Jae-Hung Han

Korea Advanced Institute of Science and Technology | KAIST · Department of Aerospace Engineering

In mechanical engineering, focusing on elastic waves is pivotal for applications, such as energy harvesting, shock mitigation, and wave manipulation. While phononic crystals have historically been a key method for managing wave propagation, this study explores a novel technique. This method introduces Gradient Refractive-Index (GRIN) lenses by alte...

Reducing structural shocks propagated as elastic waves in thin plate-like structures is of paramount importance in diverse engineering applications. In this study, a shock reduction method using elastic patches that deflect bending waves through wave refraction, while maintaining the structural stiffness and strength is presented. Elastic patches w...

In recent years, there have been several studies focused on manipulating elastic waves in thin plate structures to achieve shock reduction or energy harvesting, without being limited by frequency. An elastic patch is a promising method for such manipulation, as it can be easily applied to practical structures without compromising their stiffness or...

Periodic structures, composed of repeating and regularly connected unit cells, are widely used in various engineering fields due to their functionality, aesthetics, producibility, and unique property of passively reducing vibrations. However, analyzing these structures can be challenging due to their high degrees of freedom (DOFs), and dynamic anal...

A hoverbike is a vehicle that can fly and hover. Demand for using hoverbikes in various missions, including transport, surveillance, reconnaissance, and infiltration is increasing. While various attempts have been made to develop hoverbikes, there is still a lack of experimental verification on whether the frame structure of a hoverbike can provide...

The joint design of origami-inspired robots is one of the most distinctive features that distinguishes them from conventional robots. A joint design using material's compliance enables origami robots to implement complex transformational movements in a lightweight and simple manner. However, utilizing the continuum bending mode of materials brings...

Uniform downwash of a revolving or flapping wing is a key indicator of aerodynamic efficiency. Although the slack-angle of flexible wings can significantly alter the downwash due to the inherent aerodynamic twist, its effect on the downwash distribution for a change in planform remains unknown. In this study, the effect of wing flexibility (slack-a...

This paper introduces a novel origami pattern that enables the construction of polyhedral shapes from a planar sheet. The proposed polyhedral origami exhibits rigid foldability, which means that it can be folded without deforming its facets. The folding motion to a polyhedral shape can possess a single degree of freedom under the symmetric conditio...

Flapping-wing air vehicles (FWAVs) have significant advantages in surveillance and reconnaissance missions due to their camouflage capabilities. In such missions, autonomous flight capabilities in outdoor environments are important. An FWAV capable of autonomous flight is designed in this research. The FWAV has elevons for generating pitching and r...

This article proposes a novel thickness-accommodating method to design a void-free for flat-foldable origami pattern without self-intersection. Unlike existing methods, it enables uniform thickness distribution without any holes or voids at any location and maximizes the effective area of the unfolded state. The proposed method is applicable not on...

This study focuses on the flapping mechanisms found in recently developed biometric flapping-wing air vehicles (FWAVs). FWAVs mimic the flight characteristics of flying animals, providing advantages such as maneuverability, inconspicuousness, and excellent flight efficiency in the low Reynolds number region. The flapping mechanism is a critical par...

In flapping-wing air vehicles, the flapping mechanism is directly related to the movement of the wing making it one of the major factors in determining aerodynamic performance. In this study, a method to increase aerodynamic performance using the flapping mechanism is discussed. This paper presents a twist-coupled mechanism that can increase thrust...

In this paper, a novel concept of the adaptive vibration isolator is presented. The proposed adaptive isolator is based on the thin-walled Yoshimura-patterned tube, which is able to reconfigure its shape to tune the stiffness. Multiple numbers of reconfigurable modules compose the proposed vibration isolator; thus, the force transmissibility of the...

The crease line formed in an origami-shaped crash box (OSCB) acts as a geometric imperfection and mode inducer. Such geometric imperfections make it possible to protect occupants by lowering the peak force in the event of a collision. The OSCB also shows desirable performance as a crashworthy structure by inducing a collapsing mode with excellent e...

A lot of flapping-wing mechanisms have been proposed to mimic the flight characteristics of biological flyers. However, it is difficult to find studies that consider unsteady aerodynamics in the design of the flapping-wing mechanisms. This paper presents a systematic approach to optimizing the design parameters of a foldable flapping-wing mechanism...

