Corrugated wind-shield wall device for simulating multiple working conditions in wind tunnel experiment
By designing a corrugated windshield wall device with lifting, variable angles and variable air permeability, the problem that the windshield wall model cannot simulate multiple working conditions in the wind tunnel experiment is solved, which improves the flexibility and accuracy of the experiment and reduces costs.
Patent Information
- Application Number
- CN202510392727.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-31
- Publication Date
- 2025-07-04
AI Technical Summary
In the existing wind tunnel experiment, the wind barrier wall model is in a fixed form and cannot simulate multiple working conditions, resulting in high experimental cost, low efficiency, and low model reuse rate.
A corrugated windshield wall device with lifting, variable angle and variable air permeability is designed, including height adjustment components and angle adjustment components, to realize the simulation of various working conditions.
It improves the flexibility and accuracy of the experiment, reduces the cost of the experiment, and realizes the rapid change of model parameters under constant wind conditions, improving the universality and efficiency of the experiment.
Smart Images
Figure CN120253158A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of wind tunnel experimental equipment, and particularly relates to a corrugated windbreak device for simulating multiple working conditions in wind tunnel experiments. Background Art
[0002] Wind tunnel experiment refers to the detection of the aerodynamic performance of trains and their components by artificially simulating the airflow conditions in the real environment. This technology can simulate the running states of trains at different speeds and under different environmental conditions, and then comprehensively evaluate the aerodynamic performance of trains. Compared with other detection technologies, wind tunnel experiments have the characteristics of high precision, high controllability, and higher safety. Through the wind field parameter adjustment device, the wind tunnel experiment can real-time control the air velocity and turbulence intensity. This experimental method greatly reduces the experimental difficulty and cost, and at the same time avoids the potential risk factors of in-service vehicle experiments. Exploring the aerodynamic characteristics of trains provides technical support for the optimal design of train anti-wind performance.
[0003] The windbreak is an important windproof facility set along the railway, mainly used to reduce the impact of the oncoming wind speed on the train to ensure the safe operation of the train. It is usually composed of materials such as concrete and steel, and has high strength and durability. The windbreak along the railway can effectively reduce the influence of wind load on the train, prevent the train from overturning, and improve the running safety and stability of the train in harsh environments.
[0004] With the development of science and technology, the experimental environment and conditions of wind tunnel experiments are constantly improving. In the experiment of exploring the influence of the windbreak on the aerodynamic performance of trains, the windbreak models used have also been greatly improved, but there are still some problems. For engineering practice, different heights, shapes, and ventilation rates of the windbreak all have different effects on the aerodynamic performance of trains. The existing experiments use models with fixed shapes, resulting in the need to interrupt the experiment and replace the model when changing working conditions, consuming huge costs and time, and the model parameters are specific values with low reuse rate, causing a large amount of resource waste. Therefore, we propose a corrugated windbreak device for simulating multiple working conditions in wind tunnel experiments. Summary of the Invention
[0005] Aiming at the deficiencies of the prior art, the purpose of the present disclosure is to provide a corrugated windbreak device for simulating multiple working conditions in wind tunnel experiments. This windbreak device can simulate multiple working conditions, and can be lifted, rotated, and have variable ventilation rates.
[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions:
[0007] A corrugated windbreak device for simulating multiple working conditions in a wind tunnel experiment, including a device main body. An opening groove is provided at the upper end of the device main body, and a windbreak module is installed in the opening groove. The windbreak module includes a baffle component, a height adjustment component for adjusting the height of the baffle component, and an angle adjustment component for adjusting the angle of the baffle component.
[0008] Further, there are two groups of height adjustment components, which are respectively located on both sides of the baffle component. Each group of height adjustment components includes a double-rod support frame. The double-rod support frame includes a windward-side support rod on the windward side and a leeward-side support rod on the leeward side. A resistance-increasing rubber strip is installed on the leeward-side support rod. The bottom of the double-rod support frame is installed with a base, and the top of the double-rod support frame is installed with a terminal limit plate.
[0009] Further, the base of the height adjustment component is connected to the inner bottom of the device main body through a telescopic rod.
