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The task of modeling and analyzing intercepted multifunction radars (MFRs) pulse trains is vital for cognitive electronic reconnaissance. Existing methodologies predominantly rely on prior information or heavily constrained models, posing challenges for non-cooperative applications. This paper introduces a novel approach to model MFRs using a Bayesian network, where the conditional probability density function is approximated by an autoregressive kernel mixture network (ARKMN). Utilizing the estimated probability density function, a dynamic programming algorithm is proposed for denoising and detecting change points in the intercepted MFRs pulse trains. Simulation results affirm the proposed method's efficacy in modeling MFRs, outperforming the state-of-the-art in pulse train denoising and change point detection.

This paper presents a simple and fast closed-form solution approach for two-dimensional (2D) target localization using range difference (RD) measurements. The formulation of the localization problem is derived using a pentagram array. The target position is determined using passive radar measurements (RDs) between the target and the (N+1=10) receivers’ locations. The method facilitates the problem of target position and can be used as a counter-parallel method for spherical interpolation (SI) and spherical intersection (SX) methods in time difference of arrival (TDOA) and radar systems. The performance of the method is examined in 2D target localization using numerical analysis under the distribution of receivers in the pentagram array. The simulations are conducted using four different far-distance targets and comparatively large-area distributed receivers. The RD measurements were distorted by two different values of Gaussian errors based on ionosphedriec time delays of 20 and 50 nsec owing to the different receivers’ positions. The findings highly verified the validity of the method for addressing the problem of target localization. Additionally, a theoretical accuracy study of the method is given, which solely relies on the RD measurements.

With the growing scarcity of spectrum resources, wideband spectrum sensing is necessary to process a large volume of data at a high sampling rate. For some applications, only second-order statistics are required for spectrum estimation. In this case, a fast power spectrum sensing solution is proposed based on the generalized coprime sampling. The solution involves the inherent structure of the sensing vector to reconstruct the autocorrelation sequence of inputs from sub-Nyquist samples, which requires only parallel Fourier transform and simple multiplication operations. Thus, it takes less time than the state-of-the-art methods while maintaining the same performance, and it achieves higher performance than the existing methods within the same execution time without the need to pre-estimate the number of inputs. Furthermore, the influence of the model mismatch has only a minor impact on the estimation performance, allowing for more efficient use of the spectrum resource in a distributed swarm scenario. Simulation results demonstrate the low complexity in sampling and computation, thus making it a more practical solution for real-time and distributed wideband spectrum sensing applications.

Antenna arrays are used for signal processing in sonar and radar direction of arrival (DOA) estimation. The well-known array geometries used in DOA estimation are uniform linear array (ULA), uniform circular array (UCA), and rectangular grid array (RGA). In these geometries, the neighboring elements are separated by a fixed distance λ/2 (λ is the wavelength), which does not perform well for d greater than λ/2. Uniform rectangular arrays introduce grating lobes, which cause poor DOA estimation performance, especially for wideband sources. Random sampling arrays are sometimes practically not realizable. Periodic geometries require numerous sensors. Based on the minimization of the number of sensors, this paper developed a novel pentagram array to address the problem of DOA estimation of wideband sources. The array has a fixed number of elements with variable element spacing and is abbreviated as (FNEVES), which offers a new idea for array design. In this study, the geometric structure is designed and mathematically analyzed. Also, a DOA signal model is designed based on a spherical radar coordinate system to derive its steering manifold matrix. The DOA estimation performance comparison with ULA and UCA geometries under the multiple signal classification (MUSIC) algorithm using different wideband scenarios is presented. For further investigation, more simulations are realized using the minimum variance distortionless (MVDR) technique (CAPON) and the subtracting signal subspace (SSS) algorithm. Simulation results demonstrate the effectiveness of the proposed geometry compared to its counterparts. In addition, the SSS, through the simulations, provided better results than the MUSIC and CAPON methods.

In this research, a finite element model is established to investigate effective seismic control schemes for a self-anchored suspension bridge (SASB) with three towers. Nonlinear dynamic analyses are conducted to evaluate the seismic performance of SASB with different layout schemes of viscous dampers and buffers, which were installed in longitudinal direction and transversal direction, respectively. The responses of the SASB designed with 10 seismic control schemes are compared to ascertain suitable seismic schemes for SASBs. The results show that the number and location of lateral buffers have an important impact on the dynamic characterization of the SASB, especially for the first lateral mode and lateral fundamental frequency. To effectively increase the seismic performance of SASBs with three towers, mounting buffers between the side towers and the main girder of SASBs is an appropriate scheme. The viscous dampers can effectively decrease the dynamic reaction of the towers and longitudinal deformation of the girder under earthquake excitations. The plan involves the installation of dampers between the main concrete stiffening girder and the side towers as the optimal longitudinal seismic scheme for the SASB. The study offers important insights into the seismic design of SASBs with three towers.