Flapping-wing micro air vehicles (FWMAVs) have the capability of performing various flight modes like birds and insects. Therefore, it is necessary to understand the various flight modes of FWMAVs in order to fully utilize the capability of the vehicle. The unique flight modes of FWMAVs can be studied through the trajectory optimization. This paper...

This study investigates the effects of aerodynamic interaction on the aeroelastic characteristics of wings in proximity which is considered to be aerodynamically more efficient than the single wing case. The structural model of the wing is based on the first-order shear deformation theory and analyzed by the finite element method. The flow surround...

Experimental investigations are made for the combined effects of aspect ratio (AR), slack (β S ) and pitch angles on the aerodynamic characteristics of flexible flapping wings in hover. β S is introduced as a way to indirectly alter the flexibility of the wing. An optimum AR range of 3 to 5 based on the lift coefficient is observed depending on the...

This paper presents a novel methodology for designing the flight control system of a micro aerial vehicle (MAV); it allows the MAV to learn how to fly by itself, without the risk of damage. The proposed methodology uses a magnetic levitation–based safety-guaranteed flight test environment and deep reinforcement learning techniques to avoid the curr...

This paper presents experimental and numerical investigations on the origami-patterned tube which is acknowledged as a promising energy-absorption device. Its buckling mode leads to high performances in terms of specific energy absorption (SEA) and crush force efficiency (CFE). The polygonal tube is prefolded by following an origami pattern, which...

This paper proposes an automated aerial docking system for unmanned aerial vehicles. The proposed automated aerial docking system consists of the following two subsystems: 1) docking mechanical system and 2) vision-based deep learning detection/tracking system. A fundamental challenge during the midair docking phase is integration between the leade...

Reconfigurable structures have attracted increasing attention in numerous fields, such as aerospace, biomechanical, and civil engineering, owing to their nature to reshape and readjust without altering their original architectures. However, one of the most challenging issues in designing a reconfigurable structure is to ensure a load‐bearing capaci...

View Video Presentation: https://doi.org/10.2514/6.2022-0883.vid This paper presents an automated aerial docking system for unmanned aerial vehicle (UAV). The proposed automated aerial docking system consists of two subsystems: docking mechanical system and vision-based deep learning target detection/tracking system. One of the fundamental challeng...

In general, bending waves transfer the largest portion of shock energy in a plate-like structure. This study proposes a new shock reduction method using an elastic patch designed to defocus the bending waves through the refraction of the waves so that it is possible to effectively reduce the propagating shock for a certain target area. Elastic patc...

This paper proposes an approach to analyze the dynamic stability and develop trajectory-tracking controllers for flapping-wing micro air vehicle (FWMAV). A multibody dynamics simulation framework coupled with a modified quasi-steady aerodynamic model was implemented for stability analysis, which was appended with flight control block for accomplish...

Insects are excellent fliers because of their ability to generate precise wing kinematics and deform their wings for the sufficient production of unsteady aerodynamic forces. Most of the previous studies on the effects of wing kinematics on the aerodynamics have been limited to the use of rigid wings, and leaves the contribution of wing flexibility...

The newly proposed ground test technique for aeroelastic flutter emulation is applied to examine the effectiveness of passive flutter suppression. The technique is to substitute wind-tunnel flutter test by emulating unsteady aerodynamic force using several point-loading actuators. Besides the simplicity of the technique, the essential advantage of...

A cable-driven model support concept is suggested and implemented in this paper. In this case, it is a cable suspension and balance system (CSBS), which has the advantages of low support interference and reduced vibration responses for effective wind tunnel tests. This system is designed for both model motion control and aerodynamic load measuremen...

This paper explores the effectiveness of spin motion in mitigating the flight dispersion of a two-stage solid-propellant rocket model due to thrust misalignment. The aerodynamic coefficients of the rocket model are obtained by the use of a panel method and semi-empirical equations. A simulation program is developed to solve the equations of motion...

This paper proposes a simple and a robust bistable docking system with a deep learning based real-time drogue detection and tracking system for Unmanned Aircraft Systems (UAS) for mid-air autonomous aerial docking. Secure aerial docking mechanisms between the leader and follower aerial vehicles with effective drogue detection and tracking strategie...

Deployable structures have received much attention in the building of large structural systems in space due to the limitations in the packaging capabilities of satellites and launch vehicles. Among various categories of deployable structures, deployable truss structures are most commonly used because of their high stiffness and strength. However, d...

