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AbstractThin-walled tubes are commonly used as crucial structures for energy absorption. It is an efficient and convenient research method to establish a small-scale model of the energy-absorbing thin-walled tube for experiments. However, due to the inevitable difference between the design velocity of the test and the actual velocity of the test, it cannot meet the traditional similarity theory. Because of this limitation, this article constructs a similarity design method for the velocity distortion of the multi-cell energy-absorbing tube at the front end of the train under axial impact. Firstly, according to the motion equation of the train system, the design criterion of the similar model under the velocity distortion is derived. Then, the collision mass correction factor is derived based on the elastic-plastic structural energy equation, aiming at the error of the collision peak force and the error of the collision time, the correction factor of the wall thickness of the energy absorbing tube is obtained based on the simulation analysis results. Finally, it is verified that the velocity distortion similarity model can accurately predict the dynamic response of the prototype, and reveals the influence of the mass and wall thickness correction factors on the error. [ABSTRACT FROM AUTHOR]

The construction of large scale harbor structures at Maengbang beach, which is located on the eastern coast of Korea, is of great concern because it may cause disastrous beach erosion in the vicinity. Therefore, a hydraulic model experiment was conducted to examine the morphological changes after such construction. The water depth was scaled using the method of Van Rijn (2010), which is a well-known scale law, but the results appeared to be overestimated. The present study developed a new scale law that applies an equilibrium beach profile formula to scale the model evolution to the prototype scale. When compared with survey data observed at Maengbang beach, the proposed method showed better agreement than the method of Van Rijn (2010).

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Coupling between aero-acoustic noise and structural vibration under high-speed open cavity flow-induced oscillation may bring about severe random vibration of the structure, and even cause structure to fatigue destruction, which threatens the flight safety. Carrying out the research on vibro-acoustic experiments of scaled down model is an effective means to clarify the effects of high-intensity noise of cavity on structural vibration. Therefore, in allusion to the vibro-acoustic experiments of cavity in wind tunnel, taking typical elastic cavity as the research object, dimensional analysis and finite element method were adopted to establish the similitude relations of structural inherent characteristics and dynamics for distorted model, and verifying the proposed similitude relations by means of experiments and numerical simulation. Research shows that, according to the analysis of scale-down model, the established similitude relations can accurately simulate the structural dynamic characteristics of actual model, which provides theoretic guidance for structural design and vibro-acoustic experiments of scaled down elastic cavity model. [ABSTRACT FROM AUTHOR]

In the present study, a new method of predicting the dynamic behavior of a variable thickness (VT) cantilever plate by using a thin plate scaled model is proposed. The thin plate model, defined as the model thin (MT) plate, is designed by using the newly proposed similitude design method. The method is derived based on the transfer matrix of both the stepped thickness (ST) plate that is simplified by the VT plate and the thin plate. The thickness of the MT plate is calculated by introducing the equivalent thickness corresponding to each VT plate's vibration modals, such that a series of accurate distorted scaling laws are provided to predict each corresponding property. Moreover, an algorithm of designing the MT plate is proposed and a design process is summarized in steps. Finally, an example, where the prototype VT plate is made of 42 CrMo and the MT plate is made of NO. 45 steel, is discussed to validate the proposed design method, showing that the MT plate, which is designed by using the proposed method, can accurately predict the dynamic properties of the prototype VT plate, and showing its significance in engineering practice. [ABSTRACT FROM AUTHOR]

In designing the test model of thin-walled cylindrical shells, geometrically distorted models are widely used. This study investigates a method of designing a distorted cylindrical shell model by considering the strength requirement, which means the test model should reflect the strength situation or even failures of the prototype. The significance of this study is that it provides an acceptable process which guides the design of test models. First, governing equations are employed to derive the scaling law of the natural frequency. The harmonic response is calculated in order to obtain the scaling law of the vibration response amplitude. As the study is based on governing equations of elastic cylindrical shells, only elastic behavior is discussed. Then considering the different materials’ ultimate stress, an excitation force ratio is defined. An applicable size interval is investigated and the range of the excitation force is obtained. Finally, an aluminium alloy cylindrical shell is used as a prototype and a NO. 45 steel scaled down cylindrical shell is used as a distorted test model. The accuracy of the prediction is verified by using simulation data. [ABSTRACT FROM AUTHOR]

This study investigates the applicability of distorted models in predicting the frequencies and responses of coated thin plates. The significance of this study is that it provides the necessary scaling laws and structure size applicable intervals, which guide the design of distorted models. By comparing the effect of different coating thickness and different coating forms (single-sided coating and double-sided coatings), the direct use of a governing equation is employed to establish the scaling laws between the model and the prototype. Both complete and partial similarity is discussed. Then an aluminum-coated steel plate, which is commonly used, is analyzed as an example. Establishment of the structure size applicable interval is discussed, which should keep the same first-order natural characteristics (natural frequency and vibration mode). Applicable intervals of the distorted model under different orders are also obtained by using a numerical method. The applicability of the scaling laws and applicable intervals of coated thin plates are verified. The analytical results indicate that distorted models which satisfied the structure size applicable intervals can predict the characteristics of the prototype with good accuracy. This study provides a theoretical foundation for the design of scaled-down models of coated structures. [ABSTRACT FROM AUTHOR]

• A resistance grid can shorten the length of a tunnel ventilation model. • The influence range of a grid is less than 3 times the model equivalent diameter. • A resistance grid has little effect on the critical velocity in the model. • The on-way and local resistance factor decrease with increasing model size. • The resistance of the multiorifice plate grid is larger than that of the mesh grid. According to the equivalent design theory, the length of a tunnel model can be shortened by applying a resistance grid in a tunnel ventilation model experiment. To study the effect of a resistance grid on the ventilation model, this paper analyses the influence of the distance, number, and type of resistance grids in ventilation experiments via a series of model experiments and takes the Dabieshan Tunnel as a case study for verification. The results show that the influence range of the resistance grid decreases with an increasing number of grid holes. When the number of holes per unit area of the grid is greater than 500, the influence length is less than three times the equivalent model diameter. The critical velocity of the model is almost unaffected by the grid spacing, grid number, or grid type. For the same model material, the resistance factor of the model decreases with increasing model size, and the local resistance factor of the grid in the model also proportionally decreases. When the aperture ratio is similar, the local resistance factor of a multiorifice plate grid is greater than that of a wire mesh grid, and the local resistance factor of a square hole grid is greater than that of a circular hole grid. With increasing aperture ratio, the decrease rate of the local resistance factor of a wire mesh grid is less than that of a multiorifice plate grid. The local resistance factor in each grid decreases with an increasing number of grid groups. [ABSTRACT FROM AUTHOR]