Different Types Of Dynamic Loads Research Articles

An XFEM model of cracked functionally graded materials under different dynamic loadings

The behavior of cracked structures made of functionally graded materials (FGMs) under different types of dynamic loading is investigated by calculating the dynamic stress intensity factor (DSIF). Material properties, i.e. Young’s modulus E and mass density ρ vary exponentially and continuously along a given direction, but Poisson’s ratio υ is assumed to be constant. Therefore, this work addresses the effect of FGM grading orientation as well as the effect of dynamic loading properties on DSIF. To achieve this goal, a computer code based on the extended finite element method (XFEM) combined with the Level-Set method was developed. DSIF is assessed using an interaction integral technique. To validate the developed code, the results were compared with other work in the literature on structures under step function loading. The good correlation between the results demonstrates the efficiency of the code. Then, as part of a parametric study, the structure is subjected to triangular and rectangular loadings, which change the graded value and orientation of the FGM. The quality of the results demonstrates the robustness of the developed code.

The P2.5D finite element method for periodic structures in half-space soil with application to periodic pile rows

In this study, by using periodic pile rows (PPRs) as an example, a new finite element method, namely, the periodic 2.5D finite element method (P2.5D FEM) is developed for the periodic structure embedded in soil. Similar to the 2.5D FEM, the major advantage of the proposed P2.5D FEM is its ability to reduce the 3-D dynamic problem associated with the periodic soil-structure system to a series of 2-D problems. The considered PPR-soil system, referred to as the periodic pile-soil system (PPSS) subsequently is supposed to be subjected to a harmonic point load. To develop the P2.5D FEM for the PPSS, the harmonic point load is decomposed into its wavenumber domain components first. The response of the PPSS to each wavenumber domain load component is then resolved into a series of pseudo plane waves propagating along the z-direction. The quantities for the pseudo plane wave are discretized by the FEM along the cross-section of the PPSS, and the FEM equations for the pseudo plane waves are then established. The eigenequation for the pseudo plane waves can be developed with the aforementioned FEM equations. Summation of the eigenvectors of the eigenequation for the PPSS yields the displacement for the PPSS due to the wavenumber domain load component. Synthesizing the displacements due to all the wavenumber domain load components via the inverse Fourier transform with respect to the wavenumber yields the overall displacement of the PPSS produced by the point load. To show the capability of the proposed P2.5D FEM for the PPSS, some numerical results about the wave barrier effect of PPRs are presented. The developed P2.5D FEM in this study is applicable to the dynamic analysis of various periodic structures embedded in the half-space soil under different types of dynamic loads.

Modal Analysis and Flow through Sectionalized Pipeline Gate Valve Using FEA and CFD Technique

Sectionalized gate valves can reduce the volume of product released in the event of a buried pipeline failure or rupture. The risk of pipeline failure is a constant and common occurrence, and many factors can lead to pipeline incidents. In this paper, the free undamped vibration of the pipeline, sectionalized gate valve structure, and the dynamics of the fluid passing through the system are investigated. First and foremost, a modal analysis based on finite element analysis (FEA) is introduced as a fundamental linear dynamics analysis to provide insight into how a pipeline sectionalized gate valve structure may respond to different types of dynamic loading. Secondly, an implicit numerical analysis using computational fluid dynamics (CFD) is employed to describe physical quantities such as the flow velocity profiles at different stream positions and pressure fields at different points in a control volume. Through modal analysis, the effective mass factor shows the mass involved in each mode and helps identify modes with high potential to cause damage and prioritize efforts to address them. The CFD suggests that the sectionalized design of the gate valve leads to a strong vorticity of the fluid in the transversal direction of the flow and a decrease in efficiency due to pressure drop.

