Impulsive Modes Research Articles

Numerical investigations of seismic-resilient techniques for legged fluid storage tanks utilising magnetorheological dampers

Different energy-dissipating devices have been proposed in the literature to attenuate the destructive effects of base excitations over fluid storage tanks. These structures have numerous applications in strategic industries and their failure can result in environmental hazards and huge economic losses. Proposed techniques in the literature for seismic energy dissipation of fluid-contained tanks are mostly centred on passive and active control mechanisms. Semi-active control devices using materials with adjustable properties offer advantages of both active and passive systems while removing their drawbacks. In this paper, the performance of a Magnetorheological (MR) damper on the seismic response reduction of fluid storage tanks through the application of three different control strategies including H2/LQG, PID, FOPID, and two passive techniques, i.e. Passive On, and Passive Off has been investigated. Parameters of the semi-active controllers are optimally designed for each aspect ratio and the applied ground motion using the Hunger Game Search (HGS) technique and finally, the semi-active Clipping algorithm commands the voltage to the damper. The fluid-tank-MR damper system has been examined under three Far-Fault and three Near-Fault ground motions. Numerical simulations have demonstrated that depending on the aspect ratio, applied ground motion, and the control strategy, the MR damper can mitigate the peak relative displacements and absolute accelerations of the two major modes of the system, i.e the rigid and impulsive modes, up to 72% and 67%, respectively. This proves the efficacy of these dampers in reducing the maximum base shear and overturning moment, hence mitigating the damage risks in these structures.

Hybrid Nonlinear Passivity-Based Control Approach to Magnetic-Impulsive Spacecraft Attitude Regulation

This paper proposes two novel passivity-based control design frameworks for hybrid nonlinear time-varying dynamical systems involving an interacting amalgam of continuous-time and discrete-time dynamics whose dynamical properties evolve periodically over time. In this regard, the hybrid Kalman–Yakubovich–Popov conditions are employed in tandem with the passivity theorem to construct a three-step control design algorithm to render closed-loop dynamics stable. The proposed control architectures are subsequently exploited to regulate the attitude motion of spacecraft with magnetic and impulsive modes of operation. Practical considerations involved in implementing the proposed hybrid algorithms are then discussed in detail. Simulation results show significant improvement in the performance of the attitude control system in terms of system response, robustness, and the required magnetic and impulsive control usage as compared to a hybrid linear approach.

Impulse analysis in Kronecker form and impulse elimination for rectangular descriptor systems

Contrary to regular descriptor systems, there are various notions for impulse freeness and impulse controllability for rectangular linear descriptor systems. Moreover, rectangular descriptor systems generally do not have solutions for arbitrary initial conditions. This paper studies the conditions for free of impulse, and no impulsive modes admitting arbitrary initial conditions in the form of Kronecker canonical form (KCF) along with other equivalent and geometric conditions. The knowledge of KCF blocks significantly simplifies the analysis of the system solutions. Further, conditions for impulse controllability are investigated, and a proportional state feedback is designed such that the closed-loop system has no impulsive modes and admits arbitrary initial conditions. This makes the system solutions smooth without any restrictions on initial conditions. Physical and academic instances are provided to fortify the theory.

Nelinearno ponašanje spremnika za ukapljeni prirodni plin s različitim sustavima potresne izolacije

This study determines the effects of different types of base isolator systems on the seismic performance of liquefied natural gas (LNG) storage tanks. Nonlinear time-history analyses of the non-isolated and three different isolated models were performed for the average acceleration of seven ground motions scaled to achieve a specified safe shutdown earthquake. The ANSYS Workbench program was used in the modelling studies of the LNG liquid, inner steel tank, outer shell, ring beam, roof and concrete foundation and side wall insulation. The LS-DYNA program was used for the nonlinear analyses of the LNG liquid, inner steel tank and concrete foundation. The results of the total base shear force, sloshing height, steel tank stresses and lateral deflection were compared. The results indicated that there was no difference between the convective and impulsive modes for the LNG tanks with isolators. It was concluded that the wave motion of the liquid was different from the oscillation of the structure and the earthquake isolation times did not affect the sloshing motion. In the non-isolated system, the stress reached 400 MPa, whereas it was 350 MPa on average in the LNG tanks with isolators.

