Papers by Keyword: Dynamic Response

Abstract: Cracks significantly affect the structural integrity and functionality of mechanical components. While most existing studies focus on identifying straight cracks using dynamic response (DR) data, the characterisation of crack paths, especially curved ones, remains limited. This gap is critical, as the path of crack propagation plays a vital role in determining the severity of structural damage, particularly in critical regions of plate structures. The large number of possible crack paths has made systematic research in this area difficult. Therefore, this study proposes a novel methodology for modelling both straight and curved crack paths in plate structures to analyse their DR using the Finite element method (FEM). Straight cracks are represented by coordinate pairs, while curved cracks are defined using second-order polynomial equations. A combination-based approach is employed to generate feasible curved paths within a bounded region, allowing variation in crack shapes, lengths, and geometries. The results demonstrate that the proposed methodology effectively reduces the total number of crack path configurations from 7140, an impractically large set for detailed analysis, to a manageable subset of 288. This reduction facilitates more efficient implementation in both numerical simulations and experimental investigations without compromising the representational diversity of crack path geometries. They also show that the crack path has a greater influence on the dynamic response than crack length, offering a more comprehensive framework for crack path identification and evaluation.

Abstract: Assessment of structural responses to dynamic loads, such as impact, is essential because these loads can cause severe damage to infrastructure and pose risks to human lives. Important elements of structures, like bridge piers and building columns, are particularly vulnerable to impact loads from vehicle collisions or rockfalls. To address such critical loading, we conducted impact tests to analyze the responses of post-tensioned steel-reinforced concrete (RC) column sections under controlled impact loads. A large drop tower was used to accelerate a rigid cylindrical projectile with a flat nose, having a diameter of 100 mm, a length of 380 mm and a weight of 21.6 kg. Reaction forces were measured using load cells, while accelerometers captured high dynamic accelerations during impact. Both the reinforced concrete columns and the impactor were equipped with a speckle pattern, facilitating Digital Image Correlation (DIC) analysis. The DIC system was used to track the impactor velocity, to measure deflections, and to observe of the cracking patterns on the column surfaces. In total, six 200 mm × 300 mm × 1500 mm different column specimens were tested under two distinct impact velocities: 25 m/s and 33 m/s. The clear span was 1000 mm and the longitudinal and transverse reinforcement ratios were approximately 2 % and 0.7 %, respectively. Four columns were post-tensioned to two levels of 34 % and 67 % of their axial capacity and compared to two reference specimens with no axial force. This range of axial force was chosen to have a detailed evaluation of how different levels of post-tensioning influenced structural performance, specifically in terms of reaction force, lateral deflection and cracking patterns under impact loading. We observed that the mass of debris generated by the impact increased with impact velocity. In most cases, the debris mass also increased with a higher axial force ratio. This trend is likely due to the release of elastic energy stored within the post-tensioned specimen during the impact event, which intensified the dynamic response. Specifically, we noted a pronounced spalling of the concrete cover, primarily on the rear side of the impact, which led to the exposure of the reinforcement. The results of this study can serve as basis for analytical and numerical models and as guideline for testing additional parameters in similar specimens.

Abstract: In a nuclear power plant, the tubes array component that constitutes a cooling water heat exchanger is often subjected to cold and hot fluid flow impact, which are affected by axial stress due to thermal strain cause by these cold and hot flow impact. So, the dynamic characteristics of this tube would be changed significantly by this flow impact and even lead to failure. The axial load caused by thermal strain, the cold and hot flow impact, also markedly changes the dynamic characteristics of the tube.

Abstract: This work explores a number of approaches for estimating the parameters of a structure from measurements of its dynamic response. The study represents an initial step in a larger framework aiming for improving processes associated with model updating and the development of digital twins. In this study, the parameters of a cantilever beam, i.e. modulus of elasticity Ε and density ρ have been determined from the dynamic response calculated due to a harmonic load applied at a fixed location on the beam. The response in this study is calculated from a numerical simulation to initially examine two different approaches, based on minimization of LSR values and the use of Genetic Algorithms GA, before relying on measurement of responses for future investigations. The cantilever beam has been modelled as a finite beam based on a harmonic analysis using the dynamic stiffness method.

