Impact between fluids and solids. Comparison between analytical and FEA results

Theoretical and numerical analyses of the dynamic force acted on structures by fluid-like debris flows (d.f.) or fluids are presented. Current analyses of the interaction between d.f. and structures usually take into account a modified hydrodynamic pressure or a multiple of the hydrostatic pressure, to determine the impact force. A close examination of analytical and experimental results, mainly pertaining to hydraulic and coastal engineering, regarding the impact of water waves against coastal facilities, however, reveals that these simplified assumptions are not supported by rational presumptions. Numerical (FE) analyses have been therefore carried out and their results compared to the available theoretical and numerical results in the literature. The importance of the impulsive phase of the impact phenomenon, especially if a planar d.f. front face is parallel to the impacted structure, is put into evidence. Proposed FEA results highlight the role of fluid's speed, density and compressibility in the general problem of the impact of fluids against structures.     

Numerical simulation of hypervelocity impact on CFRP/Al HC SP spacecraft structures causing penetration and fragment ejection

A representative carbon fiber reinforced plastic/aluminum honeycomb sandwich panel (CFRP/Al HC SP) spacecraft structure has been modeled in the hydrocode AUTODYN using the state-of-the-art ADAMMO material model [Riedel W, Harwick W, White D, Clegg R. Advanced material damage models for numerical simulation codes. ESA CR(P) 4397, 2003] to study the performance of the structure during impact events that cause perforation and fragment ejection. A new procedure combining a series of existing theoretical methods has been developed and applied to derive a full set of coarse material data. The data set has been implemented in AUTODYN, and the results of the numerical simulation have been compared to experimental impact test data. For impact tests performed near the structural ballistic limit, quantitatively accurate results were obtained over a range of impact velocities and angles. A further increase in the projectile size resulted in significant destruction of the sandwich panel front face-sheet and diversion from the experimental damage measurements. Inspection of the numerical model has shown non-localized propagation of inter-laminar delaminations, possibly caused by an under-prediction of the laminate dynamic inter-laminar tensile strength. The effects of the delamination propagation occur over an extended time scale and were not found to affect the state and trends of the fragment cloud ejected into the satellite interior. Accordingly, experimental trends of fragment cloud dispersion have been qualitatively reproduced.     

Viscoelastic impact between a cylindrical striker and a long cylindrical bar

Axial impact between a cylindrical striker of finite length and a long cylindrical bar, both of linearly viscoelastic materials, is considered. General results are derived for the impact force, the particle velocity and the strain in the bar in terms of closed-contour integrals. Such results are derived also for the transfer of momentum and energy from the striker to the bar. Numerical results for a striker and a bar made of the same material but with different cross-sectional areas are compared. In viscoelastic impact, unlike elastic impact, the duration of contact may be finite and larger than two transit times for a wave front through the striker due to the formation of a tail of finite length after the main pulse. Furthermore, multiple contacts and separations of the striker and the bar may occur within a range of striker-to-bar characteristic impedance ratios. In the case of viscoelastic impact studied numerically, the duration of contact is at least as long and the momentum and energy transferred are at most as large as in elastic impact. Strains measured at three locations of a polymethyl methacrylate (PMMA) bar impacted by strikers of the same material as the bar agree well with the theoretical results.     

Analogies and differences between quasi-static indentation and hypervelocity impact morphologies on thin solar cells

Morphologies produced by quasi-static indentation on thin Hubble Space Telescope (HST) solar cells show remarkable similarities to much of the hypervelocity damage sustained by the HST solar array whilst in orbit. Quasi-static indentation tests carried out with blunt and sharp indentors reveal analogies between static and dynamic (hypervelocity) indentation indicating similar fracture mechanics processes over the energy range evaluated. Understanding the static case assists to characterise better the dynamic process and bridge the intervening gap.     

International comparison of a standard voltage transformer between Ukraine and Germany

Results are provided for international comparisons of a standard voltage transformer performed in Ukraine and Germany. Algorithms are given for the equivalence of national standards taking account of expanded uncertainty. __________ Translated from Izmeritel’naya Tekhnika, No. 11. pp. 57–58, November, 2007.     

Evolution and calibration of a numerical model for modelling of hybrid-fibre ECC panels under high-velocity impact

A material model for hybrid-fibre engineered cementitious composites (ECC) under impact loading is developed and calibrated in this paper, and size effect, appropriate erosion criteria and strain rate effect are investigated and accounted for in the model. Employing the new material model, a numerical model and modelling technique are developed to model the impact behaviour and impact process of hybrid-fibre ECC panels using LS-DYNA commercial software. The material model and the numerical model developed in this paper are validated against the experimental results.     

