Impact Dynamics of Supercavitating Projectile with Fluid/Structure Interaction

As supercavitating projectiles move at high speed, the periodic impacts ("tail-slap") on the interior surface of the cavity generally occur due to disturbances. The interactions between the projectile and the water/cavity interface are the sources of structural vibrations, which affect the guidance of the vehicle and undermine the structural reliability. The Fluid/Structure Interaction calculation procedure of the tail-slaps of supercavitating projectile is established, and the dynamic behaviours of the projectile operating in tail-slap conditions with and without considering Fluid/Structure Interaction are obtained and compared. The responses of the projectile riding a reducing cavity are studied, and the effect of Fluid/Structure Interaction is also analyzed. The results show that the angular velocity of projectile increases as the body slowing down, and the amplitude of the elastic displacement response decreases at the beginning and increases when the cavity size is close to the diameter of the tail of projectile. The effect of Fluid/Structure Interaction reduces the amplitudes and frequencies of the impact loads and the vibration responses of the body, and when the speed is higher, the effect is more apparent.

A possible probe to neutron-skin thickness by fragment parallel momentum distribution in projectile fragmentation reactions

Neutron-skin thickness is a key parameter for a neutron-rich nucleus;however,it is difficult to determine.In the framework of the Lanzhou Quantum Molecular Dynamics(LQMD)model,a possible probe for the neutron-skin thickness(δ_(np))of neutron-rich ^(48)Ca was studied in the 140A MeV ^(48)Ca+^(9)Be projectile fragmentation reaction based on the parallel momentum distribution(p∥)of the residual fragments.A Fermi-type density distribution was employed to initiate the neutron density distributions in the LQMD simulations.A combined Gaussian function with different width parameters for the left side(Γ_(L))and the right side(Γ_(R))in the distribution was used to describe the p∥of the residual fragments.Taking neutron-rich sulfur isotopes as examples,Γ_(L) shows a sensitive correlation withδ_(np) of ^(48)Ca,and is proposed as a probe for determining the neutron skin thickness of the projectile nucleus.

Application of system dynamics for assessment of sustainable performance of construction projects

Sustainable performance is expected to become a major factor when examining the feasibility of a construction project in terms of its life cycle performance. The study on which this paper is based developed a simulation model, using system dy- namics methodology, to assess the sustainable performance of projects. Three major factors are used to examine project sus- tainable performance (PSP): the sustainability of economic development (E), the sustainability of social development (S), and the sustainability of environmental development (En). Sustainable development ability (SDA) was used as a prototype to evaluate the degree of sustainable performance. The simulation software ‘ithink’ was used to help with the application of the model to a real life case. This paper explains and demonstrates the procedures used to develop the model and finally offers an approach for assessing the feasibility of a construction project in terms of its sustainable performance.

Experimental study on the penetration effect of ceramics composite projectile on ceramic/A3 steel compound targets

In order to improve the penetration of projectiles into ceramic composite armors,the nose of 30 mm standard projectile was replaced by a toughened ceramic nose,and the performance of ceramic-nose projectiles penetrating into ceramic/A3 steel composite targets has been experimentally researched.According to impact dynamics theory,,the performances of 30 mm ceramic-nose projectile and 30 mm standard projectile penetrating into the ceramic/A3 steel composite targets were analyzed and compared using DOP method,especially focusing on the effects made by different nose structures and materials.The aperture and depth of perforation of projectile into the armor plates as well as the residual mass of bullet core under the same conditions were comparatively analyzed.A numerical simulation was built and computed by ANSYS/LS-DYNA.Based on the simulated results,the penetration performance was further analyzed in terms of the residual mass of bullet core.The results show that the ceramic nose has a great effect on the protection of bullet core.

Microstructure evolution of depleted uranium impacted by steel projectile at velocity of 50m/s

The deformed microstructure evolution of depleted uranium impacted by steel projectile at a velocity of50m/s was investigated by means of confocal laser scanning microscope,electron backscatter diffraction,transmission electron microscope and indenter technique.The experimental results showed that the spherical cap crater was formed in depleted uranium target impacted by steel projectile,and the diameter and depth of the impacted crater were5.45and1.01mm,respectively.From crater rim to deep matrix,four deformed zones were classified,including twin fragmentation zone,high density deformation twin zone,low density deformation twin zone and matrix zone.Twinning was considered as the dominant plastic deformation mechanism of depleted uranium subjected to impact loadings.Besides twinning,the dislocation slipping also played an important role to accommodate the plastic deformation.Finally,the deformed microstructure evolution of depleted uranium under high velocity impact was proposed.