The start-up of a high temperature heat pipe is a complex multi-phase transition and flow heat transfer process, which may result in heat transfer oscillations, causing fluctuations in the heat pipe temperature and thus affecting the operational safety of the reactor. In this study, for the high temperature sodium heat pipe with a length of 1 000 mm and a diameter of 20 mm, the evolution law of the heat transfer oscillation was summarized through start-up experiments under vertical and horizontal conditions. The finite element thermal-mechanical simulation and thermal fatigue program analysis of a localized heat pipe reactor core design with generalized characteristics were carried out, and the stress response and the consequences of fatigue damage induced by heat pipe heat transfer oscillations were investigated. The experimental results show that the change of sodium evaporation rate causes the change of heat pipe pressure under vertical condition, which affects the evaporation and reflux balance of working medium, and causes the oscillation of heat transfer in different characteristics during start-up process. Enhancing the input power will shorten the frequency and decrease the amplitude of the oscillation. When the heat flow density increases from 9 973.71 W/m2 to 12 452.28 W/m2, the temperature oscillation amplitude decreases by nearly 30% and the oscillation period is shortened by about 40%. In the heat transfer oscillation state, the heat pipe will still maintain the heat transfer oscillation when the input power is suddenly reduced, but the waveform changes from a sawtooth shape to a trapezoid shape. The oscillation is obviously suppressed under horizontal condition. Simulation results show that, when the high temperature heat pipe heat transfer oscillation occurs, the thermal fatigue failure risk area of the localized reactor core is the inner wall of the evaporation section of the heat pipe. Fatigue damage is the largest in same-phase oscillation. The average value of the stress increases when the peak temperature difference increases due to the phase difference of oscillation, but because the decrease in the amplitude of stress of different-phase condition, the fatigue damage is reduced compared to the same-phase condition. Considering the effect of the conservatism deviation and creep on the fatigue damage, the thermal fatigue analysis is based on the safety factor K. Fatigue safety analysis results show that when the safety factor K is lower than 1.4 there is almost no risk of fatigue failure. K reaches 1.4 or more fatigue damage is gradually significant. When K=1.6 the fatigue life of the pipe wall material reduces to 3.29 years. This study is of great significance in analyzing the mechanism of heat transfer oscillation of high temperature sodium heat pipe and improving the reliability assessment of heat pipe.

Safe and reliable energy supply is the key foundation for the development of unmanned underwater vehicle (UUV). Unlike land and space missions, underwater missions are more demanding on energy, which requires higher power level, longer operating time, faster response time, and better concealment. Heat pipe cooled reactor has the advantages of large power capacity, simple structure, easy control of reactivity, and rapid thermal response. The solid-state reactor core does not require coolant and relies entirely on heat pipes to dissipate heat, thereby providing good inherent safety, controllability and concealment. Therefore, heat pipe cooled reactor is considered as one of the most promising options for UUV energy supply. In this study, a conceptual design of Nuclear Silent Thermal-Electrical Reactor (NUSTER-100) was proposed to meet the energy requirement of China’s heavy ocean UUV research and development. 109 sodium heat pipes were arranged in the reactor core for passive cooling, and the thermoelectric generators (TEGs) were employed in the reactor to convert fission heat to electric power. A set of heat pipe cooled reactor system-wild mathematical and physical models were established, including core neutron physics model, core channel heat transfer model, heat pipe model, thermoelectric conversion model and cold junction heat transfer mode. Based on the efficient and robust numerical algorithm and modular modeling ideas, heat pipe advanced reactor transient analysis code HEART was developed with independent intellectual property rights, and the key modules of HEART were validated and verified by heat pipe experiment and thermoelectric power experiment. The steady-state, cold-start transient and reactivity insertion transient conditions of NUSTER-100 were calculated and analyzed by HEART, and the full power operation characteristics of NUSTER-100 were obtained. Steady-state performance of the NUSTER-100 indicates that the solid-state core has good temperature flattening ability. The surface temperature of the heat pipe is less than 1 300 K, and the average temperature drop of the TEG module in central channel is 724 K, which can produce an electrical power of 1 207.8 W. Based on the cold-start transient thermal-hydraulic analysis, a three-stage heat pipe cooled reactor start-up scheme with high safety was proposed, and the stability and safety of heat pipe reactor under reactivity insertion transient were evaluated. The results show that the three-stage heat pipe cooled reactor start-up scheme can improve the reactor start-up efficiency. This study can provide support for the development of UUV and heat pipe cooled reactor technology in China.