Abrasive water jet cutting methods for reducing blast-induced ground vibration in tunnel excavation

Kim, Jung-Gyu,Song, Jae-Joon Elsevier 2015 International journal of rock mechanics and mining Vol.75 No.-

<P><B>Abstract</B></P> <P>This study assessed the controlling effect of abrasive water jet cutting on blast-induced ground vibration during tunnel excavation. The abrasive water jet cutting method adopted in this study includes the notch-cutting and disc-cutting methods. The abrasive water jet notch-cutting method was applied to block the propagation of blast-induced ground vibration in the transverse direction of the tunnel face, and the disc-cutting method was applied to suppress the blast-induced ground vibration in the longitudinal direction of the tunnel. The vibration-reduction effects of both methods were quantitatively investigated through experimental and numerical studies. In the experimental study, the vibration-reduction effect of notch cutting was compared with that of the line-drilling method, whereas the vibration-reduction effect of the disc cutting was measured against the case without disc cutting. In the numerical study, the effects of notch slot length and disc slot diameter were investigated. The abrasive water jet cutting method reduced the blast-induced ground vibration and was more effective than conventional drilling and blasting method in tunnel excavation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Abrasive water jet notch-cutting method applied to between boundary line-drilling holes reduced transversely transmitting vibrations. </LI> <LI> Abrasive water jet disc-cutting method applied to the bottom of blast holes reduced longitudinally transmitting vibrations. </LI> <LI> The effects of notch slot and disc slot on the vibration reduction were investigated by real-scale experiment </LI> <LI> The effects of notch slot length and disc diameter on the vibration reduction were investigated by numerical simulation. </LI> </UL> </P>

저소음 프로펠러 개발을 위한 프로펠러 진동특성 추정에 대한 연구

공연권 한국방위산업학회 2023 韓國防衛産業學會誌 Vol.30 No.2

선박 프로펠러의 진동은 날개의 손상 및 소음을 유발할 수 있으며 저소음 프로펠러를 설계하기 위해서는 프로펠러의 진동특성을 정확도 높게 추정하여 설계에 반영하여야 한다. 본 연구에서는 프로펠러의 진동특성을 정확도 높게 추정하기 위해 날개들과 허브가 전부 포함되고 날개의 요소 수가 기존 연구에 비해 약 2.2배 증가된 프로펠러 유한요소모델을 제작하였다. 기존 연구의 방법인 날개 유한요소모델에 대한 고유진동해석, 허브 상・하면이 고정 또는 고정되지 않은 프로펠러 유한요소모델에 대한 고유진동해석을 수행하였다. 고유진동해석을 통해 프로펠러의 진동특성인 고유진동수 및 모드형상을 추정하였으며추정 결과를 분석하여 프로펠러 허브가 날개 진동에 미치는 영향을 확인하였다. 또한 Impact test(충격가진시험)를 수행하였고 결과를 진동특성 추정 결과와 비교하여 진동특성 추정의 정확도를 분석하였다. 그 결과, 프로펠러에는 고유진동수와 날개모드형상이 서로 유사한 모드들이 존재했는데, 이러한 현상은 날개 진동이 허브를 통해 다른 날개의 진동에 영향을 미치는연성효과 때문에 발생하였다. 또한 프로펠러 허브는 연성효과와 허브 진동에 의해 날개 진동에 영향을 미치며 허브 상・하면이 고정되면 허브 진동은 날개 진동에 영향을 미치지 않았다. 이로부터 프로펠러의 진동특성을 정확도 높게 추정하기 위해서는 프로펠러 날개만이 아닌 프로펠러 전체에 대한 진동해석을 수행해야 함을 도출하였다. Vibration of ship propellers can cause damage to blades and propeller noise, in order to design low-noise propellers the vibration characteristics of propellers must be estimated to a high degree of accuracy and reflected in the design. In this study, in order to estimate the propeller vibration characteristics with high degree of accuracy, a propeller finite element model was created that included the hub and all blades of the propeller and increased the number of finite elements of the blades by about 2.2 times compared to previous studies. The free vibration analysis of the blade finite element model which was a method of previous studies, and the free vibration analysis of the propeller finite element model with fixed or unfixed upper and lower surfaces of the hub were performed. Natural frequencies and mode shapes, which are vibration characteristics of the propeller, were estimated through free vibration analysis, and the effect of the propeller hub on blade vibration was confirmed by analyzing the estimation results. In addition, an impact test was performed, and the accuracy of the estimation of the vibration characteristics was analyzed by comparing the test results with the estimation results of the vibration characteristics. As a result, the propeller have modes with similar natural frequencies and blade mode shapes, this phenomenon occurs because of the coupling effects in which the vibration of a blade affects the vibration of another blade through a hub. The propeller hub affects the blade vibration by the coupling effects and the hub vibration and when the upper and lower surfaces of the hub are fixed, the hub vibration does not affect the blade vibration. In order to estimate the vibration characteristics of the propeller with high degree of accuracy, it was derived that vibration analysis should be performed for the propeller, not just the propeller blade.

