Numerical simulation on truncated oval-nosed projectile penetrating into stiffened plate北大核心CSCD

[Objectives]In this paper, the numerical simulation method is used to study the anti-penetration performance and energy absorption mode of a stiffened plate, as well as the influence of different stiffened bars on the flight attitude of the projectile body.[Methods] Finite element software LS-DYNA is used to simulate the process of a truncated oval-nosed projectile penetrating a stiffened plate, and the results of the numerical simulation are compared with an experiment to verify the reliability of the numerical simulation method. The momentum method and mass equivalence method are used to predict the residual velocity of the projectile, and the applicability of different theoretical methods within different velocity ranges is compared. The deformation energy of different regions of the stiffened plate is then extracted to analyze the influence of the initial velocity of the projectile body on the energy absorption mode of the target plate. Finally, the structure of the stiffeners is changed and the influence of the relative position of the stiffeners on the penetration attitude of the projectile body is analyzed.[Results]The results show that the mass equivalence method is more accurate than the momentum method in predicting the residual velocity of the stiffened plate when the initial velocity of the projectile body is in the range of 300–900 m/s. The ratio of the deformation energy of the stiffened plate to the energy loss of the projectile body decreases with the increase of the initial velocity of the projectile body. The effect of a T-stiffened plate on trajectory is greater than that of a rectangular-stiffened plate.[Conclusions]The related calculation method and research results have certain reference value for research and engineering application surrounding the anti-penetration of stiffened plates. © 2023 Chinese Journal of Ship Research. All rights reserved.     

襄阳汉江沉管隧道设计关键技术北大核心CSCD

基于襄阳汉江沉管隧道的工程设计实践,针对该隧道强冲刷、强透水地层深厚、防洪要求高等特点,对隧道平纵布置、管节及接头止水结构、干坞选型及结构、沉管基础及回填、沉管最终接头及对接端止水结构等进行了研究。结果表明:(1)内河沉管隧道采用长距离双轴线干坞布置方式,通过格形地下连续墙、超深落底式帷幕、地下连续墙预应力锚索垂直支护和混凝土封底组合技术解决了强透水地层深基坑支护及隔水难题;(2)采用全断面顺浇技术进行整体式管节预制,实现了管节接头止水设施的全国产化;(3)在内河沉管隧道采用高精度浮式整平先铺卵石基础,并提出了强冲刷区管顶防冲保护解决方案;(4)采用了不设独立止推构造的陆域最终接头,并针对工程需求设置了大直径锁口钢管桩配合外侧止水墙的对接端支护结构及分片整体吊装双壁钢围堰二次止水结构。     

Aspects of the stability of jack-up spud-can foundations

A three-level procedure for assessing jack-up foundation stability for more or less homogenous soils is described. The objective is to provide a rational framework for these assessments that ensures their safe operation in extended year-round operations and enables their use in deeper waters than at present.

The three levels of the procedure have to be entered successively as long as foundation stability cannot be proven. The first level is a screening exercise and essentially replaces the well-known preload check. The second level compares factored foundation loads resulting from a structural analysis with foundation capacities obtained with ultimate bearing capacity formulae. The most refined third level assesses whether the displacements associated with these loads lead to an acceptable situation, i.e. capacity increase and/or load redistribution that does not result in collapse of the jack-up unit.

Since, for maximum benefit, this third-stage analysis requires a non-linear foundation model to be linked with the structural package used: such a tool is provided in the paper. Examples are given to demonstrate the impact of the assessment procedure.

This procedure forms part of the overall in-house approach to the assessment of jack-ups and has already been offered to the jack-up industry as part of the continuing efforts towards establishing common and accepted standards for jack-up assessments. Further developments have been identified and will be pursued.     

A repeated cross-sectional evaluation of car ownership

This paper studies changes in the relationship between household car ownership and income by household type. Ordered response probit models of car ownership are estimated for a sample of households repeatedly at six time points to track the evolution of income elasticities of car ownership over time. Elasticities of car ownership are found to change over time, questioning the existence of a unique equilibrium point between demand and supply that is implicitly assumed in traditional cross-sectional discrete choice car ownership models. Moreover, different household types and households that underwent household type transitions showed differing patterns of change in elasticities. Observed trends in car ownership and income clearly show behavioral asymmetry where the elasticity of procuring an additional car is greater than that of disposing a car. This too shows the inadequacy of traditional cross-sectional models of car ownership which tend to predict symmetry in behavior. The study suggests the importance of incorporating dynamic trends into the forecasting process, which can be accomplished through the use of longitudinal data.     

