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Abstract—The influence of the bottom on an echo signal from spherical scatterers is studied. The bottom is modeled by a liquid absorbing half-space. The emitter/receiver is located in the aqueous half-space. The distance between the emitter/receiver and scatterer is assumed to be large compared to the acoustic wavelengths in the water and bottom. Numerical results are obtained for acoustically rigid spherical scatterers with the same radius. The interaction between scatterers is not taken into account. The echo signal from one sphere in a wide frequency range is calculated using the method proposed in papers by R.H. Hackman and G.S. Sammelmann, an important step in the implementation of which is calculation of the scattering coefficients of the sphere. To calculate them, the authors use asymptotic formulas obtained with the saddle point method. The resulting asymptotic expressions for the scattering coefficients of the sphere make it possible to significantly reduce the number of terms in the formula for the echo signal form function. [ABSTRACT FROM AUTHOR]

To study the form function and combustion characteristics of partially‐cut stick propellants, this paper derived and established the form function of this complex geometry propellant and analyzed the influence of cutting parameters on the form function. The analysis showed that partially‐cut stick propellants retain the high progressive combustion of multi‐aperture granular propellant, which is proportional to the distance between the notch and inversely proportional to the width of the notch. Based on this, partially‐cut stick propellants with different notches were prepared, and closed vessel tests were conducted. The experimental results showed that the notch had a significant effect on the combustion characteristics of the propellant. When there were notches, the wider the notch, the faster the pressure rise. The pressure in the closed vessel for stick propellants without notches rose the fastest. The burning rate of non‐notched or narrow‐notched fluctuated, while the burning rate of wide‐notched was stable. The dynamic vivacity data showed that the wider the notch, the more stable the change of the burning surface, and the combustion characteristic was closer to the granular propellant. Based on the analysis of form function and combustion characteristics, it is recommended that the notch width be 1 mm and the distance between notches on the same side should be the length of a granular propellant for the double‐base homogeneous 19‐perforated propellant studied in this paper. [ABSTRACT FROM AUTHOR]

Inspection and specificity of the intactness of multi-layer and small-size parts like copper-clad steel rod is a hard task and requires high accuracy. The intactness of these parts is crucial due to their importance. One of the inspection methods for these parts is using ultrasonic waves. The scattering phenomenon occurs when these waves impact curved shape bodies under a special condition. The ultrasonic scattering waves contain a lot of information from the physical conditions and mechanical properties of the part. However, using these waves requires high accuracy and attention due to their complexity. One result of the ultrasonic scattering waves is the far-field backscattered frequency spectrum, form function. For the first time in this research, the form function of a copper-clad steel rod that is immersed in water is calculated using the finite element method (FEM) available in the commercial ABAQUS software. For validating the proposed model, the simulation results are compared with analytical and experimental results in the normalized frequency range of 4 £ Ka £ 10. A good agreement is observed between the three methods at the resonance frequencies, and in the overall form of obtained form function. Furthermore, the effects of the two most common defects in these rods, i.e., the corrosion and interfacial disbond between the clad and steel rod, is studied. Results show that this method can properly specify the corrosion percentage and location, and also the length and location of the interfacial disbond defect.

Mathematical models for the simulation of the operation of various projectile-throwing systems are continuously modified, simultaneously with the development of propellants. For these models, properly determined values of energetic ballistic characteristics of propellants are very important. This paper presents an original test and the results of closed vessel comparative investigations. The study analyses specific combustion characteristics of single-base propellants using conventional black powder ignition, plasma ignition, and gas ignition. The results of the study indicate the need to take into account—in the calculation of the burning rate—not only the dynamics of gas pressure changes but also the real (experimental) form function, which differs from the theoretical one resulting from the assumed geometric burning model. The obtained results allow for a critical analysis of the existing methods used for the determination of values of ballistic characteristics of propellants. Further, it will allow for creating pyrostatic test conditions that would reflect the condition of instantaneous ignition of propellant grains over their entire surface in the most realistic way. [ABSTRACT FROM AUTHOR]

Inspection and specificity of the intactness of multi-layer and small-size parts like copper-clad steel rod is a hard task and requires high accuracy. The intactness of these parts is crucial due to their importance. One of the inspection methods for these parts is using ultrasonic waves. The scattering phenomenon occurs when these waves impact curved shape bodies under a special condition. The ultrasonic scattering waves contain a lot of information from the physical conditions and mechanical properties of the part. However, using these waves requires high accuracy and attention due to their complexity. One result of the ultrasonic scattering waves is the far-field backscattered frequency spectrum, form function. For the first time in this research, the form function of a copper-clad steel rod that is immersed in water is calculated using the finite element method (FEM) available in the commercial ABAQUS software. For validating the proposed model, the simulation results are compared with analytical and experimental results in the normalized frequency range of 4 < Ka < 10. A good agreement is observed between the three methods at the resonance frequencies, and in the overall form of obtained form function. Furthermore, the effects of the two most common defects in these rods, i.e., the corrosion and interfacial disbond between the clad and steel rod, is studied. Results show that this method can properly specify the corrosion percentage and location, and also the length and location of the interfacial disbond defect. [ABSTRACT FROM AUTHOR]

