Dissertations / Theses on the topic 'Flexible pipe vibration study'

The purpose of this research is to present new methods of active and passive vibration control for flexible structures. The study includes: 1) passive viscoelastic damping treatment; 2 ) active vibration control using layered shape memory alloy (SMA); 3) combined application of viscoelastic damping treatment and SMA; 4) experiments. In order to maximize damping and save weight of the structure and cost, a partially covered double sandwich cantilever beam model has been presented. It is shown that the double sandwich beam is better than single sandwich beam for some conditions. To take into account of end loads effect of elastic structures such as robot arm or manipulator, a model of partially covered double sandwich cantilever beam with mass at free end is given and discussed. Also a more accurate model (Timoshenko model) is discussed. The experiments were done to verify the theoretical results. The active vibration control by means of layered shape memory alloy actuator is discussed. The layered structure is easy to implement in real application, especially for the existing structures. The control results are compared and discussed. The temperature effects are discussed. Also a model with combined application of viscoelastic damping treatment and shape memory alloy layer is presented. Both the vibration characteristics and control results are obtained and discussed. The vibration control results for different control schemes are compared and discussed. The temperature effects are also discussed

Thesis (M.S. in Systems Technology (Space Systems Operations)) Naval Postgraduate School, September 1993.
Thesis advisor(s): Brij N. Agrawal. "September 1993." Includes bibliographical references. Also available online.

In this study, the effect of pipe-soil relative stiffness on the behaviour of buried flexible pipes was investigated considering the pipe size, material type, stiffness, pipe-soil and natural soil-backfill interfaces and geometry of the trench using the finite element method. For this purpose, a parametric study was conducted to examine the effect of different variables on the resulting earth loads and deformations imposed on the buried pipes. Various types of trench pipe-soil cases were analysed for a certain natural ground and backfill material by the PLAXIS finite element code which allows simulating non-linear soil behaviour, the stages of construction as well as the pipe-soil interaction aspects of the problem. Loads and deformations obtained by the finite element method were compared with those calculated by the conventional approaches for different pipe-soil stiffness ratios. The finite element results obtained for the deformation of typically flexible Polyethylene pipes were then used to back-calculate the range of modulus of soil reaction, E'
, values for various pipe-soil relative stiffness and they were compared with the suggested value proposed by Howard (1977).

Position and vibration control of a flexible beam is studied analytically and in the laboratory. Two different motor types are compared as actuators throughout the thesis: a standard voltage controlled motor and a torque controlled motor. The experimental beam is controlled with a dc-servo motor at its base and is instrumented with strain gages and a potentiometer. The control law is a form of linear, direct-output feedback. State estimators augment the control law to provide rate information that is not available from the instrumentation. Accurate modeling of the system’s inherent damping characteristics is achieved by analyzing experimental data. Gains were iterated yielding minimum-gain norm and minimum-sensitivity norm solutions to meet imposed eigenvalue placement constraints. Results for the two solutions and the two systems are compared and contrasted. Experimental verification of analytical results is hampered by unmodeled system non-linearities. Several attempts at bypassing these obstacles are shown. Finally, conclusions and recommendations are made.
Master of Science
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碩士
國立臺北科技大學
能源與冷凍空調工程系碩士班
100
This study carried out thermal response experiment and thermal resistance experiment after tensile experiment for flexible heat pipe, and studied and discussed the variation of its performance. The material of the evaporator section and condenser section of the flexible heat pipe studied in this experiment was copper, the material of adiabatic section was stainless steel, the internal capillary structure was metal mesh, and pure water was used as work fluid. The evaporator section, adiabatic section and condenser section were connected to thermocouple wire to measure the temperature change, and to discuss the thermal response rate, equilibrium time and thermal resistance. The experimental results showed that the change in bend angle can influenced the overall thermal response time and temperature difference. However, the effect of bend angle on the evaporator section and condenser section declined as the drawing number increased, but the thermal response time and temperature curve trend of adiabatic section were influenced obviously. According to the thermal resistance experiment, the drawing number influenced the flexible heat pipe to a great extent, the increase in drawing number made the heat transfer more difficult relatively, so that the thermal resistance increased and the maximum heat transfer rate decreased.