Abstract: Tube truss structures are often used in large public buildings, and their safety performance under seismic effects is very important. The phoenix shape of the upper station house in the ropeway project of Shaohuashan National Forest Park in Shaanxi Province consists of 5 groups of tube truss structures forming an overall space tube truss structure form through connecting rods. The seismic response of this structure was analysed using the vibration mode decomposition response spectrum method. The results show that the overall structural vibration displacement changes in the first 10 vibration modes are concentrated in the head and the tail of each group of pipe truss structures; the internal force and displacement responses of the structure under seven different scenarios of multiple earthquakes are calculated, and the results show that the dynamic response of the structure is the largest under the unidirectional (X-direction) seismic action. The internal forces and displacements of structures under rare earthquakes are multiplicatively related to those under multiple earthquakes, and are closely related only to the coefficient of seismic influence.

Abstract: Ground vibrations are commonly observed by using a standard seismic station equipped with speed seismometers or acceleration seismometers. The seismometers include three mechanical vibrating systems (sensors) and the primary output is the wave pattern of recording velocity or acceleration of the material point oscillation. An alternative new method how it is possible to realize seismic measurements is using of the fiber-optic interferometric sensors. These interferometers are well-known for their ability to make high-precision measurements of optical path difference or changes that may be induced by a refractive index change in the interferometer or a physical displacement. The paper presents a comparison of the results of the standard seismic measurement by using seismic station and of the fiber-optic interferometric sensor. As a source of dynamic load, truck transport was chosen. When trucks passing through unevenness on the road (due to the road damage, the transition area of the bridge etc.), it generates vibrations that are transmitted to the subsoil and can adversely affect the surrounding building objects. Data comparison of the subsoil dynamic response obtained during both approaches of measurements is present in the amplitude and primary in the frequency domain.

Abstract: The dynamic responses of sandwich structures with MHS(metal hollow sphere)and closed cell aluminum foams under blast loading were simulated numerically by employing the finite element software ANSYS/LS-DYNA. Both sandwich panels and sandwich spheres were modeled. Some factors that determine the blast resistance of the sandwich structures were investigated. According to the parametric studies, the sandwich structures with thin inner face sheet and thick outer face sheet have stronger blast resistance than others. Also the results show that sandwich structures with interlaced hollow spheres have a better performance than those with paratactic hollow spheres. Moreover, it's inferred that the density graded core with the biggest density as the first impact layer and the least density as the last layer has more benefits in energy absorption. The comparison between sandwich structures with metal hollow spheres and those with aluminum foams was studied experimentally and numerically and the results demonstrate that structures with aluminum foam have advantage in energy absorption but structures with MHS are stronger and can undertake more TNT.

Abstract: In this paper, a Laplace domain boundary element method is applied for transient dynamic analysis of three-dimensional multi-domain linear piezoelectric structures. Piezoelectric materials of homogeneous sub-domains may have arbitrary degree of anisotropy. The boundary element formulation is based on a weakly singular representation of the piezoelectric boundary integral equations in the Laplace domain. To compute the time-domain solutions a convolution quadrature formula is applied for the numerical inversion of Laplace transform. Presented multi-domain boundary element method is tested on a three-dimensional problem of nonhomogeneous column which is made of two dissimilar piezoelectric materials and subjected to dynamic impact loading.

Abstract: Due to the influence of rolling force fluctuations, tube size changes and material uniformity and other factors, vibration and other phenomenon inevitably occur in the rolling process of tandem rolling mill. This vibration has a great impact on the dynamic stability of the mill and rolling reduction, and will significantly reduce the dimensional accuracy and surface quality of seamless steel pipe. In this paper, the non-linear finite element software ABAQUS is used to simulate the rolling process of seamless steel pipe. First, rolling force of the first frame with the maximum rolling force of PQF rolling mill is calculated. The reliability of rolling force calculated by the finite element method is verified by the test experiment. The dynamic response analysis of the roll is carried out to obtain the dynamic response curve of the roll in the rolling state and to provide technical support for the rolling schedule with the calculated rolling force being the load.

Abstract: Considering the effects of strain rate, the nonlinear dynamic response of two reinforced concrete(RC)structuresisstudied under seismic excitationsin this paper. Firstly, based on the model in a shaking table test, a three-dimensional finite element model of RC frame-shear wall structural model subjected to both horizontal and vertical component seismic excitations is established. The structural model is a three-story RC frame-shear wall structure, which consists of RC slabs, RC columns and transverse spandrel beams.Afringeframe is infilled by a RCshear wall.Then, According to the practice engineering, a multi-story RC frame structure is also established. Finally, the dynamic response of the structures is investigated using nonlinear seismic analytical method considering the effects of strain rate. These results may provide a reference for seismic design of RC structure.