Research on dynamic stabilityrotational speed range of rolling projectiles with different characteristics

Traditional dynamic stability analyses of the rolling projectiles are mainly based on solving the systems＇ transfer functions or angular motion＇ s homogeneous equations to obtain their charac- teristic roots. The solving processes of these methods are complex and lacking further analysis of the results. To solve this problem, Routh stability criterion is introduced to determine the stability of rolling missiles based on the transfer function model, and an important advantage of this method is that it is unnecessary to solve the system＇ s characteristic equation. Rotational speed ranges satisfy- ing the dynamic stability of rolling projectiles with four different characteristics are acquired, and the correctness of analysis results is verified by computing the system＇ s root locus. The analysis results show that the relation between stability and rotational speed for static stable missiles is opposite to that for spin-stabilized projectiles, and the relative size of gyroscopic effect and Magnus effect has an extremely important influence on the trend of the stability of the system with increasing rotational speed.

Topology optimization of reactive material structures for penetrative projectiles

Recently,reactive materials have been developed for penetrative projectiles to improve impact resistance and energy capacity.However,the design of a reactive material structure,involving shape and size,is challenging because of difficulties such as high non-linearity of impact resistance,manufacturing limitations of reactive materials and high expenses of penetration experiments.In this study,a design optimization methodology for the reactive material structure is developed based on the finite element analysis.A finite element model for penetration analysis is introduced to save the expenses of the experiments.Impact resistance is assessed through the analysis,and result is calibrated by comparing with experimental results.Based on the model,topology optimization is introduced to determine shape of the structure.The design variables and constraints of the optimization are proposed considering the manufacturing limitations,and the optimal shape that can be manufactured by cold spraying is determined.Based on the optimal shape,size optimization is introduced to determine the geometric dimensions of the structure.As a result,optimal design of the reactive material structure and steel case of the penetrative projectile,which maximizes the impact resistance,is determined.Using the design process proposed in this study,reactive material structures can be designed considering not only mechanical performances but also manufacturing limitations,with reasonable time and cost.

Rigid elliptical cross-section ogive-nose projectiles penetration into concrete targets

The elliptical cross-section ogive-nose projectile(ECOP) has recently attracted attention because it is well suited to the flattened shape of earth-penetrating weapons. However, the penetration performance of ECOPs has not been completely understood. The objective of this study was to investigate the penetration performance of ECOPs into concrete targets using a theoretical method. A general geometric model of ECOPs was introduced, and closed-form penetration equations were derived according to the dynamic cavity-expansion theory. The model was validated by comparing the predicted penetration depths with test data, and the maximum deviation was 15.8%. The increment in the penetration depth of the ECOP was evaluated using the proposed model, and the effect of the majoreminor axis ratio on the increment was examined. Additionally, the mechanism of the penetration-depth increment was investigated with respect to the caliber radius head, axial stress, and resistance.

Modified spherical cavity-expansion model for projectile penetration into concrete targets

A modified spherical cavity-expansion model is developed in this paper.(1) We introduce a piecewise hyperbolic yield criterion suitable for pressure less than fc/3 to describe the mechanical behavior in the elastic region for the elastic-plastic response and modify the crack occurrence condition for the elastic-cracked-plastic response.(2) The hyperbolic yield criterion and a piecewise equation of state (EOS) are adopted for a better description of the plastic behavior of concrete material. Then, the modified model is validated by several projectile penetration tests in both the normal strength concrete (NSC) and ultra-high performance cement-based composite (UHPCC) targets. Finally, the hydrostatic pressure of the targets under rigid ogive-nosed projectile penetrations is found to be nearly within (0, 1.6 GPa), which usually exceeds the range that the shear strength-pressure test data covered. The influence of yield criterion on depth of penetration is discussed and it is recommended that the pressure should arrive at least 400 MPa in the related triaxial compression tests.