碩士
大葉大學
機械工程研究所碩士班
96
In this study, the modal analysis was implemented to investigate the structure of exhaust pipe in the system in which no damping and no forces were applied. First of all, CAD software was used to build a model of structure of exhaust pipe according to a certain real model. Then, FEA software was used to construct the finite element models of exhaust pipe and hanger. The modal analysis was then implemented by importing the finite element models into the CAE software. In comparison with the numerical results to the ones of a car being driven with a specific RPM (revolution per minute), the frequencies and mode shapes were obtained, and the results were analyzed and discussed to realize whether they would result in resonance to the structure of exhaust pipe or not. On the other hand, the location of each hanger of exhaust pipe, the cross section and length of hanger, the elastic modulus of the material of exhaust pipe and the tube thickness of exhaust pipe were adjusted to obtain the results which were analyzed to discuss whether the adjusted parameters had effects on the constant frequency of exhaust pipe or not. From the results in this study, it was found that the location of exhaust pipe hanger and changing of the structural shape and length of hanger would have obvious effects on the constant frequency of exhaust pipe.

碩士
國立中央大學
機械工程研究所
99
The normal vibration directions of vibration-assisted magnetic abrasive finishing are all parallel or perpendicular to the surface of workpiece. It’s shortcomings are easily lead to more scratches on the surface, and difficult to obtain mirror effect. This study break through previous studies,design a mechanism of two-dimensional(XY plane) vibration assisted to magnetic abrasive finishing. In the study we will use the steel particles and SiC abrasive mixture composed of non-associative with a vibration-assisted magnetic abrasive finishing, then use the polishing pad with vibration-assisted, watch the SEM surface and surface roughness. Taguchi experiment can verify that, for the improvement of surface roughness parameters for the best: X Axis Frequency 1Hz, SiC weight of 2g, Grit weight 3.5g, slurry weight 3g, vibration platform speed 1500rpm, Vibration Amplitude 0.9mm, Grit numbers # 120, pole speed of 550rpm（A2B2C2D3E3F3G3H2）.And proved vibration assisted magnetic abrasive finishing method in the best parameter combinations, can effectively improve within 5 minutes of stainless steel surface roughness by the Ra0.14μm down to 0.03μm, to improve the rate of 78.57%, ground 25 minutes later more up to Ra0. 02μm, the surface to improve the rate increased to 85.71%. Then study to abrasive ratio, we got when slurry weight 3g, increase SiC weight 1g and diamond powder 1g, the surface roughness will get better. Can effectively improve within 5 minutes of stainless steel surface roughness by the Ra0.14μm down to 0.025μm, ground 25 minutes later more up to Ra0. 01μm, and get outstanding results in mirror effect. Use this abrasive ratio to polishing the rough stainless steel,can effectively improve within 5 minutes of stainless steel surface roughness by the Ra0.23μm down to 0.02μm, ground 25 minutes later more up to Ra0. 01μm, Show the best abrasive ratio have excellent improve capacity in surface roughness.

碩士
國立雲林科技大學
機械工程系
103
Thist hesis explores the vibration control of a planar flexible structure. The structure is composed of 13 rigid links interconnected by springs. The center of the structure is subject to a periodic disturbing force. According to the principle of dynamic vibration absorber, vibrations of the structure are minimized when the disturbance frequency is equal to certain “absorber frequencies”, which are equal to the natural frequencies of the systemwhen the center of the structure is artificially fixed in space. The natural frequencies and absorber frequencies are determined with the help of a multibody dynamics simulation software. The mode shapes associated with the absorber frequencies are also found. A physical structure is constructed for experimentation via 3D printing. In the experiments, periodic disturbance is generated by a brushless motor driving an eccentric load. By controlling the angular speed of the brushless motor, the disturbance frequency can be adjusted in order to obtain a frequency response of the planar structure.

碩士
逢甲大學
自動控制工程研究所
84
The main objective of this thesis is to study the system identification andactive vibration control effect for flexible structure. In the system identification, we use ARMA model and neural networks to identify flexible structure.The Simulation results show that neural networks has the characteristics of obvious nonliner and self-learning, so the errors made by neural networks systemidentification were reduced 50 percent less than what ARMA model caused. In the active vibration control, there are three kinds of control design lawsmentioned in the thesis, that is, robust pole-placement controller,PID controller, and neural PID controller which combines back- propagation net workandthetraditional PID controller. In addition, we differently employ shakerand PZT as the actuator to suppress the vibration from the cantilever beam.The resultsthrough experimental analysis proved that is more effective andsuccessfulto take advantage of robust pole- placement controller and neural PIDthan traditional PID controller to suppress the vibration of the cantilever beam.

