42 results about "Flexural waves" patented technology

The invention belongs to the field of polar acoustic measurement, and relates to a method for estimating the sound velocity and thickness of an ice layer by using airwaves and ice layer bending waves, which comprises the following steps of: acquiring broadband pulse sound signals by using a sensor fixed on an ice surface; recording the distance between the detonating device and the ice surface sensor; performing time-frequency analysis on the broadband pulse signal acquired by the ice surface sensor; obtaining a time-frequency spectrum of the signal through time-frequency analysis, calculating the propagation velocity of the airwave, converting the time-frequency spectrum into a group velocity spectrum, and extracting a group velocity dispersion curve of the bending wave; initializing the longitudinal wave velocity, the transverse wave velocity, the ice layer thickness and the seawater sound velocity of the ice layer; calculating an expected group velocity curve according to the sound propagation model, and constructing a cost function; and optimizing the cost function by adopting a particle swarm algorithm, and outputting a final parameter estimation value. The method can be realized only by using a single sensor, and the synchronization of transmitting equipment and receiving equipment is not required; the sound velocity and thickness of the ice layer can be inverted by using the relationship between the group velocity and the acoustic parameters.

A method includes defining a design domain for a meta-element configured to be attached to an edge of thin wall structure with an arbitrary boundary condition, and executing a topological optimization process on the design domain and providing a topology optimized shape for the meta-element. The topological optimization process includes an objective function that minimizes a reflection coefficient of flexural waves in the audible frequency range propagating towards and impinging the meta-element.

The invention discloses an acoustic black hole structure and a vibration damping device.The acoustic black hole structure comprises an acoustic black hole body and a damping layer, the acoustic black hole body is provided with a uniform thickness area and an acoustic black hole area, the acoustic black hole area is provided with a plurality of grooves, the grooves are distributed from the first end to the second end of the acoustic black hole area, and the damping layer is arranged between the first end and the second end of the acoustic black hole area. The depths of the grooves are gradually increased in the direction from the first end to the second end, and the damping layer is arranged in the acoustic black hole area. By machining the groove in the acoustic black hole area, the local bending rigidity of the acoustic black hole body is changed, the bending wave speed of the acoustic black hole body is reduced, the acoustic black hole effect is achieved, due to the arrangement of the groove, the local resonance effect can be utilized, and then structural vibration suppression in the low-frequency range is achieved; the problem that a traditional acoustic black hole structure is poor in low-frequency-band vibration reduction effect is solved, in addition, thickness cutting of an acoustic black hole area of an original structure is avoided, and the manufacturing difficulty and the requirement for the precision of machining equipment are lowered.

A system and related method can self-adaptively absorb a flexural wave acting on a beam. The method includes the steps of receiving an input signal representing a frequency response of a flexural wave acting on the beam, determining a spring constant for absorbing the flexural wave based on the input signal, a damping value of a damper acting on the beam, and a mass value of a mass acting on the beam, and applying a spring constant voltage based on the spring constant to a piezoelectric device connected to the beam. The piezoelectric device has a variable spring value that varies based on the voltage applied to the piezoelectric device. The piezoelectric device's variable spring value is approximately equal to the spring constant value when the spring constant voltage is applied to the piezoelectric device.

Disclosed are systems for absorbing and / or isolating vibrations and / or flexural waves acting upon a structure using scatterers. In one example, a system for absorbing a flexural wave acting upon a structure includes a pair of scatterers adhered to the structure using an adhesive having a property that is based on a reduction of the flexural wave at a peak frequency by the pair of scatterers.

The application discloses a steel-concrete composite beam crack discrimination method based on bending wave structural sound intensity aggregation degree testing, which comprises the following steps: dividing a to-be-tested plate into a series of scanning areas, setting a scanning path, and calculating the bending wave structural sound intensity aggregation degree; traversing the plate according to a scanning algorithm and calculating the bending wave structural sound intensity aggregation degrees of all areas; calculating the bending wave structural sound intensity aggregation degrees of all areas of the steel-concrete composite beam plate in a service period; comparing the bending wave structural sound intensity aggregation degree spectrum peak values, and if the difference between the bending wave structural sound intensity aggregation degree spectrum peak values of a scanning area of the two exceeds a preset threshold value, it is determined that the scanning area of the steel-concrete composite beam plate in the service period has cracks. The application combines the characteristics that the bending wave signal is easy to test, adopts the bending wave structural sound intensity testing technology and the structural sound intensity aggregation degree scanning algorithm, and can realize efficient discrimination and positioning of the steel-concrete composite beam cracks, and has great theoretical significance and engineering value for damage identification of the bridge.

