The dynamic analysis of concrete arch dam by employing wavenumber approach has been investigating. In previous studies, the analysis was limited for concrete gravity dam. It is well-known that the difficult approach for solving this problem relies heavily on employing a three-dimensional semi-infinite fluid element. The hyper-element is formulated in frequency domain and its application in this field has led to many especial purpose programs which were demanding from programming point of view. In this paper, the method is initially described. Subsequently, the response of Morrow Point dam-reservoir system is obtained by wavenumber approach, and the results are compared against the exact response. Based on this investigation, it is concluded that this approach can be anticipated as a great substitute for the rigorous type of analysis.

Grid dispersion is one of the criteria of validating the finite element method (FEM) in simulating acoustic or elastic wave propagation. The difficulty usually arisen when using this method for simulation of wave propagation problems, roots in the discontinuous field which causes the magnitude and the direction of the wave speed vector, to vary from one element to the adjacent one. To solve this problem and improve the response accuracy, two approaches are usually suggested: changing the integration method and changing shape functions. The Finite Element iso-geometric analysis (IGA) is used in this research. In the IGA, the B-spline or non-uniform rational B-spline (NURBS) functions are used which improve the response accuracy, especially in one-dimensional structural dynamics problems. At the boundary of two adjacent elements, the degree of continuity of the shape functions used in IGA can be higher than zero. In this research, for the first time, a two dimensional grid dispersionanalysis has been used for wave propagation in plane strain problems using B-spline FEM is presented. Results indicate that, for the same degree of freedom, the grid dispersion of B-spline FEM is about half of the grid dispersion of the classic FEM.

summary Downward continuation of potential field data plays an important role in interpretation of gravity and magnetic data. For its inherent instability, many methods have been presented to downward continue stably and precisely. The Tikhonov regularization approach is one of the most robust. It is based on a lowpass filter derivation in the Fourier spectral domain, by means of a minimization problem solution. In this manuscript, we propose an improved regularization operator for downward continuation of potential field data. First, we simply define a special wavenumber named the Cutoff wavenumber to divide the potential field spectrum into the signal part and the noise part based on the radially averaged power spectrum of potential field data. Next, we use the conventional downward continuation operator to downward continue the signal and the Tikhonov regularization operator to suppress the noise. Moreover, the parameters of the improved operator are defined by the Cutoff wavenumber which has an obvious physical significance. For computing the α parameter, it is necessary that the C-norm of the potential field must be calculated. The improved operator can not only eliminate the influence of the high-wavenumber noise but also avoid the attenuation of the signal. Experiments through synthetic gravity and real gravity data from Kohe Namak region, Ghom province, Iran show that the downward continuation precision of the proposed operator is higher than the Tikhonov regularization operator...

Phase variation of potential field data can be used as an interpretation method. This idea appears in edge detection with tilt angle or phase angle. The advantages of this quantity are its independency to body magnetization direction and also its easy computations. In this paper variations of this quantity termed local wave number are used for source parameter estimation such as body depth and susceptibility, which can be used without any prior information about source geometry. This method was applied on synthetic magnetic data and on the real magnetic data of an area in the Sar-Cheshme region. Using this method, causative body depth varies from 15 to 100 meters in different locations of the studied area, which is in agreement with the existing drilling information and forward modeling.

Flow-acoustic feedback is one of the main types of noise in a cavity, is caused by the instability of the cavity shear layer and is enhanced through an acoustic-wave feedback mechanism. The flow characteristics of the cavity boundary/shear layer and the characteristic frequencies of the flow-acoustic feedback in the cavities are studied numerically, with aspect ratios ranging from 1/2 to 4/3. The freestream Mach number is equal to 0. 11, corresponding to an Re-based cavity length of 2. 1×105. Improved Delayed Detached Eddy Simulations combined with Ffowcs Williams-Hawkings acoustic analogy are used to simulate the flow and noise characteristics of the cavities. Auto-correlation analysis of flow field fluctuations is used to establish a link between the boundary/shear layer pressure fluctuations and flow-acoustic feedback noise. For the low aspect ratio cavities investigated in this paper, convection velocities along the shear layer development direction are obtained using wavenumber-frequency analysis. The deeper the cavity, the lower the shear layer flow velocity. Correspondingly, the characteristic frequencies of the narrowband noise generated by the flow-acoustic feedback shift linearly toward the low frequency band as the cavity depth increases. The results of the predicted noise characteristic frequencies obtained using wavenumber-frequency analysis and Rossiter's empirical formula are in agreement with the calculated results.

