Development of Physics-Based Morphology Model with an Emphasis on the Interaction of Incoming Waves with Transient Bed Profile due to Scouring and Accretion using Dynamic Mesh

A physics-based morphology model [Seoul Foam] was developed using the dynamic mesh technique to explain the interaction between the sea bed, which undergoes deformation due to siltation and scouring, and the incoming waves. In doing so, OlaFlow, an Open Foam-based toolbox, was used as a hydrodynamic model. To verify the proposed physically-based morphology [Seoul Foam] in this study, numerical simulations of the shoaling process over the beach of the uniform slope were implemented. The numerical result shows that the formation process of a sand bar over the foreshore was successfully simulated. As can be easily anticipated, the size of the sand bar was closely linked to the nature of incoming waves, and in the case of a rough sea, the foreshore slope was rapidly deformed due to scouring. In mild seas, several sand waves were formed near the shoreline, and when the exposure time was the same, the size of the sand waves was not as large as in rough seas.

Flow pulsation reduction of a single-piston piezoelectric pump based on elastic cavity group and unloading valve

A piston piezoelectric (PZT) pump has many advantages for the use of light actuators. How to deal with the contradiction between the piston amount and oil delivery quality is an essence when designing the pump. In order to depress the pressure pulsation and flow pulsation in a single-piston PZT pump, a two-stage attenuator is proposed. It involves an elastic cavity group and an unloading valve. Unsteady flow inside the pump is numerically calculated and analyzed to reveal its delivery characteristic in the whole pumping cycle. The distributing process of the passive valves is obtained through the dynamic mesh technique. Influences of key design and operation factors on the delivery performance of the pump are analyzed. The results indicate that the flexible cavity group and the unloading valve arranged at the delivery port can reduce the flow pulsation by 45%. The design can effectively provide stable flow for the actuator in a certain frequency range.

Research on transient aerodynamic characteristics of windshield wipers of vehicles

Purpose The main purpose of this paper is to gain a better understanding of the transient aerodynamic characteristics of moving windshield wipers. In addition, this paper also strives to illustrate and clarify how the wiper motion impacts the airflow structure; the aerodynamic interaction of two wipers is also discussed. Design/methodology/approach A standard vehicle model proposed by the Motor Industry Research Association and a pair of simplified bone wipers are introduced, and a dynamic mesh technique and user-defined functions are used to achieve the wiper motion. Finite volume methods and large eddy simulation (LES) are used to simulate the transient airflow field. The simulation results are validated through the wind tunnel test. Findings The results obtained from the study are presented graphically, and pressure, velocity distributions, airflow structures, aerodynamic drag and lift force are shown. Significant influences of wiper motion on airflow structures are achieved. The maximum value of aerodynamic lift and drag force exists when wipers are rotating and there is a certain change rule. The aerodynamic lift and drag force when wipers are rotating downward is greater than when wipers are rotating upward, and the force when rotating upward is greater than that when steady. The aerodynamic lift and drag forces of the driver-side wiper is greater than those of the passenger-side wiper. Originality/value The LES method in combination with dynamic mesh technique to study the transient aerodynamic characteristics of windshield wipers is relatively new.

Numerical Simulation Study of Three-Dimensional Flow Field on Roots- Type Power Machine Based on Dynamic Mesh Technique

Expander which drives an electromotor to generate electricity is the core of low-temperature waste heat recovery equipment. At present, domestic expanders on waste heat recovery system mostly arise from exploration, research and improvement on the existing models of screw expanders and scroll expanders, which have complex structures and high costs. For overcoming the shortcomings mentioned above, a new roots-type power machine is researched and designed. In this paper, the working fluid of low pressure waste heat is stimulated according to both the different operating conditions and the different intake and exhaust pressure and flow, and the changing process of internal flow field is simulated over the time period using dynamic mesh technique when the power machine is in rotating work. Besides, the pressure field, velocity field and graph of mass flow rate are analyzed with the simulation results, thus obtaining the conclusion of optimum operating conditions of the roots-type power machine to guide selection method in practice, that is, selecting appropriate roots-type power machines according to different types of waste heat in industrial production. These efforts can therefore provide strong theoretical guidance and foundation for the subsequent engineering practice of waste heat recovery system on roots-type power machine, and can have a profound impact on further recovery and utilization of low-grade energy.

Maneuvering Prediction of a VLCC Model Based on CFD Simulation for PMM Tests by Using a Circulating Water Channel

Since ship maneuverability is a vitally important characteristic of ship design, several experimental techniques to determine ship maneuverability are recommended, among which using the planar motion mechanism (PMM) test for captive model in a circulating water channel (CWC) has become a new and effective way for captive model tests. This paper uses the numerical method to study the viscous hydrodynamic forces acting on a KVLCC2 model. The viscous flow around the model and its hydrodynamic forces in the oblique towing, pure sway and pure yaw test are simulated by CFD, in which the steady and unsteady RANS equations in conjunction with a RNG k-ε turbulence model are solved. By applying the dynamic mesh technique, the motion of pure sway is simulated. As a key technique for realization of pure yaw motion a new method combining the layering and local remeshing that treats restricted water region problem like in a CWC is developed. Accuracy of the proposed numerical method is confirmed by comparing the calculated hydrodynamic forces with the measured one. Then hydrodynamic derivatives of ship maneuvering movements are analyzed, and used in maneuvering prediction which is based on MMG model for turning test. Results show that the hybrid dynamic mesh technique is a practically efficient way to simulation of the pure yaw motion in CWC, which balances computational accuracy and efficiency. It also demonstrates that the present numerical model gives satisfactory results on PMM tests and maneuvering motions in terms of accuracy and it can be an economical method for engineering practices.