An experimental and modeling study of the thermomechanical behavior of an ABS polymer structural component during an impact test

An experimental and modeling study of the thermomechanical behavior of an ABS polymer structural component during an impact test is presented. The structural component was a heel of a woman's shoe made of ABS polymer material reinforced or not by a pin. Kinematics and thermal full field measurement techniques were used to observe the material and structural component during preliminary experimental tensile and impact tests. With the kinematic fields it was possible to identify the stress–strain response, which takes the necking localization into account. Positive volume variations were also observed during these tensile tests, which were associated with the crazing damage mechanisms in this type of polymer. The thermal fields measured during these tests showed high temperature variations (a few K to 25 K) in the zone where strain was localized.     

Investigation of dissolution behavior of diclofenac sodium extended release formulations under standard and biorelevant test conditions

Background: Dissolution characteristics of four extended release (ER) generic formulations of diclofenac sodium were examined. Aim: The aim of this study was to compare the drug dissolution behavior of diclofenac ER generics to clarify whether the products are characterized by comparable dissolution characteristics under the applied test conditions. Methods: The investigations were performed in the USP apparatus 2 and in the new biorelevant dissolution stress test device. Results: The experiments yielded striking differences between the generic formulations. Applying USP apparatus 2 it was noticed that the dissolution profiles of the products were distinctly affected by the stirring rate. Using the biorelevant dissolution stress test device susceptibility of the products to biorelevant stresses was observed. Change of pH within the experiments reduced the dissolution rates of all formulations and distinctly influenced their dissolution characteristics. Conclusion: The study demonstrates clearly the divergences in the dissolution behavior among the generic ER formulations of diclofenac sodium. The observed susceptibility of the tested dosage forms toward biorelevant stress bears in our interpretation the risk to cause unwanted fluctuations in drug plasma concentration profiles.     

Experimental investigation of bond characteristics between CFRP fabrics and steel plate joints under impact tensile loads

In recent years, the use of adhesively-bonded fibre-reinforced composite materials has attracted widespread attention as a viable alternative for the retrofitting of civil infrastructure such as buildings and bridges. This has been particularly the case for concrete structures. The retrofitting of metallic bridges and buildings with FRP materials, however, is still in its early stages. In real life, these structures are subjected to dynamic loads. Therefore, it is necessary to understand the bond behaviour between steel and the strengthening materials for both static and dynamic loads. To examine the bond between steel plates and carbon fibre-reinforced polymers (CFRP) fabrics, this paper describes the experimental procedures and results of double strap steel joints loaded at different loading rates (2 mm/min, 3.35, 4.43 and 5 m/s). In this test program, ultimate load-carrying capacity, effective bond length, failure mechanism and strain distribution were examined for all loading rates. Different numbers of CFRP layers with different bond lengths were investigated. Experimental findings reveal that the maximum improvement in joint capacity occurs at a rate of 3.35 m/s. It was observed that the effective bond length is insensitive to loading rate for both joints. The failure modes and strain distributions, however, exhibit little difference between static and dynamic conditions.     

一种新型楔形膜在真空中的制作方法及测试结果

提出了一种新型楔形膜在真空中的制作方法,可以替代白光干涉位移传感器中的关键元件.该方法采用两层复制技术,用有机材料SU8胶作为楔形膜中间的材料.同时,搭建了白光干涉位移传感器系统,对制作的楔形膜进行了测量.实验结果表明,该解调系统具有较好的稳定性及较高的测量精度.     

Correlation between the bond dissociation energies and impact sensitivities in nitramine and polynitro benzoate molecules with polynitro alkyl groupings

The geometries of nine CHNO nitro-contained explosive molecules were fully optimized employing the B3LYP method of density functional theory with the 6-31G* basis set. The bond dissociation energy (BDE) for removal of the NO(2) group in nitroamine molecules with nitro alkyl, and benzoate with nitro alkyl were calculated at the same level. The calculational results of B3LYP/6-31G* and B3P86/6-311G* levels showed that the strength of C-NO(2) is weaker than that of N-NO(2) bond in nitroamine molecules with nitro alkyl. The weakest bond is the C-NO(2) in these computed molecules. The relationship between the impact sensitivities and the weakest C-NO(2) bond dissociation energy values was examined. The results indicate a nearly linear correlation between the impact sensitivity and the ratio of the BDE value to the molecular total energy.     

史密斯预估补偿控制与PID控制的比较研究

比较了两种工业过程控制中的控制器,PID控制器和史密斯预估补偿控制器.介绍了四种PID参数的整定方法,分别为试凑法确定PID调节参数、Ziegler-Nichols参数整定方法、最优PID整定算法、运用Matlab/simulink中的NCD Outport(非线性控制设计输出端口模块)模块对PID参数进行最优整定.史密斯预估补偿控制器主要用于工业控制中的大延时系统控制,以提高系统的阶跃响应性能.在理论上,史密斯预估补偿控制器提供了一个有效的方法来提高控制效果.运用Matlab/Simulink仿真方案对前述两种控制方法进行了仿真比较,结果表明,在有较大延时情况下,史密斯预估补偿控制能获得比PID控制更好的结果.     