A reliable analysis of magnetic data is the correct estimation of the causative sources to plan for drilling to achieve the targets. This paper presents enhanced local wave number (ELW) method for interpretation of the magnetic data. ELW method has been proposed during the previous decades and is based on the analytic signal to estimate the location and depth of the anomalies without having any knowledge about the geometry and magnetic susceptibility of the source. Final equation in this technique, is based on the depth and position and is independent of the structural index. The normal solution of this equation is obtained by assigning ELW kx and kz (the local wave number with respect to x and z) for different values of x and heights of continuation; z within a window is centred with the peak of the analytic signal amplitude. A problem of over determined unknown parameters can be solved through a standard technique, as using the least squares approach, therefore, the Golub algorithm is used to solve a set of linear equations. The ELW technique requires computation of horizontal and vertical derivatives of the first and second orders. Due to this characteristic, any high frequency noise present in the data gets substantially enhanced, masking the response from a target. To restrict the high frequency response, a window function is designed on the basis of the maximum frequency computed from the work of Agrawal and Lal (1972). After finding these quantities the method can approximate the structure index. Although, an appropriate Matlab code for the method is introduced and tested on two dimensional synthetic data before and after adding noises. There is a peak in the curves of analytic signal and kx of ELW and also a turning point in the curve of kz of ELW which shows the position of anomaly. Existence of these features shows that final responses of ELW method are correct. Synthetic data produced from a dyke like body with dip, magnetization, declination, inclination, depth and thickness are 45º, 1 (𝐴𝑚⁄), 10º, 64º, 10m and 5m respectively. The ELW method has had reasonable responses for noises with different amplitudes up to 20nT and for noises with amplitude more than 20nT, ELW method loses its efficiency. Then, the method is tested by applying it on the real data of Golbolaghi area in Zanjan, and the results are compared with the results obtained from Model vision software. To do this a 525m profile is used. At the end, the depth and structure index are obtained as about 4m and 0.8, respectively using ELW method; also the depth is estimated at about 4.4m using model vision software. It is worthy to note that the depth of anomaly has been reported 4.5m by drilling. The parameters obtained from the introduced method for the anomalies show that the enhanced local wavenumber method and its introduced Matlab code can be a powerful tool in the studies of local anomalies. Because this method is automatic and quick, it can be used for large data sets like vast area or airborne data. This method is also used on airborne data of Damghan region in another paper.