碩士
國立臺灣海洋大學
機械與機電工程學系
98
The purpose of this thesis is to develop the effect of Vibration-Assisted turning by using a Cantilever-type flexible fixture to the machining of aluminum alloys compared with traditional fixture. At first, the computer-aided design and finite element method is used to analyze it’s structural property. Finally, we design the plane for turning by using flexible which is connect with an pizo Actuator for the purpose of vibratory machining. 　　The experiment results show the surface at this condition, cutting speed 50m/min, depth of cut 0.01mm, 100V of voltage, the surface roughness of workpiece will improve as the frequency increased, and at this condition, feed 0.15mm/rev, the flexible fixture with vibration were better than traditional turning, and the maximum approximately 35%, and at this condition, feed 0.03 mm/rev feed, flexible fixture with vibration were better than flexible fixture, and the maximum approximately 62.5%.

碩士
國立臺灣科技大學
機械工程系
100
As a common example in various kinds of structural systems, flexible beam has the light damping property which easily affects the system performance and structure safety. To compensate for this drawback active vibration control is one proven-effective technique which embeds actuators and sensors into the structures to reduce the influences of disturbances in real-time. Because applying classical active vibration control methods is unable to satisfy the increasingly stringent requirements and constraints, recently researchers have started to use advanced control methods for vibration suppression of flexible structures. This research focuses on the experimental investigation on vibration control of a flexible beam using Model Predictive Control (MPC), an advanced optimal control method which can handle constraints at each sampling step. Using the Hildreth’s optimization solver, the work considers three different MPC strategies, including a basic MPC, a terminal-state involved MPC, and a MPC combined with repetitive control (RMPC), for control design and performance evaluation. The study specifically investigates the periodic disturbance rejection performance of applied MPC methods, showing the effectiveness of RMPC. To reduce the computational burden and improve the practicability of MPC in active vibration control applications, this study also applies a recurrent neural network as fast optimization solver, to implement the aforementioned MPC strategies. Besides the parameter analysis, the experimental results particularly show the constraint handling and performance improvement by considering the input constraints in the MPC design. Finally, this thesis summarizes several concluding remarks on control parameters selection as a guideline for future designers.