A distribution-free test for the relationship between model input and output when using Latin hypercube sampling

A test for the detection of non-monotone relationships between the inputs and outputs of computer simulation models is described for use in sensitivity analyses employing Latin hypercube sampling. The test is based on the squared differences of the consecutive ranks of the output variable when the values of the output variable have been ordered by the corresponding values of an input variable. The test is distribution-free and does not require the values of the output variable to be independent of one another. Instead, the weaker assumption of exchangeability is used. The resulting test statistic is shown to be independent of Spearman's rank correlation coefficient, and a simple method for combining the two statistics is discussed. The test is illustrated with an example from a recent performance assessment for the Waste Isolation Pilot Plant.     

On mesh restrictions to satisfy comparison principles,maximum principles,and the non-negative constraint: Recent developments and new results

This article concerns mesh restrictions that are needed to satisfy several important mathematical properties—maximum principles, comparison principles, and the nonnegative constraint—for a general linear second-order elliptic partial differential equation. We critically review some recent developments in the field of discrete maximum principles, derive new results, and discuss some possible future research directions in this area. In particular, we derive restrictions for a three-node triangular (T3) element and a four-node quadrilateral (Q4) element to satisfy comparison principles, maximum principles, and the nonnegative constraint under the standard single-field Galerkin formulation. Analysis is restricted to uniformly elliptic linear differential operators in divergence form with Dirichlet boundary conditions specified on the entire boundary of the domain. Various versions of maximum principles and comparison principles are discussed in both continuous and discrete settings. In the literature, it is well-known that an acute-angled triangle is sufficient to satisfy the discrete weak maximum principle for pure isotropic diffusion. Herein, we show that this condition can be either too restrictive or not sufficient to satisfy various discrete principles when one considers anisotropic diffusivity, advection velocity field, or linear reaction coefficient. Subsequently, we derive appropriate restrictions on the mesh for simplicial (e.g., T3 element) and nonsimplicial (e.g., Q4 element) elements. Based on these conditions, an iterative algorithm is developed to construct simplicial meshes that preserve discrete maximum principles using existing open source mesh generators. Various numerical examples based on different types of triangulations are presented to show the pros and cons of placing restrictions on a computational mesh. We also quantify local and global mass conservation errors using representative numerical examples and illustrate the performance of metric.     

A dynamic simulation model for transient absorption chiller performance. Part II: Numerical results and experimental verification

This paper is the second paper out of two which present the development of a dynamic model for single-effect LiBr/water absorption chillers. The first part describes the model in detail with respect to the heat and mass balances as well as the dynamic terms. This second part presents a more detailed investigation of the model performance, including performance analysis, sensitivity checks and a comparison to experimental data. General model functionality is demonstrated.A sensitivity analysis gives results which agree very well to fundamental expectations: it shows that an increase in both external and internal thermal mass results in a slower response to the step change but also in smaller heat flow oscillations during the transient period. Also, the thermal mass has been found to influence the heat flow transients more significantly if allocated internally. The time shift in the solution cycle has been found to influence both the time to reach steady-state and the transients and oscillations of the heat flow. A smaller time shift leads to significantly faster response.A comparison with experimental data shows that the dynamic agreement between experiment and simulation is very good with dynamic temperature deviations between 10 and 25 s. The total time to achieve a new steady-state in hot water temperature after a 10 K input temperature step amounts to approximately 15 min. Compared to this, the present dynamic deviations are in the magnitude of approximately 1–3%.     

Investigation of the relationship between facial injuries and traumatic brain injuries using a realistic subject-specific finite element head model

In spite of anatomic proximity of the facial skeleton and cranium, there is lack of information in the literature regarding the relationship between facial and brain injuries. This study aims to correlate brain injuries with facial injuries using finite element method (FEM). Nine common impact scenarios of facial injuries are simulated with their individual stress wave propagation paths in the facial skeleton and the intracranial brain. Fractures of cranio-facial bones and intracranial injuries are evaluated based on the tolerance limits of the biomechanical parameters. General trend of maximum intracranial biomechanical parameters found in nasal bone and zygomaticomaxillary impacts indicates that severity of brain injury is highly associated with the proximity of location of impact to the brain. It is hypothesized that the midface is capable of absorbing considerable energy and protecting the brain from impact. The nasal cartilages dissipate the impact energy in the form of large scale deformation and fracture, with the vomer–ethmoid diverging stress to the “crumpling zone” of air-filled sphenoid and ethmoidal sinuses; in its most natural manner, the face protects the brain. This numerical study hopes to provide surgeons some insight in what possible brain injuries to be expected in various scenarios of facial trauma and to help in better diagnosis of unsuspected brain injury, thereby resulting in decreasing the morbidity and mortality associated with facial trauma.     

Validation of a method to evaluate future impact of road safety interventions,a comparison between fatal passenger car crashes in Sweden 2000 and 2010

When targeting a society free from serious and fatal road-traffic injuries, it has been a common practice in many countries and organizations to set up time-limited and quantified targets for the reduction of fatalities and injuries. In setting these targets EU and other organizations have recognized the importance to monitor and predict the development toward the target as well as the efficiency of road safety policies and interventions.