Identification of the Mechanical Joint Parameters with Model Uncertainty

Joint parameter identification is a key problem in the modeling of complex structures. The behavior of joint may be random due to the random properties of preload and joint geometries, contact surface and its finish, etc. A method is presented to simulate the joint parameters as probabilistic variables. In this method the response surface based model updating method and probabilistic approaches are employed to identify the parameters. The study implies that joint parameters of some structures have normal or nearly normal distributions, and a linear FE model with probabilistic variables could illustrate dynamic characteristics of joints.

Influence of geometric parameters on stress concentration factors of undermatched butt joint with single V-groove under three-point bending load

In order to improve the bending load-carrying capacity （BLCC） of undermatched butt joint under three-point bending load, the influence of joint geometric parameters on stress concentration factors （SCF） at the weld bottom center and the weld toe of uudermatched butt joint with single V-groove are studied respectively based on the finite element method in this paper. Results show that the reinforcement height and the cover pass width play decisive role in the BLCC for undermatched butt joint. BLCC of undermatched butt joint can be improved by choosing the appropriate joint geometric parameters.

New criterion for rock joints based on three-dimensional roughness parameters

The shear behavior of rock joints is important in solving practical problems of rock mechanics. Three group rock joints with different morphologies are made by cement mortar material and a series of CNL(constant normal loading) shear tests are performed. The influences of the applied normal stress and joint morphology to its shear strength are analyzed. According to the experimental results, the peak dilatancy angle of rock joint decreases with increasing normal stress, but increases with increasing roughness. The shear strength increases with the increasing normal stress and the roughness of rock joint. It is observed that the modes of failure of asperities are tensile, pure shear, or a combination of both. It is suggested that the three-dimensional roughness parameters and the tensile strength are the appropriate parameter for describing the shear strength criterion. A new peak shear criterion is proposed which can be used to predict peak shear strength of rock joints. All the used parameters can be easily obtained by performing tests.

The influence of joint geometric parameters on shape factor of butt joint with center through crack

In this research, the influence of such joint geometric parameters as weld width and reinforcement on shape ~actor of butt joint with center crack subjected to static loading was investigated by finite element analyses method. According to the analytical resuhs, a well fracture resistant joint shape of butt joint with center crack has been approved.

Computing in-situ strength of rock masses based upon RQD and modified joint factor: Using pressure and damage sensitive constitutive relationship

In th is study, a n e w m odel w as p re se n te d for com p u tin g stre n g th o f rock m asses based u p o n in -situo bservations o f RQD p o pularly kno w n as rock quality d esignation. This m odel links u p th e rock m assp aram eters from in -situ investigations w ith th e stre n g th p a ram eters o f jo in ted rocks obtain ed fromlaboratory scale ex p erim en tal observations. Using th e co n stitu tiv e relation, th e a u th o r derived a p ressu reand d am age sensitive plastic p a ra m e te r to d ete rm in e stre n g th o f rock m asses for varied ex te n ts ofd isco n tin u ity an d p ressu re induced dam age. The te s t results show th a t plasticity characterized byhard en in g an d softening inclusive o f dam ag e invariably d e p en d s u p o n m ean p ressu re an d e x te n t ofdefo rm atio n s alread y experien ced by rock m asses. The p re se n t w ork explores th e te s t d a ta th a t revealth e d ep en d en c e o f in -situ stren g th on increm ental jo in t p ara m e te rs o b tain ed from th e jo in t num ber,jo in t orien tatio n , jo in t roughness, gouge p a ram eters an d w a te r pressure. S ubstituting th e relationshipb e tw e e n th e RQD and m odified jo in t factor w ith th a t b e tw e e n m odulus ratio an d stren g th ratio, th em odel show s successfully th a t using d am age inclusive plastic p a ra m e te r an d RQD provides a relationshipfor estim atin g th e stre n g th o f rock m asses. One o f th e m ain objectives o f this w ork is to illustrate th a t th ep re se n t m odel is sensitive to p la s tic ity a n d dam ag e to g e th e r in estim atin g in -situ stre n g th o f rock m assesin foundations, u n d e rg ro u n d excavation an d tunnels.

