Far-field Conditions Research Articles

Spatial windowing for finite-size incident sound transmission coefficient of multi-component surfaces

Spatial windowing was introduced for alleviating problems related to the infinite behaviour of rectangular surfaces. For finite rectangular surfaces, the radiation efficiency can be computed very efficiently. Considering multi-component surfaces such as a building façade, which include both rectangular and non-rectangular surfaces (e.g., wall and window), an adjusted version of the spatial windowing is here applied, using a divide-and-conquer approach of rectangular surfaces and applying the correlation between two adjacent surfaces. Hence, the transmission coefficient and sound reduction index (SRI) of multi-component finite surfaces can be calculated. For a glass surface, the adjusted radiation efficiency presents good agreement with the non-adjusted one. Applying a convergence study to the adjusted radiation efficiency with respect to the glass surface, it was found that a coarsely divided surface approximates the relative undivided surface very well, under far-field conditions. Similar results were obtained with respect to the SRI of a single-component (glass) and a multi-component (glass and wall) surface. Applying both far-field and near-field conditions in a multi-component surface, the glass typically dominates the total SRI, especially with increasing its area. However, in the coincidence region of the wall, the SRI of the wall can be decisive for the total SRI.

On thermally driven fluid flows arising in astrophysics

We investigate a potential model for an unbounded celestial bodies of finite mass composed of a solid core and a gaseous atmosphere. The system is governed by the Navier–Stokes–Fourier–Poisson equations, incorporating no-slip boundary conditions for velocity and a specified temperature distribution on the surface of the solid core. Additionally, a positive far-field condition is imposed on the temperature. This manuscript extends the mathematical theory of open fluid systems to unbounded exterior domains addressing these physically motivated yet highly challenging combination of boundary conditions. Notably, we establish the existence of global-in-time weak solutions and demonstrate the weak-strong uniqueness principle

Comparative analysis of seismic response and vulnerability of laminated bamboo frame structure under near-field and far-field earthquake actions

The study offers an evaluation of seismic response and vulnerability for a five-story laminated bamboo frame structure, assessing the effectiveness of seismic intensity measures across various damage thresholds and the modeling uncertainties involved. A structural finite element model was developed in OpenSees software, utilizing the Pinching4 model to accurately represent the non-linear characteristics of T-shaped steel connections in beam-column joints. Two collections of earthquake records, one consisting of pulse-like near-field and the other of far-field events, were utilized to examine the structure's nonlinear behavior. Additionally, vulnerability curves for various damage states were generated using the multiple stripe analysis technique, applied to both ground motion datasets. The applicability of 24 seismic intensity measures was also analyzed across various damage limit states. The modeling uncertainty under different seismic actions was further estimated using a first-order second-moment method. Ultimately, the annual collapse probability of the structure are elucidated. Research indicates that due to the influence of joint stiffness, the overall structure demonstrates dynamic characteristics that are predominantly of the first mode shape. The spectral acceleration associated with the fundamental period achieves a reduced logarithmic standard deviation in the vulnerability analysis across various limit states. Other IMs considering higher mode effects or softening period actions no longer predominate. In most cases, the modeling uncertainty under far-field seismic action is higher than that under near-field, especially at the severe damage limit states by using an efficient intensity measure. The laminated bamboo frame structure faces a much higher collapse risk in near-field than in far-field conditions.

Nanoparticle uptake by a semi-permeable, spherical cell from an external planar diffusive field. II. Numerical study of temporal and spatial development validated using FEM

In this paper, we present a mathematical study of particle diffusion inside and outside a spherical biological cell that has been exposed on one side to a propagating planar diffusive front. The media inside and outside the spherical cell are differentiated by their respective diffusion constants. A closed form, large-time, asymptotic solution is derived by the combined means of Laplace transform, separation of variables, and asymptotic series development. The solution process is assisted by means of an effective far-field boundary condition, which is instrumental in resolving the conflict of planar and spherical geometries. The focus of the paper is on a numerical comparison to determine the accuracy of the asymptotic solution relative to a fully numerical solution obtained using the finite element method. The asymptotic solution is shown to be highly effective in capturing the dynamic behaviour of the system, both internal and external to the cell, under a range of diffusive conditions.