A review of dual-spin projectile stability

This paper gives a succinct review of dual-spinprojectile stability and some technologies relating to them.It describes how the traditional stability factors from linear projectile theory are modified to better describe a controlled dual-spin projectile.Finally,it reviews works which have investigated how different aspects of a controlled dual-spin design can affect flight stability,primarily airframe structure and canard properties.A conclusion is given,highlighting important guidelines from the enclosed discussions.

Three-dimensional coordinates test method with uncertain projectile proximity explosion position based on dynamic seven photoelectric detection screen

To objectively obtain the three-dimensional coordinates of the projectile fuze proximity explosion when projectile intersects the head of missile target, we propose a dynamic seven photoelectric detection screen test method, which is made up of six plane detection screens and a flash photoelectric dynamic detection screen. The three-dimensional coordinates calculation model of the projectile proximity explosion position based on seven plane detection screens with dynamic characteristics is established.According to the relation of the dynamic seven photoelectric detection screen planes and the time values,the analytical function of the projectile proximity explosion position parameters under non-linear motion is derived. The projectile signal filtering method based on discrete wavelet transform is explored in this work. Additionally, the projectile signal recognition algorithm using an improved particle swarm is proposed. Based on the characteristics of the time duration and the signal peak error for the projectile passing through the detection screen, the signals attribution of the same projectile passing through six detection screens are analyzed for obtaining precise time values of the same projectile passing through the detection screens. On the basis of the projectile fuze proximity explosion test, the linear motion model and the proposed non-linear motion model are used to calculate and compare the same group of projectiles proximity explosion position parameters. The comparison of test results verifies that the proposed test method and calculation model in this work accurately obtain the actual projectile proximity explosion position parameters.

Symmetry breaking in the opinion dynamics of a multi-group project organization

A bounded confidence model of opinion dynamics in multi-group projects is presented in which each group＇s opinion evolution is driven by two types of forces：（i） the group＇s cohesive force which tends to restore the opinion back towards the initial status because of its company culture;and（ii） nonlinear coupling forces with other groups which attempt to bring opinions closer due to collaboration willingness.Bifurcation analysis for the case of a two-group project shows a cusp catastrophe phenomenon and three distinctive evolutionary regimes,i.e.,a deadlock regime,a convergence regime,and a bifurcation regime in opinion dynamics.The critical value of initial discord between the two groups is derived to discriminate which regime the opinion evolution belongs to.In the case of a three-group project with a symmetric social network,both bifurcation analysis and simulation results demonstrate that if each pair has a high initial discord,instead of symmetrically converging to consensus with the increase of coupling scale as expected by Gabbay＇s result（Physica A 378（2007） p.125 Fig.5）,project organization（PO） may be split into two distinct clusters because of the symmetry breaking phenomenon caused by pitchfork bifurcations,which urges that apart from divergence in participants＇ interests,nonlinear interaction can also make conflict inevitable in the PO.The effects of two asymmetric level parameters are tested in order to explore the ways of inducing dominant opinion in the whole PO.It is found that the strong influence imposed by a leader group with firm faith on the flexible and open minded follower groups can promote the formation of a positive dominant opinion in the PO.

Perforation studies of concrete panel under high velocity projectile impact based on an improved dynamic constitutive model

The finite-depth concrete panels have been widely applied in the protective structures,and its impact resistance and dynamic fracture failures,especially the scabbing/perforation limits,under high velocity projectile impact,are mainly concerned by protective engineers,which are numerically studied based on an improved dynamic concrete model in this study.Firstly,based on the framework of the KCC(Karagozian&Case concrete)model,a dynamic concrete model is proposed which considers an independent tensile damage model and a continued transition between dynamic tensile and compressive properties.Secondly,the strength surface,equation of state and damage parameters of the proposed model are comprehensively calibrated by a triaxial compressive test with high confinement pressure,the rationality of which is further verified based on the single element tests,e.g.,uniaxial and triaxial compression as well as uniaxial,biaxial and triaxial tension.Thirdly,a series of projectile high velocity impact tests on thin and thick concrete panels are simulated,which indicates that the projectile residual velocity and dynamic fracture failures are reproduced satisfactorily,while the KCC model underestimates both the spalling and scabbing dimensions severely.Finally,based on the validated concrete model and finite element analyses approach,the validations of the existing five empirical formulae are evaluated,in terms of the depth of penetration(DOP)and scabbing/perforation limits of concrete panel.Both the Army corps of engineers(ACE)and modified National Defense Research Committee(NDRC)formulae are recommended in the design of the protective structure to avoid scabbing failure.