The present invention discloses a liquid-resistance vibration reduction device with a multi-stage segmented acoustic black hole structure, comprising a cylinder cup filled with damping fluid and a multi-stage segmented acoustic black hole structure disposed within the cylinder cup; the multi-stage segmented acoustic black hole structure comprises a plurality of acoustic black hole structures stacked in parallel with each other, each having a segmented power-finger profile; an inertial channel damping disk is disposed between two adjacent acoustic black hole structures; the multi-stage segmented acoustic black hole structure includes but is not limited to a first-stage acoustic black hole structure and a second-stage acoustic black hole structure; the inertial channel damping disk is provided with a plurality of inertial channels for passage of the damping fluid; a connecting rod of the first-stage acoustic black hole structure extends from the cylinder cup and connects to a top disk. Compared with the prior art, the present invention has the advantages of a low cutoff frequency, a wide effective bandwidth, and robust and controllable damping characteristics. The present invention utilizes a multi-stage segmented acoustic black hole structure, which can filter, grade, and focus bending waves propagating in the structure, achieving a vibration reduction effect with a lower cutoff frequency and a wider bandwidth.

The invention provides an additional locally slotted acoustic black hole board, which is mounted on a main board to be damped and comprises a black hole board main body and a damping layer, the black hole board main body is fixed on the main board to be damped and comprises a uniform thickness area and one or more acoustic black hole areas, one or more weight reduction grooves are formed in the uniform thickness area, and the damping layer is arranged on the damping layer. And a damping layer is arranged on the acoustic black hole area. According to the additional type locally-slotted acoustic black hole plate, by forming the weight reducing grooves in the non-key area of an original additional acoustic black hole plate structure, redundant materials are removed, the weight reduction of an additional structure is achieved, meanwhile, the local resonance vibration reduction effect and the energy gathering capacity of the acoustic black hole effect on bending waves are kept, and the acoustic black hole plate has the advantages of being simple in structure and convenient to use. Finally, broadband vibration control of the mainboard is achieved under the low additional mass, the overall structure meets the requirement for light weight, and the structure is particularly suitable for a plate-shaped system sensitive to the additional mass.

This bending wave speaker comprises a diaphragm and an actuator that is disposed on the diaphragm and vibrates the diaphragm. The shape of the diaphragm is a parallelogram or an ellipse. When the diaphragm is a parallelogram, the ratio of the length of a first side, which is the longest side of the parallelogram, to the length in a direction perpendicular to the first side is an irrational number. When the diaphragm is an ellipse, the ratio of the major axis to the minor axis of the ellipse is an irrational number.

The invention provides a generalized vibration model for analyzing vibration characteristics of a discontinuous core sandwich beam and a vibration transmission loss calculation method. The generalized vibration model and the vibration transmission loss calculation method have universality and expandability. According to the generalized vibration model, the interlayer beam is composed of an upper beam, a lower beam and discrete cores, and the interlayer beam comprises a coupling section containing the cores and a non-coupling section not containing the cores; when N cores are contained in the discontinuous core interlayer beam, N is larger than or equal to 2, junction points A, B, C and D of the left end and the right end of the first core and the upper beam and the lower beam from left to right are discontinuous feature points, the A end and the C end are incident ends of bending waves, and reflection matrixes # imgabs0 # of the bending waves at the incident ends and transmission matrixes # imgabs2 # # imgabs3 # # imgabs4 # of the bending waves from left end to right are that the discontinuous core interlayer beam contains N-1 cores. A reflection matrix of the bending waves at the incident end and a transmission matrix of the bending waves from the left end to the right end.

