Earticle

This study examines the dynamic characteristics of an articulated aerial work platform. The platform performs articulated joint motions and telescopic boom extension to access both upper-side and under-structure work areas. The boom system includes two articulated joints with slewing rotation, and the tip section is a multi-stage telescopic boom. Component-level dynamics of three telescopic boom components made of Strenx 960 were compared with the system-level dynamics of the fully assembled vehicle. Natural frequencies and mode shapes up to the second mode were obtained through experimental modal analysis based on frequency response functions (FRFs). For the assembled vehicle, tri-axial acceleration responses were transformed into the frequency domain using FFT, and dominant natural frequencies were identified from the spectra. The results show a clear separation between the two levels. The component-level dynamics appeared in the tens-of-hertz range. In contrast, the dominant system-level natural frequencies were observed in the low-frequency range (near 1 Hz). These findings indicate that the assembled system exhibits dominant dynamics distinct from those of individual boom components. They also highlight the need for system-level considerations when interpreting dynamic performance under practical operating conditions.

This research is to develop more effective seismic isolation system and to standardize a design processor for a seismic isolation structure system based on energy method by applying a isolation damper using HTS(High Toughness Steel which has been being studied) to the seismic isolation system. This research is conducted in four different stages. First, design two types of specimen for a shaking table test. One is not applied a seismic isolation system, the other is applied a seismic isolation system. Second, expect the dynamic characteristics of each specimen through analytical study using computer program Midas Gen ver.741. Third, compare analytical result with experimental result which will be obtained from a shaking table test next time. Lastly, suggest a design processor for a seismic isolation structure system based on energy method. In this study, our efforts especially focused on the first and second stage.

This study investigates the dynamic characteristics of telescopic booms for special-purpose vehicles fabricated with giga-grade ultra-high strength steel (UHSS) plates that have been increasingly adopted in industrial applications. In thin-walled structures such as telescopic booms, dynamic properties – particularly natural frequencies – are critical factors directly related to structural safety. Accordingly, the dynamic characteristics were experimentally measured and analyzed for identically designed booms fabricated using either imported giga-grade steel (Strenx 960) or domestic giga-grade steel (ATOS 980), both of which are widely available in the domestic market. The natural frequencies were identified based on frequency response functions (FRFs), and the corresponding mode shapes were obtained through experimental modal analysis. The results show that the nominal yield and tensile strengths provided by the manufacturers and the measured natural frequencies and mode shapes exhibit highly similar characteristics. These experimental findings confirm that the domestic UHSS exhibits a level of dynamic performance comparable to that of the imported steel of the same grade. Consequently, the results support the feasibility of applying domestic giga-grade UHSS to telescopic boom structures and highlight its potential contribution to material localization and enhanced design competitiveness in the domestic special-purpose vehicle industry.

본 연구의 목적은 주기적 모니터링을 통해 부유식 콘크리트 구조물의 구조 건전성을 평가하는 것이다. 실제 부유식 콘크리트 구조물을 대상으로 주기적 모니터링을 실시하여 동적 특성을 추출하였다. 추출된 동적 특성과 수치해석 모델을 이용하여 다음 두 가지 활동을 통해 구조 건전성을 평가하였다. 먼저, 비파괴 손상 평가기법을 이용하여 손상의 발생 및 진전을 평가하였으며, 균열도와의 비교를 통하여 그 결과의 신뢰성을 검증하였다. 다음으로, 구조계 추정기법을 이용하여 강성 저하 추이를 분석하였다. 그 결과로, 구조물의 요구 성능 확보여부를 판단할 수 있었다.

The objective of this study is to evaluate the structural integrity of the floating concrete structure through periodic monitoring. Dynamic characteristics of the actual floating concrete structure were extracted from the periodic monitoring. The structural integrity using the extracted dynamic characteristics and numerical model was evaluated by the following two activities. First, the structure damage was evaluated for occurrence and progress using the damage detection method. The reliability of the results was verified by comparison with the crack drawing. Second, the stiffness degradation trend was analyzed using the system identification method. As a result, the structural satisfy performance criteria and safety.

In this study, the seismic behavior of arch structure with lead rubber bearing(LRB) is analyzed. The arch structure is the simplest structure and has the basic dynamic characteristics among large spatial structures. Also, Large spatial structures have large vertical response by horizontal seismic vibration, unlike seismic behavior of normal rahmen structures. When horizontal seismic load is applied to the large spatial structure with isolation systems, the horizontal acceleration response of the large spatial structure is reduced and the vertical seismic response is remarkably reduced.

