Ballistic limit and residual velocity of PELE penetrating against metal target

Based on analyzing the conservation of energy of penetrator with enhanced lateral efficiency （PELE） the penetrating against metal target, a theoretical expression predicting the residual velocity of PELE perforating the target is obtained. By modifying De Marre semi-experience formula,the ballistic limit velocities of PELE penetrating into 2024 aluminum alloy and 45# steel targets are also given. The theoretical predictions fit well with experimental or simulative results.

Tide-induced Lagrangian residual velocity and dynamic analysis based on field observations in the inner Xiangshan Bay,China

In the Xiangshan Bay at the east coast of China,coastal marine pollution is conspicuous and severe in recent years.As transport of the pollutants is closely related to the coastal circulation,there is a great practical significance to investigate the circulation in this area.In this work,the surface pattern and vertical profiles of Lagrangian residual velocity(LRV)were studied based on field observation data from the inner Xiangshan Bay.By tracking GPS-GPRS drifters’trajectories,the surface LRV pattern is going out in the central deep trough and flowing inwards near the shoreside.Combined with data from two mooring stations,vertical profiles of LRV is flowing out at surface and flowing in at the bottom,consistent with the gravitational circulation induced by baroclinic effects at the estuary.However,according to the diagnostic analysis,the main mechanism driving the residual current is barotropic rather than baroclinic.The LRV equation is controlled by the tidally-averaged barotropic pressure gradient force,tidal body force and tidally-averaged turbulent stress,while the tidallyaveraged baroclinic pressure gradient force is one order of magnitude less than other forces.Additionally,the tidally mean eddy viscosity coefficient which is used in the expression of tidally-averaged turbulent stress might be not adequate and requires further studies.

Residual Characteristic of High-Velocity Steel Fragments Penetrating UHMWPE FRP Laminates

The mechanical performance of ultra-high molecular weight polyethylene fiber (UHMWPE) and its composites were proposed. Penetrated properties of different thicknesses UHMWPE FRP laminates (URP) impacted by 3.3g cubic high velocity fragments were studied. According to the ballistic experimental results and theoretical analysis, the linear relation between ballistic limit vBL and area density AD was confirmed. The relative parameters of showing experientially residual velocity vr were expressed by the function of AD. In the end, versatile experiential expression between vr and AD was found. Prediction of vr and vBL using obtained expressions under the above stated condition of impacting URP was consistent with the experimentaled results. Consequently, the two experiential relations can be used to predict the residual velocity and ballistic limit of cubic high velocity fragments impacting URP. The residual characteristic of high-velocity steel fragments penetrating UHMWPE FRP laminates can be more exactly forecasted by the two derived experiential formulas.

On residual velocities in sigma coordinates in narrow tidal channels

In shallow coastal regions where water surface fluctuations are non-negligible compared to the mean water depth,the use of sigma coordinates allows the calculation of residual velocity around the mean water surface level.Theoretical analysis and generic numerical experiments were conducted to understand the physical meaning of the residual velocities at sigma layers in breadth-averaged tidal channels.For shallow water waves,the sigma layers coincide with the water wave surfaces within the water column such that the Stokes velocity and its vertical and horizontal components can be expressed in discrete forms using the sigma velocity.The residual velocity at a sigma layer is the sum of the Eulerian velocity and the vertical component of the Stokes velocity at the mean depth of the sigma layer and,therefore,can be referred to as a semi-Lagrangian residual velocity.Because the vertical component of the Stokes velocity is one order of magnitude smaller than the horizontal component,the sigma residual velocity approximates the Eulerian residual velocity.The residual transport velocity at a sigma layer is the sum of the sigma residual velocity and the horizontal component of the Stokes velocity and approximates the Lagrangian residual velocity in magnitude and direction,but the two residual velocities are not conceptually the same.