Diverse applications including switches, deployable structures, and reconfigurable robots can benefit from bi-stability characteristics. However, the complexity of implementation and the limitation of structure configuration make it difficult to apply conventional bi-stable mechanisms to the structures that require rotational bi-stability. In this...

Experiments were conducted to examine the effect of sweep motion profile on the aerodynamic characteristics of flexible and rigid flapping wings in hover. The sweep motion was varied from triangular to sinusoidal profiles. The study revealed that the flexible wing was more sensitive to the change in motion profile by inducing a certain amount of ph...

A new approach for folding the Yoshimura cylinder is proposed in this study. The proposed concept is based on a reconfiguration process involving a cylindrical structure with the Yoshimura pattern and the bellows fold pattern. Static analyses are conducted to confirm the effectiveness of the proposed folding methodology. A special case of folding i...

Based on the advantages of the cable-driven parallel robot (CDPR), we developed a cable suspension and balance system (CSBS) as a multi-purpose device for wind tunnel tests with motion control and load measurement capability. The CSBS was designed to serve as both a wind tunnel model mount and balance. This paper suggests two novel methodologies to...

This paper presents an application of Equivalent Laminate Modeling (ELM) to predict the effective elastic, thermoelastic, and piezoelectric properties of braided composites. Here, two braided composite configurations were considered: biaxial and triaxial. The present ELM-based modeling was validated through a comparison with analytical unit cell mo...

Bi-stable mechanisms are systems with two distinct stable equilibrium positions within their range of operation. They are capable of steadily staying in positions without external power input and require less energy to move to the next stable state because of their snap-through behavior. Diverse applications including switches, deployable structure...

A study investigates the improvement of the performance of the split-type separation bolt by conducting a sensitivity analysis and optimization for design parameters using the developed mathematical model. A considered performance index includes the amount of structural shock generated in the separation process. The separation sequence of the split...

Wing flexibility is unavoidable for flapping wing flyers to ensure a lightweight body and for higher payload allowances on board. It also effectively minimizes the inertia force from high-frequency wingbeat motion. However, related studies that attempt to clarify the essence of wing flexibility remain insufficient. Here, a parametric study of a fle...

Pyrotechnic separation devices have been widely used in various missions of spacecraft in order to separate the structural parts with high reliability. Although they afford advantages of cost-effectiveness and high reliability, pyrotechnic separation devices generate an intensive dynamic response called pyroshock, which can lead to fatal damage to...

In demand of simpler and alternative ground flutter test, a new technique that emulates flutter on the ground has recently emerged. In this paper, an improvement of the test technique is made and verified through the experimental work. The technique utilizes general ground vibration test (GVT) devices. The key idea is to emulate the distributed uns...

Pyrotechnic devices have been widely utilized in various applications: spacecraft, launch vehicles, missiles, and aircraft as well as for stage separation, valve control, and booster separation. However, most pyrotechnic separators generate an intensive mechanical transient response called pyroshock, which can cause catastrophic failures in electro...

Pyrotechnically actuated devices (PADs), such as pyrotechnic separators, pyro-cutters, and pyro-valves, use a pressure cartridge to generate high operating pressure. Generally, an initiator is used as the pressure cartridge, which ignites a propellant, such as zirconium/potassium perchlorate (ZPP), electrically and generates a high-pressure gas wit...

A new folding concept for Yoshimura cylinder is proposed in this study. The preliminary study is conducted on the proposed folding concept, and the special folding condition is observed, which can significantly reduce the deformation of the material during the folding process. The appropriate problem is defined to analyze that ideal folding pattern...

Previous analysis on the lateral stability of hovering insects, which reported a destabilizing roll moment due to a lateral gust, has relied on the results of a single wing without considering a presence of the contralateral wing (wing-wing interaction). Here, we investigated the presence of the contralateral wing on the aerodynamic and flight dyna...

The interaction between an insect wing and its wake during hovering flight is inevitable. The effect of this wing–wake interaction (WWI) during stroke reversal is an intricate phenomenon that is difficult to forecast. Previous studies have mostly concentrated on the effect of aspect ratio (AR) on the leading-edge vortex (LEV) at the middle of strok...