State-space method for the analysis of the dynamic characteristics of a body motion is set up as mathematical tool for the solution of differential equation by computer. Representation of a system is described as a simple form of matrix calculation and unique form of model is available for the linear or nonlinear, time variant or time invariant, mono variable or multi variable system etc. For the analysis of state-space method a complicated vector calculation is required, but this analysis can be simplified with the specific functions of a software package. Recently as the Graphical User Interface softwares are well-developed, then it is very simplified to execute the simulation of the dynamic characteristics for the state-space model with the interactive graphics treatment. The purpose of this study is to develope the simulator for the analysis of the lateral and directional dynamic characteristics of an aircraft that is primarily to execute the simulation for the analysis of the transient response of an aircraft lateral and directional stability.

Dynamic flow characteristics of a counter-flow vortex tube is investigated using hot-wire and piezoelectric transducer (PZT) measurements. The experimental study is conducted over a range of cold air outlet ratios (Y=0.3, 0.5, 0.7, and 1.0) and inlet pressure 0.15 MPa. Temperatures are measured at the cold air outlet and along the vortex tube wall. Hot-wire is located at cold outlet and PZT is installed at inner vortex tube by mounting at throttle valve. The cold outlet temperature results show that the swirl flow of vortex tube is not axisymmetric. The hot-wire and PZT results show that there exist two distinct kinds of frequency, low frequency periodic fluctuations and high frequency periodic fluctuations. It is found that the low frequency fluctuation is consistent with the Helmholtz frequency and the high frequency fluctuation is strongly related with precession oscillation.

The dynamic characteristics of the catenary-pantograph interface in high-speed trains are evaluated. During a test run signals from accelerometers, load cells, and strain gauges attached to various parts of the pantograph assembly are collected and processed. The signals are analyzed in both the time and frequency domains to determine the dynamic characteristics of the catenary-pantograph interface constituting the critical part of the current collection system of the high-speed train. It is found that there are major frequency components of the pantograph motion at the interface that shift in direct proportion to the train speed as well as components that are stationary in the frequency domain such as the 8.5 Hz component representing the fundamental resonant mode of the panhead assembly. The contact force at the interface shows that while the mean contact force stays almost invariant, the fluctuating component is significantly dependent on the filtering frequency applied to the accelerometer signal during estimation of the inertia force of the panhead. An important implication of the finding is that analytical or numerical investigations based on lumped element models of the pantograph may provide accurate predictions on mean values of the contact force at the catenarypantograph interface, but are inherently limited in estimating high-frequency fluctuations in the contact force. Since the ratio of the fluctuating portion to the steady-state portion (i.e., the mean value) increases with increased train speed, the predictive capacity of the investigations based on numerical simulations diminishes with increasing train speed.

This paper proposes a modeling technique which is able to not only reliably and easily represent the hysteretic characteristics but also analyze the dynamic stress of a taper leaf spring. The flexible multi-body dynamic model of the taper leaf spring is developed by interfacing the finite element model and computation model of the taper leaf spring. Rigid dummy parts are attached at the places where a finite element leaf model is in contact with an adjacent one in order to apply contact model. Friction is defined in the contact model to represent the hysteretic phenomenon of the taper leaf spring. The test of the taper leaf spring is conducted for the validation of the reliability of the flexible multi-body dynamic model of the taper leaf spring developed in this paper. The test is started at an unloaded state with the excitation amplitude of $1{\sim}2mm/sec$ and frequency of 132 mm. First, the simulation is conducted with the same condition as the test. Then, the simulations are conducted with various amplitudes in a loaded state. The hysteretic diagram from the test is compared with the ones from the simulation for the validation of the reliability of the model. The dynamic stress analysis of the taper leaf spring is also conducted with the developed flexible multi-body dynamic model under a dynamic loading condition.