[0010] Further, the angle adjustment component is installed on the double-rod support frame of the height adjustment mechanism. The angle adjustment component includes an installation chamber, a lifting power component, a flipping power component, and a control module. A through hole is provided between the top and bottom of the installation chamber. The inner surface of the lifting power component is fixed to the installation chamber. A resistance-increasing rubber wheel ring is installed on the outer surface of the lifting power component. The resistance-increasing rubber wheel ring contacts the resistance-increasing rubber strip. The outer surface of the flipping power component is fixed to the installation chamber. The power output shaft of the flipping power component is connected to the baffle mechanism. The control module receives external signals to control the power output of the lifting power component and the flipping power component.
[0011] Further, the baffle component includes a wide baffle unit and a narrow baffle unit. The wide baffle units and the narrow baffle units are arranged alternately. The wide baffle units and the narrow baffle units are connected by connecting rods. Each single independent unit of the baffle component includes a windward baffle and a leeward baffle. A mechanical iris mechanism, a transmission screw rod, and a control power component are provided inside the baffle sandwich. The windward baffle and the leeward baffle are respectively provided with multiple rows of holes. Mechanical iris mechanisms are respectively installed in the holes of each row of the multiple rows of holes. A transmission ring for driving the change of its aperture is provided on the mechanical iris mechanism. A toothed belt is provided at the edge of the transmission ring. The toothed belt meshes with the transmission screw rod. The rotating screw rod is installed between the windward baffle and the leeward baffle sandwich. Both ends of the rotating screw rod are connected to the control power component.
[0012] Further, a pair of wind-blocking baffle plates are provided at the opening groove of the device main body. The wind-blocking baffle plates include a windward-side wind-blocking baffle and a leeward-side wind-blocking baffle. The wind-blocking baffle plates are both telescopic structures, and the wind-blocking baffle plates are connected to the device main body through telescopic devices. One side of the wind-blocking baffle plates contacts the baffle component.
[0013] Further, the lifting power component is a hollow servo motor, the flipping power component and the control power component are both single-output shaft servo motors, and the movements of the hollow servo motor and the single-output shaft servo motor are both controlled by a control module.
[0014] Further, gaskets for avoiding friction caused by contact are installed at the contact points between the angle adjustment installation bin and the double-rod support frame of the height adjustment mechanism, between the wind blocking plate and the device main body, and between the wind blocking baffle and the baffle assembly.
[0015] An experimental bench, the test bench includes an experimental bench main body, a car-bearing bench, a train model fixedly installed on the car-bearing bench, sensors installed on the train model, and the corrugated windbreak wall device for simulating multiple working conditions in the above-mentioned wind tunnel experiment.
[0016] A corrugated windbreak wall device for simulating multiple working conditions in a wind tunnel experiment, including a device main body, an opening groove is formed on the top surface of the device main body, and a windbreak wall module is installed in the opening groove.
[0017] Explanations for the nouns, conjunctions or adjectives involved in the above technical solutions are as follows:
[0018] Fixed connection: It refers to the connection where parts or components are fixed without any relative movement. It is divided into two types: detachable connection and non-detachable connection.
[0019] (1) Detachable connection: Use screws, splines, wedge pins, etc. to fix the components together. This connection method can be disassembled during maintenance and will not damage the parts. However, the specifications of the connecting parts must be correct (such as the length of bolts, keys, wedge pins), and they must be fastened properly.
[0020] (2) Non-detachable connection: mainly refers to welding, riveting and mortise fitting, etc. Since it needs to be forged, sawed or oxy-cut to be disassembled during maintenance or replacement, the spare parts generally cannot be used twice. At the same time, during connection, attention should be paid to process quality, technical inspection and remedial measures (such as correction, polishing, etc.).