New lead-acid battery management system based on generator regulation

A novel regulation system for a vehicle generator and lead-acid battery is proposed in this paper. By integrating the regulation method, the output voltage of the generator is determined and controlled by the algorithm to save electrical energy and protect the lead-acid battery. The regulation algorithm is implemented in Matlab/Simulink, and the logic function of the system is verified using the dSPACE/AutoBox workbench. The experimental results show that the new algorithm improves the performance of the fuel economy of the vehicle and the battery state-of-health compared to the traditional control method.     

Wheel/Rail Contact: Geometrical Study*

Before trying to ascertain the precise nature of the Wheel-Rail contact (internal stresses and strains, wear and friction, security against a derailment, dynamic behaviour of the vehicle, etc.) the geometrical problem must necessarily be solved. That is, for each position of the wheelset (this is defined by 6 parameters, of which only 4 are independent) the two dependent parameters and the coordinates of the points of contact of each wheel, and rail must be obtained. A new method is proposed of obtaining the spatial position of a wheelset with reference to the rails, from the most general point of view.     

Preview Control Algorithms for the Active Suspension of an Off-Road Vehicle

The potential performance improvement using preview control for active vehicle suspension was first recognized in the late nineteen sixties. All work done since that time has been based on optimal control theory using simple vehicle models.

In this article, the performance of quarter vehicle preview controllers when applied to a real off-road vehicle is simulated using both two degree of freedom quarter and ten degree of freedom full vehicle models. The results, which are compared with non-preview active and conventional passive suspensions, confirm that preview control reduces vertical acceleration of the body centre of gravity, which results in improved ride quality. Further, reductions in pitch and roll motion result from smaller vertical displacements of the vehicle quarters. Coupling between quarters, through the vehicle body, appears to have a smoothing effect on the control.

As an alternative to optimal control theory based controllers, a simple ad hoc preview controller based on isolating the vehicle body from dynamic loads transmitted through the suspension is proposed. Simulation results show that such a controller outperforms the optimal control theory based controllers over small discrete disturbances but responds poorly to disturbances encountered from other than steady state.     

Effect on friction of engine oil seal with engine oil viscosity

Low viscosity engine oil can improve a vehicle’s fuel economy by decreasing the friction between the engine components. Frictional torque varies with the velocity change due to different viscosity characteristics of SAE grade 5W-20, 5W-30 and 5W-40 engine oils. The viscosity for each of these grades was measured to outline the effect low viscosity engine oils have on engine friction, which may lead to improved fuel economy. Engine oil seal frictional torque increases with the shaft rotational speed for all three engine oil grades. A decrease in engine oil seal frictional torque was confirmed when low viscosity engine oil was used. Also, the leak-free performance of the engine oil with the seal satisfied the life limit durability test criteria. Thus, low viscosity engine oil may be used to improve fuel economy by decreasing the frictional loss of the engine oil seal while having no negative impact on performance due to leak-free functioning.     

Parameter identification for a LuGre model based on steady-state tire conditions

The purpose of this study was to effectively identify parameters for a LuGre friction model based on experimental measures. In earlier work related to this study (Yang et al., 2009), which was based on the characters of polygonal wear (Sueoka and Ryu, 1997), we showed a frictional vibration model for a mass on a moving belt. This model reflected lateral vibrations caused by velocity and toe-in angle. An important aspect of the present study is the improved friction model. A previous friction model, which divided the process into four parts, expressed the sable excited vibration well but failed to reflect the hysteresis loop change when vehicles accelerated or decelerated continuously. A LuGre friction model can solve this problem, but several model parameters must be obtained experimentally. We measured contact width and length of tires as vertical pressure changed; this provided a theoretical basis for apparent stiffness of a unit of tire tread. Based on tire data from Bakker E’s article in a SAE paper from 1987, we identified the Stribeck exponent and Stribeck velocity in LuGre. Then, the results were implemented in a vibration system that verified the rationality of the data.