In dissertation discuss about new created dynamic characteristics establishment of low-frequency (0,7–50 Hz) vibrations isolation system. Presented theoretical and experimental investigations. Main goal of dissertation – is creation of dynamic parameters establishment methods for low-frequency vibration isolation systems and stiff quasi-zero vibrations isolation system, also investigate their dynamical characteristics and usage possibilities. Investigation object – low-frequency vibrations isolation mechanical systems and their dynamic characteristics establishment. Wish to realize investigation goal, were solved those tasks: 1) In scientifically literature investigates types of passive and active vibration isolation systems, constructions, work principals and analyze; 2) Analyzed and theoretically introduced mechanical conceptions of dynamic characteristics establishment methods of the vibration isolation systems; 3) Created stiff quasi-zero vibration isolation method and system based on zeroing of spring stiffness; 4) Done experimental dynamic characteristics evaluations of optics tables with pneumatic isolation and stiff quasi-zero vibration isolation systems; 5) Done vibration measurement uncertainty and given results reliability evaluation. Dissertation contents introduction, three parts, general conclusion of the results, used literature and list of author’s themes published dissertations, three attachments. In introduction part discuss about investigation problems... [to full text] / Disertacijoje nagrinėjamas naujai sukurtų mechaninių pasyviųjų žemojo (0,7–50 Hz) dažnio virpesių izoliavimo sistemų dinaminių charakteristikų nustatymas. Pateikiami teoriniai ir eksperimentiniai tyrimai. Pagrindinis disertacijos tikslas – sukurti mechaninių pasyviųjų žemojo dažnio virpesių izoliavimo sistemų dinaminių parametrų nustatymo metodiką ir kvazinulinio standžio virpesių izoliavimo sistemą, ištirti dinamines jų charakteristikas ir naudojimo galimybes. Tyrimų objektas – žemojo dažnio pasyviosios virpesių izoliavimo mechaninės sistemos ir jų dinaminių charakteristik nustatymas. Siekiant įgyvendinti tyrimų tikslą, išspręsti šie uždaviniai: 1) atlikta mokslinės literatūros apie pasyviųjų ir aktyviųjų virpesių izoliavimo sistemų tipus, konstrukcijas, veikimo principus analizė; 2) išanalizuoti ir pagrįsti mechaninių pasyviųjų virpesių izoliavimo sistemų dinaminių charakteristikų nustatymo metodai; 3) sukurtas kvazinulinio standžio virpesių izoliavimo metodas ir sistema, pagrįsta spyruoklių standžio įnulinimu; 4) atliktas optinių stalų su pneumatiniais izoliatoriais ir kvazinulinio standžio virpesių izoliavimo sistemos eksperimentinis dinaminių charakteristikų įvertinimas; 5) atliktas virpesių matavimo neapibr ėžties ir gautų rezultatų patikimumo įvertinimas. Disertaciją sudaro įvadas, keturi skyriai, rezultatų apibendrinimas, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai, trys priedai. Įvadiniame skyriuje aptariama tiriamoji problema, darbo... [toliau žr. visą tekstą]

Disertacijoje nagrinėjamas naujai sukurtų mechaninių pasyviųjų žemojo (0,7–50 Hz) dažnio virpesių izoliavimo sistemų dinaminių charakteristikų nustatymas. Pateikiami teoriniai ir eksperimentiniai tyrimai. Pagrindinis disertacijos tikslas – sukurti mechaninių pasyviųjų žemojo dažnio virpesių izoliavimo sistemų dinaminių parametrų nustatymo metodiką ir kvazinulinio standžio virpesių izoliavimo sistemą, ištirti dinamines jų charakteristikas ir naudojimo galimybes. Tyrimų objektas – žemojo dažnio pasyviosios virpesių izoliavimo mechaninės sistemos ir jų dinaminių charakteristik nustatymas. Siekiant įgyvendinti tyrimų tikslą, išspręsti šie uždaviniai: 1) atlikta mokslinės literatūros apie pasyviųjų ir aktyviųjų virpesių izoliavimo sistemų tipus, konstrukcijas, veikimo principus analizė; 2) išanalizuoti ir pagrįsti mechaninių pasyviųjų virpesių izoliavimo sistemų dinaminių charakteristikų nustatymo metodai; 3) sukurtas kvazinulinio standžio virpesių izoliavimo metodas ir sistema, pagrįsta spyruoklių standžio įnulinimu; 4) atliktas optinių stalų su pneumatiniais izoliatoriais ir kvazinulinio standžio virpesių izoliavimo sistemos eksperimentinis dinaminių charakteristikų įvertinimas; 5) atliktas virpesių matavimo neapibr ėžties ir gautų rezultatų patikimumo įvertinimas. Disertaciją sudaro įvadas, keturi skyriai, rezultatų apibendrinimas, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai, trys priedai. Įvadiniame skyriuje aptariama tiriamoji problema, darbo... [toliau žr. visą tekstą] / In dissertation discuss about new created dynamic characteristics establishment of low-frequency (0,7–50 Hz) vibrations isolation system. Presented