A circular cylinder is a geometrically simple bluff body that occurs in various practical applications. As with any bluff body, it exhibits large drag forces and a strong fluctuating lift force, both related to the strong shedding of vortices from the body, which is commonly referred to as the Karman Street. Rigid splitter plates in the wake of the cylinder are known to suppress shedding from the body, and thereby result in reduced drag and fluctuating lift forces, the latter being important to reduce flow-induced vibrations of the body. In the present work, the flow past a cylinder with a downstream flexible splitter plate/flap is studied, the length (L) and flexural rigidity (EI) of the flap being the main parameters besides the flow speed (U). Two flaps length to cylinder diameter ratios (L/D), namely, a short (L/D = 2) and a long (L/D = 5) flaps have been studied, the shorter one being smaller than the recirculation zone, while the larger is longer than the recirculation zone. In both these cases, the flexural rigidity (EI) and the flow speed are systematically varied. In all cases, the flaps motion are directly visualized, the lift and drag forces are measured with a force balance, and the wake velocity field is measured using PIV. In both the long and short flaps cases, the flexural rigidity (EI) of the flexible flap has been varied over a large range of values, and it has been found that the results for flaps tip motion and forces collapse well when plotted with a non-dimensional bending stiffness (K∗), which is defined as K∗ = EI/(1/2ρU2L3). This collapse occurs across flexible flaps with different values of EI, as long as Re > 5000. The collapse is not found to be good for Re < 5000. This difference appears to be related to the large reduction in fluctuating lift for a bare cylinder in the Re range between approximately 1600 and 5000 discussed by Norberg[41]. In the long flap case, the existence of two types of periodic modes is found within the range of K∗ values from 5 × 10−6 to 1 × 10−1 studied. The first one corresponds to a local peak in amplitude at K∗ ≈ 1.5 × 10−3 that is referred to as mode I, and the second that occurs at low values of K∗ (K∗ < 3 × 10−5) that is referred to as mode II. The fluctuating lift is found to be minimum for the mode I oscillation. The mean drag is also found to reach a broad minimum that starts at K∗ corresponding to mode I and continues to be at the same low level of approximately 65% of the bare cylinder drag for all higher K∗ values, representing an approximately 35% decrease in mean drag of the cylinder. The wake measurements also show significant changes with K∗. The formation length (lf /D) obtained from the closure point of the mean separation bubble is found to continuously increase with K∗, reaching values of approximately 2.6 at mode I and thereafter only small increases are seen as K∗ is increased to large values corresponding to the rigid splitter plate case, consistent with the observed variations in the mean drag. The stream wise and cross-stream turbulent intensities and the Reynolds shear stress are all found to be strikingly lower in the mode I case compared to the bare cylinder case, and more importantly, these values are even lower than the rigid splitter plate case. This is consistent with the shedding of weaker vortices and with the minimum in fluctuating lift found in the mode I case. The results for this flap length show that the mode I flap oscillation, corresponding to K∗ ≈ 1.5 × 10−3, may be useful to reduce lift, drag, velocity fluctuations in the wake and the strength of the shed vortices. In particular, the wake fluctuations corresponding to this mode are found to be significantly lower than the rigid splitter plate case. In the short flap case (L/D = 2), it is found that there exists a richer set of flapping modes compared to the long flap, with these modes being dependent on K∗. At low K∗ values, the flap exhibits large amplitude symmetric flap motion that is referred to as mode A, while clearly asymmetric flaps motion are seen at higher K∗ values corresponding to modes B and C. Mode B corresponds to asymmetric large amplitude flapping motion, while mode C is also asymmetric with the flap clearly deflected off to one side, but having small oscillation amplitudes. At even higher K∗ values, corresponding to mode D, symmetric flaps motion are again seen with the amplitudes being smaller than in mode A. Apart from the flap tip amplitude, the non-dimensional frequency of flap tip motion also changes as the flap changes modes. In this case, there is a minimum in the fluctuating lift corresponding to mode B and C oscillation. The mean drag is found to reach a minimum again corresponding to mode C, which corresponds to an approximately 35% decrease in mean drag of the cylinder. In this case, there is a large increase in fluctuating lift (approximately 150% of the bare cylinder case) at higher values of K∗ that appears to correspond to a “resonant” condition between the structural natural frequency of the flexible splitter plate/flap and the wake shedding frequency of the bare cylinder. The wake measurements show that the formation length (lf /D) is the largest for mode C (deflected flap state), which is consistent with the observed minimum in mean drag observed for this mode. The stream wise and cross-stream turbulent intensities and the Reynolds shear stress are all found to be strikingly lower in the mode C case compared to the bare cylinder case, with the values for the Reynolds shear stress being lower than the rigid splitter plate case. This is again consistent with the minimum in fluctuating lift found in the mode C case. The results for this flap length show that the mode C flap oscillation, corresponding to K∗ ≈ 5 × 10−2 that correspond to a deflected flap state with very small oscillation may be useful to reduce lift, drag, velocity fluctuations in the wake and the strength of the shed vortices. The results from the present study show that the flexible flap/splitter plate down-stream of the cylinder exhibits a variety of mode shapes depending on the effective bending rigidity of the flap K∗ for both the long and short flaps cases. The forces and the wake are also found to be strongly dependent on this parameter K∗ with the wake fluctuations, lift fluctuations and the drag being very effectively suppressed at an intermediate value of K∗ that is found to be dependent on the plate/flap length.

碩士
國立清華大學
動力機械研究所
78
This thesis presents a theoretical and experimental study on the elastodynamic analysis and control of the flexible linkage mechanisms using piczoelectric actuators. A mixed variational principle is developed to provide the basis for deriving the finite element equation which govern the dynamic responses of the flexible links, the behaviors of the piezoelectric materials and their coupling relationships. To ensure robust stability, the LQG/LTR (Linear Quadratic Gaussian with Loop Transfer Recovery) design methodology and the classical frequency-domain approach are employed to design the control system for actively suppressing the vibratory motions of the flexible links. 　　In order to verify the mathematical model and the results of computer simulations, an experimental study on a four-bar linkage mechanism with one flexible link is performed. This experimentation not only demonstrates the capability of the piezoletric materials for vibration reductions but also provides an opportunity to examine the robustness of the control system. 　　Essentially, this thesis introduces a design methodology by incorporating smart materials into a computer-controlled intelligent machinery which are capable of both reducing link deflections and slso operating with more versatile path-generation capability.

碩士
大同工學院
機械工程研究所
81
The liquid balancer is generally used for reducing the vibration of an automatic washing machine with a flexible- supported tub. In the present study, ba- sed on the general structure of a liquid balancer, three experimental parameters such as the quantity of liquid filled, the rib shape and the number of ribs in the liquid balancer, are considered to study how these parameters mentioned above affect the eff- ectiveness of the liquid balancer directly wih an ex- periment.