Numerical optimisation of microbially induced calcite precipitation (MICP) injection strategies for sealing the aquifer's leakage paths for CO2 geosequestration application

Carbon capture and storage (CCS) in deep geological aquifers has shown to be the most viable option for mitigating the greenhouse gas effect of carbon dioxide (CO2) at a large scale. However, the underground formations often possess discontinuities in the caprocks, leaking the stored CO2. Potential leakage paths, such as abandoned wells, have been growing due to excessively unplugged oil and gas exploration wells. The leakage of CO2 from these wells is a major concern, considering their negative impact on the environment and compromising CO2 storage efficiency. Recently, microbially induced calcite precipitation (MICP) technology has proven to be an effective and sustainable method for reducing the permeability of geomaterials. Nevertheless, the MICP process involves intricate interactions among bio-chemo-hydraulics (BCH) domains to comprehend the reactive transport of biochemicals. The complex nature of the MICP process poses difficulties in setting the biochemical injection durations for a particular target distance at the given injection rate. Given this, the present study developed a coupled numerical model and employed it as a workable tool for optimising MICP injections to plug the abandoned well connecting two deep geological aquifers. Following that, the study evaluated the leakage of CO2 using flow migration rates in the untreated and MICP-treated leaky aquifer. The study proposed a novel optimisation strategy for biochemical injections under near and far-field leakage conditions. The sensitivity of biochemical injection durations on the attached bacterial amount and permeability in the leak was also determined. The observations from the present study indicated a complete reduction in the CO2 migration rates from the abandoned well due to a reduced permeability after MICP, thereby indicating the efficacy of the proposed optimisation methodology. Further, a cost analysis of the MICP treatment indicated a rational application cost with the target distance compared to the detrimental effects of CO2 leakage.

Fresnel Diffraction Model for Laser Dazzling Spots of Complementary Metal Oxide Semiconductor Cameras.

Laser dazzling on complementary metal oxide semiconductor (CMOS) image sensors is an effective method in optoelectronic countermeasures. However, previous research mainly focused on the laser dazzling under far fields, with limited studies on situations that the far-field conditions were not satisfied. In this paper, we established a Fresnel diffraction model of laser dazzling on a CMOS by combining experiments and simulations. We calculated that the laser power density and the area of saturated pixels on the detector exhibit a linear relationship with a slope of 0.64 in a log-log plot. In the experiment, we found that the back side illumination (BSI-CMOS) matched the simulations, with an error margin of 3%, while the front side illumination (FSI-CMOS) slightly mismatched the simulations, with an error margin of 14%. We also found that the full-screen saturation threshold for the BSI-CMOS was 25% higher than the FSI-CMOS. Our work demonstrates the applicability of the Fresnel diffraction model for BSI-CMOS, which provides a valuable reference for studying laser dazzling.

Analysis of acoustic radiation problems involving arbitrary immersed media interfaces by the extended finite element method with Dirichlet to Neumann boundary condition

To quantify the influence of moving immersed media on acoustic radiation, this study develops an efficient method for acoustic radiation with arbitrary immersed media interfaces based on the extended finite element method (XFEM) and the Dirichlet-to-Neumann (DtN) boundary condition. The XFEM is employed for efficient and accurate modeling of the acoustic field with boundary shape variations. It requires no modification of the computational mesh and accurately captures non-smooth solutions on the interface by constructing enrichment functions. Additionally, the DtN boundary condition simulates the far-field radiation condition by establishing the relationship between the acoustic pressure and its derivatives. Numerical examples show that the proposed method efficiently characterizes changes in the position of immersed media interfaces without re-meshing the mesh. Variations in the thickness of porous material domains alter the acoustic radiation characteristics, with thicker porous material domains resulting in more pronounced noise reduction effects. Compared to changes in the thickness of porous material domains, changes in their position significantly alter the distribution of radiation pressure, indicating that ideal noise reduction effects can be achieved by strategically placing porous materials in specific locations in practical engineering applications.

Lightweight and hierarchical carboxyl chitosan-derived carbon aerogel for electromagnetic wave absorber and heat insulation