theoretical and experimental investigations. Main goal of dissertation – is creation of dynamic parameters establishment methods for low-frequency vibration isolation systems and stiff quasi-zero vibrations isolation system, also investigate their dynamical characteristics and usage possibilities. Investigation object – low-frequency vibrations isolation mechanical systems and their dynamic characteristics establishment. Wish to realize investigation goal, were solved those tasks: 1) In scientifically literature investigates types of passive and active vibration isolation systems, constructions, work principals and analyze; 2) Analyzed and theoretically introduced mechanical conceptions of dynamic characteristics establishment methods of the vibration isolation systems; 3) Created stiff quasi-zero vibration isolation method and system based on zeroing of spring stiffness; 4) Done experimental dynamic characteristics evaluations of optics tables with pneumatic isolation and stiff quasi-zero vibration isolation systems; 5) Done vibration measurement uncertainty and given results reliability evaluation. Dissertation contents introduction, three parts, general conclusion of the results, used literature and list of author’s themes published dissertations, three attachments. In introduction part discuss about investigation problems... [to full text]

In future human spaceflight missions, with prolonged exposure to microgravity, resistive and aerobic exercises will be countermeasures for bone loss, muscle loss, and decreased aerobic capacity. Two of the exercises of interest are squats and rowing. The cyclic forces produced during these exercises are at relatively low frequencies which are likely to excite structural resonances of space vehicles. Vibration Isolation Systems (VIS) are being designed to be paired with future exploration exercise devices in order to prevent these cyclic exercise forces from impacting the space vehicle. The VIS may be configured such that a platform supports the human and exercise device. There is limited knowledge about the interaction between a human exercising and a dynamic platform. This research sought to fill part of the knowledge gap and study how the force inputs to the platform change as well as how exercise form was affected. For this research, a system which can produce dynamic responses similar to those of a prospective VIS platform was used. This system is the Computer Assisted Rehabilitation Environment (CAREN) (Motekforce Link, Amsterdam, Netherlands). Simplified sinusoidal responses were implemented in a single degree of freedom, vertical (heave) motion, and also in multi-degree of freedom, heave and pitch motion. Human subject testing was conducted using four subjects with exercise experience. The subjects completed squats and rows, while standing, in both static (platform not moving) and dynamic (with platform moving) conditions. Subjects aimed to synchronize with platform motion, at the appropriate phase. Kinetic and kinematic data were collected via force plate measurements and motion capture, respectively. Testing was completed with several predetermined frequencies for platform motion, but also at each subject’s baseline frequency, which was the measured, comfortable exercise rate for the subject. Data were processed and arranged in a presentable format. Results showed attenuation of the vertical component of forces between the comparable frequency static and dynamic platform conditions, as expected, for most subjects in the squat exercise. This was seen only in the heave with pitch condition during rows for most subjects. Results also showed increasing amplitude of forces as frequency increased, which was also expected. Knee angle range of motion was well maintained between static and dynamic conditions. These results suggest that conditions desirable for both VIS and exercise are possible. Further testing and extended analysis at additional amplitudes, frequencies, and degrees of freedom are of interest and warrant further study. This work contributed knowledge and data regarding the forces involved and human kinematics produced while exercising with platform motion. These data can further be used as inputs and requirements for VIS design work, VIS and human biomechanical modeling, and exercise countermeasure development. This work achieved the objectives of establishing an appropriate test environment and developing platform dynamics in which human-VIS interaction could be studied. It also acted as a proof-of-concept for future testing which can be conducted to answer new questions relating to dynamic platform motion effects on human activity.

