Damping Of Shock Waves Research Articles

Model predictive control policy design, solutions, and stability analysis for longitudinal vehicle control considering shockwave damping

Longitudinal vehicle control models, such as Adaptive Cruise Control (ACC) and Cooperative Adaptive Cruise Control (CACC), have been the core component of many Automated Driving Systems (ADS) or Advanced Driver Assistance System (ADAS). ACC and CACC systems make vehicles drive with faster reaction time and smaller following distance than manual vehicles, alleviating the congestions and attenuating traffic disturbances. Many existing ACC and CACC control models focus on three strategies that can indirectly mitigate congestions and damp traffic shockwaves: time headway suppression, stability improvement, and adaptive mode-switching control based on traffic conditions. Although congestion mitigation and shockwave damping are achievable with those control strategies, the improvement is often limited to the by-product effect of their main control objectives of headway suppression and system stability. Many adaptive models also need to calibrate many parameters for different road conditions.This paper proposes a new ACC and CACC framework that directly integrates the congestion shockwave damping and traffic congestion mitigation into the objective function of a dynamic control framework. A Model Predictive Control (MPC) based dynamic optimization framework is proposed to balance the trade-offs among multiple objectives, including safety, efficiency, shockwave, elasticity, and driver’s comfort. The proposed framework is applied in both ACC and CACC platoons mixed with manual vehicles, and five different control models are explored. The stability conditions of the proposed models are derived analytically and analyzed numerically. Three experimental studies, including platoon, ring-road, and traffic simulation studies, indicate promising results of proposed models in reducing shockwave propagation speed and mitigating traffic congestion under different environments compared with existing ACC and CACC models.

Effect of Unit Cell Height on the Ballistic Performance of the Body-Centered Lattice Structures

Lattice structures, produced by metal additive manufacturing technology, can be a potential alternative in armor applications, which are important parts of defense technologies due to their shock wave damping, energy absorption and light-weight properties. Despite the fact that the protection of metal lattice structures against explosives has been frequently investigated in the literature, their perforation performance is rarely studied. In this research, numerical ballistic penetration tests were carried out with Johnson-Cook strength and failure model parameters by using LS-DYNA software. AlSi10Mg alloy was chosen as a lattice material, which has high energy absorption ability. Both width and length were chosen as 4 mm for the body-centered lattice structure, while eight different cell height (3, 4, 5, 6, 7, 8, 9 and 15 mm) were used as unit cell parameters. The results show that the ballistic performance of lattice structures could be improved by optimizing the unit cell height for the body-centered lattice structures.

Проблема надійності водопровідних мереж на прикладі міста Кропивницького

The article presents the analysis of statistical data of the causes of breakages and leaks in water pipes of the distribution network of Kropyvnytskyi. Breakage statistics for pipelines with a diameter of 25 to 1100 mm during the last five years were calculated. As a result of segmental analysis, it was found that the main types of damage to the pipes of water supply system are through fistulas of steel pipes – 54.4% and corrosion – 25.6%; loss of integrity of cast iron pipes on joints – 9.7%, fractures and cracks of cast iron pipes – 6.1%; fractures in joints of polyethylene pipes and other damages – 4.2%. To characterize the reliability of the municipal water supply networks, the pipeline failure flow parameter ω was used. It was defined as the ratio of the number of failures of the water supply network section to the observation period and the length of pipe network sections of the corresponding diameter. The calculation of interval estimates for the failure rate parameter ωо for steel and cast iron pipes of the water distribution network of Kropyvnytskyi was carried out. According to the operational organization 84% of the network was laid using these pipes and analytical expressions were obtained to determine average values of ω0ср depending on their diameter. Significantly higher values of ω0ср were noted in comparison with similar ones given in the literature for other cities, which can be explained by a significant excess of the standard service life of 85% of steel and 50% of cast iron pipes in the water supply network of Kropyvnytskyi. To increase the reliability of water supply networks, it is recommended to implement the experience of European countries and replace 2% of the network per year and use polyethylene pipes. To reduce the failure factor of water supply networks, particularly in those areas where overtime pipes are used, the expediency of partial installation of water-air dampers for pressure fluctuations directly in the pipeline, in which there is a gradual and complete damping of the shock wave. Approbation of a prototype of a hydraulic shock absorber of this design was carried out in the hydraulics laboratory at Central Ukrainian National Technical University and its efficiency and high efficiency at full shock wave damping was confirmed.