In recent years, carbon aerogels derived from biomass have shown promising potential in electromagnetic wave (EMW) absorption field owing to their lightweight nature, controllable structure, environmental friendliness, and abundant pore structure. This study reports a novel type of carbon aerogels based on carboxyl chitosan (CCS) and graphene oxide (GO) with rich pores and a unique three-dimensional interconnected structure through solution mixing, freeze-drying, and pyrolysis process. The EMW absorption performances of the carboxyl chitosan/GO xerogel derived carbon aerogels (CGCAs) are adjusted by varying the content of graphene oxide (GO). The nitrogen elements inherent in chitosan can provide a large number of defects to the carbonized material, effectively capturing and attenuating EMW. Synthesized CGCAs show excellent EMW absorption performance with increasing GO content and the CGCA-6 exhibits the best performance. At a thickness of 1.7 mm, it has RLmin of −61.67 dB, and at a thickness of 1.5 mm, it has the widest effective absorption bandwidth (EAB) of 4.24 GHz (12.96–17.12 GHz). Additionally, under far-field conditions, at a thickness of 1.7 mm, the maximum radar cross-section (RCS) reduction relative to a PEC plate for the prepared CGCA-6 is 22.28 dB m2. Furthermore, the good thermal insulation capability exhibited by CGCA-6 makes it suitable for complex application scenarios. Therefore, this biomass-derived multi-functional carbon aerogel with excellent EMW absorption performance, radar stealth, infrared stealth, and thermal insulation capabilities has broad prospects for applications in EMW protection and aerospace fields.

A lightweight and efficient hollow sunken carbon@MnO2/reduced graphene oxide composite for high-performance electromagnetic wave absorption

To address the environmental and health issues stemming from electromagnetic pollution, it is crucial to investigate high-performance and practical materials for absorbing electromagnetic waves. Herein, the ternary lightweight SC@MnO2/RGO (SCMR) composites are synthesized by using a special kind of hollow sunken carbon nanoparticles (SC) as a substrate and combining MnO2 nanosheets with 2D reduced graphene oxide (RGO). The investigation results show that the minimum reflection loss (RLmin) of SCMR3 can reach −60.95 dB with a matched thickness of 1.47 mm and a frequency of 13.12 GHz, and the effective absorption bandwidth (EAB) is 4.08 GHz (13.76–17.84 GHz) at the thickness of 1.23 mm. Its excellent performance comes from high dielectric loss capability, multiple reflections, interfacial polarization, and defective polarization relaxation brought by the structure of the composite, which can effectively enable electromagnetic wave absorption and facilitates energy conversion. Furthermore, simulation-based assessment under far-field conditions elucidates the radar stealth effect, demonstrating that the maximum radar cross-section (RCS) attenuation value of SCMR3-coated perfect electrical conductor (PEC) at Phi = 0° and θ = 0° can attain 32.13 dB m2. Ultimately, this study presents a viable design methodology for developing lightweight, efficient, and application-oriented carbon-based electromagnetic wave absorption materials.

Seismic vulnerability analysis of single-layer lattice shells with different rise-to-span ratios: Focusing on the selection of Sa(T1)-based intensity measures

This study conducted a detailed examination of seismic vulnerability across different limit states for Schwedler single-layer lattice shells with differing rise-to-span ratios. A comparative analysis of seismic intensity measures, particularly those centered around Sa(T1), was performed to evaluate their effectiveness in vulnerability analysis. To comprehensively address the inherent uncertainties in seismic actions, the study selected a dual set of ground motion scenarios, encompassing both far-field and pulse-type near-field events. A novel approach was employed, integrating a multi-indicator seismic performance assessment model based on the residual seismic safety framework, aiming to thoroughly quantify the cumulative seismic damage to lattice structures. Utilizing the multiple stripes analysis technique enabled the efficient generation of analytical results for vulnerability assessments at various damage thresholds. The findings revealed that lattice shells with larger rise-to-span ratios exhibit increased seismic robustness, notably with far-field seismic events causing more significant damage than their pulse-type near-field counterparts. Furthermore, the study determined that employing seismic intensity measures which consider the effects of higher modes significantly reduces variability in the vulnerability analysis when dealing with pulse-type near-field seismic activity. As a result, the use of the seismic intensity measure IM123 is recommended for assessing the vulnerability of lattice shells with varying rise-to-span ratios, under both far-field and near-field seismic conditions.

Constructing multiple heterogeneous interfaces in one-dimensional carbon fiber materials for superior electromagnetic wave absorption

Due to impedance mismatch and a single loss mechanism, carbon fiber fails to meet the requirements for efficient absorbers in terms of lightweight construction and broad absorption band. In this study, we have successfully prepared one-dimensional beaded SiO2@SiC@C nanofiber (SSCF) composites with multiple heterogeneous interfaces by employing the electrospinning-carbothermal reduction method. The beaded SSCF composites effectively address the impedance mismatch issue by controlling silicon dioxide and silicon carbide through carbothermal reduction. This optimization enriches the defects and interfaces of carbon fibers composites, consequently enhancing the electromagnetic wave absorption performance. The SSCF composites demonstrate remarkable performance, with a minimum reflection loss of −59.53 dB at a matched thickness of 2.21 mm and a maximum absorption bandwidth of 6 GHz. This outstanding performance is attributed to the synergistic effects of the multi-phase composition, bead structure, and one-dimensional network structure. These features not only optimize impedance matching but also enhance defect loss, interface polarization loss (SiC/SiO2, C/SiO2, SiC/C, C/Air), conduction loss, and relaxation loss of the SSCF composites. Furthermore, radar cross-section analysis utilizing computer simulation technology confirms the excellent attenuation of microwave energy by the SSCF composites under realistic far-field conditions. This study provides valuable insights for designing efficient one-dimensional carbon-based electromagnetic wave absorbers.

