An analytical model of transducer array arrangement for guided wave excitation and propagation on cylindrical structures

Ultrasonic guided wave (GW) inspection is one of the non-destructive testing (NDT) techniques available for the engineering structures. Compared with other NDT techniques, guided waves can propagate a long distance with a relatively high sensitivity to defects in the structure. In order to increase the performance for pipe inspections to meet higher requirements under different conditions, the optimisation of piezoelectric transducer array design is still a need, as the technique is currently subject to a complex analysis due to wide number of guided wave modes generated. This can be done by optimising the transducer array design. In this paper, it is described an analytical mode of a set of piezoelectric transducer arrays upon torsional wave mode T(0,1) excitation in a tubular structure. The proposed analytical model for predicting signal propagation is validated by using finite element analysis in ABAQUS and three-dimensional laser vibrometer experiments for transducer array characterisations. The proposed analytical model works well and very fast for simulating transducer excitation and wave propagation along cylindrical structures. This will significantly reduce the complexity of guided wave analysis, enhancing effectively the structural health of structures and subsequently reducing the industry maintenance cost

Robust sliding mode design for uncertain stochastic systems based on H∞ control method

The official published version can be found at the link below.In this paper, the design problem of sliding mode control (SMC) is addressed for uncertain stochastic systems modeled by Itô differential equations. There exist the parameter uncertainties in both the state and input matrices, as well as the unmatched external disturbance. The key feature of this work is the integration of SMC method with H∞ technique such that the robust stochastic stability with a prescribed disturbance attenuation level can be achieved. A sufficient condition for the existence of the desired sliding mode controller is obtained via linear matrix inequalities. The reachability of the specified sliding surface is proven. Finally, a numerical simulation example is presented to illustrate the proposed method.This work was funded by The Royal Society of the U.K.;NNSF of China. Grant Numbers: 60674015, 60674089;The Technology Innovation Key Foundation of Shanghai Municipal Education Commission. Grant Number: 09ZZ60;Shanghai Leading Academic Discipline Project. Grant Number: B50

A model to simulate the spreading of oil and gas in underwater oil spills

The rapid growth of offshore oil production and undersea oil delivery pipelines increases the risk of\ud underwater oil spill. In this study, a model based on the Lagrangian particle tracking method is developed to simulate\ud the spreading of oil and gas in an underwater oil spill, which is helpful to estimate the environmental impact and to find\ud effective measures for preventing the spreading of oil. The oil droplets and gas bubbles released from the leakage point\ud are modeled by a large number of representative particles, which are divided into several groups to simulate different\ud components of oil and gas leaked from the underwater blowout. The movement of each particle in one time step\ud includes two components, a mean movement and a random walk. The mean movement is computed by combining the\ud effect of surrounding marine hydrodynamic, the buoyant jet flow near the leakage point and the rise velocity of\ud representative oil droplets or gas bubbles.The random walk method is used to simulate the turbulent diffusion. The\ud compressibility and dissolution of gas are also considered, which play an important role in deepwater. Comparing with\ud the previous models for underwater oil spill based on the integral Lagrangian control volume method, the present model\ud is more flexible in simulating the crude oil which has complex components. The model is validated by several\ud experiment cases and successfully applied to simulate the DeepSpill field expreiment, and good agreement between the\ud calculation and the observation is obtained. The fractionation of different gas bubbles or oil droplets is considered and\ud significant differences in the underwater distribution of oil droplets and gas bubbles with different sizes are clearly\ud shown in the simulated results

Adventitious shoots induction and plant regeneration from cotyledons of watermelon (Citrullus lanatus L.)

A highly efficient regeneration system is a prerequisite step for successful genetic transformation ofwatermelon cultivars (Citrullus lanatus L.). The objective of this study was to establish efficient in vitro plant regeneration for three watermelon cultivars. To achieve optimal conditions for adventitious shoot induction, the 5-day-old explants (cotyledon base portion, apical portion and hypocotyl) of three cultivars were placed on MB5 media supplemented with different concentrations and combinations of growth regulators (1.0 to 10.0 mg L-1 6-benzyladenine (BA) and 0 to 1.0 mg L-1 indole acetic acid (IAA)); the explants from seedling of different development stages (0 to 10 d) were cultured on MB5 medium containing 2.0 mg L-1 BA and 0.2 mg L-1 IAA for investigating the effect of age on adventitious shoots initiation; besides, 5-day-old seedlings were grown on optimal regeneration medium supplemented with different concentrations of kanamycin for screening the lowest lethal concentration for adventitious shoots. The results show that the basal region of cotyledon showed higher frequency of shoot formation (79.17-83.33%) than the apical region (5.23-8.25%); high  percentage of shoots regeneration was induced from 5-day-old cotyledons base portion cultured on MB5 containing 1 or 2 mg L-1 BA; the 100 mg L-1 kanamycin proved to be the optimal concentration for screening the transformants. Our results provide an efficient stable regeneration system for genetic transformation of watermelon.Key words: Watermelon (Citrullus lanatus), cotyledon, growth regulator, kanamycin, regeneration