Nonlinear vibration and primary resonance of multilayer functionally graded shallow shells with porous core

Kamran Foroutan,Liming Dai 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.48 No.3

This research studies the primary resonance and nonlinear vibratory responses of multilayer functionally graded shallow (MFGS) shells under external excitations. The shells considered with functionally graded porous (FGP) core and resting on two types of nonlinear viscoelastic foundations (NVEF) governed by either a linear model with two parameters of Winkler and Pasternak foundations or a nonlinear model of hardening/softening cubic stiffness augmented by a Kelvin–Voigt viscoelastic model. The shells considered have three layers, sandwiched by functionally graded (FG), FGP, and FG materials. To investigate the influence of various porosity distributions, two types of FGP middle layer cores are considered. With the first-order shear deformation theory (FSDT), Hooke’s law, and von-Kármán equation, the stress-strain relations for the MFGS shells with FGP core are developed. The governing equations of the shells are consequently derived. For the sake of higher accuracy and reliability, the P-T method is implemented in numerically analyzing the vibration, and the method of multiple scales (MMS) as one of the perturbation methods is used to investigate the primary resonance. The results of the present research are verified with the results available in the literature. The analytical results are compared with the P-T method. The influences of material, geometry, and nonlinear viscoelastic foundation parameters on the responses of the shells are illustrated.

Automatic resonant frequency tracking for DCX‑LLC based on magnetizing current cancellation

Cheng Gu,Qinsong Qian,Dalin Xu,Tianhao Tan 전력전자학회 2024 JOURNAL OF POWER ELECTRONICS Vol.24 No.1

The LLC resonant converter has been widely used as a DC-DC transformer (DCX) to provide a semi-regulated or unregulated bus voltage. However, due to circuit parameter variations, the switching frequency is usually different from the designed resonant frequency, which results in converter efficiency degradation. To achieve the highest efficiency under different scenarios, a novel primary-side regulation (PSR) scheme for LLCs based on magnetizing current cancellation is presented. The transformer magnetizing current component on the sampling resistor can be offset by the compensating current, which is generated by the auxiliary winding and the added compensating inductor. The effect of magnetizing current in the sampled primary resonant current can be effectively eliminated. Thus, the output current can be accurately estimated on the primary side of the LLC resonant converter. Finally, a prototype of a 20-60 V LLC is constructed to validate the theoretical analysis. In the experiment section, various scenarios are tested to assess the efficacy of the solution. It is shown that the LLC converter can always realize resonant frequency tracking with the highest transmission efficiency.

Very Accurate Output Voltage Estimation on Primary-side for LLC Resonant Solid-State-Transformer (SST)

Kim Hwi-Mun,Lee Young-Dal,Kim Da-Un,Kim Chong-Eun 대한전기학회 2024 Journal of Electrical Engineering & Technology Vol.19 No.3

Bulky traditional transformer can be replaced with solid-state-transformer (SST) thanks to fast-switching power semiconductors, such as silicon carbide FET and diode. SST implemented using LLC resonant converter can improve power efciency and minimize its highfrequency transformer. However, high isolation voltage between primary and secondary sides makes output voltage sensing much more difcult. Even though output can be monitored on secondary side, it must be also estimated for fast protection on primary side. In this paper, very accurate estimation scheme for output voltage on primary side is proposed and verifed by simulation

원판의 비선형 비대칭 강제진동응답

여명환,이원경 한국소음진동공학회 2001 한국소음진동공학회 논문집 Vol.11 No.4

An investigation into asymmetric vibrations of a clamped circular place under a harmonic excitation is made. We examine a primary resonance. in which the frequency of excitation is near the natural frequency of an asymmetric mode of the plate. We found not only a response haying the form of standing wave but also one having the form of traveling wave, which was not observed by Sridhar, Mook and ${Nayfeh}^{(1)}$

원형 외팔보의 비평면 비선형 진동현상

김명구(Myoung-Gu Kim),박철희(Chul-Hui Pak),조종두(Chong-Du Cho),박창호(Chang-Hao Piao) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5

Experimental and theoretical study of the non-planar response motions of a circular cantilever beam subject to base harmonic excitation has been presented in this paper work. Theoretical research is conducted using two non-linear coupled integral-differential equations of motion. These equations contain cubic linearities due do curvature term and inertial term. A combination of the Galerkin procedure and the method of multiple scales are used to construct a first-order uniform expansion for the case of one-to-one resonance. The results show that the non-linear geometric terms are very important for the low-frequency modes of the first and second mode. The non-linear inertia terms are also important for the high-frequency modes. We present the quantitative and qualitative results for non-planar motions of the dynamic behavior.