Year-Round Experimental Analysis of the Productivity of Vapour-Based Multistage Solar Still: A Developmental Study

The standalone vapour-based multistage solar still with stacked stages (MSS-SS) belongs to a pool of widely studied small-scale water desalination devices through solar thermal energy. This work contributes to the body of knowledge by presenting a system with new configurations. There is a need to develop small-scale systems to be reliable devices for freshwater provision, as brackish water is available for processing. The experimental study was conducted in a field under actual weather conditions, with the data logged and analysed to study the systems’ behaviour under varying meteorological conditions. A maximum distillate yield of 7790 ml, corresponded to a maximum daily average solar radiation at high range. There was a 21.8% decrease to 6090 ml at moderate daily average range and a further decline of 80.5% to 1190 ml in the low daily average range, representing a significant drop in the distillate yield caused by the insufficient heat collection at low range. The high, moderate, and low ranges corresponded to summer, spring and autumn, and winter, respectively. The lower values of the moderate range were the most optimum operationally. The impulsive modes were ideal for high rates of the heat inputs, while the continuous were for low rates. The assumption of a continuous mode and a further increase in the rate of thermal energy input caused thermal damage necessitating the augmentation of the thermal energy storage (TES) device due to a larger collector-to-basin area (CBA) ratio. The distillate yield trends from the stages were dynamic and were the inverse of the stage temperature, which was dictated by the mode and rate of the thermal energy input. These trends were such that stage 5 > 3 > 2 > 1 > 4 at moderate to high ranges and changed a low range. The summer season enhanced the cumulative saline water (SW) preheating and heat recovery to 66.8°C. The economic analysis found that at its most productive level, the cost of producing water per litre (CPL) from the vapour-based MSS-SS was R 4.05. The small-scale water purification systems are helpful, especially in remote areas.

Solar coronal heating from small-scale magnetic braids

Relaxation of braided coronal magnetic fields through reconnection is thought to be a source of energy to heat plasma in active region coronal loops. However, observations of active region coronal heating associated with an untangling of magnetic braids remain sparse. One reason for this paucity could be the lack of coronal observations with a sufficiently high spatial and temporal resolution to capture this process in action. Using new observations with high spatial resolution (250−270 km on the Sun) and high cadence (3−10 s) from the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter, we observed the untangling of small-scale coronal braids in different active regions. The untangling is associated with impulsive heating of the gas in these braided loops. We assess that coronal magnetic braids overlying cooler chromospheric filamentary structures are perhaps more common. Furthermore, our observations show signatures of spatially coherent and intermittent coronal heating during the relaxation of the magnetic braids. Our study reveals the operation of gentle and impulsive modes of magnetic reconnection in the solar corona.

Budget-constraint admissible output consensus tracking for intermittent-interaction singular multiagent networks

Budget-constraint admissible output consensus tracking design and analysis for the intermittent-interaction singular multiagent networks with given cost budgets are addressed in this paper. Two critical characteristics of many practical multiagent networks are focused. The first one is that the dynamics of each agent contains dynamical modes, as well as impulsive modes and static modes, and interactions among agents are intermittent. The second one is that the network is constrained by the cost budget, and the weighted design between tracking performances and energy consumptions should be guaranteed under budget constraints. Firstly, in virtue of the decomposition of observability, a new singular consensus tracking protocol with the dynamic output feedback is proposed by intermittent protocol states. Meanwhile, a cost index is constructed by considering both the tracking performance and the energy consumption. Then, criteria of budget-constraint admissible output consensus tracking analysis and design are given. By designing the gain matrices of consensus tracking protocols, not only multiagent networks with dynamical modes and static modes reach output consensus tracking while eliminating impulsive modes, but also the upper bound of the cost index can be kept within the cost budget; that is, the weighted design with the budget constraint is achieved. Finally, theoretical results are demonstrated by numerical simulations.