A novel method to determine the health of the industrial parts is using the ultrasound scattering waves. Any changes in the structure of the scattering object or in the boundary conditions will cause a change in the scattering field. The frequency spectrum of the scattering time signal has valuable information, which is studied by resonant ultrasound spectroscopy (RUS). Since any defect, property changes, or changes in boundary conditions can affect the scattering field. Therefore, the possible defects in the piece are detected using the response of the scattering field. One possible defect in the fiber-reinforced composites is the existence of a crack in the matrix or fibers. In the present study, the effect of crack on the far-field backscattering amplitude spectrum is investigated using the finite element method (FEM). To this end, the effect of the crack’s direction in the cylinder and matrix on the form function is scrutinized. The results show that the Rayleigh frequency modes are more sensitive to the cracks existing in the epoxy matrix than the Whispering-gallery frequency modes. Also, the existence of the crack in the aluminum cylinder has the most effect on the Whispering-gallery frequency modes. Besides, the existence of a horizontal crack in the aluminum cylinder leads to a significant reduction in these frequency modes. The validation of the research is determined by comparing the steel cylinder form function obtained from the finite element method’s information and the analytical and experimental form functions in addition to the comparison of the aluminum cylinder form function and reference form function.

Mathematical models for the simulation of the operation of various projectile-throwing systems are continuously modified, simultaneously with the development of propellants. For these models, properly determined values of energetic ballistic characteristics of propellants are very important. This paper presents an original test and the results of closed vessel comparative investigations. The study analyses specific combustion characteristics of single-base propellants using conventional black powder ignition, plasma ignition, and gas ignition. The results of the study indicate the need to take into account—in the calculation of the burning rate—not only the dynamics of gas pressure changes but also the real (experimental) form function, which differs from the theoretical one resulting from the assumed geometric burning model. The obtained results allow for a critical analysis of the existing methods used for the determination of values of ballistic characteristics of propellants. Further, it will allow for creating pyrostatic test conditions that would reflect the condition of instantaneous ignition of propellant grains over their entire surface in the most realistic way.

A novel method to determine the health of the industrial parts is using the ultrasound scattering waves. Any changes in the structure of the scattering object or in the boundary conditions will cause a change in the scattering field. The frequency spectrum of the scattering time signal has valuable information, which is studied by resonant ultrasound spectroscopy (RUS). Since any defect, property changes, or changes in boundary conditions can affect the scattering field. Therefore, the possible defects in the piece are detected using the response of the scattering field. One possible defect in the fiber-reinforced composites is the existence of a crack in the matrix or fibers. In the present study, the effect of crack on the far-field backscattering amplitude spectrum is investigated using the finite element method (FEM). To this end, the effect of the crack's direction in the cylinder and matrix on the form function is scrutinized. The results show that the Rayleigh frequency modes are more sensitive to the cracks existing in the epoxy matrix than the Whispering-gallery frequency modes. Also, the existence of the crack in the aluminum cylinder has the most effect on the Whispering-gallery frequency modes. Besides, the existence of a horizontal crack in the aluminum cylinder leads to a significant reduction in these frequency modes. The validation of the research is determined by comparing the steel cylinder form function obtained from the finite element method's information and the analytical and experimental form functions in addition to the comparison of the aluminum cylinder form function and reference form function. [ABSTRACT FROM AUTHOR]

Corrections of the reactivity values obtained by means of the ORUK (inverse solution of kinetic equations) technique are presented taking into account the changes in the neutron flux form function and the efficiency of neutron detectors when negative reactivity is inserted into the critical multiplying system. The form function and efficiency were assumed to be proportional to the neutron detector signal normalized to the integral functional of neutron flux in the core volume. The ratio of the steady-state normalized signals before and after the insertion of the negative reactivity is the correction factor to the measured value of reactivity. Two approaches to estimation of the correction to the results of reactivity measurements at the critical assemblies of RBMK are considered: the mean measured signal of many in-core detectors or the calculated values of neutron power and spectral projection amplitude of the neutron field are used to normalize and correct the signals of a few detectors. In both the cases, owing to the correction, the spread of the values of reactivity measured by different detectors was multiply reduced as compared with the results of ORUK with integral signals. [ABSTRACT FROM AUTHOR]