Nonlinear primary resonance and bifurcation analyses of a micro-resonant pressure sensor

Xiaorui Fu,Chong Li 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.2

The micro-resonant pressure sensor outputs frequency signals for which distortion does not take place over long-distance transmission. As the dimensions of the sensor decrease, the nonlinear coupling effects caused by the van der Waals force, electrostatic force, and air damping force should be considered. Here, based on the nonlinear dynamic equation, the amplitude-frequency characteristics near resonance and the equation on the displacement response far away from resonance are obtained. Using these equations, changes in the sensor’s amplitude-frequency characteristics and the vibration amplitude far away from resonance, along with the system parameters, are investigated. The variations of the chaotic vibration characteristics of the sensor with the thickness of the resonator are studied by the numerical method. The results show that the relevant parameters of the resonator have a great influence on the primary resonance and bifurcation of the sensor. The sensor changes from periodic vibration to chaotic vibration through period-doubling bifurcation in a certain range of parameters. These results can be used to determine the measurements of the resonators to ensure sensor performance.

Factors Associated with Incidental Neuroimaging Abnormalities in New Primary Headache Patients

김병수,김수경,김재문,문희수,박광열,박정욱,손종희,송태진,주민경,차명진,김병건,조수진 대한신경과학회 2020 Journal of Clinical Neurology Vol.16 No.2

Background and Purpose Deciding whether or not to perform neuroimaging in primary headache is a dilemma for headache physicians. The aim of this study was to identify clinical predictors of incidental neuroimaging abnormalities in new patients with primary headache disorders. Methods This cross-sectional study was based on a prospective multicenter headache registry, and it classified 1,627 consecutive first-visit headache patients according to the third edition (beta version) of the International Classification of Headache Disorders (ICHD-3β). Primary headache patients who underwent neuroimaging were finally enrolled in the analysis. Serious intracranial pathology was defined as serious neuroimaging abnormalities with a high degree of medical urgency. Univariable and multivariable logistic regression analyses were conducted to identify factors associated with incidental neuroimaging abnormalities. Results Neuroimaging abnormalities were present in 170 (18.3%) of 927 eligible patients. In multivariable analysis, age ≥40 years [multivariable-adjusted odds ratio (aOR)=3.37, 95% CI=2.07–6.83], male sex (aOR=1.61, 95% CI=1.12–2.32), and age ≥50 years at headache onset (aOR=1.86, 95% CI=1.24–2.78) were associated with neuroimaging abnormalities. In univariable analyses, age ≥40 years was the only independent variable associated with serious neuroimaging abnormalities (OR=3.37, 95% CI=1.17–9.66), which were found in 34 patients (3.6%). These associations did not change after further adjustment for neuroimaging modality. Conclusions Incidental neuroimaging abnormalities were common and varied in a primary headache diagnosis. A small proportion of the patients incidentally had serious neuroimaging abnormalities, and they were predicted by age ≥40 years. These findings can be used to guide the performing of neuroimaging in primary headache disorders.