Structural modeling and dynamic analysis of condensate storage tanks in nuclear power plants

Condensate storage tanks (CSTs) in nuclear power plants (NPPs) are classified as critical equipment capable of surviving strong shaking in a design basis earthquake to assure the ability to subsequently provide cooling water. Structural modeling and dynamic analysis of CSTs are complicated due to fluid-structure interaction (FSI) and coupling issues, which could have significant effects on seismic response. The capability of a number of approximate models to capture seismic response is investigated using dynamic analysis results from detailed finite element models. Modal analyses and time history analyses are carried out using both 2D and 3D models to predict the dynamic behavior of CSTs as a function of ground motion intensity. Although 2D simplified models can be used to quickly evaluate the dynamic response of CSTs when there is substantial margin to failure, a detailed 3D model is required when it is necessary to examine a limit state associated with the failure mode of the tank. The results show good agreement between the natural frequencies of convective modes determined from the 2D and 3D CST models. The difference between the frequencies of impulsive modes were found to be equal to or less than 25%.

Dynamic Behaviour and Seismic Response of Ground Supported Cylindrical Water Tanks

Liquid storage tank such as in water distribution systems, petroleum plants etc., constitute a vital component of life line systems. Reducing earthquake effects on liquid storage tanks, to minimize the environmental and economic impact of these effects, have always been an important engineering concern. In this paper, the dynamic behavior of cylindrical ground supported concrete water tanks with different aspect ratios is investigated using finite element software ANSYS. The natural frequencies and modal responses are obtained for impulsive and convective modes of vibration. The natural frequency of vibration of the tank is observed to be the lowest at maximum water depth. The fundamental impulsive frequency increases as water level reduces and for water level less than 1/3 of tank height, there is significantly no change in impulsive frequency. The effect of wall flexibility on dynamic behavior of the tank is investigated by performing the modal analysis of flexible and rigid tanks. For a partially filled tank, the results of the present study are of significant relevance. The response of the tank to the transient loading as horizontal ground motion of El Centro earthquake is studied for various water heights. As the height of water on the tank increases, the ultimate maximum seismic response parameters are also observed to be increased. The location of maximum hoop stress varies in accordance with the variations in input ground motion and water fill condition whereas shear and bending moment are maximum at the base.

Approximate discretization of regular descriptor (singular) systems with impulsive mode

Descriptor systems can describe algebraic constraints and impulsive behaviour of systems and hence represent more general and broad category of complex dynamical systems. The impulsive behaviour of descriptor systems must be eliminated as it can cause degradation and saturation in performance or even can damage the system. To eliminate impulsive modes using discrete-time controllers, discrete-time models of descriptor systems are required. This paper deals with this problem and proposes a novel discretization technique for regular descriptor systems with impulsive mode when the input is applied through a zero-order-hold device. Using the Kronecker canonical form, the system model is decomposed into exponential, static and impulsive modes. Exact discrete-time models of exponential and static modes are obtained but an approximate discrete-time model for impulsive mode is proposed using limiting value functions because exact discretization is not possible as digital devices cannot realize infinite magnitude in zero time. An upper bound on error introduced by discretization is also derived. In addition, a simulation example is presented to show the efficacy of the proposed technique.