Symmetry breaking in the opinion dynamics of a multi-group project organization

A bounded confidence model of opinion dynamics in multi-group projects is presented in which each group’s opinion evolution is driven by two types of forces:(i) the group’s cohesive force which tends to restore the opinion back towards the initial status because of its company culture;and(ii) nonlinear coupling forces with other groups which attempt to bring opinions closer due to collaboration willingness.Bifurcation analysis for the case of a two-group project shows a cusp catastrophe phenomenon and three distinctive evolutionary regimes,i.e.,a deadlock regime,a convergence regime,and a bifurcation regime in opinion dynamics.The critical value of initial discord between the two groups is derived to discriminate which regime the opinion evolution belongs to.In the case of a three-group project with a symmetric social network,both bifurcation analysis and simulation results demonstrate that if each pair has a high initial discord,instead of symmetrically converging to consensus with the increase of coupling scale as expected by Gabbay’s result(Physica A 378(2007) p.125 Fig.5),project organization(PO) may be split into two distinct clusters because of the symmetry breaking phenomenon caused by pitchfork bifurcations,which urges that apart from divergence in participants’ interests,nonlinear interaction can also make conflict inevitable in the PO.The effects of two asymmetric level parameters are tested in order to explore the ways of inducing dominant opinion in the whole PO.It is found that the strong influence imposed by a leader group with firm faith on the flexible and open minded follower groups can promote the formation of a positive dominant opinion in the PO.

A system dynamics model for billion trees tsunami afforestation project of Khyber Pakhtunkhwa in Pakistan:Model application to afforestation activities

As part of the global effort to plant billion trees,an afforestation project is launched in Pakistan in Khyber Pakhtunkhwa(KP)province to conserve existing forests and to increase area under forest cover.The present study is designed to build a Systems'model by incorporating major activities of the Billion Tree Tsunami Afforestation Project(BTTAP)with special focus on afforestation activities to estimate the growth in forest area of KP.Availability of complete dataset was a challenge.To fix the model,the raw data taken from the project office has been utilized.Planning Commission Form 1-Phase I&II helped us with additional information.We relied on the data available for one and half period of the project as rest of the data is subject to the completion of the project.Our results show that the project target to enhance area under forest differs from the target to afforest area under the project.The system dynamics'model projection shows that the forest area of KP would be 23.59 million hectares at the end of the BTTA project,thus having an increase of 3.29%instead of 2%that has been initially proposed.However,the results show that the progress to meet the target in some afforestation classes is slow as compared to other categories.Farm forestry,plantation on communal lands and owners'plantation need special focus of the authority.Deforestation would affect 0.02 million hectares area of the project.The model under study may be used as a reference model that can be replicated to other areas where billion tree campaigns are going on.

Dynamic analysis of a guided projectile during engraving process

The reliability of the electronic components inside a guided projectile is highly affected by the launch dynamics of guided projectile.The engraving process plays a crucial role on determining the ballistic performance and projectile stability.This paper analyzes the dynamic response of a guided projectile during the engraving process.By considering the projectile center of gravity moving during the engraving process,a dynamics model is established with the coupling of interior ballistic equations.The results detail the stress situation of a guided projectile band during its engraving process.Meanwhile,the axial dynamic response of projectile in the several milliseconds following the engraving process is also researched.To further explore how the different performance of the engraving band can affect the dynamics of guided projectile,this paper focuses on these two aspects:(a) the effects caused by the different band geometry;and(b) the effects caused by different band materials.The time domain and frequency domain responses show that the dynamics of the projectile are quite sensitive to the engraving band width.A material with a small modulus of elasticity is more stable than one with a high modulus of elasticity.