[0021] The beneficial effects of the present disclosure:
[0022] 1. The present invention changes the traditional fixed windbreak model for a single working condition into a corrugated windbreak model that can simulate multiple working conditions and is liftable, variable in angle, and variable in ventilation rate, so as to simulate various situations that may be encountered during the actual train operation, enabling the windbreak model to be used multiple times, improving the model utilization rate, and reducing the experimental cost. At the same time, by using the above-mentioned corrugated windbreak model that is liftable, variable in angle, and variable in ventilation rate, the parameters of the windbreak model in the wind field of the experimental area can be controlled outside the laboratory, enabling rapid change of the model parameters without stopping the wind, reducing the time cost caused by adjusting the model during the experiment and the energy loss generated during the start and stop of the wind tunnel, reducing the experimental cost, and improving the experimental efficiency.
[0023] 2. Compared with the traditional experimental scheme for specific windbreak parameters under certain working conditions, any parameter experiment within a certain range can be achieved by means of the present invention, enabling the experimental working condition parameters to change continuously and smoothly within a certain range, rather than being limited to several fixed experimental working condition parameters, so that the experiment can more precisely reflect the relationship between the experimental conditions and the experimental results, improving the flexibility and accuracy of the experiment, more realistically simulating various situations of actual train operation, and making the experimental results more universal. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.
[0025] Figure 1 It is a schematic diagram of the installation of the windbreak of the present invention;
[0026] Figure 2 It is a front view of the whole windbreak of the present invention;
[0027] Figure 3 It is a front sectional view of the whole structure of the windbreak of the present invention;
[0028] Figure 4 It is a side sectional view of the whole structure of the windbreak of the present invention;
[0029] Figure 5 It is a top view of the whole structure of the windbreak of the present invention;
[0030] Figure 6 It is a first partial structural schematic diagram of the windbreak in some embodiments of the present invention;
[0031] Figure 7 It is a second partial structural schematic diagram of the windbreak in some embodiments of the present invention;
[0032] Figure 8 It is the third partial structural schematic diagram of the windbreak wall in some embodiments of the present invention;
[0033] Reference numerals: 1, device main body; 2, opening groove; 3, windbreak wall module; 31, height adjustment component; 311, base; 312, telescopic rod; 313, double-rod support frame; 3131, windward side support rod; 3132, leeward side support rod; 3133, resistance-increasing rubber strip; 314, terminal limit plate; 32, angle adjustment component; 321, installation bin; 3211, through hole; 322, lifting power component; 3221, resistance-increasing rubber wheel rim; 323, flipping power component; 3231, power output shaft; 324, control module; 33, baffle component; 331, wide baffle unit; 332, narrow baffle unit; 333, connecting rod; 334, mechanical iris mechanism; 3341, transmission ring; 3342, toothed belt; 335, transmission screw; 336, control power component, 337, multi-row holes; 4, wind resistance baffle block; 41, windward side wind resistance baffle; 42, leeward side wind resistance baffle; 43, expander; 5, test bench main body; 6, car-bearing platform; 7, train model Specific embodiments
[0034] Next, the technical solutions in the embodiments of the present disclosure will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present disclosure.
[0035] A corrugated windbreak wall device for simulating multiple working conditions in a wind tunnel experiment, as Figures 1 to 8As shown in the figure, it includes a device main body 1. An opening groove 2 is provided at the upper end of the device main body 1. A windbreak wall module 3 is installed in the opening groove 2. The windbreak wall module 3 includes a baffle assembly 33, a height adjustment assembly 31 for adjusting the height of the baffle assembly 33, and an angle adjustment assembly 32 for adjusting the angle of the baffle assembly 33. When conducting relevant experiments on the aerodynamic impact of the windbreak wall on trains, some researchers found that the traditional fixed windbreak wall model for a single working condition cannot be used multiple times; at the same time, in the traditional experimental method, when changing the working condition parameters, it is often necessary to operate after the wind tunnel stops, resulting in time costs caused by adjusting the model and energy losses generated during the start and stop of the wind tunnel, thereby increasing the experimental cost and reducing the experimental efficiency. Therefore, designing a windbreak wall that can simulate multiple working conditions is an effective measure to optimize the wind tunnel experimental process, improve the experimental efficiency, and reduce the experimental cost, and it is also the invention significance and theoretical basis of the present invention. The windbreak wall module 3 of the present invention changes the original fixed structure to a height adjustment assembly 31, an angle adjustment assembly 32, and a baffle assembly 33 with variable forms, realizing the simulation of multiple working conditions and the functions of lifting, variable angle, and variable ventilation rate. Compared with the traditional experimental scheme for specific windbreak wall parameters, with the present invention, any parameter experiment within a certain range can be realized, and the experimental working condition parameters can be continuously and smoothly changed within a certain range, rather than being limited to several fixed experimental working condition parameters, enabling the experiment to more precisely reflect the relationship between the experimental conditions and the experimental results, improving the flexibility and accuracy of the experiment, more realistically simulating various situations of actual train operation, and making the experimental results more universal.