In order to investigate the relationship between the slivering point and burning progressivity, a set of 19-perforation propellants containing triethylene glycol dinitrate (TEGDN) with different lengths/outside diameter ratios and perforation diameters was prepared and tested in a closed vessel. The mass fraction of burnt propellant was derived from the recorded pressure-time history of 19-perforation TEGDN propellants in the closed vessel according to the gas state equation and the form function of tested propellants. Based on the form function calculation and the mass fraction of burnt propellant, instantaneous burning surface area and the burning rate were obtained. The influence of length/outside diameter ratios and perforation diameters on the progressive combustion performance is studied through the dynamic vivacity method. With an increase in the length/outsider diameter, the slivering point occurs earlier and the slivering process lasts longer. Further, the burning progressivity of surface area can be improved. For propellants with same length/outside diameter ratio, with a decreasing of perforation diameter, the slivering point lags behind and the burning progressivity becomes greater. The slivering point corresponds to the instantaneous burning area, which is related to the form function and total burning process as well. However, the total burning progressivity of propellant is a very comprehensive result of propellant under multiple actions, including the mass fraction of burnt propellant, grain size and burning rate at different pressure regions. The correlation between them can boost a better understanding on the interaction between grain size, slivering burning process and burning progressivity. [ABSTRACT FROM AUTHOR]

A model to simulate propellant combustion in a closed bomb and a method for burn rate measurement are presented. The model incorporates the 2D ICT-Cellular-Combustion-Algorithm which numerically simulates the 2D form function of an arbitrary shaped propellant cross section. With the help of preprocessing algorithms to calculate initial surface and volume and a lumped parameter model, which also takes into account pressure dependent thermochemistry, pressure vs. time curves and the dynamic vivacity can be simulated. The model is then coupled with different optimization algorithms to minimize an objective function for burn rate measurement with either pressure or vivacity data. Four different optimization algorithms are compared in detail using synthetic pressure-time and dynamic vivacity data of a 7 perforated propellant with and without white noise. The testing shows that the so called Nelder-Mead-Downhill-Simplex algorithm with a vivacity based objective function allows the most precise, robust and computationally cost effective burn rate measurement. Experimental results for 7 perforated JA2 propellant from a 306 cm3 closed bomb are used to determine Vieille′s parameters α and β. The determined values of α=0,9520±0,006319 and β=0,1522±0,007592 mm/s are in good agreement with previously reported values of α=0.9517 and β=0.1467 mm/s. With the presented model and burn rate measurement method it is possible to determine the burning rates of solid propellants with a high degree of accuracy. [ABSTRACT FROM AUTHOR]

By means of the expansion of the nondiffracting beams on plane waves with help of the Whittaker integral, an exact analytical expression of the far-field form function of the scattering of the acoustic and optical nondiffracting Lommel beams propagating in a medium containing spherical particles, considered as rigid and single spheres, is investigated in this work. The form function of the scattering of the high order Bessel beam by a rigid and isolated sphere is deduced, from our finding, as a special case. The effects of the wave number-sphere radius product ( k a ) , the polar angle ( φ ) , the propagation half-cone angle ( β ) and the scattering angle ( θ ) on the far-field form function of the scattered wave have been analyzed and discussed numerically. The numerical results show that the illumination of a rigid sphere by Lommel beams produces asymmetrical scattering. [ABSTRACT FROM AUTHOR]

The description of interior ballistics of guns are given in the paper. The mathematical model is developed for interior ballistic calculation. During the mathematical model development process geometrical properties of propellant are used as the form function. The code of the mathematical model is written in MATLAB ®. 40 mm gun firing results which got from the literature were used in the model verification process. The code solved with the parameters described in the experimental study. Results of the mathematical modal are compared with the firing results. The results showed that the standard deviation of muzzle velocity and maximum pressure in the barrel was less than 4%. Therefore the modal were verified. After verification process cylindrical, single perforated cylindrical and spherical granule shapes' effects on interior ballistics were inspected with the modal. [ABSTRACT FROM AUTHOR]

In this paper, the modeling and study of a new hybrid current controller is presented. It ensures high dynamic response with a fixed-frequency operation mode, a zero static error, and high robustness properties in regard to system parameters variations. To model the proposed nonlinear current controller, different tools are developed. In a first step, a high-frequency average model is proposed. It allows studying the average dynamic properties (bandwidth, time response, and overflow). To investigate the behavior of the current ripple due to the switching effect, a second model, based on the construction of a 3-D bifurcation diagram and the definition of a form function, is established. This model allows studying the nature of the cycle described by the state trajectory and proving that the system operates with a fixed switching frequency. Design rules of the control parameters of this controller are explained and its robustness properties are tested by numerical simulations and validated by experimental tests. [ABSTRACT FROM AUTHOR]