<p>Real-time hybrid simulation (RTHS) has demonstrated certain advantages over conventional large-scale testing. In an RTHS, the system that is under study is partitioned into a numerical and a physical substructure, where the numerical part is comprised of those elements that are easier to model mathematically, while the physical part consists of those that present a complex behavior difficult to capture in a numerical model. The most complex part of this study is the isolation system, a technology used to protect structures against earthquakes by modifying how they respond to ground motions. Unbonded Fiber Reinforced Elastomeric Isolators (UFREIs) are devices that can accomplish this task and have gained attention in recent years because of their modest but valuable features that make them suitable for implementation in low-rise buildings and in developing countries because of their low cost. Our end goal for this work is to enable the testing of scaled versions of these elastomeric isolators to understand their behavior under shear tests and realistic loading. </p> <p>A testing instrument was designed and constructed to apply a uniaxial compressive force up to 22kN and a shear force of 8kN simultaneously to the specimens. A testing program was conducted where four primary sources of signal distortion were identified as caused by the servo-hydraulic system. From these results, a mechanics-based model was developed to understand better the dynamics that the sliding table can introduce to the measured signals accounting for inertial and dissipative forces. Two Bouc-Wen models were implemented to simulate the behavior of the UFREIs. The first only accounts for the hysteretic behavior of the isolator, and the second accounts for the additional nonlinearities found in the isolator’s behavior. These models were assembled in a virtual RTHS which is available to users interested in learning the applications of RTHS of a base-isolated structure with a nonlinear component.</p> <p>An RTHS experiment was conducted in the IISL where the control system comprised a delay compensator and a proportional-integral controller, which exhibited a good tracking performance with minimal delay and low RMSE. However, it can increase the distortion of the oil-column resonance in the measured signals. The simulation captures the behavior of the isolated structure for small displacements. However, it underestimates the displacement of the full-scale specimen for large displacements. The RTHS showed a better approximation of the displacement of the full-scale structure than the theoretical behavior approximated by the Bouc-Wen models.</p>

Práce se zabývá návrhem magnetoreologické (MR) vzpěry vibroizolačního systému (VIS) pro kosmický nosič. V rešeršní části jsou popsány vybrané VIS a vzpěry těchto systémů, které byly v kosmických nosičích využity v minulosti. Každá z těchto vzpěr obsahující kapalinu byla těsněna pomocí statických těsnění a pružných vlnovců vyrobených z oceli. Důkladněji byla analyzována vzpěra pasivního systému VIS s označením ELVIS, jehož konstrukce se stala inspirací pro tuto práci. Jedná se o tříparametrický systém, v němž je tlumič uložen na pružině, jejíž tuhost přibližně odpovídá objemové tuhosti vlnovců respektive jejímu průmětu do axiálního směru (pressure thrust stiffness). V práci je představena metodika pro stanovení “pressure thrust stiffness” na základě geometrie vlnovce a také uvedeny parametry vlnovce díky kterým je možné měnit poměr mezi axiální a “pressure thrust stiffness” vlnovce. Tento poměr ovlivňuje v dané koncepci vzpěry její dynamické chování a tím i chování celého VIS. Pro predikci dynamického chování vzpěry byl vytvořen multi-body model VIS založeného na Stewartově plošině a detailnější model jediné vzpěry. Simulace provedené v tomto modelu odhalily parametry, které mají vliv na výkonost tlumiče ve VIS: časová odezva a dynamický rozsah. Díky modelu byl určen rozsah těchto parametrů, ve kterých bude zaručena efektivní funkce vzpěry ve VIS, konkrétně: časová odezva: 0-5ms, dynamický rozsah: 5-10. Před finálním návrhem vzpěry byla sestrojena vzpěra experimentální vzpěra, jejíž parametry byly přesně naměřeny a využity pro verifikaci jednotlivých modelů. Poznatky získané během experimentů byly využity při návrhu finální vzpěry. Jeden z nejdůležitějších poznatků byla nutnost náhrady feritového magnetického obvodu s ohledem na jeho křehkost. Proto byl odvozen tvarový přístup k navrhování rychlých magnetických obvodů z oceli s využitím 3D tisku, který byl následně patentován. Navržená vzpěra obsahuje magnetoreologický ventil jehož odezva je predikována na 1.2 ms a dynamický rozsah 10. V závěru práce je představena metodika, díky které byla vzpěra navržena.

