Wave Time Histories Research Articles

FINITE ELEMENT-BASED FATIGUE BEHAVIOUR OF SPRINGS IN AUTOMOBILE SUSPENSION

This paper presents the fatigue behaviour of springs used in shock absorbers in automobile suspension systems. SAE 9254 is considered as a spring material. Triangular waves with a frequency of 4 Hz and SAE standard suspension loading history (SAESUS) were used for fatigue analysis. Both load histories are scaled according to the maximum and minimum values of deflection, as spring height at full-bump and full-rebound, respectively. Finite element analysis was carried out using the linear static approach. Fatigue analysis was performed using the strain-life method. Absolute maximum principal and critical plane approaches gave results of reasonable accuracy, but later had a considerably longer solution time, while signed von Mises and signed shear approaches gave very conservative results. Thus the absolute maximum principal method is found to be the best suited. The results show that the spring did not fail before 4×10 5 cycles at 4 Hz for wave time history and 70,000 repeats for SAESUS time history at critical location.

The Development of Prefabricated Concrete Structures

This Prefabricated concrete structures have low carbon environmental protection, short construction period and engineering quality controllable feature. With the engineering background of a nine prefabricated concrete frame structure, the author established the numerical model using structural nonlinear software SNAP, and using different Peak acceleration EL Centro wave Taft wave, and Shanghai artificial SHW2 wave time history analysis. Get the angular displacement between the layers of the structure drift angle between structural. Less than the limit prescribed in the "Seismic Design".

Elastic wave propagation and time history analysis in FG nanocomposite cylinders reinforced by carbon nanotubes using a hybrid mesh-free method

Purpose – The purpose of this paper is to propose a hybrid mesh-free method based on generalized finite difference (GFD) and Newmark finite difference methods to study the elastic wave propagation in functionally graded nanocomposite reinforced by carbon nanotubes (FGNRCN). The presented hybrid mesh-free method is applied for a thick hollow cylinder, which is made of FGNRCN and excited by various mechanical shock loadings. Design/methodology/approach – The FG nanocomposite cylinder is assumed to be under shock loading. The elastic wave propagation is obtained and studied for various nonlinear grading patterns and distributions of the aligned carbon nanotubes. The distribution of carbon naotubes in FG nanocomposite are considered to vary as nonlinear function of radius, which varies with various nonlinear grading patterns continuously through radial direction. The effective material properties of functionally graded carbon nanotube are estimated using a micro-mechanical model. Findings – The mechanical shock analysis of FGNRCN thick hollow cylinder is carried out and the dynamic behavior of displacement field and the time history of radial displacement are obtained for various grading patterns. An effective hybrid mesh-free method based on GFD and Newmark finite difference methods is presented to calculate the average velocity of elastic wave propagation in FGNRCN. The average velocity of elastic wave propagation is obtained for various grading patterns and various kinds of volume fraction. The effects of some parameters on average velocity of elastic wave propagation are obtained and studied in detail. Originality/value – The calculation of elastic radial wave propagation in a FGNRCN thick hollow cylinder is presented using a hybrid mesh-free method. The effects of some parameters on wave propagation such as various grading patterns of distribution of carbon nanotubes are studied in details.

Forecasting tsunamis in Poverty Bay, New Zealand, with deep-ocean gauges

The response/transfer function of a coastal site to a remote open-ocean point is introduced, with the intent to directly convert open-ocean measurements into the wave time history at the site. We show that the tsunami wave at the site can be predicted as the wave is measured in the open ocean as far as 1,000+ km away from the site, with a straightforward computation which can be performed almost instantaneously. The suggested formalism is demonstrated for the purpose of tsunami forecasting in Poverty Bay, in the Gisborne region of New Zealand. Directional sensitivity of the site response due to different conditions for the excitation of the shelf and the bay’s normal modes is investigated and used to explain tsunami observations. The suggested response function formalism is validated with available records of the 2010 Chilean tsunami at Gisborne tide gauge and at the nearby deep-ocean assessment and reporting of tsunamis (DART) station 54401. The suggested technique is also demonstrated by hindcasting the 2011 Tohoku tsunami and 2012 Haida Gwaii tsunami at Monterey Bay, CA, using an offshore record of each tsunami at DART station 46411.