Background Logistics service workers face elevated injury rates, with ankle-related incidents comprising 23% of workplace injuries. Traditional binary foot posture classifications may oversimplify the complex biomechanical relationships affecting dynamic balance performance in occupational settings. Purpose To apply unsupervised machine learning clustering to identify distinct foot posture phenotypes among logistics service workers and compare dynamic balance performance between identified clusters using the Y-Balance Test. Study design Cross-sectional observational study Methods A total of 112 logistics service workers were analyzed using K-means clustering based on age, body mass index, work duration, navicular drop, and resting calcaneal stance position. Silhouette score analysis determined optimal cluster number. Dynamic balance was assessed using the Y-Balance Test, measuring reach distances in anterior, posteromedial, and posterolateral directions. Results Four distinct phenotypes emerged: rearfoot valgus-dominant pronated (n=22), midfoot collapse-dominant pronated (n=32), age-related (n=23), and supinated (n=35) foot types. Significant differences in dynamic balance performance were observed in the posterolateral direction (F=3.900, p=0.011). The supinated phenotype demonstrated superior posterolateral reach performance (77.76±13.63%) compared to midfoot collapse-dominant (66.18±16.37%, p=0.003) and age-related phenotypes (67.78±14.97%, p=0.018). Conclusions Unsupervised machine learning successfully identified naturally occurring foot posture phenotypes with distinct dynamic balance characteristics. Midfoot collapse-dominant pronation demonstrated greater balance impairments than rearfoot valgus patterns, supporting the implementation of phenotype-specific interventions for workplace injury prevention in logistics workers.

Ever since the network-based malicious code commonly known as a 'worm' surfaced in the early part of the 1980's, its prevalence has grown more and more. The RCS (Random Constant Spreading) worm has become a dominant, malicious virus in recent computer networking circles. The worm retards the availability of an overall network by exhausting resources such as CPU capacity, network peripherals and transfer bandwidth, causing damage to an uninfected system as well as an infected system. The generation and spreading cycle of these worms progress rapidly. The existing studies to counter malicious code have studied the Microscopic Model for detecting worm generation based on some specific pattern or sign of attack, thus preventing its spread by countering the worm directly on detection. However, due to zero-day threat actualization, rapid spreading of the RCS worm and reduction of survival time, securing a security model to ensure the survivability of the network became an urgent problem that the existing solution-oriented security measures did not address. This paper analyzes the recently studied efficient dynamic network. Essentially, this paper suggests a model that dynamically controls the RCS worm using the characteristics of Power-Law and depth distribution of the delivery node, which is commonly seen in preferential growth networks. Moreover, we suggest a model that dynamically controls the spread of the worm using information about the depth distribution of delivery. We also verified via simulation that the load for each node was minimized at an optimal depth to effectively restrain the spread of the worm.

균형과 발목 근육 특성 (근력과 유연성) 사이의 관계는 낙상 위험의 증가에 대한 규명과 낙상방지 훈련프로그램 을 발전시키기 위해서 중요할 것이다. 발목 근육 특성(근력과 유연성)과 균형사이의 관계는 이전에 연구되지 않았다. 이 연구의 목적은 발목근육특성과 균형사이의 관계를 평가하는 것이다. 16명의 건강한 참가자들이 본 연구에 자원하였 다. 동적 균형은 와이-발란스 (Y-balance) 키트를 이용하여 측정하였다. 발목 근육 특성 (근력과 유연성)은 악력계와 고니어미터를 사용하여 측정하였다. 발목내번근력과 와이-발란스 (Y-balance) 측정 수행능력 사이에 양의 상관관계를 나타냈다. 임상가들은 동적균형의 발전을 위해서 치료적 중재를 하는 동안 발목 근력을 고려해야 한다.

The relationship between balance and ankle muscle characteristics (strength and flexibility) may be important to identify those at an increased risk of falling and to develop fall-prevention training programs. The association between ankle muscle characteristics (strength and flexibility) and balance has not previously been studied. The purpose of this study assessed the relationship between ankle muscle characteristics and balance. Sixteen healthy participants volunteered to participate in the study. Dynamic balance measured using Y-balance kit. Ankle muscle characteristics (strength and flexibility) measured using hand-held dynamometer and goniometry. The results indicated a positive correlation between ankle invertor muscle strength and Y-balance test performance. Clinicians should consider ankle muscle strength during therapeutic interventions to improve dynamic balance.