[0036] As a preferred embodiment of the present invention, there are two groups of the height adjustment assemblies 31, which are respectively located on both sides of the baffle assembly 33. Each group of the height adjustment assemblies 31 includes a set of double-rod support frames 313. The double-rod support frame 313 includes a windward side support rod 3131 on the windward side and a leeward side support rod 3132 on the leeward side. A resistance-increasing rubber strip 3133 is installed on the leeward side support rod 3132. The bottom of the double-rod support frame 313 is provided with a base 311, and the top of the double-rod support frame 313 is provided with a terminal limit plate 314. The height adjustment assembly 31 is used to adjust the height, so that the windward area per unit length of the windbreak wall is flexibly adjustable; the angle adjustment assembly 32 is used to flip the baffle, so that the windward angle of the baffle is flexibly adjustable; the baffle assembly 33 is used to adjust the ventilation rate. By controlling the opening and closing aperture of the mechanical iris mechanism 334 on the baffle assembly 33, the ventilation rate of the windbreak wall is flexibly adjustable.
[0037] As a preferred embodiment of the present invention, the base 311 of the height adjustment assembly 31 is connected to the inner bottom of the device main body 1 through a telescopic rod 312.
[0038] As a preferred embodiment of the present invention, the angle adjustment assembly 32 is installed on the double-rod support frame 313 of the height adjustment mechanism. The angle adjustment assembly 32 includes an installation chamber 321, a lifting power member 322, a flipping power member 323, and a control module 324. A through hole 3211 is provided between the top and bottom of the installation chamber 321. The inner surface of the lifting power member 322 is fixed to the installation chamber 321. An anti-slip rubber wheel ring 3221 is installed on the outer surface of the lifting power member 322, and the anti-slip rubber wheel ring 3221 contacts the anti-slip rubber strip 3133. The outer surface of the flipping power member 323 is fixed to the installation chamber 321. The power output shaft 3231 of the flipping power member 323 is connected to the baffle mechanism. The control module 324 receives external signals to control the power output of the lifting power member 322 and the flipping power member 323.
[0039] As a preferred embodiment of the present invention, the baffle assembly 33 includes a wide baffle unit 331 and a narrow baffle unit 332. The wide baffle unit 331 and the narrow baffle unit 332 are arranged alternately. The wide baffle unit 331 and the narrow baffle unit 332 are connected by a connecting rod 333. Each single independent unit of the baffle assembly 33 includes a windward baffle and a leeward baffle. A mechanical iris mechanism 334, a transmission screw 335, and a control power member 336 are provided inside the baffle sandwich. Multiple rows of holes 337 are correspondingly provided on both the windward baffle and the leeward baffle, and a mechanical iris mechanism 334 is correspondingly installed in each hole of the multiple rows of holes 337. A transmission ring 3341 for driving the change of its aperture is provided on the mechanical iris mechanism 334. A toothed belt 3342 is provided at the edge of the transmission ring 3341. The toothed belt meshes with the transmission screw 335 for transmission. The rotating screw is installed between the windward baffle and the leeward baffle, and both ends of the rotating screw are connected to the control power member 336. Since the transmission screw 335 is relatively long, more bearings need to be installed between the windward baffle and the leeward baffle to prevent the unstable vibration of the transmission screw 335.