EFFECT OF FREE SURFACE BOUNDARY AND WALL FLEXIBILITY IN SEISMIC DESIGN OF LIQUID STORAGE STEEL TANKS

Fluid Structure Interaction (FSI) itself is a vast and extensive discipline. It originated from studies of aero and hydro-elasticity, which are often related to aeronautics and aerospace as well as nuclear industries. In practice, within the scope of nuclear, civil, aerospace, ocean, chemical and mechanical engineering, there are many terminologies involved, ie., flow induced vibration, aero-elasticity, hydro-elasticity, fluid structure interaction and fluid solid interaction. Typical problems include structure interaction with surface and sound waves and vibrations and stabilities of cables, pipes, plates and shells. In this paper, the effect of fluid structure interaction on the modal characteristics of a cylindrical steel water tank with and without free surface effect is considered. Acoustic structure interaction using unsymmetric pressure based formulation is used to solve the coupled system using FEM and the procedure is validated using results from published literature. Two tank models (shallow and tall) are modeled using ANSYS and modal analysis was done by considering different conditions like with slosh and without slosh. The effect of fluid mass on the convective and impulsive modes of tall and shallow aspect ratio tanks is shown. Parametric study is done for different fluid levels to characterize the variation of slosh frequencies in both rigid and flexible wall conditions. Free surface is considered in fluid alone model to predict the slosh frequencies employing rigid wall boundary. Then slosh frequencies got from both rigid and flexible wall conditions are compared with design data frequency tabulated from the GSDMA Guidelines. From this we can say that the flexibility of tank wall has a greater effect on the slosh frequencies.

Seismic analysis of rectangular water-containing structures with floating ice blocks

This paper presents a new formulation to investigate the effects of floating ice blocks on seismically-excited rectangular water-containing structures. The proposed method is based on a sub-structuring approach, where the flexible containing structure and ice-added mass are modeled using finite elements, while hydrodynamic effects are modeled analytically through interaction forces at the water–structure and water–ice interfaces, thus eliminating the need for reservoir finite element discretization. In addition to accounting for the influence of floating ice blocks and container walls' flexibility, the developed frequency- and time-domain techniques also include the effects of container geometrical or material asymmetry as well as the coupling between convective and impulsive components of hydrodynamic pressure. The proposed formulation is illustrated through a numerical example illustrating the dynamic response of symmetric and asymmetric water-containing structures covered with floating ice blocks. Obtained time- and frequency-domain responses are successfully validated against advanced finite element analyses including fluid–structure interaction capabilities. For the water-containing structures studied, the results show that the presence of floating ice blocks affects the frequency content and amplitudes of the dynamic responses corresponding to convective and impulsive modes. ► New formulation for seismically-excited ice-covered water-containing structures ► Reservoir modeled analytically thus no need for its finite element discretization ► Effects of floating ice blocks, asymmetry, convective and impulsive modes ► Obtained dynamic responses successfully validated against finite element solutions ► Example highlighting the effects of floating ice blocks on dynamic response

Jump modes analysis and observer design for discrete singular systems

This paper is concerned with the reconstructability and detectability of the jump modes of discrete singular systems. The notion of jump modes can be considered as the discrete counterpart of the impulsive modes of continuous singular systems which has been extensively studied. The effect of jump modes on the existence of reduced order normal Luenberger observers for discrete singular systems is investigated. Necessary and sufficient conditions for the existence of normal Luenberger observers and the corresponding observer design procedure are obtained.

Fundamental modes of tank-liquid systems under horizontal motions

This paper reports results on the fundamental impulsive modes of vibration of cylindrical tank-liquid systems anchored to the foundation under horizontal motion. The analyses are performed using a general purpose finite element (FE) program, and the influence of the hydrostatic pressure and the self-weight on the natural periods and modes is considered. The roof and walls are represented with shell elements and the liquid is modeled using two techniques: the added mass formulation and acoustic finite elements. Tank height to diameter ratios from 0.40 to 0.95 were used, with a liquid level at 90% of the height of the cylinder. The effect of the geometry on the fundamental modes for the tank-liquid systems is studied using eigenvalue and harmonic response analyses. Similar fundamental periods and mode shapes were found from these two approaches. The fundamental modes of tank models with aspect ratios ( H / D ) larger than 0.63 were very similar to the first mode of a cantilever beam. For the shortest tank ( H / D = 0.40 ) , the fundamental mode was a bending mode with a circumferential wave n = 1 and an axial half-wave ( m ) characterized by a bulge formed near the mid-height of the cylinder.

