Numerical Simulation of Free-Air Explosion Using LS-DYNA

2014 ◽  
Vol 553 ◽  
pp. 780-785 ◽  
Author(s):  
S.K. Hashemi ◽  
Mark A. Bradford
Keyword(s):  
Computational Modelling ◽  
Mesh Size ◽  
Arbitrary Lagrangian Eulerian ◽  
Empirical Methods ◽  
Large Structures ◽  
Pressure Distributions ◽  
Free Air ◽  
Charge Shape ◽  
Air Explosion ◽  
Parameter Values

The development of advanced computational technologies in recent years has seen studies of the effects of explosions on large structures becoming feasible and, as a consequence, the number of destructive tests and their high cost can be reduced significantly. This paper presents a study of air-burst explosion wave propagation using computational modelling based on LS-DYNA. Incident and reflected pressure waves are investigated, as well as the mesh sensitivity, different scaled distances and the charge shape. The Multi-Material Arbitrary Lagrangian-Eulerian (MM-ALE) representation is used to model the blast, and the results are validated by empirical methods. The effects of parameter values adopted in these methods are studied. The results show that LS-DYNA can effectively simulate an air-burst explosion. Additionally, the mesh size and explosive weight have a large influence on the peak incident and reflected pressures. It is observed that there is an optimum range of the mesh size in relation to the explosive weight, material properties and the scaled distance which can significantly reduce the CPU usage while having reasonable accuracy. Different charge shapes cause different pressure distributions over the air domain.

NUMERICAL PREDICTION OF SLAMMING LOADS DURING WATER ENTRY OF BOW-FLARED SECTIONS

2021 ◽  
Vol 156 (A4) ◽  
Author(s):  
Shan Wang ◽  
H B Luo ◽  
C Guedes Soares
Keyword(s):  
Mesh Size ◽  
Water Entry ◽  
Two Dimensional ◽  
Arbitrary Lagrangian Eulerian ◽  
Pressure Distributions ◽  
Good Consistency ◽  
Convergence Study ◽  
Experimental Values ◽  
Coupling Algorithm ◽  
Force Pressure

The two-dimensional water entry of bow-flared sections is studied by using a Multi-Material Arbitrary Lagrangian- Eulerian (MMALE) formulation and a penalty-coupling algorithm. A convergence study is carried out, considering the effects of mesh size, the dimension of fluids domain, and fluid leakage phenomenon through the structure. The predicted results on the wetted surface of a bow-flared section are compared with published experimental values in terms of vertical slamming force, pressure distributions at different time instances and the pressure histories at different points. Comparisons between the numerical results and measured values show satisfactory correlation. An approximation method is adopted to estimate the sectional slamming force showing good consistency for the peak forces.

scholarly journals Simulation of Wire Bonding Process Using Explicit Fem with Ale Remeshing Technology

2019 ◽  
Vol 36 (1) ◽  
pp. 47-54
Author(s):  
C. C. Yang ◽  
Y. F. Su ◽  
Steven Y. Liang ◽  
K. N. Chiang
Keyword(s):  
Time Integration ◽  
Wire Bonding ◽  
Bonding Process ◽  
Integration Scheme ◽  
Arbitrary Lagrangian Eulerian ◽  
Cracking Behavior ◽  
Free Air ◽  
Time Integration Scheme ◽  
Time Marching ◽  
The Wire

ABSTRACTThermosonic wire bonding is a common fabrication process for connecting devices in electronic packaging. However, when the free air ball (FAB) is compressed onto the I/O pad of the chip during bonding procedure, chip cracking may occur if the contact pressure is too large. This study proposes an effective simulation technique that can predict the wire ball geometry after bonding in an accurate range. The contact force obtained in the simulation can be used for possible die cracking behavior evaluation. The simulation in this study used the explicit time integration scheme to deal with the time marching problem, and the second-order precision arbitrary Lagrangian-Eulerian (ALE) algorithm was used to deal with the large deformation of the wire ball during the bonding process. In addition, the equilibrium smoothing algorithm in LS-DYNA can make the contact behavior and geometry of the bonding wire almost the same as the experiment, which can also significantly reduce the distortion of the mesh geometry after remeshing.