A Lagrangian mean theory on coastal sea circulation with inter-tidal transports I.Fundamentals

A brief review is made on the theory of the Lagrangian residual circulation and inter-tidal transports in a convectively weakly nonlinear system. In the review the emphasis is put on the systematical development of the theory and its weakness of convectively weakly nonlinear approximation. The fundamentals of a Lagrangian tidally-averaged theory on circulation with inter-tidal transport processes have been proposed for a general nonlinear coastal/estuarine system. The Lagrangian residual velocity is strictly de- fined, and it has been verified to be able to embody the velocity field of circulation. A new concept of the concentration for inter- tidal transport processes is presented. The concentration describing the inter-tidal transport processes should be a ＂Lagrangian inter-tidal concentration＂ defined and named, but not the Eulcrian tidally-averaged concentration used traditionally. The circulation described here contains a set of infinite temporal-spatial fields of velocity/concentration, each of which corresponds to a specific value of tidal phases varying continuously over one tidal cycle. When the convectively weakly nonlinear condition（ with a smaller order of eddy diffusion and sources） is approximately satisfied, a set of infinite temporal-spatial fields of velocity/concentration can be reduced to a single one.. the mass transport velocity/the Eulerian tidally averaged concentration as exhibited traditionally.

A Lagrangian mean theory on coastal sea circulation with inter-tidal transports Ⅱ. Numerical Experiments

The results of the new concept of coastal sea circulation are demonstrated by numerical simulations for the first time.The numerical experiments in three types of rectangular model seas illustrate the dependence of circulation on tidal phases due to the convectively nonlinear effect which is estimated by a newly defined drift dispersion index.Then,the present theory is applied in the Bohai Sea of China.At the Bohai Straits and the Huanghe River mouth area the circulation direction even reverses owing to different initial tidal phases which shows that the theory copes with nonlinearity well.The calculated M2 tide-induced residual circulation shows that a clockwise gyre exists in the center of an anticlockwise gyre in the central Bohai Sea due to the topographic features.In the Bohai Gulf the tide induced circulation shows a 3D structure with outflow at the surface and the inflow at the bottom which can partly explains the spread of the Huanghe River fresh water out of the Bohai Gulf and the inflow of the sediment from the Huanghe River.

Numerical Study on Inter-Tidal Transports in Coastal Seas

Inter-tidal(subtidal) transport processes in coastal sea depend on the residual motion, turbulent dispersion and relevant sources/sinks. In Feng et al.(2008), an updated Lagrangian inter-tidal transport equation, as well as new concept of Lagrangian in- ter-tidal concentration(LIC), has been proposed for a general nonlinear shallow water system. In the present study, the LIC is nu- merically applied for the first time to passive tracers in idealized settings and salinity in the Bohai Sea, China. Circulation and tracer motion in the three idealized model seas with different topography or coastline, termed as ‘flat-bottom', ‘stairs' and ‘cape' case, re- spectively, are simulated. The dependence of the LIC on initial tidal phase suggests that the nonlinearities in the stairs and cape cases are stronger than that in the flat-bottom case. Therefore, the ‘flat-bottom' case still meets the convectively weakly nonlinear condi- tion. For the Bohai Sea, the simulation results show that most parts of it still meet the weakly nonlinear condition. However, the de- pendence of the LIS(Lagrangian inter-tidal salinity) on initial tidal phase is significant around the southern headland of the Liaodong Peninsula and near the mouth of the Yellow River. The nonlinearity in the former region is mainly related to the complicated coast- lines, and that in the latter region is due to the presence of the estuarine salinity front.

Petal Failure Characteristics of a Conical Projectile Penetrating a Thin Plate at High Oblique Angle

In order to determine the impact depth of a conical projectile impacting a thin plate at high oblique angle, the residual velocity of the projectile after penetrating must be known. Based on the petal failure mode of the conical projectile impacting the thin plate at high oblique angle, the energy consumption mode of the target was determined. During the perforation process, the energy consumption of the target was completed by the saucerization, the power work of the petals, the propagation of radial cracks and petal bending. The energy formula was deduced for each energy dissipation mode and the energy consumed in the impact process was determined. The residual velocity and the ballistic limit velocity of the projectile were deduced by energy conservation principle. Comparison of the analytical results of the residual velocity to the numerical results demonstrates the accuracy and reliability of the analytical formula.