Hurricane Gustav (2008) Waves and Storm Surge: Hindcast, Synoptic Analysis, and Validation in Southern Louisiana

AbstractHurricane Gustav (2008) made landfall in southern Louisiana on 1 September 2008 with its eye never closer than 75 km to New Orleans, but its waves and storm surge threatened to flood the city. Easterly tropical-storm-strength winds impacted the region east of the Mississippi River for 12–15 h, allowing for early surge to develop up to 3.5 m there and enter the river and the city’s navigation canals. During landfall, winds shifted from easterly to southerly, resulting in late surge development and propagation over more than 70 km of marshes on the river’s west bank, over more than 40 km of Caernarvon marsh on the east bank, and into Lake Pontchartrain to the north. Wind waves with estimated significant heights of 15 m developed in the deep Gulf of Mexico but were reduced in size once they reached the continental shelf. The barrier islands further dissipated the waves, and locally generated seas existed behind these effective breaking zones.The hardening and innovative deployment of gauges since Hurricane Katrina (2005) resulted in a wealth of measured data for Gustav. A total of 39 wind wave time histories, 362 water level time histories, and 82 high water marks were available to describe the event. Computational models—including a structured-mesh deepwater wave model (WAM) and a nearshore steady-state wave (STWAVE) model, as well as an unstructured-mesh “simulating waves nearshore” (SWAN) wave model and an advanced circulation (ADCIRC) model—resolve the region with unprecedented levels of detail, with an unstructured mesh spacing of 100–200 m in the wave-breaking zones and 20–50 m in the small-scale channels. Data-assimilated winds were applied using NOAA’s Hurricane Research Division Wind Analysis System (H*Wind) and Interactive Objective Kinematic Analysis (IOKA) procedures. Wave and surge computations from these models are validated comprehensively at the measurement locations ranging from the deep Gulf of Mexico and along the coast to the rivers and floodplains of southern Louisiana and are described and quantified within the context of the evolution of the storm.

ACCOUNTING FOR LEVEE OVERTOPPING DURATION: A TEST WITH HURRICANE KATRINA CONDITIONS

Overtopping of earthen levees can result in lee side erosion, levee failure and severe flooding consequences. Erosion takes time and early design guidance did not account for overtopping duration. The potential overtopping durations associated with hurricanes depends on the time histories of the surges and waves and are usually shorter than for riverine or coastal flooding by other storm types. With significant advancements in hurricane-induced storm surge modeling, it is appropriate to improve the levee erosion response characteristics. This paper presents the results of a blind-folded comparison of a method developed by Dean, et al (2010) to two levee locations in the New Orleans area. The levees failed in one area where the waves were larger than the second area where the levees performed well. The method applied accounts for surge and wave time histories, levee geometry and grass cover quality. Results are consistent with failure at the location of higher wave heights; however, the method also predicts failure at the location where levee function was retained. At the latter location, for good quality grass cover and a wave period of 4 s, a required levee crest elevation of 5.9 m is determined compared to an actual elevation of 5.8 m. For poor grass quality and a wave period of 8 s, the method indicates a required crest elevation of 7.4 m. The method can be applied to optimize levee design, for example, through investigating the trade offs between crest elevation and levee side slopes.

MODELLING STORM SURGE WAVE OVERTOPPING OF SEAWALLS WITH NEGATIVE FREEBOARD

A Reynolds-averaged Navier-Stokes based wave model (RANS) is used to simulate storm surge wave overtopping of embankments. The model uses a wave generating boundary condition that accepts a wave time history as an input and reproduces the time history in the model. This allows a direct wave by wave simulation of recorded data. To investigate the success of the model at reproducing the wave generation, transformation and overtopping processes the model is compared with experimental laboratory data. A wave-by-wave comparison is performed for overtopping parameters such as discharge, depth and velocity. Finally the overtopping discharge predicted by the model is compared against design formulae.