NUMERICAL AND EXPERIMENTAL APPROACH FOR THE OPTIMAL DESIGN OF A DUAL PLATE UNDER BALLISTIC IMPACT

2008 ◽  
Vol 22 (09n11) ◽  
pp. 1538-1543
Author(s):  
JEONGHOON YOO ◽  
DONG-TEAK CHUNG ◽  
MYUNG SOO PARK
Keyword(s):  
Numerical Simulation ◽  
Optimization Technique ◽  
Mesh Size ◽  
Experimental Tests ◽  
Ballistic Impact ◽  
Plastic Energy ◽  
Dual Plate ◽  
Element Erosion ◽  
Parameter Values ◽  
The Impact

To predict the behavior of a dual plate composed of 5052-aluminum and 1002-cold rolled steel under ballistic impact, numerical and experimental approaches are attempted. For the accurate numerical simulation of the impact phenomena, the appropriate selection of the key parameter values based on numerical or experimental tests are critical. This study is focused on not only the optimization technique using the numerical simulation but also numerical and experimental procedures to obtain the required parameter values in the simulation. The Johnson-Cook model is used to simulate the mechanical behaviors, and the simplified experimental and the numerical approaches are performed to obtain the material properties of the model. The element erosion scheme for the robust simulation of the ballistic impact problem is applied by adjusting the element erosion criteria of each material based on numerical and experimental results. The adequate mesh size and the aspect ratio are chosen based on parametric studies. Plastic energy is suggested as a response representing the strength of the plate for the optimization under dynamic loading. Optimized thickness of the dual plate is obtained to resist the ballistic impact without penetration as well as to minimize the total weight.

Research on the Effects of Roughness on the Tactile Properties of Rice Straw Particleboard Surface

2020 ◽  
Vol 12 (6) ◽  
pp. 795-801 ◽  
Author(s):  
Xian-Qing Xiong ◽  
Ying-Ying Yuan ◽  
Yi-Ting Niu ◽  
Liang-Ting Zhang
Keyword(s):  
Surface Roughness ◽  
Rice Straw ◽  
Interior Design ◽  
Roughness Parameter ◽  
Chemical Properties ◽  
Mesh Size ◽  
Design Guidelines ◽  
Before And After ◽  
The Difference ◽  
Parameter Values

To explore the effects of roughness on the tactile properties of rice straw particleboard (RSP), the surface roughness and psychological tactile and visual experiments were conducted for RSP substrates with 0.76 g/cm3 and 0.55 g/cm3 densities after sanding with sandpaper (mesh 180#, 360#, and 600#). The effects of different sandpaper types, sanding time, and density of RSP on the surface roughness were analyzed. The experimental results are as follows. The sanding treatment had significant influence on the surface roughness characterization parameters Ra and Rpv of the RSP specimens. Surface roughness differences between the 180# and 360# mesh-prepared samples were obvious. The tactile and visual psychological values of the 360# and 600# mesh-sanded specimens were higher, and the psychological quantities of untreated and 180# mesh-sanded specimens were lower. After comparing the samples with sanding treatment of sandpaper 0∼180#, the change in surface roughness of RSP with a density of 0.76 g/cm3 was smaller than that of the specimen with a density of 0.55 g/cm3. The psychological quantity difference of RSP specimens with a density of 0.55 g/cm3 was evident. When the sanding time was 1 min., the values of the roughness characterization parameters Ra and Rpv increased slightly. After 3 min. sanding, the Ra and Rpv values stabilized. When the sanding time was 5 min, the roughness was essentially unchanged. With the change in sanding time, the measured values of the tactile psychological quantity varied greatly and the measured values of the visual psychology were very close. For the RSP substrates with higher density, the surface roughness was less after sanding with a smoother surface and better tactile properties. There were significant differences between the surface roughness of the RSPs before and after sanding. After manual sanding over the same time span, the surface roughness evaluation parameter values decreased with an increase of mesh size of the sandpaper, and the tactile properties were improved. The longer the sanding time, the smaller the difference in the surface roughness parameter values, and the smaller the difference between the tactile psychological quantity and the visual psychological quantity. To expand the research scope of RSP products, this study investigates not only the physical and chemical properties but also the subjective feelings when using the RSP products. This will provide analytical methods and design guidelines for the consideration of environmental factors in furniture and interior design.