Flow Field Characteristics for Parachute-projectile System

In the current research for parachute flow field nowadays,the size of parachutes in previous research are so large compared with their carriers that the effects of the carriers wake flow to parachute are always neglected.Different from such large parachutes,the parachute size in this paper is on the same magnitude with the carrier,thus,the carrier can obviously affect the parachute flow field.In this paper,flow field characteristics of small parachute for projectile decelerating are researched through two approaches,namely,computational fluid dynamics（CFD） simulation and wind tunnel tests.Three parachutes with various sizes are chosen for study.Firstly,the CFD simulation of flow field around these parachutes is carried out,and then the CFD simulation of parachute-projectile systems is executed.According to the simulation results,the phenomenon is observed that in the simulations of parachutes there are two vortex-rings at the wind shadow of parachutes,however,in the second simulations of parachute-projectile systems,two additional vortex-rings emerge inside the parachutes.Due to these two inner vortex-rings,the pressure inside parachutes decreases.As a result,the drag of parachute in simulation of parachute-projectile systems is about 20% smaller compared with the prior one.In order to verify the numerical results of CFD simulations,wind tunnel tests are employed.In terms of the data of the wind tunnel tests,the CFD simulation for flow field characteristics is reasonable and feasible.The results of both CFD simulation and wind tunnel tests demonstrated the influence of projectile wake flow to parachute drag can not be neglected if the parachute size is on the same magnitude with projectile.The influence to parachute drag from the ratio of projectile diameter to parachute diameter is also analyzed both in CFD simulations and wind tunnel tests.The approach combined CFD simulation and wind tunnel tests proposed can be used to guide the design of such parachute whose size is on the same magnitude with carrier.

A note on hydrodynamics from dissipative particle dynamics

We calculate current correlation functions （CCFs） of dissipative particle dy- namics （DPD） and compare them with results of molecular dynamics （MD） and solutions of linearized hydrodynamic equations. In particular, we consider three versions of DPD, the empirical/classical DPD, coarse-grained （CG） DPD with radial-direction interactions only and full （radial, transversal, and rotational） interactions between particles. To fa- cilitate quantitative discussions, we consider specifically a star-polymer melt system at a moderate density. For bonded molecules, it is straightforward to define the CG variables and to further derive CG force fields for DPD within the framework of the Mori-Zwanzig formalism. For both transversal and longitudinal current correlation functions （TCCFs and LCCFs）, we observe that results of MD, DPD, and hydrodynamic solutions agree with each other at the continuum limit. Below the continuum limit to certain length scales, results of MD deviate significantly from hydrodynamic solutions, whereas results of both empirical and CG DPD resemble those of MD. This indicates that the DPD method with Markovian force laws possibly has a larger applicability than the continuum description of a Newtonian fluid. This is worth being explored further to represent gen- eralized hydrodynamics.

A process monitoring method for autoregressive-dynamic inner total latent structure projection

As a dynamic projection to latent structures(PLS)method with a good output prediction ability,dynamic inner PLS(DiPLS)is widely used in the prediction of key performance indi-cators.However,due to the oblique decomposition of the input space by DiPLS,there are false alarms in the actual industrial process during fault detection.To address the above problems,a dynamic modeling method based on autoregressive-dynamic inner total PLS(AR-DiTPLS)is proposed.The method first uses the regression relation matrix to decompose the input space orthogonally,which reduces useless information for the predic-tion output in the quality-related dynamic subspace.Then,a vector autoregressive model(VAR)is constructed for the predic-tion score to separate dynamic information and static informa-tion.Based on the VAR model,appropriate statistical indicators are further constructed for online monitoring,which reduces the occurrence of false alarms.The effectiveness of the method is verified by a Tennessee-Eastman industrial simulation process and a three-phase flow system.

EXPERIMENTAL AND THEORETICAL STUDY ON THE HIGH-SPEED HORIZONTAL WATER ENTRY BEHAVIORS OF CYLINDRICAL PROJECTILES

In this article,the horizontal water-entry of flat-nose projectiles of two different lengths at impact velocities of 400 m/s-600 m/s is studied experimentally and theoretically.Based on the solution of the Rayleigh-Besant problem,a set of projectile dynamic equations are derived and a cavity model is built to describe the projectile＇s water entry dynamics.A parameter in the cavity model is determined by employing the principle of energy conservation.The results indicate that the flat-nose projectiles enjoy a good stability of trajectory,the drag coefficient and the velocity decay coefficient are dependent on the cavitation number,and increase along the penetration distance but with a relatively small variation.The maximum cavity radius decreases monotonically with the penetration distance.Projectiles with the same nose shapes at different initial velocities have a basically consistent cavity dimension before the deep pinching off phenomenon occurs.Good agreements are observed between results obtained by the analytical model and the experimental results.