임플랜트 고정체의 형태가 임플랜트 초기안정성에 미치는 영향

오갑용,박성화,김석규,Oh, Gap-Yong,Park, Sung-Hwa,Kim, Seok-Gyu 대한치과보철학회 2007 대한치과보철학회지 Vol.45 No.1

Statement of problem: Current tendencies of the implant macrodesign are tapered shapes for improved primary stability, but there are lack of studies regarding the relationship between the implant macrodesign and primary stability. Purpose: The purpose is to investigate the effect of implant macrodesign on the implant primary stability by way of resonance frequency analysis in the bovine rib bones with different kinds of quality. Material and method: Fifty implants of 6 different kinds from two Korean implant systems were used for the test. Bovine rib bones were cut into one hundred pieces with the length of 5 cm. Among them forty pieces of rib bones with similar qualities were again selected. For the experimental group 1, the thickness of cortical part was measured and 20 pieces of rib bones with the mean thickness of 1.0mm were selected for implant placement. For the experimental group 2, the cortical parts of the remaining 20 pieces of rib bones were totally removed and then implants were placed on the pure cancellous bone according to the surgical manual. After placement of all implants, the implant stability quotient(ISQ) was measured by three times, and its statistical analysis was done. Results: There are statistically significant differences in ISQ values among 4 different kinds of Avana system implants in the experimental group 2. For the experimental group 1, Avana system implants showed significantly different ISQ values, but when differences in the thickness of cortical parts were statistically considered, did not show any significant differences in ISQ values. Among Oneplant system implants, there are no significant differences in ISQ values for the experimental group 2 as well as for the experimental group 1. Conclusion: Within the limits of this study, bone quality and implant design have some influences on the primary stability of implants. Especially in the bone of poor quality, tapered shape of implants are more favorable for the primary stability of implants.

자발성 파열과 신정맥 혈전을 동반한 원발성 신장 혈관육종의 CT 및 MRI 소견: 증례 보고

김영환,김시형 대한영상의학회 2011 대한영상의학회지 Vol.64 No.6

Primary renal angiosarcoma is a very rare malignant mesenchymal tumor. CT shows a well-margined enhancing mass with hemorrhage, perirenal hematoma and renal vein thrombosis in the lower pole of the right kidney. MRI shows heterogeneous low- and high-signal intensities of the mass on T1- and T2-weighted images, as well as a relatively homogeneous enhancement on contrast enhanced T1-weighted images. We report here on a rare case of primary renal angiosarcoma with spontaneous rupture and venous thrombosis. 원발성 신장 혈관육종은 매우 드문 중간엽 기원의 악성 종양이다. CT에서 우측 신장 하엽에 신장 주위의 혈종과 신정맥 혈전을 동반한 일부 출혈을 하며 조영증강이 잘 되고 경계가 좋은 종괴가 관찰되었다. MRI T1 및 T2 강조영상에서 불균일한 저신호와 고신호강도를 보였으며, T1 조영증강 영상에서 비교적 균일한 조영증강을 보였다. 저자들은 자발성 파열과 신정맥 혈전을 동반한 원발성 혈관육종의 증례를 경험하였기에 이를 보고하고자 한다.

Maxillary Sinus의 inferior wall의 피질골 두께가 임플란트의 초기안정성에 미치는 영향에 대한 in vitro 연구

권택가,강봉서,김석규,양성은,이철원 대한통합치과학회 2013 대한통합치과학회지 Vol.2 No.2

rimary stability of dental implant is a very important factor of dental implant success. However, few data are available for comparing the primary stability characteristics of less 10mm cancellous and cortical bone thickness. The purpose of this study were to measure the primary implant stability according to sinus inferior wall's cortical bone thickness. Swine bones which have 6,8 and 10 mm bone height and 1 mm and 1.5 mm cortical bone thickness were selected as an experimental model. As treated specimens one side cortical bone was removed. The assemblies were divided into groups of each 30 swine bone specimens according to implant diameter (4.3D group: 4.3mm, 4.8D group: 4.8mm),total bone height (6H group: 6.0mm, 8H group: 8.0mm, 10H group: 10.0mm),and cortical bone thickness (1C: 1.0 mm, 1.5C: 1.5 mm). Implant stability as a function of resonance frequency analysis, peak insertion torque were recorded for each fixture site after placement and removal. The RFA values of 1.5C group was significantly higher than that of 1C group (p < 0.05). The peak insertion torque of 1.5C group was significantly higher than that of 1C group (p < 0.05). Within the limits of this study, thickness of cortical bone have some influences on the primary stability of implants.