Indonesia is a developing country that suffers from earthquakes and windstorms and where at least 60% of houses are non-engineered structures, built by unskilled workers using masonry and timber. The non-engineered housing units developed in urban region are also vulnerable to seismic hazard due to the use of low quality of material and constructions method. Those structures are not resistant to extreme lateral loads or ground movement and their failure during an earthquake or storm can lead to significant loss of life. This thesis is concerned with the structural performance of Indonesian low-rise buildings made of masonry and timber under lateral seismic load. The research presented includes a survey of forms of building structure and experimental, analytical and numerical work to predict the behaviour of masonry wall and traditional timber frame buildings. Experimental testing of both masonry and timber have been carried out in Indonesia to establish the quality of materials and to provide material properties for numerical simulations. The experimental study found that the strength of Indonesia-Bali clay brick masonry are below the minimum standard required for masonry structures built in seismic regions, being at least 50% lower than the requirement specified in British Standard and Eurocode-6 (BS EN 1996-1-1:2005). In contrast, Indonesian timber materials meet the strength classes specified in British Standard/Eurocode- 5 (BS EN 338:2009) in the range of strength grade D35-40 and C35).Structural tests under monotonic and cyclic loading have been conducted on building components in Indonesia, to determine the load-displacement capacity of local hand-made masonry wall panels and timber frames in order to: (1) evaluate the performance of masonry and timber frame structure, (2) investigate the dynamic behaviour of both structures, (3) observe the effect of in-plane stiffness and ductility level, and (4) examine the anchoring joint at the base of timber frame that resists the overturning moment. From these tests, the structural ductility was found to be less than two which is below the requirement of the relevant guidelines from the Federal Emergency Management Agency, USA (FEMA-306). It was also observed that the lateral stiffness of masonry wall is much higher than the equivalent timber frame of the same height and length. The experimental value of stiffness of the masonry wall panel was found to be one-twelfth of the recommended values given in FEMA-356 and the Canadian Building code. The masonry wall provides relatively low displacement compared to the large displacement of the timber frame at the full capacity level of lateral load, with structural framing members of the latter remaining intact. The weak point of the timber frame is the mechanical joint and the capacity of slip joint governs the lateral load capacity of the whole frame. Detailed numerical models of the experimental specimens were setup in Abaqus using three-dimensional solid elements. Cohesive elements were used to simulate the mortar behaviour, exhibiting cracking and the associated physical separation of the elements. Appropriate contact definitions were used where relevant, especially for the timber frame joints. A range of available material plasticity models were reviewed: Drucker-Prager, Crystalline Plasticity, and Cohesive Damage model. It was found that the combination of Crystalline Plasticity model for the brick unit and timber, and the Cohesive Damage model for the mortar is capable of simulating the experimental load-displacement behaviour fairly accurately. The validated numerical models have been used to (1) predict the lateral load capacity, (2) determine the cracking load and patterns, (3) carry out a detailed parametric study by changing the geometric and material properties different to the experimental specimens. The numerical models were used to assess different strengthening measures such as using bamboo as reinforcement in the masonry walls for a complete single storey, and a two-storey houses including openings for doors and windows. The traditional footing of the timber structures was analysed using Abaqus and was found to be an excellent base isolation system which partly explains the survival of those structures in the past earthquakes. The experimental and numerical results have finally been used to develop a design guideline for new construction as well as recommendations for retrofitting of existing structures for improved performance under seismic lateral load.