Nonstationary seismic response of a tank on a bilinear hysteretic soil using wavelet transform

A wavelet based nonlinear random vibration theory has been proposed in the present study to obtain responses of liquid storage tanks in form of instantaneous root mean square displacements of impulsive modes of the tank-liquid system supported on bilinear hysteretic (elasto-perfectly plastic) soil medium. The superstructure has been modeled by a combination of mass-spring-damper system. In order to evaluate the instantaneous root mean square values of the displacement responses of the tanks, zeroth moments of instantaneous power spectral density function (PSDF) have been evaluated. The hysteretic displacement is assumed to follow a truncated mixed Gaussian distribution. The evaluation of this zeroth moment depends on the post-yield or the pre-yield state of the hysteretic spring. The instantaneous root-mean-square (r.m.s) impulsive displacement response of the tank has been validated by simulation. A parametric study has been carried out to see the effects of the soil nonlinearity, the shear wave velocity in the soil and the height of the tank on tank responses.

Effect of Pre-stress States on the Impulsive Modes of Vibration of Cylindrical Tank-liquid Systems under Horizontal Motions

In this paper we investigate the influence of hydrostatic pressure and self-weight loads (pre-stress state) on the natural periods and mode shapes of steel cylindrical tanks and on the response under horizontal motions. The tank structure is modeled with finite elements and added mass models are used to represent the liquid. Only the impulsive component of the hydrodynamic response is considered. The natural periods and mode shapes for tank-liquid systems including and neglecting the effect of the pre-stress state are computed and compared. Three tank-liquid systems with different cylinder height to diameter ratios and slenderness ratios are considered. The numerical results show that the pre-stress state has a significant influence in the natural periods and mode shapes of tank-liquid systems with thinner walls; however, for thicker shells this effect is reduced. When the pre-stress state is neglected and included, the smaller differences in natural periods occur, for modes characterized by small circumferential wavenumbers. The steady-state response of a tank-liquid system to horizontal harmonic base accelerations was also computed. Large differences were found when the pre-stress state was neglected. A comparison of the frequency response functions shows that the peak responses occur at quite different load periods and they have significantly different amplitudes.

On impulsive algebraic multiplicities of linear time-invariant singular systems under feedback

Impulsive algebraic multiplicities of linear time-invariant singular systems under output feedback or decentralized output feedback are characterized in terms of system matrices directly. The multiplicities describe the number of impulsive modes that can be eliminated and indicate the number of finite poles that can be assigned by the respective feedback. These characterizations also lead to new regularizability conditions for singular systems.

Controllability and Elimination of Impulsive Modes in Descriptor Systems

As a refined notion, impulsive-mode controllability is suggested for the general class of linear continuous descriptor systems. This notion reveals rich properties of the general descriptor systems in terms of admissibility of initial conditions, admissibility of feedback control, and impulsive-mode elimination. The condition for impulsive-mode controllability is derived and proved to be necessary and sufficient for the existence of admissible feedback controls eliminating impulsive modes. Under impulsive-mode controllability, admissible feedback controls are constructed for eliminating impulsive modes, on the basis of numerically reliable decompositions of the system's coefficient matrices.

On impulsive modes of linear singular systems subject to decentralized output feedback

Some algebraic properties of linear singular systems at infinity under static decentralized output feedback are studied in this note. New concepts of algebraic multiplicity and geometric multiplicity of the impulsive decentralized fixed modes, and the impulsive decentralized cycle index of the singular system are defined. These concepts indicate how much a singular system can be made close to being impulse-free by decentralized output feedback, and the results are shown to be generic. The geometric multiplicity and the impulsive decentralized cycle index are determined in terms of the system matrices explicitly. The number of impulsive modes that can be eliminated is given in terms of these indexes. The impulsive decentralized cycle index is shown to characterize generic properties on controllability and observability of the closed-loop system through an individual channel (or an external channel). Illustrative examples are provided.

Constrained State Regulation of Linear Continuous-time Singular Systems

In this paper, we consider a new approach dealing with the constrained state regulation problem for the continuous-time singular systems. The basic idea is to transform the original problem into a regular reduced order one that is much easier to solve. The application of the positive invariance concept leads to a suitable regulator that eliminates all impulsive modes and keeps the states of system in the polyhedron defined by the specified constraints while transferring them asymptotically to the equilibrium point.