Civil and Environmental Engineering

Fluid hyper-element is usually utilized to model semi-infinite region in dynamic analysis of concrete gravity dams. This part of water domain is assumed to have constant depth that extends to infinity in the upstream direction. The accurate dynamic analysis of concrete gravity dam is obtained by employing two dimensional semi-infinite fluid element. The usual method for calculating the impedance matrix of fluid hyper-element is dependent on the solution of a complex eigen-value problem for each frequency. In the present study, an efficient technique is proposed which simplifies this procedure significantly, and results in great computational time savings. The accuracy of this method is tested under various conditions thoroughly and concluded that efficient technique is accurate under all practical conditions.

Different approaches are available for dynamic analysis of concrete gravity dam-reservoir systems. However, the rigorous analysis is based on FE-(FE-HE) method (i.e., Finite Element-(Finite Element-Hyper element)). This means that the dam is treated by plane solid finite elements, while the reservoir is divided into two parts, the near-field region in the vicinity of the dam, which is discretized by plane fluid finite elements, and the far-field part (assuming constant depth), which is modeled by a two-dimensional semi-infinite fluid hyper-element. A major portion of the numerical calculation time spent is on the solution of a complex eigen-value problem related to fluid hyper-element, which must be solved at each frequency. In a previous study, an efficient procedure was proposed for the required impedance matrix calculations of the fluid hyper-element, which greatly reduces the computational time. Although, the method was accurate in most practical conditions, it was estimated that it would introduce errors under certain circumstances. In this paper, a modified efficient procedure is proposed which simplifies this procedure significantly. This is envisaged to be an enhancement of the previously proposed efficient method. The approach mainly relies on mode shapes corresponding to an arbitrary frequency. A computer program is developed based on this methodology and the response of an idealized triangular dam is studied for various conditions. The results are compared against exact response and it is observed that the response in each case matches very well with the exact response.

The pressure for pavement and geotechnical engineers to incorporate sustainability into engineering projects has led to a rise in the use of recycled concrete aggregate (RCA) as fill and in pavement sublayers. Although the use of RCA has many economical, ...

Because most approximation functions employed in meshfree methods are rational functions with overlapping supports, sufficiently accurate domain integration becomes costly, whereas insufficient accuracy in the domain integration leads to suboptimal convergence. In this paper, we show that it is possible to achieve optimal convergence by enforcing variational consistency between the domain integration and the test functions, and optimal convergence can be achieved with much less computational cost than using higher-order quadrature rules. In fact, stabilized conforming nodal integration is variationally consistent, whereas Gauss integration and nodal integration are not. In this work the consistency conditions for arbitrary order exactness in the Galerkin approximation are set forth explicitly. The test functions are then constructed to be variationally consistent with the integration scheme up to a desired order. Attempts are also made to correct methods that are variationally inconsistent via modification of test functions, and several variationally consistent methods are derived under a unified framework. It is demonstrated that the solution errors of PDEs due to quadrature inaccuracy can be significantly reduced when the variationally inconsistent methods are corrected with the proposed method, and consequently the optimal convergence rate can be either partially or fully restored.

A meshfree formulation under the reproducing kernel particle method (RKPM) was introduced for modeling the penetration and perforation of brittle geomaterials such as concrete. RKPM provides a robust framework to effectively model the projectile-target interaction and the material failure and fragmentation behaviors that are critical for this class of problems. A stabilized semi-Lagrangian formulation, in conjunction with a multiscale material damage model for brittle geomaterials and a kernel contact algorithm, were introduced for penetration modeling. In this work, the accuracy of the meshfree impact and penetration formulation was studied using a series of large-caliber projectile concrete slab perforation experiments with impact velocities in the ballistic regime. These experiments were selected due to the challenging nature of concrete perforation, and the results were used to validate the effectiveness of the proposed method to model the penetration processes and the concrete target failure. Simulation results confirm the formulation's accuracy for this type of high-rate ballistic problem and establish a basis for extension to other types of impact problems. The results show the importance of properly formulating the method of domain integration to maintain accuracy in the presence of concrete fragmentation, and also highlight the method's ability to capture the fragmentation response without a need for non-physical treatments commonly used in conventional methods.

Galerkin meshfree methods can suffer from instability and suboptimal convergence if the issue of quadrature is not properly addressed. The instability due to quadrature is further magnified in high strain rate events when nodal integration is used. In this paper, several stable and convergent nodal integration methods are presented and applied to transient and large deformation impact problems, and an eigenvalue analysis of the methods is also provided. Optimal convergence is attained using variationally consistent integration, and stability is achieved by employing strain smoothing and strain energy stabilization. The proposed integration methods show superior performance over standard nodal integration in the wave propagation and Taylor bar impact problems tested.