Seismic vertical array analysis for phase decomposition

We propose a vertical array analysis method that decomposes complex seismograms into body and surface wave time histories by using a velocity structure at the vertical array site. We assume that the vertical array records are the sum of vertically incident plane P and S waves, and laterally incident Love and Rayleigh waves. Each phase at the surface is related to that at a certain depth by the transfer function in the frequency domain; the transfer function is obtained by Haskell's matrix method, assuming a 1-D velocity structure. Decomposed P, S and surface waves at the surface are estimated from the vertical array records and the transfer functions by using a least-squares method in the frequency domain; their time histories are obtained by the inverse Fourier transform. We carried out numerical tests of this method based on synthetic vertical array records consisting of vertically incident plane P and S waves and laterally incident plane Love and Rayleigh waves. Perfect results of the decomposed P, S, Love and Rayleigh waves were obtained for synthetic records without noise. A test of the synthetic records in which a small amount of white noise was added yielded a reasonable result for the decomposed P, S and surface waves. We applied this method to real vertical array records from the Ashigara valley, a moderate-sized sedimentary valley. The array records from two earthquakes occurring at depths of 123 and 148 km near the array (epicentral distance of about 31 km) exhibited long-duration later phases. The analysis showed that duration of the decomposed S waves was a few seconds and that the decomposed surface waves appeared a few seconds after the direct S-wave arrival and had very long duration. This result indicated that the long-duration later phases were generated not by multireflected S waves, but by basin-induced surface waves.

Abnormal Wave-Induced Load Effects in Ship Structures

The paper presents an approach to determine the global load effects induced on shif structures by abnormal, freak, or episodic waves. It refers to the present procedure of determining extreme values of wave-induced responses, including the recent advances of adopting time series of wave elevation as reference design conditions t calculate the wave-induced structural loads on ships in heavy weather. It is show how this procedure can be extended to account for abnormal or episodic waves Reference is made to what is presently known about abnormal or freak waves showing that although it is possible to determine the loads induced by these wave in floating and fixed structures, the present knowledge about the probability of occurrence of these waves is not enough to allow a wave design criterion to be defined in a way consistent with the present probabilistic approaches. However, it is suggested that at the present stage of knowledge it is possible to determine the load induced by abnormal waves similar to ones that have been measured at various ocean locations and that are thus realistic; a method is described to perform such calculations. Although this information cannot replace the wave-induced loads calculated with the presently established procedures, it can serve as guidance for th design. An application example is presented of a containership subjected to a wav trace that includes an episodic wave that was measured during a severe storm in Central North Sea. The measured wave time history is modified in order to investigate the influence of the wave steepness on the induced vertical motions and loads. Th loads induced by the abnormal wave are compared for the first time with extreme values from long-term distributions.

Acoustic wave propagation in a macroscopically inhomogeneous porous medium saturated by a fluid

The equations of motion in a macroscopically inhomogeneous porous medium saturated by a fluid are derived. As a verification of their validity, these equations are reduced and solved for rigid frame porous systems. The reflection and transmission coefficients and their corresponding time signals are calculated numerically using wave splitting Green’s function approach for a two-layer porous system considered as one single porous layer with a sudden change in physical properties. The results are compared to experimental results and to those of the classical transfer matrix method for materials saturated by air in the ultrasonic frequency range.

An integrated GPS–accelerometer data processing technique for structural deformation monitoring

Global Positioning System (GPS) is being actively applied to measure static and dynamic displacement responses of large civil engineering structures under winds. However, multipath effects and low sampling frequencies affect the accuracy of GPS for displacement measurement. On the other hand, accelerometers cannot reliably measure static and low-frequency structural responses, but can accurately measure high-frequency structural responses. Therefore, this paper explores the possibility of integrating GPS-measured signals with accelerometer-measured signals to enhance the measurement accuracy of total (static plus dynamic) displacement response of a structure. Integrated data processing techniques using both empirical mode decomposition (EMD) and an adaptive filter are presented. A series of motion simulation table tests are then performed at a site using three GPS receivers, one accelerometer, and one motion simulation table that can simulate various types of motion defined by input wave time histories around a pre-defined static position. The proposed data processing techniques are applied to the recorded GPS and accelerometer data to find both static and dynamic displacements. These results are compared with the actual displacement motions generated by the motion simulation table. The comparative results demonstrate that the proposed technique can significantly enhance the measurement accuracy of the total displacement of a structure.