Optimal control of jacket platforms vibrations under the simultaneous effect of waves and earthquakes considering fluid-structure interaction

Offshore platforms are very important structures that experience different types of dynamic loads throughout their service lives. In this study, the effects of the simultaneous occurrence of earthquakes and wave loads are investigated. The influences of earthquake-related water shaking on microwaves have also been considered. For this purpose, a case study is performed on the Ressalat oil platform in the Persian Gulf. The modified endurance wave analysis (MEWA) is used to produce waves corresponding to the structure's location. Moreover, the interactions between the fluid and the structure (FSI), as well as the effect of the added mass caused by the oscillation of the platform in the fluid are considered in the analysis. In order to control platform vibrations, the ideas of semi-active control using magnetic fluid dampers (MR), along with the fractional order proportional-integral-derivative (FOPID) control algorithm, are investigated. For online calculation of the gains of the control algorithm, an observer composed of 2-interval type fuzzy systems (IT2FLS) is used, whose orders, the membership functions of the fuzzy system inputs, as well as the fuzzy rules set, are optimized by Observer-Teacher-Learner-Based Optimization (OTLBO). This technique is a powerful meta-heuristic algorithm. In the used control process, the effect of actuator saturation, which is one of the problems of semi-active control systems, is considered. To evaluate the effectiveness of the proposed control, the maximum value and the root-mean-square (RMS) responses of the platform under 5 waves with different return periods and 7 far-fault earthquake records are compared. The results show that in the cases of simultaneous wave and earthquake loads, the wave load can partly reduce the maximum displacements caused by earthquakes. Also, the maximum and RMS displacement of the jacket platforms' level under wave load with a return period of 100 years and 7 earthquakes are reduced by an average of 35%, which can increase the service life of these structures by 4 times.

Optimum design of sandwich composite structures under various dynamic loads using the equivalent static load method

Sandwich composite structures are high-performance materials with greater specific strength and specific stiffness properties, than widely used conventional metals. In this study, sandwich composite structures under dynamic loads were optimized using the equivalent static load method (ESLM). First, a finite element analysis was performed on the sandwich composite structure, using the high-order sandwich panel theory (HSAPT), considering the core material to be compressible. Further, it was optimized by applying the ESLM to three different sandwich composite structures under different types of dynamic loads. The results of the proposed method and conventional dynamic response optimization method were compared. The ESLM was observed to attain a convergence at a rate 1/24 times faster than the conventional method.

Dynamic Response of Some Noncarbon Nanomaterials Using Multiscale Modeling Involving Material and Geometric Nonlinearities

Abstract Nonlinear dynamic response of some noncarbon nanomaterials, involving material and geometric nonlinearities under different types of dynamic loads, is investigated using computationally efficient multiscale modeling. Multiscale-based finite element model is developed in the framework of the Cauchy–Born rule, which couples the deformation at the atomic scale to deformation at the continuum scale. The Tersoff–Brenner type interatomic potential is employed to model the atomic interactions. The governing finite elemental equations are derived through Hamilton's principle for a dynamic system. The linearization of nonlinear discrete equations is done using Newton–Raphson method and are solved using Newmark's time integration technique. The effects of material and geometric nonlinearities, inherent damping, different types of dynamic loads, and initial strain on the transient response of noncarbon nanosheets with clamped boundary conditions are reported in detail. The present results obtained from the multiscale-based finite element method are compared with those obtained from molecular dynamics (MD) simulation for the free vibration analysis, and the results are found to be in good agreement. The present results are also compared with the results of those obtained from Kirchhoff plate model for some cases.

Response of Rubcrete Continuous Deep Beams under Sinusoidal Loads

Continuous deep beams (CDBs) are the most used members in constructions with highly exposing to different types of dynamic loads. It is well known that; the concrete is a brittle material and has a weak resistance to energy absorption. Using scrapped tire rubber enhances the concrete energy absorption for sustainability purposes. Timoshenko beam theory has been used to solve CDBs subjected to sinusoidal load and has been adopted for verification of numerical results of ANSYS APDL V.15.0. Seven concrete mixes have been simulated with different types and amounts of aggregate – rubber replacements. Several parameters have been studied like replacing type, percentages, shear span of beam to depth ratio (a/h) and load intensity. It was found that Timoshenko beam theory can be used for harmonic loading CDBs. Furthermore, replacement in general provided more ductility due to rubber elasticity property. Gravel replacement by 45% has the larger displacement values among the other types. Also, it has been noted that, the sensitive of concrete deep beams towards a/h ratio stills considerable for harmonic loads, i.e. minimizing the ratio leads to decrementing the deflection wave amplitudes.

