In this review, the analysis of melting and solidification phenomena and the mechanism of the occurrence of defects as well as the analysis of melting and solidification using the numerical simulation in laser powder bed fusion (LPBF) process were introduced. In addition, the strategies of suppression of defects were described. The melting and solidification phenomena during LPBF process are relatively similar to those during welding. Since the plume brings about the strong recoil pressure on the melt pool, the keyhole takes place. And when the depth of keyhole becomes more than a threshold, the keyhole pore remains at the bottom of melt pool. Since the plume also brings about spattering and blows out powder, the gas pores are prone to occur easily. The micro-simulation of melting and solidification enables to reproduce the real phenomena. The macro-simulation of melting and solidification phenomena is one of the effective tools to predict the optimum fabrication condition. In order to prevent the occurrence of defects, it is significant not only to obtain the optimum fabrication condition using the process map but also to develop the simulation software. In addition, the use of the monitoring and feedback control system is greatly effective. Therefore the development of the cyber-physical system is needed.
Computational models have been widely used for more than four decades to evaluate the mechanical behavior of knee joint arthroplasty. Validated computational models provide a virtual platform to develop optimal articular surfaces which achieve desired implant characteristics. This review paper provides a comprehensive overview of the computational models available to represent knee joint arthroplasty. A brief overview of knee joint anatomy and arthroplasty is provided, followed by computational model development techniques. Use of the computational models in development of knee joint arthroplasty and pre- or post-clinical evaluation is summarized. This review paper presents current modeling capabilities for implant design and stability, with further suggestions for studying the performance of implants on a population level. However, simulations must include closely corroborated multi-domain analysis in order to account for real-life variability.
One of the major purposes of fluid mechanics and engineering is to reduce the flow resistance caused by flow friction, flow separation, vortex generation, and other factors. To reduce or eliminate flow resistance, in general, flow control is performed either passively or actively. Passive flow control is performed by changing the flow channel or object shape a little and reducing the total flow resistance. On the contrary, active flow control uses a device requiring power, but it can perform various complex flow controls. In this paper, the passive flow control of jets is examined with flow characteristics, control methods, and some applications because jet flows include the essence of fluid dynamics, such as, boundary layer flow, turbulent flow, shear flow, and flow mixing. In particular, the effects of the nozzle shape, the tab, rib and vortex generator, and the orifice or notched orifice on the flow characteristics of sub- and supersonic jets are examined. Furthermore, the control and suppression of high speed jet noise by a chevron nozzle, some examples of active flow control, and other areas are examined. Globular formation of fine solid particles by flow control, lift control of airplane wings, and the flow control of a NOTAR helicopter without tail rotor are also addressed.
This paper presents a review of waveguides on lithium niobate for surface acoustic waves (SAWs), including in particular the classic literature on the topic with the intent of renewing interest in them in the context of potential applications in the burgeoning discipline of micro to nano-scale acoustofluidics. From the fundamentals of the piezoelectric effect we describe interdigital electrodes and how they generate acoustic waves, consider focusing interdigital electrodes as a simple means of laterally confining the acoustic energy propagating across a substrate, and then quickly move to waveguiding structures that provide confinement by defining either a region of slow wave velocity or a physically isolated structure. The ability to steer acoustic waves using these waveguides is considered. The many analytical, computational, and experimental tools devised by past investigators to design them are discussed in detail, as are the relative advantages and disadvantages of the waveguide designs considered over the years.