[0040] As a preferred embodiment of the present invention, a pair of wind-blocking baffle plates 4 are provided at the opening groove 2 of the device main body 1. The wind-blocking baffle plates 4 include a windward side wind-blocking baffle 41 and a leeward side wind-blocking baffle 42. The wind-blocking baffle plates 4 are both telescopic structures, and the wind-blocking baffle plates 4 are connected to the device main body 1 through a telescopic device 43. One side of the wind-blocking baffle plates 4 contacts the baffle assembly 33, ensuring a relatively stable wind field and avoiding affecting the experimental results.
[0041] As a preferred embodiment of the present invention, the lifting power member 322 is a hollow servo motor, the flipping power member 323 and the control power member 336 are both single-output shaft servo motors, and the movements of the hollow servo motor and the single-output shaft servo motor are controlled by the control module 324. The control module 324 has the functions of instantaneously receiving external control signals, outputting motor control signals, and transmitting back the current motor status.
[0042] As a preferred embodiment of the present invention, gaskets for avoiding friction caused by contact are installed at the contact points between the angle adjustment installation bin 321 and the double-rod support frame 313 of the height adjustment mechanism, between the wind blocking plate and the device main body 1, and between the wind blocking baffle and the baffle assembly 33. Anti-friction coatings are provided on all parts of the mechanical iris mechanism 334 to avoid friction caused by contact. Anti-friction sheets are pasted on all rotating shafts and lubricating oil is applied.
[0043] An experimental bench, which includes an experimental bench main body 5, a carrier bench 6, a train model 7 fixedly installed on the carrier bench 6, sensors installed on the train model 7, and the corrugated wind blocking wall device that simulates multiple working conditions in the above-mentioned wind tunnel experiment.
[0044] The working process of the present invention is as follows: When a wind tunnel experiment is required, the experimental equipment is powered on. The wind blocking baffle plate 4 on the wind blocking wall device main body 1 is fully opened, and the wind blocking wall module 3 rises out of the opening slot 2 of the wind blocking wall device main body 1. The state of the wind blocking wall is controlled and adjusted according to the parameter requirements of the required first working condition. The motor controls the height adjustment assembly 31, the angle adjustment assembly 32, and the baffle assembly 33 to be converted into the required parameter states. The contact between the wind blocking baffle and the wind blocking unit of the baffle assembly 33 is controlled, and the wind tunnel starts to blow. After the device is stable, the sensors installed on the train model 7 start to collect data. After the data is collected to the required amount, the state of the wind blocking wall is set according to the parameter requirements of the required second working condition, and the wind condition is adjusted. After the shape of the wind blocking wall is changed and stabilized without stopping the wind in the wind tunnel, the sensors installed on the train model 7 continue to collect data, and so on until the experimental tasks of all working conditions are completed. Finally, the wind tunnel stops blowing, and the wind blocking wall module 3 is retracted into the wind blocking wall device main body 1.
[0045] In the description of this specification, the descriptions with reference to terms such as "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.
[0046] The foregoing has shown and described the basic principles, main features and advantages of the present disclosure. Those skilled in the art should understand that the present disclosure is not limited by the above embodiments, and what is described in the above embodiments and the specification is only to illustrate the principles of the present disclosure. Without departing from the spirit and scope of the present disclosure, the present disclosure will have various changes and improvements, and these changes and improvements fall within the scope of the present disclosure claimed.
Claims
1. A corrugated windbreak device for simulating multiple working conditions in a wind tunnel experiment, characterized in that: It includes a device main body (1). An opening groove (2) is formed at the upper end of the device main body (1). A windbreak wall module (3) is installed in the opening groove (2). The windbreak wall module (3) includes a baffle component (33), a height adjustment component (31) for adjusting the height of the baffle component (33), and an angle adjustment component (32) for adjusting the angle of the baffle component (33).
2. The corrugated windbreak device for simulating multiple working conditions in a wind tunnel experiment according to claim 1, wherein There are two groups of the height adjustment components (31), which are respectively located on both sides of the baffle component (33). Each group of the height adjustment components (31) includes a group of double-rod support frames (313). The double-rod support frame (313) includes a windward side support rod (3131) on the windward side and a leeward side support rod (3132) on the leeward side. A resistance-increasing rubber strip (3133) is installed on the leeward side support rod (3132). The bottom of the double-rod support frame (313) is installed with a base (311), and the top of the double-rod support frame (313) is installed with a terminal limit plate (314).