This paper presents the application of an artificial neural network to develop an approach to determine and study the energy-optimal wing kinematics of a hovering bionic hawkmoth model. A three-layered artificial neural network is used for the rapid prediction of the unsteady aerodynamic force acting on the wings and the required power. When this a...

In this paper, the effect of wing aspect ratio and kinematics on wing-wake interaction at Re~10 4 , which matched the flight regime of flapping-wing micro air vehicle (FWMAV), was investigated. The dynamically scaled-up robotic model submerged in a water tank environment revealed that the wing-wake interaction augmented lift across a decrease in bo...

Pressure cartridge type separation devices which are widely used in fairing, stage separations of space launch systems, and many other aerospace fields generate much lower pyroshock and produce no high-speed debris compared to frangible explosive separation devices. However, because the operation is completed in a few milliseconds and the releasing...

This study investigated nearwake behaviors around flapping wings moving sideways. A dynamically scaled-up flapping manipulator was installed on a servo-driven towing carriage to give the sideways movement. In the single wing configuration, the wing in the windward side did not encounter any noticeable effects on the aerodynamic characteristics. The...

This experimental study investigates the effect of a uniform lateral inflow on the aerodynamic characteristics of flapping wings. Seven designated sideward ratios in the hovering condition and in the presence of a contralateral wing and a body were taken into account as variables in order to secure a better understanding of wing–wing and/or wing–bo...

Severe pyroshock can cause failure of mounted electronic equipment used in various space missions. To prevent this problem, it is important to predict the propagation path and attenuation of shock in space structures. In the case of a honeycomb sandwich panel, which is widely used in satellites, an insert is used in essential to connect with other...

Wing asymmetries can be found in real insects and flapping-wing micro air vehicles. This paper investigates some characteristics, including the trim conditions, power requirements and passive open-loop dynamics of an insect model with the asymmetry in wing mass in low-speed flight. The motion of the insect model is obtained through a simulation fra...

This paper deals with interactions of the wakes of two flapping wings on aerodynamic characteristics in hover. With dynamically scaled-up robotic wings installed in a water tank, the effects of both the shape of motion profiles and the mean flapping angle of the wings (the average location of the wings with respect to pivots) were investigated. For...

A new actuation mechanism using the twisted string concept to trigger the snap-through of a bistable buckled beam to produce an effective on/off bistable actuator is proposed. The twisted string concept combined with a pin utilizes actuation moment to actuate a bistable beam. The required actuation loads are analytically formulated using the Euler–...

Nature's flyers adopt deviating motion when they fly, however, the effect of deviating motion on the aerodynamics of flapping wings is not yet clearly understood. In this study, the aerodynamic characteristics of figure-of-eight deviating motion were investigated by comparing the aerodynamic force obtained from an experiment and the quasi-steady (Q...

In this article, a new concept of two-dimensional modular deployable truss structure is proposed. To eliminate additional needs of containment mechanism, the proposed deployable structure is designed to have bistable characteristics so that it can stay robust both in the stowed and deployed states. The deployment of each module is triggered by the...

The aerodynamic benefit for conventional vortex generator (VG) is often counterbalanced by the appearance of parasite drag. An immovable installation similar to a fixture also limited its application. To overcome those issues, this paper proposes a variable-incidence-angle vortex generator (VIVG). Counter-rotated miniature gears with a single rack-...

Honeycomb sandwich structures require inserts to be connected with other structures or devices. Impact and shock waves can be transmitted to the honeycomb structures through the inserts. To prevent malfunction of electronic components in a space structure, it is important to estimate shock propagation characteristics of the potted insert. In this p...

Pyroshock is a kind of dynamic structural shock, and the most common cause for the shock is the separation event such as stage or fairing separations of space launch vehicles. Pyroshock is characterized by high shock and acceleration level up to tens of thousands G for a very short time within a few milliseconds. The generated pyroshock is propagat...

This paper proposes two distinct actuation mechanisms to trigger a pre-compressed bistable beam clamped at both ends. These mechanisms together with the bistable beam forms an effective on-off millimeter-scale actuator for application in systems requiring two working states. The first actuation mechanism, which serves as a force input, comprises of...

This article proposes a method for damage detection using vision-based monitoring with motion magnification technique. The methods based on the vibration characteristics of structures such as natural frequency, mode shapes, and modal damping have been applied to structural damage detection. However, the conventional methods have limitations for pra...