Experimental and numerical optimization study of shock wave damping in aluminum panel sandwich

Sandwich panels with polymer composite and light core composites are widely used in aircraft and spacecraft, vessels, trains, submarines, and cars. Due to their high strength to weight ratio, high stability, and high corrosion resistance, these structures have become particularly important in the industry. Reduction in impact energy, shock waves, and noise in many industries, including the automotive and military industries. Porous materials have always been the focus of attention due to their shock-reducing effects in various protective applications. For this reason, the study of physics governing shock propagation problems in porous media is of particular importance, and the complexity of the governing equations also results in the numerical solution of these equations with many computational problems and costs. In this paper, shock wave damping is investigated numerically and experimentally in aluminum blocks with porous grains scattered inside aluminum. The deformations of the specimens in numerical simulation and experimental testing have been compared. The results show that this material behaves similarly to the aluminum foam in both static loadings (practical pressure testing) and dynamic loading (explosion simulation) results, again similar to aluminum foam.

Nitinol Spinal Vertebrae: A Favorable New Substitute

Scoliosis, kyphosis, and bone fracture are health problems, especially of the elderly throughout the world. The vertebra protects the spinal cord. Any impairment to the vertebra can lead to pain and nervousness. Ni-Ti alloy (Nitinol) helps to resolve the problem by fulfilling such requirements as for strength, durability, resistance to wear, and shockwave damping which is due to the shape memory effect. Nitinol medical applications have so far been restricted to surgical devices and orthopaedics. Little has been said about Nitinol use for medication of the spinal vertebra disorder. This article appraises the potential features of Nitinol for vertebral implantation and therapeutic prescription consistent with the specific anatomical variation. Staples, screws, cages, stents, and posterior-stabilizers made of Nitinol have passed in-vitro tests and in some cases in-vivo examinations. Using anatomically tailored Nitinol for treatment and administration of the damaged vertebra is proposed as a forecastable dream.

Blast Waves in Multi-Component Medium with Thermal Relaxation

The mathematical models of relaxing media with a structure for describing nonlinear long-wave processes are explored. The wave processes in non-equilibrium heterogeneous media are studied in terms of the suggested asymptotic averaged model. On the microstructure level of the medium, the dynamical behavior is governed only by the laws of thermodynamics, while, on the macrolevel, the motion of the medium can be described by the wave-dynamical laws. It is proved rigorously that on the acoustic level, the propagation of long waves can be properly described only in terms of dispersive dissipative properties of the medium, and in this case, the dynamical behavior of the medium can be modeled by a homogeneous relaxing medium. At the same time, the dynamical behavior of the medium cannot be modeled by a homogeneous medium even for long waves, if they are nonlinear. For a finite-amplitude wave, the structure of medium produces nonlinear effects even if the individual components of the medium are described by a linear law. The heterogeneity of the structure of medium always introduces additional nonlinearity. It is shown that the solution of many problems for multi-component media with incompressible phases can be obtained through the known solution of a similar problem for a homogeneous compressible medium by means of the suggested transformation. It is not necessary to solve directly the problem for the medium with incompressible component, and it is sufficient just to transform the known solution of the similar problem for a homogeneous medium. The scope for the suggested transformation is demonstrated by the reference to the strong explosion state in a two-phase medium. The special attention is focused on the research of blast waves in multi-component media with thermal relaxation. The dependence of the shock damping parameters on the thermal relaxation time is analyzed in order to provide a deeper understanding of the damping of shock waves in such media and to determine their effectiveness as localizing media. This problem attracts the interest also in view of the practical possibility to estimate the efficiency of medium for damping the shock wave action. To find the nature of the relaxation interaction between the components of medium and to estimate the attenuation of shock waves generated by solid explosives, we have studied experimentally both the velocity field of shock waves and the pressure at front in an air foam. The comparison of experimental and theoretical investigations of the relaxation phenomena which accompany the propagation of shock waves in foam indicates that within the scope of relaxation hydrodynamics it is possible to explain the observed phenomena and estimate the efficiency of medium as localizer of the shock wave action.