An assessment of the effect of hull girder vibration on the statistical characteristics of wave loads

Yoshitaka Ogawa,Ken Takagi 대한조선학회 2011 International Journal of Naval Architecture and Oc Vol.3 No.1

For the assessment of statistical characteristics of wave loads in the real sea state, the probability distribution of wave loads are computed based on the sufficient duration of computations in irregular waves. First of all, the estimation of wave impact loads is well modified applying the displacement potential formulation, which was proposed by one of authors, for solving Wagner’s flow model. Consequently, the present computation method is also modified. Prior to the computation in irregular waves, preliminary computation to determine the adequate number of realization of irregular waves is examined. The effect of hull girder vibration on the statistical characteristics is examined by means of the computation with/without hull girder vibration. It is found that hull girder vibration has a certain effect on the probability of occurrence of wave loads. Furthermore, computations taking account of the effect of operation, that is the effects of ship speed and course change, is conducted for the rational evaluation of the effects of hull girder vibration. It is clarified that the effect of operation on the statistical characteristics of wave loads is significant. It is verified that the evaluation without the effect of operation may overestimate the effect of hull girder vibration.

An assessment of the effect of hull girder vibration on the statistical characteristics of wave loads

Ogawa, Yoshitaka,Takagi, Ken The Society of Naval Architects of Korea 2011 International Journal of Naval Architecture and Oc Vol.3 No.1

For the assessment of statistical characteristics of wave loads in the real sea state, the probability distribution of wave loads are computed based on the sufficient duration of computations in irregular waves. First of all, the estimation of wave impact loads is well modified applying the displacement potential formulation, which was proposed by one of authors, for solving Wagner's flow model. Consequently, the present computation method is also modified. Prior to the computation in irregular waves, preliminary computation to determine the adequate number of realization of irregular waves is examined. The effect of hull girder vibration on the statistical characteristics is examined by means of the computation with/without hull girder vibration. It is found that hull girder vibration has a certain effect on the probability of occurrence of wave loads. Furthermore, computations taking account of the effect of operation, that is the effects of ship speed and course change, is conducted for the rational evaluation of the effects of hull girder vibration. It is clarified that the effect of operation on the statistical characteristics of wave loads is significant. It is verified that the evaluation without the effect of operation may overestimate the effect of hull girder vibration.

Application of Deep Learning in Motor Vibration and Noise Suppression Based on Negative Magnetostrictive Effect

Zhang Xin,Li Chunzhi,Xue Ming,Wang Wenbin,Zhu Lihua 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.3

