Modal Research of Underground Arch Structure With Elastic Support

In recent decades, terrorist attacks have been increased all over the world. For this reason, the design of blast resistant structures is very crucial. On the other hand, for decades the optimum design of structures has been an interesting subject for structural engineers and researchers as it can provide cost and behavioural efficiencies. In the current research, the optimum design of steel moment frames under blast loading has been studied. Towards that end, first, a damage index is developed based on the maximum plastic strain in the members. Then, according to the damage index, a multi-objective optimisation methodology is proposed to minimise the structural weight and the damage index. The method utilises explicit nonlinear dynamic finite element analysis as the structural analysis method and NSGA-II optimisation algorithm as the optimisation technique. At the final point, based on the proposed method a framework is developed, and two numerical examples are studied. Results of this research show that the developed method is effective in achieving optimal designs with desired cost and damage.

In order to achieve effective reduction and isolation of low-frequency vibration and noise, this paper investigates a shell-type structure element for the design of quasi-zero-stiffness (QZS) isolators. By means of nonlinear buckling technology, the structure element can be turned into a QZS structure under the static load so as to possess the ability of low-frequency vibration reduction and isolation. First of all, the buckling characteristics of the structure element are researched by using the finite element method. Then the effects of the geometric parameters of the structure element on the working load range with the low structure stiffness are summarized for the design of the QZS systems. Finally, the compound systems composed of multi shell-type structure elements in series or in parallel are constructed, and the relationship between the performances of the compound system and those of the structure element is presented, including the stiffness value and the bearing load range with the low structure stiffness.

In the processing of composites, fibre reinforcement is draped over complex three dimensional geometries, yielding local variations in the fibre volume fraction and fibre orientation with subsequent effects on the permeability of the reinforcement during resin infiltration and on the properties of the composite product. This study presents computer simulations of the draping of fabrics by following a mechanical, finite element approach. The fabric is considered as a solid continuum with mechanical properties and friction properties at interfaces. The problem is solved by applying an explicit dynamic finite element analysis. In order to incorporate the large shear deformation of fabric during draping, an updated material behaviour law was formulated on the basis of changing fibre directions. The model was implemented in a user computer subroutine and tested first in case-studies of simple in-plane shear where the predictions were also compared with experimental data from a picture frame type of shear test. Thereafter, numerical simulations focused on the draping of a fabric in a “hat” shaped mould, comprising a hemispherical cup with a wide flat rim. The predictions were compared with predictions from similar simulations without the updated material behaviour law, experimental data and predictions from a “fishnet” algorithm.

This study presents the numerical and experimental interior head impact analysis of automotive instrument panel according to the United Nations Economic Commission for Europe Regulation 21 (ECE R21). To minimize the possible injury risk for unrestrained front seat passengers due to the interior head impact with the instrument panel, the panel design needs to meet the ECE R21 standard which defines a pendulum-type head form as the impactor. The measured acceleration response of the head form should not exceed 80g continuously for more than 3ms. Motivated by the need to develop a simulation-based technique to evaluate the design of the instrument panel, a numerical model based on the explicit dynamic finite element analysis (FEA) by using the commercial FEA solver, LS-DYNA, is developed. To minimize the experimental cost, a gravity-based impactor with a smaller impact speed is develop as the test apparatus for verification purpose. The simulated results agree well with the experimental data; the average accuracy for the maximum value of impact acceleration at the head form is 95.4%. After the verification, the standard test conditions (with higher impact speed) are performed to evaluate the design. The outcome of this study can provide an efficient and cost-effective method to predict and improve the design of the instrument panel for interior head impact protection.

Long-term, body-adhered medical devices rely on an adhesive interface to maintain contact with the patient. The greatest threat to on-body adhesion is mechanical stress imparted on the medical device. Several factors contribute to the ability of the device to withstand such stresses, such as the mechanical design, shape, and size of the device. This analysis investigates the impact that design changes to the device have on the stress and strain experienced by the system when acted on by a stressor. The analysis also identifies the design changes that are most effective at reducing the stress and strain. An explicit dynamic finite element analysis method was used to simulate several design iterations and a regression analysis was performed to quantify the relationship between design and resultant stress and strain. The shape, height, size, and taper of the medical device were modified, and the results indicate that, to reduce stress and strain in the system, the device should resemble a square in shape, be short in height, and small in size with a large taper. The square shape experienced 17.5% less stress compared to the next best performing shape. A 10% reduction in device height resulted in a 21% reduction in stress and 24% reduction in strain. A 20% reduction in device size caused a 7% reduction in stress and 2% reduction in strain. A 20% increase in device taper size led to a negligible reduction in stress and a 6% reduction in strain. The height of the device had the greatest impact on the resultant stress and strain.

Dynamic numerical simulation of the spreading of detonation wave was made by use of the explicit dynamic finite element analysis program. The results of numerical simulation are in agreement with physical phenomena and laws of spreading of detonation wave. The study indicates that the calculation model and simulation method are reasonable and feasible. The volume of electronic sensor both at home and abroad is so large that it is difficult to arrange sensing elements in perforating gun. As a result, three-dimensional wave can't be measured. So we approximately substitute the relationship between the mean gun pressure and time. Taking advantage of this measuring method, gun pressure of other styles can be estimated. This is a very valuable method, and may be used for reference to manufacture and scientific research of perforating gun.

A series of extensively instrumented tests was performed on the Structural Evaluation Test Unit in the early 1990s.The purpose of these tests was to determine the response of a minimally designed cask to impacts that were more severe than the design basis impact.This test series provides an excellent opportunity for benchmarking explicit dynamic finite element analysis programs for behaviors that may be experienced by casks during regulatory and extra-regulatory impact events.This report provides the parameters of the test unit, the locations of instrumentation, the locations of inspection points, and the parameters of the four tests that were conducted.A companion report provides the results of the tests.