Modelling the Propagation of a Weak Fast-Mode MHD Shock Wave near a 2D Magnetic Null Point Using Nonlinear Geometrical Acoustics

We present the results of analytical modelling of fast-mode magnetohydrodynamic wave propagation near a 2D magnetic null point. We consider both a linear wave and a weak shock and analyse their behaviour in cold and warm plasmas. We apply the nonlinear geometrical acoustics method based on the Wentzel-Kramers-Brillouin approximation. We calculate the wave amplitude, using the ray approximation and the laws of solitary shock wave damping. We find that a complex caustic is formed around the null point. Plasma heating is distributed in space and occurs at a caustic as well as near the null point due to substantial nonlinear damping of the shock wave. The shock wave passes through the null point even in a cold plasma. The complex shape of the wave front can be explained by the caustic pattern.

Solution of the Boltzmann equation for unsteady flows with shock waves in narrow channels

Unsteady rarefied gas flows in narrow channels accompanied by shock wave formation and propagation were studied by solving the Boltzmann kinetic equation. The formation of a shock wave from an initial discontinuity of gas parameters, its propagation, damping, and reflection from the channel end face were analyzed. The Boltzmann equation was solved using finite differences. The collision integral was calculated on a fixed velocity grid by a conservative projection method. A detector of shock wave position was developed to keep track of the wave front. Parallel computations were implemented on a cluster of computers with the use of the MPI technology. Plots of shock wave damping and detailed flow fields are presented.

Deep Impactmission to Tempel 1 favours New Explosive Cosmogony of comets

The assumption that short-period (SP) comets are fragments of massive icy envelopes of Ganymede-like bodies saturated by products of ice electrolysis that underwent global explosions provides a plausible explanation of all known manifestations of comets, including the jet character of outflows, the presence of ions in the vicinity of the nucleus, the bursts and splitting of cometary nuclei, etc., with solar radiation initiating burning of the products of electrolysis in the nucleus. As shown persuasively by numerical simulation carried out in hydrodynamic approximation, the shock wave initiated by the Deep Impact (DI) impactor in the cometary ice saturated originally by the electrolysis products 2H2 + O2 is capable of activating under certain conditions exothermal reactions (of the type O2 + H2 + organics = H2O + CO + HCN + other products of incomplete burning of organics including its light and heavy pyrolyzed compounds, soot, etc.), which will slow down shock wave damping (forced detonation) and increase many times the energy release. As a result, the measured energetics of ejections and outflows from the crater have to exceed the DI energetics. Analysis of different clusters of the DI experiment data confirms these conclusions and expectations and thus it favours the planetary origin of comets.

Shock-wave damping in a foam after a condensed-substance explosion

Shock-wave damping in a foam after a condensed-substance explosion

Emission measures and heating mechanisms for stellar transition regions and coronae

In order to determine the heating mechanisms for stellar transition regions and coronae we try to determine the damping lengths for the mechanical flux(es) responsible for the heating. For the lower part of the transition regions (30,000 < T≤100,000 K) the damping lengths are consistent with Shockwave damping. This appears to be also true for the upper part of the transition region in Procyon, while for the upper part of the solar transition region the damping length is much larger.

Asymptotic laws of damping of shock waves in inhomogeneous media

The laws of damping are found for shock waves propagating through a medium with an arbitrary distribution of the density and pressure and sources of energy, mass, and momentum.

Numerical solution of a two-dimensional problem of the transient hydrodynamics of a compressible non-newtonian fluid

A solution is presented for a transient two-dimensional problem of the hydrodynamics of a compressible non-Newtonian fluid connected with the propagation and damping of shock waves in a well.

Shock-wave damping in a two-phase liquid-gas bubble medium

Shock-wave damping in a two-phase liquid-gas bubble medium

An experimental study of shock-wave damping in steel

An experimental study of shock-wave damping in steel

Damping of elastic shock waves in iron caused by viscous damping of dislocations

1. The experimental damping of shock waves in iron can be described well with a model incorporating viscous damping of dislocations in subbarrier motion; it follows that the damping of the elastic precursor of the shock wave as it travels is due primarily to stress relaxation resulting from the motion of these dislocations. 2. The ratio of the constant B characterizing the viscous damping of dislocations to the reduced density N of mobile dislocations which is found from the damping of an elastic shock wave is close to the value of this ratio found from the damping of ultrasound. Accordingly, experiments involving the damping of elastic shock waves may be considered an independent source of B/N values.

The Effect of Magnetic Field on the Damping of Shock Waves

Magnetic field damping effects on the dissipation of hydromagnetic shock waves are investigated in connection with the heating of the galactic halo and the solar corona. It is concluded that the magnetic field reduces the dissipation only to about three-quarters of the dissipation without fields. (C.E.S.)