An Efficient DOA Estimation Algorithm Based on Diagonal-Symmetric Loading

In order to solve the problem that the subspace-like direction of arrival (DOA) estimation performs poor due to the error of sources number, this paper proposes a new super-resolution DOA estimation algorithm based on the diagonal-symmetric loading (DSL). Specifically, orthogonality principle of the minimum eigenvector of the specific covariance matrix and the source number estimation based on the improved K-means method were adopted to construct the spatial spectrum. Then, by considering the signal-to-interference-to-noise ratio (SINR), the theoretical basis for selecting parameters was given and verified by numerical experiment. To evaluate the effectiveness of the proposed algorithm, this paper compared it with the methods of minimum variance distortionless response (MVDR) and new signal subspace processing (NSSP). Experimental results prove that the proposed DSL has higher resolution and better estimation accuracy than the MVDR and NSSP.

Calculated Model of Endurance Limit Estimation Based on Structural-Strain Analysis of the Critical Condition of Ferrite-Perlite Steels with Macrocracks in Ship Structures

In this study, a structural-deformation analysis of the process of crack development is performed, on the basis of which an engineering methodology is developed for assessing the endurance limit and resource of large-sized structures. A simple analytical dependence (correlation аналитическая зависимость) was obtained, which allows one to determine the critical size of macrocracks for ferritic-pearlitic steels without using the well-known Griffith formula. The results of calculating the cracks critical lengths of various steels depending on their yield strength are presented. The analytical dependence of the calculation of the fatigue limit for the most dangerous symmetric loading cycle according to the standard set of mechanical characteristics of ferrite-pearlite steel is presented. The obtained results make it possible to calculate the endurance limit of structural elements of marine equipment and other structures subject to cyclic loads

Collapse Behavior of Tensegrity Barrel-Vault Structures Based on Di-Pyramid (DP) Units

In this study, the collapse behavior of a family of tensegrity structures, i.e. di-pyramid (DP) barrel-vaults that can offer promising solutions for civil engineering applications is analyzed. Depending on whether struts’ snap or cables’ rupture dictate the occurrence of overall collapse, two different designs are considered. The effects of geometric parameters, self-stress properties, loading type, boundary conditions and strengthening schemes on the structural behavior are discussed. It is found that the structures with symmetric and ridge loading types undergo bifurcation type instability instead of limit point which is encountered in the cases with asymmetric loading type. Constraint against lateral thrust is beneficial in improving strength and initial stiffness of the studied cases, by as much as 60% and 90%, respectively. In most cases, the rate of strength variation associated with increasing self-stress levels is quite slow, while the slackness load increases by at least 400% being the primary achievements. By using non-uniform self-stress distribution, the initial stiffness of these structures can be increased up to 240%. Increasing the rise-to-span ratio improves the initial stiffness and collapse strength of the structure significantly at the expense of expedition of cables slackness. Significant gains in collapse resistance of these structures under symmetric loading are obtained with strengthened critical struts or cables, depending on which collapse case dominates, but the initial stiffness is generally not influenced by these schemes.

Investigation of heat release in metals under uniaxial stress state as a parameter of fatigue damage in metal bridges

The purpose of the issue is to study the process of heat release in metals under a symmetric loading cycle under conditions of uniaxial stress in order to assess the development of fatigue damage in the elements of metal superstructures of railroad and highway bridges. The author considered bending and axial loads of specimens with and without artificial concentrators. During the experiments, the samples were covered with matte paint, which ensured an emission coefficient of 0.95. For simultaneous fixation of thermal radiation on the upper and lower surfaces of the slots, mirrors were used. To eliminate interference from thermal radiation from surrounding objects, a fabric screen was installed between these objects and samples. As a result of experimental work, the author found that in all samples, regardless of their configuration and loading conditions, fatigue failure (the appearance of visible cracks) was preceded by a sharp increase in surface temperature at the same stress level, which the author called critical. The author during the study revealed that the magnitude of the critical stresses for the tested samples under uniaxial stress state and symmetric loading cycle does not depend on the number of concentrators, their sizes and location, but depends on the self-heating temperature and the type of deformation. Thus, the critical stress can be considered a characteristic of the material. The author also noted that at stresses greater than critical, an almost linear dependence of the temperature change on the total value of the stress increment is observed. Summarizing the noted properties of critical stresses, it can be argued that such stresses can be used to assess the development of fatigue damage when assessing the technical condition of a structure during bridge inspections. The work was performed as part of a dissertation research with the support of a grant from Russian Railways for the development of scientific and pedagogical schools.

Fracture Mechanical Properties of Rocklike Materials Under Half Symmetric Loading

The authors studied the fracture mechanical properties under half-symmetric loading in this paper. The stress distribution around the crack tip and the stress intensity factor of three kinds of notched specimens under half symmetric loading were compared. The maximum tensile stress σmax of double notch specimens was much greater than that of single notch specimens and the maximum shear stress τmax was almost equal, which means that the single notch specimens were more prone to Mode II fractures. The intensity factors KII of central notch specimens were very small compared with other specimens and they induced Mode I fractures. For both double notch and single notch specimens, KII was kept at a constant level and did not change with the change of a/h, and KII was much larger than KI. KII has the potential to reach its fracture toughness KIIC before KI and Mode II fractures occurred. Rock-like materials were introduced to produce single notch specimens. Test results show that the crack had been initiated at the crack tip and propagated along the original notch face, and a Mode II fracture occurred. There was no relationship between the peak load and the original notch length. The average value of KIIC was about 0.602 MPa×m1/2, and KIIC was about 3.8 times KIC. The half symmetric loading test of single notch specimens was one of the most effective methods to obtain a true Mode II fracture and determine Mode fracture toughness.