The suppression of vibration and noise is one of the critical problems in the optimal design of the motor. The vibration and noise caused by the magnetostrictive effect can not be ignored. In this paper, the vibration and noise caused by the magnetostrictive effect are suppressed by drilling holes in the stator and filling the holes with negative magnetostrictive material. Firstly, the electromagnetic–mechanical coupling model is established. By traversing all the drilling positions by finite element analysis (FEA), the stress value is calculated, and the drilling position corresponding to the minimum local stress is determined. It is found that the resource consumed by FEA is expensive, and the calculation time is prolonged. Deep learning is introduced as an alternative model to calculate the hole’s position and size. The Pix2Pix, Pix2PixHD, CycleGAN, and StarGAN are experimented with based on the PyTorch environment. Through the experiment, it is found that deep learning has an absolute advantage over the FEA in time which ensures a high accuracy rate. Finally, an experimental platform for measuring the strain of the motor stator is designed. According to the best positions and apertures of holes are obtained by the simulation and the actual situation, we drill holes in the motor stator and fill the holes with Ni, a negative magnetostrictive material. The result shows that the stator’s local stress is reduced by about 16%. The vibration and noise caused by the magnetostrictive effect are suppressed effectively.

Size-dependent forced vibration response of embedded micro cylindrical shells reinforced with agglomerated CNTs using strain gradient theory

H. Tohidi,S.H. Hosseini-Hashemi,A. Maghsoudpour 국제구조공학회 2018 Smart Structures and Systems, An International Jou Vol.22 No.5

This article presents an analysis into the nonlinear forced vibration of a micro cylindrical shell reinforced by carbon nanotubes (CNTs) with considering agglomeration effects. The structure is subjected to magnetic field and transverse harmonic mechanical load. Mindlin theory is employed to model the structure and the strain gradient theory (SGT) is also used to capture the size effect. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite cylindrical shell and consider the CNTs agglomeration effect. The motion equations are derived using Hamilton’s principle and the differential quadrature method (DQM) is employed to solve them for obtaining nonlinear frequency response of the cylindrical shells. The effect of different parameters including magnetic field, CNTs volume percent and agglomeration effect, boundary conditions, size effect and length to thickness ratio on the nonlinear forced vibrational characteristic of the of the system is studied. Numerical results indicate that by enhancing the CNTs volume percent, the amplitude of system decreases while considering the CNTs agglomeration effect has an inverse effect.

발전소 내 구조물 진동 제어를 위한 MR 유체가 적용된 동조질량감쇠기 설계 및 적용

송준한,이현섭,이홍기,백재호 한국CDE학회 2023 한국CDE학회 논문집 Vol.28 No.3

When several pulverizers operating simultaneously at the same rotational speed for coal pulveri- zation in a thermal plant, workers inside the nearby control structure complained of discomfort due to the vibration. Through structure and transmission path vibration measurement the phe- nomenon of vibration amplification in the structure due to resonance and the concentration of vibration energy in the roof due to structural characteristics were identified. To reduce the vibra- tion in the control room, the design of the main factors of the TMD(Tuned Mass Damper) was conducted. An analysis of the optimal mass, stiffness, and damping characteristics of the TMD was designed using a finite element analysis program ANSYS. MR(Magneto-Rheological) fluid was used for the damper of the TMD for the optimal vibration reduction effect considered to the site conditions. The optimal position of the TMD in the structure was selected, and the reduction effect was verified by conducting vibration monitoring before and after installing the vibration mitigation measures.

열차운행에 따른 근접 구조물 영향 사례

도재선(JaeSeon Do),장승엽(SeungYep Jang),박용걸(YongGul Park) 한국철도학회 2012 한국철도학회 학술발표대회논문집 Vol.2012 No.10