Online Model Identification and Updating in Multi-Platform Pseudo-Dynamic Simulation of Steel Structures – Experimental Applications

ABSTRACT A new technique is proposed for online model identification and updating in multi-platform pseudo-dynamic simulation of steel structures which brings novelty through eliminating the need for optimization during the identification stage of material/section behavior. Furthermore, the proposed procedure requires no prior information about the updated component of the numerical substructure and free of backward inconsistency. The efficiency of the proposed online model updating procedure is investigated by fourteen simulations which have real physical experimental substructures. A three span, small-scale bridge model with different pier heights is selected as the investigated structure. The simulations are performed under two different types of dynamic loads: instantaneous constant loading and strong ground motion records. The repeatability of tests, the effects of strong ground motion records and different pier heights are investigated. Furthermore completely numerical dynamic analyses with advanced models are also performed for comparison purposes. The results demonstrated that the proposed online model identification and updating procedure can be used with sufficient precision in multi-platform pseudo-dynamic simulations of steel structures.

On the special construction and materials conditions reducing the negative impact of vibrations on concrete structures

This article presents an in-depth review of the different types of dynamic loads that may occur in concrete structures. The full scope of the procedure diagnosing the harmful vibrations in buildings was also presented as well as its main features were characterized. In a broad context, special conditions are described and discussed for buildings that should be met to avoid the harmful effects of vibrations on concrete structures. On the basis of literature studies and own research, practical construction, material and technological guidelines were presented in the scope of limiting the negative impact of vibrations on concrete structures.

Dynamic elastic modulus of Xianyang loess based on microscopic analysis: a qualitative evaluation

To explore the microscopic mechanism underpinning the dynamic characteristics of saturated loess, dynamic triaxial tests were conducted on saturated loess in Xianyang City, China. The tests were performed under dynamic loads of different waveforms, confining pressures, frequencies and amplitudes. Under each dynamic load, the test included two states: one stopped after 12 loading cycles, and the other is to vibrate to the failure state. Furthermore, a scanning electron microscope test was carried out on the undisturbed samples and the sheared dynamic triaxial samples. In this paper, the dynamic elastic modulus of samples is used to represent the dynamic characteristics, and parameters such as the diameter, average abundance, average fractal dimension, and directional probability entropy of the structural units and pores are selected to describe the microstructural characteristics of samples. The results show that the dynamic elastic modulus of samples decreases with increasing number of loading cycles or axial strain and finally stabilises when different types of dynamic loads are applied. The types of dynamic loads exert a significant influence on the microstructural parameters of structural units and pores.

Analysis and Research of Friction and Wear Mechanism Based on Different Types of Dynamic Load

For sliding friction pairs formed by differential gears and gaskets, it is necessary to study the friction performance under the coupling of multiple working conditions (impact, vibration and alternating load). For example, it is of great significance to study the performance of sliding friction pair in the rear axle differential of truck and the friction and wear performance of the internal parts of aircraft and ships under the coupling condition of multiple working conditions, so as to obtain longer service life and excellent performance by improving the friction performance. The ball-disc pairs were experimentally built to simulate the friction and wear mechanism of materials under different types of dynamic loads. Under the condition of non-polluting white oil lubrication, increased the contact ratio of the pair, and made the pair reach the experimental state of no dynamic pressure lubrication, selected different types of dynamic loads (step load, damped harmonic excitation load (DHE), Short-term high load) loading method. During the experiment, force sensors and online visual ferromagnetic sensors were used to monitor friction and wear rate signals in real time, and TR200 profilometer and scanning electron microscope were used to observe and study friction characteristics. The results show that a reasonable step load can improve the friction and wear state of the ball-disk pair during the running-in period and reduce the peak wear of the surface contact portion of the pair of materials. The main wear form of the experimental pair under constant load and step load for plastic flow and squeezing deformation, the fatigue of the surface material is caused by the high frequency fluctuating load of DHE. Therefore, it is concluded that the step load has an effect on improving the friction and wear performance of the mating pair, and the DHE load has a damage effect on the mating pair.