The invention provides a complex columnar structure medium inversion method based on a high-order bending wave cut-off frequency, and the method comprises the steps: building a slurry-sleeve-cement sheath-stratum multilayer medium coupling model based on a three-dimensional elastic waveguide theory; calculating the cut-off frequency of the bending mode wave of the dipole high-order bushing according to the sizes of the inner-layer bushing and the outer-layer bushing; exciting an elastic wave field by using a piezoelectric transducer, and continuously collecting full-wave array acoustic wave signals along the well axis direction; performing Fourier transform on the full-wave train sound wave signal to obtain a frequency spectrum, and calculating frequency dispersion data of the full-wave train sound wave signal by using a frequency spectrum correlation function; according to the frequency dispersion data, summing the slowness data at each frequency in a cut-off frequency range to obtain a frequency coefficient; and correcting the calculated frequency coefficient to obtain a correction coefficient, and normalizing the obtained correction coefficient to obtain the cementation index of the whole well section. According to the method, tedious theoretical frequency dispersion curve solving is avoided, and the method is simpler and more efficient.

The application discloses a lightweight high-rigidity sandwich superstructure plate with an ultralow frequency band gap and an assembling method. The structural plate comprises a plurality of frame units arranged in a rectangular array, wherein each frame unit comprises a support frame, a base plate and a quasi-zero stiffness-inertial amplification coupled resonant unit, the support frame is connected between two base plates, and the quasi-zero stiffness-inertial amplification coupled resonant unit is arranged on the support frame and comprises a lever, a quasi-zero stiffness resonator and a mass block, the lever is hinged to the support frame, the quasi-zero stiffness resonator is located below one end of the lever and comprises a support piece, two positive stiffness elements, two negative stiffness elements and a connecting plate, the support piece is connected to the base plate, the two positive stiffness elements are vertically and symmetrically arranged at two ends of the support plate, the two negative stiffness elements are respectively connected to the inner sides of one end of the two positive stiffness elements, the mass block is connected to the other end of the lever, and the connecting plate is connected between the two negative stiffness elements, so that active control of bending wave vibration in an ultralow frequency range in engineering can be realized.

The invention relates to the technical field of mechanical structure vibration reduction and noise reduction, in particular to a low-frequency vibration isolation axial functional gradient porous beam structure and an analysis method, the structure is composed of a uniform beam area and a gradient porous beam area, the porosity in the uniform beam area section is 0, and the porosity of the gradient porous beam area section is distributed along the axial power law. The structure that the porosity changes in the axial direction in a gradient mode is adopted, the gradient change of the material characteristics (density and Young modulus) of the beam in the axial direction is achieved through the pores with the gradient change, and the energy gathering effect can be achieved through the characteristic that the impedance changes in the axial direction in a gradient mode. As vibration bending waves spread in a porous area, vibration energy is further dissipated and blocked, so that the efficient vibration reduction and isolation effect is achieved, and the situation that the weight and cost of the structure are increased due to the fact that a traditional acoustic black hole beam structure needs to be additionally laid with a viscoelastic damping material for energy absorption is avoided; and the problems of safety and use limitation caused by a gradually thinned appearance structure and the like are solved.

A vibration and noise absorber includes a thin wall structure with an arbitrary boundary condition and at least one meta-element attached to an edge of the thin wall structure. The at least one meta-element has a topology optimized shape that is a function of an objective function that minimizes a reflection coefficient of flexural waves in the audible frequency range propagating towards and impinging the at least one meta-element. In some variations, the vibration and noise absorber is a plurality of meta-elements attached to an edge of a thin wall panel such that a meta-barrier that absorbs over 99.5 percent of flexural waves in the audible frequency range is provided.

The application makes in-depth research on the field of sound wave front regulation in three-dimensional cases. A special acoustic lens is constructed by using a metasurface, so that the required target sound field is obtained, and the sound focusing, sound splitting and sound invisibility phenomena are realized. The research on acoustic lens is a challenging and innovative field. In the past, the research on acoustic lens was hindered by many factors such as too large material structure, complex transmission wave phase regulation and the like. The application designs a high-transmittance curved waveguide structure, and the length of the straight pipe at the neck of the curved waveguide can be adjusted to realize accurate control of the phase of the transmitted wave, and a complex internal structure is not needed. At the same time, the phase shift in the whole 2pi range can be realized by 8 basic units. Based on this, according to the theoretical calculation results, the 8 basic units are freely combined to construct a specific metasurface, so that effects such as sound focusing, acoustic lens, invisibility cloak and the like can be realized.

