Solution for polarimetric radar cross section measurement and calibration

The exact radar cross-section(RCS) measurement is difficult when the scattering of targets is low. Full polarimetric calibration is one technique that offers the potential for improving the accuracy of RCS measurements. There are numerous polarimetric calibration algorithms. Some complex expressions in these algorithms cannot be easily used in an engineering practice. A radar polarimetric coefficients matrix(RPCM) with a simpler expression is presented for the monostatic radar polarization scattering matrix(PSM) measurement. Using a rhombic dihedral corner reflector and a metallic sphere, the RPCM can be obtained by solving a set of equations, which can be used to find the true PSM for any target. An example for the PSM of a metallic dish shows that the proposed method obviously improves the accuracy of crosspolarized RCS measurements.

Ultrawide-band radar imagery from multiple incoherent frequency subband measurements

The problem of combined radar imagery from multiple sparse frequency subbands initially incoherent to each other is of practical importance for radar target discrimination.A new coherent processing technique based on probability density analysis of the subband data is proposed,which is applicable for radar imaging from measurements of two or more initially incoherent radar subbands.The coherence parameters for both amplitude and phase are obtained by combining modern spectral analysis with probability density estimation.The major advantage of the proposed technique lies in that it enables much more robust cohering for the sparse subband data of real-world complex targets.

Angular glint calculation and analysis of radar targets via adaptive cross approximation algorithm

Angular glint is a significant electromagnetic(EM) scattering signature of extended radar targets. Based on the adaptive cross approximation(ACA) algorithm accelerated method of moments(MoM) and the plane incident wave assumption, the narrowband, wideband and newly developed high-resolution range profile(HRRP) based angular glint calculation formulations are derived and applied to arbitrarily shaped three-dimensional(3D) perfectly electrically conducting(PEC) objects. In addition, the near-field angular glint is emphasized, which is of great importance for radarseeker applications. Furthermore, with the HRRP based angular glint, an approach to rigorously determine range resolution cells which own relatively smaller angular glint is provided. Numerical results are presented with new findings to demonstrate the usefulness of the developed formulations.

Analytical solutions for buckling of size-dependent Timoshenko beams

The inconsistences of the higher-order shear resultant expressed in terms of displacement(s) and the complete boundary value problems of structures modeled by the nonlocal strain gradient theory have not been well addressed. This paper develops a size-dependent Timoshenko beam model that considers both the nonlocal effect and strain gradient effect. The variationally consistent boundary conditions corresponding to the equations of motion of Timoshenko beams are reformulated with the aid of the weighted residual method. The complete boundary value problems of nonlocal strain gradient Timoshenko beams undergoing buckling are solved in closed forms. All the possible higher-order boundary conditions induced by the strain gradient are selectively suggested based on the fact that the buckling loads increase with the increasing aspect ratios of beams from the conventional mechanics point of view. Then, motivated by the expression for beams with simply-supported (SS) boundary conditions, some semiempirical formulae are obtained by curve fitting procedures.

SYMPLECTIC ANALYSIS FOR WAVE PROPAGATION OF HIERARCHICAL HONEYCOMB STRUCTURES

Wave propagation in two-dimensional hierarchical honeycomb structures with twoorder hierarchy is investigated by using the symplectic algorithm. By applying the variational principle to the dual variables, the wave propagation problem is transformed into a two-dimensional symplectic eigenvalue problem. The band gaps and spatial filtering phenomena are examined to find the stop bands and directional stop bands. Special attention is directed to the effects of the relative density and the length ratio on the band gaps and phase constant surfaces. This work provides new opportunities for designing hierarchical honeycomb structures in sound insulation applications.

Wave Propagation Characteristics in Thick Conventional and Auxetic Cellular Plates

Based on Mindlin plate models and Kirchhoff plate models,this study was concerned with the wave propagation characteristics in thick conventional and auxetic cellular structures,with the objective to clarify the effects of negative Poisson's ratio,shear factor and orthotropic mechanical properties on the dynamic behaviors of thick plates.Numerical results revealed that the predictions using variable shear factor in Mindlin plate models resulted in high wave frequencies,which were more significant for plates with negative values of Poisson's ratio.The present study can be useful for the design of critical applications by varying the values of Poisson's ratio.

Review of condition monitoring and fault diagnosis for marine power systems

The use of condition monitoring and fault diagnosis(CMFD)in marine power systems significantly influences ship safety.This study divides the development of CMFD for marine power systems into three periods and reviews the content,state and limitations of CMFD research for each period.According to the research achievements and engineering experience of the authors’team,typical application cases are introduced for CMFD in ships,including CMFD platforms on engineering ships,salvage ships,container ships and ro-ro ships powered by solar photovoltaic systems.Finally,prospective research directions are proposed for CMFD in marine power systems,considering the research status of CMFD and the trend toward intelligent and eco-friendly ships.

Introduction to special issue on maritime safety and smart shipping

Shipping is perhaps themost international of all the world’s great industries and one of the most dangerous.It is essential to study maritime safety and take reasonable measurements to ensure the security of life and property.With the rapid development of Artificial Intelligence,industrial upgrading is undergoing a change in the maritime industry,where many techniques have been developed to enhance maritime safety and improve the automation and intelligence of ships,equipment,and infrastructure.