Dynamic behaviour and damage characteristics of loess in Xianyang, China

In engineering practice, the in situ soil layer is under different static pressures and experiences different types of dynamic loads. To determine the influence of stress state and dynamic load type on the dynamic characteristics of, and damage evolution in, saturated loess, consolidated-undrained dynamic triaxial tests were conducted on samples subjected to different confining pressures and consolidation stress ratios. During the test, rectangular wave and sine wave were selected as types of applied dynamic load. Results show that samples with good consolidation effect, and loaded by the sine wave, exhibit relatively high strength. The deformation of the samples is influenced by their initial consolidation state and the value of dynamic stress: the better the consolidation effect of samples and the lower the applied dynamic stress, the smaller the strain difference therein; with the increase of dynamic stress, greater strain occurs in samples loaded by a rectangular wave. The influence of waveforms on the initial dynamic elastic modulus changed with the stress state: this was significantly affected by application of sine wave loading (low confining pressure, low consolidation stress ratio), significantly affected by application of rectangular wave loading (low confining pressure, high consolidation stress ratio), and slightly affected by waveforms (high confining pressure). The instantaneous application of rectangular wave load can cause consolidated samples to be strengthened in the early test stage, while damage developed rapidly with the proceeding of loading process.

State-of-the-Art Review of Metallic Dampers: Testing, Development and Implementation

Structural control systems have gained popularity for the ability to reduce the structural vibration response of civil structures subjected to different types of dynamic loads. Passive, semi-active, active and hybrid control systems have been widely utilized in various types of structures. This article presents one of the most economical and yet the most effective approaches used in structural vibration control. Herein, a comprehensive state-of-the-art review of the development and application of metallic dampers is discussed. The dampers are classified into five categories: steel, aluminum, lead, copper and shaped-memory alloy dampers. In addition, the details of various computational methods used in the analysis of metallic dampers are briefly explained. This article reveals that the use of metallic dampers is being advanced broadly owing to their low manufacturing costs, stable hysteresis behavior, resistance to ambient temperature, reliability and high energy dissipation capability. It is also concluded that mild steel is the most popular material among metallic dampers.

KDamper concept in seismic isolation of bridges with flexible piers

Contemporary seismic isolation systems for bridge applications provide (a) horizontal isolation from the effects of earthquake shaking, and (b) an energy dissipation mechanism to reduce displacements. Throughout the years many kinds of seismic isolation mechanisms have been developed, with two concepts being the most promising ones: the introduction of negative stiffness elements and the incorporation of an additional mass. The latter has led to the development of Tuned Mass Dampers (TMDs), engineering devices consisting of a mass, a spring and a viscous damper commonly used to suppress any undesirable vibrations induced by wind and earthquake loads. The negative stiffness behavior is primarily achieved by special mechanical designs involving conventional positive stiffness pre-stressed elastic mechanical elements, such as post-buckled beams, plates, shells and pre-compressed springs, arranged in appropriate geometrical configurations. Combining the beneficial characteristics of both concepts, a novel passive vibration isolation and damping concept is introduced, the KDamper. The KDamper is based on the optimal combination of appropriate stiffness elements, which include a negative stiffness element. The presence of the additional mass enables structural vibrating energy to be transferred from the structure to the device. The main advantage of the KDamper over other similar concepts including negative stiffness elements is that no reduction in the overall stiffness of the system is required.In this paper, an initial approach towards the implementation of the KDamper to the absorption of seismic excitation of structures is considered, by applying the KDamping concept to a typical single-pier bridge subjected to three different types of dynamic loading. The contribution of pier is taken into account during the analysis. A comparison with a non-isolated bridge with similar characteristics confirms that KDamper based seismic absorption designs can provide a promising alternative to the conventional seismic isolation bearings, offering numerous advantages, such as increased damping and simple technological implementations.

A Novel Approach to Control the Robotic Hand Grasping Process by Using an Artificial Neural Network Algorithm

AbstractThis paper presents an artificial neural network (ANN) trained on the patterns of slip signals; these patterns were generated by using conventional sensors with a novel design of fingertip mechanism for detecting the slippage of a grasped object under different types of dynamic loads. This design is to be used with an underactuated triple finger artificial hand based on the pulleys-tendon mechanism. The grasped object is designed in a prism shape with three direct current motors with unbalance rotating mass to generate excitation in the object. Also, this object is covered with different types of surface materials, namely, spongy rubber, glass, and wood. Three types of external loads are used to disturb the grasping process represented by quasi-static pulling on the object, the dynamic load on the object, and on the artificial arm in separate form. The mathematical modeling has been derived for the proposed design to generate the signal of contact force components ratio through using the conventional sensor signals with the aid of Matlab-Simulink software. The ANN has been trained on the basis of the patterns of force component ratio signals at slippage occurrence, in order to detect slippage and then prevent it without the need for any knowledge about the surface properties of the grasped object. The experimental results are discussed in comparison with the physical aspect of the slippage phenomenon, and they show good agreement with the physical definition of the slippage phenomenon. In addition, the network evaluation results are discussed with different parameters that govern the controller operation, such as network error, classification efficiency, and delay in response time.

