizes the domestic and foreign standards and research results of the limit requirements that influence the severity of alternating AC corrosion. In the meantime, combined with the results of pieces and indoor simulation experiments, the limits of each factor affecting AC corrosion are proposed. The results show that using AC voltage and AC current density (ACCD)/DC current density (DCCD) ratio parameters, to evaluate the severity of AC corrosion, is not rigorous, and there are still many inconsistencies in reported results. The severity of AC corrosion can be better judged using the ACCD and CP current density (CPCD) or the CP protection potential. By comparing corrosion specifications laterally with different current densities and potential levels, the degree of different specifications, experimental trends and field operability, are analyzed. It is suggested that SY/T 0087.6-2021 can be used in engineering applications. Moreover, the relationship between these two types of current densities obtained experimentally is determined on the premise of acceptable corrosion. On this basis, the influence limits of different sizes of current densities on AC corrosion are further proposed.

Effect of parameter optimization on the flow characteristics of venturi-self-excited oscillation mixer based on response surface model and multi-island genetic algorithm

Effect of parameter optimization on the flow characteristics of venturi-self-excited oscillation mixer based on response surface model and multi-island genetic algorithm

Effect of Asymmetric InAlGaN/GaN Superlattice Barrier Structure on the Optoelectronic Performance of GaN-Based Green Laser Diode

An asymmetric InAlGaN/GaN superlattice barrier structure without the first quantum barrier layer (FQB) is designed, and its effect on the optoelectronic performance of GaN-based green laser diode (LD) has been investigated based on simulation experiment and analytical results. It is found that, compared with conventional GaN barrier LD, device performance is significantly improved by using FQB-free asymmetric InAlGaN/GaN superlattice barrier structure, including low threshold current, high output power, and high photoelectric conversion efficiency. The threshold current of LD with novel structure is 16.19 mA, which is 22.46% less than GaN barrier LD. Meanwhile, the output power is 110.69 mW at an injection current of 120 mA, which is 16.20% higher compared to conventional LD, and the wall-plug efficiency has an enhancement of 9.5%, reaching 20.27%. FQB-free asymmetric InAlGaN/GaN superlattice barrier layer can reduce optical loss, suppress the polarization effect, and improve the carrier injection efficiency, which is beneficial to improve output power and photoelectric conversion efficiency. The novel epitaxial structure provides theoretical guidance and data support for improving the optoelectronic performance of GaN-based green LD.

Numerical Simulation Analysis of the Bending Performance of T-Beams Strengthened with Ultra-High-Performance Concrete Based on the CDP Model

Numerical Simulation Analysis of the Bending Performance of T-Beams Strengthened with Ultra-High-Performance Concrete Based on the CDP Model