Optimal Controls for a Single Species Fishery and the Economic Value of Research

1976 ◽  
Vol 33 (4) ◽  
pp. 793-809 ◽  
Author(s):  
C. C. Huang ◽  
Ilan B. Vertinsky ◽  
Norman J. Wilimovsky
Keyword(s):  
Optimal Allocation ◽  
Probability Distributions ◽  
Economic Value ◽  
Mesh Size ◽  
Single Species ◽  
Complete Information ◽  
Optimal Controls ◽  
Optimal Policies ◽  
Solution Methods ◽  
Parameter Values

Mathematical proofs and analyses of solution methods are presented for determining optimal policies for the management of a single species fishery under equilibrium conditions. Previous intuitive arguments for solution of optimal policies controlling mesh size and fishing rate given complete information are explicitly proven. The analysis is extended to the case where some of the parameters describing the dynamics of the population are known only imprecisely to the manager. Using probability distributions for those unknown parameter values the problem is cast as a stochastic program where expected sustained net revenues from the fishery are maximized. The associated problem of optimal allocation of research resources under uncertainty conditions is considered by evaluating the direct value of such information to management activities.Examples and algorithms are presented for the class of problems discussed.

Characteristics of Free Air Blast Loading Due to Simultaneously Detonated Multiple Charges

2014 ◽  
Vol 14 (04) ◽  
pp. 1450002 ◽  
Author(s):  
Nimasha Weerasingha Mohottige ◽  
Chengqing Wu ◽  
Hong Hao
Keyword(s):  
Numerical Simulation ◽  
Pressure Ratio ◽  
Mesh Size ◽  
Blast Load ◽  
Charge Weight ◽  
Single Charge ◽  
Air Blast ◽  
Scaled Distance ◽  
Free Air ◽  
Blast Resistant Design

Extensive research has been conducted to investigate the characteristics of blast load due to single charge explosion, including numerical simulations and experimental blast tests in both unconfined and confined environments. Further, available guidelines for blast resistant design such as UFC-3-340-02 (2008) and ASCE 59-11 (2011) provide details to predict blast loads on a structure subjected to single charge explosion. However, blast load characteristics due to multiple charge explosions are poorly discussed in available literature. In this paper, commercially available Hydrocode, AUTODYN is calibrated for single charge explosions. Based on a comparison between numerical simulation and UFC prediction, correction factors for peak reflected pressure and positive reflected impulse as a function of charge weight, scaled distance and mesh size of the numerical model are proposed to minimize the errors in simulations. The calibrated AUTODYN model is then used to conduct parametric studies to investigate the effects of charge weight, scaled distance, number of charges and distance between the charges on the characteristics of free air blast load due to simultaneous detonated multiple charges. Numerical simulation results are used to derive analytical formulas for predictions of peak reflected pressure ratio and positive reflected impulse ratio between single and multiple explosions. The discussion is made on characteristics of free air blast load due to simultaneous detonated multiple charges.