This study investigated the relationships among exercise capacity (EC), dynamic balance (DB), and gait characteristics (GCs) of patients with type-2 diabetes (T2D) and healthy controls (HCs). This observational controlled study involved 125 patients with T2D receiving treatment at a Nigerian university teaching hospital and 125 apparently healthy pa-tients’ relatives and hospital staff recruited as controls. EC maximum oxygen consumption (VO2max) was estimated following a 6-min walk test. DB and GC were assessed using the Time Up to Go Test and an accel-erometer (BTS G-Walk) assessing gait speed, step length, stride length, and cadence respectively during a self-selected walk. Data were ana-lyzed using descriptive and inferential statistics. Alpha level was set at P<0.05. The mean ages of patients with T2D and HCs were 57.6±6.6 and 60.0±7.0 years, respectively. All physical characteristics were comparable (P>0.05). There were significant differences in the VO2max and DB between patients with T2D and HCs; 7.6±0.6 mL/kg/min vs. 9.6±0.6 mL/kg/min (t=-16.6, P=0.001) and 14.2±2.1 sec vs. 10.4±1.5 sec (t=-6.37, P=0.001), respectively. Furthermore, significant differences were found in GC between patients with T2D and HCs; gait speed: 0.7±0.1 m/sec vs. 1.2±0.1 m/sec (t=-16.60, P=0.001), step length: 0.6±0.2 m vs. 0.9±0.3 m (t=-7.56, P=0.001) and stride length: 0.9±0.1 m vs. 1.1±0.5 m (t=-6.09, P=0.001). There were significant correlations between EC and gait speed in both groups (T2D: r=-0.26, P=0.032 and HCs: r=0.51, P=0.003). In conclusion, patients with T2D demonstrated lower EC, unstable DB, and altered GCs compared with HCs. Exercise interventions to improve EC and gait balance are recommended.

본 논문에서는 주차시설 등에 적용할 수 있는 시설물 맞춤형 에너지 하베스팅 블록 구조에 대하여 구조적 거동 및 발전 성능 평가를 수행하였다. 본 논문에서 제시한 개선된 에너지 블록은 수치해석 및 실험적 모델을 통하여 구현되었다. 특히, 복합소재-PZT 하이브리드 에너지 블록은 향상된 구조적 내구성 및 발전 성능 효과를 위하여 제안되었다. 복합소재로 구성된 에너지 블록의 다양한 정적 및 동적 특성을 분석하기 ABAQUS를 통해 구현한 복합소재-PZT 유한요소 모델이 적용되었다. 또한, 실험실 규모 및 현장 실험 결과는 제안한 에너지 블록 구조의 다양한 발전 성능 효과를 보여준다.

This study carried out structural behaviors and power generation performances of customized energy harvesting block structures, especially for infrastructures such as parking facility. The improved energy block structures described in this study were represented by using numerical and experimental models. In particular, the composite-PZT hybrid energy blocks are tentatively proposed for better structural durability and power generation effects. The finite element model using ABAQUS program is used for studying static and dynamic characteristics of block structures made of composite materials. In addition, we evaluated the various power generation capacities of advanced energy block structures through laboratory-scale and field experiments.

An experimental study of model truss-type vertical gate consisting of a truss and a plate was presented in this paper to examine the structural dynamics of the gates. A 1:61 scale model was constructed for the 95 m prototype gate using an acrylic truss and an acrylonitrile butadiene styrene plate. The scaled model was tested in a 1.6 m wide concrete flume for two orientations to determine the effects of gate orientation on structural vibrations. Natural frequencies of the model gate was measured and calibrated with FEM predictions. Vertical vibrations were measured under various operational conditions, including a range of bottom opening heights and different upstream and downstream water levels. The gate model with reverse direction was preferred due to its low overall vibrational response and flow level combinations. The test results also provide a basic dataset for development of operations guidelines that minimize flow-induced vibrations of the gates.

GIS(Gas Insulated Switchgear) is used in electric power system, to insure non conductivity, breaking capacity and operating reliability. The commercial dynamic analysis code COSMOS MOTION and 3-D modeling program SOLID WORKS were used to simulate dynamic analysis of the closing resistors of the GIS in this paper. To reduce chatter vibration of closing resistors, the motion of moving and fixed parts of closing resistors were simulated by varying the spring constant, the damping coefficient and the mass of moving and fixed parts. The simulated results were compared with experimental results. As a result, chatter vibration of closing resistors of the GIS could be reduced by using the results. These data can be used to determine the spring constant, the damping coefficient and mass of a moving part to reduce chatter vibration when the next model is developed.