Characterisation of underground blast-induced ground motions from large-scale field tests

An in-situ large-scale underground blast test program was conducted to investigate stress wave characteristics inside the medium, at the soil-rock interface and on the soil ground surface. The stress wave measurements were made through a vertical borehole and a horizontal borehole inside the rock mass, and along several horizontal lines arranged at the rock-soil interface and on the soil surface. Three different charge weights of 0.5, 2.5 and 10 t with loading densities of 0.5, 2.5 and 10 kg/m3, respectively, were used in the detonation. The measured stress wave time histories and their characteristic parameters, such as peak particle velocity (PPV) and peak particle acceleration (PPA), as well as the principal frequency (PF) at different locations are presented and analyzed in this paper. The results are also compared with those recorded from small-scale tests in a previous study and those from some other researchers, and the pertinent scale effects are discussed by observing differences of the stress wave intensities between the small-scale and the large-scale tests.

高速移動荷重によって鋼薄肉材構成板に生じる局部振動波の特性

On the thin-walled steel members of railway bridges, it has been clarified by measuring the vibration of a railway bridge actually that local vibration of the members increases suddenly with speeding up of train. This paper aims to elucidate the mechanism of the sudden increase of the local vibration. Firstly, the phase velocity and group velocity of the local vibration in steel component plates of thin-walled steel members are computed. Secondly, the dynamic responses of the steel component plates under high speed moving loads are analyzed. The relation the local vibration with the speeding up of the moving loads are investigated on wave form, time histories, reflection and propagation of local vibration of the plates.

Modeling a possible holocenic landslide-induced tsunami at stromboli Volcano, Italy

Stromboli is a volcanic island in the Aeolian archipelago, located in SE Tyrrhenian sea, Italy. It is characterised by a steep depression along the NW flank of the volcano called Sciara del Fuoco, that is interpreted as the partially filled scar of a large flank collapse that took place circa 5000 years ago. The large volume of material estimated to be involved in the collapse was very likely responsible for the generation of big ocean waves. This paper presents some numerical simulations concerning a tsunami scenario to the Holocene event. For the landslide we used a Lagrangian model based on the discratization of the total sliding mass in blocks of constant volume subjected to external and internal forces. Three possible slide evolutions are considered, differing by the modality of the block-block interaction. In all three cases the tsunami is simulated using a finite-element (FE) model based on the non-linear hydrodynamic equations with the addition of a forcing term to account for the excitation of sea waves by the landslide. Wave propagation and time histories all around the island are computed. The tsunami results to be very etc. Though most of the energy is radiated seaward, nonetheless very huge waves, in the order of tens of meters, attack the island, this result being almost independent from the landslide model used.

Nonlinear Performance of Offshore Platforms in Extreme Storm Waves

Dynamic-transient loading effects from extreme storm waves can have important influences on the nonlinear ultimate limit state performance of fixed offshore platforms. Recorded and synthetic storm wave time histories have been used to develop loading time histories acting on template-type platforms having natural periods in the range of 1-5 s. The interactions of these loading histories with the dynamic, nonlinear, hysteretic performance characteristics of idealized systems were analyzed. A modification to static pushover capacity analysis results is proposed to enable recognition of transient loading-structure performance characteristics. The results from the idealized systems were correlated with results from time domain nonlinear analyses of platform structure systems subjected to intense wave and earthquake loadings. For the global behavior of the platforms studied, the results based on the simplified systems are in good agreement with those from the complete analyses. ABSTRACT: Dynamic-transient loading effects from extreme storm waves can have important influences on the nonlinear ultimate limit state performance of fixed offshore platforms. Recorded and synthetic storm wave time histories have been used to develop loading time histories acting on template-type platforms having natural periods in the range of 1-5 s. The interactions of these loading histories with the dynamic, nonlinear, hysteretic performance characteristics of idealized systems were analyzed. A modification to static pushover capacity analysis results is proposed to enable recognition of transient loading-structure performance characteristics. The results from the idealized systems were correlated with results from time domain nonlinear analyses of platform structure systems subjected to intense wave and earthquake loadings. For the global behavior of the platforms studied, the results based on the simplified systems are in good agreement with those from the complete analyses.