Redesign of a Highly Loaded Transonic Turbine Nozzle Blade Using a New Viscous Inverse Design Method

2007 ◽  
Author(s):  
Kasra Daneshkhah ◽  
Wahid Ghaly
Keyword(s):  
Inverse Method ◽  
Design Method ◽  
Guide Vane ◽  
Accurate Solution ◽  
Inverse Design ◽  
Arbitrary Lagrangian Eulerian ◽  
Pressure Distributions ◽  
Transonic Turbine ◽  
Inverse Design Method ◽  
Highly Loaded

The redesign of VKI-LS89 turbine vane, which is typical of a highly loaded transonic turbine guide vane is presented. The redesign is accomplished using a new inverse design method where the blade walls move with a virtual velocity distribution derived from the difference between the current and the target pressure distributions on the blade surfaces. This new inverse method is fully consistent with the viscous flow assumption and is implemented into the time accurate solution of the Reynolds-Averaged Navier-Stokes (RANS) equations that are expressed in an arbitrary Lagrangian-Eulerian (ALE) form to account for mesh movement. A cell-vertex finite volume method is used to discretize the equations in space; time accurate integration is obtained using dual time stepping. An algebraic Baldwin-Lomax model is used for turbulence closure. The flow analysis formulation is first assessed against the LS89 experimental data. The inverse formulation that is implemented in the same code, is also assessed for its robustness and accuracy, by inverse designing the LS89 original geometry through running the inverse method with the original LS89 pressure distributions as target distributions but starting from an arbitrary geometry. The inverse design method is then used to redesign the LS89 using an arbitrary pressure distributions at a subsonic and a transonic outflow condition and the results are interpreted in terms of the blade overall aerodynamic performance.

Ship Collision Simulations Using Different Fracture Criteria and Mesh Size

2014 ◽  
Author(s):  
Mihkel Kõrgesaar ◽  
Kristjan Tabri ◽  
Hendrik Naar ◽  
Edvin Reinhold
Keyword(s):  
Mesh Size ◽  
Material Model ◽  
Fracture Criteria ◽  
Dissipation Energy ◽  
Advantages And Disadvantages ◽  
Large Structures ◽  
Plastic Dissipation ◽  
Wide Range ◽  
Ship Collision ◽  
Almost All

There is a wide range of fracture criteria available in the literature to simulate the ductile fracture in large structures. Almost all criteria depend in some form on the mesh size and some criteria also account the effect of the stress state on the fracture ductility. Furthermore, a material model employed could considerably influence the analysis results. Therefore, in this study, four different fracture criteria, three different mesh densities and two different material models are used to simulate ship collision with a rigid bulb. Thereby, plastic dissipation energy, force-displacement curves and structural failure mechanism is compared between different fracture criteria. Advantages and disadvantages of each criterion are discussed.

The use of critical state soil mechanics to characterise Christchurch soil in relation to liquefaction susceptibility

2016 ◽  
Vol 49 (4) ◽  
pp. 319-333
Author(s):  
Jeremy Tan ◽  
Rolando P. Orense ◽  
Andy O’Sullivan
Keyword(s):  
Critical State ◽  
Soil Mechanics ◽  
State Parameter ◽  
Cyclic Stress ◽  
Empirical Methods ◽  
Liquefaction Potential ◽  
Liquefaction Susceptibility ◽  
Cyclic Resistance ◽  
Stress Ratios ◽  
Parameter Values

The majority of current procedures used to deduce liquefaction potential of soils rely on empirical methods. These methods have been proven to work in the past, but these methods are known to overestimate the liquefaction potential in certain regions of Christchurch due to a whole range of factors, and the theoretical basis behind these methods cannot be explained scientifically. Critical state soil mechanics theory was chosen to provide an explanation for the soil’s behaviour during the undrained shearing. Soils from two sites in Christchurch were characterised at regular intervals for the critical layers and tested for the critical state lines (CSL). Various models and relationships were then used to predict the CSL and compared with the actual CSL. However none of the methods used managed to predict the CSL accurately, and a separate Christchurch exclusive relationship was proposed. The resultant state parameter values could be obtained from shear-wave velocity plots and were then developed into cyclic resistance ratios (CRR). These were subsequently compared with cyclic stress ratios (CSR) from recent Christchurch earthquakes to obtain the factor of safety. This CSL-based approach was compared with other empirical methods and was shown to yield a favourable relationship with visual observations at the sites’ locations following the earthquake.

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