Peridynamic model for dynamic fracture in unidirectional fiber-reinforced composites

We propose a computational method for a homogenized peridynamics description of fiber-reinforced composites and we use it to simulate dynamic brittle fracture and damage in these materials. With this model we analyze the dynamic effects induced by different types of dynamic loading on the fracture and damage behavior of unidirectional fiber-reinforced composites. In contrast to the results expected from quasi-static loading, the simulations show that dynamic conditions can lead to co-existence of and transitions between fracture modes; matrix shattering can happen before a splitting crack propagates. We observe matrix–fiber splitting fracture, matrix cracking, and crack migration in the matrix, including crack branching in the matrix similar to what is observed in recent dynamic experiments. The new model works for arbitrary fiber orientation relative to a uniform discretization grid and also works with random discretizations. The peridynamic composite model captures significant differences in the crack propagation behavior when dynamic loadings of different intensities are applied. An interesting result is branching of a splitting crack into two matrix cracks in transversely loaded samples. These cracks branch as in an isotropic material but here they migrate over the “fiber bonds”, without breaking them. This behavior has been observed in recent experiments. The strong influence that elastic waves have on the matrix damage and crack propagation paths is discussed. No special criteria for splitting mode fracture (Mode II), crack curving, or crack arrest are needed, and yet we obtain all these modes of material failure as a direct result of the peridynamic simulations.

Effect of cross-sectional warping of anisotropic sandwich laminates due to dynamic loads using a refined theory and C° finite elements

An attempt has been made to study the effect of cross-sectional warping in the symmetrically laminated anisotropic composite sandwich plates for transient loads. A higher-order shear deformation theory (HOST) is used in conjunction with the simple displacement based C° finite element method (FEM). As is well-known, the classical first-order theories hitherto considered were inadequate to describe the propagation of waves in the highly orthotropic sandwich laminates. The present theory, which is more accurate than the Reissner-Mindlin theory, is applied herein, for the evaluation of plate response to different types of dynamic loads. An explicit central difference scheme is employed for the integration of dynamic equations of equilibrium with a diagonalized mass matrix obtained by a special procedure applicable to quadrilateral isoparametric elements. The numerical results of the present investigation have been compared with the first-order shear deformation theory (FOST) and the differences between HOST and FOST are examined. The results presented here should be useful in obtaining better correlation between theory and experiment, and to numerical analysts in verifying their results.

Finite element transient analysis of composite and sandwich plates based on a refined theory and a mode superposition method

Transient dynamic response of composite and sandwich plates is obtained using a recently developed refined shear deformation theory and mode superposition technique. The free vibration response is computed using the generalized Jacobi method with a sub-space iteration technique and then the mode shapes are used for computing the dynamic response. A special mass lumping procedure is used in the dynamic equilibrium equations. Duhamel's integral is used for the time integration of uncoupled systems. The method leads to considerable saving in computation time during computer implementation for the same order of accuracy in results as compared to direct integration methods. Numerical examples are solved for different types of dynamic loads and the results compared with those available in the literature. The mode superposition method has given good results and at the same time there is considerable saving in computer time. Unlike direct numerical integration techniques, here the time step requirements are only for obtaining the variation of displacement and stress resultants with time and for closely approximating the time dependent forcing function during numerical integration of single degree of freedom modal equations.

Dynamics of laminated composite plates with a higher order theory and finite element discretization

A simple isoparametric finite element formulation based on a higher-order displacement model for dynamic analysis of multi-layer symmetric composite plates is presented with an explicit time marching scheme. As is well-known, the Kirchhoff plate theory is inadequate to describe the propagation of waves in plates. The first-order shear deformable Mindlin plate theory hitherto considered was adequate for determining responses to dynamic loads. The present higher-order theory which is more accurate than the Mindlin theory is applied, herein, for the evaluation of plate response to different types of dynamic loads. A special mass lumping scheme is adopted which conserves the total mass of the element and includes the effects due to rotary inertia terms. The parametric effects of the time step, finite element mesh, lamination scheme and orthotropy on the transient response are investigated. Several numerical examples are presented and compared with results from other sources.