This study treats the interaction of a plane compressional sound wave with a cluster of two fluid-saturated porous elastic cylinders submerged in an unbounded acoustic medium. The novel features of Biot dynamic model for description of poroelastic material behaviour along with the appropriate wave field expansions, the pertinent boundary conditions, and the translational addition theorem for cylindrical wave functions are employed to develop a closed-form solution in the form of infinite series. The theoretical model was extended to consider the case of sound diffraction by a pair of absorbing cylinders with locally reacting or extended reaction boundaries. The analytical results are illustrated with numerical examples in which two identical air-saturated glass wool cylinders are insonified by a plane sound wave at end-on/broadside incidence. The most fundamental acoustic field quantity, namely, the scattering form function amplitude is evaluated and discussed for representative values of the parameters characterizing the system. The effects of incident wave frequency, angle of incidence, and proximity of the two cylinders are examined. Particular attention has been focused on multiple scattering interactions as well as the surface reaction modelling effects. Numerical comparison is made with the case of acoustic diffraction by a pair of absorbing cylinders with locally reacting or extended reaction boundaries. Limiting cases involving two rigid cylinders and also a pair of penetrable (fluid) cylinders are considered and good agreements with well-known solutions are established. [ABSTRACT FROM AUTHOR]

A resonance acoustic spectroscopy technique is assessed for nondestructive evaluation of explosively welded clad rods. Each rod is modeled as a two-layered cylinder with a spring-mass system to represent a thin interfacial layer containing the weld. A range of interfacial profiles is generated in a set of experimental samples by varying the speed of the explosion that drives the copper cladding into the aluminum core. Excellent agreement is achieved between measured and calculated values of the resonant frequencies of the system, through appropriate adjustment of the interfacial mass and spring constants used in the wave scattering calculations. Destructive analysis of the interface in the experimental specimens confirms that key features of the interfacial profile may be inferred from resonance acoustic spectroscopy analysis applied to ultrasonic measurements. [Copyright &y& Elsevier]

Experimental optical bands of the emitting complexes (a gallium vacancy with a donor at the nearest, from the vacancy, sublattice site) VGaSAs and VGaSnGa in GaAs are investigated in a wide temperature range. The parameters of a one coordinate model of these centers are determined. A configuration coordinate diagram of the VGaSAs complex is constructed. Calculation of the field dependences of emission rates is carried out in terms of the parameters of the one coordinate model of the VGaSAs complex and the data obtained are compared with the results of experimental studies of the emission of electron holes from a deep lying center of the VGaSAs complex. [ABSTRACT FROM AUTHOR]

A new form function involving parameters β i is presented. On the basis of the form function, an initial form of tension structure was found by interpolating through the control points on boundary of the structure. The form function can be controlled by changing β i according to the pre-tension and the boundary of the structure. The final form of a tension structure should be an equilibrium system under the pretension. To examine the nature of the initial form, the FEM was used. Many examples show that the initial form gives a very ideal result for equal or unequal pre-tension in two directions of the structure. In general cases, there is little difference between the initial form and the final one. [ABSTRACT FROM AUTHOR]

The fuel pin power is an essential parameter for increasing the safety and reliability features of the reactor. Although the high-order triangle-based polynomial expansion nodal (TPEN) algorithm had been suggested for incredible accuracy and computational speed in hexagonal core analyses, the pin power reconstruction of this algorithm is not developed and assessed. This paper presents the characteristics and performances of the TPEN algorithm for pin power reconstruction. The converged nodal information obtained from sweep between coarse-mesh finite difference (CMFD) and TPEN methods is used to reconstruct the neutron flux distribution in a homogeneous fuel assembly. The modulation technique is used to obtain the heterogeneous distribution of power density. In this technique, the power density homogeneous distribution, calculated with the reconstructed neutron flux is multiplied by a form function. These functions are generated by DRAGON5. The results obtained by this algorithm are verified for various core configurations of a VVER-1000 reactor. The pin power factors show good agreement with the reference solution obtained by heterogeneous fine mesh finite element method. The largest and average relative errors found were of the order of 5% and 0.5% for TPEN, in a peripheral cell of a fuel element with the faces towards the region of the baffle/reflector. We also compared the results with those obtained from the nodal expansion method (NEM). The maximum and mean relative error of 10% and 1% are found by the NEM method. • The TPEN method is used to obtain pin power distribution. • The results of the TPEN and NEM methods is assessed for pin power reconstruction. • The fine mesh finite difference method is used to obtain the reference value. [ABSTRACT FROM AUTHOR]