Narrow Results

An analytical approach is proposed for analyzing the horizontal dynamic response of an offshore pile, considering the soil as a saturated porous medium with radial heterogeneity, and accounting for the dynamic pile–water interaction. The soil is divided radially into two zones: a homogeneous outer zone and a heterogeneous inner zone consisting of finite concentric annular sub-zones. The horizontal resistance of the radially inhomogeneous soil layer is determined using the transfer matrix method. Subsequently, by utilizing the calculated soil resistance and the hydrodynamic force acting on the pile, the solution for the horizontal vibration of the pile is derived. The accuracy of the proposed approach is validated through comparisons with results from previous studies. Furthermore, a parametric study is conducted to explore the horizontal dynamic response of offshore piles within radially inhomogeneous saturated soil. The investigation demonstrates that the horizontal dynamic response of offshore piles is significantly influenced by the level of soil disturbance, range of disturbance zone, soil permeability, and water depth.

We present a short overview of the recent efforts of our group in the design of high precision Casimir force setups. We first describe our Atomic Force Microscope based technique that allows one to simultaneously and continuously calibrate the instrument, compensate for a residual electrostatic potential, measure the Casimir force, and, in the presence of a fluid in the gap between the interacting surfaces, measure the hydrodynamic force. Then we briefly discuss a new force sensor that adapts well to Casimir force measurements in critical environments.

The hydrodynamic force (HF) evaluation plays a critical role in the numerical simulation of fluid–structure interaction (FSI). By directly using the distribution functions of lattice Boltzmann equation (LBE) to evaluate the HF, the momentum exchange algorithm (MEA) has excellent features. Particularly, it is independent of boundary geometry and avoids integration on the complex boundary. In this work, the HF of lattice Boltzmann simulation (LBS) is evaluated by using the MEA. We conduct a comparative study to evaluate two lattice Boltzmann models for constructing the flow solvers, including the LBE with single-relaxation-time (SRT) and multiple-relaxation-time (MRT) collision operators. The second-order boundary condition schemes are used to address the curve boundary. The test case of flow past a cylinder asymmetrically placed in a channel is simulated. Comparing the numerical solutions of Lattice Boltzmann method (LBM) with those of Navier–Stokes equations in the literature, the influence of collision relaxation model, boundary conditions and lattice resolution is investigated. The results demonstrate that the MRT-LB improves the numerical stability of the LBM and the accuracy of HF.

A general-purpose numerical method utilizing the Green function is proposed for evaluating hydrodynamic forces acting on offshore structures due to seismic horizontal ground excitation. This model can be applied to arbitrary-shaped structures and considers the effects of fluid compressibility and wave generation. In the proposed method, the Green function and its gradient are precisely evaluated by employing approximation formulas for infinite series efficiently. Its validity and applicability to actual structures are demonstrated through numerical experiments.

We present a short overview of the recent efforts of our group in the design of high precision Casimir force setups. We first describe our Atomic Force Microscope based technique that allows one to simultaneously and continuously calibrate the instrument, compensate for a residual electrostatic potential, measure the Casimir force, and, in the presence of a fluid in the gap between the interacting surfaces, measure the hydrodynamic force. Then we briefly discuss a new force sensor that adapts well to Casimir force measurements in critical environments.