A competitive strategy toward 1 T/2H MoS2 to balance impedance for optimizing electromagnetic wave absorption

Interface engineering and phase engineering play crucial roles in enhancing the design and development of advanced electromagnetic wave (EMW) absorbers. However, there is a lack of focus on designing phase structures and interfaces from a microscopic perspective to adjust impedance matching and EMW absorption. This study introduced a competitive strategy involving 1 T/2H MoS2. The phase structure and composition of MoS2 were controlled using a microwave hydrothermal method. By creating a diverse phase interface within the material in the form of 1 T/2H, a balance between conduction loss and polarization loss was achieved, leading to improved EMW absorption through enhanced impedance matching. The results indicated that the incorporation of the 1 T phase boosted the electron transfer capability of MoS2, increasing conduction loss. The 1 T/2H phase interface enhanced interface polarization, thereby amplifying polarization loss. At a thickness of 2.8 mm, the absorber demonstrated a minimum reflection loss of −64.9 dB and an effective absorption bandwidth of 4.6 GHz. In far-field conditions, the maximum radar cross-section (RCS) of the 1 T/2H phase MoS2 nanoflowers was −27.5 dBm2. This study elucidates the relationship between 1 T/2H phase MoS2 content and phase interfaces with impedance matching, offering a novel approach for developing high-performance MoS2-based EMW absorbing materials.

Entropy stable far-field boundary conditions for the compressible Navier-Stokes equations

We consider external compressible-flow problems with open boundaries. We begin by presenting the basic idea, namely the introduction of an infinite buffer zone around the computational domain, for the advection-diffusion equation. We discretise the problem with a summation-by-parts finite-volume scheme and prove convergence; a key step is the renormalisation of the solution. Next, we make the analogous rescaling of the entropy function for the Navier-Stokes equations and prove that a finite-volume scheme is entropy stable.Finally, we present numerical computations with a vortex governed by the Navier-Stokes equations interacting with the buffer zone. As proven, the scheme is stable, and with a sufficient number of grid points and with some numerical diffusion in the buffer zone, the reflections are modest.

Effect of far-field ambient conditions on interfacial solar vapor generation using a two-phase closed thermosyphon

Effect of far-field ambient conditions on interfacial solar vapor generation using a two-phase closed thermosyphon

A dispersion model for initial consequence analysis based on diffusion equations

Most factories use toxic or flammable chemicals in their industrial processes; this poses a risk of leakage due to accidents, which can sometimes result in mass casualties and considerable property damage. Therefore, quantitative risk prediction and assessment are necessary to protect the public and minimize losses in the event of a chemical release. Several methods can be used to evaluate chemical dispersion in the atmosphere, but most are based on the assumption of neutral buoyancy and far-field wind conditions. With this assumption, a model is valid only after a significant amount of time has elapsed from the moment chemicals are released or dispersed from a source. However, the most dangerous locations are typically close to a leak source. Therefore, a dispersion model for the initial phase of a leak is required to quantify the risk and predict the extent of damage. This study developed a dispersion model for initial consequence analysis using a three-dimensional unsteady convective diffusion equation. A continuous point source was assumed, and ethane was used as the leak material to minimize the effects of buoyancy. The unsteady concentration field developed rapidly as the diffusion coefficient and wind velocity increased, but the steady-state concentration field was not affected by wind velocity. This dispersion model also allows for the simple consideration of ground adsorption, making it scalable to real-world situations. The time to reach a steady state required for an effective emergency response was predicted, and the results were interpreted in terms of mathematical methods and physical characteristics.