With the increase of storage density and data transfer rates in optical disk drive, mechanical issues, mainly noise and vibration, become critical. Rubber materials are extensively used in various machine design application, mainly for vibration/shock/noise control devices. However, there are still a lot of difficulties in the use of designing the rubber components with complex shape and under pre-deformed state. It was demonstrated in that the variation of rubber component stiffness with the pre-deformed state were calculated by the finite element method and the reliability of numerical results were checked by compared with the measuring the deflection values. This paper presents a efficient design method of rubber mounts for anti-vibration of an optical disk thrive. With an empirical equation to estimate elastic modulus from hardness, and dynamic characteristics of rubber material of a cylindrical shape, this method is capable of predicting the dynamic characteristics of rubber components at design stage.

Dynamic loading of structures often causes excursions of stresses will into the inelastic range and the influence of geometry changes on the response is also significant in may cases. In general , the shell structures designed according to quasi-Static analysis may collapse under condition of dynamic loading. Therefore, for a more realistic prediction on the lad carrying capacity of these shell. both material and geometric nonlinear effects should be considered. In this study , the material nonlinearity effect on the dynamic response is formulated by the elasto-viscoplastic model highly corresponding to the real behavior of the material. Also, the geometrically nonlinear behavior is taken into account using a Total Lagrangian formulation. the reinforcing bars are modeled by the equivalent steel layer at the location of reinforcements, and Von Mises yield criteria is adopted for the steel layer behavior. Also, Drucker-Prager yield criteria is applied for the behavior of concrete. the shape imperfection of dome is assumed as 'dimple type' which can be expressed Wd1=Wd0(1-(r-a)m)n while the shape imperfection of wall is assumed as sinusoidal curve which is Wwi =Wwo sin(n $\pi$y/l). In numerical test, three cases of shape imperfection of 0.0 -5.0cm(opposite direction to loading ; inner shape imperfection)and 5cm (direction to loading : outward shape imperfection) and thickness of steel layer determined by steel ratio of 0,3, and 5% were analyzed. The effect of shape imperfection and steel ratio and behavior characteristics of perfect shape shell and imperfect shape shell are identified through analysis of above mentioned numerical test. Dynamic behaviors of dome and wall according toe combination of shape imperfection and steel ratio are also discussed in this paper.

A robot arm with free joints has some advantages over conventional ones. A light weight and low power consumed arm can be made by a reduction of the number of joint actuators. And this arm can easily overcomes actuator failure due to unexpected accident. In general such underactuated arm does not have controllability because of the lack of joint actuators. The two-link arm with a free joint introduced in this paper is also uncontrollable in the sense of linear system theory. However, the linearized system sometimes can not represent the inherent dynamic behavior of the nonlinear system. In this paper the dynamic characteristics of the two-link arm with a free joint in view of global motion including damping and friction effect of the joints is investigated. In the case of considering only the damping effect, the controllable goal positions are confined to a specific trajectories. But in the case of considering the friction effect, the system can be controlled to arbitrary positions using the friction of the free joint as a holding brake. Also numerical example of position control is presented.

In this study, a computer program considering initial imperfection of axisymmetric reinforced concrete shell which plastic deformation by large external loading was developed . Initial imperfection of dome was assumed as 'dimple type' which can be expressed as Wi=(Wo/h)(1-x$^2$)$^3$. The developed model applied to the analysis of dynamic response of axisymmetric reinforced concrete shell when it has initial imperfection. The initial imperfection of 0.0, -5.0, and 5cm and steel and steel layer ratio 0,3, and 5% were tested for numerical examples . The results can be summarized as follows ; 1. Dynmaic response of vertical deflection at dome crown showed slow increased if it has not inital imperfection . But the response showed relatively high amplitude when initial imperfection was inner directed (opposite direction to loading). Similar trends also appeared for different steel layer ratios. 2. Dynamic responses of radial displacement at the junction of dome and wall showed the highest amplitude when initial imperfection was inward directed (opposite direction to loading). The lowest amplitude occurred when initial imperfection was outward directed (same direction to loading). Vibration period also delayed for inward directed initial imperfection . These trends were obvious as steel layer ratio increasing. 3. The effects of imperfection for the dynamic response of radial displacement a the center of wall scarely appeared. The effects of initial imperfection of dome on the dynmaic response of the wall can be neglected. 4. Effect of steel on the dynmic response of axisymmetric shell structure was great when initial imperfection did not exist. And the effect of direction of initial imperfection (inward or outward) did not show big difference.