Summary:An important problem in the interpretation of the magnetic data is the ability to understand the characteristics of the anomalous bodies that are the sources of the measured anomalies. A great deal can be interpreted by looking at the images of the magnetic data and its spatial derivatives. A quantitative interpretation of the magnetic data usually includes estimating dip, susceptibility, and most importantly, the depth to top of the sources of an anomalous magnetic response. Methods that exist for estimating depth work either on data recorded along a profile or data interpolated onto a regular grid. The advantage of the latter approach is that the resulting images are relatively simple and quick to produce, show regional structural patterns at the area under study, and are easily overlain on other geophysical and geological maps. However, many geophysical practitioners prefer to interpret individual profiles because finer sampling intervals generally lead to more accurate results. While this approach is considerably more laborious than using gridded data as its input, a richer understanding of the geology is resulted in this case. A variety of semiautomatic methods, based on using the derivatives of the magnetic anomalies, have been developed for the determination of causative source parameters such as boundary locations and depths. One of these techniques is the analytic signal method for magnetic anomalies initially used in its complex function form. It makes use of the Hilbert transform properties. Other methods for an automatic estimation of the source depth using profile data include the Naudy method, Werner deconvolution, Euler deconvolution, and the Phillips method. For these methods, the depth estimation procedure is applied to each point along the line. At those points where a source is detected, multiple solutions are returned, each based on a different assumed model. The interpreter must choose one of these solutions based on its understanding of geology or other complementary information from other geosciences data.In recent years, we have shown the invention of some depth-estimation methods using the local wavenumber quantity. This quantity is one of the three attributes derived from the complex analytic signal. The local wavenumber is a spatial quantity (not to be confused with the Fourier wavenumber) and is analogous to the instantaneous frequency used in the analysis of temporal series. Thurston and Smith (1997) have employed the local wavenumber to estimate the depth of 2-D thin sheets and contacts, using a priori information (typically the judgment of the interpreter) to determine which model is more appropriate. This method was subsequently generalized by introducing the concept of a multimodel wavenumber (The term multimodel applies because this quantity gives the same result disregard of the source being a horizontal cylinder, a thin sheet, or a contact). However, in the case of dipping dyke model or slipping step model, the conventional multimodel wavenumber is a combination of a bell-shaped function and terms dependent on the dimensions of the source which complicate a quantitative analysis particularly the depth estimation. To extend the applicability of this method, we must define a quantity that has a bell-shaped functional form, but independent of the source dimensions, when the source of the magnetic response is either a dipping thick dyke or a sloping finite step.In this paper, we document a further broadening of the applicability scope to include the dipping thick dykes and finite sloping steps by introducing an additional multimodel wavenumber called improved multimodel wavenumber. As in Thurston and Smith (1997) and Smith et al. (1998), we assume that the sources are two dimensional. We also present a new method to estimate the source depth using profile data as input. This method is based on the least-squares fitting of both the conventional and improved multimodel wavenumber from different geometry sources.We illustrate this technique using synthetic 2-D magnetic data from a dipping dyke model and a slipping step model on a 150-km-long line of aeromagnetic data from the Northwestern part of Anarak quadrangle yielding two thick dykes between the depths of 2800 and 3000m. Using this solution as a starting point in the iterative forward modeling exercise, the measured data were in reasonable agreement with the model.

Deep drilling is a major part of construction in urban planning and is necessary for establishment of tunnels, underground parking lots and structures with deep excavations. Usually, vertical and horizontal forces acting on the location of the excavation are braced by various types of sheet pile and cut-off. The water level around the sheet pile is an essential element to determine the excavation depth. Seepage flow through soil reduces the stability of the soil body around the sheet pile, and, finally, causes boiling and heaving phenomena. In this study, by means of software based on the explicit finite difference method, the effects of various factors on the occurrence of failure mechanisms and safety factors against boiling near the sheet pile are investigated. Comparison of experimental data with numerical results indicates that FLAC can model and simulate, properly, the boiling phenomenon, which is based on the stress strain analysis.Boiling and heaving near hydraulic structures with an alluvial foundation are so destructive and undesirable that remedial issues at the downstream part of such structures are vital. Proper modeling of such hydraulic structures (i.e. coastal dikes, levees etc) before implementation can be predicted using safe models and software such as FLAC. Good adaptation of numerical results with experimental data can prescribe accurate models for practical application, specifically the modeling of critical phenomenon such as boiling and heaving. Numerical analysis was performed to show the mechanism of failure under various conditions. Comparison of the computational results with experimental data and observations shows that FLAC can model correctly the mechanism of the boiling phenomena based on stress-strain analysis. The effects of the internal friction angle, the angle between the soil and the wall, and, finally, the dilation angle, on the behavior of soil, were investigated in detail. The increase in the internal friction angle caused the safety factor to rise significantly. The results of this study indicate that dilation angle is important in occurring the type and shape of heaving and boiling. Up to 15 degrees, the dilation angle created an increasing safety factor, while, after 15 degrees, the safety factor is decreased.