각종 시설물이 밀집한 도심지에서 열차가 운행되는 경우, 열차운행에 따른 진동영향이 근접 구조물의 안정성과 사용자 인체에 영향을 줄 수 있다. 반복적인 열차진동은 근접 구조물에 균열발생 등 사용성에 문제를 발생시킬 수 있으며, 소음과 진동은 사용자에 불쾌감을 유발할 수 도 있다. 이러한 경우 열차진동에 대한 근접 구조물과 사용자에 대한 적절한 영향평가가 필요하며, 평가방법으로는 진동 및 소음계측을 통한 실측자료를 이용하는 방법이 가장 현실적이나, 설계 및 시공 단계에서 실측에 의한 방법은 여러 가지 제약이 있으므로 유사사례를 통한 수치해석적 방법이 가장 현실적인 대안으로 적용될 수 있다. 본 논문에서는 정거장 구조물과 근접 운행되는 열차의 진동영향을 고찰하기 위하여 지반진동 특성을 반영한 3차원 수치해석을 이용해 근접 구조물의 진동영향을 평가하였다. 또한 진동영향에 따른 안정성을 확보하지 못하는 경우에 대한 적용 가능한 대책공법을 제시하였다. The vibration caused by train-set performance in the complex city can influence the stability of adjacent structures as well as the human body. Repetitive vibration can lead to problems for the usability of adjacent structures by cracking etc, and induced vibration and noise can cause displeasure to users. In this case, It is necessary to assess suitably about to adjacent structures and users effecting by train-vibration. Using field measurement data of existing system is most practical evaluation method, however, there are limits to manage the measurement data in design and construction stage, using numerical analysis with similar cases can be applied to an alternative way. In this paper, to investigate the effect of the vibration induced by train which running close to the station, we evaluated vibration effect of adjacent structures through three-dimensional numerical analysis reflecting the characteristics of ground vibration. In addition, the reinforcement methods were suggested to the cases can not ensure the stability of adjacent structures against the vibration induced train.

Experimental identification of box girder bridge model under undamaged and damaged conditions considering time effect

Ahmet Can Altunisik 사단법인 한국계산역학회 2016 Computers and Concrete, An International Journal Vol.18 No.4

In this paper, it is aimed to evaluate the structural behavior of box girder bridge model under undamaged and damaged conditions considering time effect between June 2009 and February 2015 using ambient vibration tests. For this purpose, a scaled bridge model is constructed and experimental measurements are performed to determine the damage and time effect on dynamic characteristics such as natural frequencies, mode shapes and damping ratios. In the ambient vibration tests, natural excitations are provided and the response of the bridge model is measured. The signals collected from the tests are processed by Operational Modal Analysis; and the dynamic characteristics of the bridge model are estimated using Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification methods. Measurement time, frequency span and effective mode number are selected by considering similar studies found in the literature. To expose the damage and time effect on dynamic characteristics, four experimental measurement cases are considered between 2009 and 2015. The first measurement case is conducted on June 2009 under undamaged conditions. The second and third measurement cases are performed on October 2010 under undamaged and damaged conditions to emerge the damage and time effect, respectively. The fourth measurement tests are carried out on February 2015 to display the time effect on the dynamic characteristics considering same damage condition in third measurements. At the end of the study, experimentally identified dynamic characteristics are compared with each other to investigate the damage and time effects. It can be stated that the both of Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification methods are very useful to identify the dynamic characteristics of the bridge model. Maximum differences obtained as 11.98% and 112.24% between Case 1 and Case 2, 10.30% and 26.24% between Case 2 and Case 3, 12.36% and 401.50% between Case 3 and Case 4 for natural frequencies and damping ratios, respectively. It is seen that damages and environmental conditions affect the structural behavior of concrete bridges, substantially. Also, time dependent environmental conditions such as temperature, humidity and ageing are as important as cracks and damages.

Size-dependent forced vibration response of embedded micro cylindrical shells reinforced with agglomerated CNTs using strain gradient theory

Tohidi, H.,Hosseini-Hashemi, S.H.,Maghsoudpour, A. Techno-Press 2018 Smart Structures and Systems, An International Jou Vol.22 No.5

This article presents an analysis into the nonlinear forced vibration of a micro cylindrical shell reinforced by carbon nanotubes (CNTs) with considering agglomeration effects. The structure is subjected to magnetic field and transverse harmonic mechanical load. Mindlin theory is employed to model the structure and the strain gradient theory (SGT) is also used to capture the size effect. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite cylindrical shell and consider the CNTs agglomeration effect. The motion equations are derived using Hamilton's principle and the differential quadrature method (DQM) is employed to solve them for obtaining nonlinear frequency response of the cylindrical shells. The effect of different parameters including magnetic field, CNTs volume percent and agglomeration effect, boundary conditions, size effect and length to thickness ratio on the nonlinear forced vibrational characteristic of the of the system is studied. Numerical results indicate that by enhancing the CNTs volume percent, the amplitude of system decreases while considering the CNTs agglomeration effect has an inverse effect.