The invention belongs to the field of polar acoustic detection, and provides a method for carrying out Bayesian inversion on a sound source distance by utilizing an ice layer bending wave time-frequency spectrum, which comprises the following steps of: acquiring a bending wave signal propagated in an ice layer by utilizing a sensor arranged in the ice layer; the collected bending wave signals are filtered to improve the signal-to-noise ratio, the filtered bending wave signals s (t) are subjected to time-frequency analysis to obtain the time-frequency spectrum of bending waves, and t represents time; calculating a phase velocity frequency dispersion curve c (f) based on the six acoustic parameters and a bending wave frequency dispersion formula, wherein f represents frequency; generating a pseudo transmission pulse w (t); generating a receiving signal; performing Bayesian inversion; determining a final output solution; the probability density of the parameters is obtained based on the iteration process, and the average value of the probability density is the expectation of the inversion parameters according to the traversal theorem. The method is low in cost; convergence is fast, global optimization can avoid falling into a local solution, and inversion parameters are few; and the requirement of high-cost ocean survey is reduced.

The invention provides an acoustic black hole structure and an acoustic black hole assembly, and belongs to the technical field of vibration noise control. The acoustic black hole structure comprises a substrate; the at least one acoustic black hole plate is located on the substrate, the acoustic black hole plate is constructed to be of an integrated gradually-shrinking structure in the thickness direction and is provided with a first surface and a second surface which face each other in the thickness direction, the sectional area of the first surface is smaller than that of the second surface, the first surface abuts against the substrate, and the second surface abuts against the substrate; a plane, which is orthogonal to the thickness direction, of the substrate is taken as a projection plane, and the projection of the second surface coincides with the projection of the substrate in the projection along the thickness direction; the damping layer is arranged on the second surface, provided with the two opposite ends in the first direction, of the acoustic black hole plate; the acoustic black hole plate is made of nonmetal. Through the combination of a non-metal material and the structure, bending waves are captured, mechanical vibration is dissipated through the arranged damping layer, and effective absorption of the bending waves in a wide frequency range is achieved.

The invention discloses a topological metamaterial for sheet bending wave isolation and a design method of the topological metamaterial. The topological metamaterial is composed of basic unit cells (1) and sheets (2). Each basic unit cell (1) comprises a regular hexagon area (1-1) and a regular triangle stand column (1-2) which are arranged on a thin plate. A topological common unit cell (3) is obtained by clockwise rotating for 0-30 degrees along the plane normal of the thin plate, and a topological non-common unit cell (4) is obtained by anticlockwise rotating for 0-30 degrees along the plane normal of the thin plate; the topological common unit cells (3) and the topological non-common unit cells (4) are alternately arranged on the thin plate (2) to form a topological metamaterial structure; the topological metamaterials arranged alternately can generate total reflection on incident thin plate bending waves, so that effective isolation of the thin plate bending waves is realized. The system has the advantages of simple design, remarkable vibration isolation effect, high expandability and the like, and is suitable for the fields of vibration prevention of building structures, vibration isolation of precise instruments, interference resistance of aerospace vehicle structures and the like.

Disclosed herein are systems and methods of determining cement integrity behind a casing string using acoustic signals in the field of well drilling and completions. Specifically, the systems and methods evaluate the interface between cement and formation and / or cement-second casing and determine the thickness of the cement. Data are processed to determine annular compression wave velocities in a cased well using a semblance method or by stacking the amplitude of the leaked A0 mode energy that has reflected from the cement-formation or cement-second casing interface. The annular compression wave velocity is necessary to convert time domain images of the annulus into radial distance domain images for better interpretation of annular conditions. A semblance method is used to determine a velocity estimate for the annulus and annular thickness. The semblance method is used for all depths and azimuths to create detailed radial distance domain images of the annulus in cased wells.

This invention discloses a multi-directional local resonance module and its vibration-damping and isolation metamaterial tubular structure. The multi-directional local resonance module includes a matrix, a multi-directional local resonator, and a bushing ring. The multi-directional local resonator includes a triaxially adjustable elastic structure and a mass. The vibration-damping and isolation metamaterial tubular structure is composed of several multi-directional local resonance modules. The triaxially adjustable elastic structure is circumferentially distributed around the cylindrical mass and connects the mass to the bushing ring. The multi-directional local resonance modules are installed on beam or tubular matrix structures at predetermined positions via the bushing ring. This invention, through parameter design and combination design of the multi-directional local resonance modules, can achieve low-frequency, broadband, and efficient suppression of longitudinal and bending wave propagation in beam or tubular structures based on multi-directional local resonance modules, giving them strong multi-dimensional low-frequency vibration reduction and isolation capabilities in the target frequency band, and is easy to install and process.