Full-Nonlinear Simulations of Hydrodynamic Forces on a Heaving Two-Dimensional Body

A full-nonlinear computation technique based on the Mixed Eulerian-Lagrangian method is presented and validated quantitatively for a fundamental 2-D radiation problem. The time marching is performed with the 4-th order Runge-Kutta-Gill algorithm, and at each time step the integral equations for the velocity and acceleration fields are solved by applying a higher-order boundary-element method with quadratic isoparametric elements. Stable simulations over a large number of periods are possible, because an efficient absorbing beach is used to avoid wave reflections from an outer boundary and regridding is performed to avoid the cluster of nodal points on the free surface.Computed results are compared with linear-theory results of the Green function method in the time and frequency domains, measurements of the time history of waves generated by a wavemaker, and Fourier-analyzed results of hydrodynamic forces acting on an ellipse and a wedge. All of these results are in excellent agreement, confirming the validity of the calculation method.

Simulation of Time Histories of Second-Order Wave Effects by Pseudo-Linear Transformation

Abstract Simulation of the time histories of second-order wave effects is often performed by quadratic transformation of a wave time history. By the present approach, the quadratic transformation of waves is approximated by linear combinations of the products of component wave time records and their Hilbert transforms. The computational efficiency is greatly enhanced. The efficient quadratic transformation of a time history is for the time domain solution of structural dynamic response, and can also be used as a post-processor of the frequency domain solution for obtaining statistic parameters of dynamic response.

On The Measurement of Directional Wave Spectra by the New Wave Measuring System using Laser Beams

The wave measuring system applying laser beams for wave surface probes were recently developed by Experimental Tank of Yokohama National University. Laser spot projectors are set as the wave probe array under water, and He-Ne laser beams are projected vertically upward from each projectors. Images of laser spots on the wave surface are taken by a video camera, and that video pictures are processed and the digital informations of wave heights or wave slopes are obtained from processed video signals. These measured timeseries converted to the wave timehistories of multi positions by a personal computer in real time, and the directional wave spectrum is estimated by the Maximum Likelihood Method. Moreover the hard copies of 3-D graphs of directional spectra are got immediately.In this paper, principles of these new measuring systems and related numerical calculus are mentioned. And the measured examples in the Experimental Tank of Yokohama National University by these systems are shown.Consequently, these new systems showed the excellent abilities and performances.

Dynamic Analysis for Transportation of Barge-Jacket Assembly in Time-Frequency Domain

A combined time-frequency domain method is proposed to analyze the stresses of barge-jacket assembly during transportation. Starting with the motion of analysis in frequency domain, the time history of waves and motions in random seas are simulated, then the stresses are determined in time domain. The stress autocorrelation functions are calculated and the stress spectra and statistical characteristics are obtained through Fourier transformation. A computer program has been developed. The effects of barge flexibility and the forces caused by the immersion of jacket have been discussed.

ひずみ速度依存性を示す材料における塑性波伝ぱの解析 衝撃速度変化の影響

The present paper is concerned with a problem of longitudinal plastic waves in a bar subjected to tensile impact. The effect of the variation of impact velocity on the propagation plastic waves and the formation of strain plateau in the strain distribution is discussed experimentally and theoretically. Impact tensile tests of copper specimens were carried out by an impact testing apparatus using a falling weight. The plastic strain distribution of the specimen was measured and the time history of plastic waves at various stations along the specimen was observed, together with the variation of impact velocity during impact. Theoretical calculation was performed by using Malvern's strain-rate dependent theory, taking account of the attenuation of impact velocity.The results obtained are summarized as follows:(1) The experimental results showed that the strain distribution along the specimen decreased with the increase of the distance from the impact end and no strain plateau at neighborhood of the impact end appeared.(2) The theoretical results under the condition of decreasing impact velocity predicted also no strain plateau and almost agreed with the experimental results.(3) The formation of strain plateau may be limited to the case of a constant impact velocity, though it is related to the strain-rate dependent nature of material, the impact velocity and the duration of impact time.