Exact domain truncation for the Morse-ingard equations

Morse and Ingard [1] give a coupled system of time-harmonic equations for the temperature and pressure of an excited gas. These equations form a critical aspect of modeling trace gas sensors. Like other wave propagation problems, the computational problem must be closed with suitable far-field boundary conditions. Working in a scattered-field formulation, we adapt a nonlocal boundary condition proposed in [2] for the Helmholtz equation to this coupled system. This boundary condition uses a Green's formula for the true solution on the boundary, giving rise to a nonlocal perturbation of standard transmission boundary conditions. However, the boundary condition is exact and so Galerkin discretization of the resulting problem converges to the restriction of the exact solution to the computational domain. Numerical results demonstrate that accuracy can be obtained on relatively coarse meshes on small computational domains, and the resulting algebraic systems may be solved by GMRES using the local part of the operator as an effective preconditioner. These numerical results taken together combine several advanced techniques, including higher-order finite elements, geometric multigrid in curvilinear geometry, native use of complex arithmetic, and incorporation of nonlocal operators. These are tied together in a high-level simulation using the Firedrake library.

A Near-Field Imaging Method Based on the Near-Field Distance for an Aperture Synthesis Radiometer

For an aperture synthesis radiometer (ASR), the visibility and the modified brightness temperature (BT) are related to the Fourier transform when the distance between the system and the source is in the far-field region. BT reconstruction can be achieved using G-matrix imaging. However, for ASRs with large array sizes, the far-field condition is not satisfied when performing performance tests in an anechoic chamber due to size limitations. Using far-field imaging methods in near-field conditions can introduce errors in the images and fail to correctly reconstruct the BT. Most of the existing methods deal with visibilities, converting near-field visibilities to far-field visibilities, which are suitable for point sources but not good for extended source correction. In this paper, two near-field imaging methods are proposed based on the near-field distance. These methods enable BT reconstruction in near-field conditions by generating improved resolving matrices: the near-field G-matrix and the F-matrix. These methods do not change the visibility measurements and can effectively image both the point source and the extended source in the near field. Simulations of point sources and extended sources in near-field conditions demonstrate the effectiveness of both methods, with F-matrix imaging outperforming near-field G-matrix imaging. The feasibility of both near-field imaging methods is further validated by carrying out experiments on a 10-element Y-array system.

Damping loss factor identification based on energy finite element method

A new method for the identification of damping loss factor (DLF) is proposed in this paper, combining energy finite element method (EFEM), energy density testing theory and particle swarm optimization (PSO) algorithms. An experimental system is designed to identify the DLF of a rectangular plate made in steel based on the theoretical formulation. The identification results are compared with the power injection method (PIM) results. Besides, the identification method is modified by considering the range of test deviation. This research shows that the new method is less dependent on the location of the selected exciting points and the location of the measurement points in far-field conditions, and it is more consistent with the PIM method and has a higher accuracy within the correction range. In addition, the method can be used to obtain an accurate identification results with fewer measurement points compared with PIM, which is of high practicality.

UV-modification of Ag nanoparticles on α-MoCx for interface polarization engineering in electromagnetic wave absorption.

The design of electromagnetic wave absorbing materials (EWAMs) has aroused great attention with the express development of electromagnetic devices, which pose a severe EM pollution risk to human health. Herein, an Ag-doped MoCx composite was designed and constructed through a UV-light-induced self-reduction process. The UV-reduction time was controlled on the α-MoC polymer for 0.5-2 hours for modifying different amounts of Ag. As a result, α-MoC@Ag-1.5 exhibited the strongest RLmin of -56.51 dB at 8.8 GHz under a thickness of 3.0 mm and the widest EAB of 4.96 GHz (12.16-17.12 GHz) covering a substantial portion of the Ku-band at a thickness of 2.0 mm due to the synergy of the conductivity loss and abundant interfacial polarization sites. Additionally, a new strategy for computer simulation technology was proposed to simulate substantial radar cross-sectional reduction values with real far-field conditions, whereby absorbing coatings with α-MoC@Ag-1.5 were proved to contribute to a remarkable radar cross-sectional reduction of 37.4 dB m2.

Diffraction patterns of optical discs under the far-field condition

When optical discs are illuminated, bright-colored lines can often be observed on the surface of them. Starting from the oblique incident grating diffraction model, this paper analyzes the physical mechanism behind the appearance of these colored lines and provides the coordinate expression of the location of the colored lines on the optical disc under the far-field condition. The wavelength distribution of the colored lines on the optical disc under white light illumination is also given by the wave vector relationship of the diffraction process. To verify the theoretical analysis results, an experimental apparatus was designed and constructed to measure the position and color of the colored lines. The experimental data, analyzed through Gaussian process regression and direct comparison, demonstrates a good consistency with the theoretical analysis results.