The invention discloses a multi-dimensional vibration reduction gear with acoustic black hole structures, which comprises a gear ring and a hub, the gear ring is coaxially sleeved outside the hub, the inner wall of the gear ring is connected with the outer wall of the hub through a plurality of spokes, and a plurality of acoustic black hole structures are distributed on the outer wall of each spoke; wherein each acoustic black hole structure comprises a connecting section and a vibration reduction section, one end of the connecting section is connected with the spoke, the other end of the connecting section is connected with the vibration reduction section, and the thickness of the vibration reduction section is gradually reduced. The acoustic black hole structure is integrated on the gear, the double advantages of the acoustic black hole effect and the dynamic vibration absorption principle are combined, bending wave energy generated by gear vibration is effectively absorbed and dissipated, vibration attenuation in the broadband range can be achieved, and specific single-frequency vibration is effectively restrained.

System, methods, and other embodiments described herein relate to a high-Q resonant state embedded system in a continuous body. In one embodiment, a system includes a longitudinally extending body that is subject to a flexural wave. The longitudinally extending body is attached to a fixed structure at a first end. The system also includes a mechanical resonator coupled to a surface of the longitudinally extending body along a length dimension of the longitudinally extending body. The mechanical resonator is located at a distance away from a second end of the longitudinally extending body to exhibit an infinite Q factor based on physical properties of the mechanical resonator.

The invention belongs to the technical field of elastic metasurfaces, and particularly relates to a double-sided elastic metasurface which is formed by arranging a series of unit cells in the interface direction, each unit cell comprises a strip-shaped unit and a stand column, the sizes of the strip-shaped units in the unit cells are the same, every two adjacent unit cells are separated through a groove body, and the stand columns are arranged on the strip-shaped units. The stand columns in each unit cell are the same in size, and each unit cell comprises at least two stand columns. The structure is simple, the design is easy, the processing is convenient, the propagation of the bending wave can be flexibly regulated and controlled, and the application prospect in the aspects of multifunctional elastic wave device design, structural health detection and the like is realized. In addition, the invention also discloses a design method of the double-sided elastic metasurface.

The invention relates to a combined adjustable acoustic black hole which is characterized in that the combined adjustable acoustic black hole comprises a mounting base, a plurality of acoustic black hole units and dampers, each acoustic black hole unit comprises a platform part and an energy dissipation part, the platform part and the energy dissipation part are integrally formed, and the thickness of the energy dissipation part extends outwards from the front end connected with the platform part to the tail end to be gradually thinned; the platform part is fixedly connected with mounting lugs, and the acoustic black hole units are detachably mounted on the mounting seat through the mounting lugs. The invention further discloses a using method of the combined adjustable acoustic black hole. The acoustic black hole units are mounted on the mounting seat, so that vibration waves respectively enter each acoustic black hole unit for energy gathering and dissipation during propagation, and the situation that dissipation cannot be realized due to the fact that elastic waves are transmitted to another acoustic black hole unit from the tail end is prevented. The action frequency domain can be widened through the acoustic black hole units, and the purpose of more efficient bending wave energy gathering and dissipation is achieved.

The invention discloses a clamping plate double-disc type vibration reduction structure based on the acoustic black hole effect and a design method, and relates to the technical field of structural vibration reduction, noise reduction and acoustic vibration, the clamping plate double-disc type vibration reduction structure comprises a clamping plate structure and a plurality of double-disc type acoustic black hole components connected to a clamping plate middle layer in an array mode, and the centers of the upper surface and the lower surface of each double-disc type acoustic black hole component are circular boss planes; the upper circular boss plane and the lower circular boss plane are flatly attached to the two faces of the middle of the clamping plate, and the upper damping circular ring piece and the lower damping circular ring piece are attached to the edges of the upper surface and the lower surface of the double-boss disc respectively. Bending waves on the clamping plates are concentrated to the edge of the double-disc type acoustic black hole component, and vibration energy is restrained and absorbed through the damping ring pieces adhered to the upper surface and the lower surface of the structure. According to the acoustic black hole component, the strength and rigidity of the clamping plate are not damaged while the clamping plate structure is supported, and the purpose of well reducing vibration and noise can be achieved.