3. The corrugated windbreak device for simulating multiple working conditions in a wind tunnel experiment according to claim 2, characterized in that, The base (311) of the height adjustment component (31) is connected to the inner bottom of the device main body (1) through a telescopic rod (312).
4. The corrugated windbreak device for simulating multiple working conditions in a wind tunnel experiment according to claim 3, wherein The angle adjustment component (32) is installed on the double-rod support frame (313) of the height adjustment mechanism. The angle adjustment component (32) includes an installation bin (321), a lifting power component (322), a flipping power component (323), and a control module (324). A through hole (3211) is formed between the top and bottom of the installation bin (321). The inner surface of the lifting power component (322) is fixed to the installation bin (321). A resistance-increasing rubber wheel ring (3221) is installed on the outer surface of the lifting power component (322). The resistance-increasing rubber wheel ring (3221) contacts the resistance-increasing rubber strip (3133). The outer surface of the flipping power component (323) is fixed to the installation bin (321). The power output shaft (3231) of the flipping power component (323) is connected to the baffle mechanism. The control module (324) receives an external signal to control the power output of the lifting power component (322) and the flipping power component (323).
5. The corrugated windbreak device for simulating multiple working conditions in a wind tunnel experiment according to claim 4, wherein, The baffle assembly (33) includes a wide baffle unit (331) and a narrow baffle unit (332), the wide baffle unit (331) and the narrow baffle unit (332) are arranged alternately, the wide baffle unit (331) and the narrow baffle unit (332) are connected by a connecting rod (333), a single independent unit of the baffle assembly (33) includes a windward baffle and a leeward baffle, a mechanical iris mechanism (334), a transmission screw (335), and a control power member (336) are provided in the baffle sandwich, multiple rows of holes (337) are correspondingly provided in both the windward baffle and the leeward baffle, and a mechanical iris mechanism (334) is correspondingly installed in each hole of the multiple rows of holes (337); a transmission ring (3341) for driving the change of its aperture is provided on the mechanical iris mechanism (334), a toothed belt (3342) is arranged at the edge of the transmission ring (3341), the toothed belt is meshed and driven with the transmission screw (335), the rotating screw is installed between the windward baffle and the leeward baffle, and both ends of the rotating screw are connected to the control power member (336).
6. The corrugated windbreak device for simulating multiple working conditions in a wind tunnel experiment according to claim 5, characterized in that A pair of wind blocking baffle plates (4) are provided at the opening groove (2) of the device main body (1), the wind blocking baffle plates (4) include a windward side wind blocking baffle (41) and a leeward side wind blocking baffle (42), the wind blocking baffle plates (4) are both telescopic structures, and the wind blocking baffle plates (4) are connected to the device main body (1) through a telescopic device (43), and one side of the wind blocking baffle plates (4) is in contact with the baffle assembly (33).
7. The corrugated windbreak device for simulating multiple working conditions in a wind tunnel experiment according to claim 6, characterized in that, The lifting power member (322) is a hollow servo motor, the flipping power member (323) and the control power member (336) are both single-output shaft servo motors, and the movements of the hollow servo motor and the single-output shaft servo motor are both controlled by a control module (324).
8. The corrugated windbreak device for simulating multiple working conditions in a wind tunnel experiment according to claim 7, wherein Gaskets for avoiding friction caused by contact are installed at the contact points between the angle adjustment installation bin (321) and the double-rod support frame (313) of the height adjustment mechanism, the contact points between the wind blocking plates and the device main body (1), and the contact points between the wind blocking baffles and the baffle assembly (33).
9. An experimental bench, characterized in that, The test bench includes a test bench main body (5), a car support platform (6), a train model (7) fixedly installed on the car support platform (6), sensors installed on the train model (7), and a corrugated windbreak device for simulating multiple working conditions in a wind tunnel experiment according to any one of claims 1 to 8.