Joint 2D DOA and Doppler frequency estimation for L-shaped array using compressive sensing

A joint two-dimensional(2D)direction-of-arrival(DOA)and radial Doppler frequency estimation method for the L-shaped array is proposed in this paper based on the compressive sensing(CS)framework.Revised from the conventional CS-based methods where the joint spatial-temporal parameters are characterized in one large scale matrix,three smaller scale matrices with independent azimuth,elevation and Doppler frequency are introduced adopting a separable observation model.Afterwards,the estimation is achieved by L1-norm minimization and the Bayesian CS algorithm.In addition,under the L-shaped array topology,the azimuth and elevation are separated yet coupled to the same radial Doppler frequency.Hence,the pair matching problem is solved with the aid of the radial Doppler frequency.Finally,numerical simulations corroborate the feasibility and validity of the proposed algorithm.

Cramer-Rao bound and signal-to-noise ratio gain in distributed coherent aperture radar

This paper studies the estimation performance of the coherent processing parameter （CPP）, including time delay differences and phase synchronization errors among different apertures of the distributed coherent aperture radar （DCAR）. Firstly, three architectures of signal processing in the DCAR are introduced. Secondly, the closed-form Cramer-Rao bound （CRB） of the CPP estimation is derived and compared. Then, the closed-form CRB is verified by numerical simulations. Finally, when the next generation radar works in a fully coherent mode, the closed-form signal-to-noise ratio （SNR） gain of the three architectures is presented.

Wind Wave Characteristics and Engineering Environment of the South China Sea

Wave simulation was conducted for the period 1976 to 2005 in the South China Sea （SCS） using the wave model, WAVEWATCH-III. Wave characteristics and engineering environment were studied in the region. The wind input data are from the objective reanalysis wind datasets, which assimilate meteorological data from several sources. Comparisons of significant wave heights between simulation and TOPEX/Poseidon altimeter and buoy data show a good agreement in general. By statistical analysis, the wave characteristics, such as significant wave heights, dominant wave directions, and their seasonal variations, were discussed. The largest significant wave heights are found in winter and the smallest in spring. The annual mean dominant wave direction is northeast （NE） along the southwest （SW）-NE axis, east northeast in the northwest （NW） part of SCS, and north northeast in the southeast （SE） part of SCS. The joint distributions of wave heights and wave periods （directions） were studied. The results show a single peak pattern for joint significant wave heights and periods, and a double peak pattern for joint significant wave heights and mean directions. Furthermore, the main wave extreme parameters and directional extreme values, particularly for the 100-year return period, were also investigated. The main extreme values of significant wave heights are larger in the northern part of SCS than in the south- ern part, with the maximum value occurring to the southeast of Hainan Island. The direction of large directional extreme Hs values is focus in E in the northem and middle sea areas of SCS, while the direction of those is focus in N in the southeast sea areas of SCS.

Joint parameter estimation of DOD/DOA/polarization for bistatic MIMO radar

In the paper,polarization-sensitive array is exploited at the receiver of multiple input multiple output （MIMO） radar system,a novel method is proposed for joint estimation of direction of departure （DOD）,direction of arrival （DOA） and polarization parameters for bistatic MIMO radars.A signal model of polarimetric MIMO radar is developed,and the multi-parameter estimation algorithm for target localization is described by exploiting polarization array processing and the invariance property in both transmitter array and receiver array.By making use of polarization diversity techniques,the proposed method has advantages over traditional localization algorithms for bistatic MIMO radar.Simulations show that the performance of DOD and DOA estimation is greatly enhanced when different states of polarization of echoes is fully utilized.Especially,when two targets are closely spaced and cannot be well separated in spatial domain,the estimation resolution of traditional algorithms will be greatly degraded.While the proposed algorithm can work well and achieve high-resolution identification and accurate localization of multiple targets.