The present invention proposes a technology for constructing a universal obstacle-avoiding vortex acoustic tweezers that can bypass objects of any shape. The obstacle avoidance trajectory is designed according to the segmented obstacle contour, and the phase of the line sound source is controlled based on the caustic method to form a self-bending beam that propagates along a predetermined trajectory. The phase control of the one-dimensional sound source is extended to two-dimensional space, and an annular phase screen is constructed to achieve two-dimensional phase control of the annular array of planar fan-shaped transducers. The self-bending beam is rotated along the axis to construct a universal obstacle-avoiding vortex acoustic tweezers that can bypass objects of any shape. The present invention can guide the phased sound waves output by the annular array of planar fan-shaped transducers to bypass obstacles of any shape along a set trajectory, and then construct a vortex acoustic tweezers with higher positioning accuracy and control capabilities, and minimize the reflection and absorption of sound waves by the obstacle, significantly improving the sound pressure and sound radiation force in the focal area of the sound field, and realizing accurate, flexible and efficient obstacle avoidance object control.

The application discloses a casing well ultrasonic bending wave logging multi-mode signal separation method, which comprises the following steps: inputting original mixed casing well ultrasonic bending wave logging data and a related parameter file; simulating A0 mode waves in the instrument centering condition; adopting a variational mode decomposition algorithm to decompose the original mixed signal into a set of multiple scale intrinsic mode functions; taking the correlation coefficient of the reconstructed A0 mode wave and the simulated standard A0 mode wave as an inversion objective function; adopting a simulated annealing method to optimize the optimal decomposition layer number and the reconstruction vector in the inversion objective function; and calculating a reconstructed A0 mode wave A' based on the optimal decomposition layer number k and the reconstruction vector v obtained by optimizing the inversion objective function. o The application can realize adaptive decomposition of A0 and S0 mode waves of a single detector in a non-axisymmetric casing well measuring environment, and can provide accurate A0 mode waves for a method for calculating wave impedance of a post-casing medium based on A0 first wave attenuation information.

The present invention discloses a high-resolution dipole flexural wave velocity inversion method for oil and gas exploration in unconventional reservoirs such as shale and tight sandstone. The method comprises collecting conventional well logging data and array acoustic logging data from wells and performing curve preprocessing on them; processing the preprocessed monopole array and dipole array waveform data using a correlation method to obtain low-resolution P-wave velocity, P-wave arrival time, and low-resolution flexural wave velocity; establishing a numerical model based on the acquired data and performing forward simulation to obtain dipole flexural waveforms, which are then analyzed in the frequency-wavenumber domain to determine the high-order flexural wave frequency range; filtering the measured dipole array waveform data within this range and performing correlation analysis constrained by the flexural wave arrival time to obtain high-resolution dipole flexural wave velocity. The method can improve the vertical resolution of flexural wave velocity to 0.3 m, making the logging interpretation of thin interbeds more accurate and better understanding the characteristics of oil reservoirs.

Disclosed are systems and devices for absorbing flexural waves. In one example, a pair of scatterers for absorbing a flexural wave acting on a structure includes a monopole scatterer and a dipole scatterer configured to be mounted to the structure at the same location.

The invention provides a vibration characteristic analysis method for an acoustic black hole sandwich beam, which comprises the following steps of: 1) establishing a transmission matrix T and a reflection matrix R for a discontinuous core sandwich beam coupling section; 2) establishing a transmission matrix TABH containing an acoustic black hole structure and a reflection matrix RABH containing an acoustic black hole structure by using an iterative relationship of waves; 3) combining a transmission matrix TABH and a reflection matrix RABH of the upper beam embedded with the acoustic black hole, a propagation matrix F of the uniform lower beam and a reflection matrix R and a transmission matrix T of the coupling section to establish a transmission matrix and a reflection matrix containing two core bodies; 4) obtaining a transmission matrix and a reflection matrix containing N core bodies through an iteration relation; and 5) assuming that one end of the structure is a unit displacement excitation end and the other end is a free end, calculating the vibration transmission loss of the designed structure by combining the obtained transmission matrix and reflection matrix, and analyzing the vibration characteristics of the designed structure.