A platform for vibration damping, leveling, and height control of high-resolution superconducting magnets

This paper presents the development of an active 3-degree-of-freedom (DoF) vibration isolation system using zero-power magnetic suspension. The developed system is capable to suppress direct disturbances and isolate ground vibrations of the 3-DoF motions, associated with vertical translational and rotational modes. Two categories of control strategy for the actuators are proposed, i.e., local control and mode control. The latter method allows to overcome limitations of the poor performances for rotational modes exhibited by the former. A mathematical model of the system is derived and each DoF motion is treated separately for the control system. It is demonstrated analytically that the infinite stiffness to static direct disturbances can be generated and the resonance peak due to floor vibration can effectively be suppressed for the system. Moreover, the experiments have been carried out to measure the static and dynamic responses of the isolation table to direct disturbances, and transmissibility characteristic of the isolator from the floor. The results indicate good vibration isolation and attenuation performances, and show the efficacy of the developed isolator for industrialization

Предложен метод сейсмоизоляции и виброизоляции, основанный на свойствах изображений Фурье финитных функций. Разработаны модели для определения динами­ческих свойств гранулированных материалов из бытовых полимерных отходов и из изношенных шин. В будущем по­лимерные бытовые материалы могут стать неиссякаемым источником для получения материала, обладающего сейсмои­золирующими и виброизолирующими свойствами. Разработка способов использования полимерных бытовых отходов для сейсмоизоляции и виброизоляции позволит одновременно решать две проблемы: защищать от загрязнений окружающую среду и обеспечивать сейсмостойкость сооружений.

Aimed to solve current collision problems between car head and truck rear, collision simulation of a novel type multistage rear protector is achieved, structure has been designed and optimized before. Based on conservation of energy theorem and regulations of dynamic collision test, dynamic explicit finite element analysis method is applied for investigate the device. It is shown that the peak acceleration of the car body is significantly decreased and collision safety is greatly improved when the rear protector is adopted. Through the collision simulation results of dynamic acceleration and maximum deformation, it is indicated that the novel multistage rear protector has excellent energy absorption capability, not only reducing occupant injury from collision but also improving collision compatibility during the car head to truck rear collision.

A multiscale soft-contact modelling method for rough surfaces in contact with coupled slipping/sliding and rolling

This study investigates the influence of frictional properties between the spring wire and coiling tools on the deformation behavior during the coiling process with coiling pin system, using dynamic explicit finite element analysis with ANSYS LS-DYNA. The analysis focused on varying the coefficients of dynamic friction between the wire and four key tools: the wire guide, first coiling pin, second coiling pin, and pitch tool. Results revealed that the average coil diameter, stress distribution, and compressive axial force during forming were significantly affected by frictional conditions, particularly those at the second coiling pin. A reduction in the friction coefficient at the second coiling pin led to increased coil diameters and decreased stress and axial force. These findings indicate that friction at the second pin predominantly governs coil shaping and significantly impacts spring dimensions. Furthermore, deteriorated sliding properties due to inadequate lubrication may cause dimensional variation or even failure during forming. This analysis emphasizes the critical role of wire-tool friction management in ensuring spring quality and consistency.

Introducing the hierarchy into cellular materials has attracted increasing attention in the effort to pursue improved absorbed-energy abilities and impact resistance. In this paper, the dynamic crushing properties and energy absorption capacities of joint-based hierarchical honeycombs with different topologies were explored by means of explicit dynamic finite element (FE) analysis using ANSYS/LS-DYNA. Four types of joint-based hierarchical honeycombs with uniform cell-wall thickness were firstly constructed by substituting each vertex of regular honeycombs with a smaller self-similar cell (hexagon or square). The respective influences of hierarchical parameters and impact velocities on in-plane dynamic deformation modes, mechanical characteristic and energy absorption of joint-based hierarchical honeycombs were discussed. Research results showed that the hierarchy had a far greater influence on the in-plane deformation modes of honeycombs. Compared with regular honeycombs, the dynamic plateau stress and specific energy absorption of joint-based hierarchical honeycombs can be improved if the proper hierarchical parameters were chosen. Adding the joint-based hierarchy into regular honeycombs can enhance the crushing stress efficiency (CSE) of the specimens. In addition, by introducing a non-dimensional dynamic sensitivity index, the dynamic shock enhancement of hierarchical honeycombs was also investigated. These researches are useful for the multi-objective dynamic optimization design and controllable properties of cellular materials.

This paper investigates the seismic response of lightweight acceleration-sensitive non-structuralcomponents (NSCs) mounted on irregular reinforced concrete (RC) primary structures (P-structures) usingnon-linear dynamic finite element (FE) analysis. The aim of this paper is to study the influence of NSC toP-structure vibration period ratio, peak ground acceleration, NSC to P-structure height ratio, and P-structuretorsional behaviour on the seismic response of the NSCs. Representative constitutive models were used tosimulate the behaviour of the RC P-structures. The NSCs were modelled as vertical cantilevers fixed at theirbases with masses on the free ends and varying lengths so as to match the frequencies of the P-structures.Full dynamic interaction is considered between the NSCs and P-structures. A set of 21 natural and artificialearthquake records were used to evaluate the seismic response of the NSCs. The numerical results indicatethat the behaviour of the NSCs is significantly influenced by the investigated parameters. Comparisonbetween the FE results and Eurocode (EC8) predictions suggests that EC8 underestimates the response ofNSCs mounted on the flexible sides of irregular RC P-structures when the fundamental periods and heightsof the NSCs match those of the P-structures. The perceived cause of this discrepancy is that EC8 does nottake into account the amplification in the dynamic response